Remote Sensing of Vertical Profiles of Clouds and In-cloud Humidity Using a Combined Platform of Radar and Sub-Millimeter Microwave Radiometers

A combined platform of radar and multi-frequency passive microwave sub-millimeter radiometers is recommended by the 2017 Decadal Survey as a candidate measurement approach for the Clouds, Convection and Precipitation (CCP) Designated mission. This study presents a quantitative analysis on the capability of such measurements using the JPL Sub-millimeter Microwave Simulation and Retrieval Package [Jiang et al. 2017, 2019, Yue et al., 2020]. A range of microwave frequencies between 118-850 GHz has been simulated. The benefit of combined measurements from cloud radars and radiometers is evaluated on the simultaneous retrieval of vertical profiles of cloud ice particle effective radius along with ice water content, atmospheric moisture, and temperature profiles. Using a climate model simulation, we show that by reducing the uncertainty ranges of the ice cloud particle size from a factor of 2 to ±25%, the climate sensitivity uncertainty is reduced by 60% [Wang et al. 2020]. This study further demonstrates a smart observing scheme in which a radar targets the deep convective clouds based on information collected by lookahead radiometers [Swope et al. 2021]. Together, our study shows a pathway towards a better quantification of ice cloud radiative effects to constrain model simulations of ice cloud feedbacks and associated hydrological processes.