Seasonal Variations of Geomagnetic Activity at High, Middle and Low Latitudes

Details Seasonal Variations of Geomagnetic Activity at High, Middle and Low Latitudes Seasonal Variations of Geomagnetic Activity at High, Middle and Low Latitudes

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm51a..14t&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SM51A-14

Physics

2736 Magnetosphere/Ionosphere Interactions, 2431 Ionosphere/Magnetosphere Interactions (2736)

Scientific paper

The seasonal variation of geomagnetic activity with two maxima at equinoxes has been known for over 100 years. However, many aspects of this phenomenon remain unclear. One of such issues is the latitudinal dependence of the seasonal effects of geomagnetic activity. Interestingly, contrary to expectations, the seasonal effect does not increase with geomagnetic latitude, but actually decreases with it. To investigate this phenomenon in more details, we have studied the seasonal variations of geomagnetic activity indices related to different latitudinal zones: high-latitude auroral electrojet AE, AU and AL indices, middle-latitude Ap and Am indices and low-latitude Dst index for many years. Our results show that the seasonal variation in the low-latitude Dst index is two to three times higher than that of the middle- and high-latitude geomagnetic activity indices. A possible explanation of this effect is discussed. We have also studied the seasonal effects at several low-latitude geomagnetic observatories. We have found that the "equinoctial" peaks in geomagnetic activity in fact are displaced from equinoctial times towards local winter. This shift may be one month or longer. As a result, in the northern hemisphere the "equinoctial" peaks are shifted towards January-December whereas in the southern hemisphere they are shifted towards June-July. This shift of "equinoctial" maxima leads to winter-summer asymmetry in geomagnetic activity: geomagnetic disturbances appear to be stronger in local winter than in local summer. This effect is observed even at very low latitudes.

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