Introduction to Monsoons in India

Introduction to Monsoons in India
Posted on 18-08-2023

Exploring India's Tropical Monsoon Climate and Its Classification

India's climatic identity is rooted in the embrace of the 'tropical monsoon' phenomenon. The term 'monsoon' draws its origins from the Arabic word 'mousim' and the Malayan word 'monsin,' both signifying the essence of seasonality. This climatic signature is distinguished by a dramatic seasonal wind reversal, a dance orchestrated by the interplay of temperature and pressure systems. During summer, winds flow from sea to land, and in winter, the pattern shifts, with winds moving from land to sea. This rhythmic climatic symphony is particularly prominent in the tropical zones, predominantly on the eastern fringes of large landmasses. However, even beyond the confines of the tropics, as evidenced in Asia, the monsoon's sway extends to regions such as China, Korea, and Japan.

Delving into Monsoons:

Monsoons, characterized by their rhythmic shifts in wind direction, paint the portrait of seasonal transformation across India. The interplay between temperature disparities and pressure systems orchestrates this enchanting climatic ballet. During the summer months, the winds carry moisture-laden currents from the sea onto the land, bestowing life-giving rains. As the seasons transition to winter, the winds shift course, returning from the land to the sea. This climatic dynamic not only shapes India's climate but holds significance across a global canvas, with Asia's monsoonal embrace extending even to non-tropical regions like China, Korea, and Japan.

Unveiling the Classification:

The Indian Meteorological Department (IMD) has meticulously classified the monsoon phenomenon into three distinct categories, each reflecting the nuances of annual rainfall patterns:

  1. Normal Monsoon: Spanning between 96% and 104% of the Long Period Average (LPA), this category embodies the climatic equilibrium. It entails an annual rainfall rhythm that resonates with historical patterns, indicative of the climatic harmony the nation is accustomed to. This range encapsulates the essence of typical monsoon behavior, where rains nurture landscapes and facilitate agricultural pursuits.

  2. Above Normal Monsoon: Dwelling within the 104%-110% LPA bracket, this classification signals an abundance of rainfall. These are years when the monsoon exhibits a surplus of precipitation, bestowing upon the land a generous dose of life-replenishing waters. Agricultural prospects are often enhanced during these above-normal monsoons, contributing to economic prosperity.

  3. Below Normal Monsoon: Ranging from 90% to 96% of the LPA, this classification is marked by a shortage of rainfall. Such monsoons pose challenges to agriculture, water availability, and overall socioeconomic dynamics. The impact of below-normal monsoons can ripple across various sectors, underscoring the interconnectedness of climate and human activities.

Quantifying the Long Period Average (LPA):

The Long Period Average (LPA) is an invaluable metric that captures the essence of monsoon rainfall. Spanning the period between 1951 and 2000, this measure aggregates the average annual rainfall received from June to September. This historical canvas provides a backdrop against which each year's monsoon performance is evaluated.

India's tropical monsoon climate, with its captivating wind dynamics and seasonal rainfall patterns, stands as a testament to the intricate interplay of climatic forces. The monsoon's influence reverberates not only across the nation but echoes on a global scale. IMD's meticulous classification of monsoons, ranging from normal to above normal and below normal, underscores the dynamic nature of this climatic phenomenon. Each category carries its distinct implications for agriculture, water management, and societal well-being. As India continues to navigate the ebb and flow of monsoons, these classifications serve as invaluable tools for understanding and preparing for the intricate rhythms of nature.

Understanding Monsoons: Windy Seasonal Transitions

The term 'monsoon' finds its etymological roots in the Arabic word 'mawsim,' signifying season, and with each changing season, a climatic phenomenon of great significance takes center stage. Monsoons, essentially characterized as seasonal winds, orchestrate a mesmerizing dance of atmospheric dynamics. These periodic winds undergo a dramatic reversal in direction, pivoting around the shifting of seasons. This climatic symphony manifests as winds blowing from sea to land during summers and reversing their course from land to sea during winters, thus unveiling a dualistic system of seasonal winds. Historically, monsoons have held profound importance, serving as navigational aids for traders and seafarers traversing vast distances. While monsoons manifest across various geographical regions like the Indian subcontinent, central-western Africa, and Southeast Asia, their most pronounced presence adorns the Indian subcontinent.

India's Seasonal Dance with Monsoons:

In the intricate choreography of atmospheric phenomena, India plays host to two distinct manifestations of monsoons: the southwest monsoon winds during summers and the northeast monsoons during winters. The former takes shape as an outcome of the formation of an intense low-pressure system above the Tibetan Plateau. This leads to a seasonal influx of winds that usher moisture-laden currents from the sea to the land, thus encapsulating the essence of summer monsoons. The latter, on the other hand, emerges as high-pressure cells establish their dominion over the Siberian and Tibetan plateaus, precipitating the journey of winds from land to sea.

Unraveling Monsoonal Queries:

  1. Exploring the Essence of Tropical Cyclones: The enigma of tropical cyclones finds its genesis in the atmospheric dance of monsoons. During the Indian summer monsoon, spanning from June to September, extensive regions of central and western India receive over 90% of their annual precipitation. Southern and northwestern India, in turn, bask in the embrace of 50% to 75% of their annual rainfall. The climatic stage is illuminated by monthly averages ranging from 200 to 300 mm, with the peak monsoon months of July and August witnessing the most abundant deluge.

  2. Monsoons Across the Globe: The phenomenon of monsoons extends its embrace beyond India's borders, shaping the climates of diverse regions. Countries like India, Sri Lanka, Bangladesh, and Myanmar experience the impact of the southwest Indian Ocean's warm, moist air during the summer monsoon, ushering in a humid climate accompanied by torrential rainfall. Monsoons, acting as winds blowing from cold to warm regions, hold sway over the climatic narratives of not only India but also Southeast Asia.

  3. Monsoon's Features Unveiled: Monsoons, while bearing the hallmark of seasonality, exhibit distinctive features. These include being primarily relief-oriented, erratic and unpredictable, and characterized by uneven distribution. The amount of rainfall varies across time, sometimes culminating in floods or droughts. The climatic stage varies widely, with certain regions receiving abundant rainfall exceeding 200 cm, leading to flood-prone conditions, while others languish with less than 50 cm annually, experiencing semi-desert environments.

  4. The Underpinnings of Monsoon Dynamics: The inception of the monsoon can be traced to the asymmetry in land and ocean temperature responses. As summer unfurls, the land's surface heats up faster than the ocean, causing low-pressure systems to develop over land and high-pressure systems to linger over the ocean. This atmospheric contrast propels winds to flow from areas of high pressure to low pressure, yielding an ocean-to-land circulation known as a sea breeze. The monsoons' arrival is marked by the influx of moist air inland, leading to the abundant rain that characterizes summer monsoons.

  5. Global Monsoons: An Asian Symphony: The robust force of monsoons extends beyond India's shores, encompassing regions like the South China Sea, Asia, and the northern extremity of Australia. These powerful summer monsoon rains, unfurling from June to September, bless countries such as Vietnam, Thailand, Cambodia, Laos, India, and Pakistan with their life-rejuvenating touch.

Southwest Monsoon's Tapestry:

  1. Causal Fabric: The southwest monsoon unfolds with its own intricate threads, woven through an intense low-pressure system materializing over the Tibetan Plateau. Concurrently, a permanent high-pressure cell establishes its dominion over the South of the Indian Ocean, particularly to the east and northeast of Madagascar during summer.

  2. Rainfall Choreography: The canvas of the southwest monsoon is adorned with a burst of heavy rainfall across India. A symphony of climatic influences, including the intense low-pressure formation over the Tibetan Plateau, the permanent high-pressure cell in the southern Indian Ocean, subtropical jet streams, African easterly jets, and the Inter-Tropical Convergence Zone (ITCZ), coalesce to create this climatic spectacle.

  3. The Splitting Monsoon: A pivotal aspect of the southwest monsoon narrative is its bifurcation into two branches. The Arabian Sea branch and the Bay of Bengal branch emerge as the southwest monsoon encounters the Western Ghats. This divergence marks the climatic trajectory of these branches as they venture forth into different climatic realms.

Northeast Monsoon's Serenade:

  1. Origin of the Northeast Monsoon: As winter blankets the landscape, high-pressure cells take center stage over the Tibetan and Siberian plateaus. This orchestration results in the inception of the northeast monsoons, bestowing rainfall upon the southeastern coast of India, encompassing regions like Tamil Nadu's coast and the southern coast of Seemandhra.

  2. The Interplay of High-Pressure Cells: The dance of the northeast monsoons is guided by high-pressure cells that weave their magic over the Tibetan and Siberian plateaus during winters. As these high-pressure cells establish their presence, the Inter-Tropical Convergence Zone (ITCZ) and the high-pressure cells in the southern Indian Ocean migrate and evolve, further influencing the climatic narrative.

In Conclusion:

The mesmerizing symphony of monsoons, marked by the ebb and flow of winds, encapsulates the essence of India's climatic dynamics. With the southwest monsoon winds gracing the land with life-nurturing rains during summers and the northeast monsoons bestowing their touch during winters, India's climatic canvas is ever-changing. As these climatic forces paint the landscape with abundance and drench it with life, the intricate interplay between land, ocean, pressure systems, and temperature gradients holds the key to deciphering the intricate climatic tapestry that adorns the Indian subcontinent.


Thank You