Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa12b1091o&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SA12B-1091
Other
6924 Interferometry, 6944 Nonlinear Phenomena, 6984 Waves In Plasma, 6994 Instruments And Techniques, 7803 Active Perturbation Experiments
Scientific paper
It is well known that the electric field of a high power HF wave transmitted into the ionosphere will interact with the free electrons in the plasma by causing them to oscillate at the same frequency as the transmitted wave, and then to re-emit other electromagnetic waves, with frequencies near the original wave, but with the power in the new emission being much weaker than the original. This effect is known as stimulated electromagnetic emission, or SEE. On 11 and 12 November 2001, high power HF radio wave heating experiments were carried out in the ionosphere above the EISCAT observatory near Tromsø, Norway. Optical observations revealed artificial aurora in the form of rings, which lasted for several seconds before collapsing into blobs, while at the same time descending in altitude, and then disappearing. During this experiment SEE were recorded on a traditional spectrum analyzer system; this can tell us information about the relationship between the auroral rings and the local electron gyrofrequency, and thus help to determine why the rings occur. The geometry of the rings suggests a dependence of the emissions to the angle with respect to the geomagnetic field, or possibly to the spatial gradient in the HF radio wave pump beam. An angular dependence in the artificial excitation of enhanced ion-acoustic and Langmuir waves has also been seen in incoherent scatter radar (ISR) observations. In an attempt to determine if such a dependence exists in SEE, an interferometric SEE system is being developed and will be described. ISR observes Langmuir turbulence and SEE is a result of upper hybrid turbulence, either of which may accelerate electrons and produce optical emissions. The combination of angle-sensitive SEE and ISR observations, along with other available measurements, will thus help to determine if the optical emissions are due primarily to one type of turbulence or to a combination of both.
Hagfors Tor
Heinselman Craig
Isham B.
Khudukon B.
Kosch Michael J.
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