Raindrop size distribution properties associated with vertical air motion in the stratiform region of a springtime rain event from 1290 MHz wind profiler, micro rain radar and Parsivel disdrometer measurements

On 12 March 2012, a frontal rain system elongated east-west occurred over the southern coast of Korea, a frequently observation during springtime. Characteristics of raindrop size distributions (RSDs) in the stratiform region of the rain system observed by a 1290 MHz wind profiler collocated with a Parsivel disdrometer and K-band micro rain radar (MRR) are investigated. Temporal RSD variations are in close agreement between the instruments in spite of different sampling volume and height. It is found that number concentrations at small drop range around 1 mm measured from the profiler at 800 m AGL are noticeably fewer particularly at times of high rainfall rates, compared to those at the same drop range from the MRR and disdrometer. This is likely attributed to downdrafts that were enhanced below a strong bright band. Profiler Doppler spectra and RSD retrievals are susceptible to vertical air motion effects (especially at small drop range) at higher levels, compared to surface disdrometer retrievals. Thus, vertical air motion retrievals from profiler Doppler spectra were performed and showed good agreement in comparison with vertical air motions derived from a conventional method (i.e. radar reflectivity-fallspeed relation). Following this, vertical air motion effects on rain rate and mass-weighted mean diameter parameters were examined quantitatively using a profiler spectral model for conditions of updrafts and downdrafts.