FIRST VHF RADAR OBSERVATIONS OF TROPICAL LATITUDE E-REGION FIELD-ALIGNED IRREGULARITIES

Indian MST radar at Gadanki (13.5 degrees N, 79.2 degrees E, 12.5 degr ees dip) was operated during July/August 1994, to observe the 3 - m sc ale size field aligned irregularities associated with the lower E regi on. Irregularity structure was studied by using height - time variatio n of the echo intensity and weighted mean Doppler velocity. In this pa per results of three diurnal cycles of observation are presented. Fiel d perpendicular echoes were observed both during daytime and nighttime . A layered irregularity structure extending down to altitude below 86 Km was seen during the nighttime. The daytime structure showed a narr ow echoing region with significant downward slope. Doppler velocity wa s in the range of 20 - 50 ms(-1), both during day and night and was, i n general, consistent with the slope of scattering structure observed in the height - time - intensity plots.