Radio and EUV observations of a coronal hole |
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| Authors: | G A Dulk K V Sheridan S F Smerd G L Withbroe |
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| Institution: | (1) Dept. of Astro-Geophysics, University of Colorado, 80309 Boulder, Colo., USA;(2) Division of Radiophysics, CSIRO, 2121 Epping, N.S.W., Australia;(3) Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory, 02138 Cambridge, Mass., USA |
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| Abstract: | We present observations of a coronal hole made with the EUV spectroheliometer of the Harvard College aboard Skylab and with  high resolution (2–4 ) radio telescopes at Culgoora and Fleurs Australia and Bonn, West Germany. We attempt to derive the density and temperature distributions in the transition region and inner corona from the combined observations. No one standard model can explain both sets of observations; characteristically, models based on EUV data yield higher radio brightnesses than are observed, while models based on radio data yield lower EUV line intensities than are observed. The discrepancy is essentially that the electron density inferred from the EUV data is about three times that inferred from the radio data.After examining several possible modifications of the standard models we suggest that the discrepancy would disappear if the abundances of the heavier elements were increased by about a factor of 10. Such increases could result from differential diffusion in the large temperature gradient of the transition region. We conclude therefore that models which incorporate thermal diffusion, as well as mass outflow and departures from ionization equilibrium, offer the greatest hope of reconciling the EUV and radio observations of coronal holes. |
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