盛夏高原涡生成频数与初夏大气环流背景场的关系

Relationship Between the Frequency of Tibetan Plateau Vortex Generation in Midsummer and the Background Field of Atmospheric Circulation in Early Summer

基于ERA-interim再分析资料,通过客观识别法得到的高原低涡统计数据集,选取1986-2015年7月高原低涡生成频数的多发年与少发年,通过相关分析与合成分析等方法分析7月生成的高原低涡频数与6月的大气环流之间的关系.主要结果如下:(1)7月高原低涡主要生成在28°-36°N纬带内,90°E以西生成的高原涡数量占全部的74.68%;(2)高原低涡多发年,高原低层相对湿度大,尤其改则—申扎(30°-34°N,84°-90°E)与左贡(约29°N,97°E)地区;整层大气热源偏强,90°E以西地区垂直方向上各层均表现为热源.高原低涡少发年,6月32°N以南低层相对湿度小;整层大气热源弱,垂直方向上低层表现为热源,热源偏弱.(3)高原涡多发年,高原涡主要生成范围内低层被正相对涡度控制,并且相对涡度偏大;高原主体范围内基本为上升气流,低层上升速度偏大,气流低层辐合,高层辐散,强度偏强,但在高原90°E以西与90°E以东有一定差异.高原涡少发年,高原涡主要生成范围内低层被正相对涡度控制,但相对涡度偏小;高原主体范围内为上升气流,低层上升速度偏小,气流低层辐合,高层辐合,强度偏弱.

Using the Tibetan Plateau Vortex(TPV)statistical data set obtained with the objective recognition method based on ERA-interim reanalysis data,selecting the high-and low-frequency years of the plateau vortex from 1986 to 2015,and using this reanalysis data and the National Oceanic and Atmospheric Administration OLR(outgoing long-wave radiation)data,the authors of this paper study the relationship between the plateau vortex frequency generated in July and the atmospheric circulation in June with correlation analysis and composite analysis.The main results are summarized in the following points:(1)In July,the generating sources of the TPV appear mainly in the 28°-36°N latitude zone.The number of plateau vortices generated in the area west to 90°E accounts for 74.68%of the total.(2)During high-frequency years of TPV,the relative humidity of the low-level is high,especially in the areas of Shenzha(30°-34°N,84°-90°E)and Zuogong(about 29°N,97°E).The atmospheric heat source is high in the vertical direction in the area west to 90°E.The convection activity is high in the plateau south to 32°N.During low-frequency years of TPV,the relative humidity of the low-level is low in the plateau south to 32°N in June.The atmospheric heat source is low in the vertical direction of the west of 90°E.The convection activity is low in the plateau south to 32°N.(3)During high-frequency years of TPV,the low-level in the main generation range of the plateau vortex is controlled by the positive relative vorticity,and the relative vorticity is too high.It promotes updrafts over the plateau,which are favorable for low-level convergence and high-level divergence.The intensity is high,but there is a certain difference between the area west to 90°E and the area east to 90°E.In Gaize,the vertical shear of horizontal wind is less severe and weaker than in low-frequency years.During low-frequency years of TPV,the low-level in the main generation range of the plateau vortex is controlled by the positive relative vorticity,and the relative vorticity is low.It promotes updrafts over the plateau,which is favorable for low-level convergence and high-level divergence.The intensity is low.