Responses of Lower Stratospheric Water Vapor to Regional Sea Surface Temperature Changes

The variability of stratospheric water vapor (SWV) plays a crucial role in stratospheric chemistry and Earth ' s energy budget, strongly in fl uenced by sea surface temperature (SST). In this study, we systematically investigate the response of lower-SWV (LSWV) to regional sea surface temperature changes using idealized SST patch experiments within a climate model. The results indicate that LSWV is most sensitive to tropical sea surface temperature, with the strongest response occurring in late autumn and early winter. Warming of the tropical Indian Ocean and western Paci fi c (WP) leads to stratospheric drying, while warming of the tropical Atlantic (TA) and eastern Paci fi c results in stratospheric moistening. The drying impact on LSWV due to warming in the western Paci fi c Ocean exceeds the wet effect in the eastern Paci fi c Ocean by approximately 60%. The variations in tropical SST in fl uence LSWV by modulating the temperature at the tropical tropopause layer, especially over the Indo-Paci fi c warm pool through Matsuno - Gill responses. Furthermore, the response of LSWV to tropical SST changes exhibits nonnegligible nonlinearity, which indicates the importance of nonlinearity in determining the LSWV response to global surface warming. SIGNIFICANCE STATEMENT: In this study, we explore how changes in the temperature of the ocean ' s surface can affect the amount of water vapor in the stratosphere, a layer of Earth ' s atmosphere. Understanding this relationship is important because water vapor in the stratosphere can in fl uence both our climate and the chemistry of the atmosphere. Using a climate model, we found that water vapor in the lower stratosphere is especially responsive to temperature changes in tropical ocean regions. Speci fi cally, when the Indian Ocean and the western Paci fi c get warmer, the stratosphere tends to get drier. On the other hand, warming in the Atlantic and eastern Paci fi c leads to more moisture in the stratosphere. The way these changes add up is complex and not simply a sum of individual parts, especially in tropical warm pool regions. Our fi ndings have implications for how we understand and predict the impacts of climate change on stratospheric water vapor.