利用1°×1°NCEP/NCAR再分析资料,选取500 hPa分别为西风槽、切变线和切变流场影响背景下、移出高原后维持48 h以上的3次典型高原低涡个例,分析了低涡维持期间500 hPa环境场、主要影响系统、涡度与温度平流、200 hPa形势场及垂直动力结构,并利用涡度方程对总涡源和各强迫项进行了诊断分析,结果表明:(1)西风槽影响时高原低涡移动路径受槽前西南气流引导,切变线影响时低涡沿切变线自西向东移动,切变流场影响时低涡移动主要受西太平洋副热带高压(下称西太副高)进退的影响,当西太副高出现明显西伸时,可导致低涡折向西退,3次个例均持续有正涡度平流和冷平流向涡区输送;(2)西风槽和切变线影响时南亚高压为东西带状分布,切变流场影响时南亚高压为北拱形;(3)高原低涡东移发展达到最强时,3次个例在200 hPa均有低槽或低压叠加,从而形成深厚的正涡度柱;(4)500 hPa存在正涡度变率中心,低涡沿正涡度变率中心方向移动,高空槽和切变流场影响时正涡度变率主要来自水平输送项,切变线影响时主要来自辐合辐散项。
Based on NCEP reanalysis dataset of 1°×1°resolution,three typical plateau vortexes which were sustained for more than 48 hours after leaving the Qinghai-Xizang Plateau under the background respectively of "westerly-trough" ,"shear line"and "sheared flow field" are analyzed in terms of their environment,main influence system,both vorticity and temperature advection on 500 hPa,as well as situations on 200 hPa and vertical dynamical structure,in addition,total vorticity source and each forcing items are also diagnosed by using of the vorticity equation.The main characteristics during the maintenance of the plateau vortexes are as follows:(1) the plateau vortex accompanied by westerly-trough shifts following the southwest airflow in the front of westerly-trough;the plateau vortex influenced by shear line moves eastward along with the shear line;the vortex situated in a sheared flow field migrates led by subtropical high,as a result,the vortex may even recede backward if subtropical high stretches westward largely;both positive vorticity and cold advection are transported continuously to the vortexes area in three cases.(2) South Asia high on 200 hPa appears as zonal distribution under the circumstances of "westerly-trough" and "shear line" ,but as northward-arcuation in the case of "sheared flow field" .(3) Trough or low pressure emerges on 200 hPa when three vortexes reach up to their most powerful status,in other word,deep positive vorticity columnar comes into being.(4) There is a variability center of positive vorticity on 500 hPa,along which vortexes move;positive vorticity variability is mainly caused by horizontal transport when upper-trough or sheared flow field play a leading role,but mainly by convergence and divergence while shear line is dominant.
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