Introduction to special section on Entropy Properties and Constraints Related to Space Plasma Transport

Studies of entropy provide physical insight into space plasma transport, intermittency, turbulence, and information flow in the heliosphere and magnetosphere. Nonconservation of entropy in space plasmas can result from magnetic reconfiguration as well as nonadiabatic processes such as turbulent transport, thermal energy transport due to nonadiabatic particle drifts, energizations, mixing of two or more plasma populations, etc. Examination of entropy properties may provide insight into processes leading to plasma entry across the magnetopause on the dayside and nightside and processes leading to the tail pressure balance inconsistency'' and may provide constraints on which processes are most important in the dynamical transition related to substorms. Moreover, entropy-based information theory can be used to characterize the dynamics of the magnetosphere. This paper summarizes the special section that highlights state-of-the-art theoretical and observational studies of entropy, the pressure balance inconsistency, and other entropy-related issues such as those mentioned above.