class 9 geography chapter 4 pressure and wind explanation
Answers
Answer:
Climate: The sum total of weather conditions and variations over a large area for a long period of time (more than thirty years) is called climate.
Weather: The state of the atmosphere over an area at any point of time is called weather.
Monsoon: This type of climate is mainly found in the south and Southeast Asia. The climate of India is of monsoon type. The seasonal reversal in wind direction during a year is called monsoon.
Coriolis Force: An apparent force caused by the earth’s rotation is called Coriolis Force. The winds are deflected towards right in the northern hemisphere and towards the left in the southern hemisphere due to this force. This is also known as ‘Ferrel’s Law’.
CLIMATIC CONTROLS
There are six major controls of the climate of any place. They are:
Latitude, Altitude, Pressure and wind system, Distance from the sea, Ocean currents and Relief features
Factors Affecting India’s Climate
Latitude: The Indian landmass is equally divided by The Tropic of Cancer. Hence, half of India has tropical climate and another half has subtropical climate.
Altitude: While the average elevation in the coastal areas is about 30 metre, the average elevation in the north is about 6,000 metre. The Himalayas prevent the cold winds from Central Asia from entering the Indian subcontinent. Due to this, the subcontinent gets comparatively milder winters as compared to Central Asia.
Pressure and Winds: The Indian subcontinent lies in the region of north-easterly winds. These winds originate from the subtropical high-pressure belt of the northern hemisphere. After that, these winds blow towards south. They get deflected to the right due to the Coriolis force and then move towards the low pressure area near the equator.
The north-easterly winds originate and blow over the land and hence they carry very little moisture. India should have been an arid land because of these winds but that is not the case.
There is high-pressure area towards the north of the Himalayas. Cold winds from this region blow to the low pressure areas over the oceans in the south.
During summer, low-pressure area develops over interior Asia and also over northwestern India. This results in a complete reversal of the direction of winds during summer.
Air; from the high-pressure area moves over the southern Indian Ocean in a south-easterly direction. It crosses the equator and turns right towards the low-pressure areas over the Indian subcontinent.
These winds are known as the Southwest Monsoon wind. They collect moisture from the warm oceans and bring widespread rainfall over the mainland of India.
The upper air circulation in this region is dominated by a westerly flow. Jet stream is an important component of this flow. These jet streams are called subtropical westerly jet streams because they are located approximately over 27°-30° north latitude.
The westerly jet streams are responsible for western cyclonic disturbances in the north and north-western parts of India. The subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun.
The tropical jet stream (an easterly jet stream) blows over the Indian Peninsula; approximately over 14° north during the summer months.
Jet Stream:-
Fast flowing and narrow air currents are called jet streams. The streams flow at high altitudes (about 12,000 feet) in the troposphere. Their speed varies from about 110 km/h in summer to 184 km/h in winter.
Western Cyclonic Disturbance:
The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region. They usually influence the weather of the north and north-western regions of India.
Inter Tropical Convergence Zone (ITCZ):
The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes. The northeast and the southeast trade winds converge in this zone. This zone lies more or less parallel to the equator. It moves north or south with the apparent movement of the sun.
Answer:
Climate
THINGS TO ANSWER AFTER READING THE CONTEXT
What are the elements that affect the climate of a place?
Mention the mechanisms responsible for monsoon in India.
Explain the onset and withdrawal of Monsoon in India.
Write a short note on the summer season of India.
Definitions:
Weather: state of atmosphere over an area at any point of time
Climate: average of all weather conditions over a large area of land for a long period of time (more than thirty years).
The governing elements of weather and climate are:
Temperature
Atmospheric pressure
Wind
Humidity
Precipitation
The climate of India is said to be monsoon type. But, as mentioned earlier, climate is the average of all weather conditions observed over a large area of land. So, even within the country one can see variations in the climatic conditions.
❖ Monsoon is derived from Arabic word ‘mausim’ which means season.
For example, let us take temperature into consideration. One part of India, say Rajasthan will have temperature of around 50⁰C, while at the same time, Jammu may experience temperature of around 20⁰C. The same can be seen for precipitation. In Himalayas, precipitation is in the form of snowfall, while in other parts it is in the form of rain. Also, some parts will receive rainfall upto 400 cm (Meghalaya), while some will receive less than 10 cm (Ladakh and Western Rajasthan).
Also, location of a place in respect to sea is also important as it controls climatic conditions to a moderate extent. While coastal regions experience moderate climatic conditions, the interior landmass experiences the extremities of climatic and seasonal variations.
CLIMATIC CONDITIONS
There are six major controlling factors of a climate of a place:
Latitude
Altitude
Pressure and wind system
Distance from the sea
Ocean currents
Relief features
Latitude: distance of a place from the equator. As equator receives direct sunlight, the places located near it are very hot. But as one moves away from it towards the poles, the amount of sunlight received decreases, as so does the temperature.
Altitude: distance from the ground level. As one move above the ground, the thickness of air decreases, leading to decrease in temperature.
Pressure and wind system: depends on the latitude and altitude of a place and influences temperature and winds.
Distance from the sea: Sea exerts a moderating effect on the climate of a place, leading to warm days and cool nights. But as the distance from the sea increases, a place starts to experience extremities in the temperature.
Ocean currents: It mostly affects the coastal regions. The type of current flowing from the oceans (warm or cool) will accordingly affect the climate of a place.
Relief features: Relief features such as mountains act as barriers act very hot or very cold winds, thus maintain the temperatures moderate.
Coriolis force: it is a force caused by the rotation of the earth; this is responsible for deflection of winds towards the right in the Northern hemisphere and towards the left in the Southern hemisphere. Also known as Ferrel’s law.
Jet stream: high altitude westerly winds, usually above 12000 m; speed varies from 110 km/h in summer to 184 km/h in winter.
FACTORS AFFECTING INDIA’S CLIMATE
Latitude: Tropic of Cancer passes through the mid of India, from Rann of Kachchh in the west to Mizoram in the east. Places staying above the Tropic of Cancer experience tropical type of climate while the places staying below it experience subtropical type of climate.
Altitude: India has mountains in the north which prevents cold bearing winds entering the country. Because of this, India experiences milder winters.
Pressure and winds:
Pressure and surface winds
Upper air circulation
Western cyclonic disturbances and tropical cyclones
During winter, high pressure prevails over the North of Himalayas. Winds blow from this high pressure region to low pressure regions over the oceans in the south. During summer, low pressure develops over western India and interior of Asia and high pressure develops over oceans in the south. This reversal of pressure regions causes winds to blow from oceans and seas to lands, carrying with them moisture resulting in heavy rainfall. The winds are south easterly, but while moving towards the equator gets deflected towards its right, entering India through the south west direction – hence known as South west monsoons.
Jet streams that affect the Indian monsoon are subtropical westerly jet streams, which flow south of the Himalayas. These jet streams cause the cyclonic disturbances experienced by the north and north western parts of the country.