SED

The effects of plasma transport, and the linkage of the driving electric field to the overlying magnetosphere, dominate ionospheric characteristics at auroral and sub-auroral latitudes. With increasing activity level, and particularly during geomagnetic storms, the equatorward extent of such effects expands to lower latitudes. Associated with the large-scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions, solar-produced F-region ionospheric plasma is transported sunward and poleward from a source region at middle and low latitudes in the afternoon sector. As a result, a latitudinally narrow region of storm-enhanced plasma density (SED) and increased total electron content (TEC) is carried toward higher latitudes in the noon sector [Foster, 1993]. The Millstone Hill incoherent scatter radar is situated near the plasmasphere boundary layer and regularly observes SED as a spatially continuous, large-scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid- or low-latitude source region. This feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms (called the dusk effect) and constitutes a source for the enhanced F-region plasma observed in the polar cap during disturbed conditions. Within the region of SED, TEC is greatly enhanced and steep latitude gradients of TEC occur where the SED abuts the trough [Vo and Foster, 2001]. Recent M-I coupling investigations find that storm enhanced density and plumes of greatly-elevated TEC are associated with the erosion of the outer plasmasphere by strong sub-auroral polarization stream (SAPS) electric fields. The SED/TEC plumes identified at low altitudes map closely onto the magnetospheric determination of the boundaries of the plasmasphere and plasmaspheric drainage plume determined by EUV imaging from the IMAGE spacecraft [Foster et al, 2002].

GPS Plume

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