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On the Limitations of Taylor s Hypothesis in Parker Solar Probe s Measurements near the Alfven Critical Point

AuthorBourouaine, Sofiane; Perez, Jean;
KeywordsParker Data Used
AbstractIn this Letter, we present an analysis of two-point, two-time correlation functions from high-resolution numerical simulations of Reflection-driven Alfven Turbulence near the Alfven critical point r e . The simulations model the turbulence in a prescribed background solar wind model chosen to match observational constraints. This analysis allows us to investigate the temporal decorrelation of solar wind turbulence and the validity of Taylor s approximation near the heliocentric distance r(c), which Parker Solar Probe (PSP) is expected to explore in the coming years. The simulations show that the temporal decay of the Fourier-transformed turbulence decorrelation function is better described by a Gaussian model rather than a pure exponential time decay, and that the decorrelation frequency is almost linear with perpendicular wave number k(perpendicular to) (perpendicular with respect to the background magnetic field B-0). Based on the simulations, we conclude that Taylor s approximation cannot be used in this instance to provide a connection between the frequency omega of the time signal (measured in the probe frame) and the wavevector k(perpendicular to) of the fluctuations because the frequency k(perpendicular to)V(sc), (V-sc is the spacecraft speed) near r(c) is comparable to the estimated decorrelation frequency. However, the use of Taylor s approximation still leads to the correct spectral indices of the power spectra measured at the spacecraft frame. In this Letter, based on a Gaussian model, we suggest a modified relationship between omega and k(perpendicular to), which might be useful in the interpretation of future PSP measurements.
Year of Publication2018
Number of PagesL20
Date Published05/2018