Spatial Distribution and Low-frequency Disturbance Modulation of Magnetosheath Ion Polytropic Index

Abstract We, using the Cluster data from 2001 to 2010, studied spatial distribution of ion polytropic index in magnetosheath, and modulation process by low-frequency disturbances (4–18 mHz). The total 30,3283 samples is divided into two sorts: quasi-perpendicular quasi-parallel propagating ones. median increases with spreads narrowing bow shock magnetopause. indices are basically between isothermal adiabatic inner isobaric outer magnetosheath. distributions correlation coefficient (CC) perturbed number density parallel magnetic field CC ( δn , δB ∥ ) have a good those index. mostly mirror-like modes D r ≪ 1) except for some slow-mode ≥ regions near Sun–Earth line middle magnetosheath modulated mirror-like-mode 0.9 1.3. predominantly slow Alfvén For disturbances, processes indicates that disturbances.