Distinct roles of cyclones and anticyclones in setting the midwinter minimum of the North Pacific eddy activity: a Lagrangian perspective

Abstract The North Pacific storm-track activity is suppressed substantially under the excessively strong westerlies to form a distinct minimum in midwinter, which seems inconsistent with linear baroclinic instability theory. This “midwinter minimum” of has been intensively investigated for decades as test case dynamics. However, mechanisms controlling it are yet be fully unveiled and still debate. Here we investigate detailed seasonal evolution climatological density surface migratory anticyclones over Pacific, comparison its counterpart cyclones, based on Lagrangian tracking algorithm. We demonstrate that frequency cyclones maximizes whereas exhibits midwinter upstream influence, especially from Japan Sea region. In only such rare occasion prominent weakening East Asian winter monsoon allows anticyclone Sea, despite unfavorable climatological-mean conditions due persistent monsoonal cold-air outbreaks upper-tropospheric westerlies. suggests likely key understanding measured by Eulerian eddy statistics.