NCERT Exercises
1. Choose the right answer from the four alternatives given below.
(i) What causes rainfall on the coastal areas of Tamil Nadu in
the beginning of winters?
(a) South-West monsoon
(b) Temperate cyclones
(c) North-Eastern monsoon
(d) Local air circulation
Ans. (c) North-Eastern monsoon
(ii) What is the proportion of area of India which receives
annual rainfall less than 75 cm?
(a) Half
(b) One-third
(c)Two-third
(d) Three-fourth
Ans.
(b) One-third
Note – According to
Ministry of Statistics and Programme Implementation, Government of India 1/3rd
area of India receives annual rainfall less than 75 cm. According to the
Ministry the Distribution of Area according to Annual Rainfall (in MM) is
following Category: DRY 0-750 MM 30%; Medium 750-1150 MM 42%,
1150-2000 MM 20%; High More than 2000 MM 8%.
(iii) Which one of the following is not a fact regarding South
India?
(a) Diurnal range of temperature is less here.
(b) Annual range of temperature is less here.
(c) Temperatures here are high throughout the year.
(d) Extreme climatic conditions are found here.
Ans.
(d) Extreme climatic conditions are found here
(iv) Which one of the following phenomenon happens when the sun
shines vertically over the Tropic of Capricorn in the southern hemisphere?
(a) High pressure develops over North-western India due to low
temperatures.
(b) Low pressure develops over North-western India due to high
temperatures.
(c) No changes in temperature and pressure occur in
north-western India.
(d) ‘Loo’ blows in the North-western India.
Ans.
(a) High pressure develops over North-western India
due to low temperatures
2. Answer the following questions in about 30 words.
(i) What is the Inter-Tropical Convergene Zone?
Ans. The Inter Tropical Convergence Zone (ITCZ) is a low
pressure zone located at the equator where trade winds converge, and
so, it is a zone where air tends to ascend.
·
In July, the ITCZ is located
around 20°N-25°N latitudes (over the Gangetic plain), sometimes called the
monsoon trough. This monsoon trough encourages the development of thermal
low over north and northwest India. Due to the shift of ITCZ, the trade winds of
the southern hemisphere cross the equator between 40° and 60°E longitudes and
start blowing from southwest to northeast due to the Coriolis force. It
becomes southwest monsoon.
·
In winter, the ITCZ moves
southward, and so the reversal of winds from northeast to south and southwest,
takes place. They are called northeast monsoons.
(ii) What is meant by ‘bursting of monsoon’? Name the place of
India which gets the highest rainfall.
Ans.
The rain in the southwest monsoon season begins rather abruptly.
One result of the first rain is that it brings down the temperature
substantially. This sudden onset of the moisture-laden winds associated with
violent thunder and lightening is often termed as the “break” or “burst”
of the monsoons. The monsoon may burst in the first week of June in the
coastal areas of Kerala, Karnataka, Goa and Maharashtra while in the interior
parts of the country; it may be delayed to the first week of July.
Mawsynram,
located on the crest of Khasi hills in Meghalaya,
receives the highest average annual rainfall in the world.
(iii) Which type(s) of cyclones cause rainfall in north-western
India during winter? Where do they originate?
Ans.
The western cyclonic disturbances which enter the Indian
subcontinent from the west and the northwest during the winter months,
originate over the Mediterranean Sea and are brought into India by the westerly
jet stream. An increase in the prevailing night temperature generally indicates
an advance in the arrival of these cyclones disturbances.
During
winter season in northwestern India, some weak temperate cyclones from
the Mediterranean Sea cause rainfall in Punjab, Haryana, Delhi and western
Uttar Pradesh. Although the amount is meagre, it is highly beneficial
for Rabi crops. The precipitation is in the form of snowfall in the lower
Himalayas. It is this snow that sustains the flow of water in the Himalayan
Rivers during the summer months.
The
precipitation goes on decreasing from west to east in the plains and from north
to south in the mountains. The average winter rainfall in Delhi is around 53
mm. In Punjab and Bihar, rainfall remains between 25 mm and 18 mm respectively.
3. Answer the following questions in not more than 125 words.
(i) Notwithstanding the broad climatic unity, the climate of
India has many regional variations. Elaborate this statement giving suitable
examples.
Ans.
In southern India, woollen clothes are not required. In
northeastern states, winters are mild except in the hills. There are variations
in weather conditions during different seasons. These changes occur due to the
changes in the elements of weather (temperature, pressure, wind direction and
velocity, humidity and precipitation, etc.).
The
monsoon regime emphasises the unity of India with the rest of Southeast Asian
region. This view of broad unity of the monsoon type of climate should
not, however, lead one to ignore its regional variations which differentiate
the weather and climate of different regions of India. For
example, the climate of Kerala and Tamil Nadu in the south is so
different from that of Uttar Pradesh and Bihar in the north, and yet all of
these have a monsoon type of climate. The climate of India has
many regional variations expressed in the pattern of winds, temperature and
rainfall, rhythm of seasons and the degree of wetness or dryness. These
regional diversities may be described as sub-types of monsoon climate. Let us
take a closer look at these regional variations in temperature, winds and
rainfall.
While
in the summer the mercury occasionally touches 55°C in the western Rajasthan,
it drops down to as low as minus 45°C in winter around Leh. Churu in Rajasthan
may record a temperature of 50°C or more on a June day while the mercury
hardly touches 19°C in Tawang (Arunachal Pradesh) on the same day. On a
December night, temperature in Drass (Jammu and Kashmir) may drop down to minus
45°C while Thiruvananthapuram or Chennai on the same night records 20°C or
22°C. These examples confirm that there are seasonal variations in
temperature from place to place and from region to region in India.
Not
only this, if we take only a single place and record the temperature for just
one day, variations are no less striking. In Kerala and in the
Andaman Islands, the difference between day and night temperatures may be
hardly seven or eight degree Celsius. But in the Thar Desert, if the day
temperature is around 50°C, at night, it may drop down considerably upto 15°-20°C.
Now,
let us see the regional variations in precipitation. While
snowfall occurs in the Himalayas, it only rains over the rest of the country. Similarly,
variations are noticeable not only in the type of precipitation but also in its
amount. While Cherrapunji and Mawsynram in the Khasi Hills of
Meghalaya receive rainfall over 1,080 cm in a year, Jaisalmer in Rajasthan
rarely gets more than 9 cm of rainfall during the same period. Tura situated
in the Garo Hills of Meghalaya may receive an amount of rainfall in a single
day which is equal to 10 years of rainfall at Jaisalmer. While the annual
precipitation is less than 10 cm in the north-west Himalayas and the western
deserts, it exceeds 400 cm in Meghalaya.
The
Ganga delta and the coastal plains of Orissa are hit by strong rain-bearing
storms almost every third or fifth day in July and August while the Coromandal
coast, a thousand km to the south, goes generally dry during these months. Most
parts of the country get rainfall during June-September, but on the coastal
areas of Tamil Nadu, it rains in the beginning of the winter season.
In
spite of these differences and variations, the climate of India is monsoonal in
rhythm and character.
(ii) How many distinct seasons are found in India as per the
Indian Meteorological Department? Discuss the weather conditions associated
with any one season in detail.
Ans.
The climatic conditions of India can best be described in terms
of an annual cycle of seasons. The Indian
Meteorological Department and The meteorologists
recognise the following four seasons:
(i)
The cold weather season
(ii)
The hot weather season
(iii)
The southwest monsoon season
(iv)
The retreating monsoon season.
The
Cold Weather Season
Temperature: Usually,
the cold weather season sets in by mid-November in northern India. December and
January are the coldest months in the northern plain. The mean daily
temperature remains below 21°C over most parts of northern India. The night
temperature may be quite low, sometimes going below freezing point in Punjab
and Rajasthan.
There
are three main reasons for the excessive cold in north India during this
season:
(i)
States like Punjab, Haryana and Rajasthan being far away from the moderating
influence of sea experience continental climate.
(ii) The
snowfall in the nearby Himalayan ranges creates cold wave situation;
and
(iii)
Around February, the cold winds coming from the Caspian Sea and Turkmenistan
bring cold wave along with frost and fog over the northwestern parts of India.
The
Peninsular region of India, however, does not have any well-defined cold
weather season. There is hardly any seasonal change in the distribution pattern
of the temperature in coastal areas because of moderating influence of the sea
and the proximity to equator. For example, the mean maximum temperature for
January at Thiruvanantapuram is as high as 31°C, and for June, it is 29.5°C.
Temperatures at the hills of Western Ghats remain comparatively low.
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| INDIA: MEAN MONTHLY TEMPERATURES OF THE DAY IN JANUARY |
Pressure and Winds: By
the end of December (22nd December), the sun shines vertically over the Tropic
of Capricorn in the southern hemisphere. The weather in this season is
characterised by feeble high pressure conditions over the northern plain. In
south India, the air pressure is slightly lower. The isobars of 1019 mb and
1013 mb pass through northwest India and far south, respectively.
 |
| INDIA: PRESSURE AND SURFACE WINDS (JANUARY) |
As a
result, winds start blowing from northwestern high pressure zone to the low air
pressure zone over the Indian Ocean in the south. Due to low pressure gradient,
the light winds with a low velocity of about 3-5 km per hour begin to blow
outwards. By and large, the topography of the region influences the wind
direction. They are westerly or northwesterly down the Ganga Valley. They
become northerly in the Ganga-Brahmaputra delta. Free from the influence of
topography, they are clearly northeasterly over the Bay of Bengal.
During
the winters, the weather in India is pleasant. The pleasant weather conditions,
however, at intervals, get disturbed by shallow cyclonic depressions
originating over the east Mediterranean Sea and travelling eastwards across
West Asia, Iran, Afghanistan and Pakistan before they reach the northwestern
parts of India. On their way, the moisture content gets augmented from the
Caspian Sea in the north and the Persian Gulf in the south.
Rainfall: Winter
monsoons do not cause rainfall as they move from land to the sea. It is because
firstly, they have little humidity; and secondly, due to anti cyclonic
circulation on land, the possibility of rainfall from them reduces. So, most
parts of India do not have rainfall in the winter season.
However,
there are some exceptions to it:
(i) In northwestern
India, some weak temperate cyclones from the Mediterranean Sea cause
rainfall in Punjab, Haryana, Delhi and western Uttar Pradesh. Although the
amount is meagre, it is highly beneficial for Rabi crops. The
precipitation is in the form of snowfall in the lower Himalayas. It is this
snow that sustains the flow of water in the Himalayan Rivers during the summer
months. The precipitation goes on decreasing from west to east in the plains
and from north to south in the mountains. The average winter rainfall in Delhi
is around 53 mm. In Punjab and Bihar, rainfall remains between 25 mm and 18 mm respectively.
(ii)
Central parts of India and northern parts of southern Peninsula also get winter
rainfall occasionally.
(iii) Arunachal
Pradesh and Assam in the northeastern parts of India also have rains between 25
mm and 50 mm during these winter months.