UU直播 physicist vindicates 80-year-old atmospheric model
Physicist Shaun Lovejoy has produced evidence that the earth聮s atmosphere works in a rather different way than is usually assumed by numerical weather forecasters, for example. His work, to be published in Physical Review Letters, shows that the dynamics of the atmosphere from planetary scales down to 1 km, at least, are extremely close to those predicted by scale invariant but stratified cascade processes. "This demonstrates -- in the most intensive data study to date -- that the atmosphere is not divided into isotropic three-dimensional and isotropic two-dimensional turbulent ranges," says Lovejoy. "Instead, the large structures are on average the same as the smaller ones except for a progressive flattening at larger scales; they are special types of (multi) fractals."
Numerical weather (i.e., computer-based weather forecasting) and climate models are justified with a qualitatively different model of the atmosphere, in which the small structures (gusts, "turbulence," etc.) are quite different -- and separated from -- the large scale structures traditionally associated with "weather." Because of this scale separation, says Lovejoy, turbulence can be considered as no more than small, unimportant perturbations on the weather. This provides a convenient justification for global models which are incapable of resolving anything smaller than several hundred kilometres in size.
On the contrary, the "unified scaling model" first put forward by Professor Lovejoy and his colleague Daniel Scherter in the early 1980s proposes a single continuum of interacting structures ("eddies," "gusts," "vortices," etc.) with energy cascading from large scales all the way down to millimetre scales. Any intermediate separation into small and large scales is an arbitrary subjective distinction. In fact, according to Lovejoy, "the unified scaling model is itself a modern version of a much earlier cascade model, proposed by the father of numerical weather prediction, Lewis Richardson, in the 1920s."
Lovejoy and two colleagues, D. Schertzer and J.D. Stanway, used 909 satellite images spanning the scale range 1-5000 km at both visible and infrared wavelengths to show that the variability at all observed scales and at all levels of intensity is very close to that predicted for a direct scale invariant cascade starting at planetary scales.
Heavily influenced by ideas in chaos, scaling and fractals, Dr Lovejoy聮s theoretical research, much of it funded by the Natural Sciences and Engineering Research Council, has led to findings that hold promise for a better understanding of weather and earthquakes. He has looked at such disparate applications as ocean and ice surfaces, chemical pollution, low frequency human speech, hadron jets and the large scale structure of the universe. The long-term goal is a systematic investigation of the scaling symmetries of geophysical and atmospheric systems. The revolution in computing, remote sensing and image analysis techniques has allowed him to systematically gather evidence to support his position that geosystems are linked by a fundamental unifying principle.
