Spatial Controls of Lower Tropospheric Stability

Abstract

Marine low clouds play a crucial role in Earth's radiation budget. These clouds efficiently reflect sunlight and drive the magnitude and sign of the global cloud feedback. Nevertheless, the evolution of shallow cloud decks over the last decades is not well understood. A dominant control of this low cloud cover is the lower tropospheric stability, quantified by the estimated inversion strength (EIS). We quantify how regional EIS depends on local and remote surface temperature, revealing the dynamics controlling the shallow cloud characteristics on annual timescales. We find that global EIS increases with warming in tropical regions of ascent and decreases with warming in regions of descent. In addition to the West Pacific Warm Pool, the Atlantic convection regions and the central Pacific are important predictors. Focusing on subtropical ocean upwelling regions in different ocean basins, where the low cloud decks reside, EIS increases with a fairly complex pattern of remote warming and decreases with local warming. The spatial relationship between surface temperature and EIS is robust across climate models and reanalyses, allowing us to constrain the spread in historical EIS trend estimates. In the Southeast Pacific, historical surface temperature decreased, but we attribute the observed EIS increase since 1980 entirely to remote warming. Our results challenge the canonical dominance of the West Pacific Warm Pool in controlling low cloud feedbacks in the eastern Pacific and give mechanistic insights into the spatial dependence of radiative feedbacks on surface temperature patterns.