An observation of sea‐spray microphysics by airborne Doppler radar

This paper describes observations and analysis of Doppler radar data from a down-looking 94 GHz (W-Band) system operated from a NOAA WP-3 Orion research aircraft in Tropical Storm (TS) Karen. The flight took place on 5 October 2013; Karen had weakened with maximum winds around 20 m s−1. Doppler spectral moments from the radar were processed to retrieve sea-spray microphysical properties (drop size and liquid water mass concentration) profiles in the height range 75–300 m above the sea surface. In the high wind speed regions of TS Karen (U10 > 15 m s−1), sea spray was observed with a nominal mass-mode radius of about 40 µm, a radar-weighted gravitational fall velocity of about 1 m s−1, and a mass concentration of about 10−3 gm−3 at 75 m. Spray-drop mass concentration declined with height to values of about 10−4 gm−3 at 300 m. Drop mass decreased slightly more slowly with increasing height than predicted by surface-layer similarity theory for a balance of turbulent diffusion vs fall velocity.