What are the Westerlies?

Westerlies are classified as permanent or planetary winds because they blow almost in the same direction throughout the year [2]. They originate from the sub-tropical high-pressure belts and blow towards the sub-polar low-pressure belts in both hemispheres [1]. These winds are a key component of the global atmospheric circulation, specifically within the Ferrel cell [4]. Unlike seasonal winds (like monsoons) or local winds (like sea breezes), westerlies involve large areas of the globe and are driven by permanent pressure belts [2]. In the Northern Hemisphere, they blow from the southwest, while in the Southern Hemisphere, they blow from the northwest due to the Coriolis effect [3]. They are particularly strong and persistent in the Southern Hemisphere due to the vast expanse of water, earning names like the 'Roaring Forties' [1]. Consequently, they are recognized as one of the three major prevailing wind belts alongside trade winds and polar easterlies [5].

Sources

1. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Primary winds or Prevailing Winds or Planetary Winds > p. 318
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > The Westerlies > p. 319
3. [4] https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/Wx_Terms/Flight_Environment.htm
4. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Ferrel Cell > p. 317
5. [5] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 14: Climate > Pressure and Planetary Winds > p. 140