the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Mar 2024
Unique structure, radiative effects and precipitation characteristics of deep convection systems in the Tibetan Plateau compared to tropical oceans
Abstract. Using the space-borne lidar/radar observations, this study identifies deep convection systems (DCS), including deep convection core (DCC) and anvils, over Tibetan Plateau (TP) and tropical oceans (TO), and finds that DCSs over TP are less frequent, exhibiting narrower and thinner DCCs and anvils compared to those over TO. The thinner DCCs over TP exert weaker radiative cooling effects at the top of atmosphere (TOA) compared to the TO. But, the shortwave TOA cloud radiative effect (CRE) of TP anvils is stronger than that of the TO possibly due to more densely packed cloud tops over TP. It results in stronger TOA CRE of DCSs over TP than that of TO. Especially, longwave CRE of DCSs over TP is notable greater at surface and low-level atmosphere due to the distinct lower temperature and less water vapor. The width of DCSs shows a positive correlation with wind shear and atmospheric instability, and the underlying mechanisms are discussed. We also find that the impact of aerosols on cloud top heights and precipitation displays significant discrepancies between the two regions. It is because that the aerosol invigoration effect is less efficient on the TP DCSs, mainly attributed to the significantly colder cloud base. Due to competition between invigoration and radiative effects of aerosols, the correlation between precipitation and aerosols over TP is not significant. However, precipitation in the TO experiences invigoration followed by suppression with increasing aerosols, due to the dominance of aerosol radiative effect and enhancement entrainment under polluted conditions.
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RC1: 'Comment on egusphere-2024-480', Anonymous Referee #1, 29 Mar 2024
The authors use satellite retrievals by active instruments to characterise deep convective clouds on the Tibetan Plateau compared to the same cloud type in an area over the Indian Ocean to the south of India. The analysis separates convective cores and anvils. It considers radiation from surface to TOA, clouds overshooting the tropopause, cloud spatial extent and occurrence, and meteorological and aerosol controls on the clouds. The authors find differences in the character of the clouds between the two regions.
This is a comprehensive and robust characterisation of deep convective cloud features, radiative effects and controls over a region with particularly interesting geography. The paper is long, and it is hard to keep track of what results are novel versus recounting literature. Ideally, the paper would have been written with a clear and focused results section without referring to so much literature, and then discussed the literature in a dedicated discussion section. Broadly speaking the authors seems to confirm that the differences they see between the clouds in the two regions are consistent with understanding in the literature.
I can’t say I find the paper particularly novel or easy to read. However, I can see it being a useful characterisation for other scientists to build upon. So, apart from the need to address the minor comments below, I can see value in publication.
Minor comments
Title – I haven’t seen anything in the paper that makes me thing the clouds on TP are “unique”, please remove the word or justify with respect to deep convective clouds in general.
Title – “Tropical oceans” is much broader than the use here. At best tropical “Indian” ocean could be used.
L19 - “competition between invigoration and radiative effects of aerosols” I think you should be specific about what radiative effect is competing with invigoration. This is a bit vague for an abstract. Perhaps “direct” radiative effect?
intro/methods – The lack of map in the main text doesn’t help the reader. That’s your choice, but please at least refer to figS1 early on so the reader can look at where you are studying. I also do not know the motivation behind the specific TO region you’ve picked, the topical ocean is much more general that that box. What’s special about that part?
FigS1 – please mark on the sub-divisions of TP that you use in table 2.
Section 2.2 – Have ERA5 or MERRA2 been evaluated over the tibetan plateau. This seems important. ERA5 is ultimately a model with a spatial resolution that may be affected by large gradients in terrain in the region.
L168 – Presumably there’s a third criteria that there is cloud present between the base and the top?
L179 – No “high cloud” in the image despite cloud tops over 15km. What’s the definition of “high cloud”?
Eq1 – Another way to look at this is the abs(dV/dz). I think that’s a bit more intuitive to understand. It does mean that you can identify high shear as a result of strong low level winds, and weak upper level winds. Does this occur in your data? Is it you intension to include such conditions? Do you think strong low winds with weak upper winds is likely to have the same the effect as weak low winds and strong upper winds?
L195 – please can you describe the theoretical basis for using the gradient in theta_es to study the impact of conditional instability. I would have expected you would relate the environmental temperature to theta_es to look at stability. And for conditional stability you would need to consider the dry adiabat too (see AMS glossary on “conditional stability”). I did look at Li et al (2018) but I found no information to justify the approach.
Results section – this includes a lot of references and discussion for results. I suggest just not labelling those sections as “results” or calling them “results and discussion”.
Table3 – I’m surprised by how negative these CRE’s are, I think this is because they’re daytime-only? I think it would be worth labelling them as such in the caption.
L358 – fig S5 i and j are BOA DCS not ATM DCC.
Fig6 – aerosol quantiles. I suggest you refer to 30th and 70th percentiles, opposed to the numbers you put into a code function. How do the actual values of these percentiles relate to the low and high aerosol environments discussed by Fan (are you actually spanning the range of aerosol levels they did?)
L590 – do you mean previous studies over the TP? If so, be specific. Plenty of studies over other areas have studied the anvil CRE.
Technical comments
L14 – “notable” to “notably”
abstract – generally the abstract will need a grammar check by the journal. Issues are very minor.
L26 – “convections” is not grammatically correct. Change to something like “convective storms”?L369 – Can you spell out in your methods the equations for each of the atmos/BOA/TOA CREs. You’re saying “difference between all-sky and clear-sky” but it’s ambiguous which way you have done the subtraction. Please spell it out so it is clear. I assume clear minus all-sky, but the phrasing suggests the opposite to me.
L648 – “investigatingthe” needs a space
Citation: https://doi.org/10.5194/egusphere-2024-480-RC1 -
RC2: 'Comment on egusphere-2024-480', Anonymous Referee #2, 13 Apr 2024
General Comments
The focus of this study was to capture deep convective system properties over the Tibetan Plateau using satellite remote sensing observations. This research is deemed novel as not much is understood of the cloud structure and radiative effects of full deep convective systems over this region. Furthermore, it is challenging to decouple the relative influences of meteorological conditions and aerosol concentrations on the deep convective cloud structure and precipitation. Therefore, the analysis also investigated how dynamical properties such as vertical wind shear, convective instability, and vertical velocity influence cloud and precipitation development under differing aerosol loading environments. The results were supported by explanations of potential mechanisms that were theorized in previous work. However, the exact mechanisms, such as how the aerosol invigoration effect differs between warm-base and cold-base clouds, or how aerosol invigoration and aerosol radiative effects individually influence entrainment suppression, were not themselves tested or observed in this study. While it seems appropriate to speculate the potential mechanisms, the conclusions heavily relied on such mechanisms to explain the results. Therefore, I suggest that it would serve the paper better if the concluding remarks pointed to such mechanisms without stating that these mechanisms are the reason for the results.
Specific Comments
L41: What did Luo et al. (2011) find?
L70-76: These sentences are the start of a different point, so I think they would best be served in a different paragraph that discusses how spaceborne measurements--and particularly the ones that you are using--have been used for aerosol-cloud-precipitation measurements.
L106-107: Measurements are two times a day at 1:30 am/pm LST, not for the full day, between 2006-2011.
L111-112: “It is important to note that CloudSat will no longer operate during nighttime due to the battery anomaly (Witkowski et al., 2018)” seems out of place. Is this in reference to the DO-Op switch made in 2012?
L115: Is daytime SW CRE normalized to account for variability in solar insolation throughout the day? If not, that could drastically impact the results — CRE would be much more enhanced at 1:30 pm compared to the rest of the day.
L177: So anvil can be precipitating or non-precipitating?
Figure 1: Just to clarify, is this example not included in your analysis of CRE since you are ignoring systems with multiple cloud-layer profiles (i.e., systems with underlying low-level cloud)?
L208-209: What is your motivation for selecting meteorological factors the hour before the DCS was detected by CloudSat/CALIPSO? Do you want to select them before convection is initiated, or before the DCS advects into that region? Or to match up with the aerosol information?
L209-210: When you say that the convective system movement under advection is ignored, what are you suggesting? Are environments fairly homogeneous such that you do not need to consider the meteorological conditions in the region that convection moves into?
Section 3.1: Is this section considering both daytime and nighttime DCSs?
L230: Can one cloud cluster or DCS contain multiple DCCs in your analysis?
L232: It should also be discussed what the differences in convection between land and ocean are, particularly with respect to the diurnal cycle. Since land and ocean have different diurnal cycles of convection and precipitation, and that CloudSat-CALIPSO are confined to only twice-daily measurements that do not capture the full diurnal cycle, how might this influence the results that you are seeing? For example, how might the diurnal cycle be influencing the differences in the frequency and structure of convection between TO and TP?
L248-250: Why does deep convection over the TP contribute so much stratospheric pollutants?
Table 2: are these exclusively single-cell DCSs? Also, I would suggest switching the order of the TP (total) and TO so that the TP regions are consecutive.
L302: How are you getting these LW and SW CRE values? The SW CRE is from daytime-only at the 1:30 pm overpass, correct? And are you averaging over the daytime and nighttime overpasses for the LW CRE? Since the SW CRE is calculated from radiative fluxes at 1:30 pm local solar time, these measurements are more enhanced than at other times of day due to the near peak in solar insolation at this time. To capture cloud radiative effects that are more representative of what they would be throughout the day, you would need to multiply the SW radiative fluxes by the diurnally averaged insolation for that day and location (L'Ecuyer et al., 2019) and then recalculate the net CRE.
L315: The sentence starting with "In particular" is the start of a new discussion on LW BOA CRE so I would suggest starting a new paragraph.
L388: What does "the high value of CRH, the difference between all-sky and clear-sky heating rates" mean?
L461: What is the sample size of each bin for the different ACs in Figure 6?
L604-605: Your reasoning would for the enhanced SW CRE of anvils over the Tibetan Plateau could be improved if you verify whether the cloud tops are more densely packed. Perhaps take a look at cloud optical depth, which can be found in the 2B-FLXHR-LIDAR data set.
Technical Comments
L25-26: "convective activity" instead of “convection activities”
L32-32: Modify this sentence to “Although deep convective cloud is less frequent compared to other cloud types, it has a more complicated vertical structure and larger extent, thus exerting a great influence on radiation and precipitation over the Tibetan Plateau region.”
L41: Remove “Such as”
L51-52: “A complete deep convection system (DCS) should include both the deep
convective core (DCC) and the anvils” is out of place and can be removed.
L110 & 151: L'Ecuyer
L233: "Since the TO"
L239: I think you mean DCC, not DCS
L250-251: In the tropical region? Please rephrase.
Fig S2-S3: Are these mean values?
L363: By "larger", do you mean less negative?
L366-367: Are you comparing the anvil structure and radiative effects to the structure and radiative effects of the DCCs? Please clarify.
L383: Do you mean to say "below" instead of "within"?
L385-386: This is an incomplete sentence; please modify.
L388: Is "height bins with only several valid data are not shown" a typo? What is the value of "several valid data"?
L398: Remove comma after LW CRH
L463-465: This sentence is incomplete.
L555: Remove comma after While
Suggested References
L’Ecuyer, T. S., Y. Hang, A. V. Matus, and Z. Wang, 2019: Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part I: Top of Atmosphere and Surface. J. Climate, 32, 6197–6217, https://doi.org/10.1175/JCLI-D-18-0753.1.
Citation: https://doi.org/10.5194/egusphere-2024-480-RC2
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