HEATER-INDUCED ALTITUDE DESCENT OF THE EISCAT UHF ION LINE ENHANCEMENTS: OBSERVATIONS AND MODELLING.

• Main Authors: Mina Ashrafi A, M. J. Kosch A, F. Honary A
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: EISCAT
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.626.7752; http://eprints.lancs.ac.uk/6680/1/Ashrafi_ASR_2006.pdf

On 12 November 2001, artificial optical annuli were produced using the EISCAT high-frequency (HF) ionospheric Heating facility. This unusual phenomenon was induced using O-mode transmissions at 5.423 MHz with 550 MW effective isotropic radiated power and the pump beam dipped 9 degrees south. The pump frequency corresponds to the fourth electron gyro-harmonic frequency at 215 km altitude. The EISCAT UHF radar observed a persistent pump-induced enhancement in the ion line data near the HF reflection altitude. The optical and radar signatures of HF pumping started at∼230 km and descended to∼220 km within ∼60 s. This effect has been modelled using the solution to differential equations describing pump-induced electron temperature and density perturbations. The decrease in altitude of the ion line by∼10 km and changes in electron density have been modelled. The results show that an electron temperature enhancement of up to ∼5700 K can be achieved, which is not sufficient to explain the observed optical emissions. Key words: Ionospheric heating; Electron acceleration 1