S. S. Kandalgaonkar

Thunderstorm activity over India and the Indian southwest monsoon

This paper describes the results of monthly latitudinal (8°-30° N) and latitude belts (8°-10°, 10°-15°, 15°-20°, 20°-25°, and 25°-30°N) averaged seasonal thunderstorm activity over India by using monthly data from a large number of Indian stations from 1970 to 1980. The latitudinal variation in the premonsoon (March-April-May) and monsoon season (June-September) months is described and the results are discussed. An examination of the seasonal thunderstorm day activity in the first four belts indicated systematic changes in their signals of semiannual oscillation. These changes are noted to be a function of latitude and season and appear to be consistent with the seasonal migration of the Intertropical Convergence Zone and solar heating of the Indian landmass. We compare the thunderstorm day activity with the monthly mean maximum values of the surface wet-bulb (Tw) temperatures in the five latitude belts over the Indian region. By using rainfall data for the same period of study, the relationship between seasonal rainfall and number of thunderstorm days over the 11 year period is examined. The results of variation of the ratio of monthly rainfall to thunderstorm days (RTR) during different phases of the southwest monsoon are also presented. Results of the monthly mean electrical conditions of mesoscale and isolated deep convective storms at Pune are summarized. It is noted that the electrification of the premonsoon season thunderstorms dominated by a factor of 3-4 over the monsoon ones. We have examined at length the possible influence of the El Nino on the occurrence and electrification of thunderstorms over the Indian region.

Impact of a total solar eclipse on surface atmospheric electricity

A study of the impact of a total solar eclipse (TSE) on surface atmospheric electricity was made using observations of surface electrical potential gradient, conductivity, and boundary layer parameters recorded during the TSE of February 16, 1980, and on a control day at Raichur. The study showed that with the progressing of the eclipse, as a consequence of inhibited convection, the responses of turbulent mixing in the boundary layer near the ground exhibited diminution and subsequent restoration, respectively. During the next 45 min after the totality, when the surface layer remained stably stratified, the diminution in the potential gradient and the increase in the conductivity was maximum; this was about 60% and 200%, respectively, of their corresponding control day values. This result is in very good agreement with most earlier studies of solar eclipses. The study of the impact of the TSE during 3–4 hours of posteclipse showed significant cooling (∼3°C) of the entire surface air layer and a considerable drop in wind speed over the stretch (1130 km×120 km) of the totality-occupied land region. This significant and systematic phenomenon was responsible for setting up a land-sea breezelike circulation, that is, subsidence/downward air motion over the totality-occupied land region and upward over the noneclipsed land across the totality stretch. This resulted in a considerable aerosol-induced reduction in conductivity and about 5 to 8 times increase in potential gradient during the 3–4 hours of posteclipse. This response of the atmospheric electricity parameters was unlike that observed on the normal days.

Cloud liquid water content responses to hygroscopic seeding of warm clouds

The cloud liquid water content (CLWC) data in time and space from a total of 96 pairs of target (T) and control (C) experiments were analyzed in this study to compare the responses of CLWC to hygroscopic seeding of warm clouds. Our results of various approaches taken for this analysis have indicated significant modifications in the CLWC for the T clouds as against C clouds. Analysis of changes in CLWC in the T clouds after and before seeding have pointed out their increasing trend of values with increment in the number of seeded traverse in most cases. These results have shown that CLWC in the T clouds increases following the seeding treatment in the range 9–26%. Similar comparisons in the C clouds have indicated obvious diminution in CLWC that lies in the range 5–11%. These results are the clear indications of influence on microphysical growth and decay of such clouds that arises from hygroscopic seeding and not seeding respectively of warm clouds. Analysis of spatial responses of CLWC to seeding has shown that the optimum effect of seeding may be achieved for a suitable cloud in the altitude range 5750–6250 ft. (a.s.l.) in the Pune area. It is believed that this study has provided adequate support in favor of the hypothesis of hygroscopic seeding of warm clouds.