HR: 0830h
AN: SP21B-05    [Abstracts]
TI: Combination Scattering by Anisotropic Langmuir Turbulence With Application to Solar Radar Experiments
AU: * Khotyaintsev, M V
EM: ko@irfu.se
AF: Dept. of Astronomy and Space Physics, Uppsala University, Box 537, Uppsala, SE-751 21 Sweden
AU: Mel'nik, V N
EM: melnik@ira.kharkov.ua
AF: Institute of Radio Astronomy of the National Academy of Sciences of Ukraine, vul.Chervonopraporna 4, Kharkiv, 61002 Ukraine
AU: Thide', B
EM: bt@irfu.se
AF: Dept. of Astronomy and Space Physics, Uppsala University, Box 537, Uppsala, SE-751 21 Sweden
AU: Thide', B
EM: bt@irfu.se
AF: Swedish Institute of Space Physics, Box 537, Uppsala, SE-751 21 Sweden
AU: Thide', B
EM: bt@irfu.se
AF: LOIS Space Centre, Vaxjo University, Vaxjo, SE-351 95 Sweden
AU: Konovalenko, O O
EM: akonov@ira.kharkov.ua
AF: Institute of Radio Astronomy of the National Academy of Sciences of Ukraine, vul.Chervonopraporna 4, Kharkiv, 61002 Ukraine
AB: We develop a theory for radar signal scattering by anisotropic Langmuir turbulence in the solar corona due to a t+l = t process. Langmuir turbulence is considered (thought) to be generated in a cone by a narrow field-aligned electron beam e.g. by an electron beam responsible for a type III solar burst. Expressions for the scattering altitudes, frequency shifts, cross-sections, efficiency of the process, and optical depth are obtained. We show that the absolute value of the radar echo frequency shift is equal to the local plasma frequency at the scattering spot. The frequency shift is positive for the coalescence case and negative for the decay case. The minimum echo frequency shift is determined by the minimal phase velocity of the Langmuir waves, the maximum shift is determined by the electron beam velocity, but in any case can not exceed -ω_t/2 and ω_tt, where ω_t is the frequency of a radar signal. Angular characteristics of the scattered signal differ dramatically for the cases of coalescence and decay. The signal is scattered into a narrow cone high above the specular reflection point (ω_p ≪ ω_t), but in the vicinity of ω_p ~ ω_t/2 the red echo is scattered isotropically, while the blue echo is scattered into a even narrower cone. We show that the scattering efficiency increases with increase of the local plasma frequency as well as the radar frequency. One should note, that at ω_p = ω_t/2 and ω_p = ω_t efficiency goes to infinity. Strong peaks of the echo at ω_t/2 and 2ω_t, may be observed only if the velocity of electron beam exceeds c/√{3}. The considered t+l = t process is essential and can be successfully used for radar studies of the spectral energy density of anisotropic Langmuir turbulence.
DE: 6949 Radar astronomy
DE: 7509 Corona
DE: 7514 Energetic particles (2114)
DE: 7839 Nonlinear phenomena
DE: 7868 Wave/wave interactions
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly