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Physical causes of solar cycle amplitude variability
Author(s) -
Cameron R. H.,
Jiang J.,
Schüssler M.,
Gizon L.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019498
Subject(s) - sunspot , equator , dynamo , flux (metallurgy) , physics , amplitude , atmospheric sciences , polar cap , solar cycle , annual cycle , polar , maxima and minima , geophysics , climatology , ionosphere , geology , latitude , magnetic field , astronomy , solar wind , mathematics , chemistry , optics , mathematical analysis , organic chemistry , quantum mechanics
Abstract The level of solar activity varies from cycle to cycle. This variability is probably caused by a combination of nonlinear and random effects. Based on surface flux transport simulations, we show that the observed inflows into active regions and toward the activity belts provide an important nonlinearity in the framework of Babcock‐Leighton model for the solar dynamo. Inclusion of these inflows also leads to a reproduction of the observed proportionality between the open heliospheric flux during activity minima and the maximum sunspot number of the following cycle. A substantial component of the random variability of the cycle strength is associated with the cross‐equatorial flux plumes that occur when large, highly tilted sunspot groups emerge close to the equator. We show that the flux transported by these events is important for the amplitude of the polar fields and open flux during activity minima. The combined action of inflows and cross‐equatorial flux plumes provides an explanation for the weakness of the polar fields at the end of solar cycle 23 (and hence for the relative weakness of solar cycle 24).