Monsoon

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

Influences of Sea Surface Temperature and Ground Wetness on Asian Summer Monsoon

Abstract: The authors have conducted a series of experiments with a general circulation model to understand the influences of sea surface temperature (SST) and ground wetness (GW) (measured by snow amount and soil moisture content) on the Asian summer monsoon. The experiments are designed to illustrate the dominant features of monsoon response to SST and GW forcings and to delineate the relative importance of each forcing function in contributing to the variability of the monsoon. Results indicate that ocean basin-scale SST anomalies exert a stronger control on the interannual variability of the monsoon compared to GW anomalies. The impact of SST anomalies on the monsoon appears nonlinear with respect to warm and cold events. The monsoon is weakened during the warm events but changes less noticeably during the cold events. The diminution of monsoon circulation associated with the warm SST anomalies is accompanied by a broad-scale reduction in water vapor convergence and monsoon rainfall. Results also indic...

Analysis of historical changes in rainfall in the Indian Himalayas

Abstract: The present study attempts to explore changes in rainfall pattern in the Indian Himalayas during 20th century using 80-year data from 30 rain gauge stations maintained by the India Meteorological Department (IMD). Modified Mann–Kendall test (MMK) was applied to detect trend, and Pettitt–Mann–Whitney (PMW) test was employed to detect possible shift. Implication of the change is discussed in terms of percentage change over mean. The results show that the most probable year of change in annual as well as monsoon rainfall in the region is 1964. There was an increasing trend upto 1964 (corroborating with all India and nearby plains), followed by a decreasing trend in 1965–1980 (exclusive to this region). In the entire region, changes are most conspicuous over the Shivaliks and the southern part of the Lesser Himalayas. Copyright © 2008 Royal Meteorological Society

Global monsoon in a geological perspective

Abstract: Monsoon is now considered as a global system rather than regional phenomena only. For over 300 years, monsoon has been viewed as a gigantic land-sea breeze, but now satellite and conventional observations support an alternative hypothesis which considers monsoon as a manifestation of seasonal migration of the intertropical convergence zone (ITCZ) and, hence, a climate system of the global scale. As a low-latitude climate system, monsoon exists over all continents but Antarctica, and through all the geological history at least since the Phenorozoic. The time is ripe for systematical studies of monsoon variations in space and time. As evidenced by the geological records, the global monsoon is controlled by the Wilson cycle on the tectonic time scale (106–108 a). A “Mega-continent” produces “Mega-monsoon”, and its breakdown leads to weakening of the monsoon intensity. On the time scales of 104-105 a, the global monsoon displays the precessional cycles of ∼20 ka and eccentricity cycles of 100- and 400-ka, i.e. the orbital cycles. On the time scales of 103 a and below, the global monsoon intensity is modulated by solar cycles and other factors. The cyclicity of global monsoon represents one of the fundamental factors responsible for variations in the Earth surface system as well as for the environmental changes of the human society. The 400-ka long eccentricity cycles of the global monsoon is likened to “heartbeat” of the Earth system, and the precession cycle of the global monsoon was responsible for the collapse of several Asian and African ancient cultures at ∼4000 years ago, whereas the Solar cycles led to the demise of the Maya civilization about a thousand years ago. Therefore, paleoclimatology should be focused not only on the high-latitude processes centered at ice cap variations, but also on the low-latitude processes such as monsoons, as the latter are much more common in the geological history compared to the glaciations.

Variability of stalagmite-inferred Indian monsoon precipitation over the past 252,000 y

Abstract: A speleothem δ(18)O record from Xiaobailong cave in southwest China characterizes changes in summer monsoon precipitation in Northeastern India, the Himalayan foothills, Bangladesh, and northern Indochina over the last 252 kyr. This record is dominated by 23-kyr precessional cycles punctuated by prominent millennial-scale oscillations that are synchronous with Heinrich events in the North Atlantic. It also shows clear glacial-interglacial variations that are consistent with marine and other terrestrial proxies but are different from the cave records in East China. Corroborated by isotope-enabled global circulation modeling, we hypothesize that this disparity reflects differing changes in atmospheric circulation and moisture trajectories associated with climate forcing as well as with associated topographic changes during glacial periods, in particular redistribution of air mass above the growing ice sheets and the exposure of the "land bridge" in the Maritime continents in the western equatorial Pacific.

Biennial oscillation associated with the East Asian summer monsoon and tropical sea surface temperatures

Abstract: In this paper, the interannual variability of the East Asian summer monsoon (EASM) rainfall and the tropical sea surface temperature (SST) have been studied. It is found that the EASM rainfall prossesses a strong biennial signal, which is particularly pronounced over the southeast China. For the SST, the biennial oscillation is the second most significant quasi-periodic signal over the entire tropical Indian and Pacific Oceans. Results indicate that the biennial variations in the SST and EASM rainfall are closely linked. The SST pattern which is best correlated with EASM rainfall appears in the form of a double see-saw with quasi-stationary centers of action over the Indian Ocean, the Asian monsoon region and the eastern Pacific. The most pronounced SST signals are found in the equatorial eastern Pacific and Indian Ocean about two seasons preceding and following the EASM rainfall. Evidence is presented suggesting that the biennial variability of the EASM rainfall is phase-locked to a global scale biennial oscillation involving the interplay of the Asian monsoon, the Hadley and Walker circulations, and basin wide fluctuations in SST. In particular, the eastward propagation of zonal wind anomalies from the Indian Ocean to the western Pacific, which regulates the moisture fluxes from the western Pacific to the East Asian region, appears to be a key component of the biennial fluctuation associated with EASM rainfall. Results suggest that the relationship between the Asian monsoon and tropical SST is more robust in the biennial that the El Nino/Southern Oscillation (ENSO) time scale, hence raising the possibility that the biennial oscillation may be more fundamentally related to monsoon-ocean-atmosphere interaction than ENSO itself.