Satellite-Based Estimation of Cloud Top Radiative Cooling Rate for Marine Stratocumulus

Cloud top radiative cooling rate (CTRC) is the leading term in the energy budget of a marine boundary layer capped by stratocumulus. It plays a significant role in the formation, evolution, and maintenance of the stratocumulus cloud system. This study demonstrates the feasibility of estimating the CTRC, with high accuracy, from passive satellite data only. The estimation relies on a radiative transfer model with inputs from satellite-retrieved cloud parameters in combination with reanalysis sounding that is revised, in a physically coherent way, by satellite data. The satellite-based estimates CTRC agree with ground-based ones to within similar to 10%. The high accuracy largely benefits from the good capability of satellite data in constraining parameters of most influence to the CTRC such as free-tropospheric sounding, cloud top temperature, and cloud optical depth. Applying this technique, we generate a climatology of CTRC during summer over the Southern Hemisphere tropical and subtropical oceans. Plain Language Summary Everything cools radiatively. For marine low-lying clouds, the radiative cooling at the cloud top makes the ambient air heavier and sink and, equivalently, the underlying air lighter and float. This forms a vertical mixing process that brings moisture from the underlying sea surfaces upward to feed the clouds, preventing them from dissipation. Therefore, the cloud top radiative cooling rate (CTRC) is one of the most important variables for understanding the behaviors of marine low clouds and their interactions with the Earth's climate system. Despite its significance, the CTRC has rarely been retrieved, with good accuracy, from satellite, the only observational tool that offers global coverage. This study fills this gap by developing a novel remote sensing method to estimate the CTRC from satellite data at an accuracy of 10%. This new capability will help advance our understanding of many poorly understood behaviors of marine low clouds over regions with scarce observations (e.g., middle- and high-latitude oceans). More broadly, the new remote sensing products will improve the accuracy with which the future climate is predicted because our climate system is sensitive to the low cloud mixing process that is regulated by the CTRC.