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Life on Earth is critically dependent upon the continuous cycling of water between the oceans, the continents and the atmosphere. The hydrological cycle depicted as a cartoon in Fig. 1.1 is dynamic and complex. The atmospheric component of this cycle involves surface water moving into the atmosphere via wind-driven evaporation and biosphere-modulated evapo/transpiration followed by transport and dispersion,...
In this chapter we provide an overview of the basic physical processes responsible for the formation of clouds and precipitation. A number of important concepts are discussed, and terms defined, which will be used in later chapters. For more detail on these topics the reader is referred to textbooks by Pruppacher and Klett (1997), Rogers and Yau (1989), relevant chapters in Wallace and Hobbs (2006),...
In view of the nonlinear and spatiotemporally complex interactions between aerosols, clouds and precipitation, it is quite inadequate to represent aerosols by the conventional approach of atmospheric pollutant cycles, i.e. by specifying sources, burdens and sinks in terms of masses of particular aerosol components or “species”. The basic information required for modeling the role of aerosols in cloud...
Because the time for air parcels to circle the Earth on winds in the troposphere is of the same order of magnitude as the residence time of atmospheric aerosols, there is no location on the globe that is not influenced by aerosol sources. Once released into the atmosphere from primary production or produced via gas-to-particle conversion (for source details, see Chapter 3), aerosols are subject to...
In this chapter we review the methods presently available and expected in the near future to measure the effect of aerosols on clouds and precipitation, and the limitations of current measurements that make it difficult to assess this connection.
The impact of aerosols on cloud macrophysical (cloud extent, cloud thickness and liquid water path), cloud microphysical (droplet and ice crystals concentrations and size distributions), and precipitation has received a great deal of attention for over 50 years. The pioneering work of Gunn and Phillips (1957), Squires (1958), Squires and Twomey (1961), Warner (1968) and Warner and Twomey (1967), to...
The history of numerical modeling of the effect of aerosols on clouds dates back at least 50 years to the work of Howell (1949) and Mordy (1959), who considered the growth of a population of aerosol particles in a rising parcel of air. Models such as these addressed the effects of both aerosol and dynamical parameters (i.e. updraft velocity) on the number and size distribution of cloud droplets. To...
Deliberate cloud seeding, with the goal of increasing precipitation by the injection of specific types of particles into clouds, has been pursued for over 50 years. Efforts to understand the processes involved have led to a significant body of knowledge about clouds and about the effects of the seeding aerosol. A number of projects focused on the statistical evaluation of whether a seeding effect...
Aerosols impact global climate in a number of ways. First they directly affect the Earth’s radiation budget by absorbing and reflecting solar radiation and to a lesser extent altering the profile of IR absorption in the atmosphere. Second, by serving as cloud condensation nuclei (CCN) and ice nuclei (IN), they determine cloud microphysics, the formation of precipitating particles and cloud radiative...
It is recommended that a series of international projects targeted toward unraveling the complex interactions among aerosols, clouds, and precipitation be implemented. A series of international workshops and field studies are needed to address the impacts on clouds and precipitation of aerosols from a range of sources including biomass burning, dust, and industrial pollution within different regional...
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