The origin of Asian monsoons: a modelling perspective

• Published in: Climate of the Past
• Main Authors: Tardif, Delphine, Fluteau, Frédéric, Donnadieu, Yannick, Le Hir, Guillaume, Ladant, Jean-Baptiste, Sepulchre, Pierre, Licht, Alexis, Poblete Gómez, Fernando, Dupont-Nivet, Guillaume
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Gesellschaft MHB 2020
• Subjects: Earth system model; Early eocene; Tibetan plateau; Climate-change; Oligocene climate; Summer monsoon; Global monsoon; Ice-sheet; Part I; China; Indian; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-16-847-2020; https://repositorio.uchile.cl/handle/2250/175598

The Cenozoic inception and development of the Asian monsoons remain unclear and have generated much debate, as several hypotheses regarding circulation patterns at work in Asia during the Eocene have been proposed in the few last decades. These include (a) the existence of modern-like monsoons since the early Eocene; (b) that of a weak South Asian monsoon (SAM) and little to no East Asian monsoon (EAM); or (c) a prevalence of the Intertropical Convergence Zone (ITCZ) migrations, also referred to as Indonesian-Australian monsoon (I-AM). As SAM and EAM are supposed to have been triggered or enhanced primarily by Asian palaeogeographic changes, their possible inception in the very dynamic Eocene palaeogeographic context remains an open question, both in the modelling and field-based communities. We investigate here Eocene Asian climate conditions using the IPSL-CM5A2 (Sepulchre et al., 2019) earth system model and revised palaeogeographies. Our Eocene climate simulation yields atmospheric circulation patterns in Asia substantially different from modern conditions. A large high-pressure area is simulated over the Tethys ocean, which generates intense low tropospheric winds blowing southward along the western flank of the proto-Himalayan-Tibetan plateau (HTP) system. This low-level wind system blocks, to latitudes lower than 10 degrees N, the migration of humid and warm air masses coming from the Indian Ocean. This strongly contrasts with the modern SAM, during which equatorial air masses reach a latitude of 20-25 degrees N over India and southeastern China. Another specific feature of our Eocene simulation is the widespread subsidence taking place over northern India in the midtroposphere (around 5000 m), preventing deep convective updraught that would transport water vapour up to the condensation level. Both processes lead to the onset of a broad arid region located over northern India and over the HTP. More humid regions of high seasonality in precipitation encircle this arid area, due to the prevalence of the ...