![]() ![]() By contrast, high-resolution models generate highly realistic distributions and correctly identify that in autumn, for example, there is a strong likelihood of especially heavy rainfall and flooding on the southern edge of the Alps, along the Ligurian coast and in Provence. Current models massively underestimate the amount of rain that can fall in an hour. Using the example of southwestern Europe, Schär shows how high-resolution models are also able to predict extreme weather events much more accurately. "But based on the laws of physics alone, it can still provide us with a realistic picture of what's going on." It is still not feasible to create longer-term scenarios with such high-resolution models, but they do serve to make current global models more accurate. "The model doesn't know anything at all about the tropical climate," Schär enthuses. The visualization is strikingly similar to a satellite image: rain fronts shift from east to west across Africa finely structured cloud fields form off the coast of Brazil hurricanes develop in the middle of the Atlantic and then head north. To illustrate this, he and his group run a sequence on a supercomputer that simulates weather events in the Tropical Atlantic over a period of years to decades. Schär, for example, is now working with models at a much higher resolution-1 to 2 kilometers-which provide a much more accurate picture of meteorological activity. Over the next few years, scientists hope to address this imprecision. "If we don't know how many clouds are forming in the tropics, then we don't know how much sunlight is hitting the earth's surface-and hence we don't know the actual size of the global energy balance." "But predicting future climate change is still pretty imprecise," Schär says. The workaround, at present, is to add extra parameters to the model in order to map clouds. Yet it is precisely these thunderstorm cells-and where they occur-that drive atmospheric circulation, especially in the tropics, where solar radiation is highest. This scale is too coarse to map small-scale, local thunderstorm cells. In order to build a global climate model, grid points spaced around 50 to 100 kilometers apart are used. ![]()
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