What does 'Roaring Forties' refer to?

Answer: (c) The region between latitudes 40° and 50°S, where the prevailing westerly winds blow over the open oceans with great regularity and strength

The region between 40° and 50°S where westerlies blow strongly over open ocean.

The idea

Westerlies are winds whose main flow is from west towards east in the middle latitudes. Over the Southern Ocean, few continental barriers interrupt them. “Roaring Forties” names the especially exposed southern belt around forty degrees latitude. It is a latitude-and-circulation term, not a name for a local whirlwind.

Air flows poleward from subtropical highs → Coriolis adds an eastward component → Broad southern oceans offer few barriers → Strong westerlies persist → Passing fronts and lows produce stormy seas

Why the others are wrong

(a) Wrong latitudes.

Elimination technique

The word “Forties” supplies the latitude anchor, and the uninterrupted ocean setting supplies the Southern Hemisphere anchor. Together they identify the 40–50°S open-ocean westerly belt in (c).

Also know

The names Furious Fifties and Screaming Sixties extend the same association farther south. Northern middle latitudes also have westerlies but more continental interruption. Trade winds occupy lower latitudes and have an easterly component. A tropical cyclone is an individual rotating storm, different from this planetary wind belt.