Sensing Horizontally Oriented Frozen Particles with Polarimetric Radio Occultations aboard PAZ: Validation Using GMI Coincident Observations and Cloudsat a-Priori Information

The sensitivity of PAZ’s Polarimetric Radio Occultation observations to horizontally oriented frozen particles is as- sessed using coincident measurements from the Global Pre-5 cipitation Mission (GPM) core satellite’s radiometer (GMI) and ancillary information from Cloudsat. The difference be- tween the horizontal and vertical polarization of the GMI ob- served radiances at 166 GHz, indicative of horizontally ori- ented particles, is compared with the PAZ differential phase10 shift observations. A clear positive trend is observed, ex- hibiting a good correlation between the two observations. The radiometer absolute observations and polarization dif- ferences are then used to build a look up table of ice water content vertical profiles, using coincident observations be-15 tween GPM and Cloudsat. The vertical profiles of ice water content, along with the information of the radiometric po- larization differences and some simple assumptions are used to simulate the expected PAZ differential phase shift obser- vations. The validation with the PAZ and GPM coincident20 measurements shows a high correlation between the simu- lated and observed differential phase shift, therefore proving the sensitivity of polarimetric radio occultations to horizon- tally oriented frozen particles. These results demonstrate that polarimetric radio occultations can not only sense the precip-25 itation near the surface (original goal of the mission), but also the frozen particles near and well above the freezing level, providing additional detail of the cloud vertical structure.