1 Extremely NarrowBand Stimulated Radio Emissions from the E Region Observed at EISCAT

• Main Authors: V. Belyey, B. Isham, M. T. Rietveld, B. Khudukon, R. Yu. Yurik, E. D. Tereshchenko, T. Hagfors, M. Grill, A. Brekke
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Norway; Tromsø; EISCAT
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.145.5039; http://www.phys.uit.no/IPELS05/Talks&posters/Posters/Belyey_etal_IPELS-2005.pdf

Abstract. Stimulated electromagnetic emission (SEE) may occur when the nearEarth space plasma of the ionosphere is subjected to a powerful high frequency (HF, 330 MHz) electromagnetic wave tuned to match a natural E or Fregion plasma frequency. The emission is usually attributed to nonlinear interactions between HFpumpinduced ionospheric magnetoionic wave modes, and is observed in the radio spectrum as sideband peaks around the HF pump frequency. Several SEE features, among them the downshifted peak (DP), reveal a strong dependence on the offset between the pump frequency and local gyrofrequency harmonics, demonstrating the key role of the geomagnetic field in the physics of SEE. In the observations reported here, a number of extremely narrowband SEE spectral components, of the order of 1 or 2 Hz in width, were detected near the expected frequency of the DP during an HF modification campaign held at the EISCAT observatory near Tromsø, Norway in the autumn of 2004. The extreme narrowness of the lines suggests that they cannot be due to the same wavewave interactions suggested for other SEE features. The apparently geophysical variation in the frequencies of the lines, however, suggests that they are due to ionospheric interaction processes. As has been observed for the DP in the F region, the angle of arrival of these E region emissions remains nearly constant during a change in pump beam angle, suggesting, as for the DP, a role for the magnetic field in explaining the origin of these waves. The ability to compute direction angle and spectra at very high frequency and time resolution are particularly interesting features of the observational technique used for these measurements. 2