the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Dec 2024
Physical Processes Leading to Extreme day-to-day Temperatures Changes, Part I: Present-day Climate
Abstract. Extreme temperature changes from one day to another, either associated with warming or cooling, can have a significant impact on health, environment, and society. Previous studies have quantified that such day-to-day temperature (DTDT) variations are typically more pronounced in the extratropics compared to tropical zones. However, the underlying physical processes and the relationship between extreme events and the large-scale atmospheric circulation remain poorly understood. Here, these processes are investigated for different locations around the globe based on observation, ERA5 reanalysis data, and Lagrangian backward trajectory calculations. We show that extreme DTDT changes in the extratropics are generally associated with changes in air mass transport, in particular shifts from warm to cold air advection or vice versa, linked to regionally specific synoptic-scale circulation anomalies (ridge or through patterns). These dominant effects of advection are modulated by changes in adiabatic and diabatic processes in the transported air parcels, which tend to either amplify or dampen DTDT decreases (cold events) and increases (warm events) depending on the region and season. In contrast, DTDT extremes during December–February in the tropics are controlled by local processes rather than changes in advection. For instance, the most significant DTDT decreases are associated with a shift from less cloudy to more cloudy conditions, highlighting the crucial role of solar radiative heating. The mechanistic insights into extreme DTDT changes obtained in this study can help improve the prediction of such events and anticipate future changes in their occurrence frequency and intensity, which will be investigated in part II of this study.
Competing interests: Stephan Pfahl is executive editor of WCD.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
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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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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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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2024-3732', Huayu Chen, 19 Dec 2024
I am very happy to read your work! Interestingly, I have conducted similar research using Lagrangian analysis, focusing on a case study of weather whiplash (https://doi.org/10.1088/1748-9326/ad9c9a). Back to your work, I have several questions and one possible suggestion that I would like to discuss with you!
- Question-1: Your work investigates the extreme day-to-day temperature (DTDT) variations and offers a physical understanding via a Lagrangian temperature budget. While Lagrangian analysis vividly depict synoptic motions, why not employ the "Eulerian temperature budget" instead? This approach directly examines the contributions of different physical processes to DTDT variations, i.e., partial T/partial t.
- Question-2: Your manipulation leading to Eq. A1 is very interesting. However, the "advection term" in Eq. A1 does not seem to have an intuitively clear connection to advection. Could you clarify this?
- Suggestion-1: A study by Prof. Tapio Schneider provides a macroturbulence perspective (temperature gradient + mixing length) to understand synoptic temperature variability and its responses to global warming (https://doi.org/10.1175/JCLI-D-14-00632.1). It might be valuable to compare your findings with this work.
I look forward to your reply, and hope to see Part-II of your study soon!
Citation: https://doi.org/10.5194/egusphere-2024-3732-CC1 -
CC2: 'Reply on CC1', Kalpana Hamal, 17 Jan 2025
I am very happy to read your work! Interestingly, I have conducted similar research using Lagrangian analysis, focusing on a case study of weather whiplash (https://doi.org/10.1088/1748-9326/ad9c9a). Back to your work, I have several questions and one possible suggestion that I would like to discuss with you!
Thank you so much for your insightful questions and suggestions regarding our paper. We’ve read your paper on the weather whiplash case study and found it to be very exciting. It’s fascinating to see how Lagrangian analysis can be applied to the whiplash case study as well. Below, we’ve provided answers to the questions you raised in our paper.
- Question-1: Your work investigates the extreme day-to-day temperature (DTDT) variations and offers a physical understanding via a Lagrangian temperature budget. While Lagrangian analysis vividly depict synoptic motions, why not employ the "Eulerian temperature budget" instead? This approach directly examines the contributions of different physical processes to DTDT variations, i.e., partial T/partial t.
Answer: The Eulerian temperature budget focuses on changes in temperature at fixed spatial locations, breaking these changes down into contributions from various physical processes. While this approach is valuable for assessing local processes and may be well-suited for tropical regions during December–January–February, it may not capture the movement, evolution, and associated temperature changes of air parcels, particularly in the extratropics. As the advection effects are modulated by adiabatic and diabatic processes within transported air parcels, amplifying or dampening DTDT decreases (cold events) and increases (warm events). For instance, during warm events in North America, remote advection plays a significant role, with some additional contributions from surface heating. In contrast, in Australia, diabatic heating during transport is more dominant than local heating. In an Eulerian budget, this diabatic heating of the air parcels would not have been accounted for, since only local heating is captured. This underscores the importance of the Lagrangian framework for studying extreme DTDT by tracking air parcels and their trajectories, offering a comprehensive understanding of the underlying dynamics.
- Question-2: Your manipulation leading to Eq. A1 is very interesting. However, the "advection term" in Eq. A1 does not seem to have an intuitively clear connection to advection. Could you clarify this?
Answer: indicates the average temperature of the air parcels initialized on the day of the extreme events three days before their arrival at the target location and the corresponding temperature for the air parcels initialized one day earlier. The expression thus represents the difference between the air parcel's temperatures three days before their arrival. Assuming that no further temperature changes occurred during the transport, the DTDT change would only be due to these initial differences of the air parcels, which means it would be caused by changes in the advection of air parcels with different original temperatures between the previous day and the day of the event. This is why we refer to this term as an advection term.
Suggestion-1: A study by Prof. Tapio Schneider provides a macroturbulence perspective (temperature gradient + mixing length) to understand synoptic temperature variability and its responses to global warming (https://doi.org/10.1175/JCLI-D-14-00632.1). It might be valuable to compare your findings with this work.
Answer: Thank you for the suggestion. This paper investigates the underlying physical processes of DTDT extremes and their linkage to the large-scale atmospheric circulation in the present climate. We will also explore how these processes influence projected DTDT extremes under climate warming in Part II. The study by Prof. Tapio Schneider shows that the reduction of meridional potential temperature gradients, driven by the polar amplification of global warming, leads to a decrease in synoptic temperature variance near the surface. Comparing our findings with this work will offer additional insights into the dynamics of temperature extremes and their response to global warming.
-
CC3: 'Reply on CC1', Kalpana Hamal, 18 Jan 2025
As in the previous text (Reply CC1), the equations/symbols: this is the pdf version
-
CC4: 'Reply on CC3', Huayu Chen, 01 Feb 2025
Thank you so much you detailed reply, especially the interpretation of the "advection term"!
Citation: https://doi.org/10.5194/egusphere-2024-3732-CC4
-
CC4: 'Reply on CC3', Huayu Chen, 01 Feb 2025
-
RC1: 'Comment on egusphere-2024-3732', Anonymous Referee #1, 13 Jan 2025
Please find my comments in the attachment.
- AC1: 'Reply on RC1', Kalpana Hamal, 07 Apr 2025
-
RC2: 'Comment on egusphere-2024-3732', Anonymous Referee #2, 10 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-3732/egusphere-2024-3732-RC2-supplement.pdf
- AC2: 'Reply on RC2', Kalpana Hamal, 07 Apr 2025
Interactive discussion
Status: closed
-
CC1: 'Comment on egusphere-2024-3732', Huayu Chen, 19 Dec 2024
I am very happy to read your work! Interestingly, I have conducted similar research using Lagrangian analysis, focusing on a case study of weather whiplash (https://doi.org/10.1088/1748-9326/ad9c9a). Back to your work, I have several questions and one possible suggestion that I would like to discuss with you!
- Question-1: Your work investigates the extreme day-to-day temperature (DTDT) variations and offers a physical understanding via a Lagrangian temperature budget. While Lagrangian analysis vividly depict synoptic motions, why not employ the "Eulerian temperature budget" instead? This approach directly examines the contributions of different physical processes to DTDT variations, i.e., partial T/partial t.
- Question-2: Your manipulation leading to Eq. A1 is very interesting. However, the "advection term" in Eq. A1 does not seem to have an intuitively clear connection to advection. Could you clarify this?
- Suggestion-1: A study by Prof. Tapio Schneider provides a macroturbulence perspective (temperature gradient + mixing length) to understand synoptic temperature variability and its responses to global warming (https://doi.org/10.1175/JCLI-D-14-00632.1). It might be valuable to compare your findings with this work.
I look forward to your reply, and hope to see Part-II of your study soon!
Citation: https://doi.org/10.5194/egusphere-2024-3732-CC1 -
CC2: 'Reply on CC1', Kalpana Hamal, 17 Jan 2025
I am very happy to read your work! Interestingly, I have conducted similar research using Lagrangian analysis, focusing on a case study of weather whiplash (https://doi.org/10.1088/1748-9326/ad9c9a). Back to your work, I have several questions and one possible suggestion that I would like to discuss with you!
Thank you so much for your insightful questions and suggestions regarding our paper. We’ve read your paper on the weather whiplash case study and found it to be very exciting. It’s fascinating to see how Lagrangian analysis can be applied to the whiplash case study as well. Below, we’ve provided answers to the questions you raised in our paper.
- Question-1: Your work investigates the extreme day-to-day temperature (DTDT) variations and offers a physical understanding via a Lagrangian temperature budget. While Lagrangian analysis vividly depict synoptic motions, why not employ the "Eulerian temperature budget" instead? This approach directly examines the contributions of different physical processes to DTDT variations, i.e., partial T/partial t.
Answer: The Eulerian temperature budget focuses on changes in temperature at fixed spatial locations, breaking these changes down into contributions from various physical processes. While this approach is valuable for assessing local processes and may be well-suited for tropical regions during December–January–February, it may not capture the movement, evolution, and associated temperature changes of air parcels, particularly in the extratropics. As the advection effects are modulated by adiabatic and diabatic processes within transported air parcels, amplifying or dampening DTDT decreases (cold events) and increases (warm events). For instance, during warm events in North America, remote advection plays a significant role, with some additional contributions from surface heating. In contrast, in Australia, diabatic heating during transport is more dominant than local heating. In an Eulerian budget, this diabatic heating of the air parcels would not have been accounted for, since only local heating is captured. This underscores the importance of the Lagrangian framework for studying extreme DTDT by tracking air parcels and their trajectories, offering a comprehensive understanding of the underlying dynamics.
- Question-2: Your manipulation leading to Eq. A1 is very interesting. However, the "advection term" in Eq. A1 does not seem to have an intuitively clear connection to advection. Could you clarify this?
Answer: indicates the average temperature of the air parcels initialized on the day of the extreme events three days before their arrival at the target location and the corresponding temperature for the air parcels initialized one day earlier. The expression thus represents the difference between the air parcel's temperatures three days before their arrival. Assuming that no further temperature changes occurred during the transport, the DTDT change would only be due to these initial differences of the air parcels, which means it would be caused by changes in the advection of air parcels with different original temperatures between the previous day and the day of the event. This is why we refer to this term as an advection term.
Suggestion-1: A study by Prof. Tapio Schneider provides a macroturbulence perspective (temperature gradient + mixing length) to understand synoptic temperature variability and its responses to global warming (https://doi.org/10.1175/JCLI-D-14-00632.1). It might be valuable to compare your findings with this work.
Answer: Thank you for the suggestion. This paper investigates the underlying physical processes of DTDT extremes and their linkage to the large-scale atmospheric circulation in the present climate. We will also explore how these processes influence projected DTDT extremes under climate warming in Part II. The study by Prof. Tapio Schneider shows that the reduction of meridional potential temperature gradients, driven by the polar amplification of global warming, leads to a decrease in synoptic temperature variance near the surface. Comparing our findings with this work will offer additional insights into the dynamics of temperature extremes and their response to global warming.
-
CC3: 'Reply on CC1', Kalpana Hamal, 18 Jan 2025
As in the previous text (Reply CC1), the equations/symbols: this is the pdf version
-
CC4: 'Reply on CC3', Huayu Chen, 01 Feb 2025
Thank you so much you detailed reply, especially the interpretation of the "advection term"!
Citation: https://doi.org/10.5194/egusphere-2024-3732-CC4
-
CC4: 'Reply on CC3', Huayu Chen, 01 Feb 2025
-
RC1: 'Comment on egusphere-2024-3732', Anonymous Referee #1, 13 Jan 2025
Please find my comments in the attachment.
- AC1: 'Reply on RC1', Kalpana Hamal, 07 Apr 2025
-
RC2: 'Comment on egusphere-2024-3732', Anonymous Referee #2, 10 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-3732/egusphere-2024-3732-RC2-supplement.pdf
- AC2: 'Reply on RC2', Kalpana Hamal, 07 Apr 2025
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Kalpana Hamal
Stephan Pfahl
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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