What question did this study set out to answer?

To investigate the low frequency oscillations in the ionosphere associated with substorm onsets.

January 16, 2026Open Access

Low Frequency Oscillation Observed in the Ionosphere Around the Substorm Onsets

SWS. WingJohns Hopkins University Applied Physics Laboratory JJJay R. JohnsonAndrews University ERElmer C. RiveraAndrews University

Key Points

To investigate the low frequency oscillations in the ionosphere associated with substorm onsets.
Analyzed three substorm events using DMSP spacecraft and IMAGE ultraviolet auroral images.
Employed Hilbert-Huang Transform to decompose ionospheric data into intrinsic mode functions.
Identified dominant wave modes near 10 mHz and their temporal relationship with substorm onset.
Detected significant energy increase in oscillations 2-5 minutes before substorm onset.
Identified a peak in oscillation energy coinciding with electron accelerations and the expansion phase.
Observed 10 mHz oscillations providing a potential signature for the start of substorm phases.

Abstract

Abstract Three substorm events in which Defense Meteorological Satellite Program (DMSP) spacecraft are geomagnetically co‐located with substorm onset locations in IMAGE far ultraviolet auroral images are analyzed. A Hilbert‐Huang Transform is used to decompose the DMSP in the ionosphere to its intrinsic mode functions. A dominant mode near 10 mHz shows that its wave instantaneous energy starts increasing 2–5 min prior to and peaks about the commencement of sudden broadband and monoenergetic electron accelerations and the substorm expansion phase. The auroral beads exhibit azimuthal structuring with , which corresponds to the Doppler shifted kinetic ballooning frequency of 3–20 mHz and which is consistent with the 10 mHz wave. The kinetic ballooning mode can become unstable during the substorm growth phase when the pressure gradient and magnetic field‐line curvature become large. The 10 mHz oscillations thus can provide a signature marking approximately the start of the substorm expansion phase.

Perguntar à IA

Bookmark

View Full Paper