Atmospheric Component of Models

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 Earths 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.

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