Frame Dependence of the Electric Field Spectrum of Solar Wind Turbulence

TL;DR

This study analyzes electric field spectra in solar wind turbulence using ARTEMIS data, revealing frame-dependent spectral indices and confirming differences between velocity and magnetic field scaling.

Contribution

First survey of electric field spectra in solar wind turbulence showing frame dependence and new insights into the scaling of velocity and magnetic fields.

Findings

Electric field spectral index in spacecraft frame is -5/3.

In the solar wind frame, the electric field spectral index is slightly shallower than -3/2.

Compressible fluctuations have a spectral index close to -5/3.

Abstract

We present the first survey of electric field data using the ARTEMIS spacecraft in the solar wind to study inertial range turbulence. It was found that the average perpendicular spectral index of the electric field depends on the frame of measurement. In the spacecraft frame it is -5/3, which matches the magnetic field due to the large solar wind speed in Lorentz transformation. In the mean solar wind frame, the electric field is primarily due to the perpendicular velocity fluctuations and has a spectral index slightly shallower than -3/2, which is close to the scaling of the velocity. These results are an independent confirmation of the difference in scaling between the velocity and magnetic field, which is not currently well understood. The spectral index of the compressive fluctuations was also measured and found to be close to -5/3, suggesting that they are not only passive to the velocity but may also interact nonlinearly with the magnetic field.