South Asian High
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| South Asian High | |
|---|---|
| Name | South Asian High |
| Type | Atmospheric anticyclone |
| Location | Indian subcontinent, Tibetan Plateau, Himalayas |
| Altitude | Upper troposphere / lower stratosphere (~100–200 hPa) |
| Season | Northern Hemisphere summer (June–August) |
| Related | Indian Summer Monsoon, Subtropical Jet Stream, Mascarene High, East Asian Monsoon |
South Asian High is a persistent upper‑tropospheric anticyclonic circulation that forms over the Indian subcontinent and the Tibetan Plateau during the Northern Hemisphere summer. It exerts strong influence on the Indian Summer Monsoon, modulates the position of the Subtropical Jet Stream and interacts with circulations such as the Mascarene High and the Somali Jet. The system links regional heating over the Himalayas and the Tibetan Plateau to large‑scale circulation patterns spanning from the Arabian Sea to the South China Sea.
Overview
The South Asian High appears as an upper‑level anticyclone centered near the 100–200 hPa layer above the Tibetan Plateau and adjacent parts of the Indian subcontinent. It is most pronounced during boreal summer when differential heating of the Tibetan Plateau, the Himalayas, and surrounding basins produces a strong thermal high. The High is a key component of the seasonal circulation that includes the Indian Ocean Dipole, the Madden–Julian Oscillation, and the Walker circulation, and it couples to midlatitude features such as the Rossby wave train emanating toward Europe and East Asia.
Formation and Structure
The formation of the South Asian High is driven by intense solar heating of the elevated Tibetan Plateau and the contrast with adjacent oceans like the Arabian Sea and the Bay of Bengal. Orographic forcing by the Greater Himalaya and radiative warming create an upper‑tropospheric warm core that organizes into an anticyclonic circulation. Vertically, the feature spans the upper troposphere to the lower stratosphere, overlapping levels analyzed in reanalyses from ERA‑Interim, NCEP/NCAR, and MERRA. Horizontally, centers have been identified over northern India, southwestern China, and central Pakistan depending on seasonal variability and interannual drivers such as the El Niño–Southern Oscillation and the Indian Ocean Dipole.
Seasonal and Climatic Impacts
Seasonally, the South Asian High strengthens in late spring and peaks in June–August, coincident with the onset and active phase of the Indian Summer Monsoon. Its presence correlates with upper‑level divergence that facilitates deep convection over the Bay of Bengal and the Arabian Sea, while its subsident flanks suppress convection over continental interiors like Rajasthan and the Indo‑Gangetic Plain. The High also influences teleconnections to regions including East Africa, the Middle East, and Southeast Asia, interacting with modes such as the Pacific Decadal Oscillation and the North Atlantic Oscillation to modulate seasonal rainfall and temperature patterns across South Asia.
Role in Monsoon Dynamics
The South Asian High plays a dual role in controlling monsoon strength and variability. Its upper‑level anticyclonic circulation helps to establish favorable shear and divergence for monsoon troughs and monsoon depressions tracking from the Bay of Bengal into inland India. Conversely, an anomalously strong or displaced High can inhibit low‑level moisture transport by altering the Somali Jet and Findlater Jet, thereby affecting onset timing and active–break cycles of the Indian Summer Monsoon. Interactions between the High and intraseasonal oscillations such as the Madden–Julian Oscillation and regional disturbances including the Tibetan Plateau vortex influence extreme rainfall events and monsoon variability.
Variability and Trends
Interannual and decadal variability of the South Asian High is linked to drivers including El Niño–Southern Oscillation, the Indian Ocean Dipole, and anthropogenic forcing represented in coupled models like CMIP5 and CMIP6. Observational studies using satellite datasets and radiosonde archives document shifts in intensity and position over recent decades, with some analyses indicating an expansion and poleward shift similar to trends reported for the Subtropical Highs in other basins. Climate model projections under scenarios from the Intergovernmental Panel on Climate Change suggest potential changes in the High’s altitude and strength, with implications for monsoon rainfall patterns, regional temperature extremes, and hydrology across the Indus Basin, the Ganges Basin, and the Brahmaputra Basin.
Effects on Air Quality and Weather Hazards
By modulating vertical motion and transport pathways, the South Asian High affects pollution dispersion over urban centers like Delhi, Karachi, and Dhaka. Upper‑level subsidence associated with the High can lead to stagnation and buildup of aerosols and trace gases, interacting with emissions from sources such as the Hindustan Petroleum Corporation, industrial corridors, and agricultural burning zones in Punjab and Haryana. Moreover, the High’s influence on monsoon breaks can exacerbate heatwaves over North India and droughts in South India, while its interactions with cyclogenesis regions in the Arabian Sea and Bay of Bengal modulate tropical cyclone tracks that impact Sri Lanka, Myanmar, and Bangladesh.
Observational and Modeling Studies
Research on the South Asian High employs reanalysis products like ERA5 and JRA‑55, satellite missions including AIRS, AIRS/AMSU, and CALIPSO, and field campaigns such as the Asian Monsoon Experiment and the GEWEX Asian Monsoon Experiment (GAME). Modeling efforts use global and regional frameworks including the Community Earth System Model, the Weather Research and Forecasting model, and high‑resolution convection‑permitting simulations to assess dynamics, teleconnections, and future changes under scenarios from the Coupled Model Intercomparison Project. Multidisciplinary studies link the High to impacts observed by agencies and institutions like the India Meteorological Department, the National Oceanic and Atmospheric Administration, and the World Meteorological Organization.