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A. Mary Selvam
,
G. K. Manohar
,
L. T. Khemani
, and
Bh V. Ramana Murty

Abstract

Simultaneous measurements of raindrop charge, atmospheric electric field and rain intensity were made at Poona using fast response, continuous recording surface instruments during four types of rain: pre-monsoon (thunderstorm rain), monsoon rain type I (tight intermittent rain), monsoon rain type II (heavy continuous rain) and post-monsoon (thunderstorm rain). Measurements were also made of the conductivity of rainwater samples collected during the monsoon season. On some days of this period data on cloud thickness as obtained from the aircraft flights in the region were also available.

The electric field associated with negatively charged raindrops was less negative than that associated with positively charged drops. The raindrop charge spectrum showed different characteristics during the four types of rain studied. It was broadest during the pre-monsoon rain when the convective activity was a maximum. It followed a log-normal distribution during the monsoon rain type I and it was peaked and skewed to the positive side during the monsoon rain type II. Rainwater conductivity was inversely correlated with the cloud vertical thickness. The results of the present study support the warm cloud charge generation mechanism proposed by Takahashi (1974).

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B. K. Mukherjee
,
K. Indira
,
R. S. Reddy
, and
Bh V. Ramana Murty

Abstract

In an earlier study a relationship was pointed out between phases of the quasi-biennial oscillation (QBO) in the lower stratospheric (30 mb) zonal wind and percentage departures of summer monsoon rainfall of India. That study was based on analysis of wind data for Thumba (8°32′N, 76°52′E) and the rainfall data for India for a short-period (1971–76). Wind data for Balboa (9°N, 80°W), which is also an equatorial station, and rainfall activity over India are now examined for a longer period (1951–82). About 15% of the variability in rainfall over India during the summer monsoon is associated with the pattern of the QBO.

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K. R. Biswas
,
R. K. Kapoor
,
K. K. Kanuga
, and
Bh V. Ramana Murty

Abstract

An experiment on artificial stimulation of rain using a warm cloud seeding technique was undertaken in three nearby climatologically similar regions, Delhi, Agra and Jaipur in northwest India. Analysis of the data from 18 experiment-seasons has suggested a positive trend of the result, which is found significant by statistical tests.

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A. S. Ramachandra Murty
,
A. M. Selvam
,
R. Vijayakumar
,
S. K. Paul
, and
Bh V. Ramana Murty

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 volume diameter and liquid water content were recorded.

The time variations of electrical and microphysical parameters following seeding are in general within the range of their natural variability.

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