We use radiosonde data from Tamale in northern Ghana to evaluate the Z criterion latitude ϕz. We find it correlates well with other Hadley cell parameters since its variations are apparently controlled by the meridional movement of the subtropical westerly jet. Since the Hadley cell parameters correlate well with Tamale rainfall, we conjecture that it should be possible to predict northern Ghana rainfall on the basis of the southward extension of the subtropical jet once more data have been collected by the Tamale radiosonde. This conjecture is supported by data from other stations in West Africa.

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