Long-term variations in the geomagnetic activity level. I. A connection with solar activity.
Abstract
To investigate the secular variation of the geomagnetic activity level the monthly values of the aa index for the 1868 - 1988 period have been correlated with the Rz sunspot numbers. When the secular geomagnetic trend is analyzed in terms of ascending (A) and descending (D) solar activity phases, the linear correlation coefficient seems to have a different time history. A possible connection between the secular variation in the geomagnetic activity level and a type of the solar-wind macroperturbations existing in the interplanetary space during the D-phases is suggested. In fact, the geomagnetic response to transient and corotating interplanetary disturbances should be the origin of the above behaviours, provided that the considered aa set be used as proxy data for solar wind features in the near-earth environment. The role of each type of solar activity sources of interplanetary perturbations has been underlined. Moreover, an interplay between sunspot heliographic positions and polar coronal hole extensions towards the equator exists, as results from the analysis of the sunspot cycle no 19.
- Publication:
-
Annales Geophysicae
- Pub Date:
- September 1992
- Bibcode:
- 1992AnGeo..10..668B
- Keywords:
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- Geomagnetism;
- Secular Variations;
- Solar Activity Effects;
- Solar Terrestrial Interactions;
- Coronal Holes;
- Correlation Coefficients;
- Sunspot Cycle