This chapter describes several types of shocks, focusing on the ones that prevail in the heliosphere. The chapter addresses why shocks happen, describes the Rankine–Hugoniot jump conditions, reviews the classification of shocks, discusses contact and tangential discontinuities, and closes with a discussion of the physical processes yet to be explored for shocks. The sections contain specific examples such as coronal shocks, shocks driven by coronal mass ejections, planetary shocks, and the termination shock and heliopause. For further reading, we refer to Burlaga (1995), Kallenrode (2004), Gurnett and Bhattacharjee (2005), Goedbloed and Poedts (2004), Kulsrud (2005), and Opher (2009), upon whose work much of this chapter is based.

Introduction

Shock waves are an important manifestation of solar activity. They play an important role in space weather because they can accelerate particles to high energies, creating solar energetic particle (SEP) events, and produce storms at Earth (Gopalswamy et al., 2001). They also produce radio emission at various distances from the Sun, which allows us to track shock propagation throughout the corona and heliosphere.

Near the Sun, shocks are believed to be mainly driven by solar disturbances such as coronal mass ejections (CMEs). The CMEs and the SEP events associated with them are of particular importance for space weather because they endanger human life in outer space and pose major hazards for spacecraft. High-energy solar protons (> 100 MeV) can be accelerated within a short period of time (˜1 h) after the initiation of CMEs, which makes them difficult to predict, and therefore they pose a serious concern for the design and operation of both manned and unmanned space missions.