Universität zu Köln

von Papen, Michael ORCID: 0000-0001-5030-1643 and Saur, Joachim ORCID: 0000-0003-1413-1231 (2015). FORWARD MODELING OF REDUCED POWER SPECTRA FROM THREE-DIMENSIONAL K-SPACE. Astrophys. J., 806 (1). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

We present results from a numerical forward model to evaluate one-dimensional reduced power spectral densities (PSDs) from arbitrary energy distributions in k-space. In this model, we can separately calculate the diagonal elements of the spectral tensor for incompressible axisymmetric turbulence with vanishing helicity. Given a critically balanced turbulent cascade with k(parallel to) similar to k(perpendicular to)(alpha) and alpha < 1, we explore the implications on the reduced PSD as a function of frequency. The spectra are obtained under the assumption of Taylor's hypothesis. We further investigate the functional dependence of the spectral index kappa on the field-to-flow angle theta between plasma flow and background magnetic field from MHD to electron kinetic scales. We show that critically balanced turbulence asymptotically develops toward theta-independent spectra with a slope corresponding to the perpendicular cascade. This occurs at a transition frequency f(2D)(L, alpha, theta), which is analytically estimated and depends on outer scale L, critical balance exponent alpha, and field-to-flow angle theta. We discuss anisotropic damping terms acting on the k-space distribution of energy and their effects on the PSD. Further, we show that the spectral anisotropies kappa(theta) as found by Horbury et al. and Chen et al. in the solar wind are in accordance with a damped critically balanced cascade of kinetic Alfven waves. We also model power spectra obtained by Papen et al. in Saturn's plasma sheet and find that the change of spectral indices inside 9 R-s can be explained by damping on electron scales.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code von Papen, Michael UNSPECIFIED orcid.org/0000-0001-5030-1643 UNSPECIFIED Saur, Joachim UNSPECIFIED orcid.org/0000-0003-1413-1231 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-401150
DOI:	10.1088/0004-637X/806/1/116
Journal or Publication Title:	Astrophys. J.
Volume:	806
Number:	1
Date:	2015
Publisher:	IOP PUBLISHING LTD
Place of Publication:	BRISTOL
ISSN:	1538-4357
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language SOLAR-WIND TURBULENCE; MAGNETOHYDRODYNAMIC TURBULENCE; INTERSTELLAR TURBULENCE; CORRELATION TENSORS; ANISOTROPY; FLUCTUATIONS; MAGNETOSPHERE; MODULATION; RANGE; WAVES Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/40115