- 期刊
- OpenAccess
Simulations of Wind Field Effect on Two-Stream Waves in the Equatorial Electrojet
並列摘要
The wind field effect on the phase velocities of 3-to 10-meter Farley-Buneman two-stream waves in the equatorial E region ionosphere at altitudes in the range of 95-110 km is studied by numerical simulation. The behavior of this two-stream wave in the uniform wind field U(subscript n) in a plane perpendicular to the Earth's magnetic field is simulated with a two-dimensional two-fluid code in which electron inertia is neglected while ion inertia is retained. It is confirmed that, the threshold condition for the appearance of two-stream waves is V(superscript th subscript D)≈(1+ψ0) C(subscript s)/cos θ + U(subscript n); and the phase velocity of the two-stream wave at the threshold condition is V(subscript p)≈C(subscript s)+14 cosθ, where θ is the elevation angle of the wave propagation in a limited range and ψ0=v(subscript in)v(subscript en)/Ω(subscript i)Ω(subscript e). The first formula indicates that the wind field parallel (anti-parallel) to the electron drift velocity will raise (lower) the threshold drift velocity by the amount of the wind speed. This means that parallel wind is a stable factor, while anti-parallel wind is an unstable factor of two-stream waves. This may explain why high speed (larger than acoustic speed) two-stream waves were rarely observed, since larger threshold drift velocity demands larger polarization electric field. The result of the simulations at the saturation stage show that when V(superscript th subscript D) was only slightly larger than V(superscript th subscript D), the horizontal phase velocity of the Iwo-stream wave would gradually down-shift to the threshold phase velocity C(subscript n)+U(subscript n). The physical implications of which are discussed.