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On the Limitations of Taylor s Hypothesis in Parker Solar Probe s Measurements near the Alfven Critical Point
Author  Bourouaine, Sofiane; Perez, Jean; 
Keywords  Parker Data Used 
Abstract  In this Letter, we present an analysis of twopoint, twotime correlation functions from highresolution numerical simulations of Reflectiondriven 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 Fouriertransformed 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 B0). 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), (Vsc 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 Publication  2018 
Journal  ASTROPHYSICAL JOURNAL LETTERS 
Volume  858 
Number of Pages  L20 
Section  
Date Published  05/2018 
ISBN  
URL  
DOI  10.3847/20418213/aabccf 