Whistler evidence of large-scale electron-density irregularities in the plasmasphere

Large-scale structure in electron density in the plasmasphere has been identified from whistlers recorded at Eights, Antarctica, near sunspot minimum. The structures have dimensions of the order of an earth radius at the equator. Examples of the structures include an outlying peak in equatorial electron concentration near L = 4, with peak-to-valley ratio of 2, and more than 3∶1 variations in electron concentration within 30° in longitude. Once formed, the structures may be observed for several hours or more. Detailed information on the occurrence of the irregularities is not yet available, but it is believed that they tend to develop under the influence of magnetospheric convection events. The convention events tend to accentuate departure from ‘smoothness’ that originally developed through the action of ionosphere-protonosphere coupling processes and possibly through a cycle of erosion and accretion of plasma at the plasmasphere boundary in the dusk sector.