The impact of north tropical Atlantic sea surface temperature anomalies in the ensuing spring of El Niño on the tropical Indian Ocean and Northwest Pacific

Abstract

AbstractBased on the fifth generation reanalysis of European Centre for Medium–Range Weather Forecasts (ECMWF), Hadley Centre sea ice and sea surface temperature data, and ENSEMLES hindcasts, the impact of north tropical Atlantic (NTA) sea surface temperature (SST) anomalies in the ensuing spring of El Niño on the tropical Indian Ocean (TIO) and Northwest Pacific (NWP) is investigated using composites, singular value decomposition, and correlations. The anomalous SST warming in the NTA region in the decay spring of El Niño leads to a Gill‐type response of the overlying atmosphere in spring–summer. The Kelvin wave over the TIO stimulated by the NTA warming causes the anomalous easterlies in the regions of TIO and NWP, thereby the strengthening of the NWP subtropical anticyclone (NWPSA). The NTA SST warming also forces a local ascending motion, leading to a downward branch over the NWP region. This descent gives rise to the TIO‐NWP low‐level easterly anomalies and an intensification of the NWPSA. The anomalous easterly weakens the background southwesterly monsoon, accompanied by the increased atmospheric boundary layer specific humidity caused by the troposphere warming, suppressing upward latent heat fluxes, finally contributing to the North Indian Ocean (NIO) warming in summer. This indicates that the second warming of the NIO region in the following summer of El Niño may be partially attributed to the NTA warming in the ensuing spring of El Niño. This study improves our understanding of the impact of the NTA SST anomalies in the El Niño decay spring on the TIO and NWP regions, and emphasizes the importance of the NTA region in the pantropical inter‐basin interactions.