the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Jan 2024
Spatial and temporal variability of free tropospheric freezing level in Patagonia
Abstract. The free tropospheric height of the 0 °C isotherm (H0), commonly referred to as the freezing level, denotes the lowest altitude within a specific location’s atmosphere where the air temperature reaches 0 °C. This serves as an indicator for the transition between rain and snow, making it useful for monitoring and visualizing the altitude of freezing temperatures in the atmosphere. We study the spatial and temporal variability of H0 across Patagonia (41°–54° S) for the 1950–2021 period. Our results highlight the contrast around the Andes, manifested in lower/higher H0 on the western/eastern side, indicating the orographical influence on temperature vertical profiles on both sides of mountains. Our results indicate that the spatial mean value of the isotherm field in the region is 1691 meters above sea level (m.a.s.l). In terms of seasonal variability, H0 ranges from 585 m.a.s.l (winter) to 3480 m.a.s.l (summer). Moreover, the significant trends calculated over the period only show positive values in the area. This indicates an upward trend in the isotherm, averaging an increase of 8 to 61 meters per decade from 1959–2021, where the higher value is over northwestern Patagonia. Empirical orthogonal function (EOF) analysis was performed on isotherm anomalies. The first empirical orthogonal function (EOF) mode of H0 variability accounts for 84 % of the total variance, depicting a monopole structure centered in the northwest area. This mode exhibits a positive correlation with the spatial average H0 anomalies field, the Southern Annular Mode (SAM), temperature at 850 hPa in the Drake Passage, and sea surface temperature off the western coast of Patagonia; underscoring the significant role of these factors in influencing the vertical temperature profile within the region.
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Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-145', Anonymous Referee #1, 07 Feb 2024
I found the manuscript suitable for publication in this journal. I made a few comments a some suggestions directly on the text that I am attaching.
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AC1: 'Reply on RC1', Nicolás D. García-Lee, 08 Feb 2024
Thanks for your time and suggestions, we are going to apply the changes an upload in a new draft once we have all the comments of the discussion process.
To address some queries in advance:
(235) We have opted not to employ the standard deviation owing to the skewed distribution of data (Figure 5) and the presence of extreme outliers. Instead, we used the interquartile range (IQR) to measure the spread of values given its robustness in handling outliers present in this kind of data (Mardones & Garreaud, 2020). Consequently, these values do not reflect the average ± standard deviation; rather, they indicate the maximum (minimum) value of the result between (H0 + (-) IQR) of a meridional or zonal profile, respectively.
These data can be seen in Table S1 of the accompanying supplementary material (attached). Besides, these findings are closely related to those presented in Figure 7. For instance, in the meridional profile of autumn, the maximum altitude reaches 2838 mASL in the eastern zone, with a minimum of around 1066 mASL at approximately 73.5°W (referred as 2848-1066 m a.s.l in line 236). Similar logic applies to the zonal profile of autumn (maximum: 2858 mASL; minimum: 841 mASL, line 237).
This methodology is consistently applied across all seasons and to the trends depicted in Table S2.
Reference:
Mardones, P., & Garreaud, R. D. (2020). Future changes in the free tropospheric freezing level and rain–snow limit: The case of central Chile. Atmosphere, 11(11), 1259.(430) Confirmed, it represents the annual average and median.
(435) Rectified with the suggestion provided in line 434.
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AC1: 'Reply on RC1', Nicolás D. García-Lee, 08 Feb 2024
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RC2: 'Comment on egusphere-2024-145', Anonymous Referee #2, 07 Mar 2024
Review of Manuscript No: egusphere-2024-145
Title: Spatial and temporal variability of free tropospheric freezing level in Patagonia
Author(s): Nicolás García-Lee, Claudio Bravo, Álvaro Gónzales-Reyes, Piero Mardones
Recommendation: Major revision
General Comment
The study of the freezing level in the Patagonia’s atmosphere is highly relevant since there reside the largest ice fields outside the polar regions and now are under a development threat with global warming. The manuscript, however, present some major issues with the writing and presentation of the results. According to my view, addressing the following major comments could improve the quality of the manuscript.
Major comments
- Several passages of the text are hard to understand and/or could be written using more precise terms. I provide further explanation/examples in the minor comments.
- One of the most relevant results, which readers likely are most expectant, is about how fast is warming Patagonia, or is decreasing the freezing level and so glaciers; however, this result is weakly presented, mainly in the abstract and conclusion, after other results, may be of 2nd It should be presented firstly.
- Related with previous comment, the freezing level trends obtained with pure observations, i.e. from radiosonde, are not shown. The authors have presented the trends derived only from reanalysis data which have some degree of errors or uncertainties, as they have even shown. The few radiosonde observations in Patagonia should be used as much as possible, not only to validate reanalysis. For instance, the seasonality (section 3.3) and Trend of H0 (section 3.6) sections could start showing first the results derived from the radiosonde, the closest to the ground truth, and then with those from reanalysis.
- In order to give stronger emphasis to the positive trends or warming, the section of Trend of H0 (3.6) should be presented before the large-scale control (3.5), which even help to explain some possible causation of the warming. Additionally, it should be included as the first result in the trend section, the annual total trends and then, may be only the seasons with the largest and lowest values, to reduce the text.
- The discussion section, as it is currently written, seems to not deserve its inclusion. The three first paragraphs can be moved and shorten to the methodology section, while the rest of the discussion is somewhat vague, with weak physical interpretation and/or discussion of advantage or limitation of data or analyses, as well as somewhat repetitive of the results already introduced. For instance, in lines 380-387, the west-east difference in H0 is attributed to the topography but it is not explained their influence on constrating climates at both sides of the Andes, basically, big difference in continentality, cloudiness, precipitation, among others. In lines 388-395, the localized highest warming in the NW of Patagonia is attributed to SAM, but why not affect in the southern Patagonia since the indices use atmospheric variables in R1 domain, south of the whole Patagonia region. What could be the connection between the SAM, global warming, and the localized warming in the NW? What about other large-scale phenomena? Could some of them have potential impacts? It would be a great opportunity here to link with works that quantified the ice losses? How much ice mass have the glaciers lost? It is coherent with the increasing levels of H0?
- In the discussion, it could be also mentioned that the lowering of the freezing level over the windward slopes of the Andes typically observed during midlatitude frontal precipitation is not appreciable in cross-barrier climatological profiles. This is a mesoscale atmospheric phenomenon that should not be capture by the ERA5 coarse resolution. See Minder’s works: https://doi.org/10.1175/JAS-D-10-05006.1; https://doi.org/10.1175/JAS-D-12-0194.1
- Presenting unique mean annual and seasonal values of the H0, in the abstract and conclusion as a main result, for the huge whole region (> 10° latitude), does not make sense. They should be introduced as a range of values, between the lowest (in the north) and highest values (in the south).
- It should be highlighted in sec. 3.1 the overall underestimation of H0 by the ERA5, if there is some documentation of that somewhere and possible causes, as well as what could be the implication for this study.
Minor Comments
- All of them Related to major comment 1)
- The term "free tropospheric" freezing level would not be used properly here. The free troposphere refers to as the part of the atmosphere above the boundary layer, free of the friction with the earth surface, and so in this study the freezing level not necessarily is present above the boundary layer. It does not make sense in the context of this study, at least the H0 found within the boundary layer were excluded from the study. If not, I suggest to not use it, and the title could be replaced by “Spatial and temporal variability of the freezing level in the Patagonia’s atmosphere”
- In the results, discussion and conclusion, the authors refer as “modeled or simulated” data or results to those coming from the ERA5. Since the goal of the reanalysis is to use model to assimilate already observed data, and not to predict in the future, I suggest to refer to as directly reanalysis ERA5 data/results. The terms model or simulated data could be intrinsically associated with projections or predictions by the model, and so may create confusion.
- In the abstract, it should be mentioned the data used in the study.
- L41: Viale et 2019 is more appropriated reference here. doi: 10.3389/fenvs.2019.00069
- L42: “...being the SAM the primary driver of extratropical climate variability in the Southern Hemisphere.”. This strong statement should be supported by references.
- L43: The SAM topic should start in a new paragraph. The introduction has mainly a unique paragraph mixing many main topics, making them harder to capture by the readers.
- L176-180: In the text, the authors refer to as “meridional and zonal profiles” and, in the Fig4, they were labeled as Zonal and Meridional mean, respectively. This is confusing. I suggest in the label or caption refer to as “Zonally (Meridionally) averaged Latitudinal (Longitudinal) Section”, and in the text to refer as “Latitudinal and Longitudinal variations”, respectively. Please also indicate in the text when you are talking about Fig 4a and 4b.
- L182-186: These sentences are not clear. Do you refer to mountain or interquartile ranges? When it is said higher or bigger, finishing the comparison w.r.t what is higher or bigger, if not it is hard to understand. Indicate the Fig that show that. Can the AA be located on average around 72W..? Please re-write these sentences.
- L197: Please indicate you are referring now to Fig. 5.
- L200: I see skewed to the left (low values)
- L200-202: It is not clear what line (of the 3 plotted) correspond to these stated values. Please indicate
- L291: Please indicate you are referring to Fig. 8b
- L322: “with a marked and unprecedent trend in the period that began 2010”. Where was that result shown? Please provide evidences
- L362: What model do you refer to? Please see comment 1.2
- L363: It is not clear this sentence. Please rewrite.
- L364: What do you mean by “3 observed data points”? It is not clear, please explain.
- L365: What methodology? Please specify.
Citation: https://doi.org/10.5194/egusphere-2024-145-RC2 - AC2: 'Reply on RC2', Nicolás D. García-Lee, 10 May 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-145', Anonymous Referee #1, 07 Feb 2024
I found the manuscript suitable for publication in this journal. I made a few comments a some suggestions directly on the text that I am attaching.
-
AC1: 'Reply on RC1', Nicolás D. García-Lee, 08 Feb 2024
Thanks for your time and suggestions, we are going to apply the changes an upload in a new draft once we have all the comments of the discussion process.
To address some queries in advance:
(235) We have opted not to employ the standard deviation owing to the skewed distribution of data (Figure 5) and the presence of extreme outliers. Instead, we used the interquartile range (IQR) to measure the spread of values given its robustness in handling outliers present in this kind of data (Mardones & Garreaud, 2020). Consequently, these values do not reflect the average ± standard deviation; rather, they indicate the maximum (minimum) value of the result between (H0 + (-) IQR) of a meridional or zonal profile, respectively.
These data can be seen in Table S1 of the accompanying supplementary material (attached). Besides, these findings are closely related to those presented in Figure 7. For instance, in the meridional profile of autumn, the maximum altitude reaches 2838 mASL in the eastern zone, with a minimum of around 1066 mASL at approximately 73.5°W (referred as 2848-1066 m a.s.l in line 236). Similar logic applies to the zonal profile of autumn (maximum: 2858 mASL; minimum: 841 mASL, line 237).
This methodology is consistently applied across all seasons and to the trends depicted in Table S2.
Reference:
Mardones, P., & Garreaud, R. D. (2020). Future changes in the free tropospheric freezing level and rain–snow limit: The case of central Chile. Atmosphere, 11(11), 1259.(430) Confirmed, it represents the annual average and median.
(435) Rectified with the suggestion provided in line 434.
-
AC1: 'Reply on RC1', Nicolás D. García-Lee, 08 Feb 2024
-
RC2: 'Comment on egusphere-2024-145', Anonymous Referee #2, 07 Mar 2024
Review of Manuscript No: egusphere-2024-145
Title: Spatial and temporal variability of free tropospheric freezing level in Patagonia
Author(s): Nicolás García-Lee, Claudio Bravo, Álvaro Gónzales-Reyes, Piero Mardones
Recommendation: Major revision
General Comment
The study of the freezing level in the Patagonia’s atmosphere is highly relevant since there reside the largest ice fields outside the polar regions and now are under a development threat with global warming. The manuscript, however, present some major issues with the writing and presentation of the results. According to my view, addressing the following major comments could improve the quality of the manuscript.
Major comments
- Several passages of the text are hard to understand and/or could be written using more precise terms. I provide further explanation/examples in the minor comments.
- One of the most relevant results, which readers likely are most expectant, is about how fast is warming Patagonia, or is decreasing the freezing level and so glaciers; however, this result is weakly presented, mainly in the abstract and conclusion, after other results, may be of 2nd It should be presented firstly.
- Related with previous comment, the freezing level trends obtained with pure observations, i.e. from radiosonde, are not shown. The authors have presented the trends derived only from reanalysis data which have some degree of errors or uncertainties, as they have even shown. The few radiosonde observations in Patagonia should be used as much as possible, not only to validate reanalysis. For instance, the seasonality (section 3.3) and Trend of H0 (section 3.6) sections could start showing first the results derived from the radiosonde, the closest to the ground truth, and then with those from reanalysis.
- In order to give stronger emphasis to the positive trends or warming, the section of Trend of H0 (3.6) should be presented before the large-scale control (3.5), which even help to explain some possible causation of the warming. Additionally, it should be included as the first result in the trend section, the annual total trends and then, may be only the seasons with the largest and lowest values, to reduce the text.
- The discussion section, as it is currently written, seems to not deserve its inclusion. The three first paragraphs can be moved and shorten to the methodology section, while the rest of the discussion is somewhat vague, with weak physical interpretation and/or discussion of advantage or limitation of data or analyses, as well as somewhat repetitive of the results already introduced. For instance, in lines 380-387, the west-east difference in H0 is attributed to the topography but it is not explained their influence on constrating climates at both sides of the Andes, basically, big difference in continentality, cloudiness, precipitation, among others. In lines 388-395, the localized highest warming in the NW of Patagonia is attributed to SAM, but why not affect in the southern Patagonia since the indices use atmospheric variables in R1 domain, south of the whole Patagonia region. What could be the connection between the SAM, global warming, and the localized warming in the NW? What about other large-scale phenomena? Could some of them have potential impacts? It would be a great opportunity here to link with works that quantified the ice losses? How much ice mass have the glaciers lost? It is coherent with the increasing levels of H0?
- In the discussion, it could be also mentioned that the lowering of the freezing level over the windward slopes of the Andes typically observed during midlatitude frontal precipitation is not appreciable in cross-barrier climatological profiles. This is a mesoscale atmospheric phenomenon that should not be capture by the ERA5 coarse resolution. See Minder’s works: https://doi.org/10.1175/JAS-D-10-05006.1; https://doi.org/10.1175/JAS-D-12-0194.1
- Presenting unique mean annual and seasonal values of the H0, in the abstract and conclusion as a main result, for the huge whole region (> 10° latitude), does not make sense. They should be introduced as a range of values, between the lowest (in the north) and highest values (in the south).
- It should be highlighted in sec. 3.1 the overall underestimation of H0 by the ERA5, if there is some documentation of that somewhere and possible causes, as well as what could be the implication for this study.
Minor Comments
- All of them Related to major comment 1)
- The term "free tropospheric" freezing level would not be used properly here. The free troposphere refers to as the part of the atmosphere above the boundary layer, free of the friction with the earth surface, and so in this study the freezing level not necessarily is present above the boundary layer. It does not make sense in the context of this study, at least the H0 found within the boundary layer were excluded from the study. If not, I suggest to not use it, and the title could be replaced by “Spatial and temporal variability of the freezing level in the Patagonia’s atmosphere”
- In the results, discussion and conclusion, the authors refer as “modeled or simulated” data or results to those coming from the ERA5. Since the goal of the reanalysis is to use model to assimilate already observed data, and not to predict in the future, I suggest to refer to as directly reanalysis ERA5 data/results. The terms model or simulated data could be intrinsically associated with projections or predictions by the model, and so may create confusion.
- In the abstract, it should be mentioned the data used in the study.
- L41: Viale et 2019 is more appropriated reference here. doi: 10.3389/fenvs.2019.00069
- L42: “...being the SAM the primary driver of extratropical climate variability in the Southern Hemisphere.”. This strong statement should be supported by references.
- L43: The SAM topic should start in a new paragraph. The introduction has mainly a unique paragraph mixing many main topics, making them harder to capture by the readers.
- L176-180: In the text, the authors refer to as “meridional and zonal profiles” and, in the Fig4, they were labeled as Zonal and Meridional mean, respectively. This is confusing. I suggest in the label or caption refer to as “Zonally (Meridionally) averaged Latitudinal (Longitudinal) Section”, and in the text to refer as “Latitudinal and Longitudinal variations”, respectively. Please also indicate in the text when you are talking about Fig 4a and 4b.
- L182-186: These sentences are not clear. Do you refer to mountain or interquartile ranges? When it is said higher or bigger, finishing the comparison w.r.t what is higher or bigger, if not it is hard to understand. Indicate the Fig that show that. Can the AA be located on average around 72W..? Please re-write these sentences.
- L197: Please indicate you are referring now to Fig. 5.
- L200: I see skewed to the left (low values)
- L200-202: It is not clear what line (of the 3 plotted) correspond to these stated values. Please indicate
- L291: Please indicate you are referring to Fig. 8b
- L322: “with a marked and unprecedent trend in the period that began 2010”. Where was that result shown? Please provide evidences
- L362: What model do you refer to? Please see comment 1.2
- L363: It is not clear this sentence. Please rewrite.
- L364: What do you mean by “3 observed data points”? It is not clear, please explain.
- L365: What methodology? Please specify.
Citation: https://doi.org/10.5194/egusphere-2024-145-RC2 - AC2: 'Reply on RC2', Nicolás D. García-Lee, 10 May 2024
Peer review completion
Journal article(s) based on this preprint
Data sets
Spatial and temporal variability of free tropospheric freezing level in Patagonia Nicolás D. García-Lee and Piero Mardones https://doi.org/10.5281/zenodo.10493785
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Claudio Bravo
Álvaro Gonzáles-Reyes
Piero Mardones
Please read the editorial note first before accessing the preprint.
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3631 KB) - Metadata XML
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Supplement
(1068 KB) - BibTeX
- EndNote
- Final revised paper