Assertion (A): Wind patterns are clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere. Reason (R): The directions of wind patterns in the northern and southern hemispheres are governed by the Coriolis effect.

Answer: (a) Both A and R are individually true and R is the correct explanation of A

The key accepts A (true for anticyclones) with the Coriolis effect as the reason.

The idea

The sense of circulation depends on both the hemisphere and whether the centre is low or high pressure. Coriolis bends motion but does not make every wind pattern turn the same way. Northern highs circulate clockwise and northern lows anticlockwise, with the reverse in the south. A claim about all wind patterns needs that pressure-centre qualification.

Why the others are wrong

(b) R is the reason.

(c) R is true.

(d) The key treats A as true.

The trap

Cyclones spin ANTI-clockwise in the NH — A is true only for anticyclones.

Also know

A cyclone is a low-pressure circulation; an anticyclone is a high-pressure circulation. At the surface, friction allows wind to cross isobars towards a low or away from a high. Aloft, where friction is weaker, winds more nearly follow the isobars. The eye of an intense tropical cyclone is a local descending region within the larger cyclone.