Airborne W-band Radar Applications in Marine Boundary Layer and Hurricane Environments

The NOAA Physical Science Lab airborne Doppler W-band radar was deployed on the NOAA P-3 N43 aircraft during the 2024 Hurricane Season, which included two flights related to the ONR MAGPIE field experiment in Barbados (Moisture and Aerosol Gradients / Physics of Inversion Evolution). We present W-band radar results from this season to highlight and encourage future opportunities for using the NOAA PSL W-band radar in studies of the marine boundary layer, air sea interaction, hurricanes, and other high-wind environments.

The downward looking W-band Doppler radar measures vertical profiles of reflectivity, Doppler velocity, and spectrum width. From these quantities, cloud microphysical, dynamical, and QPE information are derived. It detects most non-precipitating clouds, but has a slightly lower sensitivity than Doppler lidars, which can see more optically thin clouds. The W-band signal usually starts to attenuate at rain rates of 10 mm/hr, but can still provide accurate retrievals of rain rate, vertical air motion, and cloud microphysics until the signal is completely extinguished from the column. In fact, attenuation is the basis of the rain rate retrieval. Ambient vertical air motion as a function of height is obtained by separating the fall velocity of hydrometeors from the Doppler velocity and accounting for aircraft motion. Quantitative microphysical information as a function of height can also be obtained by combining the vertical beam of the W-band with that of the Tail Doppler X-band radar. The W-band also provides an estimate of surface mean square slope, which relates to the surface wave field. When the signal is not attenuated by rain but high winds are present, vertically extended plumes of sea spray are also observable with the radar. These below-radar vertically resolved measurements can be interpreted within the context of the in-flight probe data (vertical velocity, state variables, cloud/aerosol drop size distributions) and other remote sensing retrievals below the P-3 (SFMR rain rate and surface wind speed, WSRA rain rate and surface wave metrics, X-band precipitation echoes). During MAGPIE flights, P-3 W-band radar data were obtained nearby to or collocated with airborne/land lidar vertical profiles of atmospheric humidity, temperature, clear air motion, and scattering from aerosols, as well as the Twin Otter’s in-flight probe data of vertical velocity, state estimates, and cloud/aerosol drop size distributions.