Monsoon

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

Hydrology of Dali Lake in central-eastern Inner Mongolia and Holocene East Asian monsoon variability

Abstract: Lacustrine records from the northern margin of the East Asian monsoon generate a conflicting picture of Holocene monsoonal precipitation change. To seek an integrated view of East Asian monsoon variability during the Holocene, an 8.5-m-long sediment core recovered in the depocenter of Dali Lake in central-eastern Inner Mongolia was analyzed at 1-cm intervals for total organic and inorganic carbon concentrations. The data indicate that Dali Lake reached its highest level during the early Holocene (11,500–7,600 cal yr BP). The middle Holocene (7,600–3,450 cal yr BP) was characterized by dramatic fluctuations in the lake level with three intervals of lower lake stands occurring 6,600–5,850, 5,100–4,850 and 4,450–3,750 cal yr BP, respectively. During the late Holocene (3,450 cal yr BP to present), the lake displayed a general shrinking trend with the lowest levels at three episodes of 3,150–2,650, 1,650–1,150 and 550–200 cal yr BP. We infer that the expansion of the lake during the early Holocene would have resulted from the input of the snow/ice melt, rather than the monsoonal precipitation, in response to the increase in summer solar radiation in the Northern Hemisphere. We also interpret the rise in the lake level since ca. 7,600 cal yr BP as closely related to increased monsoonal precipitation over the lake region resulting from increased temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific. Moreover, high variability of the East Asian monsoon climate since 7,600 cal yr BP, marked by large fluctuations in the lake level, might have been directly associated with variations in the intensity and frequency of the El Nino-Southern Oscillation (ENSO) events.

A Report of the Field Operations and Early Results of the South China Sea Monsoon Experiment (SCSMEX)

Abstract: The South China Sea Monsoon Experiment (SCSMEX) is an international field experiment with the objective to better understand the key physical processes for the onset and evolution of the summer monsoon over Southeast Asia and southern China aiming at improving monsoon predictions. In this article, a description of the major meteorological observation platforms during the intensive observing periods of SCSMEX is presented. In addition, highlights of early results and discussions of the role of SCSMEX in providing valuable in situ data for calibration of satellite rainfall estimates from the Tropical Rainfall Measuring Mission are provided. Preliminary results indicate that there are distinctive stages in the onset of the South China Sea monsoon including possibly strong influences from extratropical systems as well as from convection over the Indian Ocean and the Bay of Bengal. There is some tantalizing evidence of complex interactions between the supercloud cluster development over the Indian Oce...

Dynamics of the West African Monsoon Jump

Abstract: The observed abrupt latitudinal shift of maximum precipitation from the Guinean coast into the Sahel region in June, known as the West African monsoon jump, is studied using a regional climate model. Moisture, momentum, and energy budget analyses are used to better understand the physical processes that lead to the jump. Because of the distribution of albedo and surface moisture, a sensible heating maximum is in place over the Sahel region throughout the spring. In early May, this sensible heating drives a shallow meridional circulation and moisture convergence at the latitude of the sensible heating maximum, and this moisture is transported upward into the lower free troposphere where it diverges. During the second half of May, the supply of moisture from the boundary layer exceeds the divergence, resulting in a net supply of moisture and condensational heating into the lower troposphere. The resulting pressure gradient introduces an inertial instability, which abruptly shifts the midtropospheric meridional wind convergence maximum from the coast into the continental interior at the end of May. This in turn introduces a net total moisture convergence, net upward moisture flux and condensation in the upper troposphere, and an enhancement of precipitation in the continental interior through June. Because of the shift of the meridional convergence into the continent, condensation and precipitation along the coast gradually decline. The West African monsoon jump is an example of multiscale interaction in the climate system, in which an intraseasonal-scale event is triggered by the smooth seasonal evolution of SSTs and the solar forcing in the presence of land–sea contrast.

Comparative accounts of biological productivity characteristics and estimates of carbon fluxes in the Arabian Sea and the Bay of Bengal

Abstract: The Arabian Sea and the Bay of Bengal are tropical basins experiencing monsoonal wind forcing that reverses semi-annually. This brings changes in physics, chemistry and biology of the upper water column on a seasonal scale and ultimately regulates the sinking fluxes of the region. An attempt is made here to focus on factors responsible for fluxes of carbon from the upper layers to the deep sea. Higher fluxes are observed during southwest and northeast monsoon season in both the regions. In contrast to the Arabian Sea, an immense quantity of freshwater runoff together with warmer SST (∼30 °C) makes the northern bay strongly stratified. The runoff also brings in billions of tonnes of fluvial matter as well. Stratification constrains subsurface nutrient input into the surface waters thereby reducing the primary production in the Bay of Bengal. The total living carbon content in the Bay of Bengal is much lower than in the Arabian Sea. Higher downward fluxes associated with deep mixed layer and high production in the Arabian Sea during summer and winter pinpoint importance of strong winds causing mixing and upwelling during summer and evaporative cooling and convection during winter. Inability of the low-speed winds to break the stratification in the Bay of Bengal keeps the region low productive throughout the year. Therefore, river water associated with the terrigenous material due to ballast effect appears to swipe off surface producers to the deep, thereby increasing the downward fluxes of total particulates, which are sometimes even higher than that of the more productive Arabian Sea.

On the sea surface temperature high in the Lakshadweep Sea before the onset of the southwest monsoon

Abstract: The north Indian Ocean becomes the warmest area of the world oceans prior to the onset of southwest monsoon in June. During this period a zonal band of high sea surface temperature (SST), the “thermal equator” (TE), moves over this region concurrently with the Intertropical Convergence Zone (ITCZ). Using a weekly SST data set, we show that another SST high develops off southwest India in the Lakshadweep Sea in March, well before the TE moves in to the area, and that it continues to retain its identity until the onset of monsoon. The SST high has its genesis about 6 months earlier in the Bay of Bengal. The collapse of the southwest monsoon in October and the onset of the northeast monsoon trigger down welling coastal Kelvin waves that propagate along the periphery of the Bay of Bengal, forcing an equatorward East India Coastal Current, which brings low-salinity water from the bay to the southeastern Arabian Sea during the northeast monsoon (November-January). As the Kelvin waves propagate poleward along the west coast of India after turning around Sri Lanka, they radiate downwelling Rossby waves that produce a “high” in sea level off southwest India. The downwelling and the surface layer of low-salinity water provide a breeding ground for the formation of a SST high in January. By March, with the increase in solar insolation due to the northward march of the Sun and the deep stable surface layer, the high reaches a mature phase clearly evident in the Lakshadweep Sea. By May, when the thermal equator and ITCZ move over the region, the high can be seen embedded in the TE. We speculate that at this time the high helps in producing conditions that are conducive for genesis of the monsoon onset vortex.