Turbulence Upstream and Downstream of Interplanetary Shocks

The paper reviews the interaction of interplanetary (IP) shocks with the solar wind which is turbulent in nature. The coexistence of shocks and turbulence plays an important role in understanding (a) the acceleration of particles, (b) impact of highly disturbed plasma following IP shocks on the space weather and (c) the nature of the fluctuations themselves, among others. Many aspects of the IP-shock/turbulence interaction are still poorly known. For example, what is the nature of turbulence, its characteristics on spatial and temporal scales, how it decays, its relation to shock passage and many 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) energy contained within the fluctuations is roughly ten times larger for the downstream region, (2) downstream fluctuations are always more compressible than the upstream fluctuations, and (3) energy levels are kept constant for a significant time after the passage of the shock. In this paper, we emphasize that spacecraft measurements of the downstream region at a single distance from the sun should be viewed as an evolutionary record of the IP shock propagation through the plasma.