the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Apr 2024
The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity
Abstract. A unique chain connects the flow over the North Atlantic and the development of cyclones within the Mediterranean basin. One typical mechanism includes several successive processes: upper-level flow perturbations upstream cause Rossby wave breaking (RWB) events along the jet stream, which in turn develop into potential vorticity streamers. These streamers reach the Mediterranean, and through increased baroclinicity they enhance cyclonic activity in the region. Using ERA5 reanalysis data and rain gauge measurements, we provide a systematic analysis connecting wintertime North Atlantic storm track regimes and Eastern Mediterranean cyclones and rainfall. To do so, we use different detection algorithms for each element in the chain (RWBs, streamers and cyclones). A cluster analysis of upper tropospheric eddy kinetic energy reveals a favorable configuration of the storm track where North Atlantic storms are able to propagate farther northeast. This results in upper-level potential vorticity streamers forming more eastward alongside above-average precipitation over the Levant. Meanwhile, other latitudinal positions of the storm track (southward or northward) were found to hinder cyclonic activity in the region and reduce rainfall there. The intense rainy winter of 1991–1992 is brought as a test case to exemplify this mechanism in its extreme. We show that the rain-enhancing storm track regime was prominent throughout most of this season, alongside frequent streamers in the Eastern Mediterranean.
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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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RC1: 'Comment on egusphere-2024-1054', Emmanouil Flaounas, 19 Apr 2024
Review of the study entitled "The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity" by Sandler et al.
I have read the paper with great interest and I have appreciated the clarity of the methods. I found the results to be novel, they align with recent findings and contribute to the ongoing discussion on the role of large scale circulation in modulating Mediterranean weather and climate extremes in the Mediterranean. I certainly recommend the eventual publication with some revisions, mostly of minor nature.
If however I have a major concern, this relates to the presentation of the results. Actually, the text is rather dense and probably difficult to follow if someone is not well updated on the subject of this study. For reasons of better articulation, I would recommend smoother introductory phrases in each section of the results (or paragraphs) and a rather clear concluding remark. Some of the minor comments below point towards this direction.
- Introduction : There is a thorough presentation of the state of the art on the interactions between different large scale features and Mediterranean cyclones. Several of these interactions are described in detail, but most probably their understanding would be difficult if readers are less familiar with the Mediterranean region and the dynamics of the storm tracks. I would recommend to the authors to introduce a schematic on the main features of the mechanism that lead to Mediterranean cyclogenesis (perhaps somewhere at the end of the paragraph in line 43). One additional idea would be to be a bit more explicit on the objectives and motivations (last paragraph) and thus relocate some of the phrases/parts from the introduction to the main results in order to ease discussion of new findings with respect to previous studies. That would be of help to the reader to better place new results within the state of the art and take their time to process new findings.
- Data & Methods. This section is long and its technical nature makes it less attractive to the reader. Please consider inserting subsections. It also seems (except if I missed it) that Fig. 1c is not referenced in the text.
- Section 3.1/Fig. 3: How are densities and precipitation anomalies defined? Both colorbars seem to describe very small values.
- Section 3.2: Please reverse the two first phrases. In fact, NAO is mentioned once in the methods and thereafter it is mentioned here introducing a section with a very direct, albeit rather awkward way.
- Line 198: what is meant by "to increase the sample size"?
- Lines 200-201: Could you please provide a descriptive context about the connection of the western blocking high with the NAO positive phase? This will introduce the discussion on Fig. 5 in a smoother way and will articulate better the different parts of the paragraph.
- Line 208: The pressure low anomaly seems to persist before Lag 0 days (Figs 5b and 5d). Can you please comment on the cyclones occurrence respect to the green hatches. Is it possible that PV streamers and cyclone occurrences are not -always- sequential (in terms of time) to the max of MSLP in the black square in the black box of Fig. 5e. Actually, how would fig. 5 look if lag times are calculated respect to max of precipitation in the eastern Mediterranean?
- Relevant to the previous comment, is it possible that some of the cyclones in CL=5 dataset correspond to stationary lows in the southern side of Turkey/Cyprus? Therefore they might not really correspond to actual mesoscale cyclones?
- Probably a case study similar to Fig. 7 (or rearrangement of the last section) would be helpful here?
- Line 242: it's January 3rd 1992(?).
- Line 274: Probably it is better if you made reference to previous figures.
Citation: https://doi.org/10.5194/egusphere-2024-1054-RC1 -
RC2: 'Comment on egusphere-2024-1054', Anonymous Referee #2, 09 May 2024
Review of “The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity” by Sandler et al.
The paper puts winter climatological precipitation anomalies in the Middle East in the context of a dynamical chain of mechanisms that control the variability of cyclones in the Eastern Mediterranean. Namely, the large-scale variability of the Atlantic storm track, Rossby wave breaking downstream and the intrusion of PV streamers further downstream into the Mediterranean, eventually promoting cyclogenesis and precipitation in the E. Med. coast. The study confirms the relevance of this chain of events for the E. Mediterranean, a region that was overlooked in previous Mediterranean-wide studies that focused on the most intense cyclones. Further, the authors find an optimum configuration for the Atlantic storm track - extending northeastwards into the North Sea, for positive precipitation anomalies in Israel - a remarkable and clean result. I find the paper generally clear and well written and support its eventual publication in WCD after my concerns are addressed. I further suggest specific points to enhance clarity and help with the interpretation.
Specific comments:
- The NAO index is first mentioned in the methods section, without being introduced earlier in the introduction. Actually, lines 257-260 can better fit in the introduction as motivation, in my view.
- The number of cyclones considered (1058) seems too low for CL=5, it should be >3000, please clarify.
- Line 141: on which isentropic level are RWB identified?
- Line 145: The choice of considering only anticyclonic wave breaking needs a justification. Givon et al (2024) show the relevance of cyclonic breaking events for Mediterranean cyclones and precipitation. (Givon, Y., Hess, O., Flaounas, E., Catto, J. L., Sprenger, M., & Raveh-Rubin, S. (2024). Process-based classification of Mediterranean cyclones using potential vorticity. Weather and Climate Dynamics, 5(1), 133-162).
- Line 176-177: need to support this with reference(s).
- Reference to weather regimes (lines 178-182): The resemblance to known weather regimes is not as immediate as the authors state. For example, the N cluster is not a clear Atlantic Ridge but seems rather a combination of Atlantic Ridge and Greenland Blocking. The S cluster may be somewhat similar to a Scandinavian Trough (e.g., Fig. 1 in Hochman et al. 2021). (Hochman, A., Messori, G., Quinting, J. F., Pinto, J. G., & Grams, C. M. (2021). Do Atlantic‐European weather regimes physically exist?. Geophysical Research Letters, 48(20), e2021GL095574).
- Interpretation of EKE. I find the interpretation of EKE anomalies when projected on short time scales rather unintuitive. For better readability, I hope the readers can elaborate further on these by referring to the specific figure panels. For example, Line 186: Could you interpret the relation of the positive EKE anomalies to the overall high geopotential anomalies? Also, what is the meaning of the positive EKE in the southeastern Mediterranean in this dry regime? In Fig. 7a: it is unclear how is EKE related to the meandering jet/ tropopause shape. Please also elaborate where the statement in lines 248-249 can be seen in the figures.
- RWB diagnostic (Figs 1c, 4c, 7, Lines 192-195): The illustration in Fig. 1c indicates that the zonal extent of the identified RWB feature is the same as the PV streamer just to its south, as it essentially identified the tropospheric streamer. Having this in mind, it was unclear how ~30 degrees of longitude separate RWB from the PV streamers in Fig. 4, 5, 7 and the accompanying text. Also, in Fig. 7a: RWB is identified in the Bay of Biscay, but a RWB is not apparent in the plotted PV field. Please clarify this discrepancy and possibly add illustrative examples for the detection of RWB from the Mediterranean when the method is described.
- Fig. 3 caption: add units to the shaded variables and clarify the color of the hatches.
- Fig. 5 caption: add units to the shaded variables and clarify how the anomalies are defined.
- Fig. 6: add a colorbar for panels a,c.
- Composites in subsection 3.2: The choice of centralizing the composites on the high-SLP anomaly needs further motivation. Why not on the cyclones in the E. Med. or the resulting precipitation?
- Reference to Rossby wave packets: This concept is mentioned a few times throughout the text (e.g., line 213, 247, 282), but it is not directly shown and discussed in the text and figures. This notion should be then stated with caution, or elaborated further in the results.
Technical corrections:
- 1 caption: snapshop => snapshot; “5 and 3” => add “pvu”
- Line 63: a hundred => two hundred
- Line 87: replace dot by a comma
- Line 102: add “Yearly” before “accumulated”
- Line 115: delete “(described above)”
- Line 140: An => A
- Line 155: should “mm” be “%”?
- Line 207: purple => red
- Line 228: refer to Table 1 after “cyclones”.
- Line 256: the part of the sentence after “i.e.,” is unclear and seems incomplete.
Citation: https://doi.org/10.5194/egusphere-2024-1054-RC2 - AC1: 'Comment on egusphere-2024-1054', Dor Sandler, 15 Jun 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1054', Emmanouil Flaounas, 19 Apr 2024
Review of the study entitled "The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity" by Sandler et al.
I have read the paper with great interest and I have appreciated the clarity of the methods. I found the results to be novel, they align with recent findings and contribute to the ongoing discussion on the role of large scale circulation in modulating Mediterranean weather and climate extremes in the Mediterranean. I certainly recommend the eventual publication with some revisions, mostly of minor nature.
If however I have a major concern, this relates to the presentation of the results. Actually, the text is rather dense and probably difficult to follow if someone is not well updated on the subject of this study. For reasons of better articulation, I would recommend smoother introductory phrases in each section of the results (or paragraphs) and a rather clear concluding remark. Some of the minor comments below point towards this direction.
- Introduction : There is a thorough presentation of the state of the art on the interactions between different large scale features and Mediterranean cyclones. Several of these interactions are described in detail, but most probably their understanding would be difficult if readers are less familiar with the Mediterranean region and the dynamics of the storm tracks. I would recommend to the authors to introduce a schematic on the main features of the mechanism that lead to Mediterranean cyclogenesis (perhaps somewhere at the end of the paragraph in line 43). One additional idea would be to be a bit more explicit on the objectives and motivations (last paragraph) and thus relocate some of the phrases/parts from the introduction to the main results in order to ease discussion of new findings with respect to previous studies. That would be of help to the reader to better place new results within the state of the art and take their time to process new findings.
- Data & Methods. This section is long and its technical nature makes it less attractive to the reader. Please consider inserting subsections. It also seems (except if I missed it) that Fig. 1c is not referenced in the text.
- Section 3.1/Fig. 3: How are densities and precipitation anomalies defined? Both colorbars seem to describe very small values.
- Section 3.2: Please reverse the two first phrases. In fact, NAO is mentioned once in the methods and thereafter it is mentioned here introducing a section with a very direct, albeit rather awkward way.
- Line 198: what is meant by "to increase the sample size"?
- Lines 200-201: Could you please provide a descriptive context about the connection of the western blocking high with the NAO positive phase? This will introduce the discussion on Fig. 5 in a smoother way and will articulate better the different parts of the paragraph.
- Line 208: The pressure low anomaly seems to persist before Lag 0 days (Figs 5b and 5d). Can you please comment on the cyclones occurrence respect to the green hatches. Is it possible that PV streamers and cyclone occurrences are not -always- sequential (in terms of time) to the max of MSLP in the black square in the black box of Fig. 5e. Actually, how would fig. 5 look if lag times are calculated respect to max of precipitation in the eastern Mediterranean?
- Relevant to the previous comment, is it possible that some of the cyclones in CL=5 dataset correspond to stationary lows in the southern side of Turkey/Cyprus? Therefore they might not really correspond to actual mesoscale cyclones?
- Probably a case study similar to Fig. 7 (or rearrangement of the last section) would be helpful here?
- Line 242: it's January 3rd 1992(?).
- Line 274: Probably it is better if you made reference to previous figures.
Citation: https://doi.org/10.5194/egusphere-2024-1054-RC1 -
RC2: 'Comment on egusphere-2024-1054', Anonymous Referee #2, 09 May 2024
Review of “The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity” by Sandler et al.
The paper puts winter climatological precipitation anomalies in the Middle East in the context of a dynamical chain of mechanisms that control the variability of cyclones in the Eastern Mediterranean. Namely, the large-scale variability of the Atlantic storm track, Rossby wave breaking downstream and the intrusion of PV streamers further downstream into the Mediterranean, eventually promoting cyclogenesis and precipitation in the E. Med. coast. The study confirms the relevance of this chain of events for the E. Mediterranean, a region that was overlooked in previous Mediterranean-wide studies that focused on the most intense cyclones. Further, the authors find an optimum configuration for the Atlantic storm track - extending northeastwards into the North Sea, for positive precipitation anomalies in Israel - a remarkable and clean result. I find the paper generally clear and well written and support its eventual publication in WCD after my concerns are addressed. I further suggest specific points to enhance clarity and help with the interpretation.
Specific comments:
- The NAO index is first mentioned in the methods section, without being introduced earlier in the introduction. Actually, lines 257-260 can better fit in the introduction as motivation, in my view.
- The number of cyclones considered (1058) seems too low for CL=5, it should be >3000, please clarify.
- Line 141: on which isentropic level are RWB identified?
- Line 145: The choice of considering only anticyclonic wave breaking needs a justification. Givon et al (2024) show the relevance of cyclonic breaking events for Mediterranean cyclones and precipitation. (Givon, Y., Hess, O., Flaounas, E., Catto, J. L., Sprenger, M., & Raveh-Rubin, S. (2024). Process-based classification of Mediterranean cyclones using potential vorticity. Weather and Climate Dynamics, 5(1), 133-162).
- Line 176-177: need to support this with reference(s).
- Reference to weather regimes (lines 178-182): The resemblance to known weather regimes is not as immediate as the authors state. For example, the N cluster is not a clear Atlantic Ridge but seems rather a combination of Atlantic Ridge and Greenland Blocking. The S cluster may be somewhat similar to a Scandinavian Trough (e.g., Fig. 1 in Hochman et al. 2021). (Hochman, A., Messori, G., Quinting, J. F., Pinto, J. G., & Grams, C. M. (2021). Do Atlantic‐European weather regimes physically exist?. Geophysical Research Letters, 48(20), e2021GL095574).
- Interpretation of EKE. I find the interpretation of EKE anomalies when projected on short time scales rather unintuitive. For better readability, I hope the readers can elaborate further on these by referring to the specific figure panels. For example, Line 186: Could you interpret the relation of the positive EKE anomalies to the overall high geopotential anomalies? Also, what is the meaning of the positive EKE in the southeastern Mediterranean in this dry regime? In Fig. 7a: it is unclear how is EKE related to the meandering jet/ tropopause shape. Please also elaborate where the statement in lines 248-249 can be seen in the figures.
- RWB diagnostic (Figs 1c, 4c, 7, Lines 192-195): The illustration in Fig. 1c indicates that the zonal extent of the identified RWB feature is the same as the PV streamer just to its south, as it essentially identified the tropospheric streamer. Having this in mind, it was unclear how ~30 degrees of longitude separate RWB from the PV streamers in Fig. 4, 5, 7 and the accompanying text. Also, in Fig. 7a: RWB is identified in the Bay of Biscay, but a RWB is not apparent in the plotted PV field. Please clarify this discrepancy and possibly add illustrative examples for the detection of RWB from the Mediterranean when the method is described.
- Fig. 3 caption: add units to the shaded variables and clarify the color of the hatches.
- Fig. 5 caption: add units to the shaded variables and clarify how the anomalies are defined.
- Fig. 6: add a colorbar for panels a,c.
- Composites in subsection 3.2: The choice of centralizing the composites on the high-SLP anomaly needs further motivation. Why not on the cyclones in the E. Med. or the resulting precipitation?
- Reference to Rossby wave packets: This concept is mentioned a few times throughout the text (e.g., line 213, 247, 282), but it is not directly shown and discussed in the text and figures. This notion should be then stated with caution, or elaborated further in the results.
Technical corrections:
- 1 caption: snapshop => snapshot; “5 and 3” => add “pvu”
- Line 63: a hundred => two hundred
- Line 87: replace dot by a comma
- Line 102: add “Yearly” before “accumulated”
- Line 115: delete “(described above)”
- Line 140: An => A
- Line 155: should “mm” be “%”?
- Line 207: purple => red
- Line 228: refer to Table 1 after “cyclones”.
- Line 256: the part of the sentence after “i.e.,” is unclear and seems incomplete.
Citation: https://doi.org/10.5194/egusphere-2024-1054-RC2 - AC1: 'Comment on egusphere-2024-1054', Dor Sandler, 15 Jun 2024
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Hadas Saaroni
Baruch Ziv
Talia Tamarin-Brodsky
Nili Harnik
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6340 KB) - Metadata XML