Climate

Std 9- Geography- CLIMATE

1.      What do you mean by Coriolis force?

Answer:

An apparent force caused by the earth’s rotation. The Coriolis force is responsible for deflecting winds towards the right in the northern hemisphere and towards the left in the southern hemisphere. This is also known as Ferrel’s Law.

2.       “India’s climate has characteristics of tropical as well as sub-tropical climates” Discuss.

Answer:

The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh in the west to Mizoram in the east. Almost half of the country, lying south of the Tropic of Cancer, belongs to the tropical area. A1 the remaining area, north, of the Tropic, lies in the sub-tropics. Therefore, India’s climate has characteristics of tropical as well as subtropical climates.

3.      State three dominant characteristics of the Indian monsoon.

Answer:

The Indian monsoon is characterised by the following three dominant features :

•Seasonal reversal of direction in wind system: The monsoon winds blow from land to sea in winter and from sea to land in summer.

•Seasonal heavy rainfall and drought are common features of the Indian monsoon.

•In spite of local variations in climatic conditions, it unites the whole country in a single climatic thread of monsoon.

4.      What do you mean by Southern Oscillation?

Answer:

Normally when the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. But in certain years, there is a reversal in the pressure conditions and the eastern Pacific has lower pressure in comparison to the eastern Indian Ocean. This periodic change in pressure conditions is known as the Southern Oscillation.

A feature connected with the SO is the El Nino phenomenon in which a warm ocean current flows past the Peruvian Coast, in place of the cold Peruvian current, every 2 to 5 years. The changes in pressure conditions are connected to the El Nino. Hence, the phenomenon is referred to as ENSO (El Nino Southern Oscillations).

5.      Why do the Western Ghats receive more rainfall than the Eastern Ghats?

Answer:

In terms of relief, the Western Ghats are much higher in comparison to the Eastern Ghats. The Western Ghats are continuous stretches of high mountains.

Therefore, when the moisture-laden Arabian Sea branch of Southwest Monsoon first strikes the Western Ghats, it brings heavy rainfall along the windward side of the Western Ghats. In the Eastern Ghats, rain, bearing winds of Southwest Monsoon do not face such orographic barrier and hence receive a much lower amount of rainfall.

6.      The coastal areas of India do not register any significant change in temperature even during the winter and summer. Why?

Answer:

The coastal areas of India do not register any significant seasonal changes in temperature due to the following reasons :

(a) The influence of the surrounding sea keeps them with equable temperature conditions such as the mean monthly temperature of Thiruvananthapuram and Mumbai fluctuates very slightly.

(b) As we know the sea waters are reservoirs of warmth and they get heated and cooled down slowly due to conventional processes of heating and cooling and, hence, they remain warmer in winter and cooler in summer, keeping the coastal areas equable in temperature.

(c) The warm ocean currents, too, keep the coastal areas at almost equable temperatures throughout the year.

7.  Write a short note on withdrawal or retreat of monsoon.

Answer:

Withdrawal or the retreat of the monsoon is a more gradual process. The withdrawal . of the monsoon begins in the northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. The withdrawal from the southern half of the peninsula is rapid. By early December, the monsoon has withdrawn from the rest of the country.

The islands receive the very first monsoon showers, progressively from south to north, from the last week of April to the first week of May. The withdrawal takes place progressively from north to south from the first week of December to the first week of January. By this time the rest of the country is already under the influence of the winter monsoon.

8.      The western part of Rajasthan remains almost dry during the southwest monsoon season. Give three reasons in support of this statement.

Answer:

The western part of Rajasthan remains almost dry during the south-west monsoon Season because:

•These monsoon winds flow from the east, dropping much of its moisture along the path. When they reach Rajasthan, they are almost dry.

•There is no mountain high enough to check the flow of the Arabian Sea branch of monsoon winds. The Aravalli Mountains are not very high.

•The direction of the Aravalli Mountains is parallel to the direction of Arabian Sea

winds. Hence, these winds cross over Rajasthan without giving rainfall.

•The heat of the west Rajasthan desert does not allow the condensation of moisture to take place and hence, no rain is occurring..

9.      Distinguish between southwest monsoon and northeast monsoon.

Answer:

Southwest Monsoon                                                                        

(i)                 The summer period is marked by the southwest monsoons.                  

(ii)               (ii) The southwest monsoon blow in a southwest direction to the mainland of India from June to September.

(iii)             It blows in India into two branches namely the Arabian Sea branch and the Bay of Bengal branch.

(iv)              The southwest monsoon are warm winds.          

Northeast Monsoon

(i)                 The winter period is marked by the northeast monsoon.

(ii)               The northwest monsoon blow in a northeasterly direction across India from mid-November to February

(iii)             It does not possess any branches.

(iv)              These are cold winds.

10.  What do you mean by El Nino?

Answer:

This is the name given to the periodic development of a warm ocean current along the coast of Peru as a temporary replacement of the cold Peruvian current.

‘El Nino’ is a Spanish word meaning ‘the child’, and refers to the baby Christ, as this current starts flowing during Christmas. The presence of the El Nino leads to an increase in sea-surface temperature and a weakening of the trade winds in the region.

11.  What are the three features of Advancing Monsoon?

Answer:

The three features of Advancing Monsoon are :

• By early June, the low-pressure condition over the northern plains intensifies. It attracts the trade winds of the southern hemisphere.

• These south-east trade winds originate over the warm subtropical areas of the southern oceans. They cross the equator and blow in a south-westerly direction entering the Indian peninsula as the south-west monsoon.

• As these winds blow over warm oceans, they bring abundant moisture to the subcontinent. These winds are strong and blow at an average velocity of 30 km per hour.

12.  Give a brief account of the hot weather season in India.

Answer:

The period between March to May is the hot weather season or summer in India.

The characteristic features of the hot weather season are as follows :

• Due to the apparent northward movement of the sun, the global heat belt shifts northwards.

• The influence of the shifting of the heat belt can be seen clearly from temperature recordings taken during March-May at different latitudes. In March, the highest temperature is about 38° Celsius, recorded on the Deccan plateau.

• In April, temperatures in Madhya Pradesh and Gujarat are around 42°C. In May, a temperature of 45°C is common in the northwestern parts of the country. In temperature remain lower due to Peninsular India, which has moderated to influence of the oceans.

• The summer months experience rising temperature and falling air pressure in the northern part of the country. Towards the end of May, an elongated low-pressure area develops in the region extending from the Thar Desert in the northwest to Patna and Chotanagpur plateau in the east and southeast. Circulation of air begins to set in around this trough.

• Strong, gusty, hot, dry winds, locally called ‘loo’, blow during the day over the north and northwestern India. They may continue until late in the evening.

• Dust storms are common during the month of May in Punjab, Haryana, Delhi, Eastern Rajasthan, and Western Uttar Pradesh. Sometimes, they bring light rain and a pleasant cool breeze that provide temporary relief from the heat.

• High temperature during the day causes violent, localised thunderstorms by the evening. These thunderstorms are associated with violent winds, torrential downpours, often accompanied by hail. These storms are known as ‘Kaal Baisakhi’ or calamity of the month of Baisakh in West Bengal. (Any flue)

13.  Describe the effect of western cyclonic disturbances on the Indian climate?

Answer:

The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region.

They affect the climate of India in the following ways :

• By causing cyclonic rainfall in the month of winter, which is otherwise dry, the region of western cyclonic disturbances influence the weather of the north and north-western India.

• These low-pressure systems originate over the Mediterranean Sea and Western Asia and move into India, along with the easterly flow.

• They cause the much-needed winter rains over the plains and snowfall in the mountains.

• Although the total amount of winter rainfall, locally known as ‘Mahawat’ is small, it is very useful for rabi crops. These winds are called western cyclonic disturbances since they came from the western part of India.

14.  Write a brief account of the conditions and characteristics of the retreating monsoons.

Answer:

The months of October-November mark a period of transition from hot rainy season to cold dry winter conditions. With the apparent movement of the sun southwards, the low-pressure monsoon trough over the Northern Plains weakens and is gradually replaced by a high-pressure system. The low-pressure conditions shift to the Bay of Bengal.

The retreat of the monsoon is marked by clear skies and a rise in temperature. While day temperatures are high, nights are cool and pleasant. The land is still moist.

As a result, the southwest monsoon winds weaken and start withdrawing gradually from India. By the beginning of October, it withdraws from the Northern Plains. This period is known as the Retreating Monsoon

The Retreating Monsoon season is marked by clear skies and a rise in temperature. While days are warm, nights are cool and pleasant. High rate of evaporation from the land that is still moist results in high humidity and oppressive weather conditions during the day. This phenomenon is known as ‘October heat’.

The low-pressure conditions, cyber northwestern India, get transferred to the Bay of Bengal by early November. This shift is associated with the occurrence of cyclonic depressions, which originate over the Andaman Sea.

The deltas region of the Godavari, the Krishna, and the Kaveri are frequently struck by cyclones, which cause great damage to life and property. Sometimes, these cyclones arrive at the coasts of Odisha, West Bengal, and Bangladesh. The bulk of the rainfall of the Coromandel Coast is derived from depressions and cyclones.