the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Dec 2023
Future reduction of cold extremes over East Asia due to thermodynamic and dynamic warming
Abstract. Cold extremes have large impacts on human society. Understanding the physical processes dominating the changes of cold extremes is crucial for a reliable projection of future climate change. The observed cold extremes have been decreased during last several decades and this trend will continue under the future global warming. Here, we quantitatively identify the contributions of dynamic (changes in large-scale atmospheric circulation) and thermodynamic (rising temperatures resulting from global warming) effects to East Asian cold extremes in the past several decades and in a future warm climate by using two sets of large ensemble simulation of climate models. We show that the dynamic component accounts for over 80 % of the cold-month (coldest 5 % boreal winter months) surface air temperature (SAT) anomaly in the past five decades. However, in a future warm climate, the thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive. The intensity of East Asian cold extremes will decrease by around 5℃ at the end of the 21st century, in which the thermodynamic (dynamic) change contributes approximately 75 % (25 %). The present-day (1986–2005) East Asian cold extremes will almost never occur after around 2035, and this will happen eight years later due solely to thermodynamic change. The upward trend of a positive Arctic Oscillation-like sea level pressure pattern dominates the changes in the dynamic component. The finding provides a useful reference for policymakers in climate change adaptation activities.
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2806', Anonymous Referee #1, 08 Jan 2024
Authors attempted to identify the East Asian temperature extremes contributed by dynamical and thermodynamical processes. If is of scientific significance for a better understanding regional climate anomaly and extremes under warming. The results are clearly presented with logics. I suggest authors to clarify how the critical method applied, and provide more details.
Section 2.3.1, The details how the dynamic adjustment approach was applied are not clear. It is confusing how a target SLP pattern is defined in advance, based on this target field you rank the monthly fields according to their similarity to the target SLP filed, and selected 150 most similar fields. But later, you said the 100 randomly selected to construct the target SLP pattern. Quite confusing, please clarify to avoid misleading.
The target atmospheric circulation fields are global or hemisphere or regional? May be of different meanings and limitations.
Randomly select 100 from 150 fields to construct the dynamic field. Why random 100? Why not simply 150 filed combination? Any evidence or estimation for the optimum number of samples?
Readers may wonder whether the 150 fields totally capture the dynamical contribution or not. If not, the thermodynamical contribution would be overestimated. A discussion or simply analysis would help clarify.
Section 2.3.2, How the dynamic adjustment approach is applied, reads a little complicated, it is better to present in a direct and simply way.
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC1 - AC1: 'Reply on RC1', Donghuan Li, 14 Apr 2024
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RC2: 'Comment on egusphere-2023-2806', Anonymous Referee #2, 21 Jan 2024
all the comments and questions have been well addressed and revised in the current version, no further question on it.
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC2 - AC2: 'Reply on RC2', Donghuan Li, 14 Apr 2024
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RC3: 'Comment on egusphere-2023-2806', Anonymous Referee #3, 02 Feb 2024
General comments
In this study, the authors quantify the contributions of the dynamic and thermodynamic components in the observed and projected SAT anomalies under the RCP8.5 scenario. Two climate models are used (MPI-GE and CESM-LE), with respectively 100 and 40 members. The addressed questions and the methods are clearly stated. Overall, the results are presented in a coherent way. The authors show that the dynamic component accounts for most of the cold extremes during 1962-2011, while the thermodynamic changes explain most of the cold extremes in a warmer climate in 2079-2098.
Some parts should be clarified (see specific comments below) and there is a lack of discussion on the reasons which might explain the differences/similarities between the models and the observations (section 3.1) and between both models (section 3.2).
Specific comments
Introduction
L.60 - Please provide a reference.
L.63 - Maybe also provide the anomaly of this coldest day, such as in L.65,66 for comparison.
L.70 - “The model simulations indicate that the anthropogenic influences have reduced the occurrence probability of cold extremes over eastern China with intensity stronger than the record-breaking cold extreme in January 2016 (Qian et al., 2018).”: Please specify which period you are referring to? There could not have been intensities larger than the record of 2016 in the past if it is a record (the sentence is not clear).
Section 2.3
Please justify the choice of the selection of 100 random and 150 closest SLP fields: when does it converge? Is it the same as in Deser et al. (2016), figure A2 in appendix?
L.152 - “the internal dynamic component is obtained by subtracting the forced part from the total dynamic component.”: Specify that is done for each ensemble member.
Section 2.5
L.180 - “in a certain time slice”: Which time slice is taken for the definition of a cold extreme?
Section 2.6
L.196 - “we pull all the members together ratio rather than calculate it for each member.”: Remove “ratio”? (or reformulate)
Section 3.1
L.201 - First paragraph on figure 1: Please reformulate and clarify. First, are you referring to observations or PiCTL simulations? Why do you focus on the period 1962-2011, while the available period is 1920-2012, as mentioned L.136? Explain why figure 1 shows that “this is mainly caused by the dynamically-induced internal component”. What are the correlation coefficients? What is the physical meaning of the sentence “this variability is the main cause of cold extremes over East Asia in the past five decades” and how do you relate this with figure 1?
Figure 1: Why the forced and internal parts of the thermodynamic component are not shown, but described in the methods L.168? This should be clarified.
L.210 - “especially for the cold extremes happened in recent years”: Please clarify why? Looking at table 1, this is the case for 196402, 196902, 107701, 196712, 201101, 196612, so not necessarily the most recent years?
L.213 - To support the argument, the correlation coefficients could have been calculated for the different subplots, as suggested previously.
L.216 - “The two sets of large ensemble model simulations can well reproduce the relative contributions of the dynamic and thermodynamic components to the cold extremes during 1962-2011 boreal winter (Figure 2d-i).”: Please reformulate. The relative contribution does not seem very well reproduced, as the thermodynamic component is much lower within the simulations than in the observations, and the dynamical part is much larger, especially in the North of the region (figure 2 b,c vs. e,h,f,i).
L.218 - “The SAT is significantly lower than the winter SAT climatology throughout East Asia”: Considering that composites of the coldest months are selected, isn’t it expected by definition?
L.223 - “The dynamic component accounts up to 85% and 82% of the total East Asian cold-month SAT anomaly during 1962-2011 boreal winter in the MPI-GE and the CESM-LE, respectively”: Similarly, what is the percentage of the dynamic component during the whole period 1962-2011 in the observations, to compare with the simulations?
L.229 - “The cold extremes are often associated with strong East Asian winter monsoon flows, which are often accompanied with the blockings in the Urals and the intensified Siberian high.”: Please provide reference(s).
L.235 - “there is an enhanced meandering flow pattern (Figure 3b).” Please explain why.
L.236 - “The weakened westerlies may favor the blocking events, which have strong relationship with the cold extremes over East Asia.”: Please provide reference(s).
Figure 3: Plotting the climatology in contours would help to visualize the deviation or reinforcement of the dynamics with respect to the climatology. Do the models and observations have similar climatologies regarding the circulation?
Part 3.1: This part (or the discussion section) would benefit from a discussion on the differences/similarities between the observations and models obtained here for the cold extreme composites, and for total, thermodynamic and dynamic components.
Section 3.2
L.264 - “The faster increase of thermodynamic components in northern East Asia may be caused by the snow-albedo feedback, while the reason for the faster increase in dynamic component in this region is that the influence of East Asian Winter Monsoon on northern East Asia is more evident than on other subregions.” On these two aspects, please provide further explanation or cite literature.
L.262 and second paragraph of section 3.2: it should be emphasized that it is now the thermodynamic part which plays a major role (e.g. in figure 4 a,c: it is worth noting that, in approx. the first half of the period plotted in figure 4, the dynamical component explains a larger part of the total SAT, while in approx. the second half it is the thermodynamical component, in both models.)
L.270 - “The corresponding increases in the dynamic and thermodynamic components are 1.3℃ and 3.9℃,”: Please also give the percentages to compare to L.262.
L.274 - “The thermodynamic component shows some differences (Figure 5c and f).”: Specify what are these differences? What are the reasons which might explain why there are differences between both ensemble means, in the total, dynamic and thermodynamic components?
L.306 - “the projected changes in SLP exhibit a positive AO-like pattern, particularly in the MPI-GE (Figure 7a and b).”: What is the correlation of the obtained pattern with the AO SLP pattern?
L.311 - “Similar SLP changing pattern also occurs in cold months (Figure 7c and d)”: You might want to specify that you are now referring to the CESM-LE model? The results for this model (figure 7c,d and figure 8c,d) do not look similar to the MPI-GE model, especially comparing figures 7d and 7b, and figure 8d and 8b, where the SLP patterns during cold extremes are different over Eurasia. Comparing correlation coefficients with the AO SLP pattern could be useful for the interpretation/comparison of the different figures. Please reformulate this part.
L.302 - “The thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive.”: Based on figure 4 and figure 5, the dynamic component seems minor in explaining the total SAT, this should be clarified.
Section 4.1
The 3 summarized points does not exactly correspond to the 3 questions raised at the beginning in the introduction.
L.326 - “especially for the cold extremes happened in recent years.”: Why? Please see the comment about L.210.
L.328 - “The relative contributions of the dynamic and thermodynamic components to the cold extremes are well captured in the two model ensembles”: Please reformulate the conclusion, see comment about L.216.
L.333 - “In the future warm climate, the background warming is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the circulation changes are also contributive.”: The results presented in this paper (figure 4 and 5) seem to indicate that the changes in cold extreme SAT are mainly governed by the thermodynamic part; this should be emphasized (cf. comment about L.302).
L.335 - “Compared with the present day, the mean intensity of the East Asian cold extremes will decrease by approximately 5℃ at the end of the 21st century under the RCP8.5 scenario and the dynamic component contributes to a quarter of this decrease.”: It should be mentioned that this is the case in the MPI-GE and CESM-LE models.
L.342 - “Positive AO-like sea level pressure pattern upward trend is projected in both of the model ensembles”: This should be clarified, in line with comments on L.306 and L.311.
Technical Corrections
L.46 - Replace “concerned” by “concerning”?
L.47 - Typography: 2 commas
L.48 - Typography: “and even”
L.63 - “North America” or “The north of America”
L.68 - Replace “if” by “while”?
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC3 - AC3: 'Reply on RC3', Donghuan Li, 14 Apr 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2806', Anonymous Referee #1, 08 Jan 2024
Authors attempted to identify the East Asian temperature extremes contributed by dynamical and thermodynamical processes. If is of scientific significance for a better understanding regional climate anomaly and extremes under warming. The results are clearly presented with logics. I suggest authors to clarify how the critical method applied, and provide more details.
Section 2.3.1, The details how the dynamic adjustment approach was applied are not clear. It is confusing how a target SLP pattern is defined in advance, based on this target field you rank the monthly fields according to their similarity to the target SLP filed, and selected 150 most similar fields. But later, you said the 100 randomly selected to construct the target SLP pattern. Quite confusing, please clarify to avoid misleading.
The target atmospheric circulation fields are global or hemisphere or regional? May be of different meanings and limitations.
Randomly select 100 from 150 fields to construct the dynamic field. Why random 100? Why not simply 150 filed combination? Any evidence or estimation for the optimum number of samples?
Readers may wonder whether the 150 fields totally capture the dynamical contribution or not. If not, the thermodynamical contribution would be overestimated. A discussion or simply analysis would help clarify.
Section 2.3.2, How the dynamic adjustment approach is applied, reads a little complicated, it is better to present in a direct and simply way.
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC1 - AC1: 'Reply on RC1', Donghuan Li, 14 Apr 2024
-
RC2: 'Comment on egusphere-2023-2806', Anonymous Referee #2, 21 Jan 2024
all the comments and questions have been well addressed and revised in the current version, no further question on it.
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC2 - AC2: 'Reply on RC2', Donghuan Li, 14 Apr 2024
-
RC3: 'Comment on egusphere-2023-2806', Anonymous Referee #3, 02 Feb 2024
General comments
In this study, the authors quantify the contributions of the dynamic and thermodynamic components in the observed and projected SAT anomalies under the RCP8.5 scenario. Two climate models are used (MPI-GE and CESM-LE), with respectively 100 and 40 members. The addressed questions and the methods are clearly stated. Overall, the results are presented in a coherent way. The authors show that the dynamic component accounts for most of the cold extremes during 1962-2011, while the thermodynamic changes explain most of the cold extremes in a warmer climate in 2079-2098.
Some parts should be clarified (see specific comments below) and there is a lack of discussion on the reasons which might explain the differences/similarities between the models and the observations (section 3.1) and between both models (section 3.2).
Specific comments
Introduction
L.60 - Please provide a reference.
L.63 - Maybe also provide the anomaly of this coldest day, such as in L.65,66 for comparison.
L.70 - “The model simulations indicate that the anthropogenic influences have reduced the occurrence probability of cold extremes over eastern China with intensity stronger than the record-breaking cold extreme in January 2016 (Qian et al., 2018).”: Please specify which period you are referring to? There could not have been intensities larger than the record of 2016 in the past if it is a record (the sentence is not clear).
Section 2.3
Please justify the choice of the selection of 100 random and 150 closest SLP fields: when does it converge? Is it the same as in Deser et al. (2016), figure A2 in appendix?
L.152 - “the internal dynamic component is obtained by subtracting the forced part from the total dynamic component.”: Specify that is done for each ensemble member.
Section 2.5
L.180 - “in a certain time slice”: Which time slice is taken for the definition of a cold extreme?
Section 2.6
L.196 - “we pull all the members together ratio rather than calculate it for each member.”: Remove “ratio”? (or reformulate)
Section 3.1
L.201 - First paragraph on figure 1: Please reformulate and clarify. First, are you referring to observations or PiCTL simulations? Why do you focus on the period 1962-2011, while the available period is 1920-2012, as mentioned L.136? Explain why figure 1 shows that “this is mainly caused by the dynamically-induced internal component”. What are the correlation coefficients? What is the physical meaning of the sentence “this variability is the main cause of cold extremes over East Asia in the past five decades” and how do you relate this with figure 1?
Figure 1: Why the forced and internal parts of the thermodynamic component are not shown, but described in the methods L.168? This should be clarified.
L.210 - “especially for the cold extremes happened in recent years”: Please clarify why? Looking at table 1, this is the case for 196402, 196902, 107701, 196712, 201101, 196612, so not necessarily the most recent years?
L.213 - To support the argument, the correlation coefficients could have been calculated for the different subplots, as suggested previously.
L.216 - “The two sets of large ensemble model simulations can well reproduce the relative contributions of the dynamic and thermodynamic components to the cold extremes during 1962-2011 boreal winter (Figure 2d-i).”: Please reformulate. The relative contribution does not seem very well reproduced, as the thermodynamic component is much lower within the simulations than in the observations, and the dynamical part is much larger, especially in the North of the region (figure 2 b,c vs. e,h,f,i).
L.218 - “The SAT is significantly lower than the winter SAT climatology throughout East Asia”: Considering that composites of the coldest months are selected, isn’t it expected by definition?
L.223 - “The dynamic component accounts up to 85% and 82% of the total East Asian cold-month SAT anomaly during 1962-2011 boreal winter in the MPI-GE and the CESM-LE, respectively”: Similarly, what is the percentage of the dynamic component during the whole period 1962-2011 in the observations, to compare with the simulations?
L.229 - “The cold extremes are often associated with strong East Asian winter monsoon flows, which are often accompanied with the blockings in the Urals and the intensified Siberian high.”: Please provide reference(s).
L.235 - “there is an enhanced meandering flow pattern (Figure 3b).” Please explain why.
L.236 - “The weakened westerlies may favor the blocking events, which have strong relationship with the cold extremes over East Asia.”: Please provide reference(s).
Figure 3: Plotting the climatology in contours would help to visualize the deviation or reinforcement of the dynamics with respect to the climatology. Do the models and observations have similar climatologies regarding the circulation?
Part 3.1: This part (or the discussion section) would benefit from a discussion on the differences/similarities between the observations and models obtained here for the cold extreme composites, and for total, thermodynamic and dynamic components.
Section 3.2
L.264 - “The faster increase of thermodynamic components in northern East Asia may be caused by the snow-albedo feedback, while the reason for the faster increase in dynamic component in this region is that the influence of East Asian Winter Monsoon on northern East Asia is more evident than on other subregions.” On these two aspects, please provide further explanation or cite literature.
L.262 and second paragraph of section 3.2: it should be emphasized that it is now the thermodynamic part which plays a major role (e.g. in figure 4 a,c: it is worth noting that, in approx. the first half of the period plotted in figure 4, the dynamical component explains a larger part of the total SAT, while in approx. the second half it is the thermodynamical component, in both models.)
L.270 - “The corresponding increases in the dynamic and thermodynamic components are 1.3℃ and 3.9℃,”: Please also give the percentages to compare to L.262.
L.274 - “The thermodynamic component shows some differences (Figure 5c and f).”: Specify what are these differences? What are the reasons which might explain why there are differences between both ensemble means, in the total, dynamic and thermodynamic components?
L.306 - “the projected changes in SLP exhibit a positive AO-like pattern, particularly in the MPI-GE (Figure 7a and b).”: What is the correlation of the obtained pattern with the AO SLP pattern?
L.311 - “Similar SLP changing pattern also occurs in cold months (Figure 7c and d)”: You might want to specify that you are now referring to the CESM-LE model? The results for this model (figure 7c,d and figure 8c,d) do not look similar to the MPI-GE model, especially comparing figures 7d and 7b, and figure 8d and 8b, where the SLP patterns during cold extremes are different over Eurasia. Comparing correlation coefficients with the AO SLP pattern could be useful for the interpretation/comparison of the different figures. Please reformulate this part.
L.302 - “The thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive.”: Based on figure 4 and figure 5, the dynamic component seems minor in explaining the total SAT, this should be clarified.
Section 4.1
The 3 summarized points does not exactly correspond to the 3 questions raised at the beginning in the introduction.
L.326 - “especially for the cold extremes happened in recent years.”: Why? Please see the comment about L.210.
L.328 - “The relative contributions of the dynamic and thermodynamic components to the cold extremes are well captured in the two model ensembles”: Please reformulate the conclusion, see comment about L.216.
L.333 - “In the future warm climate, the background warming is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the circulation changes are also contributive.”: The results presented in this paper (figure 4 and 5) seem to indicate that the changes in cold extreme SAT are mainly governed by the thermodynamic part; this should be emphasized (cf. comment about L.302).
L.335 - “Compared with the present day, the mean intensity of the East Asian cold extremes will decrease by approximately 5℃ at the end of the 21st century under the RCP8.5 scenario and the dynamic component contributes to a quarter of this decrease.”: It should be mentioned that this is the case in the MPI-GE and CESM-LE models.
L.342 - “Positive AO-like sea level pressure pattern upward trend is projected in both of the model ensembles”: This should be clarified, in line with comments on L.306 and L.311.
Technical Corrections
L.46 - Replace “concerned” by “concerning”?
L.47 - Typography: 2 commas
L.48 - Typography: “and even”
L.63 - “North America” or “The north of America”
L.68 - Replace “if” by “while”?
Citation: https://doi.org/10.5194/egusphere-2023-2806-RC3 - AC3: 'Reply on RC3', Donghuan Li, 14 Apr 2024
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Donghuan Li
Tianjun Zhou
Youcun Qi
Liwei Zou
Wenxia Zhang
Xiaolong Chen
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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