Northwest African depressions and their relationship to jet streams

The two-fold purpose was to examine the intensity, movement, and duration of northwest African depressions and to determine if there was any relationship between the jet stream and the depressions. Northwest African lows are generally weak though they may intensify. The lows are found as open troughs or closed circulations at the 850 millibar level, but rarely higher. Cyclogenesis over northwest Africa takes place when a trough or a weak disturbance occurs in the presence of a jet stream. Upper level divergence associated with the jet stream creates favorable conditions for cyclogenesis. Further development may take place in the presence of either the polar or the subtropical jet. The depressions move in an east-northeast direction in association with an upper level trough and the jet stream. Depressions that move in a northeasterly track have the longest duration and travel the longest distance. The weakness of the relationship between the intensity of the lows and the strength of the jet probably is a result of the dominance of the subtropical jet. The impact of this jet on depressions development is less pronounced than that of the polar jet.