Southern Annular Mode (SAM)

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Context

• The Indian National Centre for Ocean Information Services (INCOIS) recently determined that the Southern Annular Mode (SAM), an essential climate trend, is crucial in determining water conditions across the Indian Ocean.

About

• It is the north-south migration of the Southern Westerly Winds across timeframes ranging from tens to hundreds of years.
• The Antarctic Oscillation is another name for it.
• They blow virtually continuously in the southern hemisphere's mid- to high latitudes.
• It is commonly described as the difference in zonal mean sea level pressure between 40° South (mid-latitudes) and 65° South (Antarctica).

Positive Southern Annular Mode

• In this mode, there is lower anomalous air pressure over Antarctica and higher anomalous air pressure over the mid-latitudes.
• The belt of strong westerly winds strengthens and contracts towards Antarctica.

Negative Southern Annular Mode

• In this mode, the belt of strong Southern Westerly Winds expands northwards towards the equator, bringing cold, wet weather to Patagonia, glacier advance, and decreased Circumpolar Deep-Water upwelling on the Antarctic Continental Shelf.

Significance

• The research helps to improve the accuracy of wave predictions and can aid in the identification of fair-weather windows.
• It will benefit the fishing industry as well as blue economy stakeholders like shipping, marine boards, and the oil industry with their multi-million-dollar operations at sea.

PRACTICE QUESTION Discuss the significance of the Southern Annular Mode (SAM) in the context of climate variability and its potential implications for the Southern Hemisphere.