Simultaneous observations of E-region irregularities by ground-based and rocket-borne techniques

During the Energy Budget Campaign (November–December 1980) E-region irregularities were observed under various geomagnetic conditions. Under disturbed conditions on the night of 30 Nov./1 Dec. the SAFARI auroral radar detected 10m wavelength irregularities north of Lycksele and measured their south to north phase velocity. Simultaneous observations of 1 m irregularities using one of the STARE auroral radars provided measurements of their SW-NE phase velocity. Associated rocket-borne measurements of electron densities over Kiruna using Langmuir probes showed vertical/temporal structure indicating irregularities in ionisation between 90 and 110 km, having a wide range of scale sizes. The power spectra of electron current variability were ‘white’ above about 90 km. 100 min later irregularities in the electric field were detected below 110 km by an E-field probe and an associated TMA release indicated the presence of turbulent regions in the neutral atmosphere between 90 and 105 km. A separate set of rocket-borne measurements under moderately disturbed conditions on the night of 15–16 November 1980 showed the presence of VLF electric fields in the frequency bands 168–5519 Hz at altitudes between 103 and 145 km at Kiruna. On the same occasion measurements of ion density fluctuations were obtained using a rocket-borne positive ion probe at Andøya. Power spectra derived from both these experiments have spectral indices near − 5 3 at those heights where the irregularities were strong. Although this would be consistent with the generation of plasma inhomogeneities by neutral air turbulence below about 95 km, these observations were at too great an altitude for this mechanism to be effective. The results are therefore tentatively interpreted as due to the decay of ion acoustic waves generated by plasma instabilities in the auroral electrojet.