TY - JOUR

T1 - Diffusive shock acceleration of high-energy charged particles at fast interplanetary shocks

T2 - A parameter survey

AU - Giacalone, Joe

N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved.

PY - 2015/1/20

Y1 - 2015/1/20

N2 - We present results from numerical simulations of the acceleration of solar energetic particles (SEPs) associated with strong, fast, and radially propagating interplanetary shocks. We focus on the phase of the SEP event at the time of the shock passage at 1AU, which is when the peak intensity at energies below a few MeV is the highest. The shocks in our study start between 2 and 10 solar radii and propagate beyond 1AU. We study the effect of various shock and particle input parameters, such as the spatial diffusion coefficient, shock speed, solar wind speed, initial location of the shock, and shock deceleration rate, on the total integrated differential intensity, I, of SEPs with kinetic energies > 10MeV. I is the integral over energy of the differential intensity spectrum at the time of the shock passage at 1AU.We find that relatively small changes in the parameters can lead to significant event-to-event changes in I. For example, a factor of 2 increase in the diffusion coefficient at a given energy and spatial location, can lead to a decrease in I by as much as a factor of 50. This may help explain why there are fewer large SEP events seen during the current solar maximum compared to previous maxima. It is known that the magnitude of the interplanetary magnetic field is noticeably weaker this solar cycle than it was in the previous cycle and this will naturally lead to a somewhat larger diffusion coefficient of SEPs.

AB - We present results from numerical simulations of the acceleration of solar energetic particles (SEPs) associated with strong, fast, and radially propagating interplanetary shocks. We focus on the phase of the SEP event at the time of the shock passage at 1AU, which is when the peak intensity at energies below a few MeV is the highest. The shocks in our study start between 2 and 10 solar radii and propagate beyond 1AU. We study the effect of various shock and particle input parameters, such as the spatial diffusion coefficient, shock speed, solar wind speed, initial location of the shock, and shock deceleration rate, on the total integrated differential intensity, I, of SEPs with kinetic energies > 10MeV. I is the integral over energy of the differential intensity spectrum at the time of the shock passage at 1AU.We find that relatively small changes in the parameters can lead to significant event-to-event changes in I. For example, a factor of 2 increase in the diffusion coefficient at a given energy and spatial location, can lead to a decrease in I by as much as a factor of 50. This may help explain why there are fewer large SEP events seen during the current solar maximum compared to previous maxima. It is known that the magnitude of the interplanetary magnetic field is noticeably weaker this solar cycle than it was in the previous cycle and this will naturally lead to a somewhat larger diffusion coefficient of SEPs.

KW - Acceleration of particles

KW - Shock waves

KW - Sun: Coronal mass ejections (cmes)

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U2 - 10.1088/0004-637X/799/1/80

DO - 10.1088/0004-637X/799/1/80

M3 - Article

AN - SCOPUS:84921506471

SN - 0004-637X

VL - 799

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 80

ER -