一例伴随西南涡的入海高原涡持续活动成因分析

Analysis of the Causes of one Sustained Enter-the-Sea Plateau Vortex Accompanied by Southwest Vortex

利用NCEP/NCAR再分析资料、历史天气图与青藏高原低涡切变线年鉴,采用天气学分析和要素诊断方法,对2013年6月4-10日伴随西南涡的入海高原涡从位涡、涡度及非绝热加热角度进行了诊断,分析了高空大值位涡、大值涡度下传以及非绝热加热在高原涡各生命阶段里的作用,以及与西南涡相遇对高原涡维持发展的影响,一定程度揭示了高原涡能够东移入海、长时间持续发展的原因。结果表明,高空急流的位置及强度变化对高原涡东移、入海发展至关重要,此例高原涡是在高空急流引导下东移入海的,而急流上携带的大值位涡、大值涡度下传是高原涡能够持续活动、最终入海并在海上保持活力的动力来源,尤其是当急流断裂处形成低槽时,低槽内的高位涡和强涡度下传为高原涡提供了充足的能量,使得高原涡强烈发展,而西南涡与高原涡相遇、重叠更使高原涡"锦上添花",达到了鼎盛,一旦失去高空的支持,高原涡迅速衰减、消亡;西南涡则不然,即使没有高空位涡、涡度的支持,西南涡仍由于非绝热加热的作用而强盛发展;高原涡、西南涡各生命阶段的视热源差异分析显示,非绝热加热对高原涡、西南涡的生成都有重要的作用,且作用方式相同,但生成之后,非绝热加热对高原涡的影响甚微,而对西南涡,非绝热加热仍然至关重要,不仅决定着西南涡的生命史长度,也决定着西南涡发展的强度。

Based on NCEP/NCAR reanalysis data, history synoptic chart and the Plateau Vortex and Shear Line Yearbook, by using synoptic analysis and diagnose method, an enter-the-sea Plateau Vortex (Qumalai vortex, named from its generation site) accompanied by a Southwest Vortex during 410 June 2013, was studied in terms of the vorticity, nonadiabatic heating and potential vorticity. In order to reveal the cause that why Qumalai Vortex can move eastward far away till onto the sea and sustain for 6 days, the function of downward spread of larger vorticity and potential vorticity from the upper air jet, nonadiabatic heating during the different life phases of Qumalai Vortex were studied, as well as the influence of encountering Southwest Vortex on Qumalai Vortex's maintenance and development. The results showed that the location and the intensity change of the upper air jet were of great importance for Qumalai Vortex to move eastward and maintain. Apart from leading Qumalai Vortex movement, as taking along larger vorticity and potential vorticity, the upper air jet provided Qumalai Vortex with vorticity and potential vorticity by way of downward spread, which gave support to Qumalai Vortex in energy continually. As Qumalai Vortex about to the sea, although the upper air jet just above Qumalai Vortex was disconnected, a trough was generated there. The downward spread of plentiful vorticity and potential vorticity in the trough into Qumalai Vortex enabled Qumalai Vortex to develop intensively, while encountering even overlapping with the Southwest Vortex made Qumalai Vortex stepping in a period of its great prosperity. Once Qumalai Vortex lost the support from the upper air, it decayed and died out soon. Unlike Qumalai Vortex, Southwest Vortex, even if without the aid of larger vorticity and potential vorticity from upper air, could still be strongly powerful and prosperous on account of nonadiabatic heating. Furthermore, the contrastive analysis of apparent heat source in their each life phase between Qumalai and Southwest Vortexes was conducted. The results indicated that over the first stage of formation, nonadiabatic heating was important for both Qumalai and Southwest Vortexes in the same way that heat was transported upward, resulting in the nonadiabatic heating profile of "bulging towards the right" which was very in favor of vorticity increase. Later, the function of nonadiabatic heating was little for Qumalai Vortex, but still crucial for Southwest Vortex. Nonadiabatic heating decided not only the length of Southwest Vortex life, but also the highest level of intensity.