Monsoon

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

Droughts/floods in the summer monsoon season over different meteorological subdivisions of India for the period 1871–1984

Abstract: Abnormalities in the performance of the Indian summer monsoon (June to September) rainfall, which provides 75–90 per cent of annual rainfall, have been studied during the period 1871 to 1984 over different meteorological subdivisions into which the country has been divided. Long homogeneous monsoon rainfall series of 29 subdivisions, prepared on the basis of a constant 306 rain gauges, have been tabulated for the users in view of their great importance. The criterion adopted in identification of drought/flood over a subdivision is the percentage of rainfall departures from normal, as officially used in the India Meteorological Department. The worst drought years were 1877, 1899, 1911, 1918, 1920, 1951, 1965 and 1972 and the worst flood years were 1892, 1933, 1961 and 1983 when many subdivisions reported extremely low and excess rainfall, respectively. The probabilities of occurrence of droughts/floods are high in Haryana, Punjab, west Rajasthan, Gujarat and Saurashtra and Kutch subdivisions. The area of the country affected by drought conditions was at a maximum during the decade 1911–1920 and at a minimum during the decade 1881–1890. The decades 1971–1980 and 1921–1930 were characterized by maximum and minimum areas, respectively, under flood conditions. The percentage area of India which suffered from drought and flood was low during the continuous three decades 1921–1930, 1931–1940 and 1941–1950.

Scale interaction in the Western Pacific Monsoon

Abstract: The lower-tropospheric scale interactions occurring in the summer monsoon of the western North Pacific are reviewed and summarised in a conceptual model. Diabatic heating produces a circulation with similar characteristics to those that are observed. In the lower troposphere the advection of vorticity by the divergent wind produces a compact, and more intense response than in the upper levels. Subsequent phase dispersion westward, and group propagation eastwards, lead to a monsoon depression in convectively suppressed conditions, a westerly jet with cross-equatorial flow, and a strong confluence region to the east of the monsoon depression.

The hydrological impact of geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)

Abstract: The hydrological impact of enhancing Earth's albedo by solar radiation management is investigated using simulations from 12 Earth System models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). We contrast an idealized experiment, G1, where the global mean radiative forcing is kept at preindustrial conditions by reducing insolation while the CO 2 concentration is quadrupled to a 4×CO2 experiment. The reduction of evapotranspiration over land with instantaneously increasing CO2 concentrations in both experiments largely contributes to an initial reduction in evaporation. A warming surface associated with the transient adjustment in 4×CO2 generates an increase of global precipitation by around 6.9% with large zonal and regional changes in both directions, including a precipitation increase of 10% over Asia and a reduction of 7% for the North American summer monsoon. Reduced global evaporation persists in G1 with temperatures close to preindustrial conditions. Global precipitation is reduced by around 4.5%, and significant reductions occur over monsoonal land regions: East Asia (6%), South Africa (5%), North America (7%), and South America (6%). The general precipitation performance in models is discussed in comparison to observations. In contrast to the 4×CO2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50% in comparison to the control, a reduction of up to 20% is simulated in G1. These changes in precipitation in both total amount and frequency of extremes point to a considerable weakening of the hydrological cycle in a geoengineered world.

African vegetation controlled by tropical sea surface temperatures in the mid-Pleistocene period

Abstract: The dominant forcing factors for past large-scale changes in vegetation are widely debated. Changes in the distribution of C4 plants—adapted to warm, dry conditions and low atmospheric CO2 concentrations1—have been attributed to marked changes in environmental conditions, but the relative impacts of changes in aridity, temperature2,3 and CO2 concentration4,5 are not well understood. Here, we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago, derived from compound-specific carbon isotope analyses of wind-transported terrigenous plant waxes. We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean. We conclude that, in the mid-Pleistocene, changes in atmospheric moisture content—driven by tropical sea surface temperature changes and the strength of the African monsoon—controlled aridity on the African continent, and hence large-scale vegetation changes.