On solar protons and polar cap absorption: constraints on an empirical relationship
International audience A large database of Solar Proton Events (SPE) from the period 1995 to 2001 is used to investigate the relationship between proton flux at geostationary orbit and Cosmic Noise Absorption (CNA) in the auroral zone. The effect of solar illumination on this relationship is studied...
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ftccsdartic:oai:HAL:hal-00317290v1 2023-11-12T04:20:17+01:00 On solar protons and polar cap absorption: constraints on an empirical relationship Kavanagh, A. J. Marple, S. R. Honary, F. Mccrea, I. W. Senior, A. High Altitude Observatory (HAO) National Center for Atmospheric Research Boulder (NCAR) Department of Communication Systems Space Science and Technology Department Didcot (RAL Space) STFC Rutherford Appleton Laboratory (RAL) Science and Technology Facilities Council (STFC)-Science and Technology Facilities Council (STFC) 2004-04-02 https://hal.science/hal-00317290 https://hal.science/hal-00317290/document https://hal.science/hal-00317290/file/angeo-22-1133-2004.pdf en eng HAL CCSD European Geosciences Union hal-00317290 https://hal.science/hal-00317290 https://hal.science/hal-00317290/document https://hal.science/hal-00317290/file/angeo-22-1133-2004.pdf info:eu-repo/semantics/OpenAccess ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317290 Annales Geophysicae, 2004, 22 (4), pp.1133-1147 [SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences info:eu-repo/semantics/article Journal articles 2004 ftccsdartic 2023-10-21T23:07:35Z International audience A large database of Solar Proton Events (SPE) from the period 1995 to 2001 is used to investigate the relationship between proton flux at geostationary orbit and Cosmic Noise Absorption (CNA) in the auroral zone. The effect of solar illumination on this relationship is studied in a statistical manner by deriving correlation coefficients of integral flux and absorption as a function of solar zenith angle limit, thus both an upper limit on the angle and the best correlated integral flux of protons are determined (energies in excess of 10MeV). By considering the correlation of various energy ranges (from the GOES 8 differential proton flux channels) with CNA the range of proton energies for which the relationship between flux and absorption is best defined is established (15 to 44MeV), thus confirming previous predictions about which proton energy ranges are most effective in giving rise to absorption during Polar Cap Absorption (PCA) events. An empirical relationship between the square root of the integral proton flux and the absorption, measured by the imaging riometer at Kilpisjärvi (IRIS), is determined and departures from linearity and possible causes are examined. Variations in spectral "hardness" and in collision frequency are demonstrated not to be significant causes of the observed departures from a linear relationship. Geomagnetic activity may be a significant factor in changing the relationship between the absorption and the square root of the integral proton flux, although it is concluded that the cause is likely to be more complex than a straightforward dependence on K p . It is suggested that the most significant factor might be a bias in the absorption estimates imposed by the presence of Solar Radio Emission (SRE), which is not routinely measured at the operating frequency of IRIS, making its precise effect difficult to quantify. SRE is known to be most prevalent under conditions of high solar activity, such as those that might give rise to solar proton events. Key words. ... Article in Journal/Newspaper Kilpisjärvi Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) Kilpisjärvi ENVELOPE(20.767,20.767,69.034,69.034) |
institution |
Open Polar |
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Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) |
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ftccsdartic |
language |
English |
topic |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences |
spellingShingle |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences Kavanagh, A. J. Marple, S. R. Honary, F. Mccrea, I. W. Senior, A. On solar protons and polar cap absorption: constraints on an empirical relationship |
topic_facet |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences |
description |
International audience A large database of Solar Proton Events (SPE) from the period 1995 to 2001 is used to investigate the relationship between proton flux at geostationary orbit and Cosmic Noise Absorption (CNA) in the auroral zone. The effect of solar illumination on this relationship is studied in a statistical manner by deriving correlation coefficients of integral flux and absorption as a function of solar zenith angle limit, thus both an upper limit on the angle and the best correlated integral flux of protons are determined (energies in excess of 10MeV). By considering the correlation of various energy ranges (from the GOES 8 differential proton flux channels) with CNA the range of proton energies for which the relationship between flux and absorption is best defined is established (15 to 44MeV), thus confirming previous predictions about which proton energy ranges are most effective in giving rise to absorption during Polar Cap Absorption (PCA) events. An empirical relationship between the square root of the integral proton flux and the absorption, measured by the imaging riometer at Kilpisjärvi (IRIS), is determined and departures from linearity and possible causes are examined. Variations in spectral "hardness" and in collision frequency are demonstrated not to be significant causes of the observed departures from a linear relationship. Geomagnetic activity may be a significant factor in changing the relationship between the absorption and the square root of the integral proton flux, although it is concluded that the cause is likely to be more complex than a straightforward dependence on K p . It is suggested that the most significant factor might be a bias in the absorption estimates imposed by the presence of Solar Radio Emission (SRE), which is not routinely measured at the operating frequency of IRIS, making its precise effect difficult to quantify. SRE is known to be most prevalent under conditions of high solar activity, such as those that might give rise to solar proton events. Key words. ... |
author2 |
High Altitude Observatory (HAO) National Center for Atmospheric Research Boulder (NCAR) Department of Communication Systems Space Science and Technology Department Didcot (RAL Space) STFC Rutherford Appleton Laboratory (RAL) Science and Technology Facilities Council (STFC)-Science and Technology Facilities Council (STFC) |
format |
Article in Journal/Newspaper |
author |
Kavanagh, A. J. Marple, S. R. Honary, F. Mccrea, I. W. Senior, A. |
author_facet |
Kavanagh, A. J. Marple, S. R. Honary, F. Mccrea, I. W. Senior, A. |
author_sort |
Kavanagh, A. J. |
title |
On solar protons and polar cap absorption: constraints on an empirical relationship |
title_short |
On solar protons and polar cap absorption: constraints on an empirical relationship |
title_full |
On solar protons and polar cap absorption: constraints on an empirical relationship |
title_fullStr |
On solar protons and polar cap absorption: constraints on an empirical relationship |
title_full_unstemmed |
On solar protons and polar cap absorption: constraints on an empirical relationship |
title_sort |
on solar protons and polar cap absorption: constraints on an empirical relationship |
publisher |
HAL CCSD |
publishDate |
2004 |
url |
https://hal.science/hal-00317290 https://hal.science/hal-00317290/document https://hal.science/hal-00317290/file/angeo-22-1133-2004.pdf |
long_lat |
ENVELOPE(20.767,20.767,69.034,69.034) |
geographic |
Kilpisjärvi |
geographic_facet |
Kilpisjärvi |
genre |
Kilpisjärvi |
genre_facet |
Kilpisjärvi |
op_source |
ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317290 Annales Geophysicae, 2004, 22 (4), pp.1133-1147 |
op_relation |
hal-00317290 https://hal.science/hal-00317290 https://hal.science/hal-00317290/document https://hal.science/hal-00317290/file/angeo-22-1133-2004.pdf |
op_rights |
info:eu-repo/semantics/OpenAccess |
_version_ |
1782336319466242048 |