الفهرس 
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Abstract
In this thesis, the propagation of ion- acoustic solitary wave and ion- acoustic shocklike soliton in a collisionless plasma at Venus ionosphere consisting of positive and negative ions, as well as solar wind streaming protons and electrons at Venus ionosphere is investigated.
In chapter 2, a reductive perturbation method is employed to derive an evolution equation describing the plasma system; namely Korteweg- deVries (KdV) equation. However, at certain values of the plasma parameters (e.g critical density of negative ions) the KdV equation becomes invalid to describe the physical system. Therefore, a modified KdV (MKdV)equation is derived. Both KdV and MKdV equations admit a solitary solution. The effects of different physical parameters on the solitary wave are highlighted.
In chapter 3, in the vicinity of the critical density of negative ions neither the KdVnor the MKdV equationscan describe the plasma system. Thus, a Gardner equation is derived at this case. Gardner equation can describe the shocklike soliton (Double layers)wave which is the motivation of this chapter away to the space observation of shocklike wave at Venus. The dependence of the profiles ofshocklike soliton wave on the physical parameters of Venusenvironment and solar wind is investigated.