The Effects of Plasma-Neutral Interactions on Neutral Dynamics

Plasma-neutral interactions are fundamental to the structure and behavior of the neutral thermosphere. This interaction, primarily through ion-neutral collisions, ties electrodynamics with hydrodynamics requiring a fully coupled ionosphere - thermosphere model to simulate and dissect the sequence of responses that occur in the neutral gas when a change occurs in the ionosphere. In particular, changes in the ion drag force prompt a hydrodynamic response that will alter several properties of the thermosphere, including neutral winds. Here, the fully coupled National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR TIEGCM) is used to evaluate how changes in mechanical coupling, through the ion drag force, alter thermosphere properties, with a focus on thermospheric neutral winds. The equatorial thermosphere anomaly (ETA) produces a transient wind system, and a dissection of the hydrodynamic processes responsible for its formation will be used to demonstrate the causal structure in neutral gas response to a change in field-aligned ion drag force. This well-behaved response elucidates processes that must be occurring in other regions of the thermosphere where more significant changes in the ion drag force occur.