Joint effects of the sea surface temperatures over North Atlantic and the tropical Indian Ocean on the interdecadal variation of warm-season precipitation in the Songhua river basin

Based on precipitation data at 100 stations over the Songhua River Basin (SRB), the reanalysis data of NCEP/NCAR and the Sea Surface Temperature (SST) from Hadley Center, the variation of SRB warm season (May—September) precipitation and its relationship with SST anomalies over the North Atlantic and the tropical Indian Ocean during 1975—2020 are investigated by statistical approaches and numerical experiments. The results show that the SRB warm season precipitation is characterized by interdecadal time scale variation with above-normal precipitation before the mid-1990s and below-normal precipitation after the mid-1990s. On the interdecadal time scale, the North Atlantic Horseshoe (NAH) mode and the Indian Ocean Basin (IOB) mode in warm season respectively have significant negative and positive relationships with simultaneous SRB precipitation, and the correlation coefficients are −0.77 and 0.68 respectively. Before the mid-1990s, the negative NAH mode can generate a wave train over Eurasia in the mid-high latitudes, which transports anomalous wave energy to Northeast Asia and causes an anomalous cyclone from the Sea of Japan to the Baikal. Meanwhile, the positive IOB mode can induce an anomalous anticyclone from the South China Sea to the Bay of Bengal by triggering Kelvin waves. As a result, the Pacific-Japanese pattern is triggered along the coast of East Asia, which induces an anomalous cyclone over the SRB. Due to the joint effects of negative NAH and positive IOB modes, the moisture from the North Pacific is transported to the SRB, increasing precipitation there. After the mid-1990s, the NAH and IOB modes change from negative and positive into positive and negative, respectively. Under the influence of positive NAH and negative IOB modes, the SRB is under the control of an anomalous anticyclone. As a result, precipitation in the SRB decreases.