Validity of the Taylor Hypothesis for Linear Kinetic Waves in the Weakly Collisional Solar Wind

TL;DR

This paper evaluates when the Taylor hypothesis holds for linear kinetic waves in the weakly collisional solar wind, finding it likely fails for whistler waves but not for kinetic Alfvén waves, impacting turbulence measurements.

Contribution

It provides a theoretical assessment of the Taylor hypothesis's validity for different plasma wave modes in the solar wind, guiding interpretation of spacecraft data.

Findings

Taylor hypothesis likely violated for whistler wave turbulence.

Taylor hypothesis remains valid for kinetic Alfvén wave turbulence.

Implications for analyzing solar wind turbulence measurements.

Abstract

The interpretation of single-point spacecraft measurements of solar wind turbulence is complicated by the fact that the measurements are made in a frame of reference in relative motion with respect to the turbulent plasma. The Taylor hypothesis---that temporal fluctuations measured by a stationary probe in a rapidly flowing fluid are dominated by the advection of spatial structures in the fluid rest frame---is often assumed to simplify the analysis. But measurements of turbulence in upcoming missions, such as Solar Probe Plus, threaten to violate the Taylor hypothesis, either due to slow flow of the plasma with respect to the spacecraft or to the dispersive nature of the plasma fluctuations at small scales. Assuming that the frequency of the turbulent fluctuations is characterized by the frequency of the linear waves supported by the plasma, we evaluate the validity of the Taylor hypothesis for the linear kinetic wave modes in the weakly collisional solar wind. The analysis predicts that a dissipation range of solar wind turbulence supported by whistler waves is likely to violate the Taylor hypothesis, while one supported by kinetic Alfven waves is not.