Monsoon

About: Monsoon is a research topic. Over the lifetime, 16087 publications have been published within this topic receiving 599888 citations.

Simulating the evolution of the Asian and African monsoons during the past 30 Myr using an atmospheric general circulation model

Abstract: At geologic timescales, many proxy data suggest a contrasting evolution of Asian and African monsoons since the Oligocene. The Asian summer monsoon increases drastically around 8 Ma, whereas the African summer monsoon gradually weakens during the Miocene. Using an atmospheric general circulation model, we simulate most of the spatial evolutions of both monsoons only accounting for the changes of paleogeography, including continental drift, orogeny, and sea level change. The paleogeographic changes modify drastically the climate over central and southern Asia between the Oligocene and the present. The retreat of an epicontinental sea warms central Eurasia in summer. The heating of this area and the uplifts of the Tibetan plateau and of the Himalayas deepen the Asian low-pressure cell and displace it northwest. This then shifts precipitation from Indochina toward the southern flank of the Himalayas. This is in good agreement with proxy data. Therefore our modeling studies support a shift and a strengthening of the Asian monsoon during the late Tertiary rather than a real "onset". We suggest that the increase in seasonal precipitation and the strengthening of the number of days with heavy rainfall over the Himalayas from 30 Ma to the present may be of critical importance to explain the long-term evolution of physical erosion of this area. We also investigate the respective impact of the Paratethys shrinkage and of the Tibetan plateau uplift through sensitivity experiments and prove that the Paratethys retreat plays an important role in monsoon evolution. The northward drift of the African continent confines summer monsoon precipitation to a thin belt which favors the stretching of the subtropical desert, in good agreement with data. We finally show that during the Oligocene, the African and Asian monsoon systems are clearly separated by the Tethys seaway. The closure of this seaway and the evolution of the Asian monsoon induce a connection between both monsoon systems in the low and middle troposphere.

Relations of Water Vapor Transport from Indian Monsoon with That over East Asia and the Summer Rainfall in China

Abstract: A diagnostic study is made to investigate the relationship between water vapor transport from Indian monsoon and that over East Asia in Northern summer. It is found that water vapor transport from Indian monsoon is inverse to that over East Asia. More (less) Indian monsoon water vapor transport corresponds to less (more) water vapor transport over East Asia and less (more) rainfall in the middle and lower reaches of the Yangtze River valley. The Indian summer monsoon water vapor transport is closely related to the in tensity of the western Pacific subtropical high in its southwestern part. The stronger (weaker) the Indian sum mer monsoon water vapor transport, the weaker (stronger) the western Pacific subtropical high in its southwestern part, which leads to less (more) water vapor transport to East Asia, and thus less (more) rain fall in the middle and lower reaches of the Yangtze River valley. Analysis of the out-going longwave radia tion anomalies suggests that the convective heating anomalies over the Indian Ocean may have significant impact not only on the Indian monsoon, but also on the East Asian monsoon.

Possible Linkage between the Monsoon Trough Variability and the Tropical Cyclone Activity over the Western North Pacific

Abstract: The present study investigates the influence of the monsoon trough (MT) on the interannual variability of tropical cyclone (TC) activity over the western North Pacific during July–November for the period 1979–2007. It is shown that the TC activity is closely related to the MT location. During the years when the MT extends eastward (retreats westward), more (less) TCs form within the southeastern quadrant of the western North Pacific. Such a relationship can be explained by the changes in large-scale environmental factors associated with the movement of the MT. An eastward extension of the MT coincides with warmed ocean surface, enhanced convection, increased relative humidity in the lower and midtroposphere, reduced vertical shear of zonal wind, intensified upper-level divergence, and low-level anomalous cyclonic vorticity over the southeast quadrant of the western North Pacific. These conditions associated with the eastern extension of the MT are favorable for TC genesis, while those associated w...