Turbulence/wave transmission at an ICME-driven shock observed by Solar Orbiter and Wind

Solar Orbiter observed an interplanetary coronal mass ejection (ICME) event at 0.8 AU on 2020 April 19. The ICME was also observed by Wind at 1 AU on 2020 April 20. An interplanetary shock wave was driven in front of the ICME. We focus on the transmission of the magnetic fluctuations across the shock and analyze the characteristic wave modes of solar wind turbulence near the shock observed by both spacecraft. The ICME event is characterized by a magnetic helicity based technique. The shock normal is determined by magnetic coplanarity method for Solar Orbiter and using a mixed coplanarity approach for Wind. The power spectra of magnetic field fluctuations are generated by applying both a fast Fourier transform and Morlet wavelet analysis. To understand the nature of waves observed near the shock, we use the normalized magnetic helicity as a diagnostic parameter. The wavelet reconstructed magnetic field fluctuation hodograms are used to further study the polarization properties of waves. We find that the ICME-driven shock observed by Solar Orbiter and Wind is a fast forward oblique shock with a more perpendicular shock angle at 1 AU. After the shock crossing, the magnetic field fluctuation power increases. Most of the magnetic field fluctuation power resides in the transverse fluctuations. In the vicinity of the shock, both spacecraft observe right-hand polarized waves in the spacecraft frame. The upstream wave signatures fall in a relatively broad and low-frequency band, which might be attributed to low-frequency MHD waves excited by the streaming particles. For the downstream magnetic wave activity, we find oblique kinetic Alfven waves with frequencies near the proton cyclotron frequency in the spacecraft frame. The frequency of the downstream waves increases by a factor of 7-10 due to the shock compression and the Doppler effect.