VLF observations of ionospheric disturbances in association with TLEs from the EuroSprite-2007 campaign

Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45 degrees N, 3.28 degrees E) and Sebha, Libya (27.02 degrees N, 14.26 degrees E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite-2007 campaign a number of Transient Luminous Events (TLEs) were captured over the Mediterranean Sea by cameras at Pic du Midi (42.94 degrees N, 0.14 degrees E) and at Centre de Recherches Atmospheriques (CRA) in southwestern France (43.13 degrees N, 0.37 degrees E). The cameras observations are compared to collected VLF AWESOME data. We consider early VLF perturbations observed on 12-13, 17-18 October and 17-18 December, 2007. The data from the two VLF receivers confirm the association between TLEs and early VLF signal perturbations with the perturbations amplitudes dependent on the observation configuration i.e. whether the TLE is near the receiver, near the transmitter, or far from both and the scattering process. The results also reveal that the early VLF perturbations can occur in the absence of a TLE.