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Dependence of decay rates of SEP events on characteristics of interplanetary medium and on radial distance

Kecskemety, K. and Daibog, D.I. and Logacheb, Yu.I. and Kota, J. and Mewaldt, R. A. (2005) Dependence of decay rates of SEP events on characteristics of interplanetary medium and on radial distance. In: Proceedings of the 29th International Cosmic Ray Conference. Vol.1. Tata Institute of Fundamental Research , Pune, India, pp. 343-346.

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The shape of the particle flux decline in solar energetic particle (SEP) events is of particular importance in understanding the propagation of energetic particles in the interplanetary medium. The majority offew-MeV particle events exhibit exponential declines indicating the importance of adiabatic deceleration and convection transport. Then value of the decay time 't depends on the differential spectral index y, solar wind speed, and on the distance from the Sun. By analyzing the dependence of ' on enviromnental plasma parameters we showed earlier that ' tends to decrease with the increase of both solar wind speed and magnetic field strength. Comparing simultaneous observations at various radial distances (at IMP, ACE, Helios, and ffiysses) we find that whereas high-energy (tens of MeVs) proton profiles sometimes are surprisingly identical at different radii, MeV protons in the same events have significantly longer decays at farther locations than near 1 AU. This is incompatible both with pure diffusive particle propagation and with trapping between converging magnetic field lines near the Sun and at the front of traveling shock, but qualitatively supports convection transport and adiabatic deceleration. Using a simple numerical model including diffusion and adiabatic cooling the time profiles are calculated and compared with observations.

Item Type:Book Section
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Mewaldt, R. A.0000-0003-2178-9111
Additional Information:Copyright TATA Institute of Fundamental Research Data from the Ulysses COSPIN LET instrument were obtained from R.G. Marsden, Helios proton data were provided by H. Kunow, IMP-8 CPME fluxes were obtained from the website of the instrument.
Group:Space Radiation Laboratory
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Space Radiation Laboratory2005-20
Record Number:CaltechAUTHORS:20150407-094446946
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56421
Deposited By: Deborah Miles
Deposited On:16 Apr 2015 14:11
Last Modified:22 Nov 2019 09:58

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