The Harmattan is a season in West Africa that occurs between the end of November and the middle of March. It is characterized by the dry and dusty northeasterly trade wind, of the same name, which blows from the

Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

over West Africa into the Gulf of Guinea. The name is related to the word in the Twi language. The temperature is cold in most places, but can also be hot in certain places, depending on local circumstances. The Harmattan blows during the dry season, which occurs during the months with the lowest sun. In this season the

subtropical ridge The horse latitudes are the latitudes about 30 degrees north and south of the Equator. They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as Subtropics, subtropical ridges, or highs. It is a h ...

of high pressure stays over the central Sahara and the low-pressure

Intertropical Convergence Zone The Intertropical Convergence Zone (ITCZ ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal e ...

(ITCZ) stays over the Gulf of Guinea. On its passage over the Sahara, the Harmattan picks up fine dust and sand particles (between 0.5 and 10 microns). It is also known as the "doctor wind", because of its invigorating dryness compared with humid tropical air.

Effects

This season differs from winter, because it is characterized by cold, dry, dust-laden wind, and also wide fluctuations in the ambient temperatures of the day and night. Temperatures can easily be as low as all day, but sometimes in the afternoon the temperature can also soar to as high as , while the relative humidity drops under 5%. It can also be hot in some regions, like in the Sahara. Ho, Ghana

The air is particularly dry and desiccating when the Harmattan blows over the region. The Harmattan brings desert-like weather conditions: it lowers the humidity, dissipates cloud cover, prevents rainfall formation and sometimes creates big clouds of dust which can result in dust storms or

sandstorms A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transporte ...

. The wind can increase fire risk and cause severe crop damage. The interaction of the Harmattan with monsoon winds can cause tornadoes.

Harmattan haze

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 Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...

. This effect is known as the Harmattan haze. It costs airlines millions of dollars in cancelled and diverted flights each year. When the haze is weak, the skies are clear. The extreme dryness of the air may cause branches of trees to die.

Health

Humidity drops to as low as 15%, which can result in spontaneous nosebleeds for some people. Other health effects on humans may include conditions of the skin (dryness of the skin), dried or chapped lips, eyes, and respiratory system, including aggravation of asthma.

References

External links

* Cold Geography of Ghana Geography of Nigeria Geography of West Africa Seasons Winds {{Seasons

Effects

Harmattan haze

Health

See also

References

External links