Seasonal Diversity of Indo-Pacific Warm Pool Volume Expansion: The Role of Climatological Subsurface Temperature Patterns

Abstract

Abstract The Indo-Pacific warm pool (IPWP) expansion under global warming has huge impacts on global climate. While recent studies have revealed the seasonal diversity of IPWP surface expansion and its climate impacts, understanding the changes in seasonality of the IPWP volume is of greater importance, especially given the crucial role of subsurface ocean in climate systems. Here, we find a significant difference in IPWP volume expansion rates across seasons from 1950–2020. The expansions of IPWP volume during boreal autumn and winter are faster compared to boreal spring and summer. This consequently weakens the seasonality of IPWP volume, particularly in the upper-layer, with a significant decreasing trend of -0.54×107 km3/decade. Further analyses suggest that this seasonal diversity in IPWP volume expansion is primarily caused by the seasonality of capacity for IPWP volume change, which is determined by the seasonal climatological Indo-Pacific subsurface temperature pattern. Furthermore, these variations may exert diverse impacts on atmospheric circulation and East Africa precipitation in rainy seasons. Specifically, the larger autumn IPWP expansion trend enhances ascending motion and precipitation over East Africa during short rains (October-November-December), while the relatively slower spring IPWP expansion leads to a decrease in rainfall during long rains (March-April-May). This study highlights the primary role of climatic subsurface Indo-Pacific Ocean temperature properties on the change of IPWP volume seasonality, which may have crucial effects on the precipitation in East Africa rainy seasons, and may hold important clues about how greenhouse warming affect oceanic seasonal cycle.