The annual course of zonal wind speed at 700 mb for latitudes 20° to 90 °N is portrayed in three ways—from monthly normal data, from monthly mean data averaged over a recent seven year period, and from 5-day mean data averaged over the same seven years. In a broad sense these representations have much in common, but the 5-day data reveal certain well-marked shorter period variations in the westerlies which appear to be related to singularities of the general circulation.

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