The effects of diffusion in the solar transition region

The role of diffusion in calculating ionic fractional abundances and relative abundances of elements to hydrogen in the solar chromosphere-corona transition region is discussed. A variable solar wind velocity is used in these calculations and both spherically and non-spherically symmetric geometries are examined. An efficient numerical method is given for solving the diffusion equations and diffusion effects on the above abundances are discussed in detail. It is found that departures of ionic fractional abundances away from their temperature positions in local ionization equilibrium can be significant but are model dependent as are chemical abundance curves, although the latter are never constant. The solar models discussed all reproduce various EUV resonance line intensities. The importance of concentration diffusion is discussed in detail. (author)