First Observation of Multiple Very-Near-Earth Reconnection Events During a Single Storm Main Phase

TL;DR

This study reports the first observation of multiple very-near-Earth reconnection events during a single storm main phase, revealing their frequency and role in energizing the ring current.

Contribution

It provides the first detailed observational evidence of multiple VNERX events occurring within a single storm main phase and their implications for space weather dynamics.

Findings

Three VNERX events observed within 12 hours during a storm main phase.

VNERX events occurred within a thin current sheet (< 1 RE thick).

VNERX are frequent, mainly occur near midnight, and drive energetic injections.

Abstract

For the first time, this paper presents three very-near-Earth reconnection (VNERX) events observed within the same 12-hour-long storm main phase. The THEMIS inner probes observed the hallmarks of three episodes of tailward retreating x-lines positioned between magnetic local time (MLT) 23-24 and radial distance 12-13 Earth radii (RE). The events occurred within a thin current sheet, < 1 RE thick. Simultaneously, dispersionless energetic particle injections above 10s of keV and magnetic field dipolarizations were observed near and earthward of geosynchronous altitude by the KOMPSAT and Arase satellites. Arase observed earthward flow bursts at or below geosynchronous altitude via ExB enhancements, suggesting VNERX ejecta proceed below geosynchronous orbit. These observations demonstrate that VNERX events, which predominantly occur during the storm main phase, can be frequent and essential for driving injections that can effectively power the ring current. However, they can be observed only at the pre-midnight sector, close to the neutral sheet.