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

Abstract

[1] 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.

Characteristics of the equatorial plasma drifts as obtained by using Canadian Doppler ionosonde over southern tip of India

“…Tiwari et al . [] have compared the Doppler drift velocities by using simultaneous HF and VHF observations over Trivandrum and suggested that Doppler velocities could be on the order of 150–200 m/s in the E region, which is in agreement with our zonal drifts. Further, they showed that these drift velocities are scale size‐dependant, which means that drift varies with scale size of the probing wavelength.…”

A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80–100 km) region

“…So, there are two distinct regions, which are contributing to the received echoes, one is below about 88 km and the other one is above that height. Similar types of height variation of echoes are reported for the HF radar also by Tiwari et al [2003] over Trivandrum, India. Since the MF radar is located near geomagnetic dip equatorial region, the latter height region is located in the bottom tail of the EEJ region and the signals belonging to this region are often primarily associated with the unstable plasma waves like type II irregularities because of gradient drift plasma instability [ Fejer and Kelley , 1980].…”

East‐west asymmetries of the equatorial electrojet 8.3 m type‐2 echoes observed over Trivandrum and a possible explanation

“…Accordingly, spectral width provides information on the turbulent flow field in the medium. Relationship between spectral width and SNR of the type‐2 echoes as a function of height has been reported earlier [ Tiwari et al , 2003]. It was shown that at lower altitudes, there exists a linear relationship between the two parameters and hence the asymmetry in spectral width is inherent to the asymmetry in the signal strength.…”