Toward Improving Ice Cloud Microphysics Retrievals For Sub-millimeter Polarimeter-Radiometers

Abstract. Ice cloud microphysical properties, such as phase, shape, size and density, introduce significant uncertainties and biases that affect our understanding of how clouds influence weather and climate. The upcoming spaceborne sub-millimeter radiometers are expected to help in reducing the ice microphysics induced uncertainties in observations. Yet our knowledge about ice microphysics in this spectrum is still limited, and comparison/validation work is still sparse.

This paper delivers a comprehensive cross-instrument closure study using active, passive remote sensing and in-situ cloud probe measurements collected during the NASA’s IMPACTS field campaign. Through combined use of two radars, one lidar and in-situ cloud probe measurements, a comprehensive best reference "truth” is generated, which is then used to validate collocated sub-mm CoSSIR radiance measurements. We found out that only through a realistic vertical hydrometeor type classification that all types of measurements can reach a closure with minimal discrepancies between simulations and observations, which is critical for generating high-quality retrievals for frozen hydrometeors.

We further present a comprehensive exploration of the scientific merit of polarimetric measurements in improving frozen hydrometeor microphysics retrievals. For the first time, we can validate previous theoretical predictions that sub-mm polarimetric signals can be used to retrieve ice particle habit and size. Moreover, we find it is possible to differentiate detailed vertical structure of hydrometeor types using both polarimetric and radiance measurements. This paper paves concrete steps in assuring timely delivery of high-quality science products for the sub-mm radiometer missions as well as possibilities of new science products beyond the mission requirements.