Correcting for interplanetary scattering in velocity dispersion analysis of solar energetic particles 

Timo Laitinen Submitted: 20150424 06:41
To understand the origin of Solar Energetic Particles (SEPs), we must study their injection time relative to other solar eruption manifestations. Traditionally the injection time is determined using the Velocity Dispersion Analysis (VDA) where a linear fit of the observed event onset times at 1 AU to the inverse velocities of SEPs is used to derive the injection time and path length of the firstarriving particles. VDA does not, however, take into account that the particles that produce a statistically observable onset at 1 AU have scattered in the interplanetary space. We use Monte Carlo test particle simulations of energetic protons to study the effect of particle scattering on the observable SEP event onset above preevent background, and consequently on VDA results. We find that the VDA results are sensitive to the properties of the preevent and event particle spectra as well as SEP injection and scattering parameters. In particular, a VDAobtained path length that is close to the nominal Parker spiral length does not imply that the VDA injection time is correct. We study the delay to the observed onset caused by scattering of the particles and derive a simple estimate for the delay time by using the rate of intensity increase at the SEP onset as a parameter. We apply the correction to a magnetically wellconnected SEP event of June 10 2000, and show it to improve both the path length and injection time estimates, while also increasing the error limits to better reflect the inherent uncertainties of VDA.
Authors: T. Laitinen, K. HuttunenHeikinmaa, E. Valtonen, S. Dalla
Projects: GOES Xrays ,SoHOLASCO

Publication Status: Accepted for publication in Astrophysical Journal
Last Modified: 20150425 18:48



Energetic Particle Diffusion In Critically Balanced Turbulence 

Timo Laitinen Submitted: 20130425 05:00
Observations and modelling suggest that the fluctuations in magnetised plasmas exhibit scaledependent anisotropy, with more energy in the fluctuations perpendicular to the mean magnetic field than in the parallel fluctuations and the anisotropy increasing at smaller scales. The scaledependence of the anisotropy has not been studied in fullorbit simulations of particle transport in turbulent plasmas so far. In this paper, we construct a model of critically balanced turbulence, as suggested by cite{GoSr1995}, and calculate energetic particle spatial diffusion coefficients using fullorbit simulations. The model uses an enveloped turbulence approach, where each 2dimensional wave mode with wavenumber k_perp is packed into envelopes of length L following the critical balance condition, Lpropto k_perp^{2/3}, with the wave mode parameters changing between envelopes. Using fullorbit particle simulations, we find that both the parallel and perpendicular diffusion coefficients increase by a factor 2, compared to previous models with scaleindependent anisotropy.
Authors: Laitinen, T., Dalla, S., Kelly, J., and Marsh, M.
Projects: None

Publication Status: Published in ApJ, 764:168, 2013, doi:10.1088/0004637X/764/2/168
Last Modified: 20130425 09:52



Energetic Particle Diffusion In Structured Turbulence 

Timo Laitinen Submitted: 20120402 07:49
In the fullorbit particle simulations of energetic particle transport in plasmas, the plasma turbulence is typically described as a homogeneous superposition of linear Fourier modes. The turbulence evolution is, however, typically a nonlinear process, and, particularly in the heliospheric context, the solar wind plasma is inhomogeneous due to the transient structures, as observed by remote and insitu measurements. In this work, we study the effects of the inhomogeneities on energetic particle transport by using spatially distributed, superposed turbulence envelopes. We find that the crossfield transport is significantly reduced, when compared to the results obtained with homogeneous turbulence. The reduction can reach an order of magnitude when the enveloping breaks the wave phase coherence along the mean magnetic field direction.
Authors: Laitinen, T., Dalla, S. and Kelly, J.
Projects: None

Publication Status: ApJ (Published)
Last Modified: 20120404 08:13




Key

 Go to main EPrint page. 
 Download Preprint. 
 Submitters Homepage. 
 Edit Entry. 
 Delete abstract. 


