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Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August 1999 and 9 July 1945

Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August 1999 and 9 July 1945
Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August 1999 and 9 July 1945
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.
Ionosphere (solar radiation and cosmic ray effects) - Radio science (ionospheric physics) - Solar physics, astrophysics, and astronomy (corona and transition region)
0992-7689
182-190
Davis, C.J.
854f0b17-697b-476a-92dd-7986346c6880
Lockwood, M.
32917473-f7d9-4773-9162-6509baad09fa
Bell, S.A.
87fb5f29-6631-4d43-83c4-e8b624e101b5
Smith, J.A.
15b087c0-3a1f-4a77-8bc7-af4194be76d3
Clarke, E.M.
8d0e22d3-ad18-4420-8629-fd3423655dcf
Davis, C.J.
854f0b17-697b-476a-92dd-7986346c6880
Lockwood, M.
32917473-f7d9-4773-9162-6509baad09fa
Bell, S.A.
87fb5f29-6631-4d43-83c4-e8b624e101b5
Smith, J.A.
15b087c0-3a1f-4a77-8bc7-af4194be76d3
Clarke, E.M.
8d0e22d3-ad18-4420-8629-fd3423655dcf

Davis, C.J., Lockwood, M., Bell, S.A., Smith, J.A. and Clarke, E.M. (2000) Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August 1999 and 9 July 1945. Annales Geophysicae, 18, 182-190.

Record type: Article

Abstract

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.

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More information

Published date: 2000
Keywords: Ionosphere (solar radiation and cosmic ray effects) - Radio science (ionospheric physics) - Solar physics, astrophysics, and astronomy (corona and transition region)

Identifiers

Local EPrints ID: 9172
URI: http://eprints.soton.ac.uk/id/eprint/9172
ISSN: 0992-7689
PURE UUID: 7878da77-c893-4e64-a2d5-98a2fd53fb1a

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Date deposited: 24 Sep 2004
Last modified: 15 Jul 2019 19:37

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Contributors

Author: C.J. Davis
Author: M. Lockwood
Author: S.A. Bell
Author: J.A. Smith
Author: E.M. Clarke

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