The anisotropy of high‐latitude nighttime F region irregularities

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Abstract
The anisotropy of intermediate‐scale, F region irregularities in the nighttime auroral zone is described. The study is based upon spaced‐receiver phase scintillation measurements made with the Wideband satellite at Poker Flat, Alaska. A systematic dependence of irregularity anisotropy with local time and magnetic latitude is observed, suggesting convective control. Sheetlike irregularities are confined to the zone of east‐west drift near the equatorward boundary of the auroral zone, and at the flow reversal, or Harang discontinuity, the cross‐field extension of the sheets is reduced. The extension of rodlike irregularities, which are observed poleward of the zonal convection boundary, also shows apparent convection dominance. Mechanisms for convection control of the anisotropy are discussed.