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Transport of Solar Energetic Particles across the Parker field due to field line meandering

Aug 1, 2015, 11:45 AM
15m
Mississippi (World Forum)

Mississippi

World Forum

Churchillplein 10 2517 JW Den Haag The Netherlands
Oral contribution SH-TH Parallel SH 03 SEP II

Speaker

Dr Timo Laitinen (Jeremiah Horrocks Institute, University of Central Lancashire, Preston, UK)

Description

Multi-spacecraft observations of Solar Energetic Particles (SEPs) show that SEPs related to a single solar eruption can be observed over a wide range of heliolongitudes. The SEP anisotropy observations suggest that interplanetary transport significantly contributes to this spreading of SEPs across the mean Parker Spiral field. However, the current transport models that describe the cross-field propagation as diffusion using the Fokker-Planck (FP) equation with a simple cross-field diffusion term, cannot reproduce the extent of SEP events without unrealistically large cross-field diffusion coefficients. Laitinen et al (2013) noted that the initial, non-diffusive propagation of charged particles along turbulently meandering field-lines provides a key to explaining the wide SEP events. Particles that initially propagate along meandering field-lines spread fast across the mean field. Thus, the resulting SEP event extent can be expected to be wider than predicted by the FP description. In this work, we implement field-line meandering into a FP modelling framework for Parker Spiral geometry. We use an SDE approach to propagate particles along field-lines that meander across the Parker Spiral field, and compare our new model with the traditional FP approach. The particle and field-line diffusion coefficients are calculated using a turbulence model that is consistent with a parallel mean free path of 0.3 AU for 10 MeV protons at 1 AU. We find that our new model results in a wide longitudinal extent of SEP events, with $\sigma=33^\circ$ for the longitudinal peak intensity distribution, consistent with SEP observations, while for the same turbulence parameters the traditional modelling only gives $\sigma=10^\circ$. Our results show that field-line meandering must be taken into account when modelling SEP propagation in interplanetary space. We discuss the effect of turbulence strength on the extent of SEP events.
Registration number following "ICRC2015-I/" 510
Collaboration -- not specified --

Primary author

Dr Timo Laitinen (Jeremiah Horrocks Institute, University of Central Lancashire, Preston, UK)

Co-authors

Dr Andreas Kopp (Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany) Dr Frederic Effenberger (Department of Mathematics, University of Waikato, Hamilton, New Zealand) Dr Michael S. Marsh (Met Office, Exeter, UK) Dr Silvia Dalla (Jeremiah Horrocks Institute, University of Central Lancashire, Preston, UK)

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