HAO Colloquium - Xueling Shi, Virginia Tech

Occurrence Statistics and Driving Mechanisms of Ionospheric Ultra-Low Frequency Waves and their Impact in Geospace

Ultra-low frequency (ULF; 1 mHz - 5 Hz) waves have been observed in geospace and on the ground for decades. They play important roles in transporting and coupling energy throughout the system and accelerating magnetospheric particles, including those in the Van Allen radiation belts. ULF pulsations in the coupled magnetosphere- ionosphere (M-I) system generate periodic ground magnetic perturbations and dB/dt that have been linked to geoelectric fields. These geoelectric fields in turn drive potentially damaging geomagnetically induced currents (GIC) in technological infrastructures such as railroads, pipelines, submarine cables and power grids.  

ULF wave signatures in the ionosphere can be detected using the Super Dual Auroral Radar Network (SuperDARN). This radar network has the advantage of wide geographic coverage at the mid-, high-, and polar latitudes in both hemispheres, continuous measurements over several solar cycles, and high time resolution data availability during special modes (e.g., ~ 6 s for THEMIS mode data). SuperDARN radars are thus ideal for analyzing the spatial, temporal, and frequency distributions of ionospheric ULF wave signatures. We use Doppler velocity measurements obtained by the SuperDARN radars and coordinated spacecraft observations to investigate the occurrence statistics and driving mechanisms of ionospheric ULF waves. The impact of ULF waves on magnetospheric particles and geoelectric field/GIC is also investigated through detailed case studies using coordinated ground and space observations. Collectively, these research findings provide better constraints on where and when ionospheric ULF waves occur, their source mechanisms, and how they might affect magnetospheric and ionospheric dynamics. 

Date and time: 
Wednesday, September 18, 2019 - 2:00pm to 3:00pm