Short Question Answers : Atmospheric Circulation and Weather Systems | Geography Class 11 - Humanities/Arts PDF Download

Q. 1. What is the weight of air on one sq. cm. surface at sea level ?
Ans. 1.03 kg.

Q. 2. What is the weight of air on one sq. inch surface at sea level ?
Ans. 6.68 kg.

Q. 3. What is approximate weight of atmospheric pressure on our body ?
Ans. About one tonne.

Q. 4. What is the rate of decrease of atmospheric pressure with altitude ?
Ans. 12 millibars per 100 metres or one inch for 300 metres.

Q. 5. Name the factors on which the pressure of a place depends.
Ans. (i) Temperature
(ii) Altitude
(iii ) Water vapour
(iv) Rotation.

Q. 6. What is normal pressure ?
Ans. 29.92 inches or 76 cms or 1013.2 millibars.

Q. 7. What is a millibar ?
Ans. A force equal to 1000 dynes per sq. cm.

Q. 8. What are isobars ?
Ans. Lines of equal pressure.

Q. 9. Name the equatorial low pressure belt.
Ans. Doldrums.

Q. 10. Name the sub-tropical high pressure belt.
Ans. Horse latitudes.

Q. 11. Name two belts of calm.
Ans. Doldrums are horse latitudes.

Q. 12. What are planetary winds ?
Ans. Permanent winds which blow throughout the year in the same direction.

Q. 13. Name the force generated by the rotation of the earth.
Ans. Coriolis force.

Q. 14. Name a natural region which gets rainfall in winter due to westerlies.
Ans. Mediterranean region.

Q. 15. What term is used for westerlies in 40°— 50° South latitudes ?
Ans. Roaring forties.

Q. 16. Name the winds which blow over prairies after descending the rocky mountains.
Ans. Chinooks.

Q. 17. Name the winds which blow over Switzerland after descending the Alps.
Ans. Foehn winds.

Q. 18. What are Anabatic winds ?
Ans. Valley winds.

Q. 19. What are Katabatic winds ?
Ans. Mountain winds.

Q. 20. Which winds are called ‘Snow eaters’ ?
Ans. Chinook winds.

Q. 21. From which word the term monsoon has been derived ?
Ans. From Arabic word ‘mausim’.

Q. 22. Name two types of atmospheric disturbances.
Ans. Cyclones and Anticyclones.

Q. 23. Name two types of cyclones.
Ans. Tropical and temperate.

Q. 24. Explain why the trades in northern hemisphere have north easterly direction.
Ans. These winds blow as N. E. trades in the northern hemisphere. These winds are deflected from their North-South direction. This deflection force of the earth’s rotation is known as Coriolis force. This force forms the basis of Ferral’s law. According to Ferral’s law, all moving bodies are deflected to the right in the northern hemisphere. Therefore, the trade winds, after deflection to the right, become N.E. trade winds.

Q. 25. “Most of the hot deserts of the world lie on the western margins of the continents”. Why?
Ans. Deserts are areas of low rainfall. Hot deserts lie in the trade wind belt. These winds give rain on the eastern margins, but trade winds get dry as these reach western margins. These are offshore winds. So these are known as Trade wind deserts such as Atacama, Kalahari, Sahara etc.

Q. 26. “Despite its location in higher latitudes; low pressure is found in sub-polar area”. Why ?
Ans. Sub-polar area has low temperatures, but a high pressure exists due to the rotation of the earth.
It causes  a centrifugal force which displaces the air outwardly. The air becomes so thin that there is no effect of low temperature on the pressure.

Q. 27. In what ways the general circulation of atmosphere affects the movement of oceanic waters ? What is ENSO ?
Ans. The general circulation of the atmosphere also affects the oceans. The large-scale winds of the atmosphere initiate large and slow moving currents of the ocean. Oceans in turn provide input of energy and water vapour into the air. These interactions take place rather slowly over a large part of the ocean. The most important is the warming and cooling of Pacific Ocean.

The warm water of the central Pacific Ocean slowly drifts towards South American coast and replaces the cool Peruvian current. Such appearance of warm water off the coast of Peru is known as the El Nino. The El Nino event is closely associated with the pressure changes in the Central Pacific and Australia. This change in pressure condition over Pacific is known as the southern oscillation. The combined phenomenon of southern oscillation and El Nino is known as ENSO.

In the years when the ENSO is strong, large-scale variations in weather occur over the world. The arid west coast of South America receives heavy rainfall, drought occurs in Australia and sometimes in India and floods in China. This phenomenon is closely monitored and is used for long range forecasting in major parts of the world.

Q. 28. What do you mean by atmospheric pressure ?
Ans. Air has weight. The atmosphere is held to the earth due to gravitational pull of the earth. It exerts its weight as pressure on the earth’s surface. It is the weight  of column of air extending from the ground to the outermost layer of the atmosphere. This is known as Atmospheric pressure. At this rate, the atmospheric pressure on each of us weighs nearly one tonne.

Q. 29. Explain the relation between pressure and temperature.
Ans. The atmospheric pressure has an inverse relation with temperature. As the air is heated, it expands and rises upwards. The higher the temperature, the lower is the pressure. On the other hand, cold air contracts and becomes heavy. It results in high pressure. The general rule is that  a rising thermometer shows a falling barometer, whereas a falling thermometer shows a rising barometer.

Q. 30. On what factors does the atmospheric pressure depend ?
Ans. The atmospheric pressure varies from place to place and time to time due to the following factors :
(i) Temperature
(ii) Altitude
(iii) Water vapour
(iv) Rotation.

Q. 31. Name the different areas of tropical cyclones.
Ans. There are different kinds of tropical cyclones.

These are known by different names in different oceans such as—
(i) Depressions in Bay of Bengal.
(ii) Hurricanes in West Indies.
(iii) Typhoons in China Sea.
(iv) Tornadoes in Atlantic ocean.
(v) Willy-willy in Australia.

Q. 32. Define the pressure gradient.
Ans. Atmospheric pressure is shown by isobars. The spacing between isobars shows pressure gradient.
Close spacing represents a steep gradient while wide spacing shows a gentle gradient. Thus the pressure gradient is rate at which the horizontal pressure changes. It is always measured at right angles to the isobars. When the pressure gradient is steep, strong winds blow. When the pressure gradient is weak, gentle winds blow. Thus the pressure gradient is defined as the change in pressure per unit distance.

Q. 33. What are local winds ? Name their different types. Name one country each where these winds blow.
Ans. Some winds of special characteristics result in different areas under local conditions. These are called local winds.
Types of local winds :
(i) Hot winds—Chinook in Canada, Foehn in Switzerland.
(ii) Dry winds—Sirocco in Southern Europe, Khamsin in Egypt, Harmatten in West Africa; Simoom of Arabia ,Santa Anna of California, Zenda of Argentina.
(iii) Cold winds—Boro and Mistral in Southern Europe, Pampero in Argentina, Buran in Siberia.

Q. 34. What do you mean by “Roaring forties ?”
Ans. Westerlies are best developed in the southern hemisphere due to vast expanse of oceans westerlies blow here strongly and regularly throughout the year.
These are a menace to shipping along cape horn route.
These brave west winds are known as ‘roaring forties’ between 40° and 50° South latitudes.

Q. 35. What is Jet Stream ?
Ans. The high velocity winds blowing at high altitudes are called Jet Stream. This strong current of air is located near 30° North latitude. It affects weather pattern of the world. High flying planes use these as ‘super tail winds’ to save time and fuel.

Q. 36. What are isobars ? Why are these reduced to sea level ?
Ans. Isobars : Isobar is combination of two words (Iso = equal, Bar = pressure). So isobars are lines of equal pressure.
Isobar is an imaginary line joining the places of equal pressure reduced to sea level. Pressure is reduced to sea level to eliminate the effects of altitude.
If a place is 300 metres high and its actual pressure is 900 millibars, its pressure reduced to sea level would be 900 + 34 = 934 millibars because the pressure decreases at the rate of 34 millibars for every 300 metres. Isobars generally run in east-west direction.