African easterly jet

The African easterly jet, is a region of the lower troposphere over West Africa where the seasonal mean wind speed is maximum and easterly. Forming due to the temperature contrast between the Sahara Desert and the Gulf of Guinea, maximum wind speeds are located at a height of 3 kilometres (1.9 mi) to the north of the monsoon trough. The jet marches northward from its southern location in January, reaching its most northerly latitude in August, and its strongest winds in September while shifting back towards the equator. Within the easterly jet, tropical waves form. Convective complexes associated with these waves can form tropical cyclones. If the feature is suppressed south of its normal location during August and September, tropical cyclogenesis is suppressed. If desertification continues across Sub-Saharan Africa, the strength of this feature would increase, though tropical wave generation is expected to decrease which could decrease the number of tropical cyclones in the Atlantic basin.

During January, it lies at 3,000 metres (9,800 ft) above sea level at the latitude of five degrees north. Winds within it rise from 30 km/h (19 mph) in January to 40 km/h (25 mph) in March. Shifting northward in April to the seventh parallel, winds within the jet increase to 45 km/h (28 mph). By June, it shifts northward into northwest Africa. The mid-level African easterly jet occurs during the Northern Hemisphere summer between 10°N and 20°N above West Africa, and the nocturnal poleward low-level jet occurs in the Great Plains of east and South Africa. The formation of the thermal low over northern Africa leads to a low-level westerly jet stream from June into October to the south of the Intertropical Convergence Zone. The jet develops because heating of the West African land mass during the Northern Hemisphere summer creates a surface temperature and moisture gradient between the Gulf of Guinea and the Sahara, and the atmosphere responds by generating vertical wind shear to maintain thermal wind balance. The jet reaches its zenith in August, lying between the 16th and 17th parallels. In September, winds maximize near 50 km/h (31 mph) between the 12th and 13th parallels. The easterly jet weakens and drops southward during October and November.

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