India likely to record normal monsoon this year
Context:
Skymet, a private weather forecasting agency, predicts a normal monsoon season for India this year, with an expected rainfall of 102% of the long-period average (LPA) from June to September.
- Scientists at the India Meteorological Department (IMD) have observed early signs of a favorable monsoon, marked by fading El Nino conditions and reduced snow cover over Eurasia.
- The IMD will issue a detailed monsoon forecast later this month.
Relevance:
GS-01 (Physical Geography)
Factors Influencing South-West Monsoon Formation:
- The differential heating and cooling of land and water create a low-pressure system over the Indian landmass, while the surrounding seas experience relatively higher pressure.
- The position of the Inter Tropical Convergence Zone (ITCZ) also plays a significant role. In summer, the ITCZ shifts over the Ganga plain, representing a broad trough of low pressure where the northeast and southeast trade winds converge. This zone moves parallel to the equator but shifts north or south with the apparent movement of the sun.
- The presence of a high-pressure area east of Madagascar, around 20°S over the Indian Ocean, significantly impacts the Indian Monsoon. The intensity and location of this high-pressure area affect the monsoon’s strength and trajectory.
- The Tibetan plateau, which experiences intense heating during summer, contributes to the formation of strong vertical air currents and a low-pressure system over the plateau, approximately 9 km above sea level.
- The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer play crucial roles in modulating monsoon patterns.
- The Southern Oscillation (SO) phenomenon also affects the monsoon. Typically, when the tropical eastern south Pacific Ocean experiences high pressure, the eastern Indian Ocean experiences low pressure. However, in certain years, there is a reversal in pressure conditions known as the SO, where the eastern Pacific experiences lower pressure compared to the eastern Indian Ocean. This periodic change influences monsoon dynamics.
Mechanism of South-West Monsoon Onset:
- ITCZ Movement: Shifting of the ITCZ dictates the onset of monsoon, with its northward movement leading to the arrival of monsoon winds from the Arabian Sea and Bay of Bengal.
- Wind Patterns: Coriolis force influences the direction of monsoon winds, which gather moisture over the Indian Ocean before reaching the subcontinent.
- Monsoon Trough: Positioning of the ITCZ over the Indo-Gangetic Plain, known as the Monsoon Trough, marks the peak monsoon season, with winds bringing rainfall to the region.
- Branches of Monsoon: Monsoon winds enter India via two branches – Arabian Sea and Bay of Bengal – with regional variations in rainfall patterns.
- Monsoon Characteristics: The monsoon exhibits periodic breaks in rainfall, influenced by the movement of the monsoon trough and regional climatic variations.
Retreating Monsoon Season:
- The retreating southwest monsoon season is characterized by clear skies and rising temperatures, often referred to as the ‘October heat’.
- While northern India experiences dry weather, the eastern part of the Peninsula receives rainfall, particularly from cyclonic depressions originating over the Andaman Sea.
- Tropical cyclones and depressions contribute to widespread rainfall along the Coromandel Coast, crucial for agriculture and water security in the region.
