Characterization of the Transmission and Generation of Turbulence at Interplanetary Shocks

We study the transmission and characteristics of turbulent magnetohydrodynamic (MHD) fluctuations from upstream to downstream regions of interplanetary (IP) shocks using the linear mode decomposition (LMD) technique of G. P. Zank et al. We perform a superposed epoch analysis (SEA) of 84 fast-forward quasi-perpendicular shock events observed by the Wind spacecraft at 1 au. We find that the intensities of various MHD modes associated with density, velocity, and magnetic field fluctuations are enhanced by ∼4–14 times across the shock. On average, the amplitude enhancement of velocity fluctuations across the shock is smaller than that of density and magnetic fluctuations. The frequency spectra reveal that the entropy, magnetic island, and Alfvén modes are the dominant contributors to the overall density, magnetic field, and velocity fluctuations, respectively, both upstream and downstream. The SEA reveals that the downstream spectral slope of various modes closely follows a f −5/3 (or k −5/3 ) power law, but the upstream spectra are slightly flatter than the downstream curves. A steeper spectral slope downstream suggests an increased energy dissipation or a stronger turbulent cascade. These findings show the usefulness of the LMD technique to decompose turbulent fluctuations into fundamental linear MHD modes, providing a deeper understanding of turbulence upstream and downstream of IP shocks.