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arXiv · 2610.30826

Nonlinear Drift Waves and Electrostatic Density Cavities in Upper Ionosphere

Hamid Saleem·Usman Saeed
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Abstract

Nonlinear drift waves are investigated to explain the mechanism for the creation of one dimensional (1D) and two dimensional (2D) electrostatic density cavities in the presence of density gradient in direction perpendicular to the geomagnetic field. Ion motion along field lines has to be neglected for the formation of density depletion because nonlinear contribution of their parallel motion overcomes the effect of drift waves which create negative nonlinear potential. It is pointed out that a straightforward but appropriate model for drift waves can explain the generation of density cavities having widths in xy-plane if the external magnetic field is assumed to be along z-axis i.e. ${\bf B}_0 = B_0 \hat{z}$. The general nonlinear equation for drift waves takes the form of Zakharov-Kuznetson (ZK) equation when ion nonlinear vorticity term is ignored and it admits the solution in the form of 2D solitary wave. In 1D case, the ZK equation reduces to Korteweg de Vries (KdV) equation which admits solution in the form of 1D soliton. In both cases, the nonlinear potential becomes negative. The order of magnitude of the amplitude and width of density cavities is found to be in agreement with the satellite observations in upper ionosphere.

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Hamid Saleem, Usman Saeed. 2026-10-22. Nonlinear Drift Waves and Electrostatic Density Cavities in Upper Ionosphere. https://arxiv.org/abs/2610.30826

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