What is the harmattan wind in the southern Sahara Desert?

The harmattan is a cool, dry trade wind that blows from the northeast or east across the western Sahara and into western Africa. It is most prominent during the late fall and winter months, typically from late November to mid-March.12

Characterized by its extreme dryness and gustiness, the wind is known for being cool at night while becoming scorchingly hot during the day. Because it is exceptionally dry, it can cause a sensation of coolness on human skin by rapidly evaporating moisture. The harmattan frequently carries large quantities of dust, which can travel hundreds of kilometers over the Atlantic Ocean, often settling on ships and interfering with aircraft operations.21

The wind occurs in spells that generally last from a few days to over a week, alternating with the moist southwesterly winds of the West African monsoon.12