A lightning climatology of northeast India:1998-2007

About 55,000 lightning flashes were recorded by the Lightning Imaging Sensor (LIS) during the 10-year period (1998-2007) in northeast India (NEI) and were analyzed to study their total climatology, seasonal, annual and inter-annual variations. The results suggest that the western region of the northeast India is prone to a maximum amount of lightning activity and the northeast and eastern part is minimal in activity. The activity shifts west and east as the season advances. It is stagnant in the western and southwestern region in the last season of the year. The highest percentage of activity is observed during the pre-monsoon season. During the annual course the activity exhibits bimodal variation giving an average value of 8.4 flashes/pass. The time series analysis of the parameter shows that the activity over NEI shows a consistent increase from 1998 to 2002 and then onwards it shows a consistent decrease. The activity in December is a characteristic feature for the region. The highest magnitude of activity is noticed in the year 2001 with 20 flashes/pass

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 analysed 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 has pointed out their increasing trend of values with increment in the number of seeded traverses 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 clearly indicate the influence on microphysical growth and decay of such clouds that arises from hygroscopic seeding and not seeding 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 (asl) in the Pune area. It is believed that this study has provided adequate support in favour of the hypothesis of hygroscopic seeding of warm clouds

Markov chain models for pre-monsoon season thunderstorms over Pune

The probabilistic distribution of the thunderstorm phenomenon during the pre-monsoon season (1 March to 18 June) over Pune, a tropical Indian station, has been examined with the help of Markov chain models using daily thunderstorm data for a period of 11 years (1970-80). The data have also been tested using Akaike's information criterion. This test has clearly indicated that the first-order Markov chain model is the best fit model for thunderstorm forecasting, which has described the appropriate period (8 days) of occurrence of thunderstorm phenomenon over Pune. Further, the steady-state probabilities and mean recurrence time of thunderstorm days and non-thunderstorm days have also been calculated for the first- and second-order Markov chain models. These computations have revealed that the observed and theoretical values of steady-state probabilities are realistically matched

Diurnal variation of lightning activity over the Indian region

Satellite (LIS) based lightning flash grid (0.5° × 0.5°) data for the Indian land mass region covering from 8°–33°N and 73°–86°E for a period of 4 years (1998–2001) were used to study the diurnal variation with one hour time resolution. The analysis revealed that there exists a strong diurnal cycle in the lightning activity with a prominent peak around 1000 UTC. An examination of seasonal diurnal variation suggests that the lightning activity was found highest in premonsoon and lowest in the postmonsoon seaso

Diurnal and seasonal variations of space charge, electric field and cloud condensation nuclei in the lowest layer of the atmosphere

The association between the onset of the monsoon and the subsequent rainfall distribution over three west coast subdivision of of India has been examined for the 50 years period

Study of thunderstorm and rainfall activity over the Indian region

Thirty years (1951-1980) of mean monthly thunderstorms days (TS) and rainfall (RF) amounts for 260 Indian observatories spread uniformly over the country were used to obtain their monthly, seasonal and zonal percentage of occurrence from all India totals. The study has revealed that there is a time lag of one month in the occurrence of peak activity of TS and RF. Seasonal analysis of these two parameters suggest that rainfall yield associated with postmonsoon season TS seems to be higher than the premonsoon season. Six zone analysis of TS and RF has suggested that there exists a wide range of variation in both parameters month after month in that zones, but the 30 year mean percentage of occurrence seems to be more or less equal in magnitude in each zone

The cloud aerosol interaction and precipitation enhancement experiment (CAIPEEX): Overview and preliminary results

While the demand for enhancing rainfall through cloud seeding is strong and persistent in the country, considerable uncertainty exists on the success of such an endeavour at a given location. To understand the pathways of aerosol-cloud interaction through which this might be achieved, a national experiment named Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) in two phases, was carried out. The rationale of CAIPEEX, the strategy for conducting the experiment, data quality and potential for path-breaking science are described in this article. Pending completion of quality control and calibration of the CAIPEEX phase-II data, here we present some initial results of CAIPEEX phase-I aimed at documenting the prevailing microphysical characteristics of aerosols and clouds and associated environmental conditions over different regions of the country and under different monsoon conditions with the help of an instrumented research aircraft. First-time simultaneous observations of aerosol, cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) over the Ganges Valley during monsoon season show very high concentrations (> 1000 cm-3) of CCN at elevated layers. Observations of elevated layers with high aerosol concentration over the Gangetic valley extending up to 6 km and relatively less aerosol concentration in the boundary layer are also documented. We also present evidence of strong cloud- aerosol interaction in the moist environments with an increase in the cloud droplet effective radius. Our observations also show that pollution increases CDNC and the warm rain depth, and delays its initiation. The critical effective radius for warm rain initiation is found to be between 10 and 12 μm in the polluted clouds and it is between 12 and 14 μm in cleaner monsoon clouds

Variations in the atmospheric electric field at tropical station during 1930-1987

The variations noticed in the atmospheric electric field recorded at Pune (18°32′N, 73°51′E, 559 m ASL), a tropical inland station located in Deccan Plateau, India, during the period 1930–1987, have been examined in relation to the variations observed in the Angstrom turbidity coefficient (β) and selected meteorological parameters. The monthly and annual mean values of the atmospheric electric field, Angstrom turbidity coefficient (β), rainfall, temperature and relative humidity for the years 1930–1938, 1957–1958, 1964–1965, 1973–1974 and 1987 were considered in the study. The results of the above study indicated gradual increases in the atmospheric electric field over the period of study (1930–1987) which is statistically significant at less than 5%level. The increases noticed during different periods varied from 30 to 109%. The increase noticed during the period (1930–1938) and (1973–1974) was maximum (109%). The Angstrom turbidity coefficient also showed systematic increases during the period of study, which is consistent. The diurnal curve of the atmospheric electric field at the station by and large, showed a double oscillation, which is generally observed in the continental environments