A Preliminary Study on Radar Bright-band over Nyingchi Region in Tibet

The cloud and precipitation in the Tibet plateau has special microphysics characteristics that attract research attentions from global meteorological community. Weather radars in Tibet plateau play an increasingly important role in the microphysics and dynamic observation of cloud and precipitation. The existence of bright-band in radar echoes limits the performance of quantitative precipitation estimation (QPE), especially in high altitude area with complex terrain where melting layer is lower and occurrence of beam blockage happen heavily. In order to reduce the influence of the bright-band on the precipitation estimation, it is necessary to identify and correct the bright-band. This paper mainly analyze melting layer characteristics observed with the C-band Chinese New Generation Weather Radar (CINRAD-CD) and Ka-band all solid-state vertical profile radar in Nyingchi during the third Tibet Plateau atmospheric science field campaign in 2015. The processing algorithm consist of the following sections: the correction of attenuated reflectivity is firstly carried out with the method of bin-by-bin correction in the groups. Secondly, based on the volume radar data from CINRAD-CD, the vertical profile of the average reflectivity factor is calculated at the unblocked azimuth. According to the vertical reflectivity profile of bright-band, the macrophysics parameters such as the top height, the bottom height, the peak height and the bright-band thickness of precipitation are calculated. For cross validation, the vertical reflectivity factor data of Ka radar are extracted, and the corresponding macrophysics parameters of the bright-band are also calculated. Finally, the bright-band identification of the two kinds of radar are validated through temperature profile captured with radiosonde at the closest time. Based on the observation data within a month, the following conclusions are drawn: (1) Two radars are able to consistently identify the bright-band.(2) The mean height of peak reflectivity value in bright-band is from ten meters to several hundred meters lower than the height of 0℃ isotherms. (3) Different from other low altitude areas, the bright-band peak height of Nyingchi is more closer to the height of 0℃ isotherm, and its thickness is smaller. (4) The vertical decline rate of reflectivity factor is larger in the bright-band range.