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Session 35 - Solar Magnetic Fields.
Display session, Tuesday, June 11
Tripp Commons,

[35.10] Radiative Heating and the Buoyant Rise of Magnetic Flux Tubes in the Solar Interior

Y. Fan (National Solar Obs.), G. H. Fisher (SSL, UC Berkeley)

We study the effect of radiative heating on the evolution of thin magnetic flux tubes in the solar interior and on the eruption of magnetic flux loops to the surface. Magnetic flux tubes experience radiative heating because the mean temperature gradient in the lower convection zone and the overshoot region deviates substantially from that of radiative equilibrium, and hence there is a non-zero divergence of radiative heat flux; and (2) The magnetic pressure of the flux tube causes a small change of the thermodynamic properties within the tube relative to the surrounding field free fluid, resulting in an additional divergence of radiative heat flux. We find that the former constitutes the dominant source of radiative heating experienced by the flux tube. In the overshoot region, the radiative heating is found to cause a quasi-static rising of the toroidal flux tubes with an upward drift velocity \sim 10^-3 | \delta |^ -1 cm s^-1, where \delta \equiv \bigtriangledown - \bigtriangledown\!_ad < 0 describes the subadiabaticity in the overshoot layer. Using numerical simulations we study the formation of ``Ømega'' shaped emerging loops from toroidal flux tubes in the overshoot region as a result of radiative heating. The initial toroidal tube is assumed to be non-uniform in its thermodynamic properties along the tube and lies at varying depths beneath the base of the convection zone. The tube is initially in a state of neutral buoyancy with the internal density of the tube plasma equal to the local external density. We find from our numerical simulations that such a toroidal tube rises quasi-statically due to radiative heating. The top portion of the non-uniform tube first enters the convection zone and may be brought to an unstable configuration which eventually leads to the eruption of an anchored flux loop to the surface.

Program listing for Tuesday