Turbulence Upstream and Downstream of Interplanetary Shocks

Abstract

The paper reviews the interaction of collisionless interplanetary (IP) shocks with the turbulent solar wind. The coexistence of shocks and turbulence plays an important role in understanding the acceleration of particles via Fermi acceleration mechanisms, the geoeffectiveness of highly disturbed sheaths following IP shocks and, among others, the nature of the fluctuations themselves. Although our knowledge of physics of upstream and downstream shock regions has been greatly improved in recent years, many aspects of the IP-shock/turbulence interaction are still poorly known, for example, the nature of turbulence, its characteristics on spatial and temporal scales, how it decays, its relation to shock passage and others. We discuss properties of fluctuations ahead (upstream) and behind (downstream) of IP shock fronts with the focus on observations. Some of the key characteristics of the upstream/downstream transition are 1) enhancement of the power in the inertial range fluctuations of the velocity, magnetic field and density is roughly one order of magnitude, 2) downstream fluctuations are always more compressible than the upstream fluctuations, and 3) energy in the inertial range fluctuations is kept constant for a significant time after the passage of the shock. In this paper, we emphasize that–for one point measurements–the downstream region should be viewed as an evolutionary record of the IP shock propagation through the plasma. Simultaneous measurements of the recently launched spacecraft probing inner parts of the Solar System will hopefully shed light on some of these questions.

Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks

“…Alternatively, the structures could have been generated by the in situ dynamics of the turbulent plasma downstream of an interplanetary shock. The downstream turbulence is dependent on conditions in the preceding solar wind (see e.g., Pitňa et al., 2016, 2021; Zank et al., 2021). These scenarios also emphasize the importance of understanding the dynamics of the solar wind.…”

Interpretation of Flat Energy Spectra Upstream of Fast Interplanetary Shocks

“…Figure 4 displays the PSD of the magnetic field in the two regions described above for the event on 2005 May 15. In the region where the energetic particle fluxes overlap, from −800 to −100 minutes from the shock, the spectrum follows a Kolmogorov-like power law, i.e., PSD( f ) ∝ f −5/3 , where f is the frequency, indicating ambient solar wind turbulence (Bruno & Carbone 2013;Pitňa et al 2021). By contrast, in the closeupstream region, from −80 to −10 minutes, we find PSD( f ) ∝ f −1 for the 2005 May 15 event, while in the other two crossings (where we have used the same time interval for the PSD's computation) the PSD is bumped at low frequencies (see Figures 5 and 6).…”

Three-day Forecasting of Solar Wind Speed Using SDO/AIA Extreme-ultraviolet Images by a Deep-learning Model

“…CIR is well known to be one of drivers of interplanetary shocks. At the leading edge and the trailing edge of the CIR, forward shocks and reverse shocks are formed, respectively (Gosling & Pizzo 1999;Pitňa et al 2021). The solar wind streams with high pressure in the CIR mainly contribute to the geomagnetic activity via magnetic reconnection with the magnetosphere of the Earth (Richardson et al 2000;Tsurutani et al 2006).…”