Observations of recurrent cosmic ray decreases during solar cycles 22 and 23
During solar cycle 22, the modulation of several hundred MeV galactic cosmic rays (GCRs) by recurrent and transient cosmic ray decreases was observed by the Ulysses spacecraft on its descent towards the solar south pole. In solar cycle 23, Ulysses repeated this trajectory segment during a similar ph...
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ftdoajarticles:oai:doaj.org/article:b8e71ef250714401ababcdd676547795 2023-05-15T18:23:21+02:00 Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 P. Dunzlaff B. Heber A. Kopp O. Rother R. Müller-Mellin A. Klassen R. Gómez-Herrero R. Wimmer-Schweingruber 2008-10-01T00:00:00Z https://doi.org/10.5194/angeo-26-3127-2008 https://doaj.org/article/b8e71ef250714401ababcdd676547795 EN eng Copernicus Publications https://www.ann-geophys.net/26/3127/2008/angeo-26-3127-2008.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.5194/angeo-26-3127-2008 0992-7689 1432-0576 https://doaj.org/article/b8e71ef250714401ababcdd676547795 Annales Geophysicae, Vol 26, Pp 3127-3138 (2008) Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 article 2008 ftdoajarticles https://doi.org/10.5194/angeo-26-3127-2008 2022-12-31T14:59:03Z During solar cycle 22, the modulation of several hundred MeV galactic cosmic rays (GCRs) by recurrent and transient cosmic ray decreases was observed by the Ulysses spacecraft on its descent towards the solar south pole. In solar cycle 23, Ulysses repeated this trajectory segment during a similar phase of the solar cycle, but with opposite heliospheric magnetic field polarity. Since cosmic ray propagation in the heliosphere should depend on drift effects, we determine in this study the latitudinal distribution of the amplitude of recurrent cosmic ray decreases in solar cycles 22 and 23. As long as we measure the recurrent plasma structures in situ, we find that these decreases behave nearly the same in both cycles. Measurements in the fast solar wind, however, show differences: in cycle 22 ( A >0) the recurrent cosmic ray decreases show a clear maximum near 25° and are still present beyond 40°, whereas we see in cycle 23 ( A <0) neither such a pronounced maximum nor significant decreases above 40°. In other words: the periodicity in the cosmic ray intensity, which can be clearly seen in the slow solar wind, appears to vanish there. Theoretical models for drift effects, however, predict quite the opposite behaviour for the two solar cycles. To closer investigate this apparent contradiction, we first put the visual inspection of the data onto a more solid basis by performing a detailed Lomb (spectral) analysis. The next step consists of an analysis of the resulting periodicities at 1 AU in order to distinguish between spatial and temporal variations, so that we can obtain statements about the question in how far there is a correlation between the in-situ data at 1 AU and those measured by Ulysses at larger latitudes. We find a good correlation being present during cycle 22, but not for cycle 23. As one potential explanation for this behaviour, we suggest the difference in the coronal hole structures between the cycles 22 and 23 due to a large, stable coronal hole structure, which is present during cycle 22, ... Article in Journal/Newspaper South pole Directory of Open Access Journals: DOAJ Articles South Pole Annales Geophysicae 26 10 3127 3138 |
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Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 P. Dunzlaff B. Heber A. Kopp O. Rother R. Müller-Mellin A. Klassen R. Gómez-Herrero R. Wimmer-Schweingruber Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
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Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
description |
During solar cycle 22, the modulation of several hundred MeV galactic cosmic rays (GCRs) by recurrent and transient cosmic ray decreases was observed by the Ulysses spacecraft on its descent towards the solar south pole. In solar cycle 23, Ulysses repeated this trajectory segment during a similar phase of the solar cycle, but with opposite heliospheric magnetic field polarity. Since cosmic ray propagation in the heliosphere should depend on drift effects, we determine in this study the latitudinal distribution of the amplitude of recurrent cosmic ray decreases in solar cycles 22 and 23. As long as we measure the recurrent plasma structures in situ, we find that these decreases behave nearly the same in both cycles. Measurements in the fast solar wind, however, show differences: in cycle 22 ( A >0) the recurrent cosmic ray decreases show a clear maximum near 25° and are still present beyond 40°, whereas we see in cycle 23 ( A <0) neither such a pronounced maximum nor significant decreases above 40°. In other words: the periodicity in the cosmic ray intensity, which can be clearly seen in the slow solar wind, appears to vanish there. Theoretical models for drift effects, however, predict quite the opposite behaviour for the two solar cycles. To closer investigate this apparent contradiction, we first put the visual inspection of the data onto a more solid basis by performing a detailed Lomb (spectral) analysis. The next step consists of an analysis of the resulting periodicities at 1 AU in order to distinguish between spatial and temporal variations, so that we can obtain statements about the question in how far there is a correlation between the in-situ data at 1 AU and those measured by Ulysses at larger latitudes. We find a good correlation being present during cycle 22, but not for cycle 23. As one potential explanation for this behaviour, we suggest the difference in the coronal hole structures between the cycles 22 and 23 due to a large, stable coronal hole structure, which is present during cycle 22, ... |
format |
Article in Journal/Newspaper |
author |
P. Dunzlaff B. Heber A. Kopp O. Rother R. Müller-Mellin A. Klassen R. Gómez-Herrero R. Wimmer-Schweingruber |
author_facet |
P. Dunzlaff B. Heber A. Kopp O. Rother R. Müller-Mellin A. Klassen R. Gómez-Herrero R. Wimmer-Schweingruber |
author_sort |
P. Dunzlaff |
title |
Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
title_short |
Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
title_full |
Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
title_fullStr |
Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
title_full_unstemmed |
Observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
title_sort |
observations of recurrent cosmic ray decreases during solar cycles 22 and 23 |
publisher |
Copernicus Publications |
publishDate |
2008 |
url |
https://doi.org/10.5194/angeo-26-3127-2008 https://doaj.org/article/b8e71ef250714401ababcdd676547795 |
geographic |
South Pole |
geographic_facet |
South Pole |
genre |
South pole |
genre_facet |
South pole |
op_source |
Annales Geophysicae, Vol 26, Pp 3127-3138 (2008) |
op_relation |
https://www.ann-geophys.net/26/3127/2008/angeo-26-3127-2008.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.5194/angeo-26-3127-2008 0992-7689 1432-0576 https://doaj.org/article/b8e71ef250714401ababcdd676547795 |
op_doi |
https://doi.org/10.5194/angeo-26-3127-2008 |
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Annales Geophysicae |
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26 |
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10 |
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3127 |
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