副热带高空急流的非地转平衡特征

Ageostrophic characteristics of subtropical upper-level jet

利用数值模式的高分辨率模拟结果研究了夏季东亚副热带西风急流短期强度变化过程中的非地转平衡特征。结果表明,急流区为非地转风的正值区,最大值区域位于急流中心北侧,主要的负值区位于急流入口区附近。急流核南侧非地转风呈反气旋式切变,入口区呈反气旋式切变,入口区北侧和出口区北侧有弱气旋式切变。非地转风对急流的强度变化及其程度均有一定的指示性,地转偏差与急流短期强度的变化有密切的联系。最大偏差风的变化超前于纬向风的变化约6h。非地转风涡度的分布存在着中尺度的特征:极值区域大小只有中尺度的范围,且正负相间。中尺度涡度极值区主要集中于3个区域:太行山脉、长白山脉以及日本本州岛。这3个区域均对应于高度超过1000m的中尺度地形区域,高空急流的非地转涡度大值区与中尺度地形对应相关。中尺度降水区分别与非地转风涡度极值密集区相对应。

High-resolution data from numerical model simulation are used to study the ageostrophic characteristics of short-term process of East Asian subtropical westerly jet in summer.The results show that jet represents positive ageostrophic area,the maximum lies to the north of jet center region and negative areas mostly lie close to the entrance of jet stream.Ageostrophic wind shows anticyclonic shear to the south of jet and in the entrance area while cyclonic shear appears in the north of entrance and exit areas.Ageostrophic wind indicates the change of jet intensity and geostrophic deviation is closely related with short-term change of jet strength.The change of maximum deviation wind occurs 6 h earlier than the change of horizontal wind.Distribution of ageostrophic vorticity takes on mesoscale characteristics while positive and negative values appear alternately.Mesoscale vorticity extremums mainly locates in 3 regions：Taihang Mountains,Changbai Mountains and Honshu Island（Japan）,all of which correspond to mesoscale terrain over 1 000 m.Maximum areas of ageostrophic vorticity of upper air jet correspond to mesoscale terrain.Mesoscale rainfall areas correspond to dense extremum areas of ageostrophic vorticity.