青藏高原东南侧复杂地形下冬季大风诊断分析

Diagnostic Analysis of Winter Gale Complex Terrain in the Southeast of Qinghai-Xizang Plateau

为了对青藏高原(下称高原)东南侧复杂地形下大风形成的物理条件有一定认识,利用NCEP资料和WPR、PBL等非常规资料,以大理国家气候观象台为代表站,选取近年大理的5个大风个例,对高原东南侧复杂地形下的冬季大风天气进行分析。结果表明,高原东南侧大风环流背景具有相似性,15°N附近的低纬地区有多个高压系统出现,35°N以北的中高纬地区有长波或者低压槽活动;高原东南侧大风的发生受垂直运动的影响,主要表现为垂直运动对高空动量的牵引作用;高原东南侧大风有低空急流的背景,低空急流的向下传输受低层风场的旋转影响;感热向下传输和潜热释放给大风的产生和维持提供了热力条件;WPR探测高度和信噪比强度可以作为大风预警的定性指标之一,并且当感热通量和潜热通量呈反位相变化时,可对大风天气进行预警指导。

In order to have some physical cognition to the typical gale formation of the southeast complex terrain in Qinghai-Xizang Plateau,five typical gale cases in winter at Dali National Climate Observatory are selected and general analysis is made based on conventional NCEP sounding data,WPR and PBL data.The results show that:(1) The gale cases have similarity circulation background.There are more than one high-pressure system on low latitude near 15°N,long wave and trough of low pressure appears in the high latitudes north of 35°N.(2) The meridional circulation shows vertical movement has the effect on the Dali gale,which mainly presented that vertical movement action of the altitude momentum.(3) Dali gale also has low-level jet background,which transported downwards influence by lower layer velocity rotation.(4) The downward transfer of sensible heat and latent heat provide thermal conditions which make the gale produce and maintain.(5) The WPR probe height and signal-to-noise ratio intensity can be used as one of the gale warning qualitative indicators in Dali.When sensible heat flux and latent heat flux present out of phase to each other,it also can be an indicator to the gale.