Summertime warm extremes over the Indochina Peninsula linked to the tropical Indian Ocean tripole mode

Abstract A new air–sea coupled variability of the sea surface temperature anomalies over the tropical Indian Ocean was observed and named as the tropical Indian Ocean tripole (IOT) in terms of its unique tripole pattern in recent studies, which peaks in boreal summer. This study found that the interannual variations of the warm extremes over the Indochina Peninsula during boreal summer can be affected by the IOT. When the positive IOT events occur, two cross-equatorial airflows are induced over the eastern and western tropical Indian Ocean, reinforcing the anomalous warm-humid westerly wind over the northern Indian Ocean. The water vapor convergence is strengthened and the anomalous middle-lower level negative geopotential height is formed over the Indochina Peninsula, leading to the local enhanced ascending motion and surplus precipitation, strongly supported by both observations and numerical simulation. These circulation anomalies favor the reduction of the local surface temperatures through increasing the cloud cover and hindering the downward solar radiation, further declining the warm extremes days. Improving to understand the warm extreme variations over the Indochina Peninsula and its impact factors is of great significance for local industrial development, agricultural production and human health.