影响山东区域切变线天气特征及大气垂直结构分析

Synoptic Features and Vertical Structures of Shear Lines Influencing Shandong Province

利用常规气象观测资料和NCEP/NCAR 1°×1°再分析资料,统计分析了2001—2010年影响山东的切变线的天气气候、环流形势、降水分布的特征和各类典型切变线的空间结构。结果表明:影响山东的切变线天气系统按其热力性质可分为冷切变线和暖切变线,冷切变线按其风场结构可分为经向切变线和纬向切变线。一年当中7、8月是切变线高发期。山东雨季典型切变线的发生与副高关系密切,经、纬向切变线分别发生在副高强大呈块状、带状分布时,西风槽东移受阻,蜕变为切变线。经向(纬向、暖)切变线在空间剖面图上与向西(北)倾斜的正涡度柱配合,且切变线上正涡度最大;切变线均上有θse能量锋区配合,冷切变线位置偏向于相对暖的气团一侧,暖切变线位置位于锋区中间;切变线的上升运动区主要位于切变线上和暖气团一侧;构成切变线的相对暖气团均具有对流不稳定性;冷切变线的水汽辐合区主要位于切变线上和切变线附近的冷气团一侧,而暖切变线的水汽辐合区则主要位于切变线上。500hPa槽是切变线降水区的后边界,冷切变线降水区出现在地面静止锋后部的偏北风里,暖切变线降水落区位于地面准东西向倒槽的偏东风里;相对较大的降水出现在700hPa和850hPa切变线在地面的投影之间的区域;切变线暖气团或相对暖气团中在合适的触发条件下还可能出现分散性的短历时强降水。

By means of the conventional weather charts and NCEP/NCAR 1°×1° reanalysis data,analyses are made of the climatic features,circulation patterns,rainfall distributions,and spatial structures of typical shear lines in Shandong Province.The results show that shear lines can be divided into cold and warm ones according to their thermodynamic properties.Cold shear lines can be divided into meridional and zonal ones according to the wind field structure.Shear lines appear frequently in July and August in a year.The occurrence of typical shear lines is closely related to the Subtropical High during rainy season.The occurrence of a meridional shear line is often accompanied by the stronger cell-shaped Subtropical High when the eastward trough is blocked,and zonal one by the band-shaped one,while westerly troughs are transformed into shear lines.Shear lines are associated with the positive vorticity column in profile,and the strongest vorticity is often found on shear lines.There areθseenergy frontal zones on shear lines,with the cold shear lines tending toward the warm side and the warm lines in the middle.The ascending motion areas locate on shear lines and the warm side.For cold shear lines,the convergence of water vapor locates on a shear line and the cold air side,but the occurrence of water vapor convergence is mainly on a shear line for warm shear lines.The rainfall area lies in the northerly flow in the rear of the ground stationary front for cold shear lines,but lies in the easterly flow of the ground inverted trough for warm shear lines,both with a trough in the 500 hPa layer as the border.Relatively large precipitation occurs in the area between the ground projections of the shear line in the layer of 700 to 850hPa.The shear-line warm air mass or relatively warm air mass may also bring the dispersive short-duration precipitation in appropriate triggering conditions.