Satellite-based Observational Study of the Tibetan Plateau Vortex: Features of Deep Convective Cloud Tops
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In this study, an east-moving Tibetan Plateau vortex (TPV) is analyzed by using the ERA-5 reanalysis and multi-source satellite data, including FengYun-2E, Aqua/MODIS and CALIPSO. The objective is to demonstrate: (i) the usefulness of multi-spectral satellite observations in understanding the evolution of a TPV and the associated rainfall, and (ii) the potential significance of cloud-top quantitative information in improving Southwest China weather forecasts. Results in this study show that the heavy rainfall is caused by the coupling of an east-moving TPV and some low-level weather systems [a Plateau shear line and a Southwest Vortex (SWV)], wherein the TPV is a key component. During the TPV’s life cycle, the rainfall and vortex intensity maintain a significant positive correlation with the convective cloud-top fraction and height within a 2.5◦ radius away from its center. Moreover, its growth is found to be quite sensitive to the cloud phases and particle sizes. In the mature stage when the TPV is coupled with an SWV, an increase of small ice crystal particles and appearance of ring- and U/V-shaped cold cloud-top structures can be seen as the signature of a stronger convection and rainfall enhancement within the TPV. A tropopause folding caused by ageostrophic flows at the upper level may be a key factor in the formation of ring-shaped and U/V-shaped cloud-top structures. Based on these results, we believe that the supplementary quantitative information of an east-moving TPV cloud top collected by multi-spectral satellite observations could help to improve Southwest China short-range/nowcasting weather forecasts.
Key wordsTibetan Plateau vortex multi-spectral satellite observations short-range/nowcasting weather forecasts cold U/V-shaped cloud top tropopause folding
本文利用FY-2E, Aqua/MODIS和CALIPSO多源卫星资料, 并结合ECMWF最新一代高时空分辨率ERA-5再分析资料, 对一个东移的高原低涡(简称TPV)进行了分析, 以期表明: (i) 卫星观测的多光谱资料有助于理解TPV及其降水的演变; (ii)利用云顶上提取的定量信息对提高中国西南地区短临天气预报具有潜在的意义. 结果表明, 本例中强降水是东移的TPV系统与低层天气系统(切变线和西南涡)发生耦合引起的, 其中TPV起到了关键作用. 在TPV发展的各个阶段中, TPV的强度及降水不仅与以高原低涡中心为圆点半径为2.5°(纬度)范围内的对流云顶面积与总面积的比值, 还与云顶高度, 具有显著的正相关关系; 而且它对云顶相态和粒子大小变化也非常敏感. 在TPV成熟阶段, 当它与低空西南涡叠加而强烈发展时, 出现的云顶小冰晶粒子增加以及环形和“U/V”字形的冷云顶结构, 可以看作TPV内部对流加强和降水增幅的信号. 从动力机制上看, 由高层非地转平衡气流引起的对流层顶折叠可能是引起环形和“U/V”字形的冷云顶结构的一个关键因素. 基于这些结果, 我们认为补充基于卫星多光谱资料提取的东移TPV的云顶定量信息可以用于提高和改善中国西南地区短期天气预报.
关键词高原低涡 卫星多光谱资料 短期天气预报 环形冷云 “U/V”字形冷云 对流层顶折叠
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This research is supported by the National Natural Science Foundation of China (Grant Nos. 41575048 and 91637105). The authors wish to thank Academician Jianmin XU, of the National Satellite Meteorological Center, for giving constructive suggestions during the paper’s revision, as well as the anonymous reviewers and editors for their inspirational comments and suggestions on this paper.
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