Traveling magnetopause distortion related to a large-scale magnetosheath plasma jet: THEMIS and ground-based observations

TL;DR

This paper presents a detailed case study of a large-scale magnetopause distortion caused by a dense, fast magnetosheath plasma jet interacting with an interplanetary discontinuity, revealing unique features not fully explained by existing models.

Contribution

It provides new observational insights into magnetopause responses to plasma jets and interplanetary discontinuities, highlighting phenomena that challenge current understanding.

Findings

Large-scale magnetopause distortion lasting 15 minutes.

Magnetosheath plasma jet's kinetic energy thrice solar wind energy.

Unique magnetic pulse pattern not matching known models.

Abstract

Here, we present a case study of THEMIS and ground-based observations on the dayside magnetopause, and geomagnetic field perturbations related to the interaction of an interplanetary directional discontinuity (DD), as observed by ACE, within the magnetosphere on 16 June 2007. The interaction resulted in a large-scale local magnetopause distortion of an 'expansion-compression-expansion' (ECE) sequence that lasted for 15 min. The compression was caused by a very dense, cold, and fast high-beta magnetosheath plasma flow, a so-called plasma jet, whose kinetic energy was approximately three times higher than the energy of the incident solar wind. The plasma jet resulted in the effective penetration of the magnetosheath plasma inside the magnetosphere. A strong distortion of the Chapman-Ferraro current in the ECE sequence generated a tripolar magnetic pulse 'decrease-peak-decrease' (DPD) that was observed at low and middle latitudes by the INTERMAGNET network of ground-based magnetometers. The characteristics of the ECE sequence and the spatial-temporal dynamics of the DPD pulse were found to be very different from any reported patterns of DD interactions within the magnetosphere. The observed features only partially resembled structures such as FTE, hot flow anomalies, and transient density events. Thus, it is difficult to explain them in the context of existing models.