Harmattan
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Template:Weather The Harmattan is a season in West Africa that occurs between the end of November and the middle of March. It is characterized by a dry and dusty northeasterly trade wind, of the same name, which blows from the Sahara over West Africa into the Gulf of Guinea.<ref name="BHarmattan">Template:Cite encyclopedia</ref> The name is related to the word Template:Lang in the Twi language.<ref>Template:Cite dictionary</ref> The temperature is cold usually at night but can be very hot in certain places during the day. Generally, temperature differences can depend on local circumstances.<ref>Geographical Review (1919): "Knox writes of this wind : The Harmattan is experienced as a wind which blows, especially in the months of December, January, and February, from the NE. and is a hot wind in some localities and a cold wind in others, according to circumstances."</ref>
The Harmattan blows during the dry season, which occurs during the months with the lowest sun. In this season, the subtropical ridge of high pressure stays over the central Sahara and the low-pressure Intertropical Convergence Zone (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 micrometres). 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,<ref name="dove press">Template:Cite journal</ref> dust-laden wind, and also wide fluctuations in the ambient temperatures between the day and night. Temperatures can easily be as low as Template:Convert early in the day, but in the afternoon the temperature can climb to as high as Template:Convert, while the relative humidity drops under 5%. It can also be hot in some regions, like in the Sahara.<ref>Template:Cite book</ref>
The air is particularly dry and desiccating when the Harmattan blows over the region.<ref name="dove press" /> 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.Template:Citation needed The wind can increase fire risk<ref>Template:Cite news</ref> and cause severe crop damage.<ref name="Saharan wind stirs cocoa market">Template:Cite news</ref> The interaction of the Harmattan with monsoon winds can cause tornadoes.<ref name=BHarmattan/>
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,<ref>Template:Cite web</ref> comparable to a heavy fog. This effect is known as the Harmattan haze. It costs airlines millions of dollars in cancelled and diverted flights each year.<ref>Template:Cite news</ref><ref name=Re>Template:Cite web</ref> When the haze is weak, the skies are clear.<ref>Template:Cite web</ref> The extreme dryness of the air may cause branches of trees to die.<ref>Template:Cite journal</ref>
Health
A 2024 study found that dust carried by the Harmattan increases infant and child mortality, as well as persistent adverse health impacts on surviving children.<ref>Template:Cite journal</ref>
Humidity can drop below 15%, which can result in spontaneous nosebleeds for some people.<ref name="Saharan wind stirs cocoa market" /> Other health effects on humans may include dryness of the skin, dried or chapped lips, eyes, and respiratory system, including aggravation of asthma.<ref>Template:Cite news</ref>