Improving the Accuracy of Climate Models by Understanding the Role of Small Ice Crystals on Radiative Transfer


Quantifying the effects of small ice crystals on long and short wave radiation has been a controversial and unsolved problem in cloud microphysics for the last 20 years.  This information is needed to model cloud effects on radiative transfer and to better represent feedbacks in General Circulation Models (GCMs).  Aircraft data suggests that the contributions of small ice crystals to the total concentration could be overestimated since large ice crystals are shattered into several hundred smaller ones by the scattering probes used to measure small crystals.  A study by DOE scientists examined the impact of different assumptions about small ice crystal concentrations using the Community Climate Model (CAM-3).  These studies revealed that the formation of ice nuclei from water droplet evaporation can be used to explain why ice crystal concentrations are greater than the concentration of particles that provide the nucleation for the growth of ice concentrations.  The data collected has contributed to improved algorithms for satellite and ground lidar observations.  Understanding these processes will lead to better representation of cloud processes and more accurate predictive capabilities of climate models particularly relating to cloud processes.


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