Spaceborne Mid- and Far-infrared Observations Improving Nighttime Ice Cloud Property Retrievals

Two upcoming missions will provide systematic spaceborne observations of upwelling far-infrared spectra. The accuracy of ice cloud property retrievals using combined spaceborne mid-to-far-infrared (MIR–FIR) measurements is examined, focusing on retrieval biases and uncertainties. Retrieval simulations demonstrate that combined MIR–FIR measurements enhance sensitivity to ice cloud properties for providing an alternative means for retrieving this information at night. However, the temperature dependence of the ice refractive index and relevant ice particle shape models need to be incorporated into the retrieval procedure to avoid systematic retrieval biases in cloud optical thickness and effective particle radius. Furthermore, prior information of subpixel cloud fractions is essential to mitigate substantial systematic retrieval biases due to inconsistent subpixel cloud fractions.