PNNL

Abstract

Shallow oceanic precipitation variability is docu-mented using three second-generation radar systems located at the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic observatory: ARM zenith radar (KAZR2), the Ka-band scanning ARM cloud radar (KaSACR2) and the X-band scanning ARM precipitation radar (XSAPR2). First, the radar systems and measurement post-processing techniques, including sea-clutter removal and calibration against colo-cated disdrometer and Global Precipitation Mission (GPM) observations are described. Then, we present how a combi-nation of profiling radar and lidar observations can be used to estimate adaptive (in both time and height) parameters that relate radar reflectivity (Z) to precipitation rate (R) in the form Z = aRß , which we use to estimate precipitation rate over the domain observed by XSAPR2. Furthermore, con-stant altitude plan position indicator (CAPPI) gridded XS-APR2 precipitation rate maps are also constructed. Hourly precipitation rate statistics estimated from the three radar systems differ because KAZR2 is more sensitive to shallow virga and XSAPR2 suffers from less attenuation than KaSACR2 and as such is best suited for characterizing inter-mittent and mesoscale-organized precipitation. Further anal-ysis reveals that precipitation rate statistics obtained by av-eraging 12 h of KAZR2 observations can be used to approx-imate that of a 40 km radius domain averaged over similar time periods. However, it was determined that KAZR2 is unsuitable for characterizing domain-averaged precipitation rate over shorter periods. But even more fundamentally, these results suggest that these observations cannot produce an ob-jective domain precipitation estimate and that the simulta-neous use of forward simulators is desirable to guide model evaluation studies.