Cyclonic and anticyclonic contributions to atmospheric energetics

Probability of cyclonic and anticyclonic vortices and their separate contributions to the Eule-
rian eddy statistics. 
Climatological-mean probability of cyclonic vortices (with local positive curvature) is 
shown in Fig. 
1
over the midwinter North Pacific. Since no threshold is set on local curvature to identify those 
cyclonic vortices, the local residual represents the corresponding probability of anticyclonic vortices. In the 
upper troposphere (Fig. 
1
a), cyclonic vortices are more likely to be observed to the north of the westerly jet axis, 
while anticyclonic vortices form more frequently to the south. A similar meridional contrast is observed across 
the lower-tropospheric eddy-driven westerly jet (Fig. 
1
b), but cyclonic vortices are often observed also around 
the jet axis. Contrastingly, the high probability of anticyclone vortices extending zonally around 20° − 25°N cor-
responds to the near-surface subtropical high-pressure belt. The lower-tropospheric statistics are overall consist-
ent with previous results from Lagrangian tracking
9
,
12
.
The new method allows us to evaluate contributions from cyclonic and anticyclonic vortices (or eddies) 
separately to the Eulerian statistics, by accumulating instantaneous contributions only at grid points where 
cyclonic or anticyclonic curvature is observed. As an example shown in Supplementary Fig. S3, curvature based 
on instantaneous unfiltered winds is used only for determining domains of cyclonic and anticyclonic vortices, and 
the separation of transient eddies from the background state has been achieved by the temporal filtering. Here, 
no threshold is set for cyclonic and anticyclonic curvature in order not to miss any circulation on the fringes of 
troughs and ridges. Figures 
2
a–b show the climatological-mean contributions from cyclonic and anticyclonic 
vortices, respectively, over the midwinter North Pacific to the variance of 300-hPa high-pass-filtered meridional 
wind fluctuations (V’V’300) as a measure of eddy activity. As in its total field, contributions to V’V’300 from the 
two polarities both maximize in the eastern North Pacific, although the anticyclonic contribution is slightly larger 
and its maximum is located slightly downstream of its cyclonic counterpart. Distribution of 300-hPa poleward 
flux of westerly momentum (U’V’300) by anticyclonic vortices is similar to but stronger than its cyclonic coun-
terpart (Figs. 
2
c–d). Both cyclonic and anticyclonic vortices yield the equatorward flux of momentum to the