Pan-Asian monsoon and its definition, principal modes of precipitation, and variability features

Here we propose a new concept, the Pan-Asian monsoon, and use empirical orthogonal function (EOF) analysis and linear regression approach to define it and to analyze the monsoon-related rainfall variability. The Pan-Asian monsoon is referred to as the monsoon occurred over the great region (60A degrees E-140A degrees E, 10A degrees S-35A degrees N), consisting of the Indian monsoon, Southeast Asian monsoon, East Asian monsoon, and Western North Pacific monsoon. The Pan-Asian monsoon region is the principal region of the summer rainfall over the Asian-Pacific monsoon region and is also water vapor channel connecting several Asian-Pacific sub-monsoon systems. The first EOF mode of the Pan-Asian monsoon precipitation (PAMP_F) shows a meridional tripole pattern with more (less) rainfall zonal belt over the Bay of Bengal (BOB), the Indo-China Peninsula, South China, the South China Sea (SCS), Philippines and the Philippine Sea, and less (more) rainfall on both sides. The first rainfall mode is associated with the weakened Somali cross-equatorial flows, enhanced southerly over the eastern coast of Australia, and strengthened westerly over the tropical Pacific. The first EOF rainfall mode shows a close relationship with the simultaneous El Nio-Southern Oscillation (ENSO) and Pacific South America (PSA). The preceding spring and simultaneous summer Antarctic Oscillation (AAO) in the western Hemisphere (AAO in Pacific) has a connection with the first summer rainfall mode of the Pan-Asian monsoon. Because the main influence factors are over the Pacific, the first rainfall mode is named as the Pacific mode. The second mode of the Pan-Asian monsoon precipitation (PAMP_S) shows a dipole pattern from northeast to southwest, which is associated with the weakened Somali cross-equatorial flows, enhanced easterlies over the Maritime Continent, and weak easterly over the tropical Pacific. The second rainfall model has a close relationship with the atmospheric convection activity and the sea surface temperature variability over the Maritime Continent and South Indian Ocean. Because the influence factors are mainly over the eastern Hemisphere, the second rainfall mode of the Pan-Asian monsoon is named as the Indian Ocean mode.