Solar heating is the ultimate energy source for the motion of both the atmosphere and the oceans with the exception of the lunar forcing of the tides. The radiant energy emitted by the sun may vary somewhat over very long periods, but a sensible idealization for most meteorological and oceanographic purposes consists in considering the solar source strength as fixed. Temporal variations in the incident radiation (and its spatial distribution) are then fixed by the astronomical relation between the positions of the earth and sun, e.g., by the seasonal progress of the earth in its solar orbit. Quite clearly, though, the motions of both the atmosphere and the oceans exhibit fluctuations whose time scales are not directly related to the astronomical periodicities of the earth-sun system. The phenomenon of weather in the atmosphere is in fact nothing more than the existence of large-scale wavelike fluctuations in the circulation of the atmosphere whose occurrence cannot be predicted, as the tides can be, by a simple almanac of assured recurrence based on past experience. Observations of oceanic motions have also revealed fluctuations at periods which bear no evident relationship with the astronomical periods which characterize the externally imposed forces.
KeywordsReynolds Stress Potential Vorticity Phase Speed Zonal Flow Vertical Shear
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