Interpretation of the Precipitation Structure Contained in Polarimetric Radio Occultation Profiles Using Passive Microwave Satellite Observations

Observationally, a major source of uncertainty in evaluation of climate models arises from the difficulty in obtaining globally distributed, fine-scale profiles of temperature, pressure, and water vapor that probe through convective precipitating clouds, from the boundary layer to the upper levels of the free troposphere. In this manuscript, a 2-yr analysis of data from the Radio Occultations through Heavy Precipitation (ROHP) polarimetric radio occultation (RO) demonstration mission onboard the Spanish Paz spacecraft is presented. ROHP measures the difference in the differential propagation phase delay (Df) between two orthogonal polarization receive states that is induced from the presence of nonspherically shaped hydrometeors along the Global Navigation Satellite System (GNSS) propagation path, complementing the standard RO thermodynamic profile. Since Df is a net path-accumulated depolarization and does not resolve the precipitation structure along the propagation path, orbital coincidences between ROHP and the Global Precipitation Measurement (GPM) constellation passive microwave (MW) radiometers are identified to provides three-dimensional precipitation context to the RO thermodynamic profile. Passive MW-derived precipitation profiles are used to simulate the Df along the ROHP propagation paths. Comparison between the simulated and observed Df are indicative of the ability of ROHP to detect threshold levels of ray-path-averaged condensed water content, as well as to suggest possible inferences on the average ice-phase hydrometeor nonsphericity. The use of the polarimetric RO vertical structure is demonstrated as a means to condition the lower-tropospheric humidity by the topmost height of the associated convective cloud structure. SIGNIFICANCE STATEMENT: The Radio Occultations and Heavy Precipitation (ROHP) experiment, orbiting onboard the Spanish Paz satellite since May 2018, has demonstrated the polarimetric RO capability to simultaneously detect the presence of precipitation alongside standard RO thermodynamic processing yielding temperature, pressure, and moisture profiles. In this investigation, ROHP data are simulated by using precipitation profiles estimated from near-simultaneous passiveMWsatellite data. Comparisons between simulated and actual ROHP data reveal the ability of the polarimetric RO signal to detect threshold levels of ray-path-averaged condensed water content, to infer the average ice-phase hydrometeor nonsphericity, and to serve as a proxy for conditioning the lower-tropospheric humidity by the topmost height of the associated convective cloud structure.