A synoptic view of the atmospheric circulation response to SST anomalies in the Kuroshio-Oyashio Extension Region: the importance of latent heating structure

The complex nature of extratropical air-sea coupling has hampered a detailed physical understanding of how the atmosphere responds to sea surface temperature (SST) anomalies over the Kuroshio-Oyashio Extension (KOE) region. Departing from the conventional approach of examining the seasonal-mean response, this study focuses on how atmospheric latent heating structures in early winter are modulated by synoptic weather patterns, and how those weather patterns selectively respond to KOE SST anomalies. The results are based on high-resolution atmospheric model experiments (1/8 degree over the North Pacific, tapering to 1 degree over the rest of the globe). While three dominant synoptic weather patterns that enhance latent heating over the KOE region are identified, only one of them, corresponding to anticyclonic baroclinic wave, systematically responds to the imposed SST anomalies. Warm SST anomalies induce stronger updrafts, which enhance atmospheric latent heating and ultimately strengthen and anchor the anomalous anticyclone over the North Pacific. Because this anticyclonic baroclinic system occurs more frequently than other types of weather patterns and has the greatest sensitivity to KOE SST anomalies, it dominates the seasonal-mean atmospheric response. The results demonstrate that a synoptic view is needed for an improved understanding of the mechanisms governing the seasonal-mean atmospheric circulation response to KOE SST forcing.