High resolution observations of drizzle from Stratocumulus using a 95 GHz FMCW radar

Marine stratus clouds cover extensive areas of the subtropical oceans, strongly reflect shortwave radiation and thus play a crucial role in the Earth's radiation budget. Drizzle has a significant effect on the cloud structure and lifetime due to depletion of cloud liquid water and boundary layer decoupling. This study uses unique radar observations of drizzling marine stratus clouds over the Southeast Pacific collected during the Tropical Atmosphere Ocean (TAO) and Stratus cruises conducted aboard the NOAA R/V Ronald H. Brown in the fall of 2004. The two upward looking millimeter wavelength Doppler radars operated during the cruise were: 1) the NOAA/ETL 35-GHz Millimeter Cloud Radar (MMCR) and 2) the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS)'s 95-GHz Frequency Modulated Continuous Wave (FMCW) compact airborne radar, developed by ProSensing Inc. The FMCW radar was operated with a spatial and temporal resolution of 5 m and 1.2 sec respectively. Due to the low power output and antenna size, the FMCW radar was sensitive only to the drizzle size droplets. Furthermore, the FMCW radar collected data from the surface with a very high spatial resolution and thus it was ideal for the study of drizzle variability and evaporation in the subcloud layer. The MMCR data were used to map the cloud structure and complimentary observations from a ceilometer and a microwave radiometer were used to study the drizzle formation/evaporation in marine stratus, and the drizzle Z-R relationship.