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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 9
Ann. Geophys., 34, 709–723, 2016
https://doi.org/10.5194/angeo-34-709-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 34, 709–723, 2016
https://doi.org/10.5194/angeo-34-709-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 31 Aug 2016

Regular paper | 31 Aug 2016

A modeling study of asymmetries in plasma irregularity characteristics near gradient reversals

Leslie J. Lamarche and Roman A. Makarevich Leslie J. Lamarche and Roman A. Makarevich
  • Geophysical Institute and Department of Physics, University of Alaska Fairbanks, Fairbanks, Alaska, USA

Abstract. Asymmetries in plasma density irregularity generation between the leading and trailing edges of the large-scale plasma density structures in the high-latitude ionosphere are investigated. A model is developed that evaluates the gradient-drift instability (GDI) growth rate differences across the gradient reversal that is applicable at all propagation directions and for the broad range of altitudes spanning the entire lower ionosphere. In particular, the model describes asymmetries that would be observed by an oblique scanning radar near density structures in the polar cap such as elongated polar patches. The dependencies on the relative orientations between the directions of the gradient reversal, plasma convection, and wave propagation are examined at different altitudinal regions. At all altitudes, the largest asymmetries are expected for observations along the gradient reversals, e.g., when an elongated structure is oriented along the radar boresight. The convection direction that results in the strongest asymmetries exhibits a strong dependence on the altitude, with the optimal convection being parallel to the gradient reversal in the E region, perpendicular to it in the F region, and at some angle between these extremes in the transitional region. Implications for observations of polar patches by oblique scanning radars within the Super Dual Auroral Radar Network are discussed. It is demonstrated that the wave propagation direction relative to the prevalent convection and gradient directions plays a critical role in controlling both the irregularity growth rate and its asymmetries near gradient reversals.

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The asymmetries between the leading and trailing edges of large-scale plasma density structures in the ionosphere are examined using a general formalism for the gradient-drift instability for arbitrary altitude and propagation direction. The asymmetry changes dramatically with propagation direction and is most likely to be observed by a ground-based radar when the radar’s boresight is parallel to the structure’s elongation direction and perpendicular to its direction of motion.
The asymmetries between the leading and trailing edges of large-scale plasma density structures...
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