The Potential of Radiometric and Polarimetric Measurements in the Submillimeter/Millimeter and Longwave Infrared Regimes for Determining Ice Cloud Parameters

We conduct polarized vector radiative transfer simulations of ice clouds for several wavelengths for remote sensing applications in the Sub-millimeter/Millimeter (sub-mm/mm) and the Infrared (IR) atmospheric window regimes. Several high sub-mm/mm frequencies have been utilized in previous radiometric and polarimetric studies to determine their feasibility for retrieving ice cloud properties. The IR atmospheric window region has also been thoroughly investigated for their feasibility to observe ice clouds, particularly thin cirrus. However, there is a lack of studies utilizing these relatively high-frequency bands or polarimetric IR observations to infer ice cloud properties.

We perform ice cloud simulations and retrievals for various combinations of ice water path (IWP) and effective diameter (D_eff). A radiative transfer model known as ARTS (Atmospheric Radiative Transfer Model) is used to incorporate the scattering/absorption/polarization properties of ice particles to explore ice cloud characteristics. The Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 (roughened 8-column aggregates) is the primary ice particle model of choice. As a separate case, a Two-Habit Model (THM) comprising of single hexagonal columns and 8-column aggregates is another ice cloud model chosen to comprise the simulated ice clouds as a way to assess the impact of using different ice particle models on retrievals. This study demonstrates that polarized sub-mm/mm and IR (Polarization Difference – PD), sub-mm/mm brightness temperature depression (ΔT_b), and IR split-window measurements (BTD) have the potential to effectively retrieve both IWP and D_eff.