About the incompressible energy cascade rate in anisotropic solar wind turbulence

ANDRÉS NAHUEL; SAHRAOUI, FOUAD; HUANG, S. Y.; HADID, L. Z.; SEBASTIEN GALTIER

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2022

0004-6361

Context. The presence of a magnetic guide field induces several types of anisotropy in solar wind turbulence. The energy cascade rate between scales in the inertial range depends strongly on the direction of this magnetic guide field, splitting the energy cascade according to the parallel and perpendicular directions with respect to magnetic guide field.Aims. Using more than 2 years of Parker Solar Probe (PSP) observations, the isotropy and anisotropy energy cascade rates are investigated. The variance and spectral anisotropy ratios, the kinetic and magnetic energies and the both normalized cross-helicity and residual energy are studied. The connection between the heliocentric distance, the local temperature of the plasma and the energy cascade components is made.Methods. Using exact relations for fully developed magnetohydrodynamic (MHD) turbulence, the incompressible energy cascade rate is computed. In particular, using the isotropy and 2D and slab assumptions, the isotropic, perpendicular and parallel energy cascade rate components are estimated.Results. The variance anisotropy ratios, for both kinetic and magnetic fields, do not exhibit a dependence with respect to the heliocentric distance, r. While the kinetic spectral anisotropy ratio shows a dependence with r, the magnetic spectral anisotropy does not. A strong correlation between the isotropic and anisotropic energy cascade rates and the temperature is found. A clear dominance of the perpendicular cascades over the parallel cascades as PSP approaches to the Sun is observed. A dominant 2D cascade/geometry over the slab component in slow solar wind turbulence in the largest MHD scales is observed.