``Slab'' modes, quasi-2-D turbulence, shear, and flux tubes in the expanding solar wind

Details ``Slab'' modes, quasi-2-D turbulence, shear, and flux tubes in the expanding solar wind ``Slab'' modes, quasi-2-D turbulence, shear, and flux tubes in the expanding solar wind

Jun 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aipc..471..161r&link_type=abstract

The solar wind nine conference. AIP Conference Proceedings, Volume 471, pp. 161-166 (1999).

Computer Science

2

Solar Wind Plasma, Sources Of Solar Wind, Magnetohydrodynamics And Plasmas

Scientific paper

Solar wind fluctuations exhibit anisotropies in both the variances of the vectors and in power spectra. The latter have only been studied observationally in two dimensions, but the result is that there seems to be a preference for power along and transverse to the mean magnetic field, with significant but lower power in between. This observation has led to the idea that the solar wind turbulence consists of two main populations, ``slab-like'' parallel propagating Alfvén waves and ``quasi-2-D'' fluctuations that have both wave vectors and fluctuations confined to a plane perpendicular to the mean field. Recent simulation studies suggest that the perpendicular component of the fluctuations may be due to the shearing of the slab modes, rather than to quasi-2-D fluctuations. Here we examine these scenarios and combinations of them using a compressible three-dimensional MHD code in spherical coordinates. Results show how nearly two-dimensional magnetohydrodynamic turbulence can be initiated and how it evolves with distance in the third dimension. Expanding flows lead to a suppression of the nonlinear cascades, mainly due to the changing transverse length scales. Quasi-2-D velocity fluctuation levels are determined more from the 2-D dynamics than from the expansion except when the velocity fluctuations are initially dominant. With expansion, quasi-2-D magnetic fluctuations always dominate the corresponding velocity fluctuations at late times. The ``slab'' modes produce perpendicular fluctuations when sheared, as in nonexpanding simulations, and these become dominant when initially equipartitioned with the quasi-2-D modes.

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