HR: 0800h
AN: SA51A-01    [Abstracts]
TI: Transient Dynamics of Secondary Radiation From a HF Pumped Magnetised Space Plasma
AU: * Norin, L
EM: ln@irfu.se
AF: Swedish Institute of Space Physics, Box 537, Uppsala, 751 21, Sweden
AU: Grach, S M
EM: sg@nirfi.sci-nnov.ru
AF: Radiophysical Research Institute, B. Pecherskaya street 25, Nizhniy Novgorod, 603950, Russian Federation
AU: Thidé, B
EM: bt@irfu.se
AF: Swedish Institute of Space Physics, Box 537, Uppsala, 751 21, Sweden
AU: Sergeev, E N
EM: evg@nirfi.sci-nnov.ru
AF: Radiophysical Research Institute, B. Pecherskaya street 25, Nizhniy Novgorod, 603950, Russian Federation
AB: In order to systematically analyse the transient wave and radiation processes that are excited by a HF radio wave injected into a magnetised space plasma, we have measured the secondary radiation, or stimulated electromagnetic emission (SEE), from a preconditioned ionosphere. The ionosphere was heated using a pump duty cycle of 200 ms (180 ms on and 20 ms off) and 100~ms (80 ms on and 20 ms off) for various pump frequencies near the fifth harmonic of the electron gyro frequency. The results presented here show that within the first ten milliseconds after pump turn-on, frequency downshifted structures of the SEE exhibit an overshoot with a maximum at t_m≈ 8 ms, whereas upshifted spectral components do not exhibit this feature. The relative magnitude of the overshoot is strongly dependent on the frequency offset of the pump from the fifth harmonic of the electron gyro frequency. A new, blue-shifted transient frequency component is identified. This component is upshifted from the pump by 14 kHz < Δ f <50 kHz and exists only for the first ten milliseconds after pump turn-on. On a slower time scale we analyse the amplitude modulation, or "ringings", of the pump, (in the Russian literature also known as "spikes"). The ringings have a frequency f_R≈ 17 Hz and we show that this phenomenon is also present in the SEE. Furthermore, the ringings in the SEE are almost perfectly synchronised to the ringings of the pump.
DE: 2403 Active experiments
DE: 2471 Plasma waves and instabilities (2772)
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly