the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Dec 2023
Recent Ice sheet surface warming events over coastal Dronning Maud Land, East Antarctica: Causes and Implications
Abstract. Sudden short-term warming events over the ice sheet surface (hereafter Ice Sheet Surface Warming (ISSW) events) can affect mass balance by sublimation and on rare occasions melting when the temperature rises above 0 °C. On the one hand, the knowledge of the frequency and duration of these warming events is essential, while on the other hand, a process-level understanding of them is crucial for incorporating in climate models and tracing their behaviour in future climate scenarios. Here, we examined the ISSW events over coastal Dronning Maud Land (cDML) in East Antarctica using the borehole temperature record of an ice core covering a period of 2014–18 CE. The borehole surface thermistor record provided accurate estimation of year-round ISST and subsurface heat flux in the region. In total, 71 warming events (> 2 ºC for > 3 days) with a maximum warming of 11 °C were recorded during the period. They mostly occurred during spring (24) and winter (23), followed by autumn (15) and least in summer (9). The general meteorological setting during these events was the occurrence of strong winds. It was found that 84 % of ISSW events occurred during strong easterly winds with high snow accumulation, while 16 % occurred during strong southeasterly winds (katabatic) without any precipitation. The study suggests that for the first case, intense downward longwave radiation associated with warm air advection (with moisture from the surrounding ocean) heated the ice sheet’s surface and led to snowfall. For the second case, turbulent mixing due to strong and dry winds from the interior of the continent (katabatic) led to ISSW. Furthermore, the synoptic conditions during ISSW events differed by changes in the relative positions of low pressure and high pressure over the southern ocean. Considering the drastic drop in accumulation in cDML since 1906 CE, a simultaneous increase in ISSW events (via their sublimation and melting rates), appears to have greater implications on the mass balance and stability of coastal Antarctic ice sheets in the long term.
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RC1: 'Comment on egusphere-2023-2515', Anonymous Referee #1, 18 Jan 2024
I unfortunately really struggled to understand / follow this manuscript, which meant it was difficult to assess its originality and importance, and ultimately very frustrating. The difficulties were related to how the manuscript was organised / structured, but more generally the quality of writing. I have tried to set out these concerns below. But perhaps an even bigger concern is that its not clear to me why investigating warming events of a few degrees when the base temperature is way below zero degrees is actually important. How would this affect surface mass balance, if surface melt would never occur? Line #374 explains the importance of atmospheric warming as 'Accurate determination of ice sheet surface temperature is vital to understanding the impact of sudden atmospheric warming events on ice sheet surface energy balance, mass balance (through melting and sublimation) and subsurface temperature distribution'. I think that these concerns raise fundamental issues about the quality of the manuscript, which would be better addressed by the authors resubmitting a freshly / properly revised manuscript. I therefore suggest that this manuscript is rejected.
General Comments
The surface / borehole temperatures are way below zero degrees centigrade, so even with anomalous short-term warming they do not cause melt of the surface or the snow/firn layer. Figure 3 shows that some of the warming events occur at temperatures of -30C. Section 3.2 states that 70 events occur with warming >2C, but the very cold base temperatures of these events is never mentioned. So these are not similar to the examples given in the Introduction that (mostly) associated with warming events causing surface melt. The Discussion mentions the work of Kittel et al. (2022) to put these results in context. But again, the Kittel et al work was focused on surface melting episodes, which does not seem to be the case here. I therefore don’t see the importance of these results, which is of huge concern.
The introduction is short and mostly okay. But I felt that the final paragraph of the Introduction was too brief and did not properly explain the aims and objectives of this manuscript to the reader. For example, the motivation to use borehole temperature measurements could be strengthened / expanded, as there are surely other approaches such as modelling / reanalysis (as used by the Sato and Simmonds reference that is included). The relevance / reasons for choosing Dronning Maud Land for a 5-year period could also be expanded upon, and some mention of the implications of these findings might mean for ice sheet warming events in general could be included to widen the scope of the study. Additionally, the Introduction contained a number of statements / sentences that should have included references for justifying the statement. Two examples are the sentence beginning on line #41 beginning ‘The ice sheet-atmospheric interaction has regional differences ..’ and the sentence beginning on line #61 beginning ‘The ISST is not always coherent …’. Finally, some of the sentences in the Introduction are rather casually written. For example, on line #37 the sentence refers to ‘high downward longwave radiation’, which should be properly described as ‘increased’ downward longwave radiation.
The data and methodology section does not really contain any information on the methodology. For example, on how the measurements and ERA5 data will be used together. This leaves it very difficult to actually know what you are doing and makes the manuscript rather incoherent. Combined with the brevity of the Introduction, this is a shortcoming. For example, the sentence on line #134 ‘Hence, we compared the 2 m air temperature with two in situ measurements and energy balance parameters with an AWS observation and RACMO2.3p2 model output (Supplementary Figures 3s, 4s and 5s)’ is impossible to follow for multiple reasons, not least because many of the things referred to are not properly explained. (Also, the term ‘energy balance parameters’ is inappropriate.) This section should be properly revised so that the reader is clear of the methodology being used, as well as any limitations.
There is a lot of careless mistakes in the manuscript, which by this stage should surely have been picked up. For example, the model is RACMO2.3p3 but referred to in places as RACMO. Another example is Eq. 1 not properly described.
The paragraph from Lines #186 to #202 is indecipherable. It needs to be completely revised, with much of this material surely being more appropriate for the methods section. But a more broader comment is that the structure of the manuscript is generally difficult to follow, and lacking in a clear structure. For example, the information in lines #205-206 should be in the methods section. This makes it very challenging to read.
ERA5 is used throughout the paper, but it is stated that ‘The validation of ERA5 dataset is elaborated in the discussion (Section 4.1).’ (line #137). So ERA5 is being used in the results without any proper understanding of how representative / accurate it is of meteorological conditions. This again points to a poorly organised / structured paper.
The paragraph from lines #205-216 is extremely difficult to follow, with an overload of information that is not clearly explained. Moreover, there is very poor linkage between sections 3.2 and 3.3, with section 3.3 repeating basic results from the earlier sub-section of ‘There were 71 significant warming events recorded for the period with a rise in temperature from 2 °C to 11 °C within 3 to 10 days of timespan.’ But I’m afraid it is just difficult to follow.
Minor comments
+ Line #71: coastal Dronning Maud Land already defined.
+ Line #77: DML not defined.
+ Line #80: Are these values the total accumulation over 2 decades? This is rather strange units, and should perhaps be shown as m w. e. per year.
+ Line #82: Do you mean high spatial variability, rather than temporal variability?
+ Caption for Figure 1 is incomplete. For example, what are the different colours in panel (a), and what dataset is being used to plot these, and if orography then why is a colour bar not included? What is the period of the climatology in panel (b), and better to refer to surface wind as either ‘near-surface’ wind or ‘wind at 10 m’. Also missing full stop. Wind roses do not have units. Etc etc. Please thoroughly check all captions.
+ Line #96: Are ma^-1 the correct way to show these units? Meters per annum? Maybe m yr^-1 is more conventional.
+ Line #97: There are a number of rather loose sentences. See ‘general comment’. This is another example by stating ‘for the study period’, when the years of the study period are not clear (do you mean the dates mentioned in the Intro?). Please fix any ambiguity in any such loose sentences.
+ Line #115: Please clarify what 1 m in height means? Above the surface?
+ Line #127: Please use proper multiplication sign, and not an x.
+ Line #127: Wrong use of semi-colon ‘;’. Please revise sentence.
+ Line #130: ‘synoptic conditions’ is wrong terminology to refer to IVT.
+ Line #134: The details of the AWS need to more explanation, such as location. Also, this contradicts the first line of this paragraph that ‘in-situ meteorological observation is unavailable’.
+ Equation (1): The symbol Q is not defined, and also LHF and G are not defined in the first sentence following the equation. This is very careless writing and should have been picked up. Please revise all the manuscript for such instances of loose writing.
+ Line #150: I don’t think that this should be a new paragraph here, but rather should be a continuation of the previous paragraph (as this is all related to explaining Eq. 1). Please check all the grammar, see comment above about use of semi-colon.
+ Line #153: T should be in italics to match Eq. 2. Please make sure that all symbols and equations are correctly formatted.
+ Equation 3: Please simply this equation as there is no need to use × so many times.
+ Line #161: Why is there a gap between these two paragraphs and not elsewhere. Please correctly format the entire manuscript and be consistent.
+ Equation 4: The symbols for latent heat of sublimation in the main text and Eq. 4 are not the same. There are other examples of this in the text. Please correct, and also for a submitted article such mistakes should not be apparent.
+ Line #165: Inappropriate heading. ‘Retrieval’ is a method, not a result. Also, the first two sentences of the subsequent first paragraph of section 3.1 contains repetition from the methods section, which should be removed.
+ Line #176: The sentence ‘To consider burial …’ needs to be much better explained.
+ Line #177: I have no idea why the sentence ‘Table 1 gives the annual surface mass balance from RACMO2.3p2 and ERA5.’ is included here, especially as this paragraph is on temperatures. Please structure the paper logically.
+ Table 1: This table needs to be revised. The comparison is not systematic, as its ERA5 precip-sublimation v RACMO SMB. Further, its RACMO2.3p2. Why are some values give to 2 decimal places and other values as integers? The fact that RACMO data is limited to June 2017 only has never been mentioned in section 2.
+ Line 186: How is ‘annual accumulation (accumulation – sublimation)’ correct ?
+ Lines #187-189: The description of RACMO2 should be in the methods section, not here.
+ Lines #190-195: Much of this should surely be in the methods section.
+ Line #205: This definition of a warming event is unclear, and also needs to be in the methods section.
+ Lines #244-255: Beginning a paragraph with ‘Case 1:’ is not appropriate. This is not a report.
Citation: https://doi.org/10.5194/egusphere-2023-2515-RC1 -
RC2: 'Comment on egusphere-2023-2515', Anonymous Referee #2, 26 Jan 2024
This manuscript presents a new and unique temperature record from boreholes in Dronning Maud Land, with a focus on surface warming events and their associated atmospheric drivers. While the topic is novel, unfortunately the methodology is not written in a clear and comprehensive way and there are issues in the presentation and analysis of the data.
I think the most concerning aspect of the manuscript is that there are many inconsistencies in the labeling of datasets and units, which makes the methodology confusing and the results less clear than they should be. For example, the text is missing a citation for ERA5 reanalysis and refers to RACMO2.3p2 as RACMO. Another example is that it’s not always clear whether “cm” of precipitation is in units of “cm water equivalent” or snow height, and when referring to the average accumulation over the study period, it’s not clear whether the authors are referring to accumulation per year or total accumulation. Multiple figures with wind roses are missing units for wind speeds and percentages, and the color bar in the mean sea level pressure anomaly figures doesn’t capture the extent of the low-pressure anomalies associated with surface warming events. Such issues in the description and presentation of the data contribute to a general lack of clarity.
The manuscript would also strongly benefit from a clearer motivation for the study. Most surface warming events described in the study occur at temperatures well below the melting point, and yet to motivate the importance of surface warming events, the authors reference studies like Kittel et al. (2021), which are focused on areas that experience surface melting and increased melt in future climates. This study would be improved if there were a clearer link between the motivation for the location of the boreholes, the baseline temperatures of surface warming events in addition to the temperature increase, and the importance of surface warming for surface mass balance and firn structure in Dronning Maud Land.
Despite gaps in the motivation for this study, the data presented are valuable in improving our understanding of the surface impacts of different types of weather systems in Dronning Maud Land and their synoptic drivers. Observations of surface temperature data over multiple years are few and far between in Antarctica and can provide key information on how the surface responds to different weather events. However, given major issues in the description of the methodology and motivation, at this stage I would suggest that the manuscript be rejected.
Major Comments
Section 2.2 Borehole temperature measurements – it would be extremely helpful to have a diagram showing the setup of the thermistors in the borehole.
I would expect the role of latent heat to be discussed in section 3.4.1 – where surface warming events are associated with precipitation, especially given that the equation for the surface energy balance is included earlier in the manuscript. The discussion is only focused on downwelling longwave radiation associated with cloud cover during the warming events. In addition, the authors briefly mention the role of warm air advection, too – the relative impacts of these processes (longwave radiation, warm air advection, and latent heat) should be quantified to give a better sense of which processes are most important to surface warming.
The first part of discussion section mostly contains information on the limitations of ERA5 in representing near surface meteorology. What’s missing from this section is a conversation about the limitations of the borehole temperature record - how this study furthers our understanding of surface warming events in Antarctica and what is still unknown in the context of the existing body of research and observation methods.
Minor Comments
P1 L25 – “and led to snowfall” – this implies that downward longwave radiation and ice sheet surface heating were prerequisites for the snowfall to occur, whereas in actuality they are co-occurring processes, no?
P2 L61 – it would be helpful to expand this explanation of the factors that influence ISST beyond the air temperature, for example a description of which processes among those listed (wind speed, topography, and the components of the surface energy balance) increase the ISST locally and which processes decrease it.
P3 L71,72 – already introduced cDML in L64.
P3 L76 – add “basal” to “oceanic melting”
P3 L77 – does this mean higher surface mass balance in the east or west?
P3 L79,80 – can you use m water equivalent per year as the units for accumulation? Also, if spatial variability in observed accumulation is important to this study, can you mark the location of the ice cores on the map?
In general, this paragraph needs to be restructured to improve clarity. I would recommend talking about spatial variability first, then long-term trends, instead of alternating between the two. For the long-term trends, I think it would be helpful to be extremely clear about the core locations and the periods.
P3 Fig 1 – panels c-e need units for wind speed and for the percentages of time (8.2, 16.5, etc?) with each wind speed. I think panels a and b could be improved for clarity and visuals (for example, increase the font sizes, also what is the grey/blue boundary in the ocean in panel a? or for panel z, can you zoom into the winds?). Finally, there is no mention of ERA5 reanalysis prior to this plot – it needs to be introduced in the methods first.
P4 L97 – mark Wohlthat Mountains on the map
P4 L99 – mean wind speed at what level? 10m?
P4 L107 – be more specific (by how many degrees? What are the mean surface temperatures in this region?)
P4 L126 – need to cite the ERA5 dataset
P5 L126 – need to cite the RACMO2.3p2 dataset
P5 L144 – define “LW”, “SW”
P5 L154 – “at all depths” (list the total number of depths/vertical resolution) one more time here)
P6 L159 – define density as the symbol in the equation
P6 L165-169 – “retrieval” and first 2 sentences belong in the methods section
P6 L169,170 – talk about the results (what is the daily avg temperature? Max/min?) before discussing dampening in temperature variations
P6 L176 – seems like this belongs in the next paragraph?
P7 Table 1 – are the units in water equivalent? If so, then please add that. Can you add the location/spatial extent of the grid cells you are using in ERA5 and RACMO2.3p2 for these calculations to the map in Fig 1?
P8 L186 – again, is this cm water equivalent per year?
P8 L205 – the definition of warming events should go in the methods section, along with the methods presented throughout this paragraph
P8 L209 – I don’t understand the need to differentiate between events where temperature stabilizes or falls. In Fig 3, the events where temperature stabilizes have a decrease in temperature just one datapoint later.
P10 L241 Fig 3 a-d clearly shows precipitation co-occurring with the surface warming, not following the surface warming. Please fix the wording. Also, what is the threshold for determining whether precipitation occurred or not? For example, Fig 3 h still shows some precipitation during the event.
P12 L273 – provide a citation or figure reference for “they are colder and drier”
P13 Fig 5 – need units for the percentages on the rose and the wind speeds in the key
P13 L297 – need p values for the r values, don’t use “more significant”, could use “higher” instead
P14 Fig 6 – the color contours don’t extend to anomalies large enough to capture the center of the low-pressure systems – extend the values for contours. It would also be helpful to see contours with the mean sea level pressure (not just the anomalies) on the map.
P15 L323 – mid-high geopotential height maps are needed to draw conclusions about wave number patterns – there is too much variability in surface pressure patterns. I would also dispute the claim that there is a high-pressure system to the east without seeing the mean sea level pressure – right now, just looking at the pressure anomaly, it’s only on the order of ~2 hPa. Contours of the mean sea level pressures (not anomalies) would be helpful to make this claim.
P15 L337 – can you plot a vertical temperature profile using ERA5 to show whether this process is occurring?
P15 L352 – results should go in the previous section, not the discussion (same goes for lines 357-372.
P17 L392 – I didn’t see any plots of analysis of individual storm tracks in the manuscript
P17 L401 – this dataset is too short to discuss trends, no? (“increased from 8 to 16 events per year after 2015”)
Citation: https://doi.org/10.5194/egusphere-2023-2515-RC2
Status: closed
-
RC1: 'Comment on egusphere-2023-2515', Anonymous Referee #1, 18 Jan 2024
I unfortunately really struggled to understand / follow this manuscript, which meant it was difficult to assess its originality and importance, and ultimately very frustrating. The difficulties were related to how the manuscript was organised / structured, but more generally the quality of writing. I have tried to set out these concerns below. But perhaps an even bigger concern is that its not clear to me why investigating warming events of a few degrees when the base temperature is way below zero degrees is actually important. How would this affect surface mass balance, if surface melt would never occur? Line #374 explains the importance of atmospheric warming as 'Accurate determination of ice sheet surface temperature is vital to understanding the impact of sudden atmospheric warming events on ice sheet surface energy balance, mass balance (through melting and sublimation) and subsurface temperature distribution'. I think that these concerns raise fundamental issues about the quality of the manuscript, which would be better addressed by the authors resubmitting a freshly / properly revised manuscript. I therefore suggest that this manuscript is rejected.
General Comments
The surface / borehole temperatures are way below zero degrees centigrade, so even with anomalous short-term warming they do not cause melt of the surface or the snow/firn layer. Figure 3 shows that some of the warming events occur at temperatures of -30C. Section 3.2 states that 70 events occur with warming >2C, but the very cold base temperatures of these events is never mentioned. So these are not similar to the examples given in the Introduction that (mostly) associated with warming events causing surface melt. The Discussion mentions the work of Kittel et al. (2022) to put these results in context. But again, the Kittel et al work was focused on surface melting episodes, which does not seem to be the case here. I therefore don’t see the importance of these results, which is of huge concern.
The introduction is short and mostly okay. But I felt that the final paragraph of the Introduction was too brief and did not properly explain the aims and objectives of this manuscript to the reader. For example, the motivation to use borehole temperature measurements could be strengthened / expanded, as there are surely other approaches such as modelling / reanalysis (as used by the Sato and Simmonds reference that is included). The relevance / reasons for choosing Dronning Maud Land for a 5-year period could also be expanded upon, and some mention of the implications of these findings might mean for ice sheet warming events in general could be included to widen the scope of the study. Additionally, the Introduction contained a number of statements / sentences that should have included references for justifying the statement. Two examples are the sentence beginning on line #41 beginning ‘The ice sheet-atmospheric interaction has regional differences ..’ and the sentence beginning on line #61 beginning ‘The ISST is not always coherent …’. Finally, some of the sentences in the Introduction are rather casually written. For example, on line #37 the sentence refers to ‘high downward longwave radiation’, which should be properly described as ‘increased’ downward longwave radiation.
The data and methodology section does not really contain any information on the methodology. For example, on how the measurements and ERA5 data will be used together. This leaves it very difficult to actually know what you are doing and makes the manuscript rather incoherent. Combined with the brevity of the Introduction, this is a shortcoming. For example, the sentence on line #134 ‘Hence, we compared the 2 m air temperature with two in situ measurements and energy balance parameters with an AWS observation and RACMO2.3p2 model output (Supplementary Figures 3s, 4s and 5s)’ is impossible to follow for multiple reasons, not least because many of the things referred to are not properly explained. (Also, the term ‘energy balance parameters’ is inappropriate.) This section should be properly revised so that the reader is clear of the methodology being used, as well as any limitations.
There is a lot of careless mistakes in the manuscript, which by this stage should surely have been picked up. For example, the model is RACMO2.3p3 but referred to in places as RACMO. Another example is Eq. 1 not properly described.
The paragraph from Lines #186 to #202 is indecipherable. It needs to be completely revised, with much of this material surely being more appropriate for the methods section. But a more broader comment is that the structure of the manuscript is generally difficult to follow, and lacking in a clear structure. For example, the information in lines #205-206 should be in the methods section. This makes it very challenging to read.
ERA5 is used throughout the paper, but it is stated that ‘The validation of ERA5 dataset is elaborated in the discussion (Section 4.1).’ (line #137). So ERA5 is being used in the results without any proper understanding of how representative / accurate it is of meteorological conditions. This again points to a poorly organised / structured paper.
The paragraph from lines #205-216 is extremely difficult to follow, with an overload of information that is not clearly explained. Moreover, there is very poor linkage between sections 3.2 and 3.3, with section 3.3 repeating basic results from the earlier sub-section of ‘There were 71 significant warming events recorded for the period with a rise in temperature from 2 °C to 11 °C within 3 to 10 days of timespan.’ But I’m afraid it is just difficult to follow.
Minor comments
+ Line #71: coastal Dronning Maud Land already defined.
+ Line #77: DML not defined.
+ Line #80: Are these values the total accumulation over 2 decades? This is rather strange units, and should perhaps be shown as m w. e. per year.
+ Line #82: Do you mean high spatial variability, rather than temporal variability?
+ Caption for Figure 1 is incomplete. For example, what are the different colours in panel (a), and what dataset is being used to plot these, and if orography then why is a colour bar not included? What is the period of the climatology in panel (b), and better to refer to surface wind as either ‘near-surface’ wind or ‘wind at 10 m’. Also missing full stop. Wind roses do not have units. Etc etc. Please thoroughly check all captions.
+ Line #96: Are ma^-1 the correct way to show these units? Meters per annum? Maybe m yr^-1 is more conventional.
+ Line #97: There are a number of rather loose sentences. See ‘general comment’. This is another example by stating ‘for the study period’, when the years of the study period are not clear (do you mean the dates mentioned in the Intro?). Please fix any ambiguity in any such loose sentences.
+ Line #115: Please clarify what 1 m in height means? Above the surface?
+ Line #127: Please use proper multiplication sign, and not an x.
+ Line #127: Wrong use of semi-colon ‘;’. Please revise sentence.
+ Line #130: ‘synoptic conditions’ is wrong terminology to refer to IVT.
+ Line #134: The details of the AWS need to more explanation, such as location. Also, this contradicts the first line of this paragraph that ‘in-situ meteorological observation is unavailable’.
+ Equation (1): The symbol Q is not defined, and also LHF and G are not defined in the first sentence following the equation. This is very careless writing and should have been picked up. Please revise all the manuscript for such instances of loose writing.
+ Line #150: I don’t think that this should be a new paragraph here, but rather should be a continuation of the previous paragraph (as this is all related to explaining Eq. 1). Please check all the grammar, see comment above about use of semi-colon.
+ Line #153: T should be in italics to match Eq. 2. Please make sure that all symbols and equations are correctly formatted.
+ Equation 3: Please simply this equation as there is no need to use × so many times.
+ Line #161: Why is there a gap between these two paragraphs and not elsewhere. Please correctly format the entire manuscript and be consistent.
+ Equation 4: The symbols for latent heat of sublimation in the main text and Eq. 4 are not the same. There are other examples of this in the text. Please correct, and also for a submitted article such mistakes should not be apparent.
+ Line #165: Inappropriate heading. ‘Retrieval’ is a method, not a result. Also, the first two sentences of the subsequent first paragraph of section 3.1 contains repetition from the methods section, which should be removed.
+ Line #176: The sentence ‘To consider burial …’ needs to be much better explained.
+ Line #177: I have no idea why the sentence ‘Table 1 gives the annual surface mass balance from RACMO2.3p2 and ERA5.’ is included here, especially as this paragraph is on temperatures. Please structure the paper logically.
+ Table 1: This table needs to be revised. The comparison is not systematic, as its ERA5 precip-sublimation v RACMO SMB. Further, its RACMO2.3p2. Why are some values give to 2 decimal places and other values as integers? The fact that RACMO data is limited to June 2017 only has never been mentioned in section 2.
+ Line 186: How is ‘annual accumulation (accumulation – sublimation)’ correct ?
+ Lines #187-189: The description of RACMO2 should be in the methods section, not here.
+ Lines #190-195: Much of this should surely be in the methods section.
+ Line #205: This definition of a warming event is unclear, and also needs to be in the methods section.
+ Lines #244-255: Beginning a paragraph with ‘Case 1:’ is not appropriate. This is not a report.
Citation: https://doi.org/10.5194/egusphere-2023-2515-RC1 -
RC2: 'Comment on egusphere-2023-2515', Anonymous Referee #2, 26 Jan 2024
This manuscript presents a new and unique temperature record from boreholes in Dronning Maud Land, with a focus on surface warming events and their associated atmospheric drivers. While the topic is novel, unfortunately the methodology is not written in a clear and comprehensive way and there are issues in the presentation and analysis of the data.
I think the most concerning aspect of the manuscript is that there are many inconsistencies in the labeling of datasets and units, which makes the methodology confusing and the results less clear than they should be. For example, the text is missing a citation for ERA5 reanalysis and refers to RACMO2.3p2 as RACMO. Another example is that it’s not always clear whether “cm” of precipitation is in units of “cm water equivalent” or snow height, and when referring to the average accumulation over the study period, it’s not clear whether the authors are referring to accumulation per year or total accumulation. Multiple figures with wind roses are missing units for wind speeds and percentages, and the color bar in the mean sea level pressure anomaly figures doesn’t capture the extent of the low-pressure anomalies associated with surface warming events. Such issues in the description and presentation of the data contribute to a general lack of clarity.
The manuscript would also strongly benefit from a clearer motivation for the study. Most surface warming events described in the study occur at temperatures well below the melting point, and yet to motivate the importance of surface warming events, the authors reference studies like Kittel et al. (2021), which are focused on areas that experience surface melting and increased melt in future climates. This study would be improved if there were a clearer link between the motivation for the location of the boreholes, the baseline temperatures of surface warming events in addition to the temperature increase, and the importance of surface warming for surface mass balance and firn structure in Dronning Maud Land.
Despite gaps in the motivation for this study, the data presented are valuable in improving our understanding of the surface impacts of different types of weather systems in Dronning Maud Land and their synoptic drivers. Observations of surface temperature data over multiple years are few and far between in Antarctica and can provide key information on how the surface responds to different weather events. However, given major issues in the description of the methodology and motivation, at this stage I would suggest that the manuscript be rejected.
Major Comments
Section 2.2 Borehole temperature measurements – it would be extremely helpful to have a diagram showing the setup of the thermistors in the borehole.
I would expect the role of latent heat to be discussed in section 3.4.1 – where surface warming events are associated with precipitation, especially given that the equation for the surface energy balance is included earlier in the manuscript. The discussion is only focused on downwelling longwave radiation associated with cloud cover during the warming events. In addition, the authors briefly mention the role of warm air advection, too – the relative impacts of these processes (longwave radiation, warm air advection, and latent heat) should be quantified to give a better sense of which processes are most important to surface warming.
The first part of discussion section mostly contains information on the limitations of ERA5 in representing near surface meteorology. What’s missing from this section is a conversation about the limitations of the borehole temperature record - how this study furthers our understanding of surface warming events in Antarctica and what is still unknown in the context of the existing body of research and observation methods.
Minor Comments
P1 L25 – “and led to snowfall” – this implies that downward longwave radiation and ice sheet surface heating were prerequisites for the snowfall to occur, whereas in actuality they are co-occurring processes, no?
P2 L61 – it would be helpful to expand this explanation of the factors that influence ISST beyond the air temperature, for example a description of which processes among those listed (wind speed, topography, and the components of the surface energy balance) increase the ISST locally and which processes decrease it.
P3 L71,72 – already introduced cDML in L64.
P3 L76 – add “basal” to “oceanic melting”
P3 L77 – does this mean higher surface mass balance in the east or west?
P3 L79,80 – can you use m water equivalent per year as the units for accumulation? Also, if spatial variability in observed accumulation is important to this study, can you mark the location of the ice cores on the map?
In general, this paragraph needs to be restructured to improve clarity. I would recommend talking about spatial variability first, then long-term trends, instead of alternating between the two. For the long-term trends, I think it would be helpful to be extremely clear about the core locations and the periods.
P3 Fig 1 – panels c-e need units for wind speed and for the percentages of time (8.2, 16.5, etc?) with each wind speed. I think panels a and b could be improved for clarity and visuals (for example, increase the font sizes, also what is the grey/blue boundary in the ocean in panel a? or for panel z, can you zoom into the winds?). Finally, there is no mention of ERA5 reanalysis prior to this plot – it needs to be introduced in the methods first.
P4 L97 – mark Wohlthat Mountains on the map
P4 L99 – mean wind speed at what level? 10m?
P4 L107 – be more specific (by how many degrees? What are the mean surface temperatures in this region?)
P4 L126 – need to cite the ERA5 dataset
P5 L126 – need to cite the RACMO2.3p2 dataset
P5 L144 – define “LW”, “SW”
P5 L154 – “at all depths” (list the total number of depths/vertical resolution) one more time here)
P6 L159 – define density as the symbol in the equation
P6 L165-169 – “retrieval” and first 2 sentences belong in the methods section
P6 L169,170 – talk about the results (what is the daily avg temperature? Max/min?) before discussing dampening in temperature variations
P6 L176 – seems like this belongs in the next paragraph?
P7 Table 1 – are the units in water equivalent? If so, then please add that. Can you add the location/spatial extent of the grid cells you are using in ERA5 and RACMO2.3p2 for these calculations to the map in Fig 1?
P8 L186 – again, is this cm water equivalent per year?
P8 L205 – the definition of warming events should go in the methods section, along with the methods presented throughout this paragraph
P8 L209 – I don’t understand the need to differentiate between events where temperature stabilizes or falls. In Fig 3, the events where temperature stabilizes have a decrease in temperature just one datapoint later.
P10 L241 Fig 3 a-d clearly shows precipitation co-occurring with the surface warming, not following the surface warming. Please fix the wording. Also, what is the threshold for determining whether precipitation occurred or not? For example, Fig 3 h still shows some precipitation during the event.
P12 L273 – provide a citation or figure reference for “they are colder and drier”
P13 Fig 5 – need units for the percentages on the rose and the wind speeds in the key
P13 L297 – need p values for the r values, don’t use “more significant”, could use “higher” instead
P14 Fig 6 – the color contours don’t extend to anomalies large enough to capture the center of the low-pressure systems – extend the values for contours. It would also be helpful to see contours with the mean sea level pressure (not just the anomalies) on the map.
P15 L323 – mid-high geopotential height maps are needed to draw conclusions about wave number patterns – there is too much variability in surface pressure patterns. I would also dispute the claim that there is a high-pressure system to the east without seeing the mean sea level pressure – right now, just looking at the pressure anomaly, it’s only on the order of ~2 hPa. Contours of the mean sea level pressures (not anomalies) would be helpful to make this claim.
P15 L337 – can you plot a vertical temperature profile using ERA5 to show whether this process is occurring?
P15 L352 – results should go in the previous section, not the discussion (same goes for lines 357-372.
P17 L392 – I didn’t see any plots of analysis of individual storm tracks in the manuscript
P17 L401 – this dataset is too short to discuss trends, no? (“increased from 8 to 16 events per year after 2015”)
Citation: https://doi.org/10.5194/egusphere-2023-2515-RC2
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