KAZR-CloudSat Analysis of Snowing Profiles at the North Slope of Alaska: Implications of the Satellite Radar Blind Zone

Abstract

Spaceborne radars provide near-global observations of clouds and precipitation, but ground clutter can result in a satellite radar blind zone as high as 2 km above the surface. As a result, satellite radars may underestimate snowfall from shallow clouds and incorrectly flag snow virga as snowfall at the surface. Ground-based radar observations provide invaluable tools to assess satellite observations of clouds and precipitation. This study investigates snowfall regimes using observations from 2011 to 2021 at the Department of Energy Atmospheric Radiation Measurement North Slope of Alaska atmospheric observatory. Snowfall events identified in the Ka-band ARM zenith radar (KAZR) are separated into regimes based on the cloud/precipitation layer characteristics: deep snowfall, shallow snowfall, and snow virga. The shallow snowfall regime accounts for nearly half of the regime occurrence (48%) followed by snow virga (28%) and deep snowfall (23%). However, more than half (62%) of the shallow snowfall is likely underestimated and/or undetected within the satellite radar blind zone. Snow virga is incorrectly flagged as snowfall for 7% of the total annual occurrence, but increases to 12% in October. The KAZR regimes and vertical structure are qualitatively compared to collocated CloudSat observations with snow certain/possible flags; the deep and shallow snowfall regime show similarities between the ground-based and spaceborne radar observations. An assessment of observable snowfall occurrence and accumulation at varying reflectivity thresholds in KAZR and CloudSat provide a reference for detection characteristics for current and planned spaceborne radars.