Winds Archives

1. With reference to “Coriolis force”, which of the following statements

With reference to “Coriolis force”, which of the following statements is/are correct?

It increases with increase in wind velocity.
It is maximum at the poles and is absent at the equator.

Select the answer using the code given below :

1 only

2 only

Both 1 and 2

Neither 1 nor 2

This question was previously asked in

UPSC IAS – 2024

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The Coriolis force is an apparent force caused by the Earth’s rotation that deflects moving objects (like wind and ocean currents) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The magnitude of the Coriolis force (F_c) is given by F_c = 2 * m * v * ω * sin(φ), where m is the mass of the object, v is its velocity, ω is the angular velocity of the Earth’s rotation, and φ is the latitude.
Statement 1: The formula shows that F_c is directly proportional to the velocity (v) of the moving object. Thus, it increases with an increase in wind velocity. This statement is correct.
Statement 2: The term sin(φ) in the formula varies with latitude. At the equator (φ = 0°), sin(0°) = 0, so the Coriolis force is zero. At the poles (φ = 90° or -90°), sin(90°) = 1 or sin(-90°) = -1, giving the maximum magnitude (directional deflection is opposite). Thus, the Coriolis force is maximum at the poles and absent at the equator. This statement is correct.
Both statements are correct.

The Coriolis force is proportional to velocity and varies with latitude, being zero at the equator and maximum at the poles.

The Coriolis force acts perpendicular to the direction of motion. It is responsible for the deflection of winds and ocean currents, influencing large-scale atmospheric and oceanic circulation patterns, including the formation of cyclones (though it does not initiate them).

2. Consider the following characteristics of a type of wind : They occu

Consider the following characteristics of a type of wind :

They occur at upper levels in the atmosphere
They are subjected to two forces, a pressure gradient force and the Coriolis force
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 :

Jet Stream

Geostrophic Wind

Westerlies

Easterlies

This question was previously asked in

UPSC CAPF – 2024

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The characteristics describe a Geostrophic Wind.

Geostrophic wind is a theoretical wind that results from an exact balance between the Coriolis force and the pressure gradient force. It flows parallel to isobars. This balance typically occurs at upper levels of the atmosphere where friction is negligible. Jet streams are a specific example of strong geostrophic winds in the upper atmosphere, but the description fits the general definition of a geostrophic wind.

The pressure gradient force acts perpendicular to isobars from high to low pressure. The Coriolis force acts at a right angle to the wind direction (to the right in the Northern Hemisphere, left in the Southern Hemisphere). In geostrophic balance, these forces are equal in magnitude and opposite in direction, causing the wind to flow parallel to isobars.

3. The speed of the wind is measured by

The speed of the wind is measured by

wind vane

wind rose

barometer

anemometer

This question was previously asked in

UPSC CAPF – 2021

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The speed of the wind is measured by an anemometer.

An anemometer is a meteorological instrument used to measure wind speed. Common types include cup anemometers, propeller anemometers, and sonic anemometers.

A wind vane measures wind direction, indicating the direction from which the wind is blowing. A wind rose is a graphical tool used to show the distribution of wind speed and direction at a particular location over a period of time. A barometer is used to measure atmospheric pressure.

4. Doldrum are 1. equatorial calms 2. calm and light winds 3. roaring

Doldrum are

1. equatorial calms
2. calm and light winds
3. roaring forties
4. variable both in position and in extent

Select the correct answer using the code given below :

1, 2 and 4

2 and 3 only

1 and 3

2, 3 and 4

This question was previously asked in

UPSC CAPF – 2019

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The correct answer is A) 1, 2 and 4. Doldrums are characterized by being equatorial calms, having calm and light winds, and being variable in position and extent. Statement 3, “roaring forties,” refers to completely different latitudes and wind patterns.

– The doldrums are a belt of low atmospheric pressure around the equator (typically between 5°N and 5°S latitude).
– This zone is characterized by calm or very light and variable winds due to the convergence of trade winds and rising air.
– The location and width of the doldrums (Intertropical Convergence Zone – ITCZ) are not fixed but shift seasonally with the overhead sun.
– The “Roaring Forties” are strong westerlies found between latitudes 40°S and 50°S, known for strong winds and large waves.

Historically, the doldrums were problematic for sailing ships that relied on wind power, as they could get stuck for days or weeks. Modern ships are less affected, but the zone is still associated with significant convective weather and squalls.

5. Consider the following statements relating to cyclone, anti cyclone an

Consider the following statements relating to cyclone, anti cyclone and trade wind :

1. The wind direction is clockwise in the cyclone of northern hemisphere
2. The planetary wind that blows from north-east to north-west is known as north-east trade wind
3. The wind direction is anti clockwise in the anticyclone of southern hemisphere
4. Both westerlies and trade winds originate from sub-tropical highs

Which of the statements given above is/are correct ?

3 and 4 only

1, 3 and 4

4 only

1, 2 and 3

This question was previously asked in

UPSC CAPF – 2015

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Statement 3: The wind direction is anti-clockwise in the anticyclone of the southern hemisphere. In the Southern Hemisphere, the Coriolis effect deflects moving air to the left. In an anticyclone (high pressure), air flows outward from the center; deflected to the left, this results in an anti-clockwise rotation. This statement is correct.
Statement 4: Both westerlies and trade winds originate from sub-tropical highs. The Subtropical High-Pressure belt (around 30° N and S) is a zone of descending air. From this high-pressure area, air flows towards the equator as Trade Winds and towards the poles as Westerlies. This statement is correct.
Statement 1: The wind direction is clockwise in the cyclone of northern hemisphere. In the Northern Hemisphere, the Coriolis effect deflects air to the right. In a cyclone (low pressure), air flows inward towards the center; deflected to the right, this results in an anti-clockwise rotation. Statement 1 is incorrect.
Statement 2: The planetary wind that blows from north-east to north-west is known as north-east trade wind. North-east trade winds blow from the north-east to the south-west (towards the equator) in the Northern Hemisphere. Statement 2 is incorrect.
Therefore, only statements 3 and 4 are correct.

The direction of wind circulation in cyclones (low pressure) and anticyclones (high pressure) is determined by the pressure gradient force and the Coriolis effect, which acts differently in the Northern and Southern Hemispheres. Planetary winds like Trade Winds and Westerlies originate from global pressure belts.

Northern Hemisphere: Cyclones (Low Pressure) – Anti-clockwise inflow; Anticyclones (High Pressure) – Clockwise outflow.
Southern Hemisphere: Cyclones (Low Pressure) – Clockwise inflow; Anticyclones (High Pressure) – Anti-clockwise outflow.
Trade Winds blow from Subtropical Highs towards the Equator. Westerlies blow from Subtropical Highs towards Subpolar Lows.

6. Which one of the following factors is NOT connected with planetary win

Which one of the following factors is NOT connected with planetary wind system ?

Latitudinal variation of the atmospheric heating

Emergence of the pressure belt

Earth's revolution around the Sun

Migration of the pressure belts due to apparent path of the Sun

This question was previously asked in

UPSC CAPF – 2015

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The planetary wind system is primarily driven by differential heating of the Earth’s surface (A), leading to pressure gradients (B) and the formation of pressure belts, modified by the Earth’s rotation (Coriolis effect, not listed). The Earth’s revolution around the Sun (C), combined with axial tilt, causes seasons and the apparent migration of pressure belts (D), which significantly affects the seasonal patterns of planetary winds. However, options A, B, and D describe atmospheric or climatological conditions/effects directly linked to the *system’s operation and seasonal variation*. Option C, Earth’s revolution itself, is the astronomical cause *leading* to the effect described in D. While connected, it can be considered less directly connected to the *atmospheric dynamics* of the wind system compared to the atmospheric heating (A), pressure belts (B), and their migration (D).

Planetary winds are driven by atmospheric pressure differences resulting from uneven heating and shaped by Earth’s rotation. Seasonal variations are caused by Earth’s revolution and tilt. Options A, B, and D are direct meteorological factors or features of the planetary wind system, while C is the astronomical cause of one of these factors (migration of belts).

The fundamental drivers of the general atmospheric circulation (planetary winds) are the unequal heating of the Earth’s surface between the equator and poles and the Earth’s rotation. Pressure belts form as a consequence of this heating distribution and the resulting air movements. The tilt of Earth’s axis and its revolution around the sun cause the seasons and the shifting of these belts and associated wind systems throughout the year.

7. Consider the following statements: Statement I: Roaring Forties are

Consider the following statements:

Statement I: Roaring Forties are strong Westerly winds found in the Southern Hemisphere, generally between the latitudes of 40° and 50°
Statement II: The strong East to West air currents are caused by the combination of air being displaced from the Equator towards the South Pole and the Earth’s rotation and there are few landmasses to serve as wind breaks

Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

This question was previously asked in

UPSC CAPF – 2014

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Both Statement I and Statement II are individually true, and Statement II is the correct explanation of Statement I. The Roaring Forties are powerful westerly winds found in the Southern Hemisphere, specifically between latitudes 40° and 50° South. Statement II accurately describes the primary factors contributing to these strong winds: the poleward movement of air from the subtropical high-pressure belts towards the subpolar low-pressure belts, deflected eastward by the Coriolis effect (caused by Earth’s rotation, making them Westerlies, i.e., blowing from the west), and the absence of significant landmasses in these latitudes of the Southern Hemisphere which allows the winds to blow unimpeded across large expanses of ocean, gaining strength.

The Roaring Forties are strong Westerly winds in the Southern Hemisphere mid-latitudes (40°-50°S). Their strength is due to the combined effect of atmospheric circulation patterns, the Coriolis effect, and the lack of continental landmasses acting as barriers.

Similar westerly winds exist in the Northern Hemisphere, but they are less consistently strong due to the presence of large continents. Further south, other zones of strong westerlies are known as the ‘Furious Fifties’ (50°-60°S) and the ‘Screaming Sixties’ (south of 60°S).

8. Which one of the following is a planetary wind ?

Which one of the following is a planetary wind ?

Monsoon

Trade

Chinook

Mistral

This question was previously asked in

UPSC CAPF – 2009

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Trade winds are a type of planetary wind.

Planetary winds, also known as prevailing winds, are large-scale, relatively constant wind patterns that blow across the globe due to differences in air pressure and the Earth’s rotation. Trade winds (blowing from subtropical high-pressure belts towards the equatorial low-pressure belt), Westerlies (blowing from subtropical highs towards subpolar lows), and Polar Easterlies (blowing from polar highs towards subpolar lows) are primary examples.

Monsoons are seasonal winds driven by differential heating of land and sea, not constant global patterns. Chinook and Mistral are examples of local winds influenced by topography and regional pressure systems.

9. The following six (6) items consist of two statements, Statement I and

The following six (6) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below.
Statement I :
Geostrophic wind blows above a height of 600 metres, parallel to the isobars.
Statement II :
Geostrophic wind is the horizontal wind velocity, in which the Coriolis force balances the horizontal pressure force.

Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

This question was previously asked in

UPSC NDA-2 – 2018

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Statement I is true: The geostrophic wind is a theoretical horizontal wind that flows parallel to the isobars. It is typically a good approximation of the wind speed and direction in the atmosphere above the friction layer (usually considered to be above 600-1000 meters), where the effects of surface friction are negligible. Statement II is true: The geostrophic wind occurs when the pressure gradient force (air moves from high to low pressure) is exactly balanced by the Coriolis force (deflection due to Earth’s rotation). This balance is the fundamental definition of geostrophic flow. Statement II provides the physical principle that explains why the geostrophic wind (as described in Statement I) blows parallel to the isobars above the friction layer.

– Pressure Gradient Force (PGF) drives air from high pressure to low pressure.
– Coriolis Force (CF) acts perpendicular to the wind direction, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
– In geostrophic balance, PGF and CF are equal in magnitude and opposite in direction (acting on the wind vector).
– Friction is negligible above the boundary layer, allowing geostrophic balance to be achieved.

Below the friction layer (in the atmospheric boundary layer), friction acts to slow down the wind, which reduces the Coriolis force. This imbalance causes the wind to blow across the isobars towards lower pressure, not parallel to them.

10. Consider the following statements : 1. The doldrums is a low pressur

Consider the following statements :

1. The doldrums is a low pressure area around Equator where the prevailing winds are calm.
2. Chinook is a hot and dry wind that blows in winter and therefore raises the temperature in a short time.

Which of the statements given above is/are correct ?

1 only

2 only

Both 1 and 2

Neither 1 nor 2

This question was previously asked in

UPSC NDA-1 – 2018

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Both statements 1 and 2 are correct. The doldrums are indeed a low-pressure belt around the equator with calm winds, and the Chinook is a hot, dry wind that can cause rapid temperature increases, often occurring in winter.

– The doldrums correspond to the Intertropical Convergence Zone (ITCZ), where air converges and rises, leading to low surface pressure and light winds.
– The Chinook is a type of Foehn wind resulting from adiabatic warming as air descends the leeward side of a mountain range. It is known for its ability to melt snow rapidly, hence the name “snow eater”.

Foehn winds like the Chinook occur when moist air is forced up a mountain, releases moisture as precipitation on the windward side, and then descends dryly and warms adiabatically on the leeward side. This can lead to significant temperature rises in valleys and plains below.