BALLOON MEASUREMENTS OF STRATOSPHERIC ION CONDUCTIVITIES OVER THE TROPICS

Conductivity measurements of negative and positive ions were made form about 20 to 35 km by two identical balloon-borne spherical probes at Hyderabad (17.5 N, 78.6 E), India on 22 April 1989 and 22 December 199 0. One balloon was launched at 0158 h IST (Indian Standard Time) which reached its ceiling around 0330 h IST. After that time, it floated fo r about 3 h, 1.5 h before sunrise and 1.5 h after sunrise. Thus it gav e data for both day- and night-time conditions at float altitude. The other balloon was launched at 0535 h IST. It gave data for daytime onl y. Several interesting results have been obtained at the float altitud es. During the night, in the flight of 22 April 1989 the conductivity values of positive ions were found to be about 1.5 times those of nega tive ions at the float altitude. During the day, in the flight of 22 A pril 1989, the positive ion conductivity values were found to increase with the increase of solar elevation angle at around 37.5 km altitude . The negative ion conductivity values, however, did not show any day night variation. In the flight of 22 December 1990, these features wer e not seen. Instead, a pocket was found where conductivity values were very high (of the order of 10(-11) mho m-1) at an altitude of about 3 2.5 km. Also in this flight, the positive ion conductivity was always found to be approximately equal to that of the negative ion conductivi ty.