Annual cycle of the mid-tropospheric easterly jet over West Africa |
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Authors: | E A Afiesimama |
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Institution: | (1) Regional Meteorological Research Institute, Nigerian Meteorological Agency, Oshodi, Lagos, Nigeria |
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Abstract: | Summary The paper examines the annual cycle of the mid-tropospheric easterly jet (MTJ) over West Africa against the background of
many reviews indicating different locations and characteristics of the jet and considering it as a summer feature. NCEP–NCAR
reanalysis zonal wind datasets for the period 1971–2000 and upper air datasets over the region are used. The results exhibit
realistic spatial structure of the easterly jet. The long-term mean of the datasets suggests that the jet over West Africa
is not only a summer feature but can also be found in winter with the same order of magnitude in the wind velocity at the
core. The jet axis is located at about lat. 2° N close to the Guinean Coast in winter and at lat. 14° N in summer. The meridional
oscillation of the jet suggests that as it advances northward, it maintains an altitude of 700 hPa in winter and transits
in mid-spring to 650 hPa and reaches 600 hPa in summer. In the retreat, it displaces to 650 hPa at the end of September rather
sharply to reach 700 hPa in October. The jet’s core has been observed to have a northeast–southwest orientation from season
to season, covering a longitude of 29° from its southernmost to the northernmost positions. |
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