SEBA Board Solution Class 9 Geography Chapter 2 Atmosphere: Structure, Air Pressure and Wind System
SEBA Board Solution Class 9 Geography Chapter 2 Atmosphere: Structure, Air Pressure and Wind System full exercise Solution by Computer Sir. Here in this page we have provided SEBA – The Board Of Secondary Education, Assam Class 9 Geography Chapter 2 all Question Answer Solution.
SEBA Board Solution Class 9 Geography Chapter 2: Overview
Board |
SEBA / Assam State Board |
Class |
9 |
Subject |
Geography |
Chapter Number |
2 |
Chapter Name |
Atmosphere: Structure, Air Pressure and Wind System |
Topic |
Solution |
1.) What is atmosphere? Write in brief with data about its structure.
The thin layer of air which surrounds the earth’s surface and reaches up to certain height is known as the Atmosphere. The atmosphere extends up to 10,000 km from the earth’s surface and the gravitational force attaches it to the earth’s surface. The atmosphere consists various types of gases like nitrogen (78%), Oxygen (20.9%), Argon (0.93%) . Carbon dioxide (0.0 36%), and other gases like neon, helium, methane, krypton, hydrogen, ozone, xeon etc (0.014%). The atmosphere along with lithosphere and hydrosphere create a favorable condition for origin, growth and sustenance of living creatures.
2.) What are the main layers of the atmosphere based on chemical composition of the gases? Write briefly about the characteristics of these layers.
The composition and chemical processes of the atmosphere extends up to 10,000 km from the earth’s surface and changes with increase in the altitude. The climatologists have divided the atmosphere into two divisions – Homosphere and Heterosphere. Homosphere This is the lower atmospheric layer and the chemical composition remains mostly same up to 80km. About 99% of the mass of all atmospheric elements is restricted up to 32 km from the earth’s surface. The Homosphere is again sub-divided into Troposphere, Stratosphere and Mesosphere. Heterosphere– In the altitude above 80 km, beyond the Mesosphere, chemical composition of the atmosphere changes. This sphere is known as Heterosphere. This consists of four layers of nitrogen, oxygen, helium and hydrogen. This is divided into Thermosphere and Exosphere. The density of the air is very little.
3.) Write with diagram about the layers of the atmosphere based on the variations in altitude and temperature and write the characteristics of each layer in brief.
The layers of the Atmosphere: -The structure and characteristic features of the atmosphere is divided into 5 categories: –
a.) Troposphere- It is the lowermost layer with an average height of 12 km. In the equatorial region the height is about 16 km and in the polar region it is 8 km. The Troposphere consists all the water vapour, dust particles and three-fourth of total atmospheric gases. The temperature in this layer is more, the temperature decreases at the rate of 6.5℃ per km ascent. All the weather phenomenon like clouds, rains, cyclones, storms etc take place in the atmosphere. The highest limit of this layer is known as Tropopause, it is 1.5 km thick and the temperature reduces to -60℃.
b.) Stratosphere- This layer is just immediately above the troposphere.There are no weather phenomena in this layer. The air pressure is -60℃ in the lower part of the Stratosphere and the upper part becomes 0℃. The horizontal wind movement in this layer aids in the flying of the Aeroplanes. The ozone layer is found in this sphere. The boundary between the Troposphere and Stratosphere known as Tropopause, the Stratosphere extends upwards to about 40 km from the Tropopause. The topmost level of the Stratosphere is known as Stratopause.
c.) Mesosphere- The layer above the Stratosphere is known as the Mesosphere, this layer extends up to 30 km height from the Stratopause. The temperature of air decreases with the increase in altitude, the minimum temperature reaches -100℃ at the uppermost boundary of the layer known as Mesopause which has an altitude of 80km.
d.) Thermosphere- The layer above the Mesopause is called Thermosphere, it extends from 80 km to 400 km. It is the lower part of the Heterosphere and the air temperature here increases with the altitude, thus this layer is known as the Thermosphere. The temperature rises up to 1650℃ and the density of the air decreases to zero. This layer also contains electrically charged ions; thus, it is also known as Ionosphere. The radio waves which are sent from the earth’s surface are reflected from this layer.
e.) Exosphere- The topmost layer of the atmosphere just above the thermosphere is known as the Exosphere which extends up to a height of 400km to 10,000 km. The atom and molecular density of the air is very low. The most prominent gases are Helium and Hydrogen which make the layer very thin. The temperature of this layer rises till 5550℃.
DIAGRAM OF LAYERS OF THE ATMOSPHERE SHOWING ALTITUDE AND TEMPERATURE:
4.) Discuss with examples the factors responsible for variation in atmospheric pressure.
Air is a gaseous matter which has weight and pressure. Similarly, the combination of different types of gases which makes the air also has pressure which keeps on changing with increase in the altitude and can be felt on the earth’s surface. This is known as Atmospheric pressure. Factors responsible for variation in atmospheric pressure are as follows:
a.) Air Temperature: The sunlight that reaches earth’s surface does not reach all the places equally due to different geographical locations, altitude. This variation in the distribution of heat makes some areas hot, some areas cold and some areas temperate. The atmospheric pressure is also different as a result. The rise in the temperature results in expansion of the air which reduces its density and the air becomes light. Light warm air can carry more moisture from the water bodies on the earth’s surface. The air pressure of this type of air is low. On the other hand, when the air becomes colder in the areas of higher altitude, the air density increases and the moisture holding capacity is also low. Thus, we see that the temperature affects the density of air. It is less near equatorial region and more in polar regions.
b.) Earth’s surface height: The areas with higher altitude have less atmospheric depth, the amount of gases present in the air decreases, the weight of the air also decreases. Hence air pressure also decreases. Thus, atmospheric pressure decreases with the altitude. With the rise of altitude for every 900 feet, there is resultant decrease in air pressure by 1 inch or 34 milibar.
5.) With the help of diagram discuss the characteristics of the major pressure belts of the world.
It is found that the air pressure is not same in every part of the earth. Some places experience high air pressure and some places experience low air pressure which affects the movement of the air. The air moves from places to high pressure to a place with low pressure. There are two types of air pressure in different parts of the earth – a. High Pressure and b. Low Pressure. These two types of pressure occur due to altitude, temperature of different places. There are four main pressure belts found in the world: –
i.) Equatorial Low Pressure Belt – In the equatorial areas which lie between 10° North Latitude and 10° South latitude experience direct sunlight throughout the year. As a result, the air is warm and the density is low causing low atmospheric pressure. The area consists of large water bodies and contains more water vapour due to high temperature which again creates low pressure belt in this area. For all these reasons, in the equatorial low pressure belt the air gets heated and moves upwards. There is no horizontal movement of the movement of the air and the air movement in this is very calm.
ii.) Sub-Tropical High-Pressure Belt -The moist and light air from the equatorial belt moves towards north and south and as it travels upwards and it becomes cold and heavy. The cold air descends towards the subtropical zones in 25° -35° North latitudes and 25° -35° South Latitudes. The cold air and the hot air mix up near the north of Tropic of Cancer and south of Tropic of Capricorn. The movement of air is downward and wind is not felt here. The air movement is downward and the wind is not felt here.
iii.) Sub-Polar Low-Pressure Belt – The Sub -Polar low-pressure belt is roughly located in 60°-70° North latitude of the northern hemisphere and 60°-70° South latitude of the Southern latitude of the Southern Hemisphere. Due to earth’s rotational movement, the air of the sub-polar regions deflects towards sub-tropical regions and low pressure is formed and there is fall in the volume of the air in both the sub-polar belts.
iv.) Polar High-Pressure Belt – The polar regions on the earth do not receive direct sunlight and is covered with snow throughout the year and is very cold. The air is also very cold and does not contain water vapor as water is present in the form of ice. The air pressure is permanently high and thus the areas of the North Pole and South Pole are known as Polar High- Pressure Belt.
DIAGRAM OF MAJOR PRESSURE BELTS OF THE WORLD.
6.) Write the importance of atmosphere towards creation of a favourable physical environment on the earth.
The atmosphere is an essential element of the earth’s physical environment. The atmosphere along with the land (Lithosphere) and water (Hydrosphere) make it possible to create a favorable environment for the origin, growth and maintenance of all the living creatures on the earth. The gases required for the human, plants and animals on the earth are provided by the atmosphere. It also helps in the distribution and circulation of heat and moisture on the earth’s surface. The atmosphere stops the harmful ultraviolet rays of the sun reaching the earth. The formation and changes of the weather and climate that takes place on the earth occurs due to the atmosphere. The rainfall also occurs due to the presence of the atmosphere. Thus, the existence of all human beings, plants and animals is supported by the atmosphere.
7.) What is wind? Discuss the factors of origin of wind.
The air which moves around the earth’s surface, the motion of the air is known as the Wind.
Factors of Origin of the Wind: -The movement of the wind depends on the temperature difference of the atmosphere and the atmospheric pressure plays an important role in the movement of the wind. The earth’s surface does not receive equal amount of sunlight on all the areas. The atmospheric pressure of the equatorial region is higher than the polar regions.When the temperature of the place increases, as a result it becomes lighter and move upwards and a low pressure is created in that place. The air movement starts from high pressure belt which has low temperature to a low-pressure region which has high temperature. On the other hand, the temperature towards the pole is relatively low, the air pressure is higher. The pressure difference causes in the movement of the air, the movement takes place from high pressure region to low pressure region. Thus, the movement of wind depends on two factors which are temperature and pressure.
8.) What is the most important reason for the origin of wind? Briefly discuss the factors determining velocity and direction of wind.
The most important reason for the origin of the wind is the temperature of the air. The temperature of the air determines pressure and the difference in the density of the pressure of the air, the wind moves from the high-pressure belt to the low-pressure belt. The main factors which influence the movement of the wind in any region are as follows: –
a.) Pressure Gradient Force-The force which is created from the difference in atmospheric pressure on the surface of the earth causes the movement of the air. This force is known as the Pressure Gradient Force and the difference between the atmospheric pressure of two places is known as pressure gradient. The velocity of the wind increases when pressure gradient is higher and velocity of the wind is low when the pressure gradient is lower.
b.) Gravitational Force- The thin envelope of air that surrounds the surface of the earth is held by the gravitational force and the pressure of the air is also influenced by the gravitational force. The gravitational force reduces as we go to higher altitude from the sea level, the air becomes lighter. The gravitational force also controls the movement of air from one place to another and the movement becomes curved.
c.) Centrifugal force – The earth’s rotation on the earth’s axis, an outward force is formed from its centre. This force is called Centrifugal Force. The wind is deflected due to the centrifugal force.
d.) Frictional Force – The Frictional force influence the velocity of the air in a negative manner. The frictional force is more when the earth’s surface is rugged in nature, i.e., more mountains and valleys, high rise buildings and scattered vegetation are present, this results in lowering of the wind velocity. The frictional force is also low when the wind blows through plain areas like snow covered lands.
9.) What do you mean by ‘Coriolis Force’? With the help of diagram briefly describe its contribution in determining the direction of wind.
The earth rotates on its axis. This rotation is known as diurnal motion, and it creates an outward force is created from its centre. This force known as the Centrifugal force and causes the deflection of the wind. This phenomenon of the wind was first discovered by a French mathematician Gasperd de Coriolis in 1844 and was named after him as the’ Coriolis Force’. When the wind moves from the high-pressure areas towards thelow-pressure areas, then Coriolis force slightly causes change in the movement in the direction of the wind. The force created by the earth’s rotation also deflects the wind toward right in a clockwise direction in the northern hemisphere and towards left in the anticlockwise direction in the southern hemisphere. The wind which moves towards the pole in the northern hemisphere blows towards north-east. The power of the Coriolis Force is not same everywhere on the earth, it is zero on the equator and slowly increases towards the polar areas and is highest on both the poles.
DIAGRAM OF CORIOLIS FORCE:
10.) What is meant by Pressure Gradient Force’? What is its contribution in air movement.
Pressure Gradient Force- The force caused from the atmospheric pressure differences on the earth’s surface influences the movement of the air. This force is known as the Pressure Gradient Force. The rate of atmospheric pressure differences between the two places is known as the pressure gradient. The amount of force caused due to pressure gradient depends on the difference pressure between two places and distance between them. The velocity of the wind is higher if the difference between pressure of the atmosphere between the two places is more or the pressure gradient is steep. The wind velocity decreases with the increase in the distance between two places. The pressure gradient also influences the movement of the air when it flows from high pressure zone to low pressure zone.
11.) Briefly discuss the contribution of the earth’s gravitational force in air movement.
The earth’s gravitational force holds the thin layer of air which surrounds the earth’s surface. The weight or pressure of air also depends on the earth’s gravitational force. The gravitational pull decreases as there are increase in the altitude from the sea level. The air becomes lighter and the air pressure also reduces. The vertical movement of air in the atmosphere from the high pressure to low pressure continues as a result of the pressure difference, the air moves from valleys towards the mountains. Due to the gravitational force the movement of air from one place another takes curved line in place of straight line.
12.) What do you mean by naming of wind? How the wind blowing over a place is named?
The naming of the wind is done on the basis of the direction of the wind i.e., in the basis of the direction in which it is blowing. For example: when the wind that blows from west direction is known as the North-Westerly Wind. The wind that blows on the surface of the earth, the direction from which comes is known as Windward, and the direction to which it blows is called Leeward.
13.) How the velocity of wind is determined? What are the units of wind velocity?
The velocity of the wind is determined by the help of an instrument known as Anemometer. Many other modern -day Anemometer instruments are available among which the Anemograph automatically records the direction and velocity of the wind. A British Scientist named Sir Francis Beaufort developed a 0-12 Number Scale of wind velocity in 1805 to understand the nature and effects of different types of wind and this instrument is called as the Beaufort Scale. The velocity of the wind is also expressed in Knot where velocity of 1 Knot means 1 nautical mile per hour or 1.854 Kilometer per hour.
14. How the classification of wind is done? Briefly discuss with examples.
The movement of air is a very complex process and it is very difficult to number the different types of wind on the whole earth. The different types of wind are as follows:
A.) Primary Wind Circulation: The movement of the air which covers the whole earth is based on the distribution of permanent pressure belts on the earth’s surface is called Primary Wind Circulation. This circulation of the air also makes environment for the circulation of other winds. The permanent winds blow without ant interruptions from the sub-tropical and polar high-pressure belts to the equatorial and sub-polar low -pressure belts in both north and south hemispheres. These winds are also known as Permanent Winds or Planetary Winds. Example: Trade Winds, Westerlies and Polar Easterly Winds.
B.) Secondary Circulation: The wind circulation in the different parts of the earth due to various physical features of the earth, different distribution of the land and water bodies and the temperature and atmospheric pressure variations that occur in different regions and seasons are called as Secondary Circulations. Example: Cyclone, Anticyclone, Air mass, Front Monsoon etc are most important Secondary Circulations. These Secondary Circulations causes various weather changes in the area and makes unstable variations in the atmospheric condition.
C.) Tertiary Circulation or Local Wind: There are some winds that are in circulation in a limited region depending on factors like differences in topography, altitude. These winds are called as Local Wind or Tertiary Circulation. These winds determine the weather of an area. Example: – Sea Breeze,Land Breeze, Mountain Wind, Valley Wind etc.
15.) What do you mean by primary circulation of wind? Show distribution of primary circulations in a diagram. Mention its important characteristics.
The movement of the air which covers the whole earth is based on the distribution of permanent pressure belts on the earth’s surface is called Primary Wind Circulation. This circulation of the air also makes environment for the circulation of other winds. The permanent winds blow without ant interruptions from the sub-tropical and polar high-pressure belts to the equatorial and sub-polar low -pressure belts in both north and south hemispheres. These winds are also known as Permanent Winds or Planetary Winds. Example: Trade Winds, Westerlies and Polar Easterly Winds.
DIAGRAM OF DISTRIBUTION OF PRIMARY CIRCULATIONS OF WIND.
16.) What is secondary circulation of wind? Discuss its contribution in determining the climate of a place with examples.
Secondary Circulation: The wind circulation in the different parts of the earth due to various physical features of the earth, different distribution of the land and water bodies and the temperature and atmospheric pressure variations that occur in different regions and seasons are called as Secondary Circulations. Example: Cyclone, Anticyclone, Air mass, Front Monsoon etc are most important Secondary Circulations. These Secondary Circulations causes various weather changes in the area and makes unstable variations in the atmospheric condition.
17.) What is local wind? Briefly discuss with examples how local wind determines the weather condition of a place.
Local Winds- The wind circulation that takes place in a limited region depending on differences of topography, altitude is known as Local Wind or Tertiary Circulation.This wind movement is also known as temporary air movement. These winds affect the weather of an area in which they blow.
Example; –
i.) Land and Sea Breeze-
ii.) Mountain and Valley Wind-
iii.) Other Local Winds-
18.) What is a cyclone? What are its types? Mention briefly how it influences the climate of a place?
Cyclones are defined as the air that moves in a rotating manner around the centre of low pressure on a large scale. It is a type of tropical storm with winds. Cyclones are type of Secondary Circulation. The atmospheric pressure is higher in the areas near the low -pressure centre of the cyclones and the wind velocity also becomes very high. Cyclones are of two types:
i.) Tropical Cyclones- When wind with high velocity starts a cyclic path of violent nature from a high- pressure region towards a low-pressure centre in the tropical region, it is called a Tropical Cyclone. The cyclonic wind blows in anticlockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere due to the rotation of the earth. The pace of tropical cyclone can vary from 120 km to 280 km per hour. Tropical cyclone usually forms during the summer season. These cyclonic activities are influenced by the presence of the oceanic environment and cause huge amount of destructions. Areas like south-eastern parts of North America, eastern part of Japan, eastern coastal region of India.
ii.) Mid-Latitude or Extra Tropical Cyclone- The cyclone that are formed in the temperate and high -latitude areas are known as Temperate Cyclone or Extra- Tropical Cyclone. These are prevalent in the areas from 30° and 65° latitudes in both the hemispheres. These cyclones are characterized by dense clouds and heavy rainfall, hail and thunderstorms are also formed. These cyclones have a diameter varying from 300 kilometers to 1500 kilometers.
19.) What is an air mass? How it is classified? What is its contribution in determining the climate of a place?
Air Mass-A huge body of air which has homogenous temperature and humidity is called Air Mass. When the air in a wide area stays stable for a certain period of time, the lower layer of the air is affected by the surface of land which lies below it. The air starts absorbing the humidity and a certain amount of changes in the air temperature and humidity is observed vertically upwards from the land. This causes a diverge movement in the air which determines the weather of the area. The movement of the divergent air, conduction of heat starts from warm region to cold region and an equilibrium in atmospheric temperature is maintained. The Air Mass can be classified into four types: –
I.) Tropical Continental Air mass (cT)
ii.) Tropical Maritime Air mass (mT)
iii.) Polar Continental Air mass (cP)
iv.) Polar Maritime Air mass(mP)
20.) What do you mean by ‘Front? How it is formed? Briefly discuss the relationship between climate and front.
Front-When two different air masses with two different temperatures, humidity, pressure, density etc come close to each other from directions, these two air masses do not mix properly and an air surface discontinuity. This is called Front and causes weather changes. The formation of Front needs two special conditions of two air masses-i. between two air masses, one air mass should be heavier and colder, ii. Tair movement should be convergent so that the air masses from opposite directions should be able to move closer to each other. A shift in the air in the frontal region is caused because of reversal direction of the pressure gradient and the advancement of the front brings out changes in air temperature, humidity and helps in the formation of the clouds in the frontal region.
21.) What do you mean by Monsoon Wind”? How it is formed? In which areas of the earth its impact is quite distinct?
.Monsoon Wind- The wind that blows in a periodical manner depending on the change of the season is called Monsoon Wind. The word ‘Monsoon’ has come from the Arabic word ‘Mausim’ and Malayan word ‘Monsin’ The change in the seasons which cause changes in the atmospheric temperature and pressure result in the change and direction of monsoon wind. During summer season the land has more temperature than the water surface which causes in the decline in the air pressure. The land areas have low pressure and water areas have high pressure and as a result the cold and moist air from oceans enter the land areas causing heavy rainfall. The monsoon winds blowing from the Arabian Ocean and Bay of Bengal during summer cause heavy rainfall in the foothills of Assam, Meghalaya etc. During winter, there is reversal in the pattern. The high temperature in the water surface causes low pressure and the low temperature on the land areas cause high temperature. The dry and cold winds from the high-pressure belt crossing over the oceans absorb water vapors and causes rainfall in the areas of Tamil Nadu etc. The areas which are most affected by the monsoon are areas surrounded by the oceans. Example: South Asia, South-East Asia, South-East China, Gulf region of Mexico etc.
22.) Write with reasons:
(a) Why do all weather phenomena occur mainly in troposphere?
(b) What would be the consequence of the increase in the amount of carbon dioxide?
(c) What is the reason behind the prevalence of high pressure of dry air than moist air?
(d) How does the ozone layer help the living-beings?
(e) Why is the air pressure highest at the sea level?
(f) What is the reason behind variation in vertical extent of the troposphere in the polar region and equatorial region?
(g) Why is horizontal movement of wind parallel to the earth’s surface not felt in the equatorial low pressure belt?
Reasons:a. The troposphere is the lowest layer of the atmosphere. The temperature, pressure and density gradually get low as there is increase in the altitude. The temperature decreases with the ascent of 6.5°C per km. Thus, for all these reasons all weather phenomena like clouds, rain, storms etc take place in the Troposphere.
b.) Carbon dioxide is a very important gas in the atmosphere. It controls the atmospheric processes and climate of the earth’s surface. The carbon dioxide can absorb the heat from the atmosphere, the solar radiation is reflected by the carbon dioxide and creates an atmosphere for the survival of the plants and animals on the earth. Plants also use carbon dioxide during photosynthesis. The use of fossil fuels like coal, petroleum etc, deforestation have increased the amount of carbon dioxide in the atmosphere. The increase in the carbon dioxide causes rise in the temperature of the atmosphere and causing global warming.
c.) The dry air in the atmosphere has less air pressure than the moist air. Gases like nitrogen, oxygen exists more in the dry air and creates high air pressure. The moist air, on the other hand has more water vapors and lowers the weight of the air. The high pressure containing moist air always moves upwards in the atmosphere and the low-pressure warm air stays in one level.
d.) The ozone layer exists in the stratosphere. The molecules of the ozone layer absorb the ultraviolet radiations of the sunlight which are harmful to the living beings and results in the rise in the temperature in the Stratosphere.
e.) The density of the air is mostly found near the surface of the oceans and seas due to the gravitational force of the earth. The more the air is dense, the more pressure it exerts. Thus, the air pressure is highest at the sea-level.
f.) The vertical height of the troposphere in the equatorial region is 16km and the polar regions is 8km. There is difference in latitudinal extent in the equator and poles. This is the reason for the variation in the vertical extension of the Troposphere in these two areas.
g.) The sun rays fall vertically on the equatorial region causing a low-pressure belt. The excessive heat causes the air to move upwards in the vertical manner which is why any horizontal movement of wind is not felt in the equatorial low -pressure belt.
23.) Give short answer to the following questions :
(a) What is the vertical extent of the atmosphere?
(b) Up to what altitude from the earth’s surface does chemical composition of gases remain almost same?
(c) What is the name of the boundaryline between homosphere and heterosphere?
(d) What is Ferrell’s Law?
(e) What is Beaufort Scale? Write briefly about the utility of this scale with example.
(f) Write in brief about Lapse Rate.
a.) The vertical extent of the atmosphere of the atmosphere is about 10,000 km.
b.) Up to 80 km altitude of the atmosphere, the chemical composition of the atmosphere remains same.
c.) The boundary line between the Homosphere and Heterosphere is known as Ionosphere.
d.) The force which is caused by the earth’s rotation is deflects the wind towards the right direction in clockwise manner in the northern hemisphere and towards left in the anticlockwise manner in the southern hemisphere. This is known as Ferrell’s Law.
e.) In order to measure the velocity of the wind, a British scientist Sir Francis Beaufort developed a 0-12 Number Scale of Wind velocity in 1805. This instrument could measure and understand the nature and impact of different types of wind. This is known as Beaufort Scale.
f.) Lapse rate- The temperature in the lower part of the Troposphere is more and it slowly decreases with increase in height. This decrease in the air temperature takes place at the rate of 6.5°C per km ascent. This is called Lapse Rate.
24.) Write short note:
(a) Homosphere
(b) Heterosphere
(c) Air temperature, earth’s surface height and air pressure relationship
(d) Polar High Pressure Belt
(e) Wind system
(f) Pressure Gradient
(g) Trade wind
(h) Horse latitude
(i) Roaring Forties
(j) Anticyclone
(k) Jet Stream
(1) Isobar
(m) Tropical Cyclone
a.) Homosphere- This is the lower atmospheric layer and the chemical composition remains mostly same up to 80km. About 99% of the mass of all atmospheric elements is restricted up to 32 km from the earth’s surface. The Homosphere is again sub-divided into Troposphere, Stratosphere and Mesosphere.
b.) Heterosphere- In the altitude above 80 km, beyond the Mesosphere, chemical composition of the atmosphere changes. This sphere is known as Heterosphere. This consists of four layers of nitrogen, oxygen, helium and hydrogen. This is divided into Thermosphere and Exosphere. The density of the air is very little.
c.) Air temperature, earth’s surface height and air pressure relationship- The distribution of the sun-rays and heat on the surface of the earth is not same at all places. The amount of heat of a region depends on the geographical location of the region, its latitudinal extent, height on the surface of the earth. All these factors cause differences of temperature, some places are cold some places are hot. The variations in the temperature affect the atmospheric pressure of the place.
d.) Polar High-Pressure Belts- The areas where there is cold temperature, the air pressure is high. In the Polar regions the temperature is extreme cold, the water of this region remains deposited in the form of ice. The air does not contain much water vapor and air pressure always remains high in both Northern and Southern Hemisphere.
e.) Wind system- The air in the state of motion is known as Wind. The movement of air depends on two factors: temperature differences of the atmosphere and atmospheric pressure difference. When the air gets heated up due to the heating of the surface of an area it moves upwards. This causes low pressure belt. Again, when the air gets colder due to the cooling down of the surface of the earth, it comes down and causes high pressure belt. The wind always moves from the high pressure to low pressure zone.
f.) Pressure Gradient- The force which is created from the difference in atmospheric pressure on the surface of the earth causes the movement of the air. This force is known as the Pressure Gradient Force and the difference between the atmospheric pressure of two places is known as pressure gradient. The velocity of the wind increases when pressure gradient is higher and velocity of the wind is low when the pressure gradient is lower.
g.) Trade Wind- The surface wind that blows from the sub-tropical high- pressure belts which are located on both the sides of 30° North and 30° South latitudes towards the equatorial low -pressure belt is known as Trade Wind. Trade Wind, due to the Coriolis force blows from the north-east to south-west direction in the Northern Hemisphere and south-east to north-west in the Southern Hemisphere.
h). Horse Latitude- The wind that blows in the sub-tropical belt with high pressure becomes very low that it becomes very difficult for the ship to move in the sea. These latitudes are located at about 30 degrees north and south of the equator. The areas are characterized by calm winds, sunny skies and little or no rainfall. A legend is very popular that in medieval times when the sailors found it very difficult to sail their ships, they used to throw the horses to reduce the load of their ships. Thus, the name of these areas has come to be known as ‘Horse Latitude’.
i.) Roaring Forties- The Roaring Forties are given to the winds known as Westerlies that blow in the Southern hemisphere lying between 40° and 50° latitudes. The area is covered by the ocean and the westerlies blow strongly in the persistent manner. This is the reason the navigators call this latitude belt as Roaring Forties.
j.) Anticyclone- After the formation of a high- pressure belt covering a wide area, a divergent wind from the centre of the pressure belt takes a cyclic path. The name was given by the meteorologist Sir Francis Galton in 1861.This cyclic path is known as Anticyclone. The atmospheric pressure becomes the highest at the centre of the anticyclone, it is also known as High Pressure Centre.
k.) Jet Stream- A very high velocity wind around 640 kilometer per hour which has similarities with the Westerlies blows towards east at high altitude in the upper limit of the Troposphere in the tropical region. This wind is known as Jet Stream. The Jet Stream brings about changes in the weather and climate of a region.
l.) Isobar- Some imaginary lines which are drawn to connect the places with equal pressure are known as Isobars. If the Isobars are drawn in a close manner, then the intensity of atmospheric pressure is said to be high. The Isobars are mainly circular or elliptical in shape.
m.)Tropical Cyclone- When the high velocity wind starts blowing from a high- pressure region and takes a cyclic path, it is violent in nature and moves around a lower pressure centre in the tropical region. This is called as Tropical Cyclone. It blows in an anticlockwise direction due to the earth’s rotational movement in the northern hemisphere and clockwise in the southern hemisphere, The velocity of a tropical cyclone can be from 120 kilometer to 280 kilometer per hour.
25.) Write the differences:
(a) Horizontal wind and Vertical wind
(b) Wind and Air mass
(c) Tropical cyclone and Extra-tropical cyclone
(d) Sea breeze and Land breeze
(e) Mountain wind and Valley wind
(f) Cyclone and Anticyclone
(g) Cold Front and Warm Front
(h) Cold wave and Hot Wave
(i) Troposphere and Stratosphere
Differences between: –
a.) Horizontal wind and Vertical wind- Winds that move parallel to the earth’s surface is called Horizontal Wind. Vertical Wind. Vertical Wind- The wind that moves vertically upwards from the surface of the earth is called Vertical wind or Current.
b.) Wind- The moving air is known as Wind. Air Mass- A huge body of air which has similar type of temperature and humidity is called Air Mass.
c.) Tropical Cyclone- When wind with high velocity from high pressure region takes a cyclic path of around a low- pressure centre in the tropical region is called Tropical Cyclone. The diameter of this type of cyclones can be a few kilometers to several hundred kilometers. Extra -Tropical Cyclone- The cyclone formed in the temperate and high-latitude regions is called Temperate Cyclone or Extra -Tropical Cyclone. The diameter varies from 300 kilometer and 1500 kilometers.
d.) Land Breeze- The wind movement from the land to the water surface is called Land Breeze. The Places like the coastal areas of the equatorial, tropical and sub-tropical regions experience this type of Land Breeze.This blows during the night time. Sea Breeze-The breeze that blows from sea to the land is called Sea Breeze. The sea breeze during the day time.
e.) Mountain Wind- The wind that blows from the mountains towards the valleys during the night time is called Mountain Wind. The wind is cold and heavy. Valley Wind- The wind that blows from the river valley or plain in an upward movement along the mountain slopes during the day time is known as Valley Wind.
f.) Cyclone –Cyclones are defined as the air that moves in a rotating manner around the centre of low pressure on a large scale. It is a type of tropical storm with winds.The atmospheric pressure is higher in the areas near the low -pressure centre of the cyclones and the wind velocity also becomes very high. Anticyclone- – After the formation of a high- pressure belt covering a wide area, a divergent wind from the centre of the pressure belt takes a cyclic path. The name was given by the meteorologist Sir Francis Galton in 1861.This cyclic path is known as Anticyclone. The atmospheric pressure becomes the highest at the centre of the anticyclone, it is also known as High Pressure Centre.
g.) Cold Front–The front in which a cold air mass shifts a warm air mass is called Cold Front. Warm Front- The front in which the warm air mass moves over the cold air mass and shifts its position is called Warm front.
h.) Cold Wave- The high-altitude cold anticyclone results in the movement of extremely cold wind particularly during winter in the areas like North -East Canada and North East Europe. This extremely cold wind which are caused by anticyclone is called Cold Wave. Hot Wave- The wind generated from the high-pressure centre of sub-tropical anticyclone remains stable and moves in a very sluggish manner. When anticyclone of sub-tropical areas reaches the USA in summer, they are warm in nature and brings good amount of rainfall. This wind is known as Hot waves.
i.) Troposphere – It is the lowermost layer with an average height of 12 km. In the equatorial region the height is about 16 km and in the polar region it is 8 km. The Troposphere consists all the water vapour, dust particles and three-fourth of total atmospheric gases. The temperature in this layer is more, the temperature decreases at the rate of 6.5℃ per km ascent. All the weather phenomenon like clouds, rains, cyclones, storms etc take place in the atmosphere. The highest limit of this layer is known as Tropopause, it is 1.5 km thick and the temperature reduces to -60℃.
Stratosphere-This layer is just immediately above the troposphere. There are no weather phenomena in this layer. The air pressure is -60℃ in the lower part of the Stratosphere and the upper part becomes 0℃. The horizontal wind movement in this layer aids in the flying of the Aeroplanes. The ozone layer is found in this sphere. The boundary between the Troposphere and Stratosphere known as Tropopause, the Stratosphere extends upwards to about 40 km from the Tropopause. The topmost level of the Stratosphere is known as Stratopause.
26.) Find out the correct answer :
(a) Where is Ozone layer located?
(1) Troposphere
(2) Stratosphere
(3) Mesosphere
(4) Thermosphere
(b) What is amount of oxygen in the atmosphere in terms of volume?
(1) 20.94%
(2) 29.01%
(3) 32.47%
(4) 78.08%
(c) The most important reason for air movement is
(1) Humidity difference
(2) Pressure difference
(3) Gravitational Force
(4) Centrifugal Force
(d) The instrument used for determination of wind velocity is (1) Wind vane (2) Anemometer (3) Beaufort scale (4) Hydrometer
(e) The unit of wind velocity is
(1) Knot
(2) Milibar
(3) Percentage
(4) Degree
(f) Monsoon wind belongs to which of the following class?
(1) Local winds
(2) Primary circulation
(3) Secondary circulation
(4) Permanent wind
(g) The name of the cyclone formed in the coastal region of the Pacific Ocean in the east is
(1) Cyclone
(2) Hurricane
(3) Willy-Willy
(4) Typhoon
Ans.
a.) Stratosphere
b.) 20.94%
c.) Pressure difference
d.) Anemometer
e.) Knot
f.) Secondary Circulation
g.) Typhoon