Physical Mechanisms Of Interannual And Interdecadal Variability Of Spring Precipitation In Northeast China

This study uses the monthly precipitation data provided by the China Meteorological Administration,using EOF,correlation analysis,wave activity flux,and other statistical analysis methods,combined with numerical model simulation,to analyze the leading mode of spring precipitation over Northeast China(NECSR).The underlying mechanisms of its interannual and interdecadal variability are estimated.Some conclusions were concluded as below:(1)The large value regions of climatic spring precipitation over Northeast China(NEC)are mainly located in the southeast of NEC,and the precipitation gradually decreases to the northwest.The minimum regions are located in the east of Inner Mongolia,the southwest of Heilongjiang,and the west of Jilin.The spatial distribution of spring precipitation standard deviation is similar to the spatial distribution of climatic precipitation.The southeastern part of NEC has a large precipitation variability,and the precipitation variability gradually decreases toward the northwest.The variance contribution of the leading mode of spring precipitation in NEC is close to 50%,and the spatial distribution of EOF1 shows a homogeneous structure throughout the region.The area with large load vectors is located in the middle and east of NEC.The corresponding time coefficient has obvious interannual and interdecadal variability.(2)The interannual variability of the leading mode of spring precipitation over NEC is mainly affected by the sea surface temperature anomaly(SSTA)over the north tropical Atlantic.When a positive SSTA occurs over north tropical Atlantic,a positive precipitation anomaly appears over it.The precipitation heats the atmosphere by releasing latent heat of condensation,and in the mid-to high-latitudes over northern hemisphere,two quasi-barotropic teleconnection wave trains are stimulated in the north and south branch.The two wave trains converge over NEC,producing a cyclonic circulation anomaly,leading to anomalies of positive precipitation in NEC.And the simulation results of the numerical model also reproduce the above-mentioned physical process,verifying the above conclusion from the perspective of dynamics.(3)The interdecadal variability of the leading mode of spring precipitation in NEC is mainly affected by SSTA in warm pool areas.When a positive SST anomaly occurs in this area,the lower-level over the warm pool will converge and the upper-level will diverge,resulting in an upward movement and an abnormally more precipitation.At the same time,the low-level divergence and the high-level convergence over equatorial central Pacific caused a downward movement,resulting in an abnormally low rainfall.This circulation structure forms a zonal closed circulation near the equator,and the precipitation anomaly field shows an east-west dipole distribution.The anomalous dipole precipitation releases the latent heat of condensation and generating an anomalous heat source in the atmosphere.Then the anomalous heat source stimulates two anomalous circulation systems over the East Asia.The NEC is affected by the anomalous cyclonic circulation,resulting in abnormally more precipitation.In addition,the simulation results of numerical model show that the anomaly of positive precipitation over Maritime Continent plays a more important role in the process of regulating its interdecadal variability rather than the anomalous less rainfall over central tropical Pacific.(4)The correlation between the interannual variability of the leading mode of spring precipitation over NEC and the SSTA over the north tropical Atlantic has undergone an interdecadal change around 1985.Before 1985,there was a significant correlation between the spring precipitation over NEC and the SSTA over the subtropical north Atlantic.This SST anomaly can trigger a Silk Road-like wave train over north hemisphere to produce a cyclonic anomaly over the southern of NEC.The southerly wind on the east side transports water vapor to NEC,causing more precipitation.After 1985,the critical area of SSTA related to spring precipitation over NEC moved to the tropical north Atlantic.This SST anomaly triggered teleconnection wave trains in the mid-to high-latitudes over the northern hemisphere,generating cyclonic anomalies in NEC and leading to more rainfall.