Parametric analysis of positive amplitude electron acoustic solitary waves in a magnetized plasma and its application to boundary layers

International audienceThe existence domain of a fully nonlinear positive amplitude electron acoustic solitary wave has been studied in a four-component plasma composed of warm magnetized electrons, warm electron beam, and energetic multi-ion species with ions hotter than the electrons (T i > T e). A Sagdeev pseudopotential technique has been used to obtain the nonlinear evolution equation for the wave propagating obliquely with the ambient magnetic field. It is observed that the ion temperatures and concentrations play a crucial role in determining the characteristics and the existence domain of the electron acoustic solitary wave. With a large cold ion population and/or a large cold to hot ion temperature ratio, the plasma tends to behave like a single ion-dominated one. The corresponding Sagdeev pseudopotential shows an extremely narrow and deep profile producing small-amplitude, narrow width, spiky solitary waves. Such solutions are found to be applicable in the bow shock, magnetosheath, and cusp regions. Comparison with CLUSTER observations agrees well with the analytical model. It has been shown that in the magnetosheath, cooler He 2+ ions are necessary to produce a positive polarity solution while a hotter species may produce a compressive (negative polarity) solution

Large-scale fields and flows in the magnetosphere-ionosphere system

Advances in our understanding of the large-scale electric and magnetic fields in the coupled magnetosphere-ionosphere system are reviewed. The literature appearing in the period January 1991–June 1993 is sorted into 8 general areas of study. The phenomenon of substorms receives the most attention in this literature, with the location of onset being the single most discussed issue. However, if the magnetic topology in substorm phases was widely debated, less attention was paid to the relationship of convection to the substorm cycle. A significantly new consensus view of substorm expansion and recovery phases emerged, which was termed the ‘Kiruna Conjecture’ after the conference at which it gained widespread acceptance. The second largest area of interest was dayside transient events, both near the magnetopause and the ionosphere. It became apparent that these phenomena include at least two classes of events, probably due to transient reconnection bursts and sudden solar wind dynamic pressure changes. The contribution of both types of event to convection is controversial. The realisation that induction effects decouple electric fields in the magnetosphere and ionosphere, on time scales shorter than several substorm cycles, calls for broadening of the range of measurement techniques in both the ionosphere and at the magnetopause. Several new techniques were introduced including ionospheric observations which yield reconnection rate as a function of time. The magnetospheric and ionospheric behaviour due to various quasi-steady interplanetary conditions was studied using magnetic cloud events. For northward IMF conditions, reverse convection in the polar cap was found to be predominantly a summer hemisphere phenomenon and even for extremely rare prolonged southward IMF conditions, the magnetosphere was observed to oscillate through various substorm cycles rather than forming a steady-state convection bay