Cyclonic and anticyclonic contributions to atmospheric energetics

Figure 3. Westerly wind acceleration by transient feedback forcing evaluated separately for cyclonic and 
anticyclonic vortices. a-b, Meridional sections of climatological-mean net westerly wind acceleration or 
deceleration as transient eddy feedback forcing (colors) by cyclonic vortices (a) and anticyclonic vortices (b) for 
midwinter (24Jan). Quantities shown are zonally averaged for the western North Pacific [150°E − 180°]. Black 
contours denote climatological-mean westerly wind speed (every 10 m/s, thick line for 0 m/s). Vectors indicate 
extended E-P flux20 associated with cyclonic and anticyclonic vortices. (c–d), Same as in a-b, respectively, but 
for the storm track over the midwinter North Atlantic [80° − 50°W]. (e–f), Same as in a-b, respectively, but for 
the storm track over the midsummer South Indian Ocean [75° − 105°E].

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Scientific Reports
| (2021) 11:13202 | 
https://doi.org/10.1038/s41598-021-92548-7
www.nature.com/scientificreports/
the distorted cyclonic vortices, which is most prominent in midwinter. The result is qualitatively similar when a 
non-zero curvature threshold is used (Supplementary Fig. S8).
Our method to identify cyclonic and anticyclonic vortices can be applied to storm tracks over other ocean 
basins as well. Figures 
3
c–d show westerly acceleration exerted by cyclonic and anticyclonic vortices, respec-
tively, over the North Atlantic (averaged over 80° − 50°W). In the lower troposphere, the westerly acceleration by 
cyclonic vortices is much stronger, while it is slightly weaker in the upper troposphere than that by anticyclonic 
vortices. Additionally, near-surface westerly deceleration by cyclonic vortices is striking along the southern 
fringe (at ~ 60°N) of the semi-permanent Icelandic Low, especially in midwinter. These characteristics are in 
common with the North Pacific storm track. Figures 
3
e–f show the corresponding westerly acceleration over 
the summertime South Indian Ocean (averaged over 75° − 105°E), where a distinct subpolar eddy-driven jet 
forms at ~ 45°S. This situation resembles that over the summertime North Pacific. Lower-tropospheric westerly 
acceleration by cyclonic vortices is much stronger than by anticyclonic vortices, while the contributions from 
cyclonic and anticyclonic vortices are comparable in the upper troposphere. These features are consistent with 
the two Northern Hemispheric oceanic storm tracks. Over the summertime South Indian Ocean, poleward 
westerly momentum flux in the upper troposphere from the subtropics into the midlatitude jet core is striking 
for both cyclonic and anticyclonic vortices.