Contradictory impacts of anomalous sea surface temperatures over the Sea of Japan in the Japan-Sea Polar-Airmass Convergence Zone

Abstract

The Sea of Japan (SOJ) has exhibited significant sea surface temperature (SST) warming in early winter, particularly in the East Korea Bay (EKB) and the subpolar oceanic front (SF). This study examined the thermodynamic impact of SST anomalies over the EKB and SF regions on the Japan-Sea polar-airmass convergence zone (JPCZ) using high-resolution numerical experiments. Results revealed that the local warm SOJ–SST anomalies played two contradictory roles in modulating the JPCZ. The anomalously warm EKB warmed the atmospheric boundary layer over the downstream region (JPCZ area) where the JPCZ prevailed, thereby decreasing sea level pressure (SLP) through hydrostatic equilibrium. The SLP decrease facilitated low-level wind convergence, intensifying the JPCZ. Enhanced moisture supplies from the sea surface due to strong winds also contributed to the JPCZ precipitation through the dominance of moisture flux convergence. In contrast, the extremely warm SF induced an anomalous surface low to the north of the JPCZ area through boundary-layer warming. Such thermodynamic changes strengthened low-level wind convergence over the SF, whereas they interrupted monsoonal winds that flowed into the JPCZ area, thereby inhibiting the JPCZ precipitation. These findings emphasize that monitoring of the local SOJ–SST warming is crucial for the accurate prediction of the JPCZ.