Heliophysics Science Division
Guru Ganguli - Abstract

Broadband Spectrum and Multi-Scale Coherent Structures Due to
Inhomogeneous Parallel Flows in the Ionosphere

Gurudas Ganguli
Naval Research Laboratory, Washington, DC

Recently it has been demonstrated by observations (FAST, AMICIST, Freja) that inhomogeneous flows, both perpendicular and parallel to the ambient magnetic field, are often encountered in ionospheric plasmas and that they are usually accompanied by broadband wave spectra. Associated with these waves are heated ions and unique nonlinear signatures that are not completely understood. Our ongoing studies indicate that an inhomogeneity in the flow velocity, even in small magnitude (i.e., dV/dx << ion gyrofrequency), modify the dispersive properties and stability of a magnetized plasma. It can reduce the threshold current for some current driven instabilities (e.g., ion-acoustic, ion cyclotron, etc.) and produce broadband wave spectra which develop into multi-scale coherent structures. The nonlinear evolution results in substantial ion heating and cross-field transport which affect the meso-scale transport properties of the region. These results are consistent with ionospheric observations and may have applications to other natural plasma environments, such as solar plasmas.