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2 Acta Geophysica

2 2009

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Ionization of the earth's atmosphere by solar and galactic cosmic rays

Usoskin I. G., Desorgher L., Velinov P., Storini M., Flückiger E., Bütikofer R., Kovaltsov G. A.

Acta Geophysica

2009

Vol. 57, no. 1

88-101

A brief review of the research of atmospheric effects of cosmic rays is presented. Numerical models are discussed, that are capable to compute the cosmic ray induced ionization at a given location and time. Intercomparison of the models, as well as comparison with fragmentary direct measurements of the atmospheric ionization, validates their applicability for the entire atmosphere and the whole range of the solar activity level variations. The effect of sporadic solar energetic particle events is shown to be limited on the global scale, even for the most severe event, but can be very strong locally in polar regions, affecting the physical-chemical properties of the upper atmosphere, especially at high altitudes. Thus, a new methodology is presented to study cosmic ray induced ionization of the atmosphere in full detail using realistic numerical models calibrated to direct observations.

Comparison of Earth's magnetospheric magnetic field models in the context of cosmic ray physics

Desorgher L., Flückiger E., Bütikofer R., Storini M., Kalegaev V.

Acta Geophysica

2009

Vol. 57, no. 1

75-87

Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000. For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages and drawbacks of the different models in the context of space weather.