TSI Seminar

Trials and tribulations in near-Earth Geospace: Extreme events in the Ionosphere and how they impact radio propagation

David Themens

Birmingham/UNB

The ionosphere, a plasma environment embedded in the upper atmosphere between 60km and 2000km altitude, is highly conductive and, by virtue of this, it can interact strongly with electromagnetic signals propagating through it across much of the radio band (frequencies < a few GHz). In the UHF band (300MHz – 3GHz), used heavily for Global Navigation Satellite Systems (GNSS) like GPS, the ionosphere can delay, bend, and scatter these signals resulting in significant positioning errors or outages. Similarly, radio telescopes on the ground can experience significant angular displacement in radio source locations and scintillation. As one tends further down in frequency, these impacts become more and more severe, where signals can eventually be completely absorbed or reflected by the ionosphere back out to space. In order to facilitate systems reliant on propagation through the ionosphere, we must be able to model and image the ionosphere. The ionosphere is, however, a highly dynamic medium, coupled both to the Earth’s Magnetosphere (and solar wind) and the atmosphere in which it is embedded. From above, solar storms, like those from May and October, can cause severe disturbances in the Earth’s Magnetosphere resulting in considerable heating in the ionosphere and the injection of highly energetic particles into the upper atmosphere. From below, waves generated in the lower atmosphere can propagate up into the ionosphere, causing severe perturbations, and climate change is causing a gradual restructuring of the ionosphere over time.