Monsoon

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

Tropical Indian Ocean Basin Warming and East Asian Summer Monsoon: A Multiple AGCM Study

Abstract: A basin-scale warming is the leading mode of tropical Indian Ocean sea surface temperature (SST) variability on interannual time scales, and it is also the prominent feature of the interdecadal SST trend in recent decades. The influence of the warming on the East Asian summer monsoon (EASM) is investigated through ensemble experiments of several atmospheric general circulation models (AGCMs). The results from five AGCMs consistently suggest that near the surface, the Indian Ocean warming forces an anticyclonic anomaly over the subtropical western Pacific, intensifying the southwesterly winds to East China; and in the upper troposphere, it forces a Gill-type response with the intensified South Asian high, both favoring the enhancement of the EASM. These processes are argued to contribute to the stronger EASM during the summer following the peak of El Nino than monsoons in other years. These model results also suggest that tropical Indian Ocean warming may not have a causal relationship to the synchronous weakening of EASM on interdecadal time scales.

Dust storm frequency in Asia: Climatic control and variability

Abstract: The dimension and environmental impact of the dust storm phenomenon has been realized only recently. There are few previous works on the climatic control of dust storm frequency, especially in the field of time series analysis. Actually, there is a poor correspondence of climatic parameter mean values and dust storm data. Although generally negative, rainfall — dust-storm correlations do not reveal the physical causes of dust storm generation, as is shown by lagged cross-correlation and spectral analysis. Temperature data may indicate seasonal variation of dust storms by extreme values, but they are no reliable defining factor owing to high persistence over shorter time series. The same is found for mean wind speeds, but negative interrelations with atmospheric pressure point to the importance of cyclogenesis and convective cells in dust storm generation in Asia. Three different seasonality patterns are described: (i) a single dust storm maximum in spring typical of summer rain areas; (ii) a single storm maximum in summer in areas with bimodal (winter and monsoonal) rainfall; (iii) an extended spring and summer dust storm maximum in areas with unimodal winter rains. Additional data from northern Africa fit into this pattern. Spectral energy of dust storm, rainfall, and temperature series for northern India and northern China (1976–1986) is mainly concentrated in the wavelength of seasonal variations, but some supra-seasonal signals indicate fluctuations between 3·6 and 5·5 years with various phase dislocations. In China, this interannual variability is supposed to be linked with dynamic shifts in circumpolar vortex dynamics.

The impact of agricultural intensification and irrigation on land-atmosphere interactions and Indian monsoon precipitation — A mesoscale modeling perspective

Abstract: article i nfo Article history: Accepted 8 February 2008 Available online xxxx Using the Regional Atmospheric Modeling System (RAMS) we show that agricultural intensification and irrigation can modify the surface moisture and energy distribution, which alters the boundary layer and regional convergence, mesoscale convection, and precipitation patterns over the Indian monsoon region. Four experiments were conducted to simulate a rain event from 16 to 20 July 2002 over the Indian region: (i) a control with Global Land Cover land use and observed Normalized Difference Vegetation Index, (ii) an irrigated crop scenario, (iii) a non-irrigated crop scenario, and (iv) a scenario for potential (natural) vegetation. Results indicate that even under active monsoon conditions, the simulated surface energy and moisture flux over the Indian monsoon region are sensitive to the irrigation intensity and this effect is more pronounced than the impact of land use change from the potential vegetation to the agricultural landscape. When model outputs were averaged over the south Asia model domain, a statistically significant decrease in mean sensible heat flux between the potential vegetation and the irrigated agriculture scenarios of 11.7 Wm −2

Predictability and the relationship between subseasonal and interannual variability during the Asian summer monsoon

Abstract: The relationship between subseasonal and interannual variability of the Asian summer monsoon has been investigated through analysis of the dominant modes of variability in the 40-year NCEP/NCAR Re-analysis, with complementary satellite and surface-based precipitation data. The hypothesis that the characteristics of monsoon subseasonal variability (i.e. weather regimes) are modulated on interannual time-scales in a systematic and therefore predictable manner has been tested. The null hypothesis is that predictability of the seasonal mean monsoon behaviour requires that the effects of the slowly varying components of the climate system be correctly simulated. An interannual mode of monsoon variability has been identified which is closely related to the observed seasonal mean all-India Rainfall (AIR). A counterpart of this mode has also been identified at subseasonal time-scales which projects strongly on to the daily AIR, confirming that a common mode of monsoon variability exists on sub-seasonal and interannual time-scales. It has been shown that the temporal behaviour of this subseasonal mode, as described by the probability distribution function (PDF) of the principal component time series, does not show any evidence of bimodality, the shape of the PDF being Gaussian. Further, it has been shown that the mean of the PDF is systematically and significantly perturbed towards negative (positive) values in weak (strong) monsoon years as categorized in terms of the seasonal mean AIR. This translation in the mean of the PDF, rather than a change in shape of the PDF, suggests that anomalous monsoons are not associated with changes in weather regimes. Further analysis has confirmed that low-frequency modulation of the basic state is primarily responsible for these shifts in the subseasonal PDFs, supporting the null hypothesis that predictability of the seasonal mean monsoon requires that the effects of the slowly varying components of the climate system be correctly simulated. Thus, model improvements to reduce systematic errors in the mean simulation and the response to low-frequency boundary forcing may improve the prospects for dynamical seasonal prediction. However, the results indicate that only a subset of the subseasonal modes are systematically perturbed either by the El Nino Southern Oscillation or in weak vs. strong monsoon years, suggesting that predictability is likely to be limited by the chaotic, internal variability of the monsoon system.

The South China Sea : paleoceanography and sedimentology

Abstract: 1. INTRODUCTION: PINXIAN WANG and QIANYU LI 2. OCEANOGRAPHICAL AND GEOLOGICAL BACKGROUND: PINXIAN WANG and QIANYU LI Bathymetry and geomorphology Oceanography Tectonic history and sedimentary basins 3. STRATIGRAPHY AND SEA LEVEL CHANGES: QIANYU LI, GUANGFA ZHONG and JUN TIAN Lithostratigraphic overview Biostratigraphic framework Isotopic and astronomical stratigraphy Stratigraphy of major shelf and slope basins Regional sea level changes Summary of South China Sea stratigraphy 4. SEDIMENTOLOGY: Zhifei Liu , Wei Huang , JIANRU LI , Pinxian wang, Rujian Wang, Kefu Yu, Jianxin Zhao Surface deposition patterns Terrigenous deposition Biogenic deposition Coral reefs Volcanic deposition Estimation of deposit mass since the Oligocene 5. UPPER WATER STRUCTURE AND PALEO-MONSOON: ZHIMIN JIAN, JUN TIAN, XIANGJUN SUN, Sea surface temperature history Thermocline depth history Vegetation history in deep-sea record Monsoon history Summary 6. DEEP WATERS AND OCEANIC CONNECTION: QUANHONG ZHAO, QIANYU LI, ZHIMIN JIAN Modern deep waters and their faunal features Late Quaternary deep-water faunas and stable isotopes Neogene and Oligocene deep-water benthic faunas from ODP Leg 184 sites Deep water evolution: evidence from carbonate preservation and isotopes Oceanic connection Summary 7. BIOGEOCHEMISTRY AND THE CARBON RESERVOIR: MEIXUN ZHAO, PINXIAN WANG, JUN TIAN, JIANRU LI Productivity and nutrient dynamics in the modern South China Sea Paleoproductivity reconstrction of the South China Sea Carbon reservoir changes 8. HISTORY OF THE SOUTH CHINA SEA - SYNTHESIS: PINXIAN WANG and QIANYU LI Evolution of the SCSBasin Evolution of the East Asian Monsoon Evolution of continent-ocean interactions