J/ApJS/230/21 Solar wind 3D magnetohydrodynamic simulation (Chhiber+, 2017)
Cosmic-ray diffusion coefficients throughout the inner heliosphere from
a global solar wind simulation.
Chhiber R., Subedi P., Usmanov A.V., Matthaeus W.H., Ruffolo D.,
Goldstein M.L., Parashar T.N.
<Astrophys. J. Suppl. Ser., 230, 21-21 (2017)>
=2017ApJS..230...21C 2017ApJS..230...21C (SIMBAD/NED BibCode)
ADC_Keywords: Sun; Models
Keywords: cosmic rays; diffusion; methods: numerical; solar wind; turbulence
Abstract:
We use a three-dimensional magnetohydrodynamic simulation of the solar
wind to calculate cosmic-ray diffusion coefficients throughout the
inner heliosphere (2R☉-3au). The simulation resolves large-scale
solar wind flow, which is coupled to small-scale fluctuations through
a turbulence model. Simulation results specify background solar wind
fields and turbulence parameters, which are used to compute diffusion
coefficients and study their behavior in the inner heliosphere. The
parallel mean free path (mfp) is evaluated using quasi-linear theory,
while the perpendicular mfp is determined from nonlinear guiding
center theory with the random ballistic interpretation. Several runs
examine varying turbulent energy and different solar source dipole
tilts. We find that for most of the inner heliosphere, the radial mfp
is dominated by diffusion parallel to the mean magnetic field; the
parallel mfp remains at least an order of magnitude larger than the
perpendicular mfp, except in the heliospheric current sheet, where the
perpendicular mfp may be a few times larger than the parallel mfp. In
the ecliptic region, the perpendicular mfp may influence the radial
mfp at heliocentric distances larger than 1.5au; our estimations of
the parallel mfp in the ecliptic region at 1 au agree well with the
Palmer "consensus" range of 0.08-0.3au. Solar activity increases
perpendicular diffusion and reduces parallel diffusion. The parallel
mfp mostly varies with rigidity (P) as P.33, and the perpendicular
mfp is weakly dependent on P. The mfps are weakly influenced by the
choice of long-wavelength power spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
dataset1.dat 43 38040 *Mean free paths (mfps) for untilted
solar dipole
dataset2.dat 55 4564800 *Mean free paths (mfps) for tilted
(30°) dipole
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Note on dataset*: Mean free paths (mfps) for protons with 445 MV rigidity
(100MeV kinetic energy) are presented in three dimensions throughout the
inner heliosphere (2-645 solar radii, or 0.0096-3AU).
A global MHD-RANS simulation of the solar wind with turbulence modeling is
used to generate background fields, and quasi-linear theory and non-linear
guiding center theory (with a random ballistic decorrelation interpretation)
are used to calculate parallel and perpendicular mean free paths,
respectively. Details of simulation parameters may be found in
Usmanov et al. (2014ApJ...788...43U 2014ApJ...788...43U).
Details on the Heliographic coordinates (HGC) used here may be found
in Franz & Harper (2000P&SS...50..217F 2000P&SS...50..217F).
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See also:
J/A+A/509/A14 : Grid of solar-metallicity wind models (Mattsson+, 2010)
J/ApJ/737/L35 : Pulsed Alfven waves in the solar wind (Gosling+, 2011)
Byte-by-byte Description of file: dataset1.dat
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Bytes Format Units Label Explanations
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1- 6 F6.2 deg HLAT [-90/90] Heliographic latitude (theta) (1)
8- 13 F6.4 AU Dist [0.009/3] Heliocentric distance (r)
15- 23 F9.7 AU lamPar [0.004/1.5] Parallel mfp (lambda-par)
25- 33 F9.7 AU lamPerp [/0.03] Perpendicular mfp (lambda-perp)
35- 43 F9.7 AU lamrr [/1.5] Radial mfp (lambda-rr)
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Note (1): The untilted dipole case is symmetric about the solar rotation axis
and therefore the data are independent of longitude, unlike the
tilted dipole case.
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Byte-by-byte Description of file: dataset2.dat
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Bytes Format Units Label Explanations
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1- 6 F6.2 deg HLON [1.5/358.5] Heliographic longitude (phi) (1)
8- 13 F6.2 deg HLAT [-90/90] Heliographic latitude (theta)
15- 20 F6.4 AU Dist [0.009/3] Heliocentric distance (r)
22- 33 F12.7 AU lamPar [/3109] Parallel mfp (lambda-par)
35- 43 F9.7 AU lamPerp [0/5.1] Perpendicular mfp (lambda-perp)
45- 55 F11.7 AU lambdrr [/487] Radial mfp (lambda-rr)
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Note (1): The heliographic longitude of the dipole's northern pole is
(arbitrarily) set to 330 deg.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Aug-2017