Sensitivity Analysis of Radiometric and Polarimetric Properties from Simulated Ice Clouds of IR and Sub-mm/mm Bands

Radiometric and polarimetric calculations of simulated ice clouds composed entirely of aggregate particles are conducted for several wavelengths in the IR and Sub-mm/mm ranges as part of NASA’s SWIRP (Compact Submm-Wave and LWIR Polarimeters for Cirrus Ice Properties) project. The scattering/absorption/polarization properties of the aggregates that were calculated at the selected bands before this study are incorporated into a radiative transfer model, ARTS (Atmospheric Radiative Transfer Model) in order to explore ice cloud characteristics in 1D spherical atmospheres.

We will focus on simulated cirrus clouds that are made to be homogeneous and composed of monodisperse ice particles eventually transitioning to homogeneous cirrus clouds containing a gamma distribution of ice particle sizes for slightly realistic cases. Simulations are performed for combinations, specific ice water path (IWP), effective diameter (D_eff), and viewing zenith angle values within a tropical atmosphere. The sensitivity analysis for these cases will primarily focus on polarization differences (PD), brightness temperature depression (ΔTb), and variations of cloud optical thickness for respective zenith angles. There will also be comparisons of the calculations among the observed wavelengths.

For Sub-mm/mm bands, preliminary PD results for a homogeneous, monodisperse cirrus cloud case shows that for 441µm (680GHz) there is sensitivity to ice scattering with PD peaking at IWP > 400 g/m² and D_eff < 200µm. 1363µm (220 GHz) results indicates a less PD peak magnitude occurring at lower IWPs (> 150 g/m²) and higher D_effs (> 300 μm).