陕西盛夏多雨年与少雨年的大气环流特征分析

Analysis on Atmospheric Circulation Characteristics of Rainy Year and Drought Year in Midsummer in Shaanxi Province

应用NCEP/NCAR1979—2004年再分析资料,针对陕西盛夏(7—8月)降水的情况,分析了汛期降水异常的大气环流特征。结果表明:陕西汛期多雨年,影响降水的主要天气系统表现为“三强一弱”,即西太平洋副热带高压、西风带蒙古低槽、乌拉尔山阻塞高压强,青藏高压弱;少雨年天气系统表现为“三弱一强”,即西太平洋副热带高压、西风带蒙古低槽、乌拉尔山阻塞高压弱,青藏高压强。另外,在多雨年,500hPa流场,在陕西中部有一条东西向的切变线或风向辐合区;850hPa形成了孟加拉湾经四川盆地到陕西和南海经鄂西北到陕西的水汽通道;少雨年500hPa河套中部为西北气流控制,850hPa水汽通道不明显或水汽输送中途减弱。

Based on the NCEP/NCAR 1979-2004 re-analysis data, the circulation characteristics of precipitation anomaly in flood season are analyzed against the condition of precipitation in midsummer （from July to August） in Shaanxi province. The results show that in rainy year, the main synoptic systems which impact precipitation show the type of ＂three strong and one weak＂, i.e. western Pacific subtropical is high, westerly belt Mongolian trough and the Ural blocking high are strong and Tibetan high is weak. On the contrary, in drought year, the main synoptic systems which impact precipitation show the type of ＂three weak and one strong＂, i.e. western Pacific subtropical is high, westerly belt Mongolian trough and the Ural blocking high are weak and Tibetan high is strong. In rainy year, 500 hPa wind is convergence field in areas of the center of Shaanxi province or the flow field has a shear line from east to west. There are two moisture channels at 850 hPa, one is in areas of Bengal Bay to Sichuan basin and Shaanxi province. The other is in areas of South China Sea to northwest of Hubei province and Shaanxi province. In drought year, the center of Hetao Area is controlled by the northwest wind at 500 hPa and the moisture channel is not obvious or the moisture transporting becomes weak at midway at 850 hPa.