Love, J. J., E. J. Rigler, and Geophysical Research Letters, 39, L04102, doi:10.1029/2011GL050702., 2012: Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23-24.
|Title:||Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23-24|
|Abstract:||Analysis is made of the geomagnetic-activity aa index 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 historical aa data, 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.|
|Subject(s):||Magnetic observatory, Recurrent geomagnetic activity, Solar-terrestrial interaction|
|Copyright Information:||Copyright 2012 American Geophysical Union.|
|OpenSky citable URL:||ark:/85065/d78g8mcv|