Thermal Conduction in the Transitino Region and its Effects on the Energy Balance of Open Coronal Regions
Thermal conductive energy flow into the transition region represents a considerable energy loss for the solar corona. Inclusion of this term lead to a new class of self-consistent models for magnetically open coronal regions. Recently a number of modifications of the thermal conductivity term were suggested, mainly in order to account for the emission measure reversal in the lower transition region. These suggestions include the contributions by ions and neutrals to thermal conduction, ambipolar diffusion, and turbulence. We show that diffusion, since it affects only the lowermost parts of the transition region, does not significantly change the global properties of the corona, unless the transition region base pressure is chosen unrealistically small. This behavior is explained in terms of the boundary layer character of the lower transition region in such models. By contrast, turbulence can enhance the conductivity more drastically and up to higher temperatures. For! large and intermediate pressures, turbulent conduction tends to flatten the lower, but to steepen the remainder of the transition region. The overall thickness of the transition region is reduced, but the total energy losses are enhanced compared to models based on the Spitzer conductivity. The minimum possible energy losses of the corona are also enhanced. The coronal temperature that minimizes the energy losses, however, does not depend much on the type of conductivity.
Proceedings of Kofu Symposium
- Pub Date:
- July 1994