Work

Observations of Compressional Structures Driven by Interaction Between Foreshock Ions and Discontinuities

Year: 2024

Type: article

Abstract: The ion foreshock is very dynamic, characterized by various transient structures that can perturb the bow shock and influence the magnetosphere‐ionosphere system. One important driver of foreshock transients is solar wind directional discontinuities (DDs) that demagnetize foreshock ions leading to a local current. If this current decreases the field strength at the DD, a hot flow anomaly (HFA) can form. Recent hybrid simulations found that when the current increases the field strength at the DD, a compressional structure forms with enhanced density and field strength opposite to HFAs. Using MMS and THEMIS observations, we confirm this situation. We demonstrate that the current geometry driven by the foreshock ions plays a critical role in the formation. The initial gyrophase of foreshock ions, due to their specular reflection, determines whether they can cross the DD. When many of the foreshock ions cannot cross the DD and the local current they drive increases the field strength at the DD, the enhanced field strength inhibits more foreshock ions from crossing the DD, further enhancing the local current. This feedback loop promotes the growth of the compressional structure. Such foreshock ion‐driven compressional structures can result in dynamic pressure enhancements in the magnetosheath, leading to magnetosheath jets. Our study enables prediction of the location and formation probability of such compressional structures and their potential geoeffectiveness.

Source: Journal of Geophysical Research Space Physics

DOI: 10.1029/2024ja032803

Authors: Terry Z. Liu, Vassilis Angelopoulos, Antonius Otto

Institutions: University of California, Los Angeles, University of Alaska Fairbanks

Language: English

Topic: Ionosphere and magnetosphere dynamics

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Science Foundation, National Aeronautics and Space Administration, Nuclear Safety and Security Commission