Some characteristics of atmospheric gravity waves observed by radio-interferometry

Observations of atmospheric acoustic-gravity waves (AGWs) are considered through their effect on the horizontal gradient G of the slant total electron content (slant TEC), which can be directly obtained from two-dimensional radio-interferometric observations of cosmic radio-sources with the Nancay radioheligraph (2.2 degrees E, 47.3 degrees N). Azimuths of propagation can be deduced (modulo 180 degrees). The total database amounts to about 800 h of observations at various elevations, local time and seasons. The main results are: a) AGWs are partially directive, confirming our previous results. b) The propagation azimuths considered globally are widely scattered with a preference towards the south. c) They show a bimodal time distribution with preferential directions towards the SE during daytime and towards the SW during night-time (rather than a clockwise rotation as reported by previous authors). d) The periods are scattered but are larger during night-time than during daytime by about 60%. e) The effects observed with the solar radio-sources are significantly stronger than with other radio-sources (particularly at higher elevations), showing the role of the geometry in line of sight-integrated observations. These observations are discussed with the help of a code (presented in Appendix) simulating propagation and absorption of AGWs, and the effects they produce on radio-astronomical observations through their interaction with the ionization.