Am Selvam

Electrical and microphysical measurements in warm cumulus clouds before and after seeding

Abstract Electrical and microphysical measurements were made in warm maritime and inland cumulus clouds, before and after seeding, by repeated aircraft penetrations at a single level, a few hundred meters above cloud base. Such measurements were also made in non-seeded clouds by single penetrations during transient flights. The electric field initially was negative in the maritime clouds which developed rain. In the cloud case which dissipated without rain it was initially positive. The field showed sign reversal with time, occasionally preceded by intensification, in all maritime clouds. The field initially was positive in inland clouds. It showed no time variation except in one cloud case where both positive and negative fields were recorded during the period of heavy rain. The droplet charge, droplet median volume diameter and liquid water content showed no marked time variation in either maritime or inland clouds. However, in the cloud case which developed heavy rain marked increases in droplet median...

Rainfall variations around a thermal power station

Abstract Rainfall data of Neyveli thermal power station and of stations within 100 km around were examined, after eliminating the secular trends for the period 1958–1974. The analysis suggested that, with respect to nearby stations in the distance range 12–25 km, rainfall at a gauge 1 km from the power station increased in the last 6 y of the period by over 25%.

Summary of Observations Indicating Dynamic Effect of Salt Seeding in Warm Cumulus Clouds

Abstract Measurements of cloud liquid water content and temperature were made along with visual observations in 32 traverses carried out in six warm cumulus clouds subjected to salt seeding. The results showed (i) a rise, of 1–2°C, in temperature, (ii) an increase, sometimes exceeding 200%, in liquid water content, and (iii) vertical growth, up to 60%, in seeded clouds which developed rain. The features noticed could be due to the possible dynamic effect of salt seeding in warm clouds.

Airborne electrical and microphysical observations in the environment of a thermal power station

Abstract Using aircraft, electrical and microphysical observations were made, on a few occasions within 15 km upwind and downwind of a thermal power station under cloud-free and in-cloud conditions. The values of the parameters measured were found to be systematically higher in the downwind region than in the upwind. Under cloud-free conditions, the concentrations of the cloud condensation nuclei and the computed cloud droplets were higher up to two times, the atmospheric electric field was higher up to seven times and the air temperature up to 2.3°C. Under in-cloud conditions, the values of the electric field and droplet charge were higher up to two times, the measured droplet concentration was higher by one and a half times, the cloud air temperature up to 1.5°C and the liquid water content up to four times. However, these differences were in general within the spatial variability found outside the plume affected area.

Characteristics of cloud drop spectra in tropical warm clouds

Characteristics of cloud drop spectra were studied using 400 samples obtained from 120 warm cumulus clouds formed during the summer monsoon season.The total concentration of cloud drops (NT) varied from 384 to 884 cm−3 and the maximum concentration was observed in the layer below the cloud-top. The width of the drop spectrum was broader in the cloud-base region and in the region below the cloud-top. The spectrum was multimodal at all levels except in the cloud-top region where it was unimodal. The concentration of drops with diameter greater than 50 μm (NL) varied from 0.0 to 0.674 cm−3.NL was larger in the cloud-base region.NL decreased with height up to the middle level and thereafter showed an increase. In the cloud-top region no large drops were present. The computed values of the liquid water varied between 0.132 and 0.536 g m−3 and the mean volume diameter (MVD) varied between 8.1 and 12.0 μm. The LWC and MVD showed a decrease with height except in the middle region of the cloud where the values were higher than the adjacent levels. The dispersion of the cloud drops was lower (0.65) in the cloud-top region and higher (1.01) in the cloud-base region.The observed cloud microphysical characteristics were attributed to vertical mixing in clouds induced by the cloud-top gravity oscillations (buoyancy oscillations) generated by the intensification of turbulent eddies due to the buoyant production of energy by the microscale-fractional-condensation (MFC) in turbulent eddies.

Universal Inverse Power-Law Distribution for Fractal Fluctuations in Dynamical Systems: Applications for Predictability of Inter-Annual Variability of Indian and USA Region Rainfall

Dynamical systems in nature exhibit self-similar fractal space–time fluctuations on all scales indicating long-range correlations and, therefore, the statistical normal distribution with implicit assumption of independence, fixed mean and standard deviation cannot be used for description and quantification of fractal data sets. The author has developed a general systems theory based on classical statistical physics for fractal fluctuations which predicts the following. (1) The fractal fluctuations signify an underlying eddy continuum, the larger eddies being the integrated mean of enclosed smaller-scale fluctuations. (2) The probability distribution of eddy amplitudes and the variance (square of eddy amplitude) spectrum of fractal fluctuations follow the universal Boltzmann inverse power law expressed as a function of the golden mean. (3) Fractal fluctuations are signatures of quantum-like chaos since the additive amplitudes of eddies when squared represent probability densities analogous to the sub-atomic dynamics of quantum systems such as the photon or electron. (4) The model predicted distribution is very close to statistical normal distribution for moderate events within two standard deviations from the mean but exhibits a fat long tail that are associated with hazardous extreme events. Continuous periodogram power spectral analyses of available GHCN annual total rainfall time series for the period 1900–2008 for Indian and USA stations show that the power spectra and the corresponding probability distributions follow model predicted universal inverse power law form signifying an eddy continuum structure underlying the observed inter-annual variability of rainfall. On a global scale, man-made greenhouse gas related atmospheric warming would result in intensification of natural climate variability, seen immediately in high frequency fluctuations such as QBO and ENSO and even shorter timescales. Model concepts and results of analyses are discussed with reference to possible prediction of climate change. Model concepts, if correct, rule out unambiguously, linear trends in climate. Climate change will only be manifested as increase or decrease in the natural variability. However, more stringent tests of model concepts and predictions are required before applications to such an important issue as climate change. Observations and simulations with climate models show that precipitation extremes intensify in response to a warming climate (O’Gorman in Curr Clim Change Rep 1:49–59, 2015).

Geostrophic balance over the Arabian Sea and Bay of Bengal regions

Geostrophic balance over the Arabian Sea and Bay of Bengal regions has been studied using the wind data obtained from the AVRO (HS-748) aircraft during the FGGE-MONEX-79.In the Arabian Sea and the Bay of Bengal regions, the observed wind south of 20°N was found to be sub-geostrophic. In the Arabian Sea region the departure at 1500 m was 75–95% and at 3050 m it was 60–65%. In the Bay of Bengal region the departure was 85–95%. In a few cases north of 20°N the observed winds at 3050 m were found to be super-geostrophic in the regions of enhanced monsoon activity, cyclonic circulation reaching up to 6000 m and in the region of monsoon trough.