Consider the following statements about anticyclones: 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?
- (a)1
- (b)2
- (c)3
- (d)None
Correct — B, 2. Statements 1 and 2 are right and statement 3 is wrong, so the count is two. An anticyclone is by definition an area where surface pressure is higher than in the surrounding region, which settles statement 1. Air sinks through the troposphere at its centre, warming and drying as it descends and killing off cloud, which settles statement 2 and explains the clear stable weather anticyclones bring. Statement 3 reverses the wind pattern — air flows outward from the high-pressure centre towards the lower pressure around it, so surface winds in an anticyclone diverge. Convergence at the surface belongs to a cyclone.
- (a)1 — Answering one means rejecting the subsidence in statement 2 as well. Subsidence is not optional in an anticyclone — the air spiralling outward at the surface has to be replaced from above, and that descending column is what makes the system dry and cloudless.
- (c)3 — Answering three accepts statement 3, which reverses the wind direction. Winds blow from high pressure towards low pressure, so at the surface of a high they move outward and diverge; converging surface winds are the mark of a low, that is, a cyclone.
- (d)None — This would require even the definition in statement 1 to be false. An anticyclone is a high-pressure system by definition, so at least one statement is certainly correct.
A cyclone and an anticyclone are mirror images. In a cyclone the pressure is lowest at the centre, surface winds spiral inward and converge, the converging air is forced to rise, it cools, condenses and produces cloud and rain. In an anticyclone the pressure is highest at the centre, air descends from aloft, warms by compression as it sinks so that its relative humidity falls, and then spreads outward at the surface. Rotation follows the Coriolis effect — high-pressure systems turn clockwise in the northern hemisphere and anticlockwise in the southern.
The reliable way to answer any statement set on pressure systems is to fix one chain of logic and read the statements against it — high pressure means sinking air means outward, diverging surface winds means clear dry weather. Statement 3 is the planted error, and it is tempting because convergence does occur in an anticyclone, but high up in the atmosphere, not at the surface where the wind is being described. Winter over north-west India is the familiar Indian example of anticyclonic conditions, when the land cools by radiation, pressure builds and the sky stays clear.
- An anticyclone is a region where surface atmospheric pressure is higher than in the surrounding area.
- Air subsides through the troposphere at the centre of an anticyclone, warming as it descends and suppressing cloud formation.
- Surface winds in an anticyclone diverge outward from the centre; converging surface winds are the signature of a cyclone.
- Anticyclones rotate clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.
Statement 3 of the question borrows the cyclone's row. Anticyclonic surface winds diverge, which is why only two of the three statements stand.
- Confusing surface divergence with the convergence that occurs aloft above an anticyclone.
- Assuming a 'how many statements' item always has exactly one false line — check each independently.
- Reversing the rotation sense between the two hemispheres.
As a how-many-statements item, as an assertion-and-reason pair on winter anticyclones over north-west India, or as a compare-and-contrast question with tropical cyclones.
Assertion (A): Anti-cyclonic conditions are formed in winter season when atmospheric pressure is high and air temperatures are low. Reason (R): Winter rainfall in Northern India causes development of anticyclonic conditions with low temperatures.
- (a) Both A and R are individually true, and R is the correct explanation of A
- (b) Both A and R are individually true, but R is NOT a correct explanation of A
- (c) A is true, but R is false
- (d) A is false, but R is true
Answer(c) A is true, but R is false
The same definition, tested as an assertion-and-reason. Its assertion restates statement 1 of the NDA item — anticyclones are high-pressure systems — while its reason inverts cause and effect, since winter rain in north India comes from western-disturbance lows, not from the high.
- practice — not a real PYQ
In an anticyclone, the air at the centre
- (a)rises and cools
- (b)descends and warms
- (c)moves horizontally only
- (d)remains stationary
Answer(b) descends and warms — the sinking air is compressed, its relative humidity falls and cloud is suppressed.
- practice — not a real PYQ
Surface winds converging towards the centre are characteristic of
- (a)an anticyclone
- (b)a cyclone
- (c)a subtropical high
- (d)a polar high
Answer(b) a cyclone — converging air is forced to rise, which is why cyclones bring cloud and rain.