Vertical Wind and Drop Size Distribution Retrieval with the CloudCube G-band Doppler Radar

Macrophysical properties of clouds are influenced by underlying microphysical processes. In practice, there is often an observational gap in bridging the two. For example, our current understanding of aerosol-cloud interaction and cloudclimate feedback is hindered by a lack of robust measurements of the distribution of drop sizes within clouds, especially for the smallest drop sizes. Doppler radar measurements have proven useful in estimating rainfall drop size distributions (DSDs) but 5 face an intermediate challenge of requiring a correction for the presence of vertical air motion. Recent advances in millimeter wave technology have made radar measurements at ever smaller wavelengths possible, allowing for analysis of non-Rayleigh scattering effects to back out estimates of vertical winds and thereby DSDs. This work demonstrates a method of deriving range-resolved DSDs using 238 GHz Doppler spectra measured by the CloudCube G-band atmospheric Doppler radar. The observations utilized are of marine boundary layer clouds during March and April 2023 in La Jolla, CA, USA, taken as 10 part of CloudCube’s participation in the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) campaign. This method first identifies “notches” in the velocity spectra and compares them to the theoretical notch velocities predicted by size dependent backscattering and terminal velocity models to estimate the range-dependent vertical wind. After removing the vertical wind, binned DSDs are retrieved from the zero-wind spectrum. Bulk properties of the precipitation are then derived including the number concentration, liquid water content, characteristic drop size, and precipitation rate. These bulk properties 15 are relatively invariant to the assumptions made in the estimation of the full DSD retrieval, potentially making large volumes of such retrievals useful tools in assessing physical models of drizzle.