Cyclonic and anticyclonic contributions to atmospheric energetics

Figure 1. Probability of cyclonic and anticyclonic vortices. a–b, Climatological probability of cyclonic vortices 
(colors; with positive curvature) at 300-hPa (a) and 850-hPa (b) over the midwinter (24Jan) North Pacific. The 
probability of anticyclonic vortices can be obtained as the local residual. Black contours indicate climatological-
mean U300 (a) and U850 (b) (m/s).

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Scientific Reports
| (2021) 11:13202 | 
https://doi.org/10.1038/s41598-021-92548-7
www.nature.com/scientificreports/
north of ~ 40°N and the poleward flux to its south. These converging fluxes thus act to accelerate the westerlies 
to the north and downstream of the prominent jet core around [32°N, 150°E]. The momentum flux diverges 
northward out of the jet core region, characteristic of a thermally driven subtropical jet
22
,
23
. Lower-tropospheric 
poleward eddy heat flux (V’T’850) by cyclonic vortices (Fig. 
2
e) is more than twice as strong as its anticyclonic 
counterpart (Fig. 
2
f), indicative of the prominent contribution from baroclinic cyclonic vortices to heat transport.
The threshold curvature for detecting cyclonic or anticyclonic vortices is not necessarily zero as in Fig. 
2
. 
For comparison, the corresponding climatological-mean probability of cyclonic and anticyclonic vortices is 
shown in Supplementary Fig. S4, with the threshold curvature equivalent to the radius of curvature of 2500 km. 
As expected, the probability decreases substantially for the two polarities, but the spatial distribution overall 
resembles that with the zero threshold. Unlike the case with the zero threshold, however, the probability of 
anticyclonic vortices is not necessarily a mirror image of its cyclonic counterpart. Along the upper-tropospheric 
westerly jet, for example, the probability for both cyclonic and anticyclonic vortices is very low. This is probably 
because the prominent westerly jet, especially in its core region, is likely to flow steadily and barely meanders 
to form vortices with small radii. Contributions to the Eulerian statistics are qualitatively similar to those with 
zero curvature threshold, but with more striking distinctions between cyclonic and anticyclonic V’T’850 (Sup-
plementary Fig. S5), highlighting the dominant poleward heat flux concentrated around cyclone centers, as 
inferred from a typical structure of extratropical cyclones
24
.
The aforementioned characteristics of the contribution from anticyclonic vortices to the Eulerian statistics 
revealed with curvature, including comparable or even slightly stronger V’V’300, greater U’V’300, and weaker