Cavitons Associated with Ion-Acoustic-Like Waves in Foreshock Transients

TL;DR

This study uses MMS data to demonstrate a causal link between ion-acoustic-like electrostatic waves and cavitons in Earth's foreshock transients, revealing consistent scaling relationships.

Contribution

It provides the first observational evidence connecting ion-acoustic-like waves with cavitons in foreshock transients using high-resolution measurements.

Findings

Scaling between wave activity and density depletion confirmed

Ion-acoustic-like waves characterized by normalized electrostatic potential fluctuations

Electric field-based representations show high variability across events

Abstract

Foreshock transients upstream of the Earth's bow shock, such as foreshock bubbles and hot flow anomalies, are often characterized by reduced-density cores and strong plasma fluctuations. These conditions provide environments where electrostatic wave activity and localized density structures can coexist. Using high-time-resolution measurements from the Magnetospheric Multiscale (MMS) mission, we investigate the relationship between bursty electrostatic wave activity and localized electron density depletions within foreshock transients. A representative case study reveals a clear scaling between wave activity and density depletion, and a statistical analysis across multiple events shows that this scaling persists when the wave activity, with characteristics consistent with ion-acoustic-like waves, is represented in terms of electrostatic potential fluctuations normalized by electron temperature. In contrast, representations based on electric field amplitude, even when similarly normalized, exhibit substantial event-to-event variability. These results provide observational evidence for a causal relationship between ion-acoustic-like electrostatic wave activity and cavitons in foreshock plasmas.