scientists have BEEN creating models of the climate and atmosphere on a systematic basis for more than a century. However, only with the development of powerful computational devices has a sophisticated simulation of the atmosphere started to become possible. The accurate modeling of turbulent liquids and gases, of which the atmosphere is of course composed, remains one of the most difficult tasks facing scientists studying the Earth. The problem is made more difficult by the lack of accurate and complete data dating back more than a few decades. Despite these difficulties, researchers have become able to create models that do represent the major features and changes of the atmosphere with a high degree of confidence.
The degree of sophistication inherent within the atmospheric component of climate models is revealed by the number of data points on the surface (the horizontal element) as well as the number of layers considered in the atmosphere (the vertical component). Currently, scientists are developing a third generation atmospheric circulation model that consists of 32 layers within the atmosphere. The coverage extends to 37 mi. (50 km.) from the surface of the Earth and the model also includes three layers of the Earth itself. Previously, a single soil layer was predicated across the surface of the Earth, but this is now supplemented by, when necessary, a snow layer and a layer of vegetative canopy.
Clearly, the rate of change of land cover across the surface of the Earth means that it would be impossible to create a model that is 100 percent accurate. However, models now represent the overall effect of the atmosphere to a satisfactory degree. For example, variables are included in the third generation models that include soil surface properties and heights, various types of surface albedo, and varying soil moisture conditions. Nevertheless, the central component of the model is the investigation of the heat exchange between the earth through the atmosphere and the ways in which this has an impact upon the climate. Understanding this has been a goal of scientists for more than a century, although it was not until the detailed observations first made in the middle of the 20th century that a real understanding of circulation became possible.
The discovery of the various wind systems and accurate mapping of them enabled a huge leap in understanding of the Earth's atmosphere as a whole. It revealed the need for more advanced understanding of the atmosphere than could be provided by a single equation, no matter how sophisticated that might be. The Norwegian meteorologist Vilhelm Bjerknes and the British physicist Lewis Fry Richardson were among the vanguard of scientists attempting to use a series of mathematical equations to represent weather changes over finite parts of the globe. This was to be achieved by dividing the surface of the earth into a grid of cells of such a scale that it was feasible to complete the equations with the tools then available. However, these attempts were unsuccessful and ultimately abandoned.
One particular problem was that it was necessary to compare results that had been calculated with real-world data and there were insufficient mechanisms to make those measurements. World War II was the impetus to measure climatic conditions (for inherently military purposes) that provided the amount of data necessary to refine and improve models. Contemporaneous improvements in computers made more rapid and wide-scale calculations possible, and a series of researchers, mostly based in the United States, were able to improve their models over the subsequent decades.
Major improvements included the division of the surface of the earth into land and water, inclusion of topographical features and the integration of increasingly more layers in the atmosphere, which both improved the sophistication of the model and enhanced its scope to heights further from the surface of the earth. It took many years, nevertheless, for modeling to be completed faster than the weather elapsed in real time and the ability to make meaningful weather forecasts has only recently become possible. However, this is now possible and the geographical scope of the coverage has grown from regional to global in nature. Regional models may be more useful for state agencies to make forecasts across their territory, but the atmospheric sys tem is global in scope and only models that include the whole globe can be really helpful in predicting the future.
Advanced modifications to the atmospheric component of climate models have included the dynamics of cloud and precipitation processes, radiation processes, and the impact of aerosols. Other areas of improvement have included the division of precipitation into frozen and liquid forms and the various forms of condensation involved with cloud formation processes. The modeling is not complete, but is advancing at a rapid rate.
sEE ALso: Atmospheric Composition; Atmospheric General Circulation Models; Atmospheric Vertical Structure; Climate Models; Climatic Data, Historical Records.
BIBLIoGRAPHY. Canadian Centre for Climate Modelling and Analysis, www.ccma.ec.gc.ca (cited November 2007); William D. Collins, et al., "The Community Climate System Model: CCSM3," Journal of Climate, (v.19/11, 2006).
John Walsh Shinawatra University
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