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Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield

[2.37] Excitation of longitudinal modes in Magnetic Flux Tubes by external p-modes

S. S. Hasan, W. Kalkofen (Center for Astrophysics, 60 Garden Street, Cambridge MA 02138)

This is a continuation of earlier work by Hasan (1997, ApJ 480, in press) on the interaction of sausage waves in a slender flux tube with p-modes in the ambient medium. In the above paper, the time-asymptotic response of a vertical tube in the solar photosphere due to the buffeting action by external p-modes was examined using linear theory. For mathematical tractability an isothermal atmosphere was assumed, which allowed the problem to be solved exactly. This study provided insight into the behavior of the tube response and its dependence on various parameters. The previous analysis has now been extended in three important respects; firstly, a realistic stratification for the flux tube and external atmospheres has been used based upon the models of Hasan and Kalkofen (1994, ApJ 436, 355). Secondly, the interaction has been treated as an initial value problem, which enables the gradual buildup of energy in flux tube oscillations to be studied. Thirdly, non-adiabatic effects involving radiative transport have been taken into account. Our calculations confirm the linear prediction that the interaction is non-resonant. We find that the response does not exhibit a monotonic variation with the p-mode degree l (for a fixed order), but increases to a maximum and then falls off sharply as l increases. For the f- mode, l_max\sim 700. The amplitude of the oscillations tend to become stationary (i.e. constant in time) implying a balance between energy input from p-modes and losses through radiative damping and leakage from boundaries. The dominant contribution to the energy flux in the upper photosphere comes from the enthalpy flux. This flux by itself appears to be insufficient for chromospheric heating, but may contribute partially to the required flux. P-modes of low order and degree appear to be most efficient for exciting longitudinal oscillations in flux tubes.

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