Sensitivity to the vertical structure of hydrometeors using Polarimetric RO
Authors: Paz Carracedo Antía , Padullés Rulló Ramon , Cardellach Galí Estel 
Published: March 2024

The Global Navigation Satellite System (GNSS) Radio Occultation (RO) technique sounds the atmosphere providing high quality vertical profiles of the thermodynamics on a global scale. The Polarimetric RO (PRO) technique is an extension of traditional RO that retrieves precipitation information in addition to the standard thermodynamic products. The technique has been demonstrated aboard the Spanish Low Earth Orbiter (LEO) PAZ, as part of the Radio Occultation and Heavy Precipitation (ROHP) experiment led by the Institut de Ci&#232;ncies de l&#8217;Espai (ICE-CSIC/IEEC) in collaboration with NOAA, UCAR, and NASA/Jet Propulsion Laboratory. This mission enables the investigation of intense precipitation events and their associated meteorological conditions by retrieving atmospheric thermodynamic variables and offering insights into the vertical structure of precipitation.The determination of the vertical structure is accomplished through the observable differential phase shift (&#916;&#934;), defined as the difference in the accumulated phase delay between the two linear polarizations (H-V) as function of the tangent point of the PRO rays. During intense precipitation events certain challenges arise in obtaining high-quality measurements of thermodynamic parameters due to signal attenuation. However, the PRO technique is less affected by attenuation, presenting an opportunity to obtain high-resolution thermodynamic profiles and information about the vertical structure of hydrometeors, simultaneously.Validation of the PRO technique with two-dimensional data has been successfully conducted using the Global Precipitation Measurement (GPM) mission gridded products (like Integrated Multi-satellitE Retrievals for GPM, IMERG). In this analysis, vertical structure validation has been performed using data from the Next Generation Weather Radars (NEXRAD), a network of dual-polarized Doppler radars operating at the S-band, covering the entire United States territory. By exploiting the dual-polarization capabilities of NEXRAD, a comparison of the specific differential phase shift (KDP) structures with the PRO observable &#916;&#934; aids in examining similarities and differences in the detection of precipitation between the two instruments.Furthermore, to explore the sensitivity of the PRO technique to various types of hydrometeors, the Weather Research and Forecasting-Advanced Research Weather Model (WRF-ARW) is employed for a comparative analysis, focusing on hydrometeor water contents. The variation of the model&#8217;s microphysics parametrizations allows for the study of the PRO technique&#8217;s sensitivity based on different assumptions about hydrometeors. Changes in these parametrizations impact total precipitation, vertical structure of hydrometeors, cloud properties, energy budget, spatial structure, among others. The validation and sensitivity study of the PRO technique will contribute to an enhanced understanding of the observables obtained and will offer insights into the phenomena characterizing intense precipitation situations.