Structure of the equatorial lower ionosphere from the Thumba Langmuir probe experiments

A Langmuir probe designed and developed at the Physical Research Laboratory, Ahmedabad has been used on a variety of rockets since 1966 from the Thumba Equatorial Rocket Launching Station, TERLS (8°31'N, 76°52'E, dip.lat. 0°47'S) to study the structure of the equatorial lower ionosphere. Good quality data is available from a set of twenty five rocket flights conducted during the period 1966 to 1978. This data has been obtained using a single standardised instrument at a single location and using a uniform procedure for data reading and analysis, and adopting a calibration procedure to convert the measured probe currents into electron densities which involves a height dependent calibration factor. The data has been used to establish the gross features of the equatorial lower ionosphere under daytime, night time, morning twilight and evening twilight periods.