After some 12 years as Editor of the Journal I have decided that it is time to move on and I will relinquish this position at the end of 2006. From the beginning of 2007 Padma Shukla will be the sole Editor and papers should be submitted to him or to any of the Associate Editors. The web address [email protected] will cease to be operative from this time. I would like to thank all those authors who have contributed to the Journal during my editorship and hope that they will continue to give it their support. I have every confidence that it will flourish under Padma's able guidance.

We consider the nonlinear interactions between upper-hybrid (UH) and Alfvén modes in a magnetized electron–ion plasma containing a fraction of stationary charged dust grains. The interaction is governed by a pair of equations for the UH wave envelope including the relativistic electron mass increase and the density and compressional magnetic field fluctuations associated with the Alfvén modes that are, in turn, driven by the ponderomotive force of the UH waves. The coupled mode equations are then Fourier analyzed to obtain a new dispersion relation, which admits new classes of modulational instabilities. The existence of a cusp-shaped UH envelope soliton is also predicted. The result can have relevance to the electron acceleration by sharply localized UH waves in the dusty magnetosphere of Saturn.

The resonant coupling between Alfvén waves is reconsidered. New results are found for cold magnetoplasmas where temperature effects are negligible.

Magnetohydrodynamic wave interactions in a linear shear flow are investigated using the Lagrangian fluid displacement ξ and entropy perturbation Δ S, in which a spatial Fourier solution is obtained in the frame of the background shear flow (Kelvin's method). The equations reduce to three coupled oscillator equations, with time-dependent coefficients and with source terms proportional to the entropy perturbation. In the absence of entropy perturbations, the system admits a wave action conservation integral consisting of positive and negative energy waves. Variational and Hamiltonian forms of the equations are obtained. Examples of wave amplification phenomena and sharp resonant-type wave interactions are obtained. Implications for the interaction of magnetohydrodynamic waves in the shear flow between fast, polar coronal-hole solar wind and slow, streamer belt solar wind are discussed.

We present an in depth study of the fluid limit of a kinetically derived collisional, current-driven instability that includes shears in the field-aligned currents as well as collisions. We show how the theory presented here generalizes other theories, including the collisionless current-driven electrostatic ion acoustic instability and its sheared collisionless version. We offer a low-frequency generalization of the zero frequency ion shear driven instability by minimizing the relative drift magnitude as well as the shears themselves. We discuss the implication of our theoretical framework both for strongly field-aligned modes and modes where the wavevectors have arbitrary angles with respect to the ambient magnetic field. We discuss the results in terms of F-region irregularity observations of coherent echoes by ionospheric radars.

A compressible model of the magnetosheath plasma flow is considered. Magnetic reconnection is assumed to occur in a region stretching from the sub-Solar point to the north. Two locations of the reconnection site are treated: two and four Earth radii from the sub-Solar point, respectively. By treating the transition layer as very thin, we solve the governing equations approximately using the method of matched asymptotic expansions. The behavior of the magnetic field and the plasma velocity close to a reconnection site during the transition from the magnetosheath to the magnetosphere is investigated. We also obtain the development of the transition layer thickness north and south of the reconnection point. The magnetopause transition layer is represented by a large-amplitude Alfvén wave implying that the density is approximately the same across the magnetopause boundary. In order to match the solutions we consider a compressible ideal magnetohydrodynamic model describing density, velocity and magnetic field variations along the outer magnetopause boundary. We also compare the analytical results with solutions from a numerical simulation. The compressible effects on the structure of the magnetic field and the total velocity evolution are visible but not dramatic. It is shown that the transition layer north of the reconnection point is thinner than to the south. The effect is stronger for reconnection at higher latitudes.

This paper presents the effect of ripple on the plasma wave excitation process and acceleration of electrons in a laser produced plasma. The plasma wave is generated by the beating of two coaxial lasers of frequencies ω1 and ω2, such that ω1-ω2≅ωp. One of the main laser beams also has intensity spikes. The nonlinearity due to the relativistic mass variation depends not only on the intensity of one laser beam but also on the second laser beam. Therefore the behavior of the first laser beam affects the second laser beam, hence cross-focusing takes place. Owing to the interaction of ripple and the main laser beams, the ripple grows inside the plasma. The behavior of the ripple in the plasma affects the excitation of the electron plasma wave as well as the electron acceleration. The amplitude of the electron plasma wave and the electron energy are calculated, in the presence of ripple.

A novel mechanism for the generation of large-scale zonal flows by small-scale Rossby waves in the Earth's ionospheric E-layer is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude magnetized Rossby waves. To describe this process a generalized Charney equation containing both vector and scalar (Korteweg–de Vries type) nonlinearities is used. The magnetized Rossby waves are supposed to have arbitrary wavelengths (as compared with the Rossby radius). A set of coupled equations describing the nonlinear interaction of magnetized Rossby waves and zonal flows is obtained. The generation of zonal flows is due to the Reynolds stresses produced by finite amplitude magnetized Rossby waves. It is found that the wave vector of the fastest growing mode is perpendicular to that of the magnetized Rossby pump wave. Explicit expression for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. A comparison with existing results is carried out. The present theory can be used for the interpretation of the observations of Rossby-type waves in the Earth's ionosphere.