Synergistic Use of Far- and Mid-Infrared Spectral Radiances for Satellite-Based Detection of Polar Ice Clouds Over Ocean

• Main Authors: Peterson, Colten A., Huang, Xianglei, Chen, Xiuhong, Yang, Ping
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Copernicus ClimateChange Service (C3S) Climate Data Store (CDS) 2022
• Subjects: Atmospheric and Oceanic Sciences; Science; Arctic
• Online Access: https://hdl.handle.net/2027.42/172281; https://doi.org/10.1029/2021JD035733

Cloud phase is an important factor affecting cloud contributions to the polar energy budget. Brightness temperature differences (BTDs) between two mid-infrared (mid-IR) spectral channels are commonly used in satellite remote sensing to determine the cloud phase, but the mid-IR has limitations for cloud phase determination in polar regions. This study explores the synergy between the far- and mid-IR for ice cloud phase determinations over polar oceans. A far-IR BTD test (BTD449-521) is developed based on the spectral variations of both ice cloud scattering and absorption properties in the far-IR “dirty window” region (400–600 cm−1 or 16.7–25 μm). Synthetic IR radiances at 1 cm−1 spectral resolution are generated using ERA5 reanalysis data for both polar regions. A subset of these spectra is used to compare the ice phase determination skill of the far-IR test with an “AIRS-Like” mid-IR BTD test (BTD1231-960) for combinations of effective ice particle diameter (Deff_ice), cloud optical depth (COD), and cloud top pressure (CTP). The far-IR test is performing better for ice clouds with the smallest Deff_ice that we have studied (20 μm) due to the sensitivity of far-IR scattering to ice particle size. The mid-IR test was either comparable to or more successful than the far-IR test for ice clouds with large particle sizes. For all Deff_ice, increasing COD leads to enhanced far-IR BTD signals due to stronger multiple scattering in the far-IR than in the mid-IR. Overall, the variations in far-IR and mid-IR BTD test performance are strongly sensitive to Deff_ice, followed by COD and CTP.Key PointsFar-infrared (IR) scattering and absorption can be used together for ice cloud detection in passive remote sensing of polar regionsThe far-IR ice phase test is most useful for ice particle effective diameters less than 40 µmBoth the far-IR and mid-IR ice phase tests are more sensitive to ice particle size than to cloud top pressure and optical depth Peer Reviewed ...