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Title: SOLAR WIND COLLISIONAL AGE FROM A GLOBAL MAGNETOHYDRODYNAMICS SIMULATION

Simple estimates of the number of Coulomb collisions experienced by the interplanetary plasma to the point of observation, i.e., the “collisional age”, can be usefully employed in the study of non-thermal features of the solar wind. Usually these estimates are based on local plasma properties at the point of observation. Here we improve the method of estimation of the collisional age by employing solutions obtained from global three-dimensional magnetohydrodynamics simulations. This enables evaluation of the complete analytical expression for the collisional age without using approximations. The improved estimation of the collisional timescale is compared with turbulence and expansion timescales to assess the relative importance of collisions. The collisional age computed using the approximate formula employed in previous work is compared with the improved simulation-based calculations to examine the validity of the simplified formula. We also develop an analytical expression for the evaluation of the collisional age and we find good agreement between the numerical and analytical results. Finally, we briefly discuss the implications for an improved estimation of collisionality along spacecraft trajectories, including Solar Probe Plus.
Authors:
; ;  [1] ;  [2]
  1. Department of Physics and Astronomy and Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
  2. NASA Goddard Space Flight Center, Greenbelt MD 20771 (United States)
Publication Date:
OSTI Identifier:
22518503
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; COLLISIONS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; MAGNETOHYDRODYNAMICS; PLASMA; PROBES; SCATTERING; SOLAR WIND; SPACE VEHICLES; TRAJECTORIES; TURBULENCE