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Title: Evolving Waves and Turbulence in the Outer Corona and Inner Heliosphere: The Accelerating Expanding Box

Abstract

Alfvénic fluctuations in the solar wind display many properties reflecting an ongoing nonlinear cascade, e.g., a well-defined spectrum in frequency, together with some characteristics more commonly associated with the linear propagation of waves from the Sun, such as the variation of fluctuation amplitude with distance, dominated by solar wind expansion effects. Therefore, both nonlinearities and expansion must be included simultaneously in any successful model of solar wind turbulence evolution. Because of the disparate spatial scales involved, direct numerical simulations of turbulence in the solar wind represent an arduous task, especially if one wants to go beyond the incompressible approximation. Indeed, most simulations neglect solar wind expansion effects entirely. Here we develop a numerical model to simulate turbulent fluctuations from the outer corona to 1 au and beyond, including the sub-Alfvénic corona. The accelerating expanding box (AEB) extends the validity of previous expanding box models by taking into account both the acceleration of the solar wind and the inhomogeneity of background density and magnetic field. Our method incorporates a background accelerating wind within a magnetic field that naturally follows the Parker spiral evolution using a two-scale analysis in which the macroscopic spatial effect coupling fluctuations with background gradients becomes a time-dependentmore » coupling term in a homogeneous box. In this paper we describe the AEB model in detail and discuss its main properties, illustrating its validity by studying Alfvén wave propagation across the Alfvén critical point.« less

Authors:
;  [1]
  1. EPSS, UCLA, Los Angeles, CA (United States)
Publication Date:
OSTI Identifier:
22663457
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 843; 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; ACCELERATION; ALFVEN WAVES; AMPLITUDES; APPROXIMATIONS; COMPUTERIZED SIMULATION; DISTANCE; EXPANSION; FLUCTUATIONS; HELIOSPHERE; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; NONLINEAR PROBLEMS; SOLAR WIND; SPECTRA; TIME DEPENDENCE; TURBULENCE; WAVE PROPAGATION

Citation Formats

Tenerani, Anna, and Velli, Marco. Evolving Waves and Turbulence in the Outer Corona and Inner Heliosphere: The Accelerating Expanding Box. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA71B9.
Tenerani, Anna, & Velli, Marco. Evolving Waves and Turbulence in the Outer Corona and Inner Heliosphere: The Accelerating Expanding Box. United States. doi:10.3847/1538-4357/AA71B9.
Tenerani, Anna, and Velli, Marco. Sat . "Evolving Waves and Turbulence in the Outer Corona and Inner Heliosphere: The Accelerating Expanding Box". United States. doi:10.3847/1538-4357/AA71B9.
@article{osti_22663457,
title = {Evolving Waves and Turbulence in the Outer Corona and Inner Heliosphere: The Accelerating Expanding Box},
author = {Tenerani, Anna and Velli, Marco},
abstractNote = {Alfvénic fluctuations in the solar wind display many properties reflecting an ongoing nonlinear cascade, e.g., a well-defined spectrum in frequency, together with some characteristics more commonly associated with the linear propagation of waves from the Sun, such as the variation of fluctuation amplitude with distance, dominated by solar wind expansion effects. Therefore, both nonlinearities and expansion must be included simultaneously in any successful model of solar wind turbulence evolution. Because of the disparate spatial scales involved, direct numerical simulations of turbulence in the solar wind represent an arduous task, especially if one wants to go beyond the incompressible approximation. Indeed, most simulations neglect solar wind expansion effects entirely. Here we develop a numerical model to simulate turbulent fluctuations from the outer corona to 1 au and beyond, including the sub-Alfvénic corona. The accelerating expanding box (AEB) extends the validity of previous expanding box models by taking into account both the acceleration of the solar wind and the inhomogeneity of background density and magnetic field. Our method incorporates a background accelerating wind within a magnetic field that naturally follows the Parker spiral evolution using a two-scale analysis in which the macroscopic spatial effect coupling fluctuations with background gradients becomes a time-dependent coupling term in a homogeneous box. In this paper we describe the AEB model in detail and discuss its main properties, illustrating its validity by studying Alfvén wave propagation across the Alfvén critical point.},
doi = {10.3847/1538-4357/AA71B9},
journal = {Astrophysical Journal},
number = 1,
volume = 843,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}