Slayt 1 - RTC, Regional Training Centre - Turkey

5- SPECTRAL MODELHow Data are RepresentedSpectral models represent the spatial variationsof meteorological variables (such asgeopotential heights) as a finite series of wavesof differing wavelengths.In the introduction, we considered thestructure of a conceptual two-wave model.Let's now look at a real data set.Consider the example of a hemispheric 500-hPaheight field in the top portion of the graphic. Ifthe height data are tabulated at 40°N latitudeevery 10 degrees of longitude (represented ateach yellow dot on the chart), there are 36points around the globe. It takes a minimum offive to seven points to reasonably represent awave and, in this case, five or six waves can bedefined with the data. The locations of thewave troughs are shown in the top part as solidred lines.When the data are plotted in the graph, the fivewave troughs are definable by the blue dots butare unequally spaced. This indicates thepresence of more than one wavelength ofsmall-scale variations. In this case, the shorterwaves represent the synoptic-scale features,while the longer waves represent planetaryfeatures.