陕西汛雨开始日期异常的气候特征及其影响系统

利用陕西省1961—2018年逐日降水资料、NCEP/NCAR再分析资料及NOAA海温资料，基于合成分析、相关分析等方法，研究了陕西汛雨开始早晚的气候特征及其影响系统。结果表明:陕西入汛日具有显著的年际和年代际变化特征，20世纪60年代主要以偏晚为主，70、80年代以偏早为主，90年代偏晚，进入21世纪以后以偏早为主，雨季主要集中在7月上旬至中旬中期。入汛偏早年，东亚副热带西风急流于6月下旬北跳，强度偏强，北跳偏早，欧亚中高纬为两槽一脊，副高偏强、偏西、偏北；低层，孟加拉湾至中国南海为巨大的气旋式距平环流，西北太平洋为显著的反气旋距平环流。入汛偏晚年，环流系统与偏早年相反。入汛早晚与冬春季海表温度相关，当冬季印度洋、春季热带北大西洋海温偏高，有利于入汛。

Climate Change Characteristics and Influential Systems of Abnormal Onset Date of the First Rainy Season in Shaanxi Province

Based on atmospheric data of NCEP/NCAR re-analysis,NOAA Sea Surface Temperature(SST)data,and the daily precipitation from 1961-2018 in Shaanxi Province,the climatic characteristics of the First Rainy Season's onset date of Shaanxi(FRSOD_SX)and influential systems areanalyzed with synthetic analysis and regression analysis.The results show that FRSOD_SX has significant interannual variability.The FRSOD_SX is later in the 1960s and earlier from the 1970s to the 1980s.While the FRSOD_SX is later in the 1990s and earlier after entering the 21st century.The rainy season is mainly concentrated in the early to mid-July.In the years with early FRSOD_SX,the East Asia subtropical westerly jet stream(SWJS)establish earlier in late June and are stronger compared with their climatological means in the upper troposphere.There is‘a two troughs and one ridge’circulation pattern above mid-high latitude.The subtropical high is stronger,westward and northward than normal.In the lower layer,there is cyclonic anomaly circulation from the bay of Bengal to the South China Sea,and anticyclonic anomaly circulation on the West Pacific Ocean.In the years with late FRSOD_SX,the circulation system is opposite to the years with early FRSOD_SX.SST anomalies(SSTA)in the preceding winter and spring are the important forcing factors that affect the FRSOD_SX.When the Indian Ocean SST in winter and tropical North Atlantic SST in spring are abnormally warm,the FRSOD_SX is earlier than normal.