Solar energetic proton propagation in the geomagnetic field
Date
2012
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
During solar proton events (SP Es), large fluxes of energetic protons spreading throughout the interplanetary medium (IPM) have access to the upper polar atmosphere where they play important roles in physical and chemical processes. The angular distribution of arriving solar energetic particles is a superposition of isotropic and anisotropic components. The isotropic component easily penetrates the magnetosphere forming a uniform background flux distribution inside the cut-off boundaries of the polar caps. We investigate the anisotropic component and the conditions that allow solar energetic protons to be focused into small spots in the polar caps, mostly near their boundaries. We examine also the dynamics of the relation between SPEs as detected through ionospheric absorption measured by a high-latitude riometer on one hand, and proton fluxes measured outside the magnetosphere by the SOHO satellite on the other. Vie find a high correlation between SOHO fluxes and absorption in some types of events (those having insignificant electron precipitation and background radio noise from the solar emission which boosts the radio signal received by the riometer causing a reduction in the measured absorption) and at some time intervals (more than ten hours after SEP onset, and within tens of hours following times of maximum flux) but not others. A probable explanation for this is that early in SPEs protons follow solar magnetic field lines and their distributions tend to be highly anisotropic, and the strong angular dependence decreases the correlation between IPM fluxes and polar cap absorption. After tens of hours the proton angular distribution becomes nearly isotropic and we find strong correlations ( correlation coefficients of up to 0.98) between the logarithm of proton integral fluxes observed at SOHO and the logarithm of polar cap absorption obtained from a NORSTAR riometer. We use these observations to construct and validate a realistic transport model that will map proton fluxes originating out ide the magnetosphere to those incident on the upper atmosphere, and vice versa. This in turn will enable riometers located outside the auroral oval to be used as a diagnostic tool to determine properties of energetic proton populations in the IPM.
Description
Bibliography: p. 229-243
Some pages are in colour.
Includes copy of copyright permission. Original copy with original Partial Copyright Licence.
Some pages are in colour.
Includes copy of copyright permission. Original copy with original Partial Copyright Licence.
Keywords
Citation
Kouznetsov, A. (2012). Solar energetic proton propagation in the geomagnetic field (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/4892