Constraining microphysics assumptions on the modeling of Atmospheric Rivers using GNSS Polarimetric Radio Occultations

Abstract. The Polarimetric Radio Occultation (PRO) technique enhances the standard Radio Occultation (RO) method by offering vertical profiles of precipitation structure and thermodynamic atmospheric profiles. PRO achieves this by utilizing two orthogonal polarizations—horizontal (H) and vertical (V)—to measure the differential phase shift (ΔΦ), which represents the difference in phase delay between the two of them. This study focuses on assessing the sensitivity of the PRO technique to the vertical structure of hydrometeors under different microphysical assumptions. To explore this sensitivity, simulations were conducted using the Weather Research and Forecasting (WRF) model, with particular attention to the effects of different microphysics schemes on the simulated ΔΦ. The study also incorporated the Atmospheric Radiative Transfer Simulator (ARTS) particle database to characterize hydrometeors based on their scattering properties. Atmospheric Rivers (ARs) were used as a case study. The simulated ΔΦ values were compared to GNSS-PRO observational data from PAZ and Spire satellites, providing a means to evaluate the performance of the WRF microphysics parameterizations. Combining water content information derived from WRF simulations with ARTS-based scattering parameters, the specific differential phase (K_dp) was computed for various hydrometeor types. This allowed for a detailed assessment of their contributions to the observable ΔΦ. Results indicate that the Goddard and WSM6 schemes are the ones that reproduce better the observations for most of the studied cases. Similarly, snow particle habits that yield a factor of ~0.1 between water content and K_dp are the ones that lead to a better match between the observations and simulations.