Space weather refers to variability that occurs in the near-Earth environment between the Sun and Earth and may affect systems. While there is daily variability, much like traditional “weather”, the most severe effects on systems occur during space-weather storms. The ionosphere, one part of the coupled Sun-Earth system, has a particularly dramatic effect on radio frequency (RF) systems during storms. Data assimilation techniques can be used to study ionospheric space weather events by producing time-evolving three-dimensional images (or 4D images) of electron density during space weather storms.

4D imaging of the ionosphere allows the progress of an ionospheric storm to be studied across large geographical regions near-continuously in latitude, longitude, altitude and time. We review our data-assimilative imaging algorithm, Ionospheric Data Assimilation Three-Dimensional (IDA3D), and present our latest results. IDA3D permits high fidelity tracking of ionospheric F-region patches, revealing their development and transport, and could be used for ionospheric corrections to radar and other applications. A study of the October -November 2003 storm period illustrates the global coverage that can be achieved with ionospheric imaging, and permits study of the development of positive and negative ionospheric storms, and important features such as Storm Enhanced Density (SED) that may have application in the FAA.s Wide Area Augmentation System (WAAS). Finally the future development envisaged for IDA3D is discussed.