Nature of Indian Monsoon

Nature of Indian Monsoon
Posted on 19-08-2023

The Indian monsoon, a critical climatic phenomenon, can be comprehended by delving into its various facets, including the onset, rainfall patterns, breaks, and retreat. The primary driver of monsoon rainfall in the Indian subcontinent remains the contrast in heating between land and sea during summer months. As temperatures surge across the northwestern plains in May, it fosters low-pressure conditions, which intensify and attract the southeasterly trade winds from the Southern Hemisphere as early as June. These winds traverse the equatorial warm currents, imbuing them with abundant moisture. Upon crossing the equator, they transform into the southwest monsoons, propelling moisture-laden air towards India.

The monsoon's arrival is marked by an abrupt initiation of rainfall that significantly lowers temperatures. This swift transition, accompanied by thunder and lightning, is termed the "break" or "burst" of the monsoon. The timing of this event varies, with coastal regions like Kerala experiencing it in early June, while inland areas may witness it in July. The temperature drop between mid-June and mid-July can range from 5°C to 8°C.

To declare the monsoon's onset over Kerala, at least 60% of 14 designated stations must report rainfall of 2.5 mm or more for two consecutive days after May 10th.

Rainfall distribution and the influence of landforms come into play as the monsoon winds approach land. The Arabian Sea and Bay of Bengal branches define the monsoon's path. The Bay of Bengal branch originates storms that bring rain to northern India's plains, while the Arabian Sea branch contributes to the west coast's rainfall. The Arabian Sea winds encounter the Western Ghats, causing heavy rainfall on the windward slopes, leading to a rain-shadow region on the leeward side. The Arabian Sea monsoon splits further, influencing central India and parts of the Gangetic plain.

The Bay of Bengal branch affects Myanmar and Bangladesh, curving into West Bengal and then bifurcating along the Ganga plains and Brahmaputra valley. Notably, the Meghalaya region, particularly Mawsynram, receives the world's highest average annual rainfall.

Dry spells called "breaks" in the monsoon occur when rain doesn't fall for a week or more during the rainy season. These interruptions vary by region, linked to factors like the frequency of rain-bearing storms and wind patterns parallel to the coast.

Monsoon retreats happen in October and November. The southwest monsoon weakens as the low-pressure trough shifts southward, prompted by the sun's apparent southward movement. This retreat initiates from western Rajasthan, advancing southward. Clear skies and higher temperatures mark this phase, referred to as the "October heat." Rain persists in eastern parts of the Peninsula, influenced by cyclonic depressions originating in the Andaman Sea. The Coromandel coast is substantially impacted by cyclonic storms, which are less frequent in the Arabian Sea.

Overall, an exploration of the Indian monsoon's characteristics sheds light on its complexity, encompassing factors like temperature gradients, wind patterns, landforms, and seasonal transitions.

Monsoons are a meteorological phenomenon characterized by seasonal shifts in the prevailing wind direction, which lead to distinct wet and dry periods in tropical regions. These alternating wind patterns are also known as periodic winds. Monsoons manifest as seasonal winds that transition from sea to land during summer and vice versa during winter, creating a dual system of seasonal air currents. India, for instance, encounters southwest monsoons during summer and northeast monsoons in winter.

Understanding the Nature of the Indian Monsoon Systematic research into the origins of rainfall within the South Asian region contributes to our grasp of the Indian monsoon, its causes, and its defining traits. Several key aspects are examined, including:

  1. Onset of the Monsoon Season: A historical assumption points to the differential heating of land and water during summer as the catalyst for the migration of monsoon winds toward the Indian subcontinent. This heating triggers a potent low-pressure system across the northern and western parts of the subcontinent. The Indian Ocean experiences high pressure during this period due to slower water warming, while a low-pressure cell in the southern part of the mainland draws southeast trade winds from the Equator to the northern hemisphere. The southwest monsoon can be seen as an extension of these southeast trades, redirected toward India after crossing the Equator. These winds intersect the Equator between longitudes 40°E and 60°E, carrying precipitation.

  2. Rain-bearing Systems and Rainfall Distribution: India witnesses two principal rain-bearing systems. Rainfall originates in the Bay of Bengal and spreads across northern India's lowlands. Additionally, the Arabian Sea's southwest monsoon current brings rain to the west coast of India. The Western Ghats' terrain contributes to orographic rainfall, as moist air is forced to ascend along the mountainous landscape. Rainfall intensity along the west coast is influenced by oceanic surface conditions and the position of the tropical jet stream along East Africa's coastline. Variations in the frequency of tropical depressions forming in the Bay of Bengal contribute to seasonal shifts in rainfall patterns.

  3. Break in the Monsoon: Periods of reduced or absent rainfall during the southwest monsoon are referred to as breaks in the monsoon. These dry spells are common and occur due to diverse factors. Rainfall may falter in northern India if rain-bearing storms are infrequent along the monsoon trough or the Intertropical Convergence Zone (ITCZ) over this region. Dry intervals along the west coast correspond to days when winds blow parallel to the shoreline.

Concluding Remarks In conclusion, a comprehensive exploration of the Indian monsoon reveals a complex interplay of climatic elements. Monsoons epitomize the seasonal reversal of wind patterns, with significant implications for precipitation and weather conditions across tropical regions. This phenomenon has historical significance, as it facilitated navigation for traders and seafarers.

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