Mathematics – Logic
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsp41a..09m&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SP41A-09
Mathematics
Logic
7536 Solar Activity Cycle (2162), 7544 Stellar Interiors And Dynamo Theory
Scientific paper
The fundamental model used to study the solar dynamo mechanism is based on the electromagnetic induction equation coupled with Ohm's law. Apart from mean-field or other phenomenological source terms (such as a Babcock-Leighton alpha-effect), the resultant dynamo equation is composed of two terms: An advection and a diffusion term. Depending on the relative importance of these two terms, the dynamo can operate either in an advection-dominated or a diffusion dominated regime. One of the parameters that determine which of these regimes the dynamo operates in is the effective magnetic diffusivity, this parameter is expected to be enhanced by convective turbulence in stellar convection zones. The diffusivity values can range from 104 cm2/s in the radiative zone (where there is no turbulence) to 1012-14 cm2/s in the upper convection zone. The depth dependence of this effective diffusivity is not particularly well-constrained and most commonly used profiles involve a relatively low diffusivity in the convection zone (1010-11 cm2/s) - which makes the dynamo operate in the advection-dominated regime. The underlying problem here is that these values of diffusivity are not consistent with theoretical considerations based on mixing-length theory, which suggest much higher values of turbulent diffusivity; this would make the dynamo operate in a diffusion-dominated regime. However, a possible solution to this inconsistency may be in the quenching effect that strong magnetic fields have on turbulence. We have recently developed a kinematic solar dynamo based on a novel numerical technique called the exponential- propagation method. Using this model, we study magnetic diffusivity quenching and discuss how its effect may reconcile the theoretically suggested turbulent diffusivity values with the effective diffusivity profiles most commonly used in this type of models.
Martens Petrus C.
Muñoz-Jaramillo Andrés
Nandy Dibyendu
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