A Reanalysis of Geomagnetic Activity during the Last 100 Years

Details A Reanalysis of Geomagnetic Activity during the Last 100 Years A Reanalysis of Geomagnetic Activity during the Last 100 Years

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh53b0330m&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH53B-0330

Other

7524 Magnetic Fields, 7537 Solar And Stellar Variability, 2162 Solar Cycle Variations (7536)

Scientific paper

Long-term geomagnetic activity presented by the aa index has recently been used to show that the heliospheric magnetic field has more than doubled during the last 100 years. However, serious concern has recently been raised on the long-term consistency of the aa index and, thereby, on the centennial rise of solar magnetic activity. Here we reanalyze geomagnetic activity during the last 100 years by calculating the recently suggested IHV index for seven stations. We find that local geomagnetic activity in all stations follows the same qualitative long-term pattern as depicted by the aa index, and has a higher average level during the last two decennia of the 20th century than in the first two decennia. This verifies the result based on the aa index that global geomagnetic activity, and thereby, the open solar magnetic field has indeed increased during the last 100 years. However, quantitatively, the estimated centennial increase varies greatly from one station to another. We find that the relative increase is higher at the high-latitude stations and lower at the low and mid-latitude stations. Moreover, we find a considerably smaller (about 24-35%) centennial increase for global geomagnetic activity than given by the aa index (about 65%). We also show that the IHV index needs to be corrected for the long-term change of the daily curve, and calculate the corrected IHV values. We find that in four out of seven stations this correction further reduces the estimated centennial increase of local geomagnetic activity.

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