NCERT Class 9 Geography Chapter 4 - Climate

Chapter 4 - Climate

Question and Answers
Question 1: Define the following terms:
a) Climate
b) Weather
c) Coriolis force
d) ITCZ
e) El Nino
Answer:

a) Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than thirty years).
b) Weather refers to the state of the atmosphere over an area at any point of time.
c) 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’.
d) The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes. This is where the northeast and the southeast trade winds converge. This convergence zone lies more or less parallel to the equator but moves north or south with the apparent movement of the sun.
e) This is a 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.

Question 2: What are the elements of weather and climate?
Answer:
The elements of weather and climate are
• Temperature
• Atmospheric pressure
• Wind
• Humidity
• Precipitation

Question 3: What are the major controls of climate of a particular place?
Answer:
There are six major controls of the climate of any place. They are: latitude, altitude, pressure and wind system, distance from the sea (continentality), ocean currents and relief features.
• Due to the curvature of the earth, the amount of solar energy received varies according to latitude.
• As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers.
• The pressure and wind system of any area depend on the latitude and altitude of the place. Thus it influences the temperature and rainfall pattern.
• The sea exerts a moderating influence on climate. As the distance from the sea increases, its moderating influence decreases and the people experience extreme weather conditions. This condition is known as continentality (i.e. very hot during summers and very cold during winters).
• Ocean currents along with onshore winds affect the climate of the coastal areas. For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.
• Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or hot winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of mountains remains relatively dry.

Question 4: Which part of India experiences the highest diurnal temperature and why?
Answer:
Difference between the temperature of day and night at any place is known as diurnal temperature. The part of India that receives the highest diurnal temperature is northwest India (mainly Rajasthan). This is because it is located far from the sea (continentality). Also it if filled with sand which gets heated up quickly during the day and gets cooled during night.

Question 5: Describe the regional variations in the climatic conditions of India with the help of suitable example.
Answer:
Regional variations of India is distinct, let us compare with regard to temperature and precipitation.
• In summer, the mercury occasionally touches 50°C in some parts of the Rajasthan desert, whereas it may be around 20°C in Pahalgam in Jammu and Kashmir.
• On a winter night, temperature at Drass in Jammu and Kashmir may be as low as minus 45°C. Thiruvananthapuram may have a temperature of 22°C.
• The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan.

Question 6: Give an account of weather conditions and characteristics of the cold season, hot season, advancing monsoon and retreating monsoon.
Answer:

• The Cold Weather Season (Winter)
→ The cold weather season begins from mid-November in northern India and stays till February. December and January are the coldest months in the northern part of India.
→ Days are warm and nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall.
→ The northeast trade winds prevail over the country. The weather is normally marked by clear sky, low temperatures and low humidity and feeble, variable winds.
→ A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances from the west and the northwest.
→ The total amount of winter rainfall locally known as ‘mahawat’ is small, they are of immense importance for the cultivation of ‘rabi’ crops.

• The Hot Weather Season (Summer)
→ From March to May, it is hot weather season in India. The summer months experience rising temperature and falling air pressure in the northern part of the country.
→ A striking feature of the hot weather season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day over the north and north-western India.
→ Dust storms are very common during the month of May in northern India. These storms bring temporary relief as they lower the temperature and may bring light rain and cool breeze.
→ This is also the season for localised thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail. In West Bengal, these storms are known as the ‘Kaal Baisakhi’.
→ Towards the close of the summer season, pre-monsoon showers are common especially, in Kerala and Karnataka. They help in the early ripening of mangoes, and are often referred to as ‘mango showers’.

• Advancing Monsoon (The Rainy Season)
→ The inflow of the south-west monsoon into India brings about a total change in the weather.
→ Early in the season, the windward side of the Western Ghats receives very heavy rainfall, more than 250 cm.
→ The maximum rainfall of this season is received in the north-eastern part of the country. Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.
→ Another phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall. Thus, it has wet and dry spells. In other words, the monsoon rains take place only for a few days at a time.
→ When the axis of the monsoon trough lies over the plains, rainfall is good in these parts. On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains, and widespread rain occur in the mountainous catchment areas of the Himalayan rivers causing devastating floods causing damage to life and property in the plains.

• Retreating/Post Monsoon (The Transition Season)
→ During October-November, with the apparent movement of the sun towards the south, the monsoon trough or the low-pressure trough over the northern plains becomes weaker.
→ This is gradually replaced by a high-pressure system. The south-west monsoon winds weaken and start withdrawing gradually. By the beginning of October, the monsoon withdraws from the Northern Plains.
→ The months of October-November form a period of transition from hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and rise in temperature.
→ While day temperatures are high, nights are cool and pleasant. The land is still moist.
→ Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day. This is commonly known as ‘October heat’.
→ The low-pressure conditions, over north-western India, get transferred to the Bay of Bengal by early November. This shift is associated with the occurrence of cyclonic depressions.

Question 7: Why is the monsoon considered as a unifying bond?
Answer:

→ The Himalayas protect the subcontinent from extremely cold winds from central Asia. This enables northern India to have uniformly higher temperatures when compared to other areas on the same latitudes.
→ Similarly, the peninsular plateau, under the influence of the sea from three sides, has moderate temperatures. Despite such moderating influences, there are great variations in the temperature conditions.
→ Nevertheless, the unifying influence of the monsoon on the Indian subcontinent is quite perceptible. The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons.
→ The Indian landscape, its animal and plant life, its entire agricultural calendar and the life of the people, including their festivities, revolve around this phenomenon. These monsoon winds bind the whole country by providing water to set the agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.

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