Transient behavior of the Asian Summer Monsoon Anticyclone associated with eastward eddy shedding

Amplification of the western Pacific anticyclone (WPA) is often linked with eastward eddy shedding from the AMA, although the processes are not well understood. This study investigates the dynamics driving eastward eddy shedding associated with the emergence of the WPA in the upper troposphere and lower stratosphere on synoptic scales.

Using reanalysis data during 1979–2019, our composite analysis reveals that amplified WPA events are tied to the upstream Silk Road (SR) wave-train pattern over midlatitude Eurasia as identified in previous studies. The quasi-stationary eastward propagating eddies result from baroclinic excitation along the westerly jet, as identified by coherent eddy heat fluxes and weakening of the low-level temperature gradient. The upper-level westerly jet is important in determining the longitudinal phase-locking of wave trains, which are anchored and amplify near the jet exit.