Characteristics of a Plateau Vortex Precipitation Event on 14 July 2014

Using various radar and disdrometer datasets from the Third Tibetan Plateau Atmospheric Science Experiment, MODIS data, surface and sounding datasets, temporal and spatial variations of one rainfall event on 14 July 2014 over Naqu in the central Tibetan Plateau is analyzed, the synoptic and meso-scale atmospheric circulations, and associated cloud-rainfall microphysical characteristics are also investigated. This rainfall process includes three stages, namely, the first stage with heavy rainfall starts in the afternoon (1400 BT) and ends at 1800 BT 14 July, the peak intensity of hourly precipitation occurs during 1500-1600 BT, which reaches 2.1 mm·h^-1. The second stage begins at 1900 BT, and the precipitation intensity weakens prominently compared with the first stage. The third stage is from 2200 BT 14 July to 0100 BT 15 July with a weaker precipitation intensity.Rainfall during the first stage is mainly produced by the development of a synoptic-scale plateau vortex and the formation of a meso-scale convergence line in front of the vortex circulation center. The radar echo propagates northeastward, and this stage ends with the weakening of the plateau vortex. Rainfall at night is mainly associated with the warm and moist southeasterly flow passing over the topography near Naqu, which provides favorable conditions of the atmospheric moisture, instability, and shallow dynamic elevation. With the intrusion of the low-level northeasterly flow, the radar echo generally propagates southeastward. Moreover, during the earlier stage of the first rainfall stage, the ascending motion is deep over the east of the vortex, exceeding 3 m·s^-1 between 3 km and 11 km above the ground level, which indicates the remarkable development of convections. During the later stage, rainfall is mainly produced by stratiform clouds, with a higher cloud top. Rainfall at night is mainly caused by stratiform clouds. The raindrop size distribution is wider (0.3-4.9 mm) than that size of 0.3-2.1 mm in the topographic rainfall, and the wider raindrop spectrum is closely associated with the larger rainfall rate.