Using Doppler radars for remote sensing of cloud water and precipitation in low layer clouds

The low layer clouds because of their persistence and large cover have a substantial impact on Earth's energy budget and climate. Remote sensing retrievals of their parameters, such as liquid water and precipitation flux is important for climate model initialization and verification. Doppler radar observations of stratocumulus clouds were synthesized under the controlled framework of the Observing System Simulation Experiments (OSSEs). Cloud radar parameters, such as radar reflectivity, Doppler mean velocity and Doppler spectrum width, were obtained from the drop spectra generated using the latest version of the CIMMS explicit microphysics model (SAMEX) in simulations of cases observed during the ASTEX, DYCOMS-II and RICO field projects. The SAMEX model has been calibrated against reality in case studies which demonstrated that the model results compare favorably with observations.

Based on performed OSSEs we quantitatively evaluate the contribution of various Doppler radar parameters to the improvement of retrievals of cloud liquid water and precipitation flux in low layer clouds. Performance of the formulation of cloud retrievals based on the radar reflectivity and mean Doppler velocity was contrasted with retrievals based on the radar reflectivity and Doppler spectrum width. The dependence of retrievals on precipitation intensity has been investigated. The sensitivity of various formulations of the retrievals to the air turbulence component of the velocity and width parameters was also evaluated.