Evaluating the Benefits of Using Longwave Infrared and Millimeter/Sub-millimeter Bands to Explore Ice Cloud Characteristics Through Polarized Vector Radiative Transfer Simulations

Abstract

A comprehensive study on evaluating the usefulness of relatively high frequency millimeter/sub-millimeter (mm/sub-mm) bands (greater than 150 GHz) and longwave infrared (LWIR) atmospheric window bands to infer ice cloud properties will be conducted for this thesis. A sizable amount of mm/sub-mm bands have been considered from radiometric and polarimetric studies to be useful for observing ice clouds with lower mm/sub-mm wavelengths (higher frequencies) being able to observe even optically thin cirrus. The LWIR atmospheric window has been thoroughly investigated for their feasibility to also observe ice clouds, especially optically thin cirrus. However, there have not been many studies conducted using several of these relatively high frequency bands or polarimetric LWIR observations to infer ice cloud properties. There have also not been many studies using simulated ice clouds composed of the latest ice particle habit mixtures and single-scattering properties. The single-scattering property databases have considered dependencies such as surface roughness and ambient temperature. This thesis will be focusing on performing simulations on ice clouds using the wavelengths of 440.87 μm (680 GHz), 707.06 um (424 GHz), 922.44 um (325 GHz), 1362.69 um (220 GHz), and 1638.21 um (183 GHz) for the mm/sub-mm regime and 8.6 um, 10.6 um, and 12 um wavelengths of the IR regime. The Atmospheric Radiative Transfer Model (ARTS) will be used to conduct the simulations for 1D atmospheres corresponding to the tropical region. The ice cloud simulations were performed for combinations of ice water path (IWP) and effective diameter (Dvevfvf). IWP and Dvevfvf look-up tables (LUT) were created in order to evaluate the feasibility of retrieving these values. These LUTs were then used to retrieve IWP and Dvevfvf for the 1D vertically heterogeneous ice cloud scenarios which will be using 3D ice clouds produced by Cloudgen – a stochastic cloud generator. The brightness temperature (Tvb) parameters that were used to infer the cloud properties are the split-window technique (BTD), brightness temperature depression relative to clear-sky (Tvb), and the polarization difference (PD).