Simultaneous radar observations of the electrojet plasma irregularities at 18 and 54.95 MHz over Trivandrum, India

Abstract

Observations of equatorial electrojet (EEJ) plasma irregularities made using a newly established 18 MHz coherent backscatter radar at Trivandrum are presented. Also presented are the simultaneous observations of the electrojet plasma irregularities made using a collocated 54.95 MHz radar. These correspond to 8.3 m and 2.7 m scale irregularities, respectively. The statistics of spectral parameters observed at the two scale sizes are also presented and compared in detail. An interesting and new aspect of these observations is that the 8.3 m irregularities have significant anisotropy in the plane perpendicular to magnetic field in contrast to that reported for 3 m irregularities. While type-1 and type-2 spectra could be distinctly observed at 2.7 m, it is rather difficult to distinguish at 8.3 m. The type-2 velocities for the two scale sizes are pretty close to each other below 102 km, but the velocities for 8.3 m are less than that of 2.7 m above. Type-1 velocities are quite close to each other only at altitudes of the peak electrojet when clear type-1 echoes are observed. Spectral widths are remarkably different at the two scale sizes. The ratio of spectral width corresponding to 2.7 m to that at 8.3 m is close to 1.4, quite similar to that reported earlier from Jicamarca. The observed difference in the velocities and spectral width at the two scale sizes are attributed to the effects of anomalous collision of electrons caused by the large-scale turbulence present in the EEJ. The above observations are found to be consistent with the EEJ instability theories and related simulation works.