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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 7
Ann. Geophys., 15, 908–917, 1997
© European Geosciences Union 1997
Ann. Geophys., 15, 908–917, 1997
© European Geosciences Union 1997

  31 Jul 1997

31 Jul 1997

Type-1 echoes from the mid-latitude E-Region ionosphere

C. Haldoupis1, D. T. Farley2, and K. Schlegel3 C. Haldoupis et al.
  • 1Physics Department, University of Crete, Iraklion, Greece
  • 2School of Electrical Engineering, Cornell University, Ithaca, NY, USA
  • 3Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany

Abstract. This paper presents more data on the properties of type-1 irregularities in the nighttime mid-latitude E-region ionosphere. The measurements were made with a 50-MHz Doppler radar system operating in Crete, Greece. The type-1 echoes last from several seconds to a few minutes and are characterized by narrow Doppler spectra with peaks corresponding to wave phase velocities of 250–350 m/s. The average velocity of 285 m/s is about 20% lower than nominal E-region ion-acoustic speeds, probably because of the presence of heavy metallic ions in the sporadic-E-layers that appear to be associated with the mid-latitude plasma instabilities. Sometimes the type-1 echoes are combined with a broad spectrum of type-2 echoes; at other times they dominate the spectrum or may appear in the absence of any type-2 spectral component. We believe these echoes are due to the modified two-stream plasma instability driven by a polarization electric field that must be larger than 10 mV/m. This field is similar in nature to the equatorial electrojet polarization field and can arise when patchy nighttime sporadic-E-layers have the right geometry.

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