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

C. Haldoupis (1) , D. T. Farley (2) , K. Schlegel (3)

1 Physics Department
2 School of Electrical Engineering
3 MPI Aeronomie - Max-Planck-Institut für Aeronomie

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.

Domaines: Océan, Atmosphère; Sciences de la Terre

C. Haldoupis, D. T. Farley, K. Schlegel. Type-1 echoes from the mid-latitude E-Region ionosphere. Annales Geophysicae, 1997, 15 (7), pp.908-917. ⟨hal-00316295⟩