SST variability in the East Asian marginal sea: mechanisms for local and remote atmospheric impacts

Abstract:

The Japan/East Sea (JES), a part of East Asian Marginal Seas, is a semi-enclosed sea located upstream of the North Pacific storm track. SST variability in the JES and the ensuing air-sea process are important for local winter atmospheric condition. It is believed that the marginal sea processes also influence the storm track evolution far downstream. Dynamical processes leading to local and remote atmospheric circulation response to leading JES SST anomaly patterns are investigated using a hemispheric WRF atmospheric model with two-way multi-nesting capabilities. The atmospheric circulation in direct contact with anomalous diabatic forcing exhibits a linear baroclinic response with respect to sign of SST anomalies; that is, the northwesterly surface wind is strengthened (weakened) and the local precipitin is enhanced (reduced) over the warm (cold) SSTs. The linearity of the local response confirms the importance of fine-scale SST patterns to the predictability of regional weather and climate conditions. The downstream response, in contrast, is nonlinear, with an enhanced intraseasonal equivalent barotropic ridge emerging in the Gulf of Alaska irrespective of the polarity of JES SST anomalies. This downstream blocking high response is maintained by the positive low-frequency height tendency due to transient eddy vorticity flux convergence associated with altered storm track. The significant remote response in the North Pacific storm track and the blocking suggests that the marginal sea process is an active part of the North Pacific climate variability.