EISCAT
Eiscat and the High Latitude Ionosphere
Science objectives of the Eiscat experiment
This part of the upper
atmosphere of our planet Earth
is one of the most exciting regions. Ranging from about 90 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 high energetic electrons and protons are accellerated 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.
In this method, 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 antennas. The scatter
takes place at thermal fluctuations of the ionospheric electron gas.
Therfore mainly informations about the ionospheric electrons can be
obtained. 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
Example of EISCAT electron density data
The height and time resolution of the method is about 1 kilometer and 1
minute, respectively. Many other ionospheric quantities can be estimated
with the above parameters, like conductivities, currents, heating rates,
electric fields, travelling ionospheric disturbances (TIDs).
We use the incoherent scatter facilities of
EISCAT, a multi-national organisation to study the high latitude
ionosphere. It operates several of the most modern and most advanced
incoherent scatter radars, located in Norway, Sweden, Finland and on Svalbard
(Spitzbergen).
Some studes which have been performed in the past years are:
- electrodynamics and thermodynamics of the ionospheric E-region
- combined experiments with ground-based magnetometers in order to study
ionospheric currents
- convetion patterns of the high latitude ionosphere
- magnetospheric processes associated with particle precipitation
- studies of TIDs and calculations of the parameters of gravity waves
causing these TIDs.
- non-linear interaction of gravity waves
- plasma instabilities in the E-region
- ionosphere - thermosphere interaction using additionally Faby-Perot
interferometers
- influence of space weather on the ionophere
- ionospheric modification experiments with HEATING using EISCAT as a
diagnostic tool
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