What is Mascarene High (MH)? The Indian Ocean Dipole (IOD)

This high-pressure region located between 25°S-35°S and 40°E-90°E near the Mascarene Islands in the southern Indian Ocean is a source of Southwest monsoon in India. Since, it is a high pressure are, it is also known as Mascarene high.

characteristics: 

• The Mascarene High (MH) is a semi-permanent subtropical high-pressure zone in the South Indian Ocean.
• It is also called the Indian Ocean subtropical high, which is a high-pressure area located between 20° to 35° South latitude and 40° to 90° East longitude.
• It is a region from where the cross-equatorial winds blow to India.
• It has been named after the Mascarene Islands, in the Indian Ocean east of Madagascar consisting of the islands belonging to Mauritius as well as the French Réunion Islands.
• Apart from its large influence on African and Australian weather patterns, it also helps in driving the inter-hemispheric circulation between the Indian Ocean in the south and subcontinental landmass in the north.

The Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia. The IOD affects the climate of Australia and other countries that surround the Indian Ocean Basin, and is a significant contributor to rainfall variability in this region.

Positive event:

warmer sea surface temperatures in the western Indian Ocean relative to the east

easterly wind anomalies across the Indian Ocean and less cloudiness to Australia's northwest

less rainfall over southern Australia and the Top End.

Negative event:

cooler sea surface temperatures in the western Indian Ocean relative to the east

winds become more westerly, bringing increased cloudiness to Australia's northwest

more rainfall in the Top End and southern Australia.