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

Abstract

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.

Detection of Radio Emission From Fireballs

“…However, because the signal strength depends on the inverse-cube of the distance to the meteor, there should be many very bright nearby RFI sources on the horizon but these are not observed. This pattern is also inconsistent with non-specular reflections, which are preferentially located in a relatively small region of the sky that satisfies the requirement that the pointing vector is perpendicular to the geomagnetic field (Bourdillon et al 2005;Close et al 2011).…”

“…They most often occur when the radar is pointed perpendicular to the geomagnetic field, but do not necessarily satisfy the specular reflection requirement. These types of trails can last from seconds to several minutes but are typically much weaker than specular trails, and therefore high power large-aperture radars are required to detect them (Bourdillon et al 2005;Sugar et al 2010;Close et al 2011).…”

“…The observed transients are also inconsistent with light curves from non-specular echoes, which vary greatly from one to the next, following no particular pattern. More importantly, however, non-specular echoes are weaker and more rare than overdense specular echoes (Bourdillon et al 2005;Close et al 2011). Therefore, if the LWA1 were seeing non-specular reflections, it should also see many more bright specular reflections scattering from the same transmitters.…”

Meteorological Storm Influence on the Ionosphere Parameters

“…Numerous experimental and theoretical works have been devoted to studying the effect of AGW on sporadic layers in the E-region of the ionosphere [59,63,64,71,[76][77][78][79][80][81]. These studies have considered various aspects of AGW influence, including the effect of waves on the inhomogeneity of horizontal winds at the heights of the E-region of the ionosphere, on the perturbation of the critical frequency of the layer, and on the recombination processes in the upper mesosphere and lower thermosphere.…”

Radar observations of simultaneous traveling ionospheric disturbances and atmospheric gravity waves

“…The reason why TIDs are observed in the F region but not in the E region is the ion lifetime; in E region ion production and loss are too fast to allow significant compressions to persist. An exception is sporadic E layers or sodium layers which occasionally show oscillations caused by AGWs [ Miller and Smith , ; Bourdillon et al , ; Williams et al , ].…”