Dynamical understandings of midlatitude transient eddy activity,
especially its midwinter minimum over the North Pacific, are still
limited, partly because Eulerian eddy statistics are incapable of
separating cyclonic and anticyclonic contributions. Here we evaluate the
two contributions separately based on local curvature of instantaneous
flow fields to compare their seasonality between the North Pacific and
North Atlantic storm-tracks. The anticyclonic contribution is found
crucial for the midwinter minimum of the North Pacific transient eddy
activity. Eddy energetics reveals that the net efficiency of the
anticyclonic contribution in replenishing total transient eddy energy
over the North Pacific exhibits a pronounced midwinter minimum, while
that of the cyclonic counterpart does not in harmony with precipitation
that peaks around midwinter. This study suggests that more attention
should be paid to anticyclones in studying midlatitude storm-track
dynamics.