Role of High-Frequency Transient Eddy Feedback Forcing in the Evolution of East Asia-Pacific Events

In this study, the dynamic features of East Asia-Pacific (EAP) events are investigated in terms of high-frequency transient eddy feedback forcing (TEFF) through the geopotential height tendency equation. One important finding is that the TEFF anomalies contribute greatly to the development and maintenance of the high-and mid-latitude centers of the EAP event during its evolution. In particular, in the mid-troposphere, the anomalous TEFF can account for approximately 50% of the amplification of the high-latitude center before the peak of EAP event, and then it counteracts the decay process to some extent. The feedback forcing anomalies could be decomposed into two components: one is associated with the divergence or convergence of the high-frequency transient eddy heat flux (TEFF_heat) and the other is associated with that of the vorticity flux (TEFF_vor). These two components usually reinforce each other in the lower troposphere but counteract each other in the upper troposphere. Thus, the total TEFF anomaly is less important in the upper troposphere than in the lower troposphere. It is evident that the TEFF_vor anomalies account for a predominant fraction of the total TEFF anomaly in positive EAP events; in contrast, in negative events, the contribution of the TEFF_heat anomalies increases to such an extent that they are at least comparable to the TEFF_vor anomalies. The increased importance of the TEFF_heat anomalies in the formation of negative EAP events might be related to the enhanced lower-tropospheric baroclinicity over the area east of Lake Baikal.