AAS 204th Meeting, June 2004
Session 20 Magnetic Fields
SPD Oral, Monday, May 31, 2004, 10:00-11:30am, 702

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[20.09] Are surface magnetic fields responsible for the solar irradiance variation?

A. D. Crouch, P. Charbonneau (Universite de Montreal)

Observations over the last 25 years have shown that the total solar irradiance varies on the same timescale as the solar magnetic activity cycle (11 years). The irradiance fluctuates by about 0.1% and peaks during solar maximum. The cause of the positive correlation between magnetic activity and irradiance is still unclear. We investigate the influence of surface magnetic fields on heat transport in the solar convection zone and their role in the subsequent energy output at the solar photosphere. We consider simplified two-dimensional models of heat transport by convection based on the diffusion approximation. Modelling the effect of magnetic fields on convection is very complicated. Our approach is based on two observations. Broadly speaking, the presence of strong surface magnetic fields tends to suppress convection and block heat transport. Consequently, sunspots (large-scale magnetic flux tubes) appear darker than the surrounding photosphere. In contrast, small-scale magnetic flux tubes appear brighter. We account for both of these effects by modifying the diffusion coefficient in magnetised regions (according to their size and other parameter such as temperature). We track the evolution over several solar cycles and determine the correlation between the flux output at the surface and the surface magnetic filling factor. We are then able to investigate what conditions are necessary for heat to be stored in the subsurface layers over timescales comparable to the solar cycle.

The author(s) of this abstract have provided an email address for comments about the abstract: ash@ASTRO.UMontreal.CA

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