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1. INDIAN WINDS AND MONSOONS!!
A PowerPoint presentation
to know more about our
country’s winds and
monsoons…

2. FIRST,LET US KNOW ABOUT INDIAN
WINDS…
The winds at the surface may be classified into
four main types, i.e.(1) the planetary winds, (2)
the monsoon winds, (3) cyclones and
anticyclones (4) local winds.
Today, we shall speak about the local winds and
monsoon winds of India.

4. MONSOON WINDS IN INDIA…
 The type of wind system in which there is a complete or almost
complete reversal of prevailing direction from season to season
is known as the monsoon winds. The largest and best
developed monsoonal area in the world is SE Asia including
India. During the summer (April to September) the interior of the
continents is intensely heated. This creates a low pressure into
which winds are drawn from over the cooler surrounding
oceans. In India South-west monsoon wind blows in summer. As
the air from over the oceans is very moist, it results in heavy
rainfall. During the winter (October to March) the continental
interior becomes much cooler than the surrounding oceans; the
wind direction is thus reversed, blowing from the continental
high pressure to the low pressure over the oceans. This creates
the NE monsoon over India, which is generally a cool and dry
wind.

6. THE DISTRIBUTION OF RAINFALL IN INDIA…
The distribution of rainfall is controlled by the relief
features of the land and the direction of the rain-
bearing winds. The average annual rainfall in our
country is about 120 cm.Most of it comes during
four months from the South-West monsoons.
Indian Peninsula divides the summer monsoon
current into two branches,namely the Arabian Sea
branch and Bay of Bengal branch. The monsoon
winds originating over the Arabian Sea further split
into three branches.
The Arabian and Bay of Bengal branches’
information is listed in the following slides.

7. THE THREE SUB-BRANCHES OF THE ARABIAN SEA BRANCH…
 Its one branch is obstructed by the Western Ghat climbs and becomes cool
as a result; the windward side of the Sahyadris and Western Coastal Plain
receive very heavy rainfall ranging between 250 cm and 400 cm. After
crossing the Western Ghats, these winds descend and get heated up. This
reduces humidity in the winds. As a result, these winds cause little rainfall
east of the Western Ghats. This region of low rainfall is known as the rain-
shadow area and includes parts of Maharashtra and Karnataka.
 Another branch of the Arabian Sea monsoon strikes the coast North of
Mumbai. Moving along the Narmada and Tapi River valleys, these winds
cause rainfall in extensive areas of central India. Thereafter, they enter the
Ganga plains and mingle with the Bay of Bengal branch.
 A third branch moves northwards through Kacchh, Saurashtra and western
Rajasthan which fail to get adequate rainfall. This is due to the absence of
mountain barrier in Kacchh, parallel position of the Aravalli ranges, shutting
effect of the hot and dry air from Baluchistan obstructing the upward
movement of the moisture by the overlying dry air. In Punjab and Haryana, it
too joins the Bay of Bengal branch. These two branches, reinforced by each
other, cause rains in the western Himalayas.

8. THE BAY OF BENGAL BRANCH…
 The Bay of Bengal branch strikes the coast of Myanmar and part of
South-East Bangladesh. But the Arakan Hills along the coast of
Myanmar deflect a big portion of this branch towards the Indian
subcontinent. From here, this branch splits into two under the
influence of the Himalayas and the thermal low in North-West India.
 Its one branch moves westward along the Ganga plains reaching as
far as the Punjab plains. The other branch moves up the Brahmaputra
valley in the North and the North-East, causing widespread rains. Its
sub-branch strikes the Garo and Khasi hills of
Meghalaya.Mawsynram, located on the crest of Khasi hills, receives
the highest average annual rainfall (1141 cm) in the world. The Tamil
Nadu coast remains dry during this season.
 There are two factors responsible for Tamil Nadu remaining dry:-
 i. The Tamil Nadu coast is situated parallel to the Bay of Bengal
branch.
 ii. It lies in the rain shadow area of the Arabian Sea branch of the
South-West.

9. THE DISTRIBUTIONAL PATTERN OF RAINFALL IN INDIA…
 In general, the distributional pattern of rainfall shows
two main trends:-
 i. It steadily declines towards the West and the North-
West from the Bengal and Orissa coasts.
 ii. From the West and the East coasts, it exhibits
declining trends towards the interior parts of the
Peninsula.
 The general direction of winds in this season is from
South-West to North-East in the major part of the
country. However due to the presence of the Himalaya,
these are south-easterly and easterly in the North-East
and Ganga Plain.

11. LOCAL WINDS IN INDIA…

12. BASIC INFORMATION AND EXAMPLES OF LOCAL WINDS IN INDIA…
 Winds, caused by local factors and confined to a limited area
compared to planetary winds, are called local winds. Some well
known examples of local winds are given below:
 Land breeze: It is a common local wind that affects only coastal area.
During the night the land becomes very much cooler than the sea as
land is quickly chilled than the sea. The air adjacent to the surface is
also chilled with the result that there is a marked high pressure over
land. Thus the cooler, heavier, denser air over the land flows towards
the sea and land breeze occurs.
 Sea breeze: Unlike land breeze it blows the opposite way from the
sea to the land. During the day,land becomes quickly heated
compared to sea.With the result there is a marked low pressure over
the land. Thus air is drawn into the land from the comparatively high
pressure area of the adjacent seas or oceans. The southernly sea
breeze in summer is highly welcome in Kolkata.
 Now we are going to look at some information on the ‘Loo’,another
local wind in India.

14. KNOW ABOUT THE LOCAL WIND ‘LOO’…
The Loo is a strong, hot and dry summer
afternoon wind from the west which blows over
the western Indo-Gangetic Plain region of North
India and Pakistan. It is especially strong in the
months of May and June. Due to its very high
temperatures (45 °C–50 °C ), exposure to it
often leads to fatal heatstrokes.
Since it causes extremely low humidity and high
temperatures, the Loo also has a severe drying
effect on vegetation leading to widespread
browning in the areas affected by it during the
months of May and June.

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