Abstract
In the autumn of the year 2000, four radio receivers capable of tracking various beacon satellites were set up along the southwestern coast of Greenland. They are used to reconstruct images of the ionospheric plasma density distribution via the tomographic method. In order to test and validate tomographic imaging under the highly variable conditions often prevailing in the high-latitude ionosphere, a time interval was selected when the Sondrestrom incoherent scatter radar conducted measurements of the ionospheric plasma density while the radio receivers tracked a number of beacon satellites. A comparison between two-dimensional images of the plasma density distribution obtained from the radar and the satellite receivers revealed generally good agreement between radar measurements and tomographic images. Observed discrepancies can be attributed to F region plasma patches moving through the field of view with a speed of several hundred meters per second, thereby smearing out the tomographic image. A notable mismatch occurred around local magnetic midnight when a magnetospheric substorm breakup occurred in the vicinity of southwest Greenland (identified from ground-based magnetometer observations). The breakup was associated with a sudden intensification of the westward auroral electrojet which was centered at about 69° and extended up to some 73° corrected geomagnetic latitude. Ground-based magnetometer data may thus have the potential of indicating when the tomographic method is at risk and may fail. We finally outline the application of tomographic imaging, when combined with magnetic field data, to estimate ionospheric Joule heating rates.
Highlights
The high-latitude ionosphere is strongly coupled to the magnetosphere and influenced by its dynamic variations
Since solar wind-magnetosphere-ionosphere interaction is most direct in the auroral zone and polar cap in a broad sense the high-latitude ionosphere can be highly variable on time scales of solar wind changes, which may be less than a few minutes
The measurements from an array of receivers are converted into relative Total Electron Content (TEC) profiles and ingested into an inversion algorithm which renders a threedimensional image of the ionospheric plasma density distribution
Summary
The high-latitude ionosphere is strongly coupled to the magnetosphere and influenced by its dynamic variations. Similar verification concepts were employed by Foster et al (1994) and Mitchell et al (1995) The former examined storm-time observations of the mid-latitude ionosphere and showed that largescale discrete F region ionization enhancements and a deep ionospheric trough were recognized in both, incoherent scatter radar data and tomographic images. The latter demonstrated, by comparing tomographic images with EISCAT observations of the ionospheric plasma density, that the tomographic method can render accurate results in the auroral zone if the ionosphere remains stable. We summarize the results and elaborate on future work
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