Is the numerical integration of nonlinear partial differential equations the only way to tackle atmospheric complexity? Or do cascade dynamics repeating scale after scale lead to simplicity? Using 1000 orbits of TRMM satellite radiances from 11 bands in the short wave ( visible, infra red) long wave ( passive microwave) and radar regions and 8.8 to 20,000 km in scale, we find that the radiance gradients follow the predictions of cascade theories to within about +/- 0.5%, +/- 1.25%, +/- 5.9% for the short waves, long waves and reflectivities respectively and with outer scales varying between approximate to 5,000 to approximate to 32,000 km. Since the radiances and dynamics are strongly coupled, we conclude that weather can be accurately modeled as a cascade process. Citation: Lovejoy, S., D. Schertzer, V. Allaire, T. Bourgeois, S. King, J. Pinel, and J. Stolle ( 2009), Atmospheric complexity or scale by scale simplicity?, Geophys. Res. Lett., 36, L01801, doi: 10.1029/2008GL035863.