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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 6
Ann. Geophys., 27, 2449–2456, 2009
https://doi.org/10.5194/angeo-27-2449-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 2449–2456, 2009
https://doi.org/10.5194/angeo-27-2449-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  18 Jun 2009

18 Jun 2009

A potential lag between the open solar magnetic source flux and solar EUV and X-ray emissions as measured by the Earth's ionosphere during total solar eclipses

C. J. Davis1, S. A. Bell2, R. Stamper1, A. W. V. Poole3, L. A. McKinnell3,4, and P. Wilkinson5 C. J. Davis et al.
  • 1Rutherford Appleton Laboratory, Chilton, Oxfordshire, OX11 0QX, UK
  • 2HM Nautical Almanac Office, UK Hydrological Office, Admiralty Way, Taunton, TA1 2DN, UK
  • 3Department of Physics and Electronics, Rhodes University, Grahamstown, South Africa
  • 4Hermanus Magnetic Observatory, Hermanus, South Africa
  • 5IPS Radio and Space Services, Haymarket, NSW 1240, Australia

Abstract. Measurements of the ionospheric E-region during total solar eclipses have been used to provide information about the evolution of the solar magnetic field and EUV and X-ray emissions from the solar corona and chromosphere. By measuring levels of ionisation during an eclipse and comparing these measurements with an estimate of the unperturbed ionisation levels (such as those made during a control day, where available) it is possible to estimate the percentage of ionising radiation being emitted by the solar corona and chromosphere. Previously unpublished data from the two eclipses presented here are particularly valuable as they provide information that supplements the data published to date. The eclipse of 23 October 1976 over Australia provides information in a data gap that would otherwise have spanned the years 1966 to 1991. The eclipse of 4 December 2002 over Southern Africa is important as it extends the published sequence of measurements. Comparing measurements from eclipses between 1932 and 2002 with the solar magnetic source flux reveals that changes in the solar EUV and X-ray flux lag the open source flux measurements by approximately 1.5 years. We suggest that this unexpected result comes about from changes to the relative size of the limb corona between eclipses, with the lag representing the time taken to populate the coronal field with plasma hot enough to emit the EUV and X-rays ionising our atmosphere.

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