Behera et al., On the cross-tropopause transport of water by tropical convective overshoots: a mesoscale modelling study constrained by in situ observations during TRO-Pico field campaign in Brazil

The authors simulated cloud convective clusters and their overshooting tops, deep convection whose cloud top heights are higher than tropopause. The model which the authors used was BRAMS, Brazilian RAMS, and their data was measured during the TRO-pico intensive observation period, where the TRO-pico focused on the water budget measurements between the troposphere and the stratosphere by use of balloon-borne particle and water vapor sensors, and S-band radar, in Brazil. The authors showed, for example, approximately one kilo tons of water vapor was transported from the troposphere to the stratosphere by one overshoot. This paper should be accepted after minor revises because their method and data are quite unique, their results are reasonable, and they thoroughly described what they did in detail, without any ambiguous points.

Minor comments:

L. 75: The authors should write the relative humidity with respect to ice.

L. 85: Are there several IOPs? If so, the authors should describe whole TRO-pico campaign very briefly.

L.170: The authors should add the main aim to introduce NU21 for the simulation and/or the characteristics of Eq. 1; it would imply the results of L. 389, L. 435, and L. 487-492.

L. 226 and Figure 1: The authors should point out “three cells” by arrows in the figure.

Section 6.2 and Figure 8:

- The authors should define “the total mass budget” clearly; Was it integrated by time and whole area (1840km x 1640km)? The authors should add that liquid was neglected.

- L. 433: The author should write “kilo tons (kt)” because kt is usually used for “knot.” The authors should explain how to calculate 8 kt, which is probably “ice+WV at 17:30” – “ice+WV at 15:00.”

- The authors should explain the legends in Fig. 8. I believe that “17 km < 18 km” denotes of overshoot whose cloud top heights were 17 – 18 km. “intensity” in the caption would be cloud top heights of overshooting tops? The authors should also describe the length of arrows and check “color blindness”; e.g., https://en.wikipedia.org/wiki/Color_blindness

Table 1: The authors should describe the method how to count overshoot. For example, I draw three cases of overshooting tops (see the attached); are they one overshoot or two overshoots?

Review: On the cross-tropopause transport of water by tropical convective overshoots: a mesoscale modelling study constrained by in situ observations during TRO-Pico field campaign in Brazil  (https://doi.org/10.5194/acp-2021-543)

Overview:  This paper examines perform three simulations of an observational case of stratospheric overshoots using the BRAMS (Brazilian version of RAMS) mesoscale model.  The observed cases were from the TRO-Pico field campaign in Brazil.  The case studied occurred on 13 March 2012 in Bauru, São Paulo State, Brazil. two lightweight balloon-borne hygrometers intercepted a hydrated stratospheric air parcel originating from two different overshooting plumes. The runs are used to estimate the sensitivity to the model setup, with the intent of studying the physical processes associated with overshoots.  They first run a reference case, then run a case with the shape of the hydrometeors changed, and last increase the vertical resolution.  However, it appears that the higher vertical resolution case had issues, so they do not include that simulation in the lower stratosphere water budget analysis. However, they show that the model can produce convective plumes somewhat similar to that observed by radar as well as stratospheric water enhancements.  They then provide estimates of water flux due to overshooting events. Essentially, they end up comparing 2 cases of the model, and neither case exactly duplicates the observations, but are reasonable. I would recommend some more examination of why the two runs differ, and perhaps consider some other perturbation to the runs to better understand the differences.  Some more discussion of the issues with the high vertical resolution run, and how it may be improved are also warranted. I have listed some questions below to be considered in revision.  Additionally, the paper needs editing by a native English speaker.  It is mostly understandable, but still needs some work.  I give two examples here (but did not spend the time doing this for the entire manuscript).  i) “Water vapour (WV), a component of the lower stratosphere, is exhibited extensively to be a part of the stratospheric chemistry, and consequently, in the ozone layer balance (Shindell, 1999, 2001; Herman et al., 2002).”, this sentence could be rewritten “Water vapour (WV) concentrations in the stratosphere impact both chemistry (Shindell, 1999, 2001; Herman et al., 2002) and the earth’s radiative balance.” ii) “The tropical belt establishes” should be changes to “The tropical tropopause layer serves as …”

Questions/Comments to consider in revision:

1)  In regards to the nu21 simulation, can you describe what the change in the shape parameter from 2 to 2.1 actually means?  The text says: A larger ν implies a larger modal diameter with a narrower distribution width.   Please give quantitative values at least in regards to model diameter in the text and a sense of the distribution width?

2) Why does the high vertical resolution simulation produce unrealistic results (too much convection)?

3)  In Figure 7, the last panel is a water vapor flux.  That is not a hydrometeor (as indicated by the caption).  Is it just calculated based on vertical velocity and gaseous H2O?  The caption should indicate what is plotted.

4)  This figure confuses me; it could be made more understandable with a more detailed figure caption.  Is the black line just the sum of the 5 hydrometeors + water vapor?  What is ice?  Is that just the sum of the 5 hydrometeors?  And, what does it mean that the colors show the intensity of the event?  Aren’t you showing the altitude of the event as opposed to intensity?  And, why does the plot start off with no water vapor in the region of interest?  The caption (as well as the text) should say that this is a plot with respect to the unperturbed state.  And, why doesn’t the run go out any further in time?  (as that is what is needed to assess how reversible the flux into the stratosphere was.)

5)  Conclusion 3 says: “It further indicates that the rest of the 32% ice (principally pristine ice and snow) progresses further up in the stratosphere.”  Was the model run long enough to verify this? 

6)  Conclusion 4 says “For this case study, a single overshooting plume injects about 4.15 kt of ice above the 380K level.”  Where does this value of 4.15 kt come from?  Is this an average of the two model simulations?  If I then apply Conclusion 3, which seems to say that 32% is irreversibly injected into the stratosphere, then I get close to the 1.34 kt noted as the minimum in the upper limit range noted.

7)  In regards to the calculation of the lower limit, is that just making an estimate based on what is water vapor at the end of the simulation?  And, another question, why is the ref simulation 2.5 hours, and the nu21 simulation 3.5 hours?  Isn’t the amount of water vapor at the simulation end going to be a function of how long the simulation actually was?

8) This seems to be results for a specific meteorological event, and not necessarily extractable to a general case, so I question the final conclusion that this study provides “a road map to upscale the impact of overshooting convection on the stratospheric water vapour at a continental scale.”

The manuscript describes high-resolution numerical simulations of convection over Brazil during the TRO-Pico balloon campaign. The case studied was chosen because of in situ balloon measurments of stratospheric air which had been moistened by an overshoot from convection in the few hours prior to the measurements. The measurements allow a validation of the simulations. The simulations then allow an assessment of plausible values for the quantity of water injected into the stratosphere by the overshoot from convection. This whole study constitutes a step in a long-term research effort to evaluate the impact of overshoots for the water budget of the lower stratosphere. The style should be improved, and some suggestions are made below. One may regret that there are not more simulations to explore the sensitivity to different parameters, and that out of the three only two are realistic enough to justify the quantitative analysis, but overall the manuscript describes a very interesting case study on a very challenging topic, it is well informed and well documented. I advise minor revisions. 

Major points

1. l65-69: this paragraph is extremely important as  it sets the long-term strategy followed by this research group, involving field campaigns and numerical simulations at different resolutions. This is therefore a key pargraph. It would be good to make it a bit more precise and expand a bit. What is considered nececssary as 'fine-scale' simulations? In upscaling or generalizing results from fine-scale simulations to a larger scale, with parameterizations in mind, how do the authors suggest to tackle the issue of representativity? What do they expect the key variables from the large-scale state and circulation to be? What are candidates (for the large-scale variables that would, in a parameterization, influence the occurence or not of overshoots)? CAPE near the surface? The stability near the tropopause? How do these questions influence the design of case studies? 

2. l87-93: for readers not very familiar with balloon technology, it would be worthwhile to explain a bit more (what are the different balloons inflated with, which are closed, which are open, what are typical ascent rates, flight durations, maximum altitudes? What are the payloads for different balloons, what are advantages and disadvantages?) and include references for interested readers

3. A major concern is that the authors have only very few simulations to explore the uncertainty on the impacts of overshoots. Thisi is understandable these simulations are costly, and time-consuming to set up, store and analyze. Nonetheless, the simulations that have been made essantially sample the uncertainty due to the model setup. Another set of simulations that would be of interest would be similar simulations (same model setup as the reference simulation for example), but with variations of the large-scale conditions (artificial modifications of, say, lower level humidity, and/or mid-tropospheric humidity, and/or upper tropospheric stability...) to explore the sensitivity of the overshoots to these environmental factors. In the long-term strategy to guide parameterizations, the influence and relative importance of different environmental factors are crucial to estimate, at least qualitatively. It is not reasonable to expect new simulations to be carried out, but such considerations should be explained in a discussion or when sketching perspectives. 

4. For the validation, section 4.2, why is the focus so much on the local values? The vertical profiles in different location should be explored? Do simulated vertical profiles, in some places, reproduce the main features of the vertical profiles from 

balloon measurements? 

Minor comments  / suggestions: 

l5 meteorological model -> climate model (the impact is for climate rather than weather forecasting)

l4-6: the sentence is a bit odd in the sense that it suggests three scales: local scale (cloud-resolving model), intermediate scale (mesoscale modelling?) and the global scale (climate models). What is meant exactly for the intermediate scale is not clear. 

l9 numerical simulations depend on ...

l19: '... could establish a forcing scheme...' -> 'could inform the development of / provide guidance for...'

l23: is exhibited extensively to be a part -> is known to play an important role in? 

l24: was also an element in the formation of polar stratospheric clouds

l29: 'the supercooled temperature field': there is a confusion here. The temperature field is a well-defined physical field. Supercooled water droplets are a thermodynamic phenomenon concerning water.

l29: 'drives the abundance' -> 'constrains the abundance'? 'determines...' ? 

l32: beyond the level of positive.. -> above the level of zero radiative heating? 

l33: known as the cold-trap...

l34-35: It is never certain if such modelling studies 'explain' the abundance of water vapor... perhaps it is better to write: 'These trajectory studies have found agreement with ...' 

l35: the text should mention that the studies considered here are just the first studies; the reader is otherwise surprised not to find certain more recent studies, which in fact are commented later in the text

l38: 'conclude' -> show? demonstrate? 

l39: 'the processes of WV entering into the stratosphere' -> 'the processes determining the WV entering into...'

l42: 'Recently many case studies'

l52: 'studies report' -> 'studies suggest'? bring evidence..? 

l53: 'at a large scale' -> 'on a large scale'? 

l63: 'no studies can' -> 'it has not been possible to ..'? 

l70: observational -> observed

l72: a range of estimations -> a range of estimates

l72: the remaining 'water'? 

l85: 'It' : needs to be explained, too abrupt as it is

l87: equipped with -> based on ? 

l92: only the WV measuring instruments were flown: Pico-SDLA...

l107: reference for the ETA model? 

l116: 1200g -> 1.2 kg as on line 89, for consistency and for the reader to easily recognize which balloon is referred to 

l122-124: relationship between the two measurements? 

l128: decayed -> decaying?

l156: determine -> solve

l159: reproduces

l161-162: about the simulations of Liu et al (2010): it reads as if these simulations could be very similar to the ones carried out here; more precisions would be welcome. Were these simulations validated against observations? How? 

l168: before the paragraph explaining the technical setup, the modelling strategy (and in particular the overall choices and compromises for the nesting and domains) should be explained

l171: presentation? 

l183: this top is rather low given the height of the phenomena of interest; what is the vertical coordinate? What gives confidence to the authors that this model depth is sufficient? 

l187: 'which varies between 2 and 10s for the coarsest / exterior grid' ? 

l204: 'all the three' -> the three? 

l209: interpreting -> comparing? 

l212: 'we determine the cloud top for this range of altitude': ambiguous formulation

l231: is it 'earlier' or 'later'? 

l237: remove 'now'

l238: with tops typically at 9 to 10 km altitude? 

l243-244: By 15:00 UT, the deep convection altitude in HVR is also higher than in REF...

l249-250: good point, but the formulation is somewhat clumsy; this should be reformulated

l261: higher than REF and NU21: could this be quantified? 

l267: inertial gravity wave: should this be internal gravity wave? 

l268-269: given that there are only 3 simulations, it is unfortunate to leave one out. Are there not uses that could still be of relevance? (Sensitivity..?)

l366-368 and l372-373: redundant, the second occurence could be removed

l388-393: very descriptive of model output, but could some more physical interpretation be suggested

l396: no need for a new paragraph

l399-401: this sentence is not very clear; it could read as a criticism of that previous study, yet that study is by the same authors

l501: add 'the simulated': 'the simulated' overshooting plumes reaching...

l513: would it be possible to attempt to translate these numbers into a change of the ppmv content of water vapor, with appropriate assumptions on the volume affected by the injection?