Development and application of the Round-trip Drifting Sounding System (RDSS)

Cao, Xiaozhong; Guo, Qiyun; Luo, Haowen; Yang, Rongkang; Zhang, Peng; Guo, Jianping; Wang, Jincheng; Xiao, Die; Du, Jianping; Sun, Zhongliang; Liu, Shijun; Chen, Sijie; Huang, Anfan

doi:10.5194/egusphere-2025-2012

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https://doi.org/10.5194/egusphere-2025-2012

Preprints

17 Jun 2025

| 17 Jun 2025

Development and application of the Round-trip Drifting Sounding System (RDSS)

Xiaozhong Cao, Qiyun Guo, Haowen Luo, Rongkang Yang, Peng Zhang, Jianping Guo, Jincheng Wang, Die Xiao, Jianping Du, Zhongliang Sun, Shijun Liu, Sijie Chen, and Anfan Huang

Abstract. Meteorological sounding primarily refers to the balloon-borne radiosonde, which conducts a ground-to-uppe-rair “ascent phase” sounding. This paper introduces the Round-trip Drifting Sounding System (RDSS), an innovative system characterized by three observation phases—'Ascent-Drift-Descent' (ADD)—in which all three phases of sounding observation are executed through single balloon launch. Several key technologies were successfully developed, including the carrier (zero-pressure dual-mode meteorological balloon), the payload (System-on-Chip (SoC) module for meteorological sounding), air-to-ground data reception and ground-to-air control command transmission. RDSS data processing framework based on 'Internet cloud + Instrument terminal' was established. Data quality control methods and data assimilation techniques of RDSS were also developed. An interactive experiment encompassing observations and forecasting was conducted to evaluate the quality of experimental data at each phase of RDSS. The quality evaluation results indicate that the data quality in the RDSS 'ADD' phases meets the breakthrough targets outlined in WMO CIMO-8. The observation quality of wind and temperature in both the ascent and descent phases meets the ideal targets specified in WMO CIMO-8. A numerical experiment on the impact of RDSS data assimilation on forecasting demonstrated a 2 % reduction in precipitation forecast error at 06:00 and 18:00 (UTC), along with an average 1 % improvement in precipitation forecast accuracy following the assimilation of RDSS data. Furthermore, a new trajectory prediction method for RDSS, based on CMA-MESO, achieved an average simulated landing-point error of less than 40 km. Notably, the accuracy of first guess positioning and trajectory prediction for Typhoon 'Saola' in 2023 was significantly enhanced through RDSS data assimilation, reducing the average trajectory prediction error by 40 %. On January 1, 2024, operational observations using RDSS commenced at four stations in Guangdong, China. Starting in July 2024, an operational experiment at one hundred and twenty-seven stations within the China Meteorological Administration (CMA) was planned, with the goal of achieving full operational capability at all CMA stations by 2026.

Received: 29 Apr 2025 – Discussion started: 17 Jun 2025

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Journal article(s) based on this preprint

21 May 2026

Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)

Xiaozhong Cao, Qiyun Guo, Haowen Luo, Jincheng Wang, Rongkang Yang, Die Xiao, Yinfeng Liu, Zhongliang Sun, Shijun Liu, Sijie Chen, Anfan Huang, Guo Jianping, and Peng Zhang

Atmos. Meas. Tech., 19, 3231–3251, https://doi.org/10.5194/amt-19-3231-2026,https://doi.org/10.5194/amt-19-3231-2026, 2026

Short summary

Xiaozhong Cao, Qiyun Guo, Haowen Luo, Rongkang Yang, Peng Zhang, Jianping Guo, Jincheng Wang, Die Xiao, Jianping Du, Zhongliang Sun, Shijun Liu, Sijie Chen, and Anfan Huang

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2012', Anonymous Referee #1, 11 Jul 2025

Synopsis: The manuscript describes a novel upper air balloon observing system, consisting of a double balloon setup that allows for measurements during a long drift phase in the stratosphere and during the descent phase. The start of the drift phase and of the descent phase can be triggered remotely and steering the height is possible as well. The manuscript also describes the potential for using the system for targeting observations and how assimilation of the data improves analysis and forecasts.
Overall comment: It is certainly desirable to make better use of weather balloons than is currently the case with many conventional radiosondes where only data collected during the ascent phase are used. The longer residence of the balloons in the lower stratosphere may be useful for observing certain features there, e.g. gravity waves, with more detail. The authors claim a cost advantage of the new system launched at relatively few stations compared to maintaining or even enhancing the relatively dense Chinese radiosonde observation network for targeting if severe weather is approaching. While it is encouraging that the data of the new observing system have already been assimilated by weather forecast models in China, the impact on forecasts has been relatively weak but seemingly consistent. The papers referenced in this context (e.g. Wang et al. 2023) are in Chinese and thus impossible for me to follow. I did not try to use automatic translation for this. The results are based on relatively short validation periods (30 days) or on a case study. Overall I do not consider the results presented as rigorous proof that the additional measurement data from the drifting balloons improve the quality of analyses and forecasts. While the figures generally support the statements in the text their technical quality is partly poor and should be improved.
This leads to the following assessment
Scientific significance: fair

Scientific quality: fair

Presentation quality: fair
As such I require the following major revisions:
1) Some figures are practically unreadable, please redraw or omit:
Fig. 12 is unreadable
Fig. 11a): Please use thicker lines or make figure sharper. Red color is used for both showing the simulated vertical speed and the circle for highlighting the descent phase. This is confusing.
Fig. 9: What do the dots exactly mean? For me it would be logical if red is the start of the ascent phase, green is the start of the drift phase and blue is the start of the descent phase. The end of the black lines would then be the location where the payload reaches the surface. However this is not consistent with how the colors are labelled.
Fig. 8: The T-logp diagrams are almost unreadable and they also have different scales. For a publication in a serious journal these must be redrawn.
Fig. 7: Is it possible to zoom in? Most of the information East of Wuhan appears unimportant. The red writing in the chart is unreadable. Should it be "Wuhan"?
Fig. 6: The 3D-plot is not helpful. Is it possible to draw the same trajectory informationinto panel b), using a multi-colored polygon with the color scheme indicating the height of the balloon?
Fig. 4: Same suggestion as for Fig. 6, draw the info of panel b) into panel a). While looking fancy, the extreme exaggeration of the vertical coordinate compared to the horizontal ones is somewhat misleading.
2) The added value of the RDSS compared to a sounding system that has just an ascent and a descent phase is unclear and appears limited. ECMWF reported about successfully assimilating descent data https://www.ecmwf.int/sites/default/files/elibrary/102021/20225-newsletter-no-169-autumn-2021_1.pdf,
similar to what is reported in this manuscript. There is very little information about the quality of data collected during the drift phase, except for the caveat that radiation errors may be larger than during ascent and descent due to lacking motion of the balloon relative to the atmosphere. However I wonder if the information during the drift may be useful for analyzing gravity wave activity, for example. This aspect is getting increasing attention.
The authors appear to see the drift phase more as an opportunity to steer the balloon, less as a measurement period.

However the chance to steer the balloon depends a lot on favorable wind conditions. So for targeting one needs to launch the balloon at the right position so that it can descend later into a weather system of interest. Wouldn't that be possible also with conventional radiosondes?
The question is really if the money invested into the drifting capability would not be better invested into e.g. balloons that can reach as high up as possible (e.g. https://www.researchgate.net/publication/384155227_Seasonal_and_geographic_viability_of_high_altitude_balloon_navigation)

or into better humidity sensors that can measure reliably under cold low-pressure conditions.
3) There is little information about availability of these data to the public. They are potentially valuable for weather centers around the globe or for atmospheric climate reanalysis. It would be important for the reader to know whether these data can be accessed and used under a general public license.
Apart from that I have a few minor comments:
Table 3: Please explain what "Airspeed" means. Is it the data transmission rate in bits per second?
l295ff: It is mentioned that the effect of radiation in the drift phase is greater than during ascent/descent. Can you quantify that, ideally with a plot or table showing the increased measurement uncertainty during the drift phase. It is unclear to the reader how the CFD correction model works and how it performs.
4.2: The assessment is rather crude, particularly for humidity. Having just one value for the whole troposphere is insufficient by today's standard. Can you give a profile of the humidity measurement uncertainty?
l368f: .. track the occurence of the eintire convective system and the changes .. in real time... is a bit strong wording, given the fine grained structure visible in the RADAR picture which is by no means resolvable with a few radiosondes, even with drifting capability.
l425: results from one month are not conclusive. There should be at least three months (e.g. used as minimum by ECMWF when upgrading their system), ideally from different seasons, to cover any dependency on the annual cycle.
l534: The reduction of the forecast trajectory error in one typhoon event must be considered anectotal. While encouraging it is certainly not science-grade evidence of an improvement.
l550: It is not obvious from the material presented that the RDSS really reduces costs compared to conventional radiosondes. This needs more detailed explanation.
l567ff: This statement on data availability is unacceptable by today's open science standards.

Citation: https://doi.org/10.5194/egusphere-2025-2012-RC1
- CC1: 'Reply on RC1', Hui Xiao, 17 Jul 2025
  
  The Round-trip Drifting Sounding System (RDSS) has been widely and effectively applied in our daily operational regional numerical weather prediction model since January 2024. After assimilation processing, the data collected by the RDSS can provide more accurate and comprehensive basic information for the regional numerical weather prediction model, effectively improving the prediction effect.
  For instance, in 2025, we published a paper titled "Collaborative assimilation experiment of Beidou radiosonde and drone-dropped radiosonde based on CMA-TRAMS" in Atmospheric and Oceanic Science Letters (Wen et al., 2025). The research results show:
  1.The accuracy of typhoon track prediction has been significantly improved, and the error has been remarkably reduced. The collaborative assimilation of the Round-trip Drifting Sounding System (RDSS) and the drone-dropped radiosonde reduced the 72-hour track error of Typhoon “Haikui” by 66.8 kilometers and the 90-hour error by 82.4 kilometers. The accurate prediction of the typhoon's landing along the coast at the junction of Fujian province and Guangdong province is of decisive significance for disaster prevention deployments in Guangdong, such as personnel evacuation and port protection.
  2.There has been a breakthrough in the prediction ability of the landing point, and the landing positioning accuracy has been enhanced. The collaborative assimilation greatly corrected the northerly path deviation in the control group's prediction, making the landing point closer to the actual situation (at the junction of the coastal areas of Fujian and Guangdong provinces), and securing crucial emergency response time for the coastal areas of Guangdong.
  3.The reliability of the prediction of wind and rain impacts has been strengthened, and the wind and rain fields have been improved. The collaborative assimilation significantly enhanced the accuracy of wind speed and precipitation predictions when the typhoon made landfall, which was more in line with the actual situation. The TS score for 50mm heavy precipitation in the 72-hour forecast increased from 0.33 to 0.75 (a 127% increase), and the TS score for 100mm rainstorm increased from 0.18 to 0.39 (a 117% increase). The significant improvement in the extreme precipitation score is crucial for flood control and drainage in Guangdong.
  
  In addition, the RDSS boasts substantial and far-reaching prospects for future development, with immense potential to revolutionize meteorological observation and prediction practices in relevant fields.
  1.Filling the observational gap in the South China Sea. The RDSS can cover the South China Sea area where traditional observations are scarce, breaking through the key data bottleneck for typhoon prediction in Guangdong and providing high-quality vertical profiles of temperature, humidity, pressure, and wind for model initialization.
  2.The potential for operational multi-source collaborative observations. The collaboration with drone-dropped radiosondes has verified the high-benefit path of "sea-air stereo observations". In the future, a regular collaborative observation network can be established in Guangdong to strengthen the monitoring of the formation and tracks of severe typhoons in the South China Sea.
  3.Precise typhoon track, wind, and rain predictions can directly serve emergency management in Guangdong. For example, it can optimize wind prevention measures in the Pearl River Delta urban agglomeration (such as traffic control and power supply assurance), and enhance the flood disaster early warning ability caused by rainstorms in the coastal areas of eastern Guangdong (such as Shantou and Chaozhou).
  4.Driving force for the upgrade of the regional numerical model. Based on the successful assimilation experience of CMA-TRAMS, it can promote the integration of the RDSS data into the high-resolution regional model in Guangdong (such as CMA-GD), strengthening the short-term and nowcasting prediction and the early warning ability for rapid typhoon intensification.
  
  In summary, the RDSS has showcased breakthrough value in enhancing Guangdong's typhoon disaster preparedness. By bridging critical data gaps over the South China Sea and collaborating with drone-based sounding, it has significantly improved the accuracy of typhoon track forecasts (with errors reduced by up to 82 km), the precision of landfall location predictions, and the reliability of wind and rain impact forecasts (particularly for extreme precipitation). Practical application cases, such as Typhoon “Haikui”, have proven pivotal for Guangdong's disaster response decisions, including evacuations and port protection measures. Its future potential is substantial: it will enable the establishment of a routine observation network over the South China Sea, support the development of smart disaster prevention systems in the Guangdong-Hong Kong-Macao Greater Bay Area, drive upgrades to regional high-resolution numerical models, and facilitate the transition from reactive response to proactive typhoon risk management. The RDSS has become a benchmark for precision meteorological services and is widely recognized as an indispensable "data cornerstone" for the disaster mitigation infrastructure of the Greater Bay Area.
  References: Wen et al. Collaborative assimilation experiment of Beidou radiosonde and drone-dropped radiosonde based on CMA-TRAMS. Atmospheric and Oceanic Science Letters, 2025, 18(2): 100555.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC1
- CC2:
  'Reply on RC1', Haowen Luo, 17 Jul 2025
  
  We thank Referee #1 (RC1) for her/his positive evaluation of our research. We have addressed RC1’s comments and inquires point by point and revised the manuscript carefully. please refer to the attachment. We would like to once again express our sincere gratitude to the RC1 for their constructive feedback, which has significantly strengthened our manuscript. Thank you!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC2
  - AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
    
    On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
    We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
    We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
    Sincerely yours,
    [Xiaozhong Cao]
    [China Meteorological Administration]
    [caoxzh@cma.gov.cn]
    
    Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1
RC2:
'Comment on egusphere-2025-2012', Anonymous Referee #2, 16 Jul 2025
The Round-trip Drifting Sounding System (RDSS) proposed in this study demonstrates significant innovation and holds promising application potential. It is recommended for publication after minor revision. The RDSS’s key advantage lies in completing a continuous atmospheric observation cycle of "ascent (1 hour) - drifting (4 hours) - descent (1 hour)" with a single balloon launch. Notably, the drifting phase provides continuous observation of the lower stratosphere, while the descent phase provides atmospheric vertical profiles over remote areas far from the launch site. This effectively addresses the gap in traditional sounding observations at 06 and 18 UTC. Furthermore, by utilizing long-distance drifting, RDSS expands the capability for vertical atmospheric sounding in remote regions through the descent observations.
Field experiments conducted in the Yangtze River Basin successfully tackled several key technical challenges. Compared to China's previous-generation L-band sounding system, RDSS exhibits reduced observation errors, particularly in tropospheric wind fields and humidity. Additionally, RDSS possesses a degree of mobility, suggesting potential for targeted observation campaigns. The study also presents preliminary results from RDSS data assimilation and forecast impact experiments, indicating a significant improvement in the skill of 12-24 hour accumulated precipitation forecasts initialized at 06UTC and 18UTC.

Specific Recommendations for Revision:
Table 1: The horizontal lines in the three-line table vary in thickness. It is recommended to standardize the line weight.

Table 4: Words are hyphenated across lines. It is recommended to adjust the table format to prevent word breaks.

Figure 6(a): The 3D plot lacks clarity. It is recommended to replace it with a 2D plot, using different colors to represent trajectory altitudes.

Figure 7: This figure solely displays radar reflectivity for a specific weather event and has weak relevance to the main focus of the paper. It is recommended for deletion.

Figures 8(a)-(c): The three T-logP diagrams are unclear. Furthermore, they have differing vertical axis ranges and inconsistent sizes, which is unsuitable for formal journal publication. It is strongly recommended to redraw these figures uniformly.

Figure 9:
(a): This panel merely illustrates the experimental domain and provides limited information. It is recommended for deletion; the location can be described textually in the main body.

(b): The symbols are confusing and undefined. It is recommended to recreate this figure with clear labeling of all symbols in the legend. The caption should provide a detailed explanation of the figure's content.

Figure 12: The image is unclear and primarily demonstrates the trajectory visualization software's output. It has minimal connection to the paper's core innovations and technical content. It is recommended for deletion.

Data Assimilation Experiments: The assimilation application experiments using RDSS data in this paper are relatively limited. It is recommended that subsequent research focuses on: (a) Further refining assimilation techniques for RDSS second-level data (e.g., data thinning methods); (b) Conducting more extensive numerical forecast assimilation impact experiments utilizing additional observational data; (c) Conducting a thorough evaluation of the forecast skill improvement offered by RDSS compared to China's conventional L-band sounding system.

"Zhuang Z R, Wang R C (2019), Wang J C, et al." - Literature duplication.

The two attached papers also studied and confirmed the impact and value of the RDSS data on numerical forecasting. It is recommended to include them.

ZHANG Xin, WANG Qiuping, MA Xulin, et al. 2025. The Influence of New Round-Trip Drifting Sounding Observation on the Quality of Numerical Prediction in the Middle and Lower Reaches of the Yangtze River [J]. Chinese Journal of Atmospheric Sciences, 49(1): 245−256. doi:10.3878/j.issn.1006-9895.2304.22224
Zhang, X., Sun, L., Ma, X., Guo, H., Gong, Z., Yan, X. Can the Assimilation of the Ascending and Descending Sections’ Data from Round-Trip Drifting Soundings Improve the Forecasting of Rainstorms in Eastern China? Atmosphere 2023, 14, 1127. https://doi.org/10.3390/ atmos14071127
Citation: https://doi.org/10.5194/egusphere-2025-2012-RC2
- CC3:
  'Reply on RC2', Haowen Luo, 17 Jul 2025
  
  We thank Referee #2(RC2) for her/his positive evaluation of our research. We have addressed RC2’s comments and inquires point by point and revised the manuscript carefully. We appreciate adopts the same handling method for the parts with the same revision opinions as RC1, and subsequently will uniformly handle and modify the original manuscript based on the opinions of the handling editor. Please refer to the attachment. We would like to once again express our sincere gratitude to the RC2 for his/her constructive feedback, which has significantly strengthened our manuscript. Thank you!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC3
  - AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
    
    On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
    We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
    We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
    Sincerely yours,
    [Xiaozhong Cao]
    [China Meteorological Administration]
    [caoxzh@cma.gov.cn]
    
    Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1
RC3:
'Comment on egusphere-2025-2012', Anonymous Referee #3, 04 Aug 2025

Review of Development and application of the Round-trip Drifting Sounding System (RDSS)

by Cao et al
General
I have just completed a rereview of "The Beidou Navigation Radiosonde Observation Experiment and Data Evaluation"

by Lebao Yao et al (with Xiaozhong Cao as a co-author) submitted to Atmospheric Research.

When the request for review from Copernicus arrived I clicked accept thinking that this was the other paper.

The two papers do not seem to have been coordinated as I would expect: in terms of content - there is some overlap,

the name of the sounding system differs and there is no reference to Yao et al in this manuscript.
I find the 'Round-trip' in the title a misleading name. In English a round-trip finishes at the point of origin -

not the case with the RDSS. Yao et al use the term Beidou Navigation Radiosonde. In places this manuscript refers

to the 'ADD' (Ascent-Drift-Descent) system instead of RDSS. ADD seems a more accurate name to me.
More explanation of the overall design would be useful. What is the purpose of the 'drift' stage?

What determines how long the drift stage is? How much does it add to the batteries required?

Will the drift and descent stages be reported on the GTS? If so what BUFR format will be used for the drift stage?

At recent WMO meetings (eg TECO 2022) there has been discussion of reducing the environmental impact of

radiosondes and other instruments. The reduced weight of the new radiosonde is a step in that direction,

but has there been any effort to reduce plastic use or the toxic elements in circuit boards?

Are there plans to refurbish and reuse some of the radiosonde instruments?
There should also mention of the WMO Global Basic Observing Network (GBON, https://community.wmo.int/en/activity-areas/wigos/gbon ) as CMA is planning to use these drift radiosondes operationally

GBON technical regulations specify that there should be soundings to 30 hPa and a subset to 10 hPa.

To what extent would this be met in the tests so far?
One could read this manuscript and think that NWP still revolves almost entirely around radiosonde profiles - not true.

There is one mention of aircraft reports and almost nothing about satellite observations.

In practice satellite observations are now hugely important and radiosondes are less so although still very useful

(partly for validation/verification). Below are three references (of many) to support this view.
Bauer, P., Thorpe, A. & Brunet, G. The quiet revolution of numerical weather prediction. Nature 525, 47-55 (2015). https://doi.org/10.1038/nature14956
Bormann N, Lawrence H, Farnan J (2019) Global observing system experiments in the ECMWF

assimilation system. ECMWF Technical Memorandum 839, 24 pp. https://doi.org/10.21957/sr184iyz
https://community.wmo.int/en/meetings/8th-wmo-impact-workshop-home (2024, final report and presentations)

Detailed comments
17 "Meteorological sounding primarily refers to the balloon-borne radiosonde"

The satellite community would disagree. Rewrite.
21 "zero-pressure dual-mode meteorological balloon" what does zero-pressure mean?
18 "uppe-rair" > "upper-air"
46-47 "Since the 19th century, the balloon-borne radiosonde has served as the primary tool for direct measurements of

47 upper-air meteorological elements below 30 km and is extensively utilized globally (Gallice et al., 2011)."

The use of radio with balloon soundings only started in the 1930s or so (20th century), with early operational systems

in the 1940s. A better reference would be Pettifer (2009).

Pettifer R (2009) From observations to forecasts, part 2. The development of in situ upper air

measurements. Weather 64:302-308. https://doi.org/10.1002/wea.484
48 "For over a century" - "For about eighty years"
49 "one measurement" - "one profile"
54 "as Russia's decrease from twice-daily" - "as Russia's temporary decrease from twice-daily"

See https://www.ecmwf.int/sites/default/files/elibrary/2016/18147-global-radiosonde-network-under-pressure.pdf
61-63 "The United States and other countries have successfully assimilated airborne sonde data into their model

systems, resulting in a 20%-40% reduction in errors in hurricane trajectory predictions (Stephen et al., 2013;

Wang et al., 2015)."

"20%-40% reduction in errors" seems too high to me for modern NWP systems with good assimilation of satellite data,

Majumdar (2016) already referenced is more balanced.
68 "The upper-air balloon system, known as ValBal, developed by the Stanford Space Program in the United States,

has accomplished multi-day flights at altitudes ranging from 10 km to 25 km (Sushko et al., 2011)."

I hadn't heard of ValBal, I suspect that it was a short-lived research system.

On the contrary the WindBorne system (Johnson et al, 2024) is active and currently providing data on the GTS

Johnson, A., Wang, X., Hutchinson, T., & Creus-Costa, J. (2024). Impact of WindBorne observation assimilation on prediction of a TPV merger case from THINICE. Journal of Geophysical Research: Atmospheres, 129, e2024JD041395. https://doi.org/10.1029/2024JD041395
81 "descent data" see also Ingleby et al (2022)

Ingleby, B., Motl, M., Marlton, G., Edwards, D., Sommer, M., von Rohden, C., Vömel, H., and Jauhiainen, H.: On the quality of RS41 radiosonde descent data, Atmos. Meas. Tech., 15, 165-183, https://doi.org/10.5194/amt-15-165-2022, 2022.
95 'more than a century' - 'about 80 years' (prior to the 1940s there were tiny numbers of research flights that

mostly relied on someone finding and returning the instrument package and recorded data)
106 "ascends at approximately 400 meters per minute" convert to metres per second
186 "The ascent phase of meteorological sounding generally lasts less than one hour."

It is usually 1.5 to two hours for most radiosondes. Or is this a statement about RDSS?
193 "hydrogen loss" It should have been stated earlier that hydrogen is the lifting gas.
232 "The positioning accuracy of SoC is 0.8 meters horizontally and 1.3 meters vertically"

1.3 meters vertically sounds better than I would expect - please provide some evidence for this.

Is the accuracy worse near the surface (due to reflection or ducting of the signals)?
242-243 "The GTH3 participated in WMO UAII2022(Upper-Air Instrument Intercomparison Campaign organized by the

World Meteorological Organization (WMO) and co-organized by the Deutscher Wetterdienst (DWD) in 2022)"

Their table lists

Tianjin Huayuntianyi Special Meteorological Sounding Tech. Co., Ltd. HT-GTS(U)2-1 (GTH3)

I think it is worth giving the manufacturer name here and probably the alternate radiosonde name (HT-GTS(U)2-1).

Is the current "GTH3" the same as that tested in UAII2022 or a development of it?
Table 4 caption "The planetary boundary layer (PBL) ranges from 2 to 7 kilometers" - should say "Free Troposphere"

other parts of the caption also need changing.
317-318 "Comparative tests led to the selection of conical parachutes"

Please provide more details of the parachute, such a a diagram, dimensions and any vents.
319 "As a result, RDSS achieves a stable descent speed of approximately 6 m/s ± 1 m/s"

Is this true even in the stratosphere? Please show some example profiles and/or mean and standard deviation profiles.

Ingleby et al (2022) report much faster descent speeds in the stratosphere

(even with a parachute) and a lot of variation from one flight to another.
"4.1 Field experiment ..."

What is the distribution (above ground level) of the lowest descent point received?

This depends on the orography and how close to a receiving station it lands.
359 "the fifth generation of ECMWF (ERA5) was used to evaluate the QC data of RDSS (Minola et al. 2020; Roja et al. 2011),"

"the fifth generation of ECMWF reanalysis (ERA5, Hersbach et al, 2020) was used to evaluate the quality of RDSS data,"

I'm not sure how relevant Minola et al is. Roja et al predates ERA5 and doesn't appear in the references.

Hersbach H et al (2020) The ERA5 global reanalysis. Q J R Meteorol Soc 146:1999-2049. https://

doi.org/10.1002/qj.3803
Table 5. 'EAR5' should be 'ERA5'; 'troposphere top' should presumably be 'tropopause', units of RH are "%RH".

'{SD of] radiosonde data and ERA5' should be 'radiosonde data minus ERA5'

IMPORTANT: Please provide mean differences for temperature.

What quality control (including comparison with ERA5) was used to exclude outliers?

What 'saturation vapour pressure' equation is used for RH? As discussed with Lebao Yao, I think there are

differences in the definition of RH between the radiosonde and ERA5. It is cleaner to start from ERA5

specific humidity and temperature and then make sure you are comparing like with like.

Note. The 'drift' temperature differences seem too large to be usable (despite the processing described above).

It would be useful to know the mean wind speeds for the different phases.
Figure 7. Wuhan should be better marked (there is something written in red that I can't read).

Perhaps a coloured X or other symbol, described in the caption would be better.
Figure 9b. A lot of green 'descent' dots are close to the 'ascent' point.

I wondered if green is actually the start of the drift phase and blue the start of descent?

Some people are red-green colour blind, changing one of the colours would help them.

(Unlike reviewer 2 I find the orientation given by Fig 9a useful.)
411-412 "With the four-dimensional ensemble forecast error is introduced into the CMA global data

assimilation system, and the H-4DEnVar assimilation scheme is developed."

The English here is strange/unclear. What is the H in H-4DEnVar?
Figure 10 caption. Stage that positive values indicate benefit when descent data is used.

Precipitation thresholds in mm?
449-452 "Targeted observations ... " This is overstated. They have "sometimes been a frontier field"

The impact of targeted observations is almost always less than one or two years work on improving the baseline

NWP system (Lorenc pers comm) - and improving the baseline tends to reduce the benefit of targeted observations.

"Majumdar & Sharanya, 2016" should be "Majumdar, 2016"

Two quotes from his 'Conclusions and Discussion':

"The fact that many results are inconclusive is not surprising, for several reasons. ..."

"In summary, the initial vision that the Global Observing System would ultimately be supplemented by networks on an adaptive basis, or even optimized into a fully adaptive network, has not been realized."
500 '5.3.3 Targeted observations experiment of Typhoon'
I was surprised by this section because surely the biggest impact on TC forecasting comes from improving the

analysis and forecast one, two or three days before landfall.

In the online discussion a response was "The RDSS can cover the South China Sea area" where would they be launched from?
For another view see

Magnusson, L., Majumdar, S.J., Dahoui, M.L., Bormann, N., Bonavita, M., Browne, P.A., et al. (2025) The role of observations in ECMWF tropical cyclone initialisation and forecasting. Quarterly Journal of the Royal Meteorological Society, 151(768), e4924. Available from: https://doi.org/10.1002/qj.4924
A few quotes form this:

"The strongest impact came from withholding of microwave radiance observations ..."

"Scatterometer data improved the forecasts ..."

"While the aircraft-borne data (dropsonde, flight-level data) were mostly beneficial, further investigations on how to best use this data in the TC core are needed."
552 'century-old' - '20th century'
556 'RDSS is essentially a mature system.' I would say it is close to maturity (but not there yet).

No data have been provided on the GTS yet as far as I know.

Some of my questions in the general comments need answering/clarification.

References
Where the papers are in Chinese please indicate this.

Many readers will not be able to read such papers, I suggest removing some of the less relevant ones.
632 "Majumdar, S. J.: A review of targeted measurements" this is the whole of the tile, delete

": targeted measurements to improve numerical forecasts of high-impact weather events over the past two decades,

particularly during the THORPEX era (2005-14), are evaluated"
660 "Tan et al ... doi:10.3969/j.issn.1004-4965.2006.01.003." I couldn't find this despite the doi.

Citation: https://doi.org/10.5194/egusphere-2025-2012-RC3
- AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
  
  On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
  We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
  We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
  Sincerely yours,
  [Xiaozhong Cao]
  [China Meteorological Administration]
  [caoxzh@cma.gov.cn]
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2012', Anonymous Referee #1, 11 Jul 2025

Synopsis: The manuscript describes a novel upper air balloon observing system, consisting of a double balloon setup that allows for measurements during a long drift phase in the stratosphere and during the descent phase. The start of the drift phase and of the descent phase can be triggered remotely and steering the height is possible as well. The manuscript also describes the potential for using the system for targeting observations and how assimilation of the data improves analysis and forecasts.
Overall comment: It is certainly desirable to make better use of weather balloons than is currently the case with many conventional radiosondes where only data collected during the ascent phase are used. The longer residence of the balloons in the lower stratosphere may be useful for observing certain features there, e.g. gravity waves, with more detail. The authors claim a cost advantage of the new system launched at relatively few stations compared to maintaining or even enhancing the relatively dense Chinese radiosonde observation network for targeting if severe weather is approaching. While it is encouraging that the data of the new observing system have already been assimilated by weather forecast models in China, the impact on forecasts has been relatively weak but seemingly consistent. The papers referenced in this context (e.g. Wang et al. 2023) are in Chinese and thus impossible for me to follow. I did not try to use automatic translation for this. The results are based on relatively short validation periods (30 days) or on a case study. Overall I do not consider the results presented as rigorous proof that the additional measurement data from the drifting balloons improve the quality of analyses and forecasts. While the figures generally support the statements in the text their technical quality is partly poor and should be improved.
This leads to the following assessment
Scientific significance: fair

Scientific quality: fair

Presentation quality: fair
As such I require the following major revisions:
1) Some figures are practically unreadable, please redraw or omit:
Fig. 12 is unreadable
Fig. 11a): Please use thicker lines or make figure sharper. Red color is used for both showing the simulated vertical speed and the circle for highlighting the descent phase. This is confusing.
Fig. 9: What do the dots exactly mean? For me it would be logical if red is the start of the ascent phase, green is the start of the drift phase and blue is the start of the descent phase. The end of the black lines would then be the location where the payload reaches the surface. However this is not consistent with how the colors are labelled.
Fig. 8: The T-logp diagrams are almost unreadable and they also have different scales. For a publication in a serious journal these must be redrawn.
Fig. 7: Is it possible to zoom in? Most of the information East of Wuhan appears unimportant. The red writing in the chart is unreadable. Should it be "Wuhan"?
Fig. 6: The 3D-plot is not helpful. Is it possible to draw the same trajectory informationinto panel b), using a multi-colored polygon with the color scheme indicating the height of the balloon?
Fig. 4: Same suggestion as for Fig. 6, draw the info of panel b) into panel a). While looking fancy, the extreme exaggeration of the vertical coordinate compared to the horizontal ones is somewhat misleading.
2) The added value of the RDSS compared to a sounding system that has just an ascent and a descent phase is unclear and appears limited. ECMWF reported about successfully assimilating descent data https://www.ecmwf.int/sites/default/files/elibrary/102021/20225-newsletter-no-169-autumn-2021_1.pdf,
similar to what is reported in this manuscript. There is very little information about the quality of data collected during the drift phase, except for the caveat that radiation errors may be larger than during ascent and descent due to lacking motion of the balloon relative to the atmosphere. However I wonder if the information during the drift may be useful for analyzing gravity wave activity, for example. This aspect is getting increasing attention.
The authors appear to see the drift phase more as an opportunity to steer the balloon, less as a measurement period.

However the chance to steer the balloon depends a lot on favorable wind conditions. So for targeting one needs to launch the balloon at the right position so that it can descend later into a weather system of interest. Wouldn't that be possible also with conventional radiosondes?
The question is really if the money invested into the drifting capability would not be better invested into e.g. balloons that can reach as high up as possible (e.g. https://www.researchgate.net/publication/384155227_Seasonal_and_geographic_viability_of_high_altitude_balloon_navigation)

or into better humidity sensors that can measure reliably under cold low-pressure conditions.
3) There is little information about availability of these data to the public. They are potentially valuable for weather centers around the globe or for atmospheric climate reanalysis. It would be important for the reader to know whether these data can be accessed and used under a general public license.
Apart from that I have a few minor comments:
Table 3: Please explain what "Airspeed" means. Is it the data transmission rate in bits per second?
l295ff: It is mentioned that the effect of radiation in the drift phase is greater than during ascent/descent. Can you quantify that, ideally with a plot or table showing the increased measurement uncertainty during the drift phase. It is unclear to the reader how the CFD correction model works and how it performs.
4.2: The assessment is rather crude, particularly for humidity. Having just one value for the whole troposphere is insufficient by today's standard. Can you give a profile of the humidity measurement uncertainty?
l368f: .. track the occurence of the eintire convective system and the changes .. in real time... is a bit strong wording, given the fine grained structure visible in the RADAR picture which is by no means resolvable with a few radiosondes, even with drifting capability.
l425: results from one month are not conclusive. There should be at least three months (e.g. used as minimum by ECMWF when upgrading their system), ideally from different seasons, to cover any dependency on the annual cycle.
l534: The reduction of the forecast trajectory error in one typhoon event must be considered anectotal. While encouraging it is certainly not science-grade evidence of an improvement.
l550: It is not obvious from the material presented that the RDSS really reduces costs compared to conventional radiosondes. This needs more detailed explanation.
l567ff: This statement on data availability is unacceptable by today's open science standards.

Citation: https://doi.org/10.5194/egusphere-2025-2012-RC1
- CC1: 'Reply on RC1', Hui Xiao, 17 Jul 2025
  
  The Round-trip Drifting Sounding System (RDSS) has been widely and effectively applied in our daily operational regional numerical weather prediction model since January 2024. After assimilation processing, the data collected by the RDSS can provide more accurate and comprehensive basic information for the regional numerical weather prediction model, effectively improving the prediction effect.
  For instance, in 2025, we published a paper titled "Collaborative assimilation experiment of Beidou radiosonde and drone-dropped radiosonde based on CMA-TRAMS" in Atmospheric and Oceanic Science Letters (Wen et al., 2025). The research results show:
  1.The accuracy of typhoon track prediction has been significantly improved, and the error has been remarkably reduced. The collaborative assimilation of the Round-trip Drifting Sounding System (RDSS) and the drone-dropped radiosonde reduced the 72-hour track error of Typhoon “Haikui” by 66.8 kilometers and the 90-hour error by 82.4 kilometers. The accurate prediction of the typhoon's landing along the coast at the junction of Fujian province and Guangdong province is of decisive significance for disaster prevention deployments in Guangdong, such as personnel evacuation and port protection.
  2.There has been a breakthrough in the prediction ability of the landing point, and the landing positioning accuracy has been enhanced. The collaborative assimilation greatly corrected the northerly path deviation in the control group's prediction, making the landing point closer to the actual situation (at the junction of the coastal areas of Fujian and Guangdong provinces), and securing crucial emergency response time for the coastal areas of Guangdong.
  3.The reliability of the prediction of wind and rain impacts has been strengthened, and the wind and rain fields have been improved. The collaborative assimilation significantly enhanced the accuracy of wind speed and precipitation predictions when the typhoon made landfall, which was more in line with the actual situation. The TS score for 50mm heavy precipitation in the 72-hour forecast increased from 0.33 to 0.75 (a 127% increase), and the TS score for 100mm rainstorm increased from 0.18 to 0.39 (a 117% increase). The significant improvement in the extreme precipitation score is crucial for flood control and drainage in Guangdong.
  
  In addition, the RDSS boasts substantial and far-reaching prospects for future development, with immense potential to revolutionize meteorological observation and prediction practices in relevant fields.
  1.Filling the observational gap in the South China Sea. The RDSS can cover the South China Sea area where traditional observations are scarce, breaking through the key data bottleneck for typhoon prediction in Guangdong and providing high-quality vertical profiles of temperature, humidity, pressure, and wind for model initialization.
  2.The potential for operational multi-source collaborative observations. The collaboration with drone-dropped radiosondes has verified the high-benefit path of "sea-air stereo observations". In the future, a regular collaborative observation network can be established in Guangdong to strengthen the monitoring of the formation and tracks of severe typhoons in the South China Sea.
  3.Precise typhoon track, wind, and rain predictions can directly serve emergency management in Guangdong. For example, it can optimize wind prevention measures in the Pearl River Delta urban agglomeration (such as traffic control and power supply assurance), and enhance the flood disaster early warning ability caused by rainstorms in the coastal areas of eastern Guangdong (such as Shantou and Chaozhou).
  4.Driving force for the upgrade of the regional numerical model. Based on the successful assimilation experience of CMA-TRAMS, it can promote the integration of the RDSS data into the high-resolution regional model in Guangdong (such as CMA-GD), strengthening the short-term and nowcasting prediction and the early warning ability for rapid typhoon intensification.
  
  In summary, the RDSS has showcased breakthrough value in enhancing Guangdong's typhoon disaster preparedness. By bridging critical data gaps over the South China Sea and collaborating with drone-based sounding, it has significantly improved the accuracy of typhoon track forecasts (with errors reduced by up to 82 km), the precision of landfall location predictions, and the reliability of wind and rain impact forecasts (particularly for extreme precipitation). Practical application cases, such as Typhoon “Haikui”, have proven pivotal for Guangdong's disaster response decisions, including evacuations and port protection measures. Its future potential is substantial: it will enable the establishment of a routine observation network over the South China Sea, support the development of smart disaster prevention systems in the Guangdong-Hong Kong-Macao Greater Bay Area, drive upgrades to regional high-resolution numerical models, and facilitate the transition from reactive response to proactive typhoon risk management. The RDSS has become a benchmark for precision meteorological services and is widely recognized as an indispensable "data cornerstone" for the disaster mitigation infrastructure of the Greater Bay Area.
  References: Wen et al. Collaborative assimilation experiment of Beidou radiosonde and drone-dropped radiosonde based on CMA-TRAMS. Atmospheric and Oceanic Science Letters, 2025, 18(2): 100555.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC1
- CC2:
  'Reply on RC1', Haowen Luo, 17 Jul 2025
  
  We thank Referee #1 (RC1) for her/his positive evaluation of our research. We have addressed RC1’s comments and inquires point by point and revised the manuscript carefully. please refer to the attachment. We would like to once again express our sincere gratitude to the RC1 for their constructive feedback, which has significantly strengthened our manuscript. Thank you!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC2
  - AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
    
    On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
    We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
    We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
    Sincerely yours,
    [Xiaozhong Cao]
    [China Meteorological Administration]
    [caoxzh@cma.gov.cn]
    
    Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1
RC2:
'Comment on egusphere-2025-2012', Anonymous Referee #2, 16 Jul 2025
The Round-trip Drifting Sounding System (RDSS) proposed in this study demonstrates significant innovation and holds promising application potential. It is recommended for publication after minor revision. The RDSS’s key advantage lies in completing a continuous atmospheric observation cycle of "ascent (1 hour) - drifting (4 hours) - descent (1 hour)" with a single balloon launch. Notably, the drifting phase provides continuous observation of the lower stratosphere, while the descent phase provides atmospheric vertical profiles over remote areas far from the launch site. This effectively addresses the gap in traditional sounding observations at 06 and 18 UTC. Furthermore, by utilizing long-distance drifting, RDSS expands the capability for vertical atmospheric sounding in remote regions through the descent observations.
Field experiments conducted in the Yangtze River Basin successfully tackled several key technical challenges. Compared to China's previous-generation L-band sounding system, RDSS exhibits reduced observation errors, particularly in tropospheric wind fields and humidity. Additionally, RDSS possesses a degree of mobility, suggesting potential for targeted observation campaigns. The study also presents preliminary results from RDSS data assimilation and forecast impact experiments, indicating a significant improvement in the skill of 12-24 hour accumulated precipitation forecasts initialized at 06UTC and 18UTC.

Specific Recommendations for Revision:
Table 1: The horizontal lines in the three-line table vary in thickness. It is recommended to standardize the line weight.

Table 4: Words are hyphenated across lines. It is recommended to adjust the table format to prevent word breaks.

Figure 6(a): The 3D plot lacks clarity. It is recommended to replace it with a 2D plot, using different colors to represent trajectory altitudes.

Figure 7: This figure solely displays radar reflectivity for a specific weather event and has weak relevance to the main focus of the paper. It is recommended for deletion.

Figures 8(a)-(c): The three T-logP diagrams are unclear. Furthermore, they have differing vertical axis ranges and inconsistent sizes, which is unsuitable for formal journal publication. It is strongly recommended to redraw these figures uniformly.

Figure 9:
(a): This panel merely illustrates the experimental domain and provides limited information. It is recommended for deletion; the location can be described textually in the main body.

(b): The symbols are confusing and undefined. It is recommended to recreate this figure with clear labeling of all symbols in the legend. The caption should provide a detailed explanation of the figure's content.

Figure 12: The image is unclear and primarily demonstrates the trajectory visualization software's output. It has minimal connection to the paper's core innovations and technical content. It is recommended for deletion.

Data Assimilation Experiments: The assimilation application experiments using RDSS data in this paper are relatively limited. It is recommended that subsequent research focuses on: (a) Further refining assimilation techniques for RDSS second-level data (e.g., data thinning methods); (b) Conducting more extensive numerical forecast assimilation impact experiments utilizing additional observational data; (c) Conducting a thorough evaluation of the forecast skill improvement offered by RDSS compared to China's conventional L-band sounding system.

"Zhuang Z R, Wang R C (2019), Wang J C, et al." - Literature duplication.

The two attached papers also studied and confirmed the impact and value of the RDSS data on numerical forecasting. It is recommended to include them.

ZHANG Xin, WANG Qiuping, MA Xulin, et al. 2025. The Influence of New Round-Trip Drifting Sounding Observation on the Quality of Numerical Prediction in the Middle and Lower Reaches of the Yangtze River [J]. Chinese Journal of Atmospheric Sciences, 49(1): 245−256. doi:10.3878/j.issn.1006-9895.2304.22224
Zhang, X., Sun, L., Ma, X., Guo, H., Gong, Z., Yan, X. Can the Assimilation of the Ascending and Descending Sections’ Data from Round-Trip Drifting Soundings Improve the Forecasting of Rainstorms in Eastern China? Atmosphere 2023, 14, 1127. https://doi.org/10.3390/ atmos14071127
Citation: https://doi.org/10.5194/egusphere-2025-2012-RC2
- CC3:
  'Reply on RC2', Haowen Luo, 17 Jul 2025
  
  We thank Referee #2(RC2) for her/his positive evaluation of our research. We have addressed RC2’s comments and inquires point by point and revised the manuscript carefully. We appreciate adopts the same handling method for the parts with the same revision opinions as RC1, and subsequently will uniformly handle and modify the original manuscript based on the opinions of the handling editor. Please refer to the attachment. We would like to once again express our sincere gratitude to the RC2 for his/her constructive feedback, which has significantly strengthened our manuscript. Thank you!
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-CC3
  - AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
    
    On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
    We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
    We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
    Sincerely yours,
    [Xiaozhong Cao]
    [China Meteorological Administration]
    [caoxzh@cma.gov.cn]
    
    Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1
RC3:
'Comment on egusphere-2025-2012', Anonymous Referee #3, 04 Aug 2025

Review of Development and application of the Round-trip Drifting Sounding System (RDSS)

by Cao et al
General
I have just completed a rereview of "The Beidou Navigation Radiosonde Observation Experiment and Data Evaluation"

by Lebao Yao et al (with Xiaozhong Cao as a co-author) submitted to Atmospheric Research.

When the request for review from Copernicus arrived I clicked accept thinking that this was the other paper.

The two papers do not seem to have been coordinated as I would expect: in terms of content - there is some overlap,

the name of the sounding system differs and there is no reference to Yao et al in this manuscript.
I find the 'Round-trip' in the title a misleading name. In English a round-trip finishes at the point of origin -

not the case with the RDSS. Yao et al use the term Beidou Navigation Radiosonde. In places this manuscript refers

to the 'ADD' (Ascent-Drift-Descent) system instead of RDSS. ADD seems a more accurate name to me.
More explanation of the overall design would be useful. What is the purpose of the 'drift' stage?

What determines how long the drift stage is? How much does it add to the batteries required?

Will the drift and descent stages be reported on the GTS? If so what BUFR format will be used for the drift stage?

At recent WMO meetings (eg TECO 2022) there has been discussion of reducing the environmental impact of

radiosondes and other instruments. The reduced weight of the new radiosonde is a step in that direction,

but has there been any effort to reduce plastic use or the toxic elements in circuit boards?

Are there plans to refurbish and reuse some of the radiosonde instruments?
There should also mention of the WMO Global Basic Observing Network (GBON, https://community.wmo.int/en/activity-areas/wigos/gbon ) as CMA is planning to use these drift radiosondes operationally

GBON technical regulations specify that there should be soundings to 30 hPa and a subset to 10 hPa.

To what extent would this be met in the tests so far?
One could read this manuscript and think that NWP still revolves almost entirely around radiosonde profiles - not true.

There is one mention of aircraft reports and almost nothing about satellite observations.

In practice satellite observations are now hugely important and radiosondes are less so although still very useful

(partly for validation/verification). Below are three references (of many) to support this view.
Bauer, P., Thorpe, A. & Brunet, G. The quiet revolution of numerical weather prediction. Nature 525, 47-55 (2015). https://doi.org/10.1038/nature14956
Bormann N, Lawrence H, Farnan J (2019) Global observing system experiments in the ECMWF

assimilation system. ECMWF Technical Memorandum 839, 24 pp. https://doi.org/10.21957/sr184iyz
https://community.wmo.int/en/meetings/8th-wmo-impact-workshop-home (2024, final report and presentations)

Detailed comments
17 "Meteorological sounding primarily refers to the balloon-borne radiosonde"

The satellite community would disagree. Rewrite.
21 "zero-pressure dual-mode meteorological balloon" what does zero-pressure mean?
18 "uppe-rair" > "upper-air"
46-47 "Since the 19th century, the balloon-borne radiosonde has served as the primary tool for direct measurements of

47 upper-air meteorological elements below 30 km and is extensively utilized globally (Gallice et al., 2011)."

The use of radio with balloon soundings only started in the 1930s or so (20th century), with early operational systems

in the 1940s. A better reference would be Pettifer (2009).

Pettifer R (2009) From observations to forecasts, part 2. The development of in situ upper air

measurements. Weather 64:302-308. https://doi.org/10.1002/wea.484
48 "For over a century" - "For about eighty years"
49 "one measurement" - "one profile"
54 "as Russia's decrease from twice-daily" - "as Russia's temporary decrease from twice-daily"

See https://www.ecmwf.int/sites/default/files/elibrary/2016/18147-global-radiosonde-network-under-pressure.pdf
61-63 "The United States and other countries have successfully assimilated airborne sonde data into their model

systems, resulting in a 20%-40% reduction in errors in hurricane trajectory predictions (Stephen et al., 2013;

Wang et al., 2015)."

"20%-40% reduction in errors" seems too high to me for modern NWP systems with good assimilation of satellite data,

Majumdar (2016) already referenced is more balanced.
68 "The upper-air balloon system, known as ValBal, developed by the Stanford Space Program in the United States,

has accomplished multi-day flights at altitudes ranging from 10 km to 25 km (Sushko et al., 2011)."

I hadn't heard of ValBal, I suspect that it was a short-lived research system.

On the contrary the WindBorne system (Johnson et al, 2024) is active and currently providing data on the GTS

Johnson, A., Wang, X., Hutchinson, T., & Creus-Costa, J. (2024). Impact of WindBorne observation assimilation on prediction of a TPV merger case from THINICE. Journal of Geophysical Research: Atmospheres, 129, e2024JD041395. https://doi.org/10.1029/2024JD041395
81 "descent data" see also Ingleby et al (2022)

Ingleby, B., Motl, M., Marlton, G., Edwards, D., Sommer, M., von Rohden, C., Vömel, H., and Jauhiainen, H.: On the quality of RS41 radiosonde descent data, Atmos. Meas. Tech., 15, 165-183, https://doi.org/10.5194/amt-15-165-2022, 2022.
95 'more than a century' - 'about 80 years' (prior to the 1940s there were tiny numbers of research flights that

mostly relied on someone finding and returning the instrument package and recorded data)
106 "ascends at approximately 400 meters per minute" convert to metres per second
186 "The ascent phase of meteorological sounding generally lasts less than one hour."

It is usually 1.5 to two hours for most radiosondes. Or is this a statement about RDSS?
193 "hydrogen loss" It should have been stated earlier that hydrogen is the lifting gas.
232 "The positioning accuracy of SoC is 0.8 meters horizontally and 1.3 meters vertically"

1.3 meters vertically sounds better than I would expect - please provide some evidence for this.

Is the accuracy worse near the surface (due to reflection or ducting of the signals)?
242-243 "The GTH3 participated in WMO UAII2022(Upper-Air Instrument Intercomparison Campaign organized by the

World Meteorological Organization (WMO) and co-organized by the Deutscher Wetterdienst (DWD) in 2022)"

Their table lists

Tianjin Huayuntianyi Special Meteorological Sounding Tech. Co., Ltd. HT-GTS(U)2-1 (GTH3)

I think it is worth giving the manufacturer name here and probably the alternate radiosonde name (HT-GTS(U)2-1).

Is the current "GTH3" the same as that tested in UAII2022 or a development of it?
Table 4 caption "The planetary boundary layer (PBL) ranges from 2 to 7 kilometers" - should say "Free Troposphere"

other parts of the caption also need changing.
317-318 "Comparative tests led to the selection of conical parachutes"

Please provide more details of the parachute, such a a diagram, dimensions and any vents.
319 "As a result, RDSS achieves a stable descent speed of approximately 6 m/s ± 1 m/s"

Is this true even in the stratosphere? Please show some example profiles and/or mean and standard deviation profiles.

Ingleby et al (2022) report much faster descent speeds in the stratosphere

(even with a parachute) and a lot of variation from one flight to another.
"4.1 Field experiment ..."

What is the distribution (above ground level) of the lowest descent point received?

This depends on the orography and how close to a receiving station it lands.
359 "the fifth generation of ECMWF (ERA5) was used to evaluate the QC data of RDSS (Minola et al. 2020; Roja et al. 2011),"

"the fifth generation of ECMWF reanalysis (ERA5, Hersbach et al, 2020) was used to evaluate the quality of RDSS data,"

I'm not sure how relevant Minola et al is. Roja et al predates ERA5 and doesn't appear in the references.

Hersbach H et al (2020) The ERA5 global reanalysis. Q J R Meteorol Soc 146:1999-2049. https://

doi.org/10.1002/qj.3803
Table 5. 'EAR5' should be 'ERA5'; 'troposphere top' should presumably be 'tropopause', units of RH are "%RH".

'{SD of] radiosonde data and ERA5' should be 'radiosonde data minus ERA5'

IMPORTANT: Please provide mean differences for temperature.

What quality control (including comparison with ERA5) was used to exclude outliers?

What 'saturation vapour pressure' equation is used for RH? As discussed with Lebao Yao, I think there are

differences in the definition of RH between the radiosonde and ERA5. It is cleaner to start from ERA5

specific humidity and temperature and then make sure you are comparing like with like.

Note. The 'drift' temperature differences seem too large to be usable (despite the processing described above).

It would be useful to know the mean wind speeds for the different phases.
Figure 7. Wuhan should be better marked (there is something written in red that I can't read).

Perhaps a coloured X or other symbol, described in the caption would be better.
Figure 9b. A lot of green 'descent' dots are close to the 'ascent' point.

I wondered if green is actually the start of the drift phase and blue the start of descent?

Some people are red-green colour blind, changing one of the colours would help them.

(Unlike reviewer 2 I find the orientation given by Fig 9a useful.)
411-412 "With the four-dimensional ensemble forecast error is introduced into the CMA global data

assimilation system, and the H-4DEnVar assimilation scheme is developed."

The English here is strange/unclear. What is the H in H-4DEnVar?
Figure 10 caption. Stage that positive values indicate benefit when descent data is used.

Precipitation thresholds in mm?
449-452 "Targeted observations ... " This is overstated. They have "sometimes been a frontier field"

The impact of targeted observations is almost always less than one or two years work on improving the baseline

NWP system (Lorenc pers comm) - and improving the baseline tends to reduce the benefit of targeted observations.

"Majumdar & Sharanya, 2016" should be "Majumdar, 2016"

Two quotes from his 'Conclusions and Discussion':

"The fact that many results are inconclusive is not surprising, for several reasons. ..."

"In summary, the initial vision that the Global Observing System would ultimately be supplemented by networks on an adaptive basis, or even optimized into a fully adaptive network, has not been realized."
500 '5.3.3 Targeted observations experiment of Typhoon'
I was surprised by this section because surely the biggest impact on TC forecasting comes from improving the

analysis and forecast one, two or three days before landfall.

In the online discussion a response was "The RDSS can cover the South China Sea area" where would they be launched from?
For another view see

Magnusson, L., Majumdar, S.J., Dahoui, M.L., Bormann, N., Bonavita, M., Browne, P.A., et al. (2025) The role of observations in ECMWF tropical cyclone initialisation and forecasting. Quarterly Journal of the Royal Meteorological Society, 151(768), e4924. Available from: https://doi.org/10.1002/qj.4924
A few quotes form this:

"The strongest impact came from withholding of microwave radiance observations ..."

"Scatterometer data improved the forecasts ..."

"While the aircraft-borne data (dropsonde, flight-level data) were mostly beneficial, further investigations on how to best use this data in the TC core are needed."
552 'century-old' - '20th century'
556 'RDSS is essentially a mature system.' I would say it is close to maturity (but not there yet).

No data have been provided on the GTS yet as far as I know.

Some of my questions in the general comments need answering/clarification.

References
Where the papers are in Chinese please indicate this.

Many readers will not be able to read such papers, I suggest removing some of the less relevant ones.
632 "Majumdar, S. J.: A review of targeted measurements" this is the whole of the tile, delete

": targeted measurements to improve numerical forecasts of high-impact weather events over the past two decades,

particularly during the THORPEX era (2005-14), are evaluated"
660 "Tan et al ... doi:10.3969/j.issn.1004-4965.2006.01.003." I couldn't find this despite the doi.

Citation: https://doi.org/10.5194/egusphere-2025-2012-RC3
- AC1: 'Re: egusphere-2025-2012-ACs', Xiaozhong Cao, 28 Aug 2025
  
  On behalf of all my co-authors, I would like to thank you for the opportunity to revise our manuscript entitled “[Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)]” (Manuscript ID: [egusphere-2025-2012]). We also greatly appreciate the editors and RC1,RC2 and RC3 for their time and constructive comments, which have helped us to significantly improve the quality of our manuscript.
  We have carefully considered all the comments and have made extensive revisions to the manuscript accordingly. Below is our point-by-point response to the RC1,RC2 and RC3’ comments. All changes in the revised manuscript have been highlighted using the ‘Track Changes’ function in Microsoft Word.
  We believe that our manuscript has now been improved and is suitable for publication in [Atmospheric Measurement Techniques (AMT)]. We look forward to hearing from you regarding our submission.
  Sincerely yours,
  [Xiaozhong Cao]
  [China Meteorological Administration]
  [caoxzh@cma.gov.cn]
  
  Citation: https://doi.org/10.5194/egusphere-2025-2012-AC1

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Xiaozhong Cao on behalf of the Authors (10 Sep 2025) Author's response

EF by Mario Ebel (12 Sep 2025) Manuscript Author's tracked changes

ED: Referee Nomination & Report Request started (23 Sep 2025) by Chunlüe Zhou

RR by Anonymous Referee #1 (30 Sep 2025)

Suggestions for revision or reasons for rejection

Revision of revised manuscript

Synopsis: The quality of the text and the figures got a lot better in the revised manuscript.
It is a long but overall quite interesting read.
The only remaining major point is a lack of assessment of the statistical significance of the assimilation experiment results. This was pointed out in the first review and was acknowledged by the author's response. Yet this point has not been adequately addressed.

Another point that came into my mind is the question whether the drifting balloons could "escape" when drifting away over the ocean and perhaps the communication channel gets lost, and how far they could drift uncontrollably. It may be worth a sentence how this issue is addressed or that this is actually not an issue with this system.

More specific review points:

Abstract: As was pointed out by reviewers, the assimilation experiments with ADDRS data revealed positive but (so far) not statistically significant results. This has been acknowledged by the authors in their response. In the abstract, however, there is still the very detailed description of the improvements (statistically not significant) and of the dates of operational implementation (not so important for the scientific reader.
To be better in balance with the text, one should shorten the last paragraph in lines 28-37 to something like:
Numerical assimilation and forecasting experiments showed a positive (albeit not yet significant) impact on forecast quality both for general cases and for Tropical cyclone cases. The operational launching and assimilation of more than 100 such radiosondes started on 1 July 2024 and the number of stations is still growing.

l93: was organizational developed .. please omit "organizational"

l115-116: "achieving an approximate vertical stability" sounds a bit strange. Perhaps rephrase to, ..with gravity, so that its height stays approximately constant.

l130: The ground data-receiver ..

l345ff: one should use integer percentages here, e.g. 78% instead of 77,68% since the uncertainty of this number is likely a lot larger than hundredths of a percent and readability is enhanced.

Although it has been acknowledged by the authors, there is still no mention in the results section of the revised manuscript that the positive assimilation results are not (yet) statistically significant. This is however an important element of good scientific practice and it is important to allow the reader a balanced assessment of the progress achieved. It is already a big success that the the positive results achieved so far led to an operational adoption of the system, and the authors could state that they are confident that they will achieve scientifically significant improvements in terms of several scores once the data records get longer and the number of case studies gets larger.

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RR by Anonymous Referee #2 (10 Oct 2025)

RR by Bruce Ingleby (25 Oct 2025)

Suggestions for revision or reasons for rejection

Second review of
Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)
By Cao et al, October 2025

General
=======

This is an interesting but time-consuming manuscript to review, partly because of the novel technique described but also due to cultural and language differences.
It is improved from the first version but in some cases material in the "response" should have been included in the main manuscript. I think that the importance of radiosondes in NWP and particularly the value of targeted observations is still overstated - points that I made last time.
I have performed observing system experiments with and without dropsondes (mostly dense US dropsondes
in the vicinity of tropical storms; which has similarities to the Typhoon targeting of section 5.3.3)
I found very noisy results. Sometimes the extra profiles improve forecasts, sometimes they degrade them.
Thus I would place little weight on a single case as shown in section 5.3.3, and even a one-month experiment (mentioned in section 5.2) is too short to give robust results (a point also made by another reviewer).
The authors haven't really responded to my questions about the drift phase: the main considerations
determining how long it is. There is also the question of whether 'drift' data are good enough to be used in NWP, it seems not for temperature (expected) but to my surprise the wind results (table 5) also appear worse than the ascent/descent winds - it would be very useful to understand this better.

In the response the paragraph starting
"The GTH3 radiosonde uses the HC103M2 capacitive thin-film polymer humidity sensor ..."
and Table 3 are very useful. They should be included in the main text.
Please provide details of the temperature and pressure sensors too.

Detailed comments
=================

19 "The balloon-borne radiosonde observations constitutes" - "Balloon-borne radiosonde observations constitute" (delete "The", remove final "s" - better English)

20 "uppe-air" spelling

35/36 "an operational experiment" - "a pre-operational experiment"

37 "was operation over one year, which will achieve full operational capability by 2026."
"provided data over one year, and will achieve full operational capability by 2026."

40 "within comprehensive meteorological measurement framework (Ingleby and Coauthors., 2016)." -
"within a comprehensive meteorological measurement framework (Ingleby et al., 2016)."

57/58 "Currently, the radiosonde observations are still very useful for validation/verification satellite observations (Bauer et al.,2015; Bormann et al.,2019; WMO et al.,2024)."
The authors have taken three references that I suggested, but not made the main point that I was making.
I suggest something more like this:
"In recent decades satellite soundings have played an increasing role in Numerical Weather Prediction
(NWP) and they are now the observations contributing most to forecast skill (Bauer et al.,2015; Bormann et al.,2019; WMO, 2024). Radiosonde profiles still provide an important contribution to forecast skill and
help with the calibration/validation of satellite soundings and the verification of the resulting forecasts." (If the authors do not wish to "own" this statement it should be included as a comment from
A reviewer.)
(More on satellite cal/val if required can be found in
Newman, S., Carminati, F., Lawrence, H., (...), Salonen, K., Bell, W. 2020
Assessment of new satellite missions within the framework of numerical weather prediction
Remote Sensing 12(10), 1580

Radio occultation is now more important than radiosonde profiles as a reference for satellite soundings, see Bauer, P., G. Radnóti, S. Healy, and C. Cardinali, 2014: GNSS Radio Occultation Constellation Observing System Experiments. Mon. Wea. Rev., 142, 555–572, https://doi.org/10.1175/MWR-D-13-00130.1.
)

62 "Numerous studies" - "Several studies"

62/63 "significantly enhance" - "enhance" (the improvements are fairly minor)

63 "reported about" - "reported"

65 "airborne radiosonde" - "dropsonde"

65/66 "leading to a 10–15% reduction in errors associated with hurricane trajectory predictions"
Overstated.

80,81 "Nonetheless, due to high costs and limited ascent rates, they are not viable solutions for long-term
operational balloon sounding data collection. Furthermore, these balloons very slow ascent rates "
The WindBorne balloons are now quasi-operational (details). The issue of slow ascent rate (mentioned twice,
better rewritten) is a problem for temperature and humidity, but not for wind - upper level wind is very important for NWP.

88 "This paper introduce" - "This paper introduces"

91 "within" - "with"

93 "The ADDRS was organizational developed", delete "organizational"

94 "domestic units" - "organisations"

Figure 1. It would be more consistent to refer to "balloon" rather than "ball"

Figure 2. '"Ascent-drift-descent" ("add" )subsystem' - '"Ascent-drift-descent" ("ADD") subsystem'

114 "controlled aeration" - I'm not sure what this means (delete or reword)

116/117 "vertical stability. Subsequently," I suggest deleting the sentence stating subsequently and just saying "vertical stability, starting the drift phase."

118 "predefined duration" as I said in my first review I think there should be some discussion (here or elsewhere) about the considerations used to decide the duration.

120/121 "Subsequent to this separation .... mission segment." I suggest omitting this sentence, once it has separated the balloon has to come down sooner or later. Calling this a mission segment puzzled me (did this refer to the descent phase? - no).

159-161 "Compared ... observations." I was not familiar with the work of Anand/Vernier and others,
I would say that they are addressing a different issue. I see that you have already discussed their work
On lines 77-81 and to me the comparison here is unhelpful. I suggest omitting this sentence.

161-165 The rest of this paragraph seems to repeat what is said elsewhere and could also be omitted?

171 'the aeration volume' - 'the volume'

179 "precise control of aeration" - "precise control of density"? Or "precise control of the mass of air in the balloons"?
I am not familiar with "aeration" in this context and would suggest avoiding use of a novel word unless essential. "Aeration" could be omitted from lines 181 and 184 (or replaced by "optimum" on line 184).
Please include an indication of how much hydrogen is used in each balloon in the optimal configuration.

185-186 "controls the aeration of dual-mode balloon" - "controls the performance of dual-mode balloons"

226-227 "requiring a minimum operational time of six hours."
Why does it require at least six hours? Related to my question on line 118.

235 "reduce the size, weight, and power consumption." Perhaps add "(The amount of plastic, and toxic materials in the circuit boards, has also been reduced.)" From response to first review.

Table 4. In the viewer I am using (preview) most of the numbers just appear as dots/circles.

257 "the gravity or altitude" - "the altitude"?

285 "the Guide to Operational Upper-Air Meteorological Observation"
Does this mean WMO No. 8 (or a CMA document) - please clarify.

291 "The effect of radiation [in the drift phase] ..."
Is it not partly that there is very little ventilation of the sensors in this phase?

294 "Vaisala RS41 radiosonde software often flags such data as invalid"
What do you mean by "such data"? Vaisala RS41 does not usually have a "flat drift phase".
Either explain better or delete the sentence.

306 " refine the simulation-based error correction equations (Yang et al., 2022)."
It would be useful to give an indication of the magnitude of the errors involved.

307 "Vertical wind data extracted by parachute landing" - "Vertical wind data during the parachute descent"

316 "Guo et al, 2018" ("Evaluation of wind performance of domestic Beidou dropsonde of ball-loading")
It would be very useful to have a summary of the results of Guo et al in English.

317 "selection of conical parachutes" - please include some of the details of the large conical parachutes mentioned in the 'response' but not in the main text. Please also give the string length used.

318 "a stable descent speed of approximately 6 m/s" From Figure 11 the initial descent speed is much higher (as seen by Ingleby et al (2022)) this should be mentioned here. Replace 'stable' with 'low-level'?
Do you see the large case-to-case variation in descent speed reported by Ingleby et al (2022)?

325,326 "The ADDRS network spans six stations" - "The ADDRS radiosondes were launched from six stations"
(I think this is what you mean.)

347,348 "and the effect of daytime was better than nighttime" - "somewhat worse than the daytime performance"

349 "outer ball" - "outer balloon"

351,352 "the drift height should basically meet the 30hPa requirement of GBON (WMO, 2020)."
The GBON requirement for some ascents to reach 10 hPa should also be mentioned.

257 "The simulated and observed trajectories" - do the simulated trajectories include NWP forecasts?
More information required.

258 "A color gradient based on pressure altitude" The colour gradient is too subtle for me to make out.
Use different (larger) markers when a multiple of 200 hPa is crossed?

Table 5.
This is very interesting, but raises some questions.
How were the RH comparisons performed? (Which SVP equation was used?) Some details in the response should be included in the main text.
For the "drift" results I understand the temperature results being worse than the ascent/descent results, but I don't understand it for wind. This should be mentioned in the text and an explanation attempted if possible. (How strong a function of pressure are the wind results in the stratosphere?)

For the descent temperatures there is some sign of a warm bias, especially at upper levels, which was discussed by Ingleby et al (2022) - the European biases may be larger in magnitude due to larger fall-speeds but to see this more clearly further results (as a function of height or fall-speed) would be needed. If the upper-level temperatures are biased there is a question of whether they should be assimilated or not.

382 "The applications in weather analysis" - "The applications to weather analysis" (more grammatical)
This subsection doesn't actually show NWP analyses. "A case study" might be more accurate.

394 "trajectory data" - "trajectories" (for ADDRS is it just the ascent trajectory?)
What time and how far downstream was the ADDRS descent?

395 "At 19:15 on the night of the 8th" - is the time in UTC? Also the other times in this section.

428 "vertical sparring methods" should "sparring methods" be "spacing"

462 "an important method" - "a possible method"

463 "they significantly enhance" - "they sometimes enhance" (as it stands the text overstates the
Importance of targeted observations in my opinion)

464 ", which is crucial for predicting extreme weather disasters" - delete (overstatement)

467 "power system" - "steering system"?

532,533 "Therefore, the demand for vertical profile data of the internal interface of Typhoon 'SAOLA' became imperative." Overstatement, perhaps "Therefore forecasters wanted profiles of the interior of
Typhoon 'SAOLA'." Please add "Note also the importance of the steering flow and use of satellite data to analyse the wider environment of tropical storms (Magnusson et al, 2025)." If the authors do not wish to
'Own' this statement it should be included as a comment from a reviewer.

540 "required air capacity" - "hydrogen" or "gas" rather than "air"

544 "Late test results" - "Test results"

561 rewrite

563 "As well as ADDRS represents a next-generation approach" - "ADDRS represents a possible next-generation approach"

579 "<or ethical concerns>" - delete (or explain)

Data availability:
"https://www.geodata.cn/collect/site/#/" When I tried this I had an error message "502 Bad Gateway"
I managed to connect to "https://www.geodata.cn/" - all in Chinese except for an 'English version'
Link which redirects to "http://wdcrre.data.ac.cn". In this website a keyword search for radiosonde gave no results.

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ED: Reconsider after major revisions (04 Nov 2025) by Chunlüe Zhou

Dear authors,

Three reviews have been received. It’s acknowledged that clear improvements are in the language, figure quality, and overall presentation of the manuscript. After careful consideration of the second-round reviews, I concluded that the manuscript still requires major revisions before publication. The key issues that must be addressed in the next revision were summarized below.
1. Statistical significance of the assimilation experiment results (Reviewer #1 & #3):
Both Reviewers #1 and #3 emphasized that the current assessment of the assimilation experiments lacks discussion of statistical significance or robustness. Reviewer #1 specifically noted that this issue had already been raised in the first round and was acknowledged by the authors but not adequately addressed in the revision. Reviewer #3 also questioned the reliability of conclusions drawn from relatively short or limited assimilation periods, and expressed concern about the significance of a single case presented in Section 5.3.3.
2. Quality and usability of drift-phase data:
Both Reviewer #1 (briefly) and Reviewer #3 (in detail) raised questions about the drift-phase observations—their duration, data quality, and practical usefulness for NWP. Reviewer #1 asked whether the drifting balloons might lose communication when moving over the ocean and how such cases are handled. Reviewer #3 also noted that wind data from the drift phase appear less accurate than ascent/descent data.
3. Instrumentation details and discussion balance:
Reviewer #3 appreciated the additional technical information provided in the authors’ response (e.g., the paragraph describing the humidity sensor and Table 3) and strongly suggested that such content be integrated into the main text. The reviewer also noted that the importance of radiosondes for NWP may be somewhat overstated, and recommended revising the discussion section to provide a more balanced interpretation.

In light of these points, I invite you to submit a thoroughly revised version that explicitly addresses all the concerns. More details can be found in the
individual review reports. Please include a detailed point-by-point response letter explaining how each issue has been handled and where changes appear in the manuscript.
Your revised submission will be sent back to the reviewers for fast re-evaluation. Thank you again for your efforts in improving this manuscript.

Sincerely,
Chunlüe Zhou, Sun Yat-sen University
Atmospheric Measurement Techniques

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AR by Xiaozhong Cao on behalf of the Authors (08 Dec 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (13 Jan 2026) by Chunlüe Zhou

RR by Anonymous Referee #3 (21 Jan 2026)

Suggestions for revision or reasons for rejection

Rereview of Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS) by Cao et al
January 2026

General

This manuscript describes a major ongoing/forthcoming change to Chinese operational radiosondes and a
novel three-phase measurement pattern (I'm not sure whether other operators will try that pattern).
It would be very helpful to understand the phase out of the old Chinese radiosondes and the phase in of
the new. The WMO BUFR code includes 'radiosonde type', in December 2025 we saw small numbers of the
old radiosonde types (200, 201 and 202), but the vast majority of Chinese reports had the radiosonde type
set to missing which is not helpful. We saw ascent profiles, but no Chinese descent profiles.
Some information on the progress/plans for the transition would be very useful.

The manuscript has been improved and contains a lot of good information.
As with the previous review some issues mentioned in the authors response should be included
in the main manuscript, notably in the discussion of the drift and descent phases.

1. Drift phase: reporting issues and the quality of winds

The author response states that:
"Sensor Response and Balloon Dynamics:Under the relatively calm conditions of the
drift phase, the radiosonde's motion can be more susceptible to fine-scale turbulence
and the pendulum motion of the radiosonde suspended under the balloon. This can
potentially add high-frequency noise to the wind measurements that is not
representative of the synoptic-scale flow the model resolves."

The authors suggest that they have addressed these issues in the discussion section - I struggle to see
where (there are only two instances of "pendulum" and two of "turbulence" in the revised manuscript,
none of these in the context of the drift phase). NB The track check document shows all changes since the
original submission, it should just show the changes in the latest revision to make it more useful.

IF there is evidence of more pendulum motion during the drift phase then it should be presented
in the main manuscript.
[Note to ADDRS research team. You might want to consider adding a (small, cheap) accelerometer to your
radiosonde. I have spoken to some of the authors of the paper below and they agree that accelerometer
output could be used to improve the filtering of pendulum motion.
Marlton GJ, Harrison RG, Nicoll KA, Williams PD. 2015 A balloon-borne accelerometer technique for
measuring atmospheric turbulence. Rev. Sci. Instrum. 86, 016109. doi:10.1063/1.4905529 ]

Also in the author response:
"If the drift phase is too long, the data may become obsolete for the intended assimilation cycle."
"Challenges in Data Assimilation: Standard data assimilation systems, including the
one used in this study, are primarily optimized for conventional, quasi-vertical
profiles. The assimilation of observations with significant horizontal drift presents a
more complex challenge for the observation operator, which typically assumes the
observation is located at a single horizontal point. This mismatch can contribute to the
increased errors seen in Table 5."

Some NWP systems now allow for horizontal drift in their processing of ascents (and descents),
see Pauley and Ingleby (2022), figure 7 and associated text. This improves the fit between observations
and model background in the stratosphere. (Probably worth mentioning this and the reference in main text.)
The ECMWF system splits BUFR profiles into 5 (originally 15) minute sub-profiles and treats the
sub-profiles as vertical, but other methods are also in use.
For WindBorne both NCEP and ECMWF treat the data as a series of single-level points (like aircraft data).
This raises questions about how the "drift" phase of ADDRS data should be reported and used.
To me it makes sense if there is some 'batching' of the reports, but there is no need to wait for the
descent to start before sending earlier parts of the drift phase.
The comment about the "mismatch" above seems to suggest that the whole drift phase is being compared with
model fields at a single latitude/longitude - which would indeed add (unnecessary) representation error.
These issues and the processing used in your study should be discussed in the main text.

Pauley P, Ingleby B (2022) Assimilation of in-situ observations. In: Park SK, Xu L (eds) Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications (Vol. IV). Springer.
https://link.springer.com/book/10.1007/978-3-030-77722-7

2. 'We agree that the term "a pre-operational experiment" more accurately describes the
nature of our study, which was conducted to evaluate the system's performance and
potential prior to its full operational deployment. As suggested, we have replaced "an
operational experiment" with "a pre-operational experiment" on [Page 1, L 30] of the
revised manuscript and throughout the manuscript, including in the abstract,
introduction, and conclusion sections.'
Searching the resubmitted manuscript only the abstract has been changed to "pre-operational".

Detailed comments

54-55 "radiosonde profiles still provide a crucial contribution to forecast skill and are fundamental for the
calibration and validation of satellite soundings (Newman et al., 2020)."
This is not a point made by Newman et al (perhaps omit that reference) and arguably the cal/val of
satellite soundings would be fine with radio occultation but not radiosonde data.
From my point of view the most important contribution is now in the the independent validation/verification
of NWP forecasts. I suggest changing the text to:
"radiosonde profiles still provide an important contribution to forecast skill, help with the
calibration and validation of satellite soundings and allow independent verification of forecast fields."

60-63 "Dropsonde data assimilation has been shown to
hurricane trajectory forecast errors associated with an approximate reduction of 10-15% in specific contexts,
such as short-term (0-48h) predictions over ocean basins using the GFS model, as demonstrated in multi-year
statistical analyses( (Ingleby, 2021; Cohn et al., 2013; Wang et al., 2015)."
Grammar error, and as I said before other studies (perhaps with better use of satellite data) show much
less impact, I suggest
"Some multi-year studies (Cohn et al., 2013; Wang et al., 2015) suggest that assimilation of dropsonde
data can reduce hurricane trajectory short-range forecast errors by 10-15%. However other studies reviewed
by Majumdar (2016) show less impact."
"Ingleby, 2021" is not a relevant reference here (it could be omitted from the references).

68 "Johnsonet al., 2024" - "Johnson et al., 2024"

74-75 "slower ascent can reduce the accuracy of vertical resolution due to issues like sensor response
time and radiative errors"
slower ascent would surely increase the accuracy of vertical resolution in the case of large response time
(but might make radiative errors worse)!

78-79 "Another conducted an extensive analysis by compiling four years of radiosonde data collected without
parachutes across various seasons and altitudes, highlighting the scientific value of descent data (Ratnam et al., 2014; Ingleby et al., 2022)." .
This conflates two different studies with different data (some of which used parachutes).
Perhaps "Studies by Ratnam et al., 2014 and Ingleby et al., 2022 looked at the quality and value of radiosonde descent data."

Table 1 "In the weather-sensitive area without a station, the active fusing
drifting ccontroller is carried out and the descent measurement is started" -
"In a weather-sensitive area without a station, the inner balloon can be detached
and the descent started"

119 "The balloon launch station"
Q. Is the launched manned or automated?

153 "Variations in air pressure and temperature within the outer balloon"
Delete "air" (the balloon contains hydrogen).

204 "DdiOctyl" - " DiOctyl"?

214 "The ADDRS payload unlike operational radiosonde," - "The ADDRS payload is unlike an operational radiosonde."

221-223 "Besides GTH3 ... significantly reducing" better as
"Compared to the previous operational radiosonde, the GTS12 L-band Secondary Wind-sounding radar system,
the GTH3 significantly reduces ..."

227 "reducing" - "reduced"

239 "ORUC(" - "ORUC ("

289 "and can" - "and it can"

309 "Jensen et al, 2010" This is a good paper but it doesn't deal with radiosonde descent data so I am unsure
or its relevance here.

344 "black dots represent receive radiosonde data stations of ADDRS" - "black dots represent ADDRS receiving stations"

354 "launches,of" - "launches, of"

Figure 6. The caption says "(a) drifting height; (b) descent height" but there is no (a) and (b); should just say
"drift height"?
The bar heights show percentage occurrence. I was surprised that the total bars are higher than both daytime and nighttime. On reflection the percentages may be calculated for all flights, but I think it would be better if
"daytime" showed the percentages for daytime flights and similarly for "nighttime".

377 "verification FY-3D" - "verification of FY-3D"

387-388 "Table 5 ... ascent phase compared with descent phase"
404-405 "And (Ingleby et al., 2022) noted that ECMWF's operational system excludes descent temperatures
above 150hPa during assimilation due to these biases." [The biases have not been described.]
From the author response response "We agree with the reviewer that a warm bias is evident in descent
temperatures, particularly at higher altitudes, and that this bias is closely linked to
descent rate. Ingleby et al. (2022) systematically investigated this issue ..."
The warm bias issue should be mentioned in this section of the main text.
It would be very useful to know typical and maximum descent rates of ADDRS at the start of the descent phase.

400-402 "We also note that the discrepancies between the measured wind and temperature data during the drift phase
and the ERA5 reanalysis data are significantly larger, a phenomenon consistent with most radiosonde data
comparisons at high altitudes (typically above 300hPa) against ERA5 (Liu, B et al., 2021)."
See general comment 1 and issues about representation error and the question of whether a single
latitude/longitude was used for ERA5 comparison with the drift data.
B Liu et al, 2021 was not accepted and it shows winds but not temperatures so is not an ideal reference.
Other sources would be better eg Fig 7 of Pauley and Ingleby (2022) (this shows results over Europe) or Ingleby 2017, ECMWF Tech Memo 807, Figure 3.11 shows O-B results for China, with a modest local maximum in wind differences at 300-250 hPa.

550-551 "ADDRS discharge radiosonde observations station" - "ADDRS launch station"?

551 "discharge time" - "launch time"? (or time at which descent should start?)

560-561 "expected that 'SAOLA' would land" - "expected that 'SAOLA' would make landfall"

601-603 "We are confident that statistically significant improvements in precipitation forecast skills will be achieved as the data records lengthen and the number of case studies, particularly for extreme precipitation events, increases in the future."
I think this sentence should be deleted, it makes claims that will never be put to the test (because the old
radiosondes will be withdrawn soon), and when I run OSEs without radiosonde data the main impact is on upper level winds and low level temperatures.

610 'theEditor' - 'the editor'

613 'platform((' - 'platform ('

614 'December this year' 'December 2025' presumably

613 https://www.r7tec.com/html/report/20040875-1.htm This (data availability) link exists, but doesn't indicate
in English how to access the data or register.

There are various references in the wrong order

Liu references should be in order of initials. Lau should come before Liu.

759-762 Wang, J. H. et al 2015 and WMO references are not in alphabetical order

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RR by Anonymous Referee #1 (22 Jan 2026)

Suggestions for revision or reasons for rejection

l72f: Grammar error - Please rephrase the sentence starting with While early.... as:

Early stratospheric balloon systems also faced questions about their.....

l78f: Grammar error - please rephrase the sentence:

An extensive analysis that compiled four yearsof radiosonde data collected without parachutes across various seasons and altitudes, highlighted the scientific value of descent data(Ratnametal., 79 2014;Inglebyetal.,2022).

l80f: On account of ... this sentence also sounds awkward. This is now the third instance, so language editing is highly recommended for the whole article.

l91ff: This innovative ... this sentence is redundant, compare with l83ff

l108: The inner ballon does not burst, and the buoyancy ...

l112: ... begin to descend

l315: ... ability to perform temporally intensive ...

l322: More than ten comparative tests .... were carried out.

l323: of the conical parachute

l326: The parachute area should be tailored to match the radiosonde weight

l408: Please specify in the table caption how the difference was calculated. Was it obs-ERA5 or ERA5-obs

Table 5: Do you mean Above Tropopause and Below Tropopause? Below Troposphere makes no sense, since that would be at the surface or below!

l411: potential to capture (not potential for capture)

l417: in tracking the occurence

l434: suggests intensive upward motion

l445: Unlike GTS12 radiosondes, the ADDRS radiosondes provide measurement data of both ascent and descent phase for numerical weather prediction (NWP), achieving ...

l491: Targeted observations have sometimes been a frontier field in atmospheric science.

l591: This sentence is unclear. Do you mean: ADDRS represents a possible next-generation approach for upper air sounding, adding substantial flexibility compared to currently operational sounding systems. ?

l607: what do you mean with "continuous deepening of the measurement data"? Please rephrase or omit.

l610: to the editor

l612ff: Contrary to the statement of the authors This web link still does not work (on 22 Jan 2026), so the data must be considered unavailable.

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ED: Publish subject to minor revisions (review by editor) (23 Feb 2026) by Chunlüe Zhou

AR by Xiaozhong Cao on behalf of the Authors (04 Mar 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Apr 2026) by Chunlüe Zhou

AR by Xiaozhong Cao on behalf of the Authors (06 Apr 2026)

Journal article(s) based on this preprint

21 May 2026

Development and application of the Ascent-Drift-Descent Radiosonde System (ADDRS)

Xiaozhong Cao, Qiyun Guo, Haowen Luo, Jincheng Wang, Rongkang Yang, Die Xiao, Yinfeng Liu, Zhongliang Sun, Shijun Liu, Sijie Chen, Anfan Huang, Guo Jianping, and Peng Zhang

Atmos. Meas. Tech., 19, 3231–3251, https://doi.org/10.5194/amt-19-3231-2026,https://doi.org/10.5194/amt-19-3231-2026, 2026

Short summary

Xiaozhong Cao, Qiyun Guo, Haowen Luo, Rongkang Yang, Peng Zhang, Jianping Guo, Jincheng Wang, Die Xiao, Jianping Du, Zhongliang Sun, Shijun Liu, Sijie Chen, and Anfan Huang

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This study aims to introduce in-situ profiling techniques and cost-effective technology for upper-air observation—the Round-trip Drifting Sounding System (RDSS)—which reduces costs relative to intensive sounding and achieves three sounding phases: Ascent-Drift-Descent (ADD). The RDSS not only provides additional data for weather analysis and numerical prediction models but also makes substantial contributions to targeted observations.


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