Plasma collective modes driven by velocity gradients

Open Access
Publisher Website
Google Scholar
Abstract
Collisional modes driven by shear in the plasma flow velocity V∥, parallel to the magnetic field, are shown to exist over significant scale distances while subject to the constraints imposed by gradients in the transverse velocity VE ∝ E×B. These constraints make the modes localized over finite distances around the surfaces where VE reaches a maximum or a minimum. Composite modes that can be constructed as a sequence or a superposition of these “elementary” normal modes can be excited in regions where the transverse velocity acquires a plateau type of profile that is assumed to be formed after macroscopic Kelvin‐Helmholtz modes associated with the shear of VE have reached their saturation stage. Thus a significant rate of longitudinal plasma momentum transport in the transverse direction to the magnetic field can be produced. The relevance of this analysis to the fluctuations observed in the auroral F region is discussed.