Abstract
An RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip 14°N) along with other experiments, as a part of equatorial spread F (ESF) campaign, to study the nature of irregularities in electric field and electron density. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of vertical and horizontal electric field fluctuations are presented here. Scale sizes of electric field fluctuations were measured in the vertical direction only. Strong ESF irregularities were observed in three regions, viz., 160-190 km, 210-257 km and 290-330 km. Some of the valley region vertical electric field irregularities (at 165 km and 168 km), in the intermediate-scale size range, observed during this flight, show spectral peak at kilometer scales and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of a new type. Scale sizes of vertical electric field fluctuations showed a decrease with increasing altitude. The most prominent scales were of the order of a few kilometers around 170 km and a few hundred meters around 310 km. Spectra of intermediate-scale vertical electric field fluctuations below the base of the F region (210-257 km) showed a tendency to become slightly flatter (spectral index n = -2.1 ± 0.7) as compared to the valley region (n = -3.6 ± 0.8) and the region below the F peak (n = -2.8 ± 0.5). Correlation analysis of the electron density and vertical electric field fluctuations suggests the presence of a sheared flow of current in 160-330 km region.Keywords: Ionosphere (Electric fields and currents; ionospheric irregularities); Radio science (ionospheric physics)
Highlights
It is very well known that the ionospheric electric ®eld plays an important role in low-latitude electrodynamics
From the spectral characteristics of electric ®eld they suggested that the medium-scale gravity waves could be a source for the observeductuations of zonal ®elds in the post-sunset F-region
The vertical electric ®eld exhibits the ®rst major peak at 135 km. This peak is co-located with a very sharp layer of electron density wherein the electron density increased by a factor of 30 in a vertical extent of 5 km (Raizada and Sinha, 1999)
Summary
It is very well known that the ionospheric electric ®eld plays an important role in low-latitude electrodynamics. Raizada: First in situ measurement of electric ®elductuations latitudes are coherent for the temporal scales of the order of few tens of minutes They attributed the observeductuations in E and F-region electric ®elds to medium-scale gravity waves. Electric ®eld measurements in the equatorial regions have been carried out using both ground-based and in situ techniques. The ground-based technique which has yielded very signi®cant data on the F region electric ®elds is the 50 MHz incoherent scatter radar at Jicamarca In this technique, electric ®elds are derived from the drifts, which are measured directly by using two radar beams perpendicular to the geomagnetic ®eld at F region altitudes (Woodman, 1970; Balsley, 1975; Woodman et al, 1977; Fejer et al, 1979, 1991; Kudeki et al, 1999). By mounting the conductor pairs in suitable directions, the electric ®elductuations in dierent directions can be measured This method provides measurement of electric ®elductuations in the rocket frame of reference. The eect of contact potential dierence between two sensors must be kept at minimum by applying proper conducting coating on all sensors
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