Improving the Nowcasting of Strong Convection by Assimilating Both Wind and Reflectivity Observations of Phased Array Radar: A Case Study

With the advent of the phased array radar (PAR) technology, it is possible to capture the development and evolution of convective systems in a much shorter time interval and with higher spatial resolution than via traditional Doppler radar. Research on the assimilation of PAR observations in numerical weather prediction models is still in its infancy in China. In this paper, the impact of assimilating PAR data on model forecasts was investigated by a case study of a local heavy rainfall event that occurred over Foshan city of Guangdong Province on 26 August 2020, via a series of sensitivity experiments. Both the retrieved three-dimensional wind and hydrometeor fields were assimilated through the nudging method with the Tropical Regional Assimilation Model for South China Sea_Rapid Update Cycle_1km (TRAMS_RUC_1km). The temperature and moisture fields were also adjusted accordingly. The results show that significant improvements are made in the experiments with latent heat nudging and adjustment of the water vapor field, which implies the importance of thermodynamic balance in the initialization of the convective system and highlights the need to assimilate PAR radar observations in a continuous manner to maximize the impact of the data. Sensitivity tests also indicate that the relaxation time should be less than 5 min. In general, for this case, the assimilation of PAR data can significantly improve the nowcasting skill of the regional heavy precipitation. This study is the first step towards operational PAR data assimilation in numerical weather prediction in southern China.