Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.2402s&link_type=abstract
American Astronomical Society, SPD meeting #40, #24.02; Bulletin of the American Astronomical Society, Vol. 41, p.860
Astronomy and Astrophysics
Astronomy
Scientific paper
Several years ago, it was discovered that photospheric ephemeral regions (EPRs) cover the Sun like a magnetic carpet. From this, we update the Babcock-Leighton dynamo. We alter the idea of sunspot fields appearing in the photosphere de novo from eruptions originating deep inside the Sun. Instead we consider that sunspots form near the photosphere by the rapid accumulation of like-sign field from EPRs. This would occur only under special circumstances in regions where the temperature structure is highly superadiabatic and also contains a large subsurface horizontal magnetic field (lower latitudes). Under these circumstances, a downflow from the Sun's surface would scour large regions of neutral hydrogen and thereby amass magnetic elements (EPRs) into active regions through a percolation or sorting process. The enhanced convection provides the flow with the unique ability to separate field, into field-free and field-filled magnetic regions. We refer to this as superadiabatic percolation; the field behaves in a "sticky fashion,” with like-sign field elements attracted into generally bipolar regions, their orientation governed by Babcock's subsurface field pattern. The special photospheric conditions are not commonly met; hence magnetic elements generally undergo normal percolation, wherein magnetic elements are sorted by motions similar to diffusive Brownian motion. We develop cellular automata (CA) models that allow these processes to be calculated; thereby obtain both small-scale and large-scale solar models. Our small-scale model is compared with Hinode observations. Our large-scale CA dynamo model suggests that fields from decaying bipolar magnetic regions (BMRs) drift on the photosphere driven by subsurface magnetic forces. Our shallow dynamo model shares a commonality with the B-L dynamo: the Sun's polar field serves as the seed for the next cycle's sunspot fields. Using this basis, we (GRL, 2005) predicted that from cycle #23's polar field, cycle #24 would be very weak with Rz 80, now possibly less.
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