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Title: DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM

Abstract

A double power law or a power law with exponential rollover at a few to tens of MeV nucleon{sup −1} of the event-integrated differential spectra has been reported in many solar energetic particle (SEP) events. The rollover energies per nucleon of different elements correlate with a particle's charge-to-mass ratio (Q/A). The probable causes are suggested as residing in shock finite lifetimes, shock finite sizes, shock geometry, and an adiabatic cooling effect. In this work, we conduct a numerical simulation to investigate a particle's transport process in the inner heliosphere. We solve the focused transport equation using a time-backward Markov stochastic approach. The convection, magnetic focusing, adiabatic cooling effect, and pitch-angle scattering are included. The effects that the interplanetary turbulence imposes on the shape of the resulting SEP spectra are examined. By assuming a pure power-law differential spectrum at the Sun, a perfect double-power-law feature with a break energy ranging from 10 to 120 MeV nucleon{sup −1} is obtained at 1 au. We found that the double power law of the differential energy spectrum is a robust result of SEP interplanetary propagation. It works for many assumptions of interplanetary turbulence spectra that give various forms of momentum dependence of a particle's mean free path. Themore » different spectral shapes in low-energy and high-energy ends are not just a transition from the convection-dominated propagation to diffusion-dominated propagation.« less

Authors:
; ;  [1]
  1. Physics and Space Sciences Department, Florida Institute of Technology, Melbourne, FL 32901 (United States)
Publication Date:
OSTI Identifier:
22518478
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 821; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; CONVECTION; COOLING; DIFFUSION; ENERGY SPECTRA; HELIOSPHERE; LIFETIME; MARKOV PROCESS; MEAN FREE PATH; MEV RANGE; RADIATION TRANSPORT; SCATTERING; SOLAR NEUTRONS; SOLAR PROTONS; SUN; TRANSPORT THEORY; TURBULENCE

Citation Formats

Zhao, Lulu, Zhang, Ming, and Rassoul, Hamid K., E-mail: lzhao@fit.edu. DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM. United States: N. p., 2016. Web. doi:10.3847/0004-637X/821/1/62.
Zhao, Lulu, Zhang, Ming, & Rassoul, Hamid K., E-mail: lzhao@fit.edu. DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM. United States. doi:10.3847/0004-637X/821/1/62.
Zhao, Lulu, Zhang, Ming, and Rassoul, Hamid K., E-mail: lzhao@fit.edu. Sun . "DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM". United States. doi:10.3847/0004-637X/821/1/62.
@article{osti_22518478,
title = {DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM},
author = {Zhao, Lulu and Zhang, Ming and Rassoul, Hamid K., E-mail: lzhao@fit.edu},
abstractNote = {A double power law or a power law with exponential rollover at a few to tens of MeV nucleon{sup −1} of the event-integrated differential spectra has been reported in many solar energetic particle (SEP) events. The rollover energies per nucleon of different elements correlate with a particle's charge-to-mass ratio (Q/A). The probable causes are suggested as residing in shock finite lifetimes, shock finite sizes, shock geometry, and an adiabatic cooling effect. In this work, we conduct a numerical simulation to investigate a particle's transport process in the inner heliosphere. We solve the focused transport equation using a time-backward Markov stochastic approach. The convection, magnetic focusing, adiabatic cooling effect, and pitch-angle scattering are included. The effects that the interplanetary turbulence imposes on the shape of the resulting SEP spectra are examined. By assuming a pure power-law differential spectrum at the Sun, a perfect double-power-law feature with a break energy ranging from 10 to 120 MeV nucleon{sup −1} is obtained at 1 au. We found that the double power law of the differential energy spectrum is a robust result of SEP interplanetary propagation. It works for many assumptions of interplanetary turbulence spectra that give various forms of momentum dependence of a particle's mean free path. The different spectral shapes in low-energy and high-energy ends are not just a transition from the convection-dominated propagation to diffusion-dominated propagation.},
doi = {10.3847/0004-637X/821/1/62},
journal = {Astrophysical Journal},
number = 1,
volume = 821,
place = {United States},
year = {Sun Apr 10 00:00:00 EDT 2016},
month = {Sun Apr 10 00:00:00 EDT 2016}
}