Characterization of Shallow Oceanic Precipitation using Profiling and Scanning Radar Observations at the Eastern North Atlantic ARM Observatory

Description

Shallow oceanic precipitation variability is documented using three state-of-the-art 2nd generation radars located at the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic observatory: the Ka-band ARM zenith radar (KAZR2), the Ka-band ARM scanning cloud radar (KaSACR2) and the X-band scanning ARM precipitation radar (XSAPR2). First, the sensors and radar data post-processing techniques, including sea clutter removal and radar cross-comparisons are described. Then, we present how a combination of profiling radar and lidar observations can be used to estimate flexible (both in time and height) parameters that relate rain rate (R) to radar reflectivity (Z) in the form Z= αR^β. These flexible relationships are used to estimate rain rate over the domain observed by XSAPR2. XSAPR2 domain rain rate statistics differ from those estimated using the profiling KAZR2; that is because while KAZR2 is more sensitive to light shallow virga from stratiform clouds, XSAPR2 is better suited for the characterization of precipitation from cloud systems with mesoscale organization. Constant altitude, gridded XSAPR2 rain rate maps are presented and the need to select rain rate detection thresholds according to domain size is discussed. We find that rain rate statistics obtained by averaging 3, 12 or 24h of profiling observations can be used to approximate that of a domain of 2,220 km2 averaged over time periods of 3, 12 and 24h respectively. However, no amount of temporal averaging can be used to capture shorter term variability.