Temperature-Dependent Optical Properties of Ice Crystals in the Far-Infrared Regime

A database of temperature-dependent hexagonal ice aggregate optical properties in the far-infrared (FIR) spectrum is developed to support FIR missions, particularly the current Polar Radiant Energy in the Far InfraRed Experiment and the upcoming Far-infrared-Outgoing-Radiation Understanding and Monitoring. Based on this data set, simulations of the brightness temperatures (BTs) in the 100-667 cm-1 FIR region are conducted for an anvil-like ice cloud in a tropical atmosphere. The results show nonnegligible impact of ice cloud temperature on simulated BTs, which can be as large as 3 K due to the difference between fixed 160 or 270 K cloud temperature and the benchmark counterpart, varying in accordance with the ambient temperature profile for a cloud residing between 249.6 and 199.6 K. To enhance the accuracy of FIR radiative transfer modeling, it is recommended to incorporate temperature-dependent optical properties of ice clouds.