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 B⊥ ${B}_{\perp }$ 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 m∼36−90 $m\sim 36-90$, which corresponds to the Doppler shifted kinetic ballooning frequency of 3–20 mHz and which is consistent with the ∼ ${\sim} $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 ∼ ${\sim} $10 mHz oscillations thus can provide a signature marking approximately the start of the substorm expansion phase.
Observations from the Little Bunker
Last updated: January 14, 2026 06:18 PM
Atmospheric CO₂
428.7 ppm
+18.1
ppm/year
Atmospheric CH₄
1940.59 ppb
+-0.24
ppb/year
Global Temperature
+1.48 °C
Peak: +1.73°C
World Population
8.1 billion
+67
million/year