Estimating raindrop size distributions and vertical air motions with spectral difference using vertically pointing radar

Abstract

AbstractDoppler spectra measured by vertically pointing radars are inherently linked to raindrop size distributions (DSDs). But, accurate estimation of DSDs remains challenging because raindrop spectra are broadened by atmospheric turbulence and shifted by vertical air motions. This paper presents a novel method to estimate vertical air motions that there is no need to assume a model for DSD at each range gate. The theory of the new method is that the spectral difference between the adjacent range gates is contributed by vertical air motions and the variability of DSDs. The contribution of the change of DSDs is estimated by looking up the prepared tables (LUTs) of raindrop velocity difference and shape function difference. Then, the vertical air motions can be estimated by minimizing the cost function of the two spectra between the adjacent range gates. The retrieval algorithm is applied to three cases including a stratiform and two convective observed by a C band vertically pointing radar in Longmen, Guangdong province of China in June 2016. Before that, the spectrum broadening effect is removed by the traditional deconvolution method with a wind profiler. The vertical profiles of precipitation parameters are also retrieved to investigate the microphysical process. The precipitation parameters retrieved near the surface are compared with the ground data collected by a two-dimensional video disdrometer(2DVD) and the results show good agreements.