Creation of solitons and density cavities by lower hybrid waves

Formation of Korteweg-de Vries (KdV) solitons by nonlinear lower hybrid waves (LHWs) is not possible in usual electron ion plasma because a dispersive term does not have a suitable form. It is pointed out that the dispersion characteristics of electrostatic LHWs are modified in the presence of field-aligned shear flow to produce KdV solitons with negative electrostatic potential as it has been observed by satellites in the upper ionosphere. Plasma density decreases within the solitary structures. The parallel electron velocity shear v e 0 = v e 0 ( x ) z ̂ also gives rise to unstable waves in the intermediate frequency range in linear limit whereas the ambient magnetic field B 0 = B 0 z ̂ is assumed to be constant. The instability and structure size depend upon the electron parallel velocity shear parameter S e = 1 Ω e d v e 0 ( x ) d x (where Ω e is the electron gyrofrequency) and the propagation direction with respect to the ambient magnetic field B0. The theoretical model is applied to the upper ionosphere, and the estimated width of the structures turns out to be of the order of 70 m, which is closer to the observations.