A possible remote tropical forcing for the interannual variability of peak summer muggy hot days in Northeast China

Abstract

The peak summer (July–August; JA) muggy hot weather over Northeast China (NEC) negatively impacts local socioeconomic development and human health. This study investigates the physical connection between sea surface temperature (SST) and year-to-year variations in the number of peak summer muggy hot days (MHDs) in NEC (PSMHDNEC) for the period 1979–2018. We found that on the interannual timescale, SST anomalies (SSTAs) over the tropical North Australia (TNA) sector have a stable and significant negative correlation with PSMHDNEC since the early summer of June; however, the strongest negative correlation occurs in the JA. Our further analyses indicate that the SST cooling over the TNA sector could form a large-scale atmospheric teleconnection emanating northwest of the TNA through the profound in situ diabatic cooling anomalies tied to the SST cooling, which propagates poleward from the northeastern Pacific Ocean. This teleconnection might remotely strengthen the local-scale anticyclonic anomaly centered near NEC, a critical system responsible for a higher PSMHDNEC. Under such circumstances, the NEC region is dominated by high-pressure anomalies, facilitating the establishment of localized MHD-favorable environmental conditions (e.g., increased surface air temperature and enhanced downward solar radiation flux with suppressed convection activities). During years of negative SSTAs over TNA, local SSTAs can persist from early summer until JA via the wind–evaporation–SST feedback. Therefore, it appears that SSTAs over the TNA sector may be a significant remote tropical forcing factor for the interannual variability of PSMHDNEC, and the corresponding June SST cooling may act as a potential predictability source physically contributing to a higher PSMHDNEC.