摘要:利用青藏高原第三次科学实验的C波段双偏振雷达（C-POL）的观测资料、ERA-Interim 0.125°（纬度）×0.125°（经度）气象再分析资料、常规气象探空资料，对2014年7月30日午后发生在西藏那曲地区的冰雹强对流天气过程进行了天气诊断及雷达回波特征分析。结果表明：1）此次冰雹强对流过程发生在有切变线伴随的高原低涡东移过程中，低涡尾部前倾的切变线为这次冰雹的发生提供了动力、水汽条件。2）强对流天气的水汽输送主要来自从孟加拉湾、印度及尼泊尔翻越喜马拉雅山脉的水汽，强对流发生前水汽输送显著增加，低层水汽集中在400 hPa以下，有明显的辐合及垂直输送。3）那曲400 hPa以下为假相当位温随高度递减区，也是水平辐合及垂直上升运动的重合区，有明显的对流不稳定能量集聚及动力抬升条件。4）雷达回波图上可看到，此次强对流天气主要由局地新生的多个中γ尺度孤立对流单体造成，其移动路径与切变线前西南气流一致。大部分单体水平尺度不大，生命史短，但仍有部分单体强度大，生命史较长。局地气流辐合扰动会导致新的单体产生，单体的发生、发展及维持离不开低层气流辐合提供的动力条件。5）在距离高度显示图上表现出了弱单体雹云特征，雹云云顶伸展至16 km，高于夏季平原地区普遍对流云高度，但未突破对流层顶，0℃层远低于平原地区，为深厚强对流降水；强降水中心位于云团下部，即有降雹也有降水，降雹以霰粒为主；垂直方向存在强烈的入流和上升气流，悬挂回波出现在入流上升气流之上，中层辐合区的气流下沉区对应降雹区；中层辐合区与上层的高空辐散区配合导致对流风暴的垂直增长和强烈发展。
关键词:青藏高原/
冰雹强对流天气/
对流单体/
雷达回波特征
Abstract:Through the use of C-band dual-polarization radar datasets from the Third Tibetan Plateau Atmospheric Scientific Experiment, ERA-Interim 0.125°(latitude)×0.125°(longitude) reanalysis data, and conventional meteorological radiosonde data, the diagnostic analysis and radar echo feature extraction of a hailstorm severe convective weather process in the Naqu area of Tibet on the afternoon of 30 Jul 2014 are conducted. Results show that: 1) The hailstorm severe convective weather process occurs during the eastward movement of a plateau vortex accompanied by shear lines. The forward-tilting shear lines at the rear of the vortex provide energy and water vapor for this process. 2) The water vapor provided for the severe convective weather mainly comes from the Bay of Bengal, India, and Nepal, which strengthens significantly before the severe convective weather. The water vapor in the lower layer concentrates below 400 hPa, with obvious convergence and upward transportation. 3) Under the obvious convective instability, energy accumulation, and dynamic uplift conditions below 400 hPa in Naqu, the overlap area of the pseudo-equivalent potential temperature decreases with the height, horizontal convergence, and upward movement. 4) The radar echo images show that the severe convective weather is obviously local and is mainly caused by multiple γ mesoscale isolated convection cells, the movement path of which is consistent with the southwest airflow in front of shear lines. Most of the cells have small horizontal scales and short life, whereas some cells have large horizontal scales and long life. Local airflow convergence may cause the production of new cells, and the occurrence, development, and maintenance of cells depend on the low-level airflow convergence to provide dynamic conditions. 5) The range height indicator shows the characteristics of a weak hail cloud, with the top reaching approximately 16 km but not breaking through the top of the troposphere, which is higher than the general convective clouds in plain areas, and the 0℃ layer being lower than that in plain areas. The cloud indicates deep strong convective precipitation, and the precipitation center is located at the bottom of the cloud, including precipitation and hail dominated by radon particles. Strong inflows and updrafts occur in the vertical direction. The suspended echoes appear above the inflowing updrafts, with the airflow sinking zone below the middle-level convergence zone corresponding to the hail zone. The combination of the middle-level convergence and high-level divergence leads to the upward growth and strong development of convective storms.
Key words:the Tibetan Plateau/
Hailstorm severe convective weather/
Convection cell/
Radar echo feature
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