Coupled Ocean/Atmosphere Impacts to the Satellite Detection of Nocturnal Maritime Low Clouds

Accurate observations of maritime low clouds are important for transportation interests via both air and sea, improving our understanding of boundary layer processes, and measuring Earth’s radiation budget. The nighttime maritime low cloud extent is often determined in meteorological satellite imagery using the brightness-temperature difference between the longwave infrared (e.g. 11 µm) and shortwave infrared (e.g. 3.9 µm) window bands. However, this nighttime low-cloud detection can be contaminated with false low cloud (FLC) signals caused by the slight differences in atmospheric contribution between these two infrared window bands. This most commonly occurs in regions of warm and moist air over localized cold regions of water.

This research introduces a novel method for estimating global patterns of FLCs. We use radiative transfer equations applied to numerical model data to approximate the strength and extent of FLC signals. The results reveal a seasonal variability of these errors in addition to highlighting geographical regions more prone to the overstatement of low cloud extent. Insights from this research can help forecasters and researchers identify regions and conditions where algorithm refinement or additional sensor assessment may be needed for accurate assessment of nighttime low cloud detection. We also present preliminary results demonstrating that FLC analysis can be extended to continental regions, which is complicated by surface types with emissivities unique to each band. Finally, we look ahead to future sensor capabilities and theorize about techniques applicable to new sensors which could help mitigate these errors.