the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Jul 2023
Future changes in North Atlantic winter cyclones in CESM-LE – Part 2: A Lagrangian analysis
Abstract. Future changes in extratropical cyclone structure and dynamics may lead to important impacts, but are not yet fully understood. In the first part of this study, we have applied a composite approach together with potential vorticity (PV) inversion to study such changes in the dynamics of North Atlantic cyclones. Here, this is complemented with the help of a Lagrangian perspective, making use of air parcel trajectories to investigate the causes of altered PV anomalies as well as the role that cyclone airstreams play in shaping these changes. Intense cyclones in the extended winter seasons of two periods, 1990–2000 and 2091–2100, are studied in Community Earth System Model Large Ensemble (CESM-LE) simulations, and backward trajectories are calculated from the cyclone area as a basis to construct cyclone-centered composites of Lagrangian tendencies and their projected future changes. Our results show that diabatic processes on a timescale of 24 hours shape the cyclones' low-level PV distribution and corroborate that the increasing moisture content along with enhanced ascent in warm conveyor belts leads to amplified latent heat release and larger low- and mid-level PV anomalies near the cyclone center in a warmer climate. In contrast, projected upper-level PV changes are due to a combination of several processes, in addition to cloud-diabatic PV changes mainly anomalous PV advection and likely also radiative PV generation in the lower stratosphere above the cyclone center. For instance, enhanced poleward advection is the primary reason for a projected decrease in upper-level PV anomalies south of the cyclone center. Warm conveyor belt outflow regions are projected to shift upward, but there is not robust change in the associated upper-level PV anomalies due to compensation between enhanced low-level PV generation and upper-level PV destruction. In summary, our 2-part study points to future changes in the relative importance of different processes for the dynamics of intense North Atlantic cyclones in a warming climate, with important consequences for the near-surface wind pattern. In particular, a larger role of cloud diabatic processes is projected affecting the cyclones through PV production in the lower troposphere. The role of other mechanisms, in particular radiative changes near the tropopause, should be investigated in more detail in future studies.
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Notice on discussion status
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.
- Preprint
(3517 KB) - Metadata XML
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Supplement
(814 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-1382', Anonymous Referee #1, 30 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1382/egusphere-2023-1382-RC1-supplement.pdf
- AC1: 'Reply on RC1', Edgar Dolores Tesillos, 23 Oct 2023
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RC2: 'Comment on egusphere-2023-1382', Anonymous Referee #2, 14 Sep 2023
This paper is the second part of a study looking at the future changes of extratropical cyclones in the CESM model. In this part the authors use Lagrangian trajectory analysis to investigate the pathways of the air parcels and changes in their characteristics on their way to different horizontal and vertical locations in composites of extratropical cyclones.
The results mostly corroborate the findings of the earlier paper, and of other studies, in finding that increased moisture in a warmer climate leads to increased diabatic heating and therefore larger PV production in mid levels. The upper level features are more complex, especially due to the level of focus often being above the tropopause.
I especially like the composite figures showing the tendencies over the past 24 hours, which gives a good understanding of the features of the cyclones.
I have a few comments that I hope might improve some aspects of the manuscript.
General comments
- I wonder at the choice of 250hPa as a level to focus on. This was considered in paper 1 also, but in that paper it is shown that the tropopause average pressure is close to 300 or even 350hPa. If the focus of the study is on the dynamics of the cyclones themselves, then would it not be better to look at a level within the troposphere, where the WCB outflow is having a more direct impact? This also makes the average of the trajectories over the cyclone area at the this level difficult to interpret, and possibly not very useful.
- Figs 4, 5, 6: In the section describing these figures, there is a lot of jumping around between these and the horizontal composites. This is because the 700hPa horizontal composites are discussed along with 4, 5, 6, then the 250hPa composites. It might be easier to read and follow if the trajectories from 700hPa are all combined into a single figure that can be discussed with the 700hPa horizontal composites. Then the same for the 250hPa trajectories. The way it is currently presented gives a slightly misleading impression that trajectories at different levels but the same location are more strongly related than they really are.
More specific comments
- Line 12-14: This sentence is hard to read - consider rewording.
- Line 31: Remove the additional comma.
- Figure 1: Since you later discuss the two branches of the WCB, I suggest adding the cyclonic branch onto this schematic.
- In the Methods section I would like a bit more information. I understand this is part 2, but it would be good to have some extra information so the paper can stand alone. For example, Which months? What area? NH or North Atlantic? How many storms does this make? Which cyclone identification?
- Line 147-148: This argument only really works for the 700hPa trajectories, since at the higher level the trajectories are not so likely to be coming from above.
- Line 167: Typo in the units.
- Figures 4, 5, 6: It may be nice to include the 5-95th percentile range on these figures too.
- Line 246: I find this more northward motion very interesting. Is this associated with a more poleward propagation of the cyclones? Or can you not infer that from this information? Is it possible to explain this feature in more detail?
- Line 249: Similarly to the previous comment, I find it interesting that there is a weakening in the westerly flow. It would be good to link this to projections of a weakened Jetstream either here or in the conclusions/discussion.
- Line 381: Typo in “cyclones”.
- Figure S1: More information is needed in the caption - what level is this showing?
Citation: https://doi.org/10.5194/egusphere-2023-1382-RC2 - AC2: 'Reply on RC2', Edgar Dolores Tesillos, 23 Oct 2023
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RC3: 'Comment on egusphere-2023-1382', Anonymous Referee #3, 19 Sep 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1382/egusphere-2023-1382-RC3-supplement.pdf
- AC3: 'Reply on RC3', Edgar Dolores Tesillos, 23 Oct 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-1382', Anonymous Referee #1, 30 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1382/egusphere-2023-1382-RC1-supplement.pdf
- AC1: 'Reply on RC1', Edgar Dolores Tesillos, 23 Oct 2023
-
RC2: 'Comment on egusphere-2023-1382', Anonymous Referee #2, 14 Sep 2023
This paper is the second part of a study looking at the future changes of extratropical cyclones in the CESM model. In this part the authors use Lagrangian trajectory analysis to investigate the pathways of the air parcels and changes in their characteristics on their way to different horizontal and vertical locations in composites of extratropical cyclones.
The results mostly corroborate the findings of the earlier paper, and of other studies, in finding that increased moisture in a warmer climate leads to increased diabatic heating and therefore larger PV production in mid levels. The upper level features are more complex, especially due to the level of focus often being above the tropopause.
I especially like the composite figures showing the tendencies over the past 24 hours, which gives a good understanding of the features of the cyclones.
I have a few comments that I hope might improve some aspects of the manuscript.
General comments
- I wonder at the choice of 250hPa as a level to focus on. This was considered in paper 1 also, but in that paper it is shown that the tropopause average pressure is close to 300 or even 350hPa. If the focus of the study is on the dynamics of the cyclones themselves, then would it not be better to look at a level within the troposphere, where the WCB outflow is having a more direct impact? This also makes the average of the trajectories over the cyclone area at the this level difficult to interpret, and possibly not very useful.
- Figs 4, 5, 6: In the section describing these figures, there is a lot of jumping around between these and the horizontal composites. This is because the 700hPa horizontal composites are discussed along with 4, 5, 6, then the 250hPa composites. It might be easier to read and follow if the trajectories from 700hPa are all combined into a single figure that can be discussed with the 700hPa horizontal composites. Then the same for the 250hPa trajectories. The way it is currently presented gives a slightly misleading impression that trajectories at different levels but the same location are more strongly related than they really are.
More specific comments
- Line 12-14: This sentence is hard to read - consider rewording.
- Line 31: Remove the additional comma.
- Figure 1: Since you later discuss the two branches of the WCB, I suggest adding the cyclonic branch onto this schematic.
- In the Methods section I would like a bit more information. I understand this is part 2, but it would be good to have some extra information so the paper can stand alone. For example, Which months? What area? NH or North Atlantic? How many storms does this make? Which cyclone identification?
- Line 147-148: This argument only really works for the 700hPa trajectories, since at the higher level the trajectories are not so likely to be coming from above.
- Line 167: Typo in the units.
- Figures 4, 5, 6: It may be nice to include the 5-95th percentile range on these figures too.
- Line 246: I find this more northward motion very interesting. Is this associated with a more poleward propagation of the cyclones? Or can you not infer that from this information? Is it possible to explain this feature in more detail?
- Line 249: Similarly to the previous comment, I find it interesting that there is a weakening in the westerly flow. It would be good to link this to projections of a weakened Jetstream either here or in the conclusions/discussion.
- Line 381: Typo in “cyclones”.
- Figure S1: More information is needed in the caption - what level is this showing?
Citation: https://doi.org/10.5194/egusphere-2023-1382-RC2 - AC2: 'Reply on RC2', Edgar Dolores Tesillos, 23 Oct 2023
-
RC3: 'Comment on egusphere-2023-1382', Anonymous Referee #3, 19 Sep 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1382/egusphere-2023-1382-RC3-supplement.pdf
- AC3: 'Reply on RC3', Edgar Dolores Tesillos, 23 Oct 2023
Peer review completion
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Edgar Dolores-Tesillos
Stephan Pfahl
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3517 KB) - Metadata XML
-
Supplement
(814 KB) - BibTeX
- EndNote
- Final revised paper