Periodicities of the Geomagnetic Variation Field at Huancayo, Peru

Abstract

RECENT analyses of stratospheric winds have uncovered the rather fascinating phenomenon of an equatorial stratospheric wind oscillation of approximately 26 months1. Although the apparent wind oscillation seems to have its largest amplitude at about 25 km, it has been suggested by Stacey and Westcott2 that these stratospheric fluctuations extend to ionospheric heights. They performed a spectral analysis of the mean monthly values of the horizontal component of the geomagnetic field on magnetically quiet days, Hq, for Huancayo (12° S.), Apia (14° S.) and Alibag (19° N.). Their results indicated spectral peaks at periods of approximately 26–27 months for Alibag and Apia but not for Huancayo. For all three stations there was also an increase of spectral density at a period of about 12 months. These results were somewhat surprising in view of the fact that at stratospheric levels the maximum amplitude of the 26-month wind fluctuation is found close to the equator and then decreases poleward. Ths amplitude of the annual variation, on the other hand, increases with increasing latitude. The two seem to be equal at a latitude of about 15°. To the extent that ionospheric oscillations as manifested by the oscillation of Hq are related to the stratospheric wind oscillation, one should find the more pronounced 26-month period at the lowest latitude station.