NCERT Solutions for Class 11 Geography Chapter 10 Atmospheric Circulation and Weather Systems

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 10 Atmospheric Circulation and Weather Systems Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Atmospheric Circulation and Weather Systems NCERT Solutions for Class 11 Geography Chapter 10

Atmospheric Circulation and Weather Systems Questions and Answers Class 11 Geography Chapter 10

Question 1.
Multiple choice questions :
(i) If the surface air pressure is 1,000 mb, the air pressure at 1 km above the suface will be –
(a) 700.inb
(b) 1,100 mb
(c) 900 mb
(d) 1,300 mb
(c) 900 mb.

(ii) The Inter Tropical Convergence Zone normally occurs
(a) near the equator
(b) near the Tropic of Cancer
(c) near the Tropic of Capricorn
(d) near the Arctic Circle
(a) near the equator

(iii) The direction of wind around a low pressure in northern hemisphere is T…………
(a) clockwise
(b) perpendicular to ispbar
(c) anti-clockwise
(d) parallel to isobars
(a) clockwise.

(iv) Which one of the following is the source region for the formation of air masses?
(a) the Equatorial Forest
(b) the Himalayas
(c) the Siberian Plain
(d) the Deccan ‘Plateau
(b) the Himalayas

Question 2.
Answer the following questions in about 30 words :
(i) 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?
The atmospheric pressure is expressed in units of mb and Pascals. The widely used unit is kilo Pascal written as hPa. Because, the pressure decreases with height. At any elevation it varies from place to place and its variation is the primary cause of air motion, i.e. wind which moves from high pressure areas to low pressure areas.

(ii) While the pressure gradient force is from north to south, Le. from the subtrophical high pressure to the equator in the northern hemisphere, why are the winds north easterlies in the tropics.
The higher pressure gradient force, the more is the velocity of the wind and the larger is the deflection in the direction of wind. The coriolis force acts perpendicular to the pressure gradient force. As a result of these two forces operating perpendicular to each other, in the low pressure areas the wind blows around it. 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.

(iii) What are the geotrophic winds?
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 geotrophic wind.

(iv) Explain the land and sea breezes.
Pressure gradient from sea to land is created and the wind blows from the sea to the land as the sea breeze. 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 and hence land breeze results.

Question 3.
Answer the following questions in about 150 words each :
(i) Discuss the factors affecting the speed and direction of wind.
Following three factors affect the speed and direction of the wind :
Pressure of Gradient Force – This is the driving force and wind moves from high pressure to low pressure. This force is produced by the difference in atmospheric pressure.

Frictional Force – The frictional force is present near the earth’s surface. It affects the speed of the wind. It is the greatest at the surface 208 and its influence generally extends. It may effect the direction of surface winds. Over the sea surface, the friction is minimal.

Coriolis Force – It develops due to the rotation of the earth about its axis. It affects the direction of the wind. It deflects the wind to the right in the northern hemisphere and to the left in the southern hemisphere. The deflection is more when the speed of the wind is high. It is maximum at the poles and is absent at the equator.

(ii) 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?

There are two intermediate zones of sub-tropical highs in the vicinity at 30°N and S and two sub-polar lows in the vicinity at 60°N and S.

The sub-tropical high pressure is located between the tropics on 25° to 3J° north and south latitudes. A calm conduction is erected in this region. These regions are also called horse latitudes because in early days the sailing vessels with horses found it difficult to sail under such calm conditions. These are controlled by pressure gradient and rotation of the earth. Two factors are responsible for general subsistence of air belts.

The warm air of the equatorial low pressure belt gradually gets in its ascent. On reaching upper layers, it slants, moving towards the poles. It further cools and begins to subside in a zone between 20° and 35° latitudes. Among two factors, first, cooling of the air results in increased / density, which accounts for its subsidence.

Second, owing to the rotation of the earth from west to east, poleward directed winds are deflected eastwards. Because of the subsidence of air, the areas between the tropics and 35°N and S develop into high pressure belts. The winds coming from the sub-tropic and polar areas converge in the zone between 45°N and S and the Arctic and Antarctic circles respectively.

(iii) Why does tropical cyclones originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?
Tropical cyclones are notorious for their violence and for causing widespread destruction. These develop over oceans, particularly in tropical regions. Hence, their major climatic significance is in causing widespread rainfall. Most of the tropical cyclones develop in a belt of 8° to 15° north and south latitudes.

Tropical cyclones are characterised by circular and asymmetrical isobars. They have very low pressure at the centre, and the pressure gradient is very steep and winds are very strong. Their velocity ranges between 170-200 km per hour. Rainfall is torrential and is evenly distributed around the centre. They move from east to west with the trades. They are most prominent in the Pacific ocean.

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