THE UNIFIED SCALING MODEL OF ATMOSPHERIC DYNAMICS AND SYSTEMATIC ANALYSIS OF SCALE-INVARIANCE IN CLOUD RADIANCES

The unified scaling model of the atmosphere links the large and small scale dynamics by a single scaling but anisotropic regime, rather than distinct isotropic two- and three-dimensional turbulent regimes as po sited in the standard model. We argue that the study of mesoscale clou ds is a particularly stringent test for the standard model and we pres ent (perhaps the first) systematic analysis of the scaling of energy s pectra of satellite radiances over five wavelength channels and spanni ng the range of scales from 160 m to 4000 km (the entire mesoscale). T he study mostly involved 15 consecutive scenes of AVHRR data (1.1 km r esolution, 512 x 512 pixels) taken over the same location at the same local time in February 1986. This data was chosen because it was expec ted to provide a very sensitive indicator of the mesoscale break in th e scaling predicted by the standard model of atmospheric dynamics (the ''mesoscale gap''). Over the entire range, with surprisingly little s cene-to-scene variation, the (isotropic) energy spectrum (E (k)) was f ound to follow the scaling form E (k) almost-equal-to k(-beta) where k is a wavenumber, and beta is the spectral exponent. This type of beha viour is exactly as predicted by the unified scaling model of the atmo sphere as the outcome of anisotropic nonlinear cascade dynamics. It is hard to see how these results can be reconciled with the standard mod el.