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Ann. Geophys., 21, 863-867, 2003
www.ann-geophys.net/21/863/2003/
© European Geosciences Union 2003
Reconstructing the long-term cosmic ray intensity: linear relations do not work
K. Mursula1, I. G. Usoskin2, and G. A. Kovaltsov3
1Department of Physical Sciences, P.O.B. 3000, FIN-90014, University of Oulu, Finland
2Sodankylä Geophysical Observatory (Oulu unit), P.O.B. 3000, FIN-90014, University of Oulu, Finland
3Ioffe Physical-Technical Institute, RU-194021, St. Petersburg, Russia
Abstract. It was recently suggested
(Lockwood, 2001) that the cosmic ray intensity in the neutron monitor energy
range is linearly related to the coronal source flux, and can be reconstructed
for the last 130 years using the long-term coronal flux estimated earlier.
Moreover, Lockwood (2001) reconstructed the coronal flux for the last 500 years
using a similar linear relation between the flux and the concentration of
cosmogenic 10 Be isotopes in polar ice. Here we show that the applied linear
relations are oversimplified and lead to unphysical results on long time
scales. In particular, the cosmic ray intensity reconstructed by Lockwood
(2001) for the last 130 years has a steep trend which is considerably larger
than the trend estimated from observations during the last 65 years.
Accordingly, the reconstructed cosmic ray intensity reaches or even exceeds the
local interstellar cosmic ray flux around 1900. We argue that these unphysical
results obtained when using linear relations are due to the oversimplified
approach which does not take into account the complex and essentially nonlinear
nature of long-term cosmic ray modulation in the heliosphere. We also compare
the long-term cosmic ray intensity based on a linear treatment with the
reconstruction based on a recent physical model which predicts a considerably
lower cosmic ray intensity around 1900.
Key words. Interplanetary physics
(cosmic rays; heliopause and solar wind termination) – Geomagnetism and
paleomagnetism (time variations, secular and long-term)
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