MONSOON IN INDIA
- Monsoons involve a significant shift in wind direction between seasons. During the wet season, winds blow from the ocean towards the land, bringing moist air and heavy rainfall. During the dry season, winds reverse direction, blowing from the land to the ocean, resulting in dry conditions
- The wet season is marked by heavy and sustained rainfall, often leading to flooding and lush vegetation growth. The dry season, in contrast, has little to no rainfall, leading to drought conditions in some regions
- Monsoons are most commonly associated with South Asia, particularly the Indian subcontinent. Other regions that experience monsoon patterns include Southeast Asia, parts of Africa, Australia, and the southwestern United States
- Monsoons play a crucial role in the climate and agriculture of affected regions. They provide essential water for crops and replenish groundwater supplies. However, they can also cause destructive flooding and landslides
- The Indian monsoon is a significant and complex weather phenomenon that has a profound impact on the climate, agriculture, and economy of the Indian subcontinent one of the most well-known and studied monsoon systems is the Indian monsoon, which significantly affects the climate and economy of India and its neighbouring countries.
- Southwest Monsoon: Occurs from June to September. Winds blow from the southwest, bringing moisture-laden air from the Indian Ocean, resulting in heavy rainfall over the Indian subcontinent.
- Northeast Monsoon: Occurs from October to December. Winds blow from the northeast, bringing drier air, although the southeastern coast of India and Sri Lanka receive some rainfall during this period.
- The Southwest Monsoon from June to September delivers over 70% of India's annual rainfall. Typically, the monsoon reaches the Andaman Sea in the third week of May and moves onto the mainland through Kerala, with June 1 being the usual start date.
- Its progression is characterised by surges, advancing rapidly to central India before slowing down.
- By the end of June, it generally reaches north Uttar Pradesh, Delhi, and surrounding areas, covering the entire country by July 15. An early or timely onset does not ensure consistent or adequate rainfall throughout the season, nor does a delayed onset necessarily lead to below-average rainfall.
- The total rainfall from June to September is influenced by various factors and exhibits natural year-to-year variability, making each monsoon season unique. The distribution of rainfall is as important as the total amount.
- The India Meteorological Department (IMD) predicts 'above normal' rainfall for this season, estimated to be 106% of the Long Period Average of 880 mm (based on 1971-2020 data).
- This forecast of increased rainfall is largely due to the expected development of La Niña conditions, which typically enhance the Indian monsoon, and a positive phase of the Indian Ocean Dipole (IOD)
The Indian Monsoon is broadly divided into two main branches, each with distinct characteristics and regions of influence: the Arabian Sea Branch and the Bay of Bengal Branch.
Arabian Sea Branch
Characteristics:
- Source: Originates from the southwestern part of the Arabian Sea.
- Path: Moves towards the western coast of India.
- Onset: Typically hits the Kerala coast around June 1st, marking the official start of the Southwest Monsoon.
Key Features:
- Western Ghats: The moist air from the Arabian Sea rises when it encounters the Western Ghats, causing heavy rainfall on the windward side.
- Progression: Advances northwards along the western coast, bringing significant rainfall to regions such as Goa, Karnataka, Maharashtra, and Gujarat.
- Reach: Extends into central and northwestern India, contributing to the monsoon rains in these areas.
Bay of Bengal Branch
Characteristics:
- Source: Originates from the southeastern part of the Bay of Bengal.
- Path: Moves towards the eastern coast of India and then travels northwestwards.
Key Features:
- Northeastern India: Initially brings heavy rainfall to northeastern states such as Assam, Meghalaya, and West Bengal as it hits the Eastern Himalayas.
- Progression: Moves across the Indo-Gangetic Plain, covering Bihar, Uttar Pradesh, and eventually reaching northern India including Delhi.
- Distribution: Influences the monsoon patterns in central and northern India, often merging with the Arabian Sea branch to provide widespread rainfall.
Coriolis Force
The Coriolis Force is an apparent force resulting from the Earth's rotation. It influences the rotational movement seen in tropical cyclones, causing monsoon winds to deflect eastward and blow from the southwest to the northeast. Since the Earth's rotation is constant, the Coriolis Force experienced by air at a specific latitude and velocity remains steady.
Mascarene High
The Mascarene High is a significant high-pressure zone that drives the southwest monsoon winds toward the Indian subcontinent. Forming by mid-April, the strength of this high-pressure area is crucial in determining the intensity of the Indian monsoon. A stronger high leads to stronger winds and a more robust monsoon. A delayed formation of the Mascarene High can result in a delayed onset of the monsoon in India.
Indian Summer
High-pressure winds move towards low-pressure areas. The Himalayas play a key role in summer heating by blocking cold northern air, allowing for warmer conditions. During summer, India becomes extremely hot, and surrounding ocean temperatures rise. This creates a pressure gradient between the cooler sea air and the warmer land air, particularly over Rajasthan. Consequently, monsoon winds are drawn towards the low-pressure area over India.
Indian Ocean Dipole
In 1999, N.H. Saji and colleagues from Japan’s University of Aizu identified the Indian Ocean Dipole (IOD), an ENSO-like phenomenon in the Indian Ocean. The IOD has three phases: positive, negative, and neutral. During the positive IOD phase, sea surface temperatures in the western Indian Ocean are warmer than in the eastern part. Conversely, during the negative phase, the eastern Indian Ocean is warmer. No significant gradient exists during the neutral phase. Positive IOD phases are associated with significantly higher Indian summer monsoon rainfall compared to negative IOD phases.
El Niño
El Niño refers to the occasional appearance of a warm ocean current off the coast of Peru, temporarily replacing the cold Peruvian current. Named after the infant Christ ("El Niño" means "the child" in Spanish) because it occurs around Christmas, El Niño leads to increased sea-surface temperatures and reduced trade winds in the region.
El Niño Southern Oscillation (ENSO)
The El Niño Southern Oscillation (ENSO) describes the cyclic variations in sea surface temperatures around the equatorial Pacific Ocean. ENSO's unpredictable nature has long challenged forecasters. It affects global weather patterns, especially in countries bordering the Pacific Ocean, by influencing air circulation.
Intertropical Convergence Zone (ITCZ)
The ITCZ is a broad low-pressure area found in equatorial latitudes where the northeast and southeast trade winds converge. This zone shifts north and south following the sun’s apparent movement. The position and strength of the ITCZ significantly affect the Indian Monsoon.
Tropical Easterly Jet (TEJ)
The TEJ plays a crucial role in initiating the southwest monsoon. This jet stream flows over the Indian Ocean near Madagascar, intensifying the high-pressure cell and triggering the southwest monsoon. Persistent high summer temperatures over Tibet help develop the easterly jet, leading to heavy rainfall in India. Conversely, if the Tibetan Plateau retains its snow cover, the easterly jet does not form, resulting in reduced monsoon rainfall in India. Thus, years with extensive snow in Tibet are typically followed by weaker monsoons and less rainfall
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For Prelims: Southwest monsoon El Nino, Coriolis Force For Mains: GS I- Monssons and their effects on Indian Agriculture |
Source: Indianexpress
