RÉSUMÉ

The Ecosphere, which sustains life on Earth, encompasses two major fluid masses − the atmosphere and oceans. Both of these fluid bodies are in turbulent motion, driven by thermal forcing (e.g. temperature gradients) induced by solar radiation and to a lesser extent by gravitational forcing exerted by celestial objects (e.g. tidal forcing). External forcing occurs over a myriad of well-defined space-time scales, but instabilities and strong non-linearities of resulting fluid motions lead to an almost continuous spectrum of mutually interacting flow phenomena. The scales of external forcing and those imposed by the density stratification (buoyancy effects) and Earth's rotation (Coriolis forces), however, leave imprints in the spectrum signifying distinct flow regimes with intrinsic dynamical balances. Large-scale motions affected by Earth's rotation tend to be strongly anisotropic, the study of which falls in the realm of Geophysical Fluid Dynamics. The "urban" and "man" scale motions, on the other hand, are dominated by the turbulence phenomenon and are dealt in Environmental Fluid Dynamics. Collectively, all scales of motions and their complex interactions with physical, chemical and biological processes help to maintain the properties of the Ecosphere within narrow windows conducive for the existence of life, yet such motions exhibit profound variability and incredible diversity that defy predictability. Some dominant flow phenomena occurring in the atmosphere and oceans, dynamical processes leading to such motions, and issues related to their prediction (forecasting) are briefly discussed in this paper.