Numerical Study of Plasma Density Gradient Effects on Farley-Buneman Waves Traveling in the Equatorial E Region

Abstract

AB STRACTIn this pa per, a two-di men sional nu mer i cal study of a plasma den sity gra di ent ef fect on Farley-Buneman waves (FB waves) is per formed via a two-fluid code in which the elec tron in er tia is ne glected while the ion in er tia is re tained. We fo cused the sim u la tions on the in ter ac tion be tween a sin gle wave mode and the back ground E re gion where the ver ti cal den sity gra di ent pro file and the weaker than FB thresh old am bi ent elec tric field were con sid ered. From 2D den sity con tour maps, it was found that the FB wave grows in the re gion ofÑN e is the elec tron den sity gra di ent and v E is the elec tric field), the ini tial growth rate was in rea son able agree ment with the pre dic tion of the com bined lin ear the ory of Farley-Buneman and gra di ent drift in sta bil i ties, and the prop a ga tion speed was mod u lated by the gra di ent strength. Ac cord ing to the phase ve loc ity eval u ated by the Fou rier anal y sis and peak to peak es ti ma tion method, the den sity gra di ents were found to have an ef fect of low er ing the phase ve loc ity at sat u ra tion, which is smaller than ion-acous tic speed for large scale waves, and the re sults dem on strated that the re duc tion of phase ve loc ity by a den sity gra di ent ef fect was larger for a lon ger wave length wave than shorter wave length curve. It was also found that the plau si ble den sity gra di ent ef fects seem to be re lated to the thick ness of the den sity gra di ent re gion and ver ti cal elec tric field where the FB wave was trav el ing. The thicker un sta ble layer would cause a greater phase ve loc ity re duc tion than the thin ner un sta ble layer might cause, and the large driving electric field would reduce the wavelength dependence of density gradient effect on the saturation phase velocity.

Phase Velocity Analysis of Projected Wave Motion Along Oblique Radar Beams - A Numerical Study of Type-1 Radar Echoes

“…They also pointed out that some statistical studies using HF radar in the aurora region whose researchers also reached the same conclusion (e.g., Hanuise et al 1991;Milan et al 1997Milan et al , 2001Lacroix and Moorcroft 2001). To clarify density gradient effects on FB waves, Fern and Kuo (2009b) performed 2D simulations of plasma density gradient effect on saturated FB waves and found that density gradient effects were related to the thickness of an unstable layer and ambient vertical electric field (which was parallel to vertical density gradient distribution).…”