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| Titel |
Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August, 1999 and 9 July, 1945 |
| VerfasserIn |
C. J. Davis, M. Lockwood, S. A. Bell, J. A. Smith, E. M. Clarke |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 18, no. 2 ; Nr. 18, no. 2, S.182-190 |
| Datensatznummer |
250013906
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| Publikation (Nr.) |
 copernicus.org/angeo-18-182-2000.pdf |
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| Zusammenfassung |
Swept-frequency (1-10 MHz) ionosonde
measurements were made at Helston, Cornwall (50°06'N, 5°18'W)
during the total solar eclipse on August 11, 1999. Soundings were made every
three minutes. We present a method for estimating the percentage of the ionising
solar radiation which remains unobscured at any time during the eclipse by
comparing the variation of the ionospheric E-layer with the behaviour of the
layer during a control day. Application to the ionosonde date for 11 August,
1999, shows that the flux of solar ionising radiation fell to a minimum of
25±2% of the value before and after the eclipse. For comparison, the same
technique was also applied to measurements made during the total solar eclipse
of 9 July, 1945, at Sörmjöle (63°68'N, 20°20'E)
and yielded a corresponding minimum of 16±2%. Therefore the method can detect
variations in the fraction of solar emissions that originate from the unobscured
corona and chromosphere. We discuss the differences between these two eclipses
in terms of the nature of the eclipse, short-term fluctuations, the sunspot
cycle and the recently-discovered long-term change in the coronal magnetic
field.
Key words: Ionosphere (solar radiation and cosmic ray
effects) - Radio science (ionospheric physics) - Solar physics, astrophysics,
and astronomy (corona and transition region) |
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