Magnetospheric control of ionospheric TEC perturbations via whistler-mode and ULF waves

TL;DR

This study demonstrates that high-latitude ionospheric TEC perturbations are driven by magnetospheric ULF-modulated whistler-mode waves causing electron precipitation, which enhances understanding of magnetosphere-ionosphere coupling and improves TEC prediction.

Contribution

It provides direct observational evidence linking ULF-modulated whistler waves to ionospheric TEC perturbations, clarifying the underlying mechanisms of magnetosphere-ionosphere interactions.

Findings

Peak-to-peak dTEC amplitudes ~0.5 TECU

High correlation (~0.8) between modeled and observed dTEC during conjugacy

Matching spectra of whistler waves and dTEC at ULF frequencies

Abstract

The weakly ionized plasma in the Earth's ionosphere is controlled by a complex interplay between solar and magnetospheric inputs from above, atmospheric processes from below, and plasma electrodynamics from within. This interaction results in ionosphere structuring and variability that pose major challenges for accurate ionosphere prediction for global navigation satellite system (GNSS) related applications and space weather research. The ionospheric structuring and variability are often probed using the total electron content (TEC) and its relative perturbations (dTEC). Among dTEC variations observed at high latitudes, a unique modulation pattern has been linked to magnetospheric ultra low frequency (ULF) waves, yet its underlying mechanisms remain unclear. Here using magnetically-conjugate observations from the THEMIS spacecraft and a ground-based GPS receiver at Fairbanks, Alaska, we provide direct evidence that these dTEC modulations are driven by magnetospheric electron precipitation induced by ULF-modulated whistler-mode waves. We observed peak-to-peak dTEC amplitudes reaching ~0.5 TECU (1 TECU is equal to 10$^6$ electrons/m$^2$) with modulations spanning scales of ~5--100 km. The cross-correlation between our modeled and observed dTEC reached ~0.8 during the conjugacy period but decreased outside of it. The spectra of whistler-mode waves and dTEC also matched closely at ULF frequencies during the conjugacy period but diverged outside of it. Our findings elucidate the high-latitude dTEC generation from magnetospheric wave-induced precipitation, addressing a significant gap in current physics-based dTEC modeling. Theses results thus improve ionospheric dTEC prediction and enhance our understanding of magnetosphere-ionosphere coupling via ULF waves.