Dayside plasma structure under IMF Bz>0: a hemispheric view

Radio tomography is an experimental technique for imaging the spatial structure of the ionospheric plasma density on horizontal scales of tens to hundreds of kilometres. Measurements of total electron content, made at a chain of stations, are inverted in a reconstruction algorithm to create an image of the distribution of electron density. The method is particularly suitable for studying ionospheric structures such as troughs, blobs and patches in the auroral and polar regions. The International Ionospheric Tomography project comprises receiver chains in Scandinavia, Greenland and Alaska and can provide near-simultaneous images of the large-scale plasma distributions in three different longitude sectors. Observations are presented from a case study of the wintertime dayside ionosphere under conditions of stable, positive IMF Bz. The tomographic images reveal the spatial distributions of the plasma over an extended region of the northern hemisphere spanning from magnetic noon to late afternoon. The density structure is discussed in terms of the high-latitude plasma convection pattern for the pertinent IMF that is supported by flow measurements from DMSP satellites. This case study presents some of the first simultaneous tomography images from both sides of the Atlantic.