eprintid: 1460412
rev_number: 30
eprint_status: archive
userid: 608
dir: disk0/01/46/04/12
datestamp: 2015-03-20 10:34:51
lastmod: 2020-06-16 04:48:14
status_changed: 2015-03-20 10:34:51
type: article
metadata_visibility: show
item_issues_count: 0
creators_name: Thomas, SR
creators_name: Owens, MJ
creators_name: Lockwood, M
title: The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation
ispublished: pub
divisions: UCL
divisions: A01
divisions: B04
divisions: C06
keywords:  22-year cycle. Cosmic rays. Heliospheric current sheet. Solar variability. Polarity reversal.
note: The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-013-0341-5
abstract: Abstract
The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar-cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted as qA>0 cycle) or negative (qA<0) polarities. This results in the onset of the peak cosmic-ray flux at Earth occurring earlier during qA>0 cycles than for qA<0 cycles, which in turn causes the peak to be more dome-shaped for qA>0 and more sharply peaked for qA<0. In this study, we demonstrate that properties of the large-scale heliospheric magnetic field are different during the declining phase of the qA<0 and qA>0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, we also demonstrate that these polarity-dependent heliospheric differences are evident during the space-age but are much less clear in earlier data: using geomagnetic reconstructions, we show that for the period of 1905 – 1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic-ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age.

date: 2014-01
vfaculties: VMPS
oa_status: green
full_text_type: other
primo: open
primo_central: open_green
verified: verified_manual
elements_source: crossref
elements_id: 1002175
doi: 10.1007/s11207-013-0341-5
lyricists_name: Thomas, Simon
lyricists_id: THOMA34
full_text_status: public
publication: Solar Physics
volume: 289
number: 1
pagerange: 407 - 421
issn: 0038-0938
citation:        Thomas, SR;    Owens, MJ;    Lockwood, M;      (2014)    The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation.                   Solar Physics , 289  (1)   407 - 421.    10.1007/s11207-013-0341-5 <https://doi.org/10.1007/s11207-013-0341-5>.       Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/1460412/2/Hale.pdf