A multi-year research observational campaign
entitled, “Cloud Aerosol Interaction and Precipitation Enhancement
(CAIPEEX)” was conducted by the Indian Institute of Tropical Meteorology
(IITM), Pune during the period 2009-2011 over different parts of the
country. The objectives of the program were: (1) to understand the role
of aerosols in the rainfall processes in the clouds and (2) to carry out
cloud seeding experiments in research mode for rain enhancements using
modern techniques.
During the period May to September 2009, the cloud and aerosol
observations were conducted over different parts of country using
instrumented aircraft Total 220 hrs of flying was done. In the monsoon
and post-monsoon seasons of 2010 and 2011, the cloud seeding experiments
were conducted over the rain-shadow areas of peninsular India from
Hyderabad base. Total 200 and 250 hours of flying was done in the years
2010 and 2011 respectively.
Modern techniques such as (1) hired instrumented aircraft for
measuring the atmospheric state parameters, aerosols and cloud
microphysical parameters (2) equipped for seeding by flares and salt
powder, (3) radar for monitoring the potential clouds, (4) pilot to
ground connectivity and internet connectivity for real time transfer of
data, (5) half hourly INSAT satellite data, weather data from IMD sites
(6) high resolution weather models for the forecasting etc., were used
in the program.
The Indian rainfall shows different types of trends over different
regions and over different time periods. The studies carried out so
far have suggested that there is increasing trend in the extreme
rainfall events (>10cm/day) and decreasing trend in the moderate
(2-5cm/day) and low rainfall events (<2cm/day) over central India. It
is also established that there is approximately a natural 30-year
cyclicity in the monsoon rainfall. Under such a decreasing phase of
monsoon rainfall that is persisting for the recent three and half
decades, a decreasing trend of monsoon rainfall is also persisting.
Additionally, the factors like global warming and increasing
loading of aerosols over India have established potential to modulate
the natural rainfall variability to certain extent as a part of short
term variability.
