Processes leading to plasma losses into the high-latitude atmosphere

Abstract

The visible aurora is a majestic and concrete manifestation of the loss of energetic particles from the magnetosphere to the polar ionosphere (Figure 3.1). Auroral intensity is proportional to the total energy flux of particles that enter the ionosphere, and there is a direct relation between the altitude of auroral emissions and the energy of individual precipitating particles. Auroral emissions occur over a variable, though in general large portion of the polar ionosphere, their distribution and intensity reflecting the variety of processes that act on auroral particles before they precipitate into the ionosphere. Auroras are most common and brightest within a roughly circular region, referred to as the ‘auroral oval’ that is several degrees wide and lies near 70° magnetic latitude. Additionally, highly variable and important auroral emissions occur throughout the region poleward of the auroral oval that is referred to as the ‘polar cap’. The auroral oval and the polar cap region encircled by the oval are magnetically connected to most of the volume of the magnetosphere. When projected along magnetic field lines to the ionosphere, areas in the equatorial plane of the magnetosphere are reduced in scale by a factor of 106. It is therefore possible to use maps of auroral and precipitating particle phenomena in the ionosphere to identify regions and physical processes throughout the very much larger regions of the magnetosphere