scholarly journals BoBBLE: Ocean–Atmosphere Interaction and Its Impact on the South Asian Monsoon

2018 ◽  
Vol 99 (8) ◽  
pp. 1569-1587 ◽  
Author(s):  
P. N. Vinayachandran ◽  
Adrian J. Matthews ◽  
K. Vijay Kumar ◽  
Alejandra Sanchez-Franks ◽  
V. Thushara ◽  
...  
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Ocean Atmosphere ◽  
Ocean Atmosphere Interaction ◽  
Atmosphere Interaction ◽  
The Impact

AbstractThe Bay of Bengal (BoB) plays a fundamental role in controlling the weather systems that make up the South Asian summer monsoon system. In particular, the southern BoB has cooler sea surface temperatures (SST) that influence ocean–atmosphere interaction and impact the monsoon. Compared to the southeastern BoB, the southwestern BoB is cooler, more saline, receives much less rain, and is influenced by the summer monsoon current (SMC). To examine the impact of these features on the monsoon, the BoB Boundary Layer Experiment (BoBBLE) was jointly undertaken by India and the United Kingdom during June–July 2016. Physical and biogeochemical observations were made using a conductivity–temperature–depth (CTD) profiler, five ocean gliders, an Oceanscience Underway CTD (uCTD), a vertical microstructure profiler (VMP), two acoustic Doppler current profilers (ADCPs), Argo floats, drifting buoys, meteorological sensors, and upper-air radiosonde balloons. The observations were made along a zonal section at 8°N between 85.3° and 89°E with a 10-day time series at 8°N, 89°E. This paper presents the new observed features of the southern BoB from the BoBBLE field program, supported by satellite data. Key results from the BoBBLE field campaign show the Sri Lanka dome and the SMC in different stages of their seasonal evolution and two freshening events during which salinity decreased in the upper layer, leading to the formation of thick barrier layers. BoBBLE observations were taken during a suppressed phase of the intraseasonal oscillation; they captured in detail the warming of the ocean mixed layer and the preconditioning of the atmosphere to convection.

Investigating the sensitivity of the onset and withdrawal of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model

2020 ◽  
Author(s):  
Shiwansha Mishra ◽  
Dilip Ganguly ◽  
Puneet Sharma
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Anthropogenic Emissions ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Monsoon System ◽  
Asian Summer ◽  
The Impact

<p>While the monsoon onset is recognized as a rapid, substantial, and sustained increase in rainfall over large parts of south Asia, the withdrawal marks the return to dry conditions. Normally, the south Asian summer monsoon onset occurs around 1<sup>st</sup> June over extreme south of peninsular India, which gradually advances to extreme northwest of India by around 15<sup>th</sup> July. The withdrawal starts from northwest India from around 1st September and from extreme south peninsular India by around 30th September. The determinations of the onset and withdrawal dates of monsoon have great economic significance for this region as they influence many agriculture and water resource management decisions in one of the most highly populated regions of the world. Several studies involving global model simulations have shown that changing aerosol emissions could result in significant changes in the seasonal mean precipitation distribution over India. A few studies also show that presence of absorbing aerosols in the foothills of Himalayas and over the Tibetan plateau could increase the moisture convergence over India thereby causing an advancement and intensification of the monsoon precipitation. However, most of the previous studies, which investigated the impact of anthropogenic emissions on the monsoon, are limited to understanding the impact of various emission changes on the seasonal mean monsoon characteristics. In the present study, we try to understand the sensitivity of the onset and withdrawal period of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model (CESM1.2). We diagnose the onset and withdrawal of the south Asian monsoon by analyzing the variability in vertically integrated moisture transport (VIMT) over the south Asian region and following the definition of hydrologic onset and withdrawal index (HOWI) defined by Fasullo et al. (2002). We examined the effect of changing emissions anthropogenic aerosol, greenhouse gases and both on the onset and withdrawal of the south Asian summer monsoon system. Our preliminary results suggest that increases in the emissions of aerosols and greenhouse gases from anthropogenic sources from pre-industrial to present day could possibly result in significant delay in the onset and advancement in withdrawal of the south Asian summer monsoon system thereby shortening the length of the monsoon season. More results with greater detail will be presented.</p>

scholarly journals Trapping, chemistry and export of trace gases in the South Asian summer monsoon observed during CARIBIC flights in 2008

2015 ◽  
Vol 15 (5) ◽  
pp. 6967-7018 ◽  
Author(s):  
A. Rauthe-Schöch ◽  
A. K. Baker ◽  
T. J. Schuck ◽  
C. A. M. Brenninkmeijer ◽  
A. Zahn ◽  
...  
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
Particle Dispersion ◽  
Atmospheric Pollutants ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Air Masses ◽  
Asian Summer

Abstract. The CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) passenger aircraft observatory performed in situ measurements at 10–12 km altitude in the South Asian summer monsoon anticyclone between June and September 2008. These measurements enable us to investigate this atmospheric region, which so far has mostly been observed from satellites, using the broad suite of trace gases and aerosols measured by CARIBIC. Elevated levels of a range of atmospheric pollutants were recorded e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles and several volatile organic compounds. The measurements provide detailed information about the chemical composition of air in different parts of the monsoon anticyclone, particularly of ozone precursors. While covering a range of 3500 km inside the monsoon anticyclone, CARIBIC observations show remarkable consistency, i.e. with regular latitudinal patterns of trace gases during the entire monsoon period. Trajectory calculations indicate that these air masses originated mainly from South Asia and Mainland Southeast Asia. Using the CARIBIC trace gas and aerosol measurements in combination with the Lagrangian particle dispersion model FLEXPART we investigated the characteristics of monsoon outflow and the chemical evolution of air masses during transport. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 95° E. The photochemical ages of the air in the southern part of the monsoon anticyclone were consistently younger (less than 7 days) and the air masses mostly in an ozone forming chemical regime. In its northern part the air masses were older (up to 13 days) and had unclear ozone formation or destruction potential. Based on analysis of forward trajectories several receptor regions were identified. In addition to predominantly westward transport, we found evidence for efficient transport (within 10 days) to the Pacific and North America, particularly during June and September, and also of cross-tropopause exchange, which was strongest during June and July. Westward transport to Africa and further to the Mediterranean was the main pathway during July.

A Moist Entropy Budget View of the South Asian Summer Monsoon Onset

2019 ◽  
Vol 46 (8) ◽  
pp. 4476-4484
Author(s):  
Ding Ma ◽  
Adam H. Sobel ◽  
Zhiming Kuang ◽  
Martin S. Singh ◽  
Ji Nie
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Onset ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Summer Monsoon Onset ◽  
Asian Summer ◽  
Entropy Budget

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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