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https://doi.org/10.5194/egusphere-2024-2112
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the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2024-2112
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
16 Jul 2024
| 16 Jul 2024
Synoptic perspective on the conversion and maintenance of local available potential energy in extratropical cyclones
Abstract. Extratropical cyclones are the predominant weather system in the midlatitudes. They intensify through baroclinic instability, a process in which available potential energy (APE) is converted into kinetic energy (KE). While the planetary-scale conversion of APE to KE is well understood as a mechanism for maintaining the general atmospheric circulation against dissipation, the synoptic-scale perspective on this conversion is less explored. In this study, we analyze the three-dimensional distribution of APE and the physical processes that consume APE for an illustrative case study and a climatology of 285 intense North Atlantic extratropical cyclones in the winters 1979–2021 using the ERA5 reanalysis. We utilize a recently introduced local APE framework that allows APE to be quantified at the level of individual air parcels. The geographical APE distribution is shown to be controlled by the large-scale upper-level circulation. Cyclones draw energy from the upper-tropospheric polar APE reservoir along with the development of the associated upper-level trough. This upper-level APE is converted into KE by air descending along the trough's western flank and acts as the incipient cyclone's primary source of KE. Conversely, KE is converted back into APE during the ascent ahead of the trough, reflecting the deceleration of air parcels as they exit the cyclone region. The diabatic dissipation of APE due to surface sensible heat fluxes along the Gulf Stream front is small compared to the adiabatic conversion of APE to KE, since most of the APE is concentrated and consumed in the middle to upper troposphere and cannot be exposed to surface diabatic forcing. In conclusion, by employing a local APE framework, this study provides a detailed investigation of the synoptic dynamics linking extratropical cyclones and planetary-scale energetics.
How to cite. Federer, M., Papritz, L., Sprenger, M., and Grams, C. M.: Synoptic perspective on the conversion and maintenance of local available potential energy in extratropical cyclones, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-2112, 2024.
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 preprint. The responsibility to include appropriate place names lies with the authors.
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CC1: 'Comment on egusphere-2024-2112', Kevin Bowley, 15 Aug 2024
Publisher’s note: this comment is a copy of RC1 and its content was therefore removed on 16 August 2024.
Citation: https://doi.org/10.5194/egusphere-2024-2112-CC1 -
RC1: 'Comment on egusphere-2024-2112', Kevin A. Bowley, 16 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2112/egusphere-2024-2112-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2024-2112', Lance F. Bosart, 25 Aug 2024
A) Overview: Federer et al. (2024): Synoptic Perspective on the Conversion and Maintenance of Local Available Potential Energy in Extratropical CyclonesThe authors are to be commended for preparing a well-evidenced story and well-written story on the often challenging concept of atmospheric energetics in general and available potential energy in particular. I learned something from reading this paper.B) Specific comments on Federer et al. (2024): Synoptic Perspective on the Conversion and Maintenance of Local Available Potential Energy in Extratropical Cyclones
1. Line 104: Why is omega only computed at 500-hPa. Wouldn’t a lower level (e.g., 850-hPa or 700-hPabe be better for sampling and quantifying thermal advection?
2. Line 112: Is it possible that your criterion for identifying CAOs could be sensitive to your choice of the 850-hPa level for air-sea temperature differences? Could shallow cold air be a problem in some situations?
3. Line 134: ….given by the product of omega and the buoyancy……
4. General question: What is the vertical resolution of your dataset? How well are you resolving shallow Arctic air outbreaks over continents and oceans?
5. Lines 142-148: I had trouble visualizing this somewhat convoluted text. Suggestion: Inserting a schematic diagram here that depicts the calculation of the reference state would be most helpful to the reader.
6. Lines 150–151: Curious to learn why you chose not to compute reference states for DJF, MAM, JJA, and SON?
7. Figure 1: Could, say, 700-hPa vertical motion be added to the six figure panels so that the locations of major ascent and descent regions relative to trough and ridge positions can be better pictured?
8. Figure 1: Labels 1a, 1b, 2c, etc. need to be defined in the figure captions. Label latitude and longitude lines.
9. Figure 1f: There appears to be a remnant cyclone near Iceland in panel 1f that is a remnant of cyclone 1b in panel 1e.
10. Figure 1: There appear to be three cold surges based on equatorward-directed trough extensions in Fig. 1. Significance? How do the three cold surges.
11. Figure 1: Cyclone 2a, and especially cyclone 3b, are not directly associated with an upper-level trough in their formative stages. Significance?
12. Lines 185-187: Please be more specific about where the APE decline is occurring.
13. Figure 2 caption: Please indicate directions at either ends of the cross-section lines (e.g., west or east, etc.) for reference purposes.
14. Lines 202-203: This sentence needs further elaboration since Fig. 2c is devoid of vertical motion.
15. Figure 3: Geography is hard to distinguish from the color shading and black contours.
16. Figure 3: SLP contours are very difficult to follow because they are so faint in Fig. 3 (and in Fig. 1)
17. More on Fig. 3. So, is it fair to say that APE generation equatorward of the jet axis acts to increase APE in lower latitudes (with a minor offset by diabatic processes in the vicinity of midlatitude cyclones)? If so, what can we conclude about these APE changes from a general circulation perspective?).
18. Line 247: Check whether AOE has been defined previously.
19. Figure 4: SLP contours are too faint to be see properly, especially in the vicinity of the trajectory swaths.
20. Figure 4b: How sensitive do you think the split between subsiding and ascending trajectories shown in Fig. 4b would be to the starting time and location of the trajectory computations? Presumably, the expected trajectory differences could be linked to the governing dynamics?
21. Lines 264–272: So, presumably the extent and magnitude of latent heat release in ascending trajectories would be very sensitive to the air mass in which the trajectories originate. For example, Mediterranean and Gulf of Mexico cyclones that have access to tropical and subtropical air masses would exhibit different APE changes in conjunction with ascending trajectory swarms than the higher-latitude example referenced in this paper? How should we interpret such differences?
22. Figure 5 (and accompanying text). Have you checked whether a mesoscale trailing trough behind the main trough could be altering the larger-scale QG ascent-descent dipoles? Would it be helpful to add the position of the surface cyclone to Figs. 5a,b to assist the reader in better understanding the relationship between the trajectory evolution and the surface cyclone location?
23. Lines 288-292: While I think that your conclusions mentioned here are correct to first order, it might be a good idea to allow for considerable variability the would likely be seen in a much larger sample of cases (e.g., a secondary trough deepening downstream into a pre-existing trough vs. a weakening trough that was lifting out to the northeast (among other possible trough-ridge scenarios).
24. Lines 294-311: Very interesting perspective on APE conversion that is well supported by the trajectories shown in Fig. 6 and the APE tendency plots shown in Fig. 7. An obvious question….that really cannot be addressed here….is how general this result would would be across a variety of cyclone evolutions at different times of the year and the choice of where and when to initiate the trajectories.25. Fig. 7: Would it be helpful to rescale the y-axes in Fig. 7 so as to make it more obvious how much smaller the diabatic APE tendency is compared to the adiabatic APE tendency?26. Line 316 (first bullet): How might this finding change (or not change) if you looked at Arctic PV extrusions across all longitudes as a function of season?27. Line 320 (second bullet): While I agree with this conclusion, to play the contrarian a bit and reference “Animal Farm” meteorology…..while all cyclones may be equal, some cyclones may be more equal than other cyclones. How do we find these “more equal” cyclones and how can we understand why there are "more equal cyclones” with regard to where they form, how they evolve, and how they contribute to APE generation? For example, 1) How “unequal” are continental cyclones from oceanic cyclones?, and 2) Are APE changes sensitive to whether cyclones are moving mostly poleward (e.g., cyclones along the east coasts of Asia and North America) or moving mostly equatorward (e.g., lee cyclones east of major north-south mountain barriers? Just curious……28. Line 325: Same question as previously with regard to how general your conclusions are.29: Lines 316-327: What about cyclone families? Lots of cyclones are a part of cyclone families. With respect to cyclone-related APE changes, might there be any relationship between cyclone family duration and overall APE changes?30. Figure 9: This figure, comprised of 12 panels, is very difficult to read and assimilate. It is also insufficiently labeled (e.g., orange contours on panels e-h). Might four, four-panel figures work better….and not overwhelm readers? Failing that, perhaps include an option to choose magnifying glasses with the journal when reading this article?31. Text supporting Fig. 9 is a big help in sorting through the overly small figures. For example, the conclusions mentioned on lines 355-358 are well supported by the individual panels in Fig. 9. Likewise, for panels (e-h) and (i-l).32. Do the very small differences between panels 9n and 9o reflect a smaller time difference and/or the rotation of the precipitation shield around the composite cyclone?33. How sensitive are the results shown in Fig. 10 to the domain size over which the calculations were made?34. There is little if any downward extrusion of PV in figure panel 11a. Is this an artifact of the cross section location choice and/or does it reflect that at the time the cyclone maximum intensification that the PV is mostly “used up” (so to speak)?35. There needs to be addition al labeling of the lines in Fig. 11 (e.g., panels e and f are devoid of contour labels). Additional labels would make it easier for a reader to follow the text better on lines 425-431.36. There is a factor 4 difference in the vertical scale for Figs. 12c and 12d. Consider using the same vertical scale for these two figure panels to facilitate a better understanding of the difference in the adiabatic and diabatic APE tendencies?37. Discussion surrounding Fig. 12 is excellent.38. Nice synthesis in section 5.1. Would be to comment how the results from a sample of 285 intense NATL cyclones might differ from a much larger overall sample of cyclones?39. Lines 479-485: I fully agree with this interpretation from a synoptic-dynamic/weather map perspective.40. Lines 485-495: How might your results differ if you distinguished between cyclogenesis associated positively tilted versus negatively tilted troughs? Typically, positively (negatively) tilted troughs are associated with the strongest jet in the southwesterly (northwesterly) flow downstream (upstream) of a titled trough axis.41. Lines 505-513: I am still pondering this conclusion because there is so much variability between individual cyclones. Might comparing cyclones in NW versus SW flow possibly be helpful?42. Lines 520-522: Good point. I had never thought this concept though previously in the depth needed to better appreciate the differences.43. Lines 533-541: Interesting point. Would it be helpful to distingush between high versus low dynamical tropopause storms?44. Lines 542-546: It might be helpful to distinguish between early season cyclones(when the troposphere is still relatively warm and the dynamic tropopause is still relatively high), from midseason cyclones (when the baroclincity is strongest), and late season cyclones (when warm sector CAPE is becoming a factor in cyclone development and intensification.Lance BosartDistinguished Professor EmeritusDepartment of Atmospheric and Environmental Sciences DAES-Room 435Harriman Campus - ETEC Building1220 Washington AvenueAlbany, NY 12222Citation: https://doi.org/10.5194/egusphere-2024-2112-RC2 -
AC1: 'Final author comments on egusphere-2024-2112', Marc Federer, 02 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2112/egusphere-2024-2112-AC1-supplement.pdf
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
CC1: 'Comment on egusphere-2024-2112', Kevin Bowley, 15 Aug 2024
Publisher’s note: this comment is a copy of RC1 and its content was therefore removed on 16 August 2024.
Citation: https://doi.org/10.5194/egusphere-2024-2112-CC1 -
RC1: 'Comment on egusphere-2024-2112', Kevin A. Bowley, 16 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2112/egusphere-2024-2112-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2024-2112', Lance F. Bosart, 25 Aug 2024
A) Overview: Federer et al. (2024): Synoptic Perspective on the Conversion and Maintenance of Local Available Potential Energy in Extratropical CyclonesThe authors are to be commended for preparing a well-evidenced story and well-written story on the often challenging concept of atmospheric energetics in general and available potential energy in particular. I learned something from reading this paper.B) Specific comments on Federer et al. (2024): Synoptic Perspective on the Conversion and Maintenance of Local Available Potential Energy in Extratropical Cyclones
1. Line 104: Why is omega only computed at 500-hPa. Wouldn’t a lower level (e.g., 850-hPa or 700-hPabe be better for sampling and quantifying thermal advection?
2. Line 112: Is it possible that your criterion for identifying CAOs could be sensitive to your choice of the 850-hPa level for air-sea temperature differences? Could shallow cold air be a problem in some situations?
3. Line 134: ….given by the product of omega and the buoyancy……
4. General question: What is the vertical resolution of your dataset? How well are you resolving shallow Arctic air outbreaks over continents and oceans?
5. Lines 142-148: I had trouble visualizing this somewhat convoluted text. Suggestion: Inserting a schematic diagram here that depicts the calculation of the reference state would be most helpful to the reader.
6. Lines 150–151: Curious to learn why you chose not to compute reference states for DJF, MAM, JJA, and SON?
7. Figure 1: Could, say, 700-hPa vertical motion be added to the six figure panels so that the locations of major ascent and descent regions relative to trough and ridge positions can be better pictured?
8. Figure 1: Labels 1a, 1b, 2c, etc. need to be defined in the figure captions. Label latitude and longitude lines.
9. Figure 1f: There appears to be a remnant cyclone near Iceland in panel 1f that is a remnant of cyclone 1b in panel 1e.
10. Figure 1: There appear to be three cold surges based on equatorward-directed trough extensions in Fig. 1. Significance? How do the three cold surges.
11. Figure 1: Cyclone 2a, and especially cyclone 3b, are not directly associated with an upper-level trough in their formative stages. Significance?
12. Lines 185-187: Please be more specific about where the APE decline is occurring.
13. Figure 2 caption: Please indicate directions at either ends of the cross-section lines (e.g., west or east, etc.) for reference purposes.
14. Lines 202-203: This sentence needs further elaboration since Fig. 2c is devoid of vertical motion.
15. Figure 3: Geography is hard to distinguish from the color shading and black contours.
16. Figure 3: SLP contours are very difficult to follow because they are so faint in Fig. 3 (and in Fig. 1)
17. More on Fig. 3. So, is it fair to say that APE generation equatorward of the jet axis acts to increase APE in lower latitudes (with a minor offset by diabatic processes in the vicinity of midlatitude cyclones)? If so, what can we conclude about these APE changes from a general circulation perspective?).
18. Line 247: Check whether AOE has been defined previously.
19. Figure 4: SLP contours are too faint to be see properly, especially in the vicinity of the trajectory swaths.
20. Figure 4b: How sensitive do you think the split between subsiding and ascending trajectories shown in Fig. 4b would be to the starting time and location of the trajectory computations? Presumably, the expected trajectory differences could be linked to the governing dynamics?
21. Lines 264–272: So, presumably the extent and magnitude of latent heat release in ascending trajectories would be very sensitive to the air mass in which the trajectories originate. For example, Mediterranean and Gulf of Mexico cyclones that have access to tropical and subtropical air masses would exhibit different APE changes in conjunction with ascending trajectory swarms than the higher-latitude example referenced in this paper? How should we interpret such differences?
22. Figure 5 (and accompanying text). Have you checked whether a mesoscale trailing trough behind the main trough could be altering the larger-scale QG ascent-descent dipoles? Would it be helpful to add the position of the surface cyclone to Figs. 5a,b to assist the reader in better understanding the relationship between the trajectory evolution and the surface cyclone location?
23. Lines 288-292: While I think that your conclusions mentioned here are correct to first order, it might be a good idea to allow for considerable variability the would likely be seen in a much larger sample of cases (e.g., a secondary trough deepening downstream into a pre-existing trough vs. a weakening trough that was lifting out to the northeast (among other possible trough-ridge scenarios).
24. Lines 294-311: Very interesting perspective on APE conversion that is well supported by the trajectories shown in Fig. 6 and the APE tendency plots shown in Fig. 7. An obvious question….that really cannot be addressed here….is how general this result would would be across a variety of cyclone evolutions at different times of the year and the choice of where and when to initiate the trajectories.25. Fig. 7: Would it be helpful to rescale the y-axes in Fig. 7 so as to make it more obvious how much smaller the diabatic APE tendency is compared to the adiabatic APE tendency?26. Line 316 (first bullet): How might this finding change (or not change) if you looked at Arctic PV extrusions across all longitudes as a function of season?27. Line 320 (second bullet): While I agree with this conclusion, to play the contrarian a bit and reference “Animal Farm” meteorology…..while all cyclones may be equal, some cyclones may be more equal than other cyclones. How do we find these “more equal” cyclones and how can we understand why there are "more equal cyclones” with regard to where they form, how they evolve, and how they contribute to APE generation? For example, 1) How “unequal” are continental cyclones from oceanic cyclones?, and 2) Are APE changes sensitive to whether cyclones are moving mostly poleward (e.g., cyclones along the east coasts of Asia and North America) or moving mostly equatorward (e.g., lee cyclones east of major north-south mountain barriers? Just curious……28. Line 325: Same question as previously with regard to how general your conclusions are.29: Lines 316-327: What about cyclone families? Lots of cyclones are a part of cyclone families. With respect to cyclone-related APE changes, might there be any relationship between cyclone family duration and overall APE changes?30. Figure 9: This figure, comprised of 12 panels, is very difficult to read and assimilate. It is also insufficiently labeled (e.g., orange contours on panels e-h). Might four, four-panel figures work better….and not overwhelm readers? Failing that, perhaps include an option to choose magnifying glasses with the journal when reading this article?31. Text supporting Fig. 9 is a big help in sorting through the overly small figures. For example, the conclusions mentioned on lines 355-358 are well supported by the individual panels in Fig. 9. Likewise, for panels (e-h) and (i-l).32. Do the very small differences between panels 9n and 9o reflect a smaller time difference and/or the rotation of the precipitation shield around the composite cyclone?33. How sensitive are the results shown in Fig. 10 to the domain size over which the calculations were made?34. There is little if any downward extrusion of PV in figure panel 11a. Is this an artifact of the cross section location choice and/or does it reflect that at the time the cyclone maximum intensification that the PV is mostly “used up” (so to speak)?35. There needs to be addition al labeling of the lines in Fig. 11 (e.g., panels e and f are devoid of contour labels). Additional labels would make it easier for a reader to follow the text better on lines 425-431.36. There is a factor 4 difference in the vertical scale for Figs. 12c and 12d. Consider using the same vertical scale for these two figure panels to facilitate a better understanding of the difference in the adiabatic and diabatic APE tendencies?37. Discussion surrounding Fig. 12 is excellent.38. Nice synthesis in section 5.1. Would be to comment how the results from a sample of 285 intense NATL cyclones might differ from a much larger overall sample of cyclones?39. Lines 479-485: I fully agree with this interpretation from a synoptic-dynamic/weather map perspective.40. Lines 485-495: How might your results differ if you distinguished between cyclogenesis associated positively tilted versus negatively tilted troughs? Typically, positively (negatively) tilted troughs are associated with the strongest jet in the southwesterly (northwesterly) flow downstream (upstream) of a titled trough axis.41. Lines 505-513: I am still pondering this conclusion because there is so much variability between individual cyclones. Might comparing cyclones in NW versus SW flow possibly be helpful?42. Lines 520-522: Good point. I had never thought this concept though previously in the depth needed to better appreciate the differences.43. Lines 533-541: Interesting point. Would it be helpful to distingush between high versus low dynamical tropopause storms?44. Lines 542-546: It might be helpful to distinguish between early season cyclones(when the troposphere is still relatively warm and the dynamic tropopause is still relatively high), from midseason cyclones (when the baroclincity is strongest), and late season cyclones (when warm sector CAPE is becoming a factor in cyclone development and intensification.Lance BosartDistinguished Professor EmeritusDepartment of Atmospheric and Environmental Sciences DAES-Room 435Harriman Campus - ETEC Building1220 Washington AvenueAlbany, NY 12222Citation: https://doi.org/10.5194/egusphere-2024-2112-RC2 -
AC1: 'Final author comments on egusphere-2024-2112', Marc Federer, 02 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2112/egusphere-2024-2112-AC1-supplement.pdf
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Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
Lukas Papritz
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
European Centre for Medium-Range Weather Forecasts (ECMWF), Bonn, Germany
Michael Sprenger
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
Christian M. Grams
Institute of Meteorology and Climate Research Troposphere Research (IMKTRO), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
now at: Federal Office of Meteorology and Climatology, MeteoSwiss, Zurich Airport, Switzerland
This study provides a novel Lagrangian perspective on cyclogenesis grounded in atmospheric energetics. While the energetics framework is commonly used to understand the planetary scale circulation, its application to synoptic scales is less explored. The authors establish a close connection between extratropical baroclinic zones and local available potential energy, and further analyze air parcel trajectories to link conversions between potential and kinetic energy to specific features of the developing cyclones. The results of this study offer insights into the local, synoptic and large scale contributions to cyclogenesis that are relevant for diverse disciplines in atmospheric and climate sciences.
This study provides a novel Lagrangian perspective on cyclogenesis grounded in atmospheric...
Short summary
Although extratropical cyclones in the North Atlantic are among the most impactful midlatitude weather systems, the potential for their growth on synoptic scales is not well understood. Here we show how they convert potential into kinetic energy through the descent of cold upper-tropospheric air from high latitudes. Surface processes, such as ocean heat exchange, have a smaller effect. Understanding these dynamics helps to explain the processes that maintain storm tracks.
Although extratropical cyclones in the North Atlantic are among the most impactful midlatitude...