QX气象Meteorological Monthly1000-0526气象编辑部中国北京qx-40-9-103310.7519/j.issn.1000-0526.2014.09.001P458研究论文Articles南支槽与孟加拉湾风暴结合对一次高原暴雪过程的影响A Case Study on the Effect of Southern Branch Trough in the Subtropical Westerlies Combined with Storm over the Bay of Bengal on Plateau Snowstorm索渺清SUOMiaoqing
利用NCEP/NCAR逐6 h 1°×1°再分析资料与常规和非常规观测资料,对2007年11月云南德钦高原暴雪产生的原因进行了研究,探讨南支槽与孟加拉湾风暴结合对高原东南部强烈天气的影响过程。结果表明:(1) 在南支槽和孟加拉湾风暴结合的天气尺度条件下,槽前偏南风低空急流受高原大地形阻挡产生的高原切变线是高原暴雪的直接影响系统;(2) 由于地形和冷空气的作用,上升运动向北倾斜使高原对流层中上层首先出现上升运动,整层上升运动在高原切变线和次级环流上升支的共同作用下强烈发展。孟加拉湾风暴北上与南支槽结合、高原切变线北移和风暴低压临近使德钦上升运动出现三次增强;(3) 南支槽前偏南风低空急流向北输送水汽,部分水汽被抬升到高空,部分水汽绕过高原东南角向下游输送。高空水汽经高原上空沿着高空西风急流向下游远距离输送。高、低空水汽通道不重合往往会影响高原及其下游强降水落区的预报。受高空水汽输送影响,高原东南部纵向岭谷区具有高层大气最先增湿的特征,近地层水汽通量长时间强烈辐合有利于高原暴雪的形成;(4) 上游冷空气沿南支西风到达孟加拉湾,促使南支槽加深和维持有利于引导孟加拉湾风暴北上,南支槽前偏南风低空急流把暖湿空气输送上高原,同时横槽转竖冷空气从高原南下,冷暖空气在德钦交汇形成强锋区也是暴雪产生的一个有利条件。(5) 高原暴雪的锋区结构具有中纬度锋面天气特征,在暴雪发生的锋区附近,满足倾斜位涡发展和条件性对称不稳定。
Using NCEP (1°×1°) 6 h reanalysis data and the conventional and unconventional observational data, a case study on the plateau snowstorm that occurred in November 2007 was performed to explore the generation process of the severe weather over the southeast part of Tibetan Plateau due to combination of Southern Branch Trough (SBT) in the subtropical westerlies and storm of Bay of Bengal (BOB). The results show that: (1) The plateau snowstorm synoptic scale condition is formed by the combination of SBT and storm of BOB. The plateau shear line produced by low-level jet is the direct influence system. (2) Because of the effect of the terrain and cold air, upward movement sloping to the north makes upward movement first appears in the mid-upper troposphere over the plateau. Both the plateau shear and the ascending branch of secondary circulation of the upper jet stream enhance the upward motion. Due to the combination of SBT and storm of BOB, the northward moving of plateau shear line and the nearing storm causes the ascending motion of Deqin to strengthen three times. (3) The southern lower-level jet occurs in front of the trough, which transports moisture to the north, and part of water vapor is lifted to the high level while other part of the water vapor passes by the southeast corner of plateau to the downstream. Meanwhile the high-level water vapor travels over the plateau along the upper westerly jet downstream advection over a long distance. High and low water vapor channels do not overlap, often affecting the plateau and its downstream forecast in heavy rainfalls. Due to the high-level water vapor transportion, the longitudinal range-gorge region of southeast plateau has the characteristics of upper atmosphere being moistured first, and surface layer moisture flux strong convergence for a long time is conducive to the formation of the plateau snowstorm. (4) The cold air upstream along the southern branch of the westerly to the BOB, deepens and maintains SBT, which is beneficial to the northward moving of the storm BOB. The cold air from the plateau and the warm air from BOB meet over Deqin, forming strong front, which is the main synoptic system of snowstorm. (5) The frontal structure of plateau snowstorm has the mid-latitude frontal synoptic characteristics. Snowstorm occurs near frontal zone, meeting the slantwise vorticity development and conditional symmetric instability.
南支槽孟加拉湾风暴高原暴雪southern branch trough (SBT)storm of Bay of Bengalplateau snowstorm国家重点基础研究发展计划(973计划)2010CB950404灾害天气国家重点实验室基金2009LASW-B12中国气象局预报员专项CMAYBY2014-089国家重点基础研究发展计划(973计划)(2010CB950404)、灾害天气国家重点实验室基金(2009LASW-B12) 和中国气象局预报员专项(CMAYBY2014-089) 共同资助引言
暴雪是我国北方冬季常见的灾害性天气,也是低纬高原(下称高原)地区主要且多发的灾害性天气,有时还伴有强寒潮和大风,对工农业生产、畜牧业、交通运输和人民生活影响较大。高原暴雪对高原经济的发展和人民的生产生活造成相当大的影响(周陆生等,2000;仓决等,2008;刘光轩,2008;假拉等,2008)。从20世纪70年代起,国内外就开始对暴雪机理进行研究(Bennetts et al, 1979; Emanuel, 1979; 王文辉等,1979;Sanders et al, 1985; Sander, 1986; Moors et al, 1988),但主要集中在我国东部地区(朱爱民等,1993;宫德吉等,2000;胡中明,2003;周雪松等,2008;董啸等,2010;孙欣等,2011;张迎新等,2011)。由于高原复杂的地形以及观测资料匮乏,高原暴雪的研究还有很多基础性、关键性的问题亟待解决。1996年9月中旬, 中国气象局在青海西宁召开了“牧区雪灾气象服务工作研讨会”, 首次对全国牧区雪灾气象服务进行科学分析和研究讨论,以促进对高原暴雪的深入研究。随后,高原暴雪的研究得到了加强(周陆生等,2000;董安祥等,2001;马林等,2001;王勇等,2006;王文等,2000; 2001;邓远平等,2000;王子谦等,2010;周倩等, 2011, 吕爱民等,2013)。
(a) Configuration of SBT, storm path and precipitation [thick/thin line represents SBT/contour (unit: dagpm) at 500 hPa, colorful line for precipitation, shaded for topography and for the Sidr center]; (b) time evolution of precipitation (bar), temperature (red curve) and dew point temperature (purple curve) at Deqin from 14 to 17 November 2007; (c) life history of Sidr
The geopotential height, temperature and relative vorticity at 500 hPa in the (a) brew, (b) snowstorm, (c) snow to rain, (d) end stage from 14 to 17 November 2007
-5 s-2),点划线表示3000 m地形,*代表德钦所在位置,粗实线表示南支槽,代表锡德中心位置]
]]>-5 s-2), dotted line for the 3000 m topography, symbol * for the location of Deqin, thick line for SBT, and for the Sidr center]
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650 hPa (left) and 300 hPa (right) jet stream and divergence in the (a, b) brew, (c, d) snowstorm, (e, f) snow to rain, (g, h) end stage from 14 to 17 November 2007
Average moisture flux (arrow, unit: g·cm-1·s-1·hPa-1) from 14 to 17 November 2007 at 700 hPa (a) and 400 hPa (b); (c) The configuration of heavy snow (rain) center with the high (solid line) or low (dotted line) moisture flux/channel (thick dashed/thick solid line, unit: g·cm-1·s-1·hPa-1); (d) Longitude-altitude cross-section of the moisture flux (arrow, unit: g·cm-1·s-1·hPa-1) along Deqin in the brew stage
(a) Time evolution of temperature advection over Deqin from 13 to 17 November 2007 (shaded for cold advection, unit: 10-5 K·s-1); (b) 24-h variable temperature at 650 hPa in the snowstorm period (shaded for △T < 0, unit: K); 305 K (c) and 315 K (d) isentropic potential vorticity and stream field (shaded for IPV ≥0.5 PVU) in the beginning of snowstorm stage
Latitude-altitude cross-section of θse (solid line, unit: K), M (dashed line, unit: m·s-1) and vorticity (shaded, unit: 10-5 s-1) along Deqin in the (a) brew, (b) snowstorm stage (terrain in shadow)
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