Nonlinear Vortical Structures Research Articles

Nonlinear Wave Structures and Plasma−Dust Effects in the Earth’s Atmosphere

The interaction of charged dust grains with nonlinear vortical structures in the Earth’s atmosphere is analyzed. Certain aspects of the atmosphere−ionosphere interaction, in particular, mechanisms for the appearance of dust grains at ionospheric altitudes, are discussed. It is shown that, at certain altitudes, there are regions in the wavenumber space in which conditions leading to the excitation of acoustic−gravity waves are satisfied. The interaction of nonlinear acoustic−gravity waves with dust grains of meteoric origin at ionospheric altitudes, which leads to the mixing and redistribution of dust grains over the region where vortices exist, is investigated. The possibility of formation of vertical and horizontal dust flows in dusty ionospheric plasma as a result of modulational instability is analyzed. The dynamics of dust grains in dust devils frequently arising in the atmosphere above well-heated surfaces is modeled. The vortical structure of such a dust devil is characterized by a reduced pressure in the center, which facilitates the lifting of small dust grains from the surface. The formulated model is used to calculate the trajectories of dust grains in dust devils with allowance for the influence of the electric field generated in the vortex by colliding dust grains. The calculations show that dust devils play an important role in the transport of dust grains.

Excitation of Rossby waves by HF electromagnetic seismic origin emissions in the earth's mesosphere

Interaction of high-frequency seismo-electromagnetic emissions with the weakly ionized gas of the ionospheric D-layer is considered. It is shown that through the earth's ionosphere weakly damped high-frequency electron cyclotron electromagnetic waves can propagate. These new type of waves easily reach the ionospheric D-layer where they interact with the existing electrons and ions. Acting on electrons ponderomotive force is taken into account and corresponding modified Charney equation is obtained. It is shown that only nonlinear vortical structures with negative vorticity (anticyclone) can be excited. The amplitude modulation of electromagnetic waves can lead to the excitation of Rossby waves in the weakly ionized gas. The corresponding growth rate is defined. Depending on the intensity of the pumping waves generated by seismic activity different stable and unstable branches of oscillations are found. Detection of the new oscillation branches and energetically reinforcing Rossby solitary vortical anticyclone structures may be serve as precursors to earthquake.

Formation of tripolar vortices in toroidal ion-temperature-gradient driven modes in the presence of dust contamination

A system of nonlinear equations that governs the dynamics of toroidal-ion-temperature-gradient (TITG) driven modes in the presence of dust contamination is presented. In the linear limit, a local dispersion relation is derived and analyzed for a flat density profile case. In the nonlinear case, and by taking some specific profiles of equilibrium density, ion temperature, magnetic field, and sheared plasma flows, the stationary solutions of the nonlinear system can be represented in the form of a tripolar vortex solution. Numerical results obtained in the present study show that the inclusion of dust modifies the nonlinear vortical structures, and the amplitude of the normalized potential is found to be increased in the presence of negatively charged dust grains. The results of our present investigation would be useful to understand some linear as well as nonlinear properties of TITG modes in a dust-contaminated tokamak plasma.

Nonlinear vortical structures in the Earth’s ionosphere

The influence of charged particles and the Earth’s magnetic field on the possibility of the formation of solitary dipole vortical structures in the different layers of the Earth’s ionosphere is considered for the first time. It is shown that such influence manifests itself only in the E and F layers and leads to the destruction of the vortical structures. The magnetized Rossby vortices in the E layer are found. The damping decrement due to induction inhibition of the Rossby waves in the F layer is defined. The nonlinear equations describing the vortical formation dynamics in the D, E and F layers are obtained.

Numerical simulation of nonlinear structures in channel flow transition

Introduction T HE objective of this computational study is to investigate the development of nonlinear vortical structures in plane channel flow transition by the visualization of threedimensional vortex lines. It has long been recognized that transition may be viewed as a sequence of events that is triggered by two-dimensional Tollmien-Schlichting waves that become three-dimensional, leading to nonlinear wave interactions. In a recent experiment, Williams used hot film probes in a water channel boundary layer to create a data base containing three-dimensional instantaneous velocity and vorticity components documenting the evolution of the high shear layer and the formation of hairpin vortices. He then used this data base to obtain three-dimensional vortex lines. In this work, a similar technique is used to visualize the flowfield structures. In order to extract information from the computational data base, which provides the three-dimensional instantaneous velocity/vorticity field in over a quarter million grid points, vortex lines were calculated at time intervals that can be viewed sequentially. In addition, vorticity contours and velocity vector plots for the secondary flow are presented for a comparison with the findings inferred from the vortex line plots. Although flow visualization by vortex lines have been utilized in other numerical studies,' the present results effectively capture the continuous evolution of the flow, enabling the identification of various vortical structures.