Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23-24

Geophysical Research Letters
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Abstract

[1] Analysis is made of the geomagnetic-activityaaindex covering solar cycle 11 to the beginning of 24, 1868–2011. Autocorrelation shows 27.0-d recurrent geomagnetic activity that is well-known to be prominent during solar-cycle minima; some minima also exhibit a smaller amount of 13.5-d recurrence. Previous work has shown that the recent solar minimum 23–24 exhibited 9.0 and 6.7-d recurrence in geomagnetic and heliospheric data, but those recurrence intervals were not prominently present during the preceding minima 21–22 and 22–23. Using annual-averages and solar-cycle averages of autocorrelations of the historicalaadata, we put these observations into a long-term perspective: none of the 12 minima preceding 23–24 exhibited prominent 9.0 and 6.7-d geomagnetic activity recurrence. We show that the detection of these recurrence intervals can be traced to an unusual combination of sectorial spherical-harmonic structure in the solar magnetic field and anomalously low sunspot number. We speculate that 9.0 and 6.7-d recurrence is related to transient large-scale, low-latitude organization of the solar dynamo, such as seen in some numerical simulations.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23-24
Series title Geophysical Research Letters
DOI 10.1029/2011GL050702
Volume 39
Year Published 2012
Language English
Publisher American Geophysical Union
Contributing office(s) Geologic Hazards Science Center
Description L04102
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geophysical Research Letters
Country United States