2. A monsoon is a seasonal change
in the direction of the prevailing
wind. This wind shift typically
brings about a marked change in
local weather. It almost always
refers to the Asian monsoon, a
large region extending from India
to Southeast Asia where monsoon
conditions prevail.
3. The ITCZ shifts northwards as the sun is overhead at the Tropic of
Cancer. Insolation over Northern India increases, causing air to rise
and creating low pressure. Equatorial maritime (Em) and Tropical
maritime (Am) air is drawn north and diverted northeast due to
the Coriolis force. The humid unstable air results in rainfall.
Amounts are increased as air is forced aloft over the Himalayas and
Western Ghats. The rainfall is vital for the cultivation of rice.
4. Low temperatures over central Asia
create areas of high pressure, at the
same time, the sub-tropical jet and
ITCZ shift south. Air moving out
from the area of high pressure is very
dry and becomes drier as it crosses
over the Himalayas, causing clear
skies and sunny weather over most of
India from November to May.
5. Monsoonwinds are causedwhen
the Sunheats the atmosphere. It is
a shift in windthat occurs due to
a change in local weather. Simply
speaking, when, there are
differences in temperatures
between the oceans and the
continents, monsoonwinds occur.
6. In areas such as SouthernAsia,
winds blow fromlandto ocean
mostof the year, making the
climate dry. However, during
certain months of the year, the
winds beginto blowfromthe
oceanto the landmaking the air
moist. This moist oceanair is what
causes the monsoonrains over
many countries.
7. Many partsof the world
experience monsoons to some
extent. Probably the mostfamous
are the Asianmonsoons, which
affect India, China, Japan, and
Southeast Asia. Monsoons also
impact portions of central Africa,
where their rainis critical to
supporting life in the areasouth
of the Sahara Desert.
8. The South-West monsoon
becomes a weak current and
withdraws fromPunjab by mid-
September. It leaves the Ganga
deltaby late October. By early
November, it leaves the southern
part of the peninsula. These
particular months from
September to November are
termedas the periodof
'retreating monsoon'. During
this time, the days are hot,
nightsare cool and the daily
range of temperature is high.
9. Intensificationof the low-pressure
conditionover the northernplains.
This attracts the trade winds of the
southernhemisphere, which start
over the southernoceans. These
winds enter the Indianpeninsula,
moving in south-westerly
direction, thus bringing abundant
moisture. These are strongwinds
and blowat about 30 kmph.
