scholarly journals Relative Roles of Land–Sea Distribution and Orography in Asian Monsoon Intensity

2009 ◽  
Vol 66 (9) ◽  
pp. 2714-2729 ◽  
Author(s):  
Zhongfeng Xu ◽  
Congbin Fu ◽  
Yongfu Qian
Keyword(s):  
Indian Ocean ◽  
South Asian ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Circulation ◽  
Eurasian Continent ◽  
The Indian Ocean ◽  
Asian Summer

Abstract The relative impacts of various land–sea distributions (LSDs) and mountains on Asian monsoon extent and intensity are assessed using a series of AGCM simulations. The air–sea coupling effects are not considered in this study. All simulations were integrated with zonal mean SST, globally uniform vegetation, soil color, and, except several simulations, soil texture. The results show that the LSD plays a more fundamental role than orography in determining the extent of Asian and African monsoons. The tropical zonal LSD and Asian mountains both play a crucial role for establishing summer monsoon convection over the South Asian region. The monsoon circulation index (MCI1) defined by the difference of zonal wind between 850 and 200 hPa is used to measure the intensity of the South Asian summer monsoon. The large-scale meridional land–sea thermal contrast between the Eurasian continent and the Indian Ocean only induces a 1.8 m s−1 increase of MCI1. The presence of the Indian subcontinent and Indochina peninsula (Asian mountains), however, induces a 6.6 (7.4) m s−1 increase of MCI1 associated with the release of latent heat of condensation. Clearly, the tropical subcontinental-scale zonal LSD and the Asian mountains almost equally contribute to the increase of MCI1 and play a more important role than the large-scale meridional LSD between the Eurasian continent and the Indian Ocean. Possible mechanisms of how the tropical subcontinental-scale zonal LSD and Asian mountains impact the Asian summer monsoon circulation and precipitation are also discussed.

scholarly journals Seasonal-to-Interannual Prediction of the Asian Summer Monsoon in the NCEP Climate Forecast System Version 2

2013 ◽  
Vol 26 (11) ◽  
pp. 3708-3727 ◽  
Author(s):  
Xingwen Jiang ◽  
Song Yang ◽  
Yueqing Li ◽  
Arun Kumar ◽  
Xiangwen Liu ◽  
...  
Keyword(s):  
South Asian ◽  
Large Scale ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Circulation ◽  
Climate Forecast System ◽  
Circulation Patterns ◽  
Intercomparison Project ◽  
Asian Summer ◽  
Monsoon Indices

Abstract The NCEP Climate Forecast System (CFS) is an important source of information for seasonal climate prediction in many Asian countries affected by monsoon climate. The authors provide a comprehensive analysis of the prediction of the Asian summer monsoon (ASM) by the new CFS version 2 (CFSv2) using the hindcast for 1983–2010, focusing on seasonal-to-interannual time scales. Many ASM features are well predicted by the CFSv2, including heavy monsoon rainfall centers, large-scale monsoon circulation patterns, and monsoon onset and retreat features. Several commonly used dynamical monsoon indices and their associated precipitation and circulation patterns can be predicted several months in advance. The CFSv2 has better skill in predicting the Southeast Asian monsoon than predicting the South Asian monsoon. Compared to CFS version 1 (CFSv1), the CFSv2 has increased skill in predicting large-scale monsoon circulation and precipitation features but decreased skill for the South Asian monsoon, although some biases in the CFSv1 still exist in the CFSv2, especially the weaker-than-observed western Pacific subtropical high and the exaggerated strong link of the ASM to ENSO. Comparison of CFSv2 hindcast with output from Atmospheric Model Intercomparison Project (AMIP) and Coupled Model Intercomparison Project (CMIP) simulations indicates that exclusion of ocean–atmosphere coupling leads to a weaker ASM. Compared to AMIP, both hindcast and CMIP show a more realistic annual cycle of precipitation, and the interannual variability of the ASM is better in hindcast. However, CMIP does not show any advantage in depicting the processes associated with the interannual variability of major dynamical monsoon indices compared to AMIP.

scholarly journals The First Transition of the Asian Summer Monsoon, Intraseasonal Oscillation, and Taiwan Mei-yu

2008 ◽  
Vol 21 (7) ◽  
pp. 1552-1568 ◽  
Author(s):  
Chih-wen Hung ◽  
Huang-Hsiung Hsu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Eastern Africa ◽  
Monsoon Circulation ◽  
Close Monitoring ◽  
Maritime Continent ◽  
The Indian Ocean ◽  
Asian Summer

Abstract This study reveals the close relationship between the first transition of the Asian summer monsoon (ASM), the tropical intraseasonal oscillation (TISO), and the mei-yu in Taiwan, which occurs climatologically between mid-May and mid-June. For about half of the years in 1958–2002, the first transition of the Asian summer monsoon can be classified as a sharp onset, which is characterized by an abrupt reversal of the monsoon flow from northeasterly to southwesterly. The evolution of the large-scale monsoon circulation and convection in the sharp-onset years is characterized by an eastward-propagating TISO from eastern Africa and the western Indian Ocean to the Maritime Continent. Upon the arrival of the TISO in the Maritime Continent, a sharp onset of the ASM occurs, and a channel supplying moist air in the lower troposphere is well established across the Indian Ocean to the South China Sea (SCS). This channel consists of the Somali jet, transporting the moisture from the Southern Hemisphere to the Northern Hemisphere, and the southwesterly monsoon, delivering the moisture across the Indian Ocean to the SCS and the western North Pacific. This efficient and persistent transport of moisture to the SCS and surrounding areas presumably provides a favorable condition for the maintenance of the mei-yu front and the development of convective systems. This also marks the onset of the Taiwan mei-yu season. Because a strong TISO signal, which tends to occur concurrently with the sharp onset of the ASM, is often observed prior to the onset of the first transition and Taiwan mei-yu, a close monitoring of the TISO can be informative for the weather forecasters in Taiwan to project the initiation of the Taiwan mei-yu.

Linking Observations of the Asian Monsoon to the Indian Ocean SST: Possible Roles of Indian Ocean Basin Mode and Dipole Mode

2010 ◽  
Vol 23 (21) ◽  
pp. 5889-5902 ◽  
Author(s):  
Jianling Yang ◽  
Qinyu Liu ◽  
Zhengyu Liu
Keyword(s):  
Indian Ocean ◽  
Atmospheric Circulation ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Ocean Basin ◽  
Indian Ocean Basin Mode ◽  
Basin Mode ◽  
The Indian Ocean ◽  
Asian Summer

Abstract The authors investigate the relationship between sea surface temperature (SST) in the tropical Indian Ocean (TIO) and the seasonal atmosphere circulation in the Asian monsoon region (AMR) using the maximum covariance analyses (MCAs). The results show that the Asian monsoon circulation is significantly correlated with two dominant SST anomaly (SSTA) modes: the Indian Ocean Basin mode (IOB) and the Indian Ocean dipole mode (IOD). The peak SSTA of the IOB appears in spring and has a much stronger relationship with the Asian summer monsoon than the peak of the IOD does, whereas the peak SSTA for the IOD appears in fall and shows a stronger link to the Asian winter monsoon than to the Asian summer monsoon. In addition, the IOB in spring has a relatively stronger link with the atmospheric circulation in summer than in other seasons. The large-scale atmospheric circulation and SSTA patterns of the covariability of the first two dominant MCA modes are described. For the first MCA mode, a warm IOB, persists from spring to summer, and the atmospheric circulation is enhanced by the establishment of the climatological summer monsoon. The increased evaporative moisture associated with the warm IOB is transported to South Asia by the climatological summer monsoon, which increases the moisture convergence toward this region, leading to a significant increase in summer monsoon precipitation. For the second MCA mode, a positive IOD possibly corresponds to a weaker Indian winter monsoon and more precipitation over the southwestern and eastern equatorial TIO.

scholarly journals Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions

2021 ◽  
Vol 7 (23) ◽  
pp. eabg3848
Author(s):  
Steven C. Clemens ◽  
Masanobu Yamamoto ◽  
Kaustubh Thirumalai ◽  
Liviu Giosan ◽  
Julie N. Richey ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
South Asian ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Precipitation Amount ◽  
Monsoon Precipitation ◽  
Orbital Eccentricity ◽  
South Asian Summer Monsoon ◽  
Asian Summer

South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric carbon dioxide changes at Earth’s orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising carbon dioxide levels is fully consistent with dynamics of the past 0.9 million years.

scholarly journals Delivery of halogenated very short-lived substances from the West Indian Ocean to the stratosphere during Asian summer monsoon

2017 ◽  
Author(s):  
Alina Fiehn ◽  
Birgit Quack ◽  
Helmke Hepach ◽  
Steffen Fuhlbrügge ◽  
Susann Tegtmeier ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Source Region ◽  
West Indian ◽  
The West ◽  
West Indian Ocean ◽  
Asian Summer

Abstract. Halogenated very short-lived substances (VSLS) are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical West Indian Ocean in July and August 2014, we measured the VSLS, methyl iodide (CH3I) and for the first time bromoform (CHBr3) and dibromomethane (CH2Br2), in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian transport model Flexpart with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the West Indian Ocean surface to the stratosphere for July 2000–2015. We found that the West Indian Ocean is a strong source region for CHBr3 (910 pmol m−2 h−1), very strong for CH2Br2 (930 pmol m−2 h−1), and average for CH3I (460 pmol m−2 h−1). The atmospheric transport from the tropical West Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime), convection above the Indian Ocean lifts oceanic air masses and VSLS towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLS towards India and Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2). The entrainment of CHBr3 and CH3I from the West Indian Ocean to the stratosphere during Asian summer monsoon is less than from previous cruises in the tropical West Pacific Ocean during boreal autumn/early winter, but higher than from the tropical Atlantic during boreal summer. In contrast, the projected CH2Br2 entrainment was very high because of the high emissions during the West Indian Ocean cruise. The 16-year July time series shows highest interannual variability for the short-lived CH3I and lowest for the long-lived CH2Br2. During this time period, a small increase of VSLS entrainment from the West Indian Ocean through the Asian monsoon to the stratosphere is found. Overall, this study confirms that the subtropical and tropical West Indian Ocean is an important source region of halogenated VSLS, especially CH2Br2, to the troposphere and stratosphere during the Asian summer monsoon.

scholarly journals Upper tropospheric CO and O<sub>3</sub> budget during the Asian Summer Monsoon

2016 ◽  
Author(s):  
B. Barret ◽  
B. Sauvage ◽  
Y. Bennouna ◽  
E. Le Flochmoen
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Satellite Data ◽  
Large Scale ◽  
Transport Model ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Gangetic Plain ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. During the Asian Summer Monsoon, the circulation in the Upper Troposphere-Lower Stratosphere (UTLS) is dominated by the Asian Monsoon Anticyclone (AMA). Pollutants convectively uplifted to the upper troposphere are trapped within this anticyclonic circulation that extends from the Pacific Ocean to the eastern Mediterranean basin. Among the uplifted pollutants are ozone (O3) and its precursors, such as carbon monoxide (CO) and nitrogen oxides (NOx). Many studies based on global modelisation and satellite data have documented the source regions and transport pathways of primary pollutants (CO, HCN) into the AMA. Here, we aim to quantify the O3 budget by taking into consideration anthropogenic and natural sources. We first use CO and O3 data from the Metop-A/IASI sensor to document their tropospheric distributions over Asia, taking advantage of the useful information they provide on the vertical dimension. These satellite data are used together with MOZAIC/IAGOS tropospheric profiles recorded in India to validate the distributions simulated by the global GEOS-Chem chemistry transport model. Over the Asian region, UTLS monthly CO and O3 distributions from IASI and GEOS-Chem display the same large-scale features. UTLS CO columns from GEOS-Chem are in agreement with IASI, with a low bias of 11 ± 9% and a correlation coefficient of 0.70. For O3, the model underestimates IASI UTLS columns over Asia by 14 ± 26% but the correlation between both is high (0.94). GEOS-Chem is further used to quantify the CO and O3 budget through sensitivity simulations. For CO, these simulations confirm that South-Asian anthropogenic emissions have a more important impact on enhanced concentrations within the AMA (∼25 ppbv) than East-Asian emissions (∼10 ppbv). The correlation between enhanced emissions over the Indo–gangetic–Plain and monsoon deep convection is responsible for this larger impact. Consistently, South-Asian anthropogenic NOx emissions also play a larger role in producing O3 within the AMA (∼8 ppbv) than East-Asian emissions (∼5 ppbv) but Asian lightning produced NOx are responsible for the largest O3 production (10–14 ppbv). Stratosphere to Troposphere Exchanges (STE) are also important in transporting O3 in the upper part of the AMA.

scholarly journals Interannual Variability in the Large-Scale Dynamics of the South Asian Summer Monsoon

2015 ◽  
Vol 28 (9) ◽  
pp. 3731-3750 ◽  
Author(s):  
Jennifer M. Walker ◽  
Simona Bordoni ◽  
Tapio Schneider
Keyword(s):  
Interannual Variability ◽  
South Asian ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Sea Breeze ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Near Surface ◽  
Asian Summer

Abstract This study identifies coherent and robust large-scale atmospheric patterns of interannual variability of the South Asian summer monsoon (SASM) in observational data. A decomposition of the water vapor budget into dynamic and thermodynamic components shows that interannual variability of SASM net precipitation (P − E) is primarily caused by variations in winds rather than in moisture. Linear regression analyses reveal that strong monsoons are distinguished from weak monsoons by a northward expansion of the cross-equatorial monsoonal circulation, with increased precipitation in the ascending branch. Interestingly, and in disagreement with the view of monsoons as large-scale sea-breeze circulations, strong monsoons are associated with a decreased meridional gradient in the near-surface atmospheric temperature in the SASM region. Teleconnections exist from the SASM region to the Southern Hemisphere, whose midlatitude poleward eddy energy flux correlates with monsoon strength. Possible implications of these teleconnection patterns for understanding SASM interannual variability are discussed.

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