Ionization dynamics under the influence of geomagnetic storms
The Earth ionosphere becomes highly variable during extreme space-weather events.
Observations from the Global Positioning System (GPS) in conjunction with tomographic
imaging have the potential to characterise its disturbed behaviour. In this
project, a four-dimensional tomographic technique is employed to reveal the temporal
evolution and spatial distribution of ionisation in the ionosphere on a large scale (over
Europe and the USA). The effects of geomagnetic storms on the dynamics of the
plasma are investigated throughout the recent solar maximum, when the intensity of
geornagnetic storms is greatest.
The results presented in this thesis show, for the first time, a wide area view of the
ionosphere during storm-time. Electron-density images of the disturbed mid/high
latitude ionosphere and Total Electron Content (TEC) maps are produced over North
America and Europe for several severe storms. Using both ground-based and Low
Earth Orbit satellite-based GPS data as well as available ionosonde data during storm
periods, improvements in imaging of ionospheric structures at storm time are made.
A case-study for the 29th - 30th October 2003 storm shows the detailed evolution of
ionisation in space and in time throughout the entire period of a complex storm. The
peak heights of the disturbed F region were redistributed (uplifted) both over Europe
and the USA around dusk for several major storm events. This uplift propagated
westwards. Investigations into common features of storms indicated that positive or
negative storm effects correlated with local time. In addition, the strongest enhancement
in TEC and the highest uplift were in the USA sector.
The project achievements are twofold. Firstly, abnormal behaviour of the disturbed
ionosphere,such as enhancements in electron density and TEC and sudden uplifts of
the peak height, is shown using a new GPS imaging technique. Secondly, the results will
provide important experimental inputs into physical models of ionospheric storms and
also contribute to the further understanding the dynamics of ionisation and underlying
mechanisms of severe storms on a global scale.