Dual Doppler radar analysis of the 3D wind fields associated with subtropical squall lines

This paper discusses the application of a 3D wind retrieval method to the Hong Kong and Guangzhou Doppler weather radars (separated by about 100 km) in the analysis of the structures of subtropical squall lines. The retrieval method is based on the minimization of a cost function under the constraints of fitting the radial velocity measurements from the two radars, conserving rain-water content and observing the continuity equation. It is applied to two cases of subtropical squall lines over southern China. In both cases, the method is found to depict the horizontal wind distribution associated with the squall line very well. The retrieved winds show many salient features of the airflow such as mesoscale waves and convergent flow along the squall line. The vertical wind distribution also appears to be reasonable, such as the depiction of updrafts at the locations of strong radar echoes, though the magnitude of the vertical velocity is in general on the low side considering the intensity of the convective development. The wind retrieval method presented in this paper has the potential application for wind analysis of severe convective storms in day-to-day weather forecasting.