Synergistic Influence of Eurasian Soil Moisture and Pacific Sea Surface Temperature Anomalies on August Out-Of-Phase Precipitation Pattern in Northern China

Abstract

This study delves into the interannual variability of August precipitation in northern China, revealing that the leading mode exhibits a zonal out-of-phase pattern, with a dividing line around 100°E. The western region (WNC) serves as a positive precipitation anomaly center, contrasting with the eastern region (ENC) as a negative anomaly center. This precipitation disparity is largely due to contrasting dynamic and moisture conditions between these regions, influenced by a quasi-barotropic anomalous cyclonic circulation over Central Asia and anomalous anticyclonic circulation over Mongolia. Further analysis reveals that land and oceanic processes are pivotal in modulating this precipitation pattern. Specifically, soil moisture anomalies over Eurasia and sea surface temperature (SST) anomalies in the central and eastern Pacific are critical. In August, Eurasian soil moisture anomalies influence the local thermal processes, leading to eastward-propagating Rossby wave circulations. Simultaneously, SST anomalies in the central and eastern Pacific initiate an anomalous meridional Pacific-Japan (PJ) wave train. These circulation anomalies induce opposing conditions that promote precipitation in WNC and suppress it in ENC, thus establishing the observed out-of-phase precipitation pattern. In our study, Eurasian soil moisture and Pacific SST anomalies contribute approximately 44.9% and 21.2%, respectively, to the linear variance of precipitation pattern, collectively accounting for around 54.8% of the observed variation. Further investigation is required to gain a deeper understanding of this phenomenon.