Abstract
Abstract. We present two event studies illustrating the detailed relationships between plasma convection, field-aligned currents, and polar auroral emissions, as well as illustrating the influence of the Interplanetary Magnetic Field's y-component on theta aurora development. The transpolar arc of the theta aurorae moves across the entire polar region and becomes part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the POLAR UVI instrument provides measurements of auroral emissions. Ionospheric electrostatic potential patterns are calculated at different times during the evolution of the theta aurora using the KTH model. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Paraboloid Model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed. Keywords. Ionosphere (Plasma convection; Polar ionosphere) – Magnetospheric physics (Magnetosphereionosphere interactions)
Highlights
The global distribution of the aurora has a qualitative as well as a quantitative dependence on the interplanetary magnetic field (IMF)
Due to the limited view of all-sky cameras and photometers on low-altitude satellites, these arcs were considered relatively isolated features. It was not until imaging instruments were flown on high-altitude spacecraft, such as Dynamics Explorer 1 (e.g. Frank et al, 1982, 1986) and Viking (e.g. Murphree et al, 1987), that the existence of so-called transpolar arcs (TPAs), luminous features extending across the polar region linking the dayside aurora to the nightside oval, became clear
This paper addresses the class of high-latitude aurora that involves moving transpolar arcs forming theta aurora as they traverse the highest latitudes
Summary
The global distribution of the aurora has a qualitative as well as a quantitative dependence on the interplanetary magnetic field (IMF). Observations indicate that TPAs may be associated with either sunward or antisunward flow, as well as a variety of convection patterns, including a four-cell pattern (Frank et al, 1986; Gusev and Troshichev, 1990; Jankowska et al, 1990; Zanetti et al, 1990), a dominant one-cell (Hoffman et al, 1985), a three-cell ( Carlson et al, 1988; Zanetti et al, 1990; Jankowska et al, 1990), or a distorted two-cell (Robinson and Mende, 1990; Marklund et al, 1991) These studies are all based on isolated observations of single TPAs and represent different stages of theta aurora evolution relating to changing IMF Bx and By conditions during northward IMF. In both events the transpolar arc moves across the entire polar region and eventually becomes part of the opposite side of the auroral oval
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