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READY RECKONER OF INDIANGEOGRAPHY |21|

Indian Monsoon (i) The offshore meteorological conditions.
(ii) The position of the equatorial jet stream along
Onset of the Monsoon the eastern coast of Africa.
• During April and May when the sun shines vertically

over the Tropic of Cancer, the large landmass in the Frequency of tropical depressions depends on
position of ITCZ/ monsoon trough.
north of Indian Ocean gets intensely heated. This
causes the formation of an intense low pressure in Break in the Monsoon:
the north-western part of the subcontinent.
During the south-west monsoon period after having rains
• Since the pressure in the Indian Ocean in the south of for a few days, if rain fails to occur for one or more weeks,
it is known as break in the monsoon. These dry spells are
the landmass is high as water gets heated slowly, the
quite common during the rainy season.
low pressure cell attracts the southeast trades across
the Equator. These breaks in the different regions are due to different
reasons:
These conditions help in the northward shift in the
position of the ITCZ. The southwest monsoon may thus, (i) In northern India rains are likely to fail if the rain-
be seen as a continuation of the southeast trades bearing storms are not very frequent along the
monsoon trough or the ITCZ over this region.
deflected towards the Indian subcontinent after crossing

the Equator. These winds cross the Equator between 40°E (ii) Over the west coast the dry spells are associated with
and 60°E longitudes. days when winds blow parallel to the coast.
After withdrawal of westerly jet streams, easterly jet EI-Nino and the Indian Monsoon:

stream sets in at 15 degree N, thereby resulting in burst of
EI-Nino is a complex weather system that appears once
monsoon in India.
every three to seven years, bringing drought, floods and
other weather extremes to different parts of the world.
Entry of Monsoon into India:
The system involves oceanic and atmospheric phenomena
The southwest monsoon sets in over the Kerala coast by
th
st
1 June and to reach Mumbai and kolkata 10 and 13 th with the appearance of warm currents off the coast of
June. Peru in the Eastern Pacific and affects weather in many
places including India.
Rain-bearing Systems and Rainfall Distribution
EI-Nino is merely an extension of the warm equatorial
There seem to be two rain-bearing systems in India. current which gets replaced temporarily by cold Peruvian
current or Humbolt current. This current increases the
1. In Bay of Bengal causing rainfall over the plains of
temperature of water on the Peruvian coast by 10°C. This
north India.
results in:
2. Arabian Sea current of the south- west monsoon
(i) Distortion of equatorial atmospheric circulation
which brings rain to the west coast of India. Much of
the rainfall along the Western Ghats is orographic as (ii) Irregularities in the evaporation of sea water
the moist air is obstructed and forced to rise along the
(iii) Reduction in the amount of planktons which further
Ghats.
reduces the number of fish in the sea
The intensity of rainfall over the west coast of India is,
however, related to two factors:

Indian Monsoon
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