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Harry van Loon and Roy L. Jenne


In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice.

A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.

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John M. Wilcox, Philip H. Scherrer, Leif Svalgaard, Walter Orr Roberts, Roger H. Olson, and Roy L. Jenne


The solar magnetic sector structure has a sizable and reproducible influence on tropospheric and lower stratospheric vorticity. The average vorticity during winter in the Northern Hemisphere north of 2ON latitude reaches a minimum approximately one day after the passing of a sector boundary, and then increases during the following two or three days. The effect is found at all heights within the troposphere, but is not prominent in the stratosphere, except at the lower levels. No single longitudinal interval appears to dominate the effect.

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