EISCAT-CAWSES-Copernicus

The high latitude part of the upper atmosphere of planet Earth is one of the most exciting regions. Ranging from about 80 km to several 1000 km altitude it contains phenomena like the beautiful visible aurora, high current streams of several 100000 A (auroral electrojet), heating due to particles and currents and changes in ion composition and motion. It is unique compared to other ionospheric regions on Earth, since the magnetic field lines originating here stretch out far into the tail of the magnetosphere (sometimes even into interstellar space). Along these field lines highly energetic electrons and protons are accelerated towards the Earth moving in spiral orbits. These particles cause several of the effects mentioned above.

In addition, high electric fields are present which are primarily caused by the solar wind, flowing past the magnetosphere. Many phenomena in the high latitude ionosphere (geographic latitude between about 60 and 75 degrees) are still poorly understood.

Our main tool for investigations is the incoherent scatter technique. High power (around 1 MW) radio pulses are transmitted into the ionosphere with large antennas. A tiny fraction of the emitted power is scattered back and received with the same or other antennas. The scatter takes place at thermal fluctuations of the ionospheric electron gas. Therefore we get mainly information about the ionospheric electrons. But since these electrons are electrostatically coupled to the ions, we can also measure ion properties.

In general four parameters can be obtained with the incoherent scatter technique:

• Electron Density
• Electron Temperature
• Ion Temperature
• Ion drift

The height and time resolution of the method is typically a few kilometers and 1 minute respectively, but can be much better. Many other ionospheric quantities can be estimated from the above parameters, like conductivities, currents, heating rates, electric fields, travelling ionospheric disturbances (TIDs) and so on.

The research facilities of EISCAT, a multi-national organisation to study the high latitude ionosphere, include several of the most modern and most advanced incoherent scatter radars, located in Norway, Sweden, Finland and on Svalbard (Spitzbergen).