Radiation radiative forcing

It has become clear only recently that the atmospheric sierosol plays an important role for the climate on earth. It is common to distinguish between direct and indirect effects of the aerosols on the climate. Aerosols effect directly the radiation balance of the earth due to scattering and absorption of electromagnetic radiation (radiative forcing). On the other hand they influence the physics and chemistry of the atmosphere as condensation nuclei for cloud droplets and their chemical reactions with atmospheric trace gases. Though these indirect aerosol effects are difficult to quantify, they are at least as important as the direct radiative forcing. An especially important and complex example for the indirect influence of aerosols on the chemistry and radiation balance of the earth is the role of stratospheric aerosol particles on the polar ozone depletion, which is discussed in more detail below. 

Typical cloud albedos for thick clouds in the boundary layer are 0.5 over the ocean in midlatitudes i.e., half of the incoming solar radiation is scattered back out to space (Baker, 1997). This approximation, Eq. (JJ), illustrates why a change in the number of cloud droplets and their size affects the cloud albedo and hence the radiative forcing (see Problem 9). 

Chou, M. D., and W. Zhou, Estimation and Model Validation of the Surface Solar Radiation and Cloud Radiative Forcing Using TOGA COARE Measurements, J. Clim., 10, 610-620 (1997). 

Chou, M.-D., W. Zhao, and S.-H. Chou, Radiation Budgets and Cloud Radiative Forcing in the Pacific Warm Pool during TOGA COARE, J. Geophys. Res., 103, 16967-16977 (1998). 

Freckleton, R. S., S. Pinnock, and K. P. Shine, Radiative Forcing of Halocarbons A Comparison of Line-by-Line and Narrow-Band Models Using CF4 as an Example, J. Quant. Spectrosc. Radiat. Transfer, 55, 763-769 (1996). 

Harrison, E. F., P. Minnis, B. R. Barkstrom, V. Ramanathan, R. D. Cess, and G. G. Gibson, Seasonal Variation of Cloud Radiative Forcing Derived from the Earth Radiation Budget Experiment, J. Geophys. Res., 95, 18687-18703 (1990). 

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