Chapter – 4 Climate class 9 Notes Geography PDF Download

Introduction

• The climate of a place is defined as the average weather conditions over a thirty-year period. 
• The state of the atmosphere over a certain area at any given time is referred to as weather. 
• The elements of weather and climate are temperature, air pressure, wind, humidity, and precipitation. 
• The basis for dividing the year into seasons — summer, winter, or rainy — is determined by generalised monthly atmospheric conditions. 
• The climate of India is monsoon-like. 
• Monsoon is a seasonal wind reversal that occurs throughout the year. 
• The temperature varies dramatically from one place to the next. 
• The type of precipitation, as well as its amount and distribution, varies from one section of India to the next. 
• Temperature differences are less noticeable at the coast. It's the case.

Climatic Controls

• The interplay of latitude, altitude, distance from the sea, pressure and wind system, ocean currents and relief features determine climatic conditions of a place.

Factors Affecting India’s Climate

• Indian climate is influenced by latitude, altitude, pressure, and winds. From the Rann of Kuchchh to Mizoram, the Tropic of Cancer runs through the heart of the country. 
• From the equator to the poles, the air temperature normally drops. As one ascends from the earth's surface to greater altitudes, temperature and air pressure drop. 
• The Himalayas block central Asian cold winds from accessing the subcontinent. 
• Various atmospheric factors, such as pressure and surface winds, upper air circulation, western cyclonic disturbances, and tropical cyclones, influence India's climate and weather.
• The sea has a cooling effect on the climate. Extreme weather conditions are experienced by people who live far from the shore. This is referred to as 'continentality.' 
• The climate of coastal locations is also affected by ocean currents. 
• The Coriolis Force is an apparent force created by the earth's rotation. 
• The direction of the wind changes with the seasons. In the winter, they are damp from north to south, while in the summer, they are exactly opposite, bringing moisture. 
• In the troposphere, jet streams are thin belts of high-altitude (over 12,000 m) westerly winds. 
• The westerly flow from the Mediterranean region brings in the western cyclonic disturbances, which are weather phenomena that occur during the winter months.

The Indian Monsoon

• The climate of India is strongly influenced by monsoon winds.
• The Arab traders who noticed these winds named it as monsoon.

Following facts are important to understand mechanism monsoons:

• The differential heating and cooling of land and water.
• The Inter Tropical Convergence Zone (ITCZ) is a broad trough of low pressure in equatorial latitudes where the northeast and the southeast trade winds converge.
• The presence of the high pressure area, east of Madagascar.
• The intense heating of Tibetan plateau during summer.
• The movement of the westerly jet stream to the north of the Himalayas and the presence of of the tropical easterly jet stream over the Indian peninsula during summer.
  • Apart from his changes in the pressure conditions over the southern oceans also affect monsoon.
  • The periodic change in pressure conditions known as ‘Southern Oscillation’ or SO affects monsoon too.
  • El Nino is a warm ocean current that flows past the Peruvian coast in place of the cold Peruvian current, every 2 to 5 years.

The Onset of the Monsoon and Withdrawal

• The monsoon are pulsating winds affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas.
• Monsoon arrives at the southern tip of the Indian peninsula generally by first week of June.
• Sudden increase and continuation of the monsoon for several days is called as ‘burst’.
• The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the north western part of the Ganga plains.
• The withdrawal or the retreat of the monsoon is a more gradual process which begins in the northwestern states of India by early September.
• The retreating monsoon or the transition season sees the change from hot rainy season to dry winter conditions.
• The low pressure conditions over northwestern India get transferred to the Bay of Bengal by early November causing cyclonic depressions originating over the Andaman Sea.

Distribution of Rainfall

• Owing to the nature of monsoons, the annual rainfall is highly variable from year to year.
• Areas of high rainfall are liable to be affected by floods while areas of low rainfall are drought prone.

The Seasons

• The cold weather season, the hot weather season, the advancing monsoon, and the retreating monsoon are the four main seasons of India, with minor regional variations. 
• Northeast trade winds prevail over India throughout the winter season. The days are hot and the nights are chilly. 
• Frost is widespread in the north, while snowfall is common on the Himalayan higher elevations. 
• The northern areas of the country face rising temperatures and declining air pressure throughout the summer months. 
• The strong, gusty, hot, dry winds known as loo that blow during the day over north and northwestern India are a notable element of the hot weather season.
• The north-western area of the country receives the most rainfall as the monsoon approaches, i.e. during the rainy season. 
• Dust storms are widespread in northern India. 
• Localized thunderstorms with strong gusts and torrential downpours, which are frequently accompanied by hail. They are known as 'Kaal Baisakhi' in West Bengal. 
• The monsoon, which begins in June and lasts for a month, covers the majority of the Indian Peninsula and the central part of the country. 
• The monsoon has 'breaks' in its rainfall, resulting in wet and dry periods. 
• The intensity, frequency, and duration of the dry and wet episodes alternate, creating major floods in some areas and droughts in others. 
• The monsoon had left the Northern Plains by the beginning of October. Due to the high temperature and humidity, the weather becomes unpleasant at this time.

Monsoon as a Unifying Bond

• The dependence of farmers on rain, a change in seasonal cycle, variance in temperature, the needs of humans, plants and animals, festival dates etc., all depend on monsoon in India. In this way monsoon is a unifying bond for Indians.