Harmattan

The Harmattan is a seasonal weather pattern in West Africa. It occurs from late November until the middle of March. This season is defined by a dry, dusty northeasterly trade wind. This wind travels from the Sahara Desert toward the Gulf of Guinea.

People sometimes call it the "doctor wind." They use this name because the air feels invigorating. This is a contrast to the heavy, humid air found in the tropics. The season marks the dry period when the sun is at its lowest.

This wind moves because of specific pressure systems in the atmosphere. During this time, a subtropical ridge of high pressure stays over the central Sahara. At the same time, a low-pressure area called the Intertropical Convergence Zone stays over the Gulf of Guinea. This difference in pressure drives the wind across the continent. As the Harmattan blows over the Sahara, it picks up fine dust and sand. These particles are very small, measuring between 0.5 and 10 micrometres.

The wind then carries this heavy load of dust into West Africa.

The weather during the Harmattan is very different from a typical winter. It is characterized by cold, dry, and dust-laden winds. The season also brings wide fluctuations in temperature between day and night. Temperatures can be quite low in the early morning hours. However, they can climb very high in the afternoon. In some regions, like the Sahara, the wind can feel quite hot. These temperature changes depend on local circumstances in different areas.

Historically, researchers have documented these unique wind patterns. In 1919, a writer named Knox described the wind in a geographical review. He noted that the Harmattan blows from the northeast. He observed that it could be a hot wind in some localities. In other places, it could be a cold wind. This early documentation helped describe how the wind changes based on location. The season remains a major part of the West African climate cycle.

The physical effects of the Harmattan are quite intense. The air is extremely dry and desiccating, which means it dries things out. Relative humidity can drop below 5 percent during this time. This extreme dryness can cause the branches of trees to die. The wind also dissipates cloud cover and prevents rainfall from forming.

Sometimes, the wind creates large clouds of dust. These can result in intense dust storms or sandstorms. The wind can also increase the risk of fires and cause crop damage.

One of the most visible results is known as the Harmattan haze. This happens when the heavy amount of dust in the air limits visibility. The haze can be so thick that it blocks the sun for several days. This effect is comparable to a very heavy fog.

This haze has a major impact on transportation. It costs airlines millions of dollars every year. This cost comes from having to cancel or divert many flights. When the haze is weak, the skies return to being clear.

The Harmattan also has significant impacts on human health. The extreme dryness can cause skin to become dry and lips to become chapped. It can also affect the eyes and the respiratory system. For people with asthma, the dust can cause the condition to worsen. If humidity drops below 15 percent, some people may experience spontaneous nosebleeds.

A study from 2024 found that the dust increases mortality in infants and children. It also found persistent adverse health impacts on children who survive. Finally, the interaction between Harmattan winds and monsoon winds can even cause tornadoes.