Vertical Variability of Rain Drop Size Distribution

Ground based weather radars are heavily relied in generating mosaic of rainfall products for hydrological applications.  The rainfall products are then adjusted with rain gauges wherever they are available and reliable.  This operational routine is currently adopted in the US and a number of other countries worldwide.  Despite gauge adjustment, rainfall products suffer from the time-height ambiguity between altitude of radar measurement and rainfall at the ground.  The vertically pointing radars are great toll to fill the gap between the ground level and the first available radar elevation and to determine the measurements uncertainties between scanning radar and in-situ measurements. Micro Rain Radar (MRR) is a K-band radar that estimates rainDrop Size Distribution (DSD) profiles from Doppler spectra determined by drops falling at different velocities and at different heights.  Another application of the MRR is the investigation on the DSD variability through precipitation column in vertical within measurements cells.  The latter information is linked to well-known problem of the non-uniform beam filling from Global Precipitation Measurement (GPM) mission Dual Frequency Precipitation Radar (DPR).  During GPM Ground Validation Iowa Flood Studies (IFloodS) field experiment, data collected with 2D video disdrometers (2DVD), Autonomous OTT Parsivel² Units (APU), and MRR profilers at different sites were available.  In three different sites co-located APU, 2DVD and MRR are available and covered by the S-band Dual Polarimetric Doppler radar (NPOL).  This represents a perfect setup to compare disdrometers, MRR and NPOL data and to evaluate the uncertainties of those measurements.  First the performance of disdrometers and MRR in determining reflectivity factor (Z), rainfall rate (R), mean mass-weighted raindrop diameter (D_mass), normalized intercept parameter (N_w) and gamma shape parameter (µ) has been evaluated and then the MRR based parameters have been compared with the ones obtained from NPOL data at the two lowest elevations.  Furthermore, the vertical variability of DSD and integral rainfall parameters within the MRR bins (from ground to 1085 m each 35 m) has been investigated in order to provide some insight on the variability of the rainfall microphysical characteristics within about 1 km above the ground.