Global impacts of a Foreshock Bubble: Magnetosheath, magnetopause and ground-based observations

TL;DR

This study demonstrates that Foreshock Bubbles have a significant global impact on Earth's magnetosphere, affecting plasma flows and magnetopause position, confirmed through multipoint observations and ground magnetometer data.

Contribution

First observational evidence showing Foreshock Bubbles cause global magnetospheric disturbances, extending understanding beyond localized effects.

Findings

Foreshock Bubbles modify upstream pressure and magnetopause position.

Magnetosheath plasma accelerates sunward and outward flows.

Ground magnetometers detect magnetopause motion over 7 hours.

Abstract

Using multipoint observations we show, for the first time, that Foreshock Bubbles (FBs) have a global impact on Earth's magnetosphere. We show that an FB, a transient kinetic phenomenon due to the interaction of backstreaming suprathermal ions with a discontinuity, modifies the total pressure upstream of the bow shock showing a decrease within the FB's core and sheath regions. Magnetosheath plasma is accelerated towards the the intersection of the FB's current sheet with the bow shock resulting in fast, sunward, flows as well as outward motion of the magnetopause. Ground-based magnetometers also show signatures of this magnetopause motion simultaneously across at least 7 hours of magnetic local time, corresponding to a distance of 21.5 RE transverse to the Sun-Earth line along the magnetopause. These observed global impacts of the FB are in agreement with previous simulations and in stark contrast to the known localised, smaller scale effects of Hot Flow Anomalies (HFAs).