J/ApJS/230/21Solar 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 (SIMBAD/NED BibCode)ADC_Keywords: Sun; ModelsKeywords: cosmic rays; diffusion; methods: numerical; solar wind; turbulenceAbstract: 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:

FileName Lrecl Records Explanations

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

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). Details on the Heliographic coordinates (HGC) used here may be found in Franz & Harper (2000P&SS...50..217F).

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

Bytes Format Units Label Explanations

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)

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.

Byte-by-byte Description of file: dataset2.dat

Bytes Format Units Label Explanations

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)

Note (1): The heliographic longitude of the dipole's northern pole is (arbitrarily) set to 330 deg.

History: From electronic version of the journal(End)Prepared by [AAS], Emmanuelle Perret [CDS] 07-Aug-2017

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