The Role of Particle Diffusion in the Lower Transition Region: Revised Interpretation of Emission Measures
We have calculated energy-balance models of the solar chromosphere-corona transition region for T < 105 K including the effects of particle diffusion. Here we show how the diffusion of atoms and ions affects the neutral and ionized hydrogen and helium number densities vs. temperature in the transition region. Diffusion substantially increases n H1 for T > 25,000 K and decreases n H1 (while decreasing n p ) between 8000 and 18,000 K. Diffusion substantially increases n HeI for T > 35,000 K and decreases n HeI (while increasing n HeII) between 9000 and 25,000 K, and increases n HeIII for T < 60,000 K. These results suggest that the use of emission measure techniques that ignore the effects of diffusion may be unreliable.
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