The Harmattan is a dry and dusty West African trade wind. It blows south from Sahara into the Gulf of Guinea between the end of November and the middle of March (winter).
On its passage over the desert it picks up fine dust particles (between 0.5 and 10 micrometres). When the Harmattan blows hard, it can push dust and sand all the way to North America.
In some countries in West Africa, the heavy amount of dust in the air can severely limit visibility and block the sun for several days, comparable to a heavy fog. The effect caused by the dust and sand stirred by these winds is known as the Harmattan haze, and costs airlines millions of dollars in cancelled and diverted flights each year.The interaction of the Harmattan with monsoon winds can cause tornadoes.
In Niger, people say that men and animals become increasingly irritable when this wind has been blowing for a while, giving it a bad reputation However, the cool wind brings relief from the oppressive heat, which is why the Harmattan has earned the nickname “The Doctor”.