POSITIVE AND NEGATIVE-ION DENSITIES AND MOBILITIES IN THE MIDDLE ATMOSPHERE OVER INDIA - ROCKET MEASUREMENTS

This paper discusses the results from four rocket experiments conducte d from Thumba, India, during the Indian Middle Atmosphere programme (I MAP). These rockets carried instrumented Gerdien Condenser payloads to measure ion densities and their mobilities. In the first two flights only positive ion measurements were attempted while the other two meas ured both positive and negative ion values. The results show that the positive ion density profiles go through a minimum around 62 km, as ex pected from the ion production models for this region. The ion density distribution is a function of solar zenith angle. An asymmetry with r espect to noon is seen in these measurements, which is not expected th eoretically. The positive ion mobilities indicate the ions to be water clusters, of the type H+ (H2O)n with n = 2 or 3, similar to the earli er reported ones. The negative ion density profile exhibits a maximum around 85 km, which is not predicted by the currently available ion de nsity models and theories of D-region ionisation processes. The negati ve ion mobility measurements show the ions to have a mass range of 30- 60 amu, which is within the range of mass spectrometric measurements.