陕西省 年极端秋雨成因分析OACSTPCD

Based on the monthly reanalysis data provided by NCEP at a resolution of 2.5°×2.5° and monthly SST data provided by NOAA,this study analyzed the causes of extreme autumn rain in Shaanxi province during autumn 2021 through the perspectives of SST,large-scale circulation,and water vapor transport.The analysis reveals a 2-4 year resonance period between the SST anomaly in the Niño3.4 region and autumn precipitation in Shaanxi province,with a positive correlation existing between the SST in early winter and the precipitation in the following autumn.In September to November 2021,the La Niña event with two peaks significantly expanded the range controlled by the subtropical high.The position of the subtropical high ridge was 1 degree north of the climatic state,and the westward ridge point was 23 degrees west of the climatic state,resulting in the main rain belt shifting to the west and north.The abnormal anticyclone from the middle and low northwest Pacific Ocean to the northern part of North China and the abnormal cyclone center on the northern side of the Bay of Bengal caused the abnormal convergence of the air flow in the eastern part of the northwest of China.In autumn 2021,the net water vapor inflow in Shaanxi was 66.7%higher than that in the climatic state,especially the abnormal water vapor transport at the eastern boundary in the middle and lower layers,which further enhanced the uplift of the cold cushion in the lower layers,resulting in more precipitation than usual in Shaanxi.