Consider the following characteristics of a type of wind : 1. They occur at upper levels in the atmosphere 2. They are subjected to two forces, a pressure gradient force and the Coriolis force 3. When the forces balance, air moves at right angles to the pressure gradient, parallel to the isobars Identify the type of wind on the basis of the given characteristics :
- A.Jet Stream
- B.Geostrophic Wind
- C.Westerlies
- D.Easterlies
Correct answer
Explanation
The correct answer is B, Geostrophic Wind. A geostrophic wind blows high above the surface, where the pressure gradient force and the Coriolis force balance and the air flows parallel to the isobars.
Air starts moving from high to low pressure under the pressure gradient force. As it moves, the Earth's rotation deflects it through the Coriolis force, to the right in the Northern Hemisphere and to the left in the Southern. Near the ground, friction slows the wind and it crosses the isobars at an angle. At about 2–3 km and above, friction is negligible, so the two forces come into balance and the wind blows parallel to the isobars, at right angles to the pressure gradient.
A is wrong: a jet stream is a narrow belt of very fast wind near the tropopause, a special case of upper-air flow rather than the general balance described here.
C is wrong: the westerlies are planetary surface winds blowing from the subtropical highs towards the subpolar lows.
D is wrong: the easterlies, such as the trade winds, are also surface planetary winds.
Exam tip: pressure gradient force balanced by Coriolis force, no friction, flow parallel to isobars = geostrophic wind.
Practice Questions
View allBroadly both birth and death rates are low in which one of the following stages of demographic transition model?
- A.High stationary stage
- B.Early expanding stage
- C.Late expanding stage
- D.Low stationary stage
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In this last stage both the birth rate and the death rate are low, so the population grows very slowly or stays almost steady.
Read the full explanation →Which one of the following is the deepest, inland and protected port on the east coast of India ?
- A.Chennai
- B.Paradip
- C.Tuticorin
- D.Visakhapatnam
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It is the deepest landlocked and well-protected port on India's east coast. Visakhapatnam port in Andhra Pradesh lies in a natural harbour cut into the land, sheltered by the Dolphin's Nose headland, which protects ships from the waves of the Bay of Bengal.
Read the full explanation →Which one of the following is a permeable rock that allows water to pass through it?
- A.Granite
- B.Limestone
- C.Quartzite
- D.Sill
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Water passes through limestone along its joints and bedding planes, and slowly dissolves the rock as it goes. Limestone is a sedimentary rock made mainly of calcium carbonate.
Read the full explanation →Which one of the following major river basins of India is the shortest in length and smallest in terms of catchment area?
- A.Cauvery
- B.Mahi
- C.Penner
- D.Sabarmati
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Of the four, the Sabarmati is both the shortest river and the one with the smallest basin. The Sabarmati rises in the Aravalli hills of Rajasthan and flows about 370 km south-west through Gujarat, past Ahmedabad and Gandhinagar, into the Gulf of Khambhat.
Read the full explanation →Consider the following statements regarding the rotation of the Earth : 1. Since the Earth rotates by 15° each hour, time zones normally differ by one hour 2. At the International Date Line, the calendar day changes - advancing a day for eastward travel, dropping back a day for westward travel 3. Daylight saving time advances the clock by one hour 4. The Moon rotates and revolves about the Earth in the same direction that the Earth revolves around the Sun Which of the statements given above is/are correct ?
- A.1 only
- B.3 and 4 only
- C.1, 3 and 4
- D.2, 3 and 4
Show answer
Only statement 2 is wrong, because it reverses the date-line rule. The Earth turns 360° in 24 hours, or 15° every hour, so neighbouring standard time zones are usually one hour apart (statement 1).
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