Q. 1 What is the unit used in measuring pressure? Why is the pressure measured at station level reduced to the sea level in preparation of weather maps? Or
What is atmospheric pressure? Explain about different atmospheric belts. Or
Explain horizontal distribution of atmospheric pressure on the Earth.


 Answer Key Points: -
Atmospheric pressure or barometric pressure (after the barometer) is the force of air that is exerted on per unit of Sea Surface by the air.
1) It is measured from the mean sea level to the top of the atmosphere.
2) Millibar or Pascal is the unit for measuring pressure.
3) The atmospheric pressure is expressed in units of Millibar (MB). At sea level, the average atmospheric pressure is 1,013.2 Millibar.
4) Due to gravity, the air at the surface is denser so it has higher pressure.
5) Press-ure measure at a station is reduced to sea level to offset the effect of altitude.

Q. 2 Explain the Vertical distribution and Horizontal distribution of atmospheric pressure on the Earth. 
 Answer Key Points: -
 Vertical Distribution of Pressure: -
In the lower atmosphere the pressure decreases rapidly with height. The decrease amounts to about 1 mb for each 10 meters increase in elevation. It does not always decrease at the same rate. Maximum Atmospheric Pressure is at the sea level under normal conditions and it decreases with altitude.

 Horizontal Distribution of Pressure: -
The distribution of atmospheric pressure across the latitudes is known as horizontal distribution of atmospheric pressure over the globe. Small differences in pressure are highly significant in terms of the wind direction and purposes of comparison. The sea level pressure distribution is shown on weather maps.

Q. 3 Give the importance of atmospheric pressure.
 Answer Key Points: -
1) It is very important factor in bringing changes in weather.
2) Variations in the atmospheric pressure are responsible for horizontal movement of air called wind.
3) Wind transport heat and moisture from one place to another and help in the occurrence of precipitation.

Q. 4 Give the characteristics of trade winds.
 Answer Key Points: -
1) They blow as the northeast trades in the Northern hemisphere and southeast trades in the southern hemisphere.
2) They travel from 30° north and 30° south towards the equator they become hot and dry so they do not cause much rainfall here.
3) Trade winds blow a specific path with the speed of 15 to 25 km per hour the speed is more in winters than in the summers.
4) The north eastern and south eastern trade winds converge near the equator called the Inter-tropical convergence zone.

Q. 5 Discuss the factors affecting the speed and direction of wind. Or
What factors affect direction and velocity of winds? 
 Answer Key Points: -
The air in horizontal motion is called wind. Air is set in motion due to the differences in atmospheric pressure. The wind blows from high pressure to low pressure. Following factors affect the direction and velocity of winds.
1) Pressure Gradient Force: - The driving force for wind is called ‘Pressure Gradient Force’. It is produced when there is a difference in pressure across a surface. The pressure gradient is strong where the isobars are close to each other and is weak where the isobars are apart.
2) Frictional Force: - The wind at the surface experiences friction. It affects the speed of the wind. It is greatest at the surface and its influence generally extends up to an elevation of 1 – 3 km. Over the sea surface the friction is minimal.
3) Coriolis Force: - The rotation of the Earth about its axis affects the direction of the wind. This force is called the Coriolis force after the French physicist who described it in 1844. It affects the flow of direction of planetary wind system e.g. to the right direction in the northern hemisphere and to the left in the southern hemisphere. They oscillate (move) with the apparent movement of the sun.
4) Centripetal Acceleration: - Due to the inward acceleration of air towards the center of rotation on the rotating Earth, it is possible for the air to maintain a curved path about a local axis of high or low pressure. It is known as centripetal acceleration.
5) Pressure and Wind: - The velocity and direction of the wind are the net result of the wind generating
forces. The winds in the upper atmosphere (2-3 km above the surface) are free from frictional effect of the surface and are controlled by the pressure gradient and the Coriolis force. When isobars are straight and when there is no friction, the pressure gradient force is balanced by the Coriolis force and the resultant wind blows parallel to the isobar. This wind is known as the geostrophic wind.

Q. 6 What do you mean by ‘Geostrophic Wind’? On what factors does their pattern depend?
 Answer Key Points: -
When isobars are straight and when there is no friction, the pressure gradient force is balanced by the Coriolis force and the resultant wind blows parallel to the isobar. This wind is known as the geostrophic wind. The pattern of these winds largely depends on: -

1) Latitudinal variation of atmospheric heating.
2) Emergence of pressure belts.
3) The migration of belts following apparent path of the sun.
4) The distribution of continents and oceans.
5) The rotation of Earth.

Q. 7 Write a detailed note on Coriolis force.
 Answer Key Points: -
The rotation of the Earth about its axis affects the direction of the wind. This force is called the Coriolis force after the French physicist who described it in 1844. It affects the flow of direction of planetary wind system e.g. to the right direction in the northern hemisphere and to the left in the southern hemisphere.
1) The deflection is more when the wind velocity is high. The Coriolis force is directly proportional to the angle of latitude. It is maximum at the poles and is absent at the equator.
2) Tropical cyclones are not formed near the equator because Coriolis force is zero at the equator.
3) They oscillate with the apparent movement of the sun. In the northern hemisphere in winter they move southwards and in the summer northwards.
4) Coriolis force is also responsible for alternating (different) motion of Ocean Currents.

Q. 8 While the pressure gradient force is from north to south, i.e. from the subtropical high pressure to the equator in the northern hemisphere, why are the winds north easterlies in the tropics?
 Answer Key Points: -
1) Rotation of the Earth also affects the wind movement. The force exerted by the rotation of the Earth is known as the Coriolis force. Due to this effect, winds move to the right from their original direction
in northern hemisphere and to the left in the southern hemisphere. The deflection is more when the wind velocity is high. The Coriolis force is directly proportional to the angle of latitude. It is maximum at the poles and is absent at the equator. The Coriolis force acts perpendicular to the pressure gradient force.
2) The pressure gradient force is perpendicular to an isobar. The higher pressure gradient
force results in more velocity of the wind and larger deflection in the direction of wind. As a result of these two forces operating perpendicular to each other, in the low-pressure areas the wind blows around it. Therefore, when pressure gradient force is from south to north then winds move from south to north easterlies.

Q. 9 Draw a simplified diagram to show the general circulation of the atmosphere over the globe. What are the possible reasons for the formation of subtropical high pressure over 30° N and S latitudes? 
 Answer Key Points: -
1) The general circulation of the atmosphere also sets in motion the ocean water circulation which influences the Earth’s climate.
2) The large-scale winds of the atmosphere initiate large and slow moving currents of the ocean, which in turn provide input of energy and water vapour into the air.
3) These interactions take place rather slowly over a large part of the ocean.
4) The air at the Inter Tropical Convergence Zone (ITCZ) rises because of convection caused by high insolation and a low pressure is created.
5) The winds from the tropics converge at this low pressure zone. The converged air rises along with the convective cell. It reaches the top of the troposphere up to an altitude of 14 km. and moves towards the poles.
6) This causes accumulation of air at about 30° N and S. Part of the accumulated air sinks to the ground and forms a subtropical high.
7) Another reason for sinking is the cooling of air when it reaches 30° N and S latitudes.

Q. 10 Give the main features of ‘Trade Winds’.
 Answer Key Points: -
 The trade winds or easterlies are the permanent east-to-west blowing winds that flow in the Earth's equatorial region (between 30°N and 30°S latitudes).
1) They blow as the North-east trades in the Northern hemisphere and South-east trades in the Southern
hemisphere.
2) Its name ‘Trade’ comes from German word ‘Trade’ meaning ‘Track’. So trade wind means the wind that blow with high speed in the same direction through a specific path.
3) They travel from 30° north and 30° south towards the equator they become hot and dry so they do not cause much rainfall here.
4) The trade winds follow a specific path with the speed of 15 to 25 km per hour. The speed is more in winters than in the summers.
5) The north eastern and southeastern trade winds converge near the equator and the area is called inter-tropical convergence zone.
6) The trade winds also transport nitrate- and phosphate-rich Saharan dust to all Latin America. They are converted into ‘Monsoon Winds’ in the Indian Ocean.
7) It may be pointed out that the zone of trade winds is called Hadley Cell on the basis of the convective model prepared by Hadley for the entire Earth.
8) These winds are on-shore on the eastern sides of the continents, so they bring rainfall on the eastern sides but they are off-shore on the western sides of the continents so these parts always remain dry.
9) Because of this very reason, most deserts of the world are located in the western parts of the continents.

Q. 11 Give the main features of ‘Westerlies’.
 Answer Key Points: -
1) The winds blowing from Sub Tropical High Pressure Belts to the Sub Polar Low Pressure Belts between 30° to 60°N of the Equator in the temperate latitudes are called Westerlies or Brave West Winds.
2) According to the sound created by westerlies these latitudes are often called ‘Roaring Forties’, ‘Furious Fifties’ and ‘Shrieking Sixties’ these are the dreaded terms for navigators.
3) They are called westerlies because they flow from Western side (due to the Coriolis Effect) in both hemispheres.
4) They blow from warm areas to cold areas and cause much rainfall especially on the Western margins of the continents.
5) There is a regular flow and uncertainty of temperature leads to occurrence of cyclones and anticyclones
6) The Westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.

Q. 12 Give the main features of ‘Polar Winds’. 
 Answer Key Points: -
1) The winds blowing from the polar high pressure belts towards the sub-polar low pressure belts are
called polar winds.
2) They flow from North East to South West direction in the Northern Hemisphere and from South East to North West direction in the Southern Hemisphere under the influence of Coriolis force.
3) They flow from cold areas to warm areas and do not cause much rainfall. Their capacity to absorb moisture it is also very little due to low temperature.
4) These winds give birth to cyclones when they come in contact with the westerlies. This brings a great change in the weather and heavy rainfall occurs.

Q. 13 What are the features of El-Nino or ENSO? 
 Answer Key Points: -
The term ENSO composed of EL means El-Nino and SO means Southern Oscillation (Movement back and forth at a regular speed). This is a combined climatic phenomenon mainly occurs in the Southern Hemisphere just below the Equator in the Pacific Ocean. It has 2 phases: -
 First Phase: - (La-Nina): - The name La-Niña originates from Spanish, meaning "the girl". During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5 °C. An appearance of La Niña exists for at least five months.
1) In the first phase ‘Trade Winds’ or ‘Tropical Easterlies’ pushes the warm ocean current towards the Western Pacific Ocean as trade winds blow from east to west and make the Pacific Ocean water warm around the countries of Australia, New-Zealand and Indonesia.
2) Here the warm ocean currents affect the surrounding atmosphere and increase the temperature as well as the moisture in the air.
3) Warm air rises and leads to formation of clouds which cause rainfall in the Western Pacific Ocean.
4) When the air becomes dry and cold it travels to the Eastern Pacific Ocean side and comes down near the region of South America and makes this region cold and creates high pressure.
5) Then at the surface this cold air again travels towards the Western Pacific Ocean as low Pressure is created here.
6) This entire process makes a cycle which is called the ‘Walker Circulation’ or the ‘Walker Cell’ after its discoverer ‘Sir Gilbert Thomas Walker’
 Second Phase (EI-Nino): - El Niño originates from Spanish, meaning "the boy". It is a complex weather system that appears once every three to seven years, that affects the weather patterns of
different parts of the world.
1) Sometimes when ‘Trades Winds’ are weaker in a few months of the year then a warm ocean current from the Western Pacific Ocean move towards the Eastern Pacific Ocean along the coast of Peru and temporary replace the Cold Peruvian Current or Humbolt Current.
2) Here the warm ocean currents affect the surrounding atmosphere and increase the temperature as well as the moisture in the air.
3) Warm air rises and leads to formation of clouds which cause rainfall in the Eastern Pacific Ocean, but on the other hand the area around Western Pacific Ocean countries of Australia, New-Zealand and Indonesia do not have rain, even the interior parts of Australia face problem of floods.
4) This current increases the temperature of water on the Peruvian coast by 10° C. The system also affects weather in many places in the world including India.

Q. 14 What are winds? Explain different types of winds. Or
Explain about mountain and valley winds. Or
What are Land-Sea Breezes? Or
What factors determine the pattern of planetary winds? 
 Answer Key Points: -
The horizontal motion of air is called wind. It usually blows from a high pressure area to a low pressure area. Winds are of following types: -
1) Planetary Winds: - These are also known as permanent or prevailing winds. Planetary winds blow over vast areas of continents and oceans throughout the year in a particular direction. They blow from high pressure belts to low pressure belts. Planetary winds are divided into three categories according to pressure belts and temperature zones: - A) Easterlies or Trade Winds, B) Westerlies and Polar Winds.
2) Seasonal or Periodic Winds: - The winds which change their direction with the change in season are called seasonal or periodic winds e.g. Monsoon Winds.
3) Local Winds: - The winds which are caused by differential heating and cooling of the Earth’s surface and affect the local areas. Land-Sea Breezes and Mountain and Valley Winds are the examples of local winds.
A) During the day the land heats up faster and becomes warmer than the sea. So the warm & rising air
creates a low pressure area over the land, on the other hand the sea is relatively cool and the pressure over sea is normally high. Thus, pressure gradient from sea to land is created and the wind blows from the sea to the land which is known as sea breeze.
B) In the night the reversal of condition takes place. The land loses heat faster and is cooler than the sea. The pressure gradient is from the land to the sea. This breeze is known as land breeze.
Land and Sea Breezes are formed due to differential in cooling of land and water.
 In mountainous regions, during the day the slopes get heated up and air moves upslope and to fill the gap the air from the valley blows up the valley. This wind is known as the valley breeze. During the night the slopes get cooled and the dense air descends into the valley as the mountain wind.


Q. 15 Give the difference between air and airmass.
 Answer Key Points: -
1.
Air is the mixture of gases which forms the Earth's atmosphere and which we breathe.
Airmass is defined as a large body of air having little horizontal variation in temperature and moisture.
2.
Air is in thin layers.
A mass is massive and thick.

3.
Air can have different temperature and humidity.
Airmass is homogeneous with regard to temperature and humidity.
4.
Air can start flowing from any place depending upon pressure conditions.
Air masses originate from specific source regions.
5.
Air helps us in studying the complications of atmosphere.
Air masses help us in studying the cyclones and anticyclones.

Q. 16 What is air mass? In how many categories are air masses categorized on the basis of their source regions?
 Answer Key Points: -
The air with distinctive characteristics in terms of temperature and humidity is called an air mass. In other words, it is defined as a large body of air having little horizontal variation in temperature and moisture. The homogenous surfaces, over which air masses form, are called the source regions. The air masses are classified according to the source regions into five major source regions. These are: -
1) Warm tropical and subtropical oceans: Maritime tropical (mT);
2) The subtropical hot deserts: Continental tropical (cT);
3) The relatively cold high latitude oceans: Maritime polar (mP);
4) The very cold snow covered continents in high latitudes: Continental polar (cP);
5) Permanently ice covered continents in the Arctic and Antarctica: Continental arctic (cA).

Q. 17 What is a front? How many types of front are there? Explain all of them. 
 Answer Key Points: -
When two different air masses meet, the boundary zone between them is called a front. The process of formation of the fronts is known as frontogenesis. The fronts occur in middle latitudes and are characterised by steep gradient in temperature and pressure. They bring abrupt changes in temperature and cause the air to rise to form clouds and cause precipitation. There are four types of fronts: -
1) Cold Front: - When the cold air moves towards the warm air mass, its contact zone is called the cold front.
2) Warm Front: - If the warm air mass moves towards the cold air mass, the contact zone is a warm front.
3) Stationary Front: - When there is no movement among different airmasses and the front remains stationary, it is called a stationary front.
4) Occluded Front: - When warm air mass is fully lifted above the land surface by the cold air mass, it is called the occluded front.

Q. 18 Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?
 Answer Key Points: -
At the equator, the Coriolis force is zero and the wind blows perpendicular to the isobars. The low pressure gets filled instead of getting intensified. That is the reason why tropical cyclones are not formed near the equator.
1) Torrential rain occurs in the eye of the cyclone. The strong spirally circulating wind around the center is called the eye.

2) The diameter of the circulating system can vary between 150 and 250 km. The eye is a region of calm with subsiding air. Around the eye is the eye wall, where there is a strong spiraling ascent of air to greater height reaching the tropopause. The wind reaches maximum velocity in this region, reaching as high as 250 km per hour.
3) From the eye wall rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region. Due to torrential rain, winds blowing from that region are humid. It brings precipitation in oceanic regions. Due to torrential rains, heavy rain takes place on eastern coast of India and north east coast of China.

Q. 19 What is a tropical cyclone? Give its two examples. What are the favourable conditions for its formation?
 Answer Key Points: -
Tropical cyclones are circular shaped violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges. This is one of the most devastating natural calamities.
Cyclones in the Indian Ocean and Hurricanes in the Atlantic are its biggest examples. They have anti-clockwise direction in Northern Hemisphere and clockwise direction in Southern Hemisphere due to Coriolis Effect.
 Conditions: - The Cyclones of the tropics are thermal in origin which require conditions of: -
1) Large sea surface with temperature higher than 27° C.
2) Presence of the Coriolis force.
3) Small variations in the vertical wind speed.
4) A pre-existing weak low-pressure area or low-level-cyclonic circulation.
5) Upper divergence above the sea level system.

Q. 20 Write a detailed note on Tornado. 
 Answer Key Points: -
The word tornado comes from the Spanish word tornado (past participle of to turn, or to have torn) A tornado is a funnel-shaped rapidly rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud.
They are generally narrow in diameter compared with other storms, so their destruction is confined to a narrow path. Tornadoes are formed over land surface usually occur in groups. Tornado strength is measured on the Fujita scale.
 Features: -
1) Tornadoes generally occur where cold and warm fronts converge mainly in middle latitudes on all
continents (except Antarctica).
2) North of the equator, tornadoes rotate in a counterclockwise direction. South of the equator, they rotate in a clockwise direction.
3) The tornado over the sea is called water spouts.
4) Tornadoes move at 30-40 miles per hour with winds reaching over 300 miles per hour near the center.
5) These violent storms are the demonstration of the atmosphere’s adjustments to varying energy distribution.
6) The potential and heat energies are converted into kinetic energy in these storms and the restless atmosphere again returns to its stable state.

Q. 21 Write a detailed note on Thunderstorm. 
 Answer Key Points: -
1) A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic (Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound.) effect on the Earth's atmosphere, known as thunder.
2) Relatively weak thunderstorms are sometimes called thundershowers.
3) Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all.
4) Thunderstorms may line up in a series or become a rain band, known as a squall line.
5) Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes.
6) Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones.
7) Thunderstorms result from the rapid upward movement of warm, moist air, sometimes along a front.
8) Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes.
9) Thunderstorms are responsible for the development and formation of many severe weather phenomena and great hazards.
10) Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.