GPS ionospheric imaging of the north polar ionosphere on 30 October 2003

Maps of electron content retrieved from a 3-dimensional assimilation process of GPS TEC measurements are applied to observe the north polar ionosphere in the evening of 30 October 2003. Their reliability for large-scale imaging is discussed in comparison with GPS data coverage and radar observations. The electron content results are interpreted together with the behaviour of the Interplanetary Magnetic Field (IMF). The images show a region of ionisation expanding across the polar cap from the day to the night side between 20:00 and 21:30 UT. A patch-like structure is observed at successive times with locations approaching the night side ionosphere. At corresponding time the IMF Bz was steadily negative. To explain the observations, an anti-sunward plasma transport is proposed. Consecutively to 21:30 UT a low electron content is imaged polward of 70°N coinciding with an increasing and then positive IMF Bz. During a further phase of negative IMF Bz an enhanced electron content appears at night side mid-latitudes beyond 50°N. The assimilation images are a useful observational tool of the large-scale distribution of electron content, especially together with further data of ionospheric parameters.