scholarly journals On the Role of the African Topography in the South Asian Monsoon

2016 ◽  
Vol 73 (8) ◽  
pp. 3197-3212 ◽  
Author(s):  
Ho-Hsuan Wei ◽  
Simona Bordoni
Keyword(s):  
South Asian ◽  
General Circulation ◽  
Asian Monsoon ◽  
Circulation Model ◽  
Atmospheric Model ◽  
South Asian Monsoon ◽  
The South ◽  
East African Highlands ◽  
Somali Jet

Abstract The Somali jet, a strong low-level cross-equatorial flow concentrated in a narrow longitudinal band near the coast of Somalia, is a key feature of the South Asian monsoon (SAM) circulation. Previous work has emphasized the role of the East African highlands in strengthening and concentrating the jet. However, the fundamental dynamics of the jet remains debated, as does its relation to the SAM precipitation. In this study, numerical experiments with modified topography over Africa are conducted with the GFDL atmospheric model, version 2.1 (AM2.1), general circulation model (GCM) to examine the influence of topography on the Somali jet and the SAM precipitation. It is found that when the African topography is removed, the SAM precipitation moderately increases in spite of a weakening of the cross-equatorial Somali jet. The counterintuitive precipitation increase is related to lower-level cyclonic wind anomalies, and associated meridional moisture convergence, which develop over the Arabian Sea in the absence of the African topography. Potential vorticity (PV) budget analyses along particle trajectories show that this cyclonic anomaly primarily arises because, in the absence of the blocking effect by the African topography and with weaker cross-equatorial flow, air particles originate from higher latitudes with larger background planetary vorticity and thus larger PV.

scholarly journals The influence of vegetation on the ITCZ and South Asian Monsoon in HadCM3

2012 ◽  
Vol 3 (1) ◽  
pp. 91-111 ◽  
Author(s):  
M. P. McCarthy ◽  
J. Sanjay ◽  
B. B. B. Booth ◽  
K. Krishna Kumar ◽  
R. A. Betts
Keyword(s):  
Northern Hemisphere ◽  
South Asian ◽  
Vegetation Cover ◽  
Large Scale ◽  
Asian Monsoon ◽  
Global Dynamics ◽  
South Asian Monsoon ◽  
The South ◽  
Tropical Vegetation

Abstract. The role of extra-tropical vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre Climate Model (HadCM3). Alternative representations of present day vegetation from observations and a dynamic vegetation model were used as the land-cover component for a number of HadCM3 experiments under a nominal present day climate state, and are shown to induce perturbations to the simulated global dynamics. This results in a shift in the location of the Inter Tropical Convergence Zone (ITCZ) and changes in the South Asian monsoon circulation. This has a significant impact on the Indian land precipitation compared to the standard configuration of HadCM3. This large-scale forcing is consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics. This analysis demonstrates that uncertainties in the representation of present day vegetation cover can result in significant perturbations to the simulated climate. The role of the Northern Hemisphere extra-tropics is further demonstrated with a fourth representation of vegetation cover produced by imposing simulated changes in Northern Hemisphere extra-tropical vegetation from the end of the 21st century on the present day climate. This experiment shows that through similar processes extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model, with a particular influence on the monsoon onset. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change and its impact on the tropics and South Asian monsoon in the latest generation of Earth System models.

scholarly journals Synoptic Preconditions for Extreme Flooding during the Summer Asian Monsoon in the Mumbai Area

2014 ◽  
Vol 15 (1) ◽  
pp. 229-242 ◽  
Author(s):  
Marco Lomazzi ◽  
Dara Entekhabi ◽  
Joaquim G. Pinto ◽  
Giorgio Roth ◽  
Roberto Rudari
Keyword(s):  
Time Series ◽  
South Asian ◽  
Asian Monsoon ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Value Added ◽  
South Asian Monsoon ◽  
Flood Events ◽  
The South ◽  
Synoptic Conditions

Abstract The summer monsoon season is an important hydrometeorological feature of the Indian subcontinent and it has significant socioeconomic impacts. This study is aimed at understanding the processes associated with the occurrence of catastrophic flood events. The study has two novel features that add to the existing body of knowledge about the South Asian monsoon: 1) it combines traditional hydrometeorological observations (rain gauge measurements) with unconventional data (media and state historical records of reported flooding) to produce value-added century-long time series of potential flood events and 2) it identifies the larger regional synoptic conditions leading to days with flood potential in the time series. The promise of mining unconventional data to extend hydrometeorological records is demonstrated in this study. The synoptic evolution of flooding events in the western-central coast of India and the densely populated Mumbai area are shown to correspond to active monsoon periods with embedded low pressure centers and have far-upstream influences from the western edge of the Indian Ocean basin. The coastal processes along the Arabian Peninsula where the currents interact with the continental shelf are found to be key features of extremes during the South Asian monsoon.

scholarly journals The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

2021 ◽  
Vol 17 (3) ◽  
pp. 1243-1271
Author(s):  
Francesco S. R. Pausata ◽  
Gabriele Messori ◽  
Jayoung Yun ◽  
Chetankumar A. Jalihal ◽  
Massimo A. Bollasina ◽  
...  
Keyword(s):  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Season ◽  
Dust Emission ◽  
Northern Africa ◽  
South Asian Monsoon ◽  
The South ◽  
Airborne Dust ◽  
Orbital Parameters ◽  
Humid Period

Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ∼6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

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