An RH-560 rocket¯ight 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 ®eld 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 ®eld¯uctuations are presented here. Scale sizes of electric ®eld¯uctuations were measured in the vertical direction

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... y. 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 ®eld irregularities (at 165 km and 168 km), in the intermediate-scale size range, observed during this¯ight, 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 ®eld¯uctuations 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 ®eld¯uctuations below the base of the F region (210±257 km) showed a tendency to become slightly¯atter (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 ®eld¯uctuations suggests the presence of a sheared¯ow of current in 160±330 km region.