Polar cap arcs and the plasma sheet

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Abstract
This letter suggests that most of the so‐called ‘polar cap arcs’ with the sun‐aligned orientation at the high geomagnetic latitude region occurring during the quiescent magnetosphere are actually a part of discrete arcs in the auroral oval as a consequence of the poleward widening of the quiet auroral oval. This suggestion is based on (1) a detailed examination of two months of DMSP electron precipitation data and simultaneous auroral observations, (2) the observed widening in the latitudinal extent of the auroral oval precipitation to the very high geomagnetic latitude (≳80°) and the simultaneous occurrence of the sun‐aligned arcs, and (3) the conjugate widening of the quiet auroral oval over both the northern and southern polar regions. The new interpretation of the ‘polar cap arcs’ is discussed in terms of the present understanding of the solar wind‐magnetospheric interaction.