Showing papers on "Solar transition region published in 1980"

Non-Maxwellian Velocity distribution functions associated with steep temperature gradients in the solar transition region

Abstract: We show that, in the presence of the steep temperature gradients characteristic of EUV models of the solar transition region, the electron and proton velocity distribution functions are non-Maxwellian and are characterized by high energy tails. We estimate the magnitude of these tails for a model of the transition region and compute the heat flux to be a maximum of 30% greater than predicted by collision-dominated theory.

The energy balance of the solar transition region

Abstract: It is shown how the observed distribution of the emission measure with temperature can be used to limit the range of energy deposition functions suitable for heating the solar transition region and inner corona. The minimum energy loss solution is considered in view of the work by Hearn (1975) in order to establish further scaling laws between the transition region pressure, the maximum coronal temperature and the parameter giving the absolute value of the emission measure. Also discussed is the absence of a static energy balance at the base of the transition region in terms of measurable atmospheric parameters, and the condition for a static energy balance is given. In addition, the possible role of the emission from He II in stabilizing the atmosphere by providing enhanced radiation loss is considered.

Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. Paper 2: The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen

Abstract: Non-Maxwellian electron velocity distribution functions, previously computed for Dupree's model of the solar transition region are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation.

Nonequilibrium ionization due to thermal diffusion and mass flows

Abstract: Recent calculations of diffusion coefficients are used in the continuity equation to compute ion populations of carbon in the solar transition region. Thermal diffusion causes strong departures from ionization equilibrium in the region where the temperature gradient is steepest. Mass-conserving flows are also included in our calculations. These dominate over thermal diffusion depending on the magnitude of the flows and also lead to departures from ionization equilibrium. These results have important implications for the interpretation of EUV line emission.

Common origin for UV and radio fluctuations

Abstract: Brightness temperature fluctuations induced by a shock wave transit through the solar transition region are computed at several decimetric wavelengths. A simplified method previously used to reproduce the observed UV line intensity fluctuations is shown to give oscillation amplitudes which are consistent with experimental results. The detectability of shock-induced radio fluctuations is briefly discussed, to check the possibility of a common origin for the observed UV and radio phenomena.

Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. I - Estimate of the electron velocity distribution functions. II - The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen

Abstract: Non-Maxwellian electron velocity distribution functions, computed for Dupree's (1972) model of the solar transition region in a previous paper, are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation.