The Atmospheric Pressure

1. Trough and ridge are

Trough and ridge are

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elongated area of low pressure and of high pressure respectively
elongated areas of low pressure
elongated areas of high pressure
elongated area of high pressure and of low pressure respectively
This question was previously asked in
UPSC CAPF – 2022
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In meteorology, a trough is an elongated area of relatively low atmospheric pressure. It is often associated with fronts and can lead to unsettled weather. A ridge is an elongated area of relatively high atmospheric pressure. Ridges are typically associated with stable atmospheric conditions and fair weather.
Trough and ridge are terms used in meteorology to describe the shape of isobars (lines of equal pressure) on a weather map, indicating areas of relatively low and high pressure respectively.
Troughs extend away from the center of a low-pressure system, while ridges extend away from the center of a high-pressure system. These features are important for understanding atmospheric circulation and predicting weather patterns.

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2. Consider the following statements: Statement I: The Doldrums is a l

Consider the following statements:

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  • Statement I: The Doldrums is a low pressure area around the Equator where the prevailing winds are calm
  • Statement II: Low pressure is caused by the heat at the Equator which makes the air rise and travel both Northwards and Southwards
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 Doldrums is indeed a low-pressure belt located around the Equator, known for calm or light winds, variable winds, and frequent convectional rainfall. This low pressure is a direct result of intense solar heating at the Equator, which causes the air to warm, become less dense, and rise. As the air rises, it diverges towards the poles at higher altitudes, creating the low-pressure area at the surface and leading to relatively calm horizontal surface winds.
The Doldrums (Intertropical Convergence Zone or ITCZ) is an equatorial low-pressure zone characterized by calm winds. The intense heat at the equator causes air to rise (convection), creating this low pressure and leading to the characteristic weather conditions.
The rising air in the Doldrums cools adiabatically, leading to condensation and heavy convectional rainfall. The zone shifts slightly north and south with the apparent movement of the sun. The calmness is due to the predominantly vertical movement of air rather than strong horizontal winds, posing a historical challenge for sailing ships.

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3. Which one among the following forces is most powerful in determining m

Which one among the following forces is most powerful in determining movement of wind including its velocity ?

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Gravitational force
Centrifugal force
Frictional force
Pressure gradient force
This question was previously asked in
UPSC CAPF – 2011
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The Pressure Gradient Force (PGF) is the primary force that initiates air movement, i.e., wind. It is the force that pushes air from areas of high pressure to areas of low pressure. The strength of the wind is directly proportional to the magnitude of the pressure gradient (the rate of pressure change over distance).
Pressure gradient force is fundamental to atmospheric circulation. Air flows from high pressure to low pressure, and this movement constitutes wind. Other forces like Coriolis force and friction modify the direction and speed of the wind, but PGF is the initial driver.
While other forces influence wind, their roles are different: Gravitational force keeps the atmosphere bound to the Earth. Centrifugal force is relevant in curved motion but not the primary cause of wind. Frictional force acts opposite to the direction of motion, slowing down the wind, especially near the surface.

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4. Which one of the following is the usual unit of measurement for Air Pr

Which one of the following is the usual unit of measurement for Air Pressure used in India ?

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Centimeter
Millibar
Milligram
Milliliter
This question was previously asked in
UPSC NDA-2 – 2023
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In meteorology, including in India, air pressure is commonly measured and reported in millibars (mb) or hectopascals (hPa). One millibar is equal to one hectopascal (1 mb = 1 hPa). While the standard international unit for pressure is the Pascal (Pa), millibars/hectopascals remain widely used for atmospheric pressure due to historical conventions and convenience (standard atmospheric pressure at sea level is approximately 1013.25 mb or hPa). Centimeter, Milligram, and Milliliter are units of length, mass, and volume respectively.
Millibar (mb) or Hectopascal (hPa) are the standard units for measuring atmospheric pressure in meteorology.
A mercury barometer or an aneroid barometer are common instruments used to measure air pressure. Pressure is a force per unit area; 1 Pascal is defined as one Newton per square meter (N/m²).

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5. Consider the following statements about anticyclones : 1. Anticyclon

Consider the following statements about anticyclones :

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  • 1. Anticyclones are high pressure systems.
  • 2. Air in the centre of the system must be subsiding.
  • 3. Anticyclones are characterized by converging winds.

How many of the above statements is/are correct?

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1
2
3
None
This question was previously asked in
UPSC NDA-2 – 2022
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Let’s evaluate each statement:
1. Anticyclones are high pressure systems: This is correct. Anticyclones are defined as areas of high atmospheric pressure, relative to their surroundings.
2. Air in the centre of the system must be subsiding: This is correct. High pressure at the surface is associated with descending air (subsidence) from aloft. As air descends, it warms and dries, leading to stable atmospheric conditions and often clear skies.
3. Anticyclones are characterized by converging winds: This is incorrect. Anticyclones are characterized by diverging winds at the surface, flowing outwards from the high-pressure center. In the Northern Hemisphere, these winds diverge clockwise, and in the Southern Hemisphere, they diverge counter-clockwise due to the Coriolis effect. Convergence occurs aloft above the anticyclone.
Anticyclones are stable weather systems associated with sinking air, high pressure, and diverging winds near the surface, typically bringing fair weather.
In contrast to anticyclones, cyclones (low-pressure systems) are characterized by converging winds at the surface, rising air, and often bring cloudy skies, precipitation, and unstable weather.

6. Which one of the following weather conditions indicates a sudden fall

Which one of the following weather conditions indicates a sudden fall in barometer reading ?

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Stormy weather
Calm weather
Cold and dry weather
Hot and sunny weather
This question was previously asked in
UPSC NDA-1 – 2015
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A barometer measures atmospheric pressure. A sudden fall in barometer reading indicates a rapid decrease in atmospheric pressure. Falling atmospheric pressure is often associated with approaching low-pressure systems. Low-pressure systems are typically accompanied by unstable atmospheric conditions, rising air, cloud formation, precipitation, and often, stormy weather. Conversely, rising pressure indicates stable conditions (usually associated with clear or fair weather), and steady high pressure indicates calm, dry, and often clear weather. A sudden fall specifically points towards a rapidly developing or approaching weather disturbance, which is characteristic of stormy weather.
A sudden drop in atmospheric pressure (barometer reading) indicates unstable weather conditions, often preceding or accompanying storms.
Forecasters use changes in atmospheric pressure to help predict weather changes. A steady fall may indicate rain, while a rapid fall often indicates a strong storm or depression approaching. High pressure generally leads to clear, calm, and stable weather.

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7. How is strong pressure gradient represented on a weather map ?

How is strong pressure gradient represented on a weather map ?

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Closely spaced isobars
Widely spaced isobars
Closely spaced isobars at the periphery
A set of two widely spaced isobars followed by two closely spaced isobars
This question was previously asked in
UPSC CDS-2 – 2024
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On a weather map, isobars are lines connecting points of equal atmospheric pressure. The pressure gradient is the rate of change of pressure over a horizontal distance. A strong pressure gradient indicates a large change in pressure over a short distance, which results in high wind speeds. On a weather map, this is visually represented by isobars that are drawn very close together. Conversely, widely spaced isobars indicate a weak pressure gradient and light winds.
The pressure gradient force is one of the primary forces driving wind. It acts perpendicular to isobars, from areas of high pressure to areas of low pressure.
The closer the isobars, the stronger the pressure gradient, and consequently, the stronger the pressure gradient force and potentially higher wind speeds (though other factors like the Coriolis effect and friction also influence wind).

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