Two causes of the 2004 hot summer in East Asia

Abstract

Japan and neighboring regions experienced record-breaking hot weather during the 2004 summer. Two kinds of teleconnection patterns are considered to account for the anomalous anticyclone over these regions. One, originating from the western North Pacific (WNP), was responsible for the anomalous hot weather during the second half of June. The other, embedded in the mid-latitude Asian Jet, was discernable during early July. The Asian summer monsoon (ASM) was stronger than normal, which was consistent with the warmer Asian land surface in the pre-monsoon season. During the boreal spring, enhancement of convection occurred over the tropical Indian Ocean (IO) and WNP. These anomalous tropical heat sources are responsible for anticyclonic circulation extending over the Asian continent and resultant increase in the land surface temperature due to suppression of rainfall. The enhancement of thermal gradient between the Asian continent and the adjacent oceans are consistent with the strong ASM. An east-west asymmetric air-sea heat exchange across South China Sea is newly proposed to explain the connection between the ASM intensity and the localized convection to the east of the Philippines in June.