K. S. V. Subbarao

Small-scale (∼3 m) E region irregularities at and off the magnetic equator

VHF backscatter radar observations at and off the magnetic equator (Trivandrum and Gadanki, respectively) have been analyzed to study the small-scale (∼3 m) irregularities at E region altitudes. The Doppler spectra observed at Gadanki invariably resemble type 2 (gradient drift instability) Doppler spectra in contrast to the spectra at Trivandrum where both type 1 and type 2 occur. The type 2 irregularities (at Gadanki) are attributed to the presence of steep (vertical) electron density gradients, which are necessary for the growth of gradient drift instabilities at the off magnetic equatorial latitude of Gadanki. The observed irregularity drifts at lower altitudes ( 101 km) to magnetic field line-linked F region electric fields at the magnetic equator.

Post-sunset F-region vertical velocity variations at magnetic equator

The vertical drift velocity of the F-region in the post-sunset period at the magnetic equatorial station Trivandrum has been studied using a HF phase path sounder. The study revealed the presence of quasi-periodic fluctuations with periods in the range 4 30 min superposed on a steady vertical motion as a regular feature of the equatorial F-region in the post-sunset period. The fluctuations in the vertical velocity arc attributed to the east west electric field fluctuations generated by internal atmospheric gravity waves. The vertical velocity fluctuations can provide the necessary seed perturbations for the growth of equatorial spread-F irregularities.

Equatorial E and F region zonal electric fields in the postsunset period

The E and F region eastward electric fields in the postsunset period obtained from VHF backscatter radar and ionosonde observations respectively at the magnetic equatorial station at Trivandrum are compared. It is found that the F region eastward electric field is greater than the E region electric field indicating latitudinal gradients in the E region electric field.

Response of night-time equatorial F-region to magnetic disturbances

Abstract The response of the equatorial night-time F -region to magnetic stormtime disturbances has been examined using mainly ionograms recorded at Trivandrum and magnetograms recorded at high, middle and low latitudes during the magnetic storm of 23–26 November 1986. The analysis revealed a close coupling between the equatorial F -region and high latitude magnetic field disturbances originating in solar wind-magnetosphere interactions. The presence of spread- F on ionograms during this period is found to be consistent with the Rayleigh-Taylor instability mechanism for the growth of the irregularities.

Distortions in the height structure of the equatorial electrojet during counter electrojet events

This paper presents simultaneous observations made near the magnetic equator during counter electrojet events using a coherent VHF backscattcr radar, magnetometer and digital ionosonde to understand the physical processes that generate the counter electrojet conditions. The VHF backscatter radar gives the height structure of the drift velocity or the ionization irregularities, the equatorial electrojet current variations are obtained from the magnetometer and the digital ionosonde provides the presence of blanketing E-layers at the F-region heights which give rise to the backscatter signals. These observations have provided direct experimental evidence for the theoretically predicted distortions in the height structure of the polarization electric field in the equatorial electrojet due to the local effects of shearing zonal neutral winds.

Night-time equatorial F-region zonal plasma drifts from VHF backscatter radar observations

Abstract Night-time equatorial F -region plasma drifts are deduced from VHF backscatter radar observations of F -region irregularities. The zonal drifts reveal large vertical shears. It is found that the irregularity polarization electric field (though small compared to the ambient field) is significant in affecting the observed zonal drifts.