Analysis of intraseasonal oscillation characteristics of crop growing season precipitation in the Songhua River basin

Using high-resolution gridded daily precipitation data derived from observations at 2416 meteorological stations across China during 1961-2023,daily NCEP/NCAR reanalysis data and daily NOAA outgoing longwave radiation (OLR) data,this paper analyzes the 10-30-day intra seasonal oscillation (ISO) of precipitation of precipitation in the crop growing season (May-September) over the Songhua River Basin,and explores the mechanisms responsible for the basin-scale dominant precipitation mode and its active ISO events.The results show that at 200 hPa in the troposphere,a 10-30-day Eurasian teleconnection patttern (EU) of vorticity anomalies propagates eastward across mid-high latitudes from Western Europe to the Northwest Pacific,modulating anomalous atmospheric circulation over the Songhua River Basin.During the wet phase of intraseasonal precipitation anomalies in the basin,positive vorticity advection occurs over the Songhua River Basin together with upper-tropospheric divergence.The negative vorticity anomaly center above the basin is connected to that over the Tibetan Plateau,which stretches the bottom of the anomalous low-level cyclonic circulation over the basin southwestward to form a long and narrow shear zone.Warm and moist air originating from the Bay of Bengal,the South China Sea and tropical western Pacific are transported northward to the Songhua River Basin by southwesterly winds ahead of the shear line,thereby enhancing precipitation.In contrast,precipitation decreases when the two upper-level positive vorticity centers are linked.Therefore,the mid-high-latitude anomalous EU plays a crucial modulating role in the intraseasonal variability of precipitation over the Songhua River Basin throughout the crop growing season.