Tomographic imaging of a large-scale travelling ionosphericdisturbance during the Halloween storm of 2003

The most intense ionospheric storm observed in recent times occurred between 29 and 31 October 2003. The disturbances to the high-latitude regions set off several large-scale travelling ionospheric disturbances (LSTIDs), wave-like perturbations in the ionospheric electron density. This paper investigates one particular TID on 31 October 2003 using North American Global Positioning System (GPS) receiver network data and a tomographic imaging technique. The TID has an estimated period of 30&min and an estimated horizontal wavelength of 700&km and propagates south-westward over North America. The tomographic reconstruction of the wave is validated using a simulation of the observations and with independent observations from ionosondes and the CHAMP planar Langmuir probe. The results are discussed in the context of the magnetic and ionospheric conditions that may have contributed to the launch of the wave. Large-scale TIDs are challenging to study over large regions of the Earth, and the GPS network here is shown to offer a unique perspective on the spatial and temporal variation of the TID. The experimental results are backed up by simulations that show a denser network of receivers, as is available in more recent years, would produce improved accuracy in the TID imaging.