Quantifying Ionospheric Response to Extreme Forcing: ICON IVM Observations of Pristine vs. Perturbed Conditions

The low-latitude ionosphere is a region of complex multi-scale dynamics, where plasma density and transport are shaped by both solar-driven geomagnetic activity and lower-atmospheric forcing. In this study, we utilize in-situ measurements from the Ion Velocity Meter (IVM) onboard the Ionospheric Connection Explorer (ICON) to quantify ionospheric variability across a range of geophysical conditions. We establish a "pristine" baseline of quiet-time observations to characterize the nominal day-to-day fluctuations in ion density and vertical/meridional drifts.

We perform a detailed spectral analysis using Windowed Fourier Transforms (WFT) and Wavelet analysis to investigate the power and spectral slopes of ionospheric fluctuations. This approach allows us to identify the characteristic scales of energy injection and dissipation during three distinct forcing scenarios: (1) the intense geomagnetic storm of November 3–4, 2021; (2) the large-scale atmospheric pressure pulse following the Hunga Tonga-Hunga Ha'apai eruption (January 2022); and (3) a period of significant lower-atmospheric gravity wave activity on July 7, 2021.

Our results compare the spectral evolution of ionospheric turbulence and wave-like perturbations between these events and the pristine baseline. Preliminary findings suggest that while the November storm drives broad-band enhancements in spectral power associated with prompt penetration electric fields, the July gravity wave and Tonga events exhibit distinct spectral signatures linked to localized coupling processes. These comparisons provide a comprehensive view of how different forcing mechanisms redistribute energy and drive variability in the low-latitude ionosphere and new insights into the relative efficiency of internal (lower-atmospheric) versus external (solar) drivers in shaping the ionospheric environment.