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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, 925–934, 1997
https://doi.org/10.1007/s00585-997-0925-1
© European Geosciences Union 1997
Ann. Geophys., 15, 925–934, 1997
https://doi.org/10.1007/s00585-997-0925-1
© European Geosciences Union 1997

  31 Jul 1997

31 Jul 1997

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

A. Bourdillon1, E. Lefur1, C. Haldoupis2, Y. Le Roux3, J. Ménard3, and J. Delloue4 A. Bourdillon et al.
  • 1Laboratoire Structures Rayonnautes, UPRES-4 CNRS 6095, Université de Rennes 1, Rennes, France
  • 2University of Crete, Iraklion, Crete, Greece
  • 3France Télécom, CNET/LAB/SAR/TSI, Lannion, France
  • 4Laboratoire de Physique de l'Exosphère, Université Pierre et Marie Curie, Paris, France

Abstract. HF radar observations of mid-latitude spo- radic-E irregularities carried out with the Valensole radar in South France are compared with simultaneous ionosonde measurements underneath the irregularity zones. In a previous study of Valensole radar data, it has been shown that HF backscatter from the night-time mid-latitude E region is usually associated with large- scale wave-like modulations. To obtain more informa- tion on the geophysical conditions prevailing during backscatter events, a new experiment was performed which also included a vertical ionosonde beneath the scattering region. The data to be presented here are from two periods when radar scattering appeared simulta- neously with large variations in the virtual height and the Doppler velocity of F-layer re¯ected echoes mea- sured with the vertical ionosonde, indicating very clearly the passage of atmospheric gravity waves (AGWs). The e.ect of the atmospheric waves on the sporadic-E layer is not always as marked as it is in the F region. In the ®rst event, the passage of the AGWs is accompanied by an upward followed by a downward movement of the Es-layer. The apparent descending movement of the Es-layer from 135 to 110 km in less than 10 min corresponded to a positive (downward) Doppler velocity of 35 m/s measured by the vertical ionosonde, and was accompanied by a range variation in the radar scattering region with a negative rate of about 90±110 m/s. In the second event, the Es-layer is not as strongly disturbed as in the previous one, but, nevertheless, the range varia- tions of the scattering region can still be associated with height ¯uctuations of the Es-layer.

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