The Potential for Discriminating Microphysical Processes in Numerical Weather Forecasts Using Airborne Polarimetric Radio Occultations

Abstract

Accurate representation of cloud microphysical processes in numerical weather and climate models has proven challenging, in part because of the highly specialized instrumentation required for diagnosing errors in simulated distributions of hydrometeors. Global Navigation Satellite System (GNSS) polarimetric radio occultation (PRO) is a promising new technique that is sensitive to hydrometeors and has the potential to help address these challenges by providing microphysical observations that are relevant to larger spatial scales, especially if this type of observing system can be implemented on aircraft that can target heavy precipitation events. Two numerical experiments were run using a mesoscale model configured with two different microphysical parameterization schemes for a very intense atmospheric river (AR) event that was sampled by aircraft deploying dropsondes just before it made landfall in California, during the CalWater 2015 field campaign. The numerical experiments were used to simulate profiles of airborne polarimetric differential phase delay observations. The differential phase delay due to liquid water hydrometeors below the freezing level differed significantly in the two experiments, as well as the height of the maximum differential phase delay due to all hydrometeors combined. These results suggest that PRO observations from aircraft have the potential to contribute to validating and improving the representation of microphysical processes in numerical weather forecasts once these observations become available.

Calibration and validation of the Polarimetric Radio Occultation and Heavy Precipitation experiment aboard the PAZ satellite

“…The calibration of the receiving system is critical in assessing the uncertainty level of the measurement and therefore to associate geophysical quantities like rain intensity to each phase measurement . This would enable a wide range of studies and concepts taking full advantage of PRO capabilities, such as those proposed in Padullés et al (2018), Turk et al (2019), and Murphy et al (2019).…”

Benefits of a Closely-Spaced Satellite Constellation of Atmospheric Polarimetric Radio Occultation Measurements

“…Using common metrics such as geopotential height anomaly correlation scores, assimilation of these RO data into NWP models has been demonstrated to lead to an improved overall forecast predictive skill [18,19]. However, the ability of these same RO observations to capture dense vertically resolved (p, T and q) profiles in and near regions of heavy precipitation may provide insight to reveal the role of free tropospheric water vapor influencing underlying cloud-convective processes [20,21].The idea of using RO for examining the thermodynamic makeup of convective clouds is not new [22,23] and has recently been summarized [24]. In this manuscript, we describe the potential advantages of collecting time-sequential RO from a constellation (or "train") of closely spaced low Earth-orbiting satellites tracking the same transmitting GNSS satellite.…”

“…The idea of using RO for examining the thermodynamic makeup of convective clouds is not new [22,23] and has recently been summarized [24]. In this manuscript, we describe the potential advantages of collecting time-sequential RO from a constellation (or "train") of closely spaced low Earth-orbiting satellites tracking the same transmitting GNSS satellite.…”

Microwave single-scattering properties of non-spheroidal raindrops

“…The specific differential phase K dp is a measure of the difference in attenuation between the vertical and horizontal polarization in a unit volume. It is therefore sensitive to non-spherical particles and useful for radio occultation retrievals of rain and ice particles (Murphy et al, 2019). The K dp differences between the Chebyshev and spheroid models are small however.…”