Many key issues in dynamical meteorology and physical oceanography depend on interactions among diverse spatial scales. Atmospheric examples are the role of small-scale gravity waves in the zonal-mean momentum balance in the middle atmosphere, the role of tropical cyclones in the large scale energy and momentum balances of the troposphere, or even the direction of spectral cascades of variance in the mesoscale. In the ocean issues of this type include: understanding the detailed physics of the very narrow boundary currents that occur along many coastlines, and the role of mesoscale eddies...