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Journey to the centre of the cloud for better climate prediction

Dr Sachin Gunthe and his team at IIT Madras are busy measuring the tiny particles of aerosols on which water vapor condenses to form clouds. The particles, technically called cloud condensation nuclei (CCN) play an important role in the formation of clouds and precipitation, and influence atmospheric chemistry and physics, the hydrological cycle and climate. The scientists are measuring and modeling Cloud Condensation Nuclei (CCN) in Indian continental and marine environment for acquiring high-quality field data during different levels of manmade pollution at certain locations spanning three seasons over one year. The team is also developing methods for efficient description and prediction of CCN properties and concentrations.

The paucity of such observations over India is highly contradictory to its global relevance as major source of aerosol particles and their role in radiation budget, precipitation, and hydrological cycle. Precise measurement of CCN will help their accurate representation in climate models. This will help better climate predictions through assessment of response of cloud characteristics and rainfall processes to increasing anthropogenic aerosol concentrations. Atmospheric and climate scientists consider inaccurate CCN data as one of the largest uncertainties in the current understanding of the climate change. 

One of the crucial challenges is to determine the ability of aerosol particles to act as CCN under relevant atmospheric conditions, an issue that has received increasing attention over the past years.Elevated concentrations of CCN (in a sense of aerosols) tend to increase the concentration and reduce the size of droplets in the cloud. Apart from changing the optical properties and the radiative effects of clouds on climate, this may lead to the suppression of precipitation in the shallow and short lived clouds and more precipitation in deep convective clouds.Substantial progress has been made in recent years in understanding the source processes that produce cloud-active aerosols, the properties that enable aerosols to act as CCN, the effects of aerosols on cloud physics and precipitation, and the consequences for the climate system. In order to incorporate the effects of CCN in meteorological models at all scales, from large eddy simulation (LES) to global climate models (GCM), knowledge of the spatial and temporal distribution of CCN in the atmosphere is essential. 

Several studies have reported CCN measurements from various regions around the world.The actual influence and relative importance of aerosol size distribution, chemical composition, and mixing state on the variability and predictability of CCN concentrations are still under study.As compared to the global scenario, observations are even more important over India as due to three distinct meteorological seasons aerosol sources and properties are distinctly different; decisively during monsoon season. This study aims to develop robust methods for calibration of CCN counter obtain high-quality CCN data in either high altitude pristine or urban marine region during distinct seasons for full one year or longer and develop application, and substantiation of different formalism for efficient description and prediction of CCN properties and concentration under different environmental conditions. 

“We are measuring cloud condensation nuclei (CCN) which play an important role in the formation of clouds & precipitation, and influence the hydrological cycle and climate”