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ISSN 1006-9895

CN 11-1768/O4

影响夏季青藏高原横切变线演变的动力和热力作用分析
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作者单位:

1.中国气象局武汉暴雨研究所;2.中国气象局气象干部培训学院

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高原与盆地暴雨旱涝灾害四川省重点实验室开放研究基金项目(SZKT202003),国家自然科学基金项目(91937301,42030611)


Dynamic and Thermodynamic Effects on the Evolution of the Transverse Shear Line over the Tibetan Plateau in Boreal Summer
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China Meteorological Administration Training Centre

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    摘要:

    青藏高原横切变线(简称切变线)是引发青藏高原夏季暴雨的主要天气系统之一。本文基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,简称ECMWF)提供的ERA-5再分析资料,选取14个生成于6-8月、生命史为38小时且引发高原暴雨的切变线个例进行合成分析,探究动力和热力作用对夏季切变线生成和强度演变的影响。结果表明:(1)500hPa切变线生成于伊朗高压和西太平洋副热带高压两高之间的鞍形场中,处于580dagpm闭合低值中心和272K高温中心内、比湿大值区的北侧;200hPa南亚高压北部边缘、西风急流入口区南侧。(2)切变线强度表现出明显的日变化特征,在当地时间(LT=UTC+6h)23时最强,13时最弱。(3)涡度收支诊断表明,青藏高原上空高低层散度变化对切变线强度变化具有指示意义,500hPa涡度最大值(最小值)出现时间滞后于辐合作用最大值(最小值)3小时。(4)切变线演变过程中,切变线发展时位涡随之增大。位涡收支诊断表明,青藏高原上空的水汽和非绝热加热对切变线的生成和发展演变起到重要作用。当边界层感热加热增强时,低层辐合增强,上升运动增强,在充足的水汽配合下,凝结潜热释放使非绝热加热中心抬高至大气中层,有利于切变线生成及发展。

    Abstract:

    The Tibetan Plateau transverse shear line (TPTSL) is one of the main weather systems over the Tibetan Plateau. Based on the ERA-5 reanalysis datasets provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), 14 cases of TPTSL which causes heavy rainfall and generates in June-August with a lifetime of 38 hours are selected and composited to reveal the impact of dynamic and thermodynamic forcing on the intensity evolution of TPTSL s. The results are as follows. (1) At 500hPa, the TPTSL generates in the saddle field between the Iran high and the western Pacific subtropical high, and is located in the low-pressure center contoured by 584dagpm and warm center contoured by 272K, to the north of the specific humidity center. At 200hPa, the TPTSL is located in the northern margin of the South Asian High and to the south of the entrance region of the westerly jet stream. (2) The intensity of TPTSL at 500hPa shows an obvious diurnal variation with the strongest at 23LT and the weakest at 13LT (LT=UTC+6h). (3) The vorticity budget reveals that the variation of the divergence at the upper and the convergence at the lower layers over the Tibetan Plateau is indicative of the intensity of TPTSL, and the vorticity at 500hPa gets maximum 3 hours later than that of the convergence. (4) Potential vorticity (PV) increases with the development of the TPTSL. The PV budget shows that the water vapor and diabatic heating play an important role in the generation and evolution of the TPTSL. The enhanced sensible heating leads to an intensified ascent. With sufficient water supply, the latent heating releases and the diabatic heating center rises to the middle layer, which is favorable for the generation and development of the TPTSL.

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  • 收稿日期:2021-04-02
  • 最后修改日期:2021-08-09
  • 录用日期:2021-09-02
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