Changes in Clouds and the Tropical Circulation in Global Kilometer-Scale Simulations under Different Warming Patterns

Abstract One-year-long global kilometer-scale simulations with prescribed sea surface temperatures are presented that are used to study how clouds, convection, and the tropical circulation change under two different warming patterns. The warming patterns, one of which exhibits La Niña–like characteristics and the other an El Niño–like feature, are added to the historical year 2020 and derived from past observed sea surface temperatures. They contain both signatures of natural variability and climate change. Climate sensitivities distinctly differ depending on the warming pattern, mainly due to diverse changes in low clouds over the eastern tropical Pacific. These changes are connected with alterations in larger-scale circulations. Processes related to the interaction between clouds, convection, and circulation are further examined with a focus on the tropical Pacific. Better understanding those processes helps elucidate apparent discrepancies between recent observed trends over the tropical Pacific and trends simulated by low-resolution global climate models. Evidence suggests an active role of moisture dynamics in shaping low-level moist static energy anomalies over the western tropical Pacific and a positive feedback of resulting moist convection on larger-scale zonal circulations, including over the eastern Pacific subsidence region. Complementary to the global kilometer-scale simulations, the same experiments are conducted with a lower-resolution model version in which convection is parameterized. Even though climate sensitivities and the broad responses are not strongly changed, the differences in the convection-permitting experiments might still be consequential in global coupled climate simulations.