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In this paper, we present observations of equatorial spread F (ESF) irregularities madeusing a newly installed 18MHz radar located at Trivandrum. We characterize the morphologyand the spectral parameters of the 8.3-m ESF irregularities which are found to be remarkablydifferent from that observed so extensively at the 3-m scale size. We also present statistical resultsof the irregularities in the form of percentage occurrence of the echoes and spectral parameters(SNR, Doppler velocity, Spectral width). The Doppler spectra are narrower, less structured andless variable in time as compared to those observed for 3-m scale size. We have never observedthe ESF irregularity velocities to be supersonic here unlike those at Jicamarca, and thevelocities are found to be within ±200ms–1. The spectral widths are found to beless than 150ms–1. Hence, the velocities and spectral width both are smaller than those reported for 3-m scalesize. The velocities and spectral widths are further found to be much smaller than those of theAmerican sector. These observations are compared with those reported elsewhere anddiscussed in the light of present understanding on the ESF irregularities at differentwavelengths. Key words. Ionoshphere (equatorial ionosphere, plasmawaves and instabilities; ionospheric irregularities

Radar Observations of 8.3-m scale equatorial spread F irregularities over Trivandrum