Effects of Finite Frequency in Turbulence Spectral Observations

In situ observations of turbulence spectrum in space plasmas are usually interpreted as wavenumber spectrum, assuming that the fluctuation frequency is negligible in the plasma flow frame. It is conventional that turbulence is described by the power spectrum in wavenumber space. However, recent progress in magnetized plasma turbulence has recognized the importance of the finite-frequency effects. We explore the effects of nonzero frequency on turbulence spectral observations. The finite frequency can be caused by either propagating waves such as the Alfven waves or the nonlinear broadening of non-propagating structures. The results may have an impact on the interpretation of recent Parker Solar Probe data.