Effects of Clouds on

All the calculated actinic fluxes discussed so far refer to a cloudless sky. The effects of clouds are 

TABLE 3.13 Percentage Change of Calculated Actinic Flux at the Earth s Surface Using Best Estimate Albedos as a Function of Solar Zenith Angle and Selected Wavelengths When Model Aerosol Concentrations Are Either Zero or Doubled  

FIGURE 3.25 Calculated ratio of transmission of UV and visible light to the earth s surface in the presence of aerosol particles compared to that with no aerosol particles for typical continental aerosol particles at (a) average summer RH and (b) high summer RH and for urban aerosol particles with (c) average RH and (d) high RH. (Adapted from Erlick and Frederick, 1998.) 

TABLE 3.14 Calculated Enhancements or Depressions of Actinic Fluxes above and below Perfectly Light-Diffusing Clouds of Different Optical Depths  

Conditions Cloud optical depth Above cloud Below cloud 

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Walcek, C. J., W. R. Stockwell, and J. S. Chang, Theoretical Estimates of the Dynamic, Radiative, and Chemical Effects of Clouds on Tropospheric Trace Gases, Atmos. Res., 25, 53-69 (1990). 

An increase in aerosol particles that can act as CCN can increase the number of cloud droplets and their size distribution, both of which can affect the light scattering properties of clouds and hence climate. We first briefly discuss the effects of clouds on climate and then the potential impacts of anthropogenic aerosols on the formation and properties of clouds. 

FIGURE 14.50 Schematic of energy balance in warm pool in western Pacific Ocean used to deduce the net effect of clouds on solar radiation. All numbers are given in W m2 (adapted from Ramanathan et at., 1995). 

Hartmann, D. L., Radiative Effects of Clouds on Earth s Climate , in Aerosol-Cloud-Climate Interactions (P. V. Hobbs, Ed.), pp. 151-173, Academic Press, San Diego, 1993. 

Liao, H., and J. H. Seinfeld, Effect of Clouds on Direct Aerosol Radiative Forcing of Climate, J. Geophys. Res., 103, 3781-3788... 

Clouds The discussion of solar UV variability in proceeding paragraphs has assumed cloud free conditions. However, in most parts of the world this is the exception, usually there are either broken cloud fields or a more or less homogeneous cloud cover. In general, clouds reduce solar radiation, but the amount of reduction is extremely variable due to the variable nature of clouds. For the estimation of the effect of clouds on solar irradiance, the most important par-... 

CLOUD PHYSICS is a discipline within meteorology concerned with the properties of atmospheric clouds and the processes that operate within them, the diversity of phenomena intrinsic to natmal clouds, the interactions of clouds with the atmosphere, and the effects of clouds on climate. The discipline covers the range from single clouds to large-scale weather systems and even weather on a global scale. 

Cloud physicists draw on the well-developed sciences of chemistry, physics, and fluid dynamics to study these phenomena. Such topics as the thermodynamics of moist air, the physics of the growth of water droplets and ice particles, radiation, effects of clouds on climate, electrification, and chemical conversion processes are all part of this discipline. Major research tools include computers for numerical simulation and aircraft and radars for observation, along with wind firrmels and cold rooms for the study of the properties of cloud and precipitation particles. 

Two clond types, stratocnmnlns and cirras, cover the greatest portion of the earth s snrface and are therefore the most important clond types from the standpoint of the effect of clouds on climate. The focused observations reveal that stratocumulus have a net cooling effect on the planet. However, the net effect of cirrus on climate is still nnclear. The details of the cirrus cloud microphysics, including the mean, maximum, and effective (radiatively important) particle size, crystal shape, temperature, and height in the atmosphere, affect their radiative properties. This is an active area of research. 

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