[A-AS08] Multiple scale structure and their interactions in Asian monsoon system

[AAS08-01] Impact of accumulation of high moist static energy air mass on the Asian summer monsoon system

*Terao Toru¹, Fumie Murata², Yusuke Yamane³, Masashi Kiguchi⁴, Azusa Fukushima⁵, Masahiro TANOUE⁶, Hideyuki Kamimera⁷, Taiichi Hayashi⁸ (1.Faculty of Education, Kagawa University, 2.Faculty of Science and Technology, Kochi University, 3.Faculty of Education, Tokoha University, 4.Institute for Future Initiatives, The University of Tokyo, 5.Faculty of Humanity, Kobe Gakuin University, 6.Center for Global Environmental Research, National Institute for Environmental Studies, 7.National Research Institute for Earth Science and Disaster Prevention, 8.Center for Southeast Asian Studies, Kyoto University)

Keywords:convective quasi-equilibrium, moist static energy, boundary layer, Asian monsoon, Bay of Bengal, diurnal variation

Asian summer monsoon system is characterized by midlatitude significant atmospheric heating over the relatively high latitudinal region associated with the Eurasian Continent and Tibetan and Iranian Plateaus. Recently, essential roles of the high moist static energy airmass (HMSEAM) accumulated over the lower troposphere over the Asiatic region have been recognized under the cencept of the convective quasi-equilibrium (CQE) theory. It was shown that the accumulation of HMSEAM correspond with the abrupt onset of the Asian monsoon. The onset process can be recognized as a regime shift of the atmospheric circulation. This paper propose a conceptual model to understand the establishment of the Asian monsoon system. It focused on the accumulation of the lower tropospheric HMSEAM, and tranportation of HMSEAM to the upper troposphere through the active convection. It accumulated as the high dry static energy airmass (HDSEAM), and pushes the isentropic surface down, to make the tropospheric heating over the subtropical region of Eurasia-Pacific region. In the present study, utilizing the high spatio-temporal resolution ERA5 dataset, we diagnose the behavior of HMSEAM and HDSEAM over the Asian region, to describe the climatological thermodynamic structure, onset and withdrawal processes, and intraseasonal variability of Asian monsoon system. We also focuse on the diurnal variation of the HMSEAM and HDSEAM, which plays significant role in the lower troposphere. The distribution of the amount of HMSEAM is highly asymmetric both between summer and winter season, and Northern and Southern hemisphere. The high amount of HMSEAM is observed only over the Asiatic region and in summer season. We identified the importance of the lower tropospheric hot and humid air flow over the Bay of Bengal, which contain highest HMSEAM density. We compared ERA5 analysis with local observations over Northeastern Indian subcontinent. The appearance of this HMSEAM air flow correspond with the abrupt monsoon onset. Upper tropospheric HDSEAM is confined in the strong anti-cyclonic circulation, Tibetan High, and shows intraseasonal variability. Using the TRMM / GPM dataset, we can diagnose the radiative and convective heating processes separately for clear sky (rain and convection free) region, and rainy region. From this perspective, we would like to discuss how we can contribute to the AsiaPEX research community.