3.11 Energy fluxes

About 2/3 of the convective energy flux near the solar surface consists of ionization energy (Figure 21View Image). Thermal energy accounts for a little over 1/6 of the flux and acoustic energy a little under 1/6 of the flux (Stein and Nordlund, 1998Jump To The Next Citation Point). Hence, including ionization of hydrogen, helium, and the other abundant electron donors in the equation of state is necessary to achieve solar values for the velocities and temperature fluctuations. For an ideal gas to be able to carry the solar flux both the vertical velocities and the temperature fluctuations would have to be larger than is observed. Above temperatures of order the He ii ionization energy (∼ 105 K) most of the energy is transported as thermal energy and an ideal gas equation of state for a fully ionized plasma would be a good approximation.
View Image

Figure 21: The average thermal, ionization, acoustic, and kinetic fluxes plus their sum, the total energy flux, as a function of depth. The thermal plus ionization energy fluxes together are the internal energy flux (not plotted), and this plus the acoustic flux constitutes the enthalpy or convective flux. The enthalpy flux plus the kinetic energy flux is the total energy flux transported by fluid motions. (The viscous flux is very small.) Energy is transported upward through the convection zone near the surface mostly as ionization energy (∼ 2/3) and thermal energy (∼ 1/3). The kinetic energy flux is downwards and is 10 – 15% of the total flux near the surface. At larger depths (outside of this plot) both the upward enthalpy flux and the downward kinetic energy flux increase, with the kinetic energy flux reaching about the net solar flux and the enthalpy flux reaching about twice the net solar flux.

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