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:https://doi.org/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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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

Status: final response (author comments only)

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

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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Short summary

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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