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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 11
Ann. Geophys., 34, 927–941, 2016
https://doi.org/10.5194/angeo-34-927-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The 14th International Symposium on Equatorial Aeronomy

Ann. Geophys., 34, 927–941, 2016
https://doi.org/10.5194/angeo-34-927-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 03 Nov 2016

Regular paper | 03 Nov 2016

Observational evidence for new instabilities in the midlatitude E and F region

David L. Hysell1, Miguel Larsen2, and Michael Sulzer3 David L. Hysell et al.
  • 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, USA
  • 2Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
  • 3Arecibo Observatory, Arecibo, Puerto Rico

Abstract. Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during moderately disturbed conditions are presented. The observations indicate the presence of patchy sporadic E (Es) layers, medium-scale traveling ionospheric disturbances (MSTIDs), and depletion plumes associated with spread F conditions. New analysis techniques are applied to the dataset to infer the vector plasma drifts in the F region as well as vector neutral wind and temperature profiles in the E region. Instability mechanisms in both regions are evaluated. The mesosphere–lower-thermosphere (MLT) region is found to meet the conditions for neutral dynamic instability in the vicinity of the patchy Es layers even though the wind shear was relatively modest. An inversion in the MLT temperature profile contributed significantly to instability in the vicinity of one patchy layer. Of particular interest is the evidence for the conditions required for neutral convective instability in the lower-thermosphere region (which is usually associated with highly stable conditions) due to the rapid increase in temperature with altitude. A localized F-region plasma density enhancement associated with a sudden ascent up the magnetic field is shown to create the conditions necessary for convective plasma instability leading to the depletion plume and spread F. The growth time for the instability is short compared to the one described by [Perkins(1973)]. This instability does not offer a simple analytic solution but is clearly present in numerical simulations. The instability mode has not been described previously but appears to be more viable than the various mechanisms that have been suggested previously as an explanation for the occurrence of midlatitude spread F.

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Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during moderately disturbed conditions are presented. Plasma irregularities in both ionospheric regions were observed. We investigate the role of neutral atmospheric dynamics and instabilities in causing the ionospheric disturbances. A number of viable instability mechanisms rooted in neutral dynamics are identified.
Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during...
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