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Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23–24
Author(s) -
Love Jeffrey J.,
Joshua Rigler E.,
Gibson Sarah E.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl050702
Subject(s) - earth's magnetic field , maxima and minima , sunspot , solar minimum , dynamo , physics , solar cycle , sunspot number , ionospheric dynamo region , autocorrelation , solar dynamo , geophysics , maxima , magnetic field , geology , mathematics , solar wind , dynamo theory , geomagnetic storm , mathematical analysis , statistics , art , quantum mechanics , performance art , art history
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.