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Keith -- that is what we call Maximum Potential Intensity, which isn't so much a manifestation of the global circulation, but one illustrating what we understand about the circulation of a tropical cyclone and the factors that impact its intensity. All that goes into it are temperatures at the ocean's surface and aloft (at the outflow layer) plus a bunch of other physical variables (drag coefficients and the like), allowing us to come up with a max. theoretical intensity of both wind speed and pressure. This circulation assumes a Carnot cycle for the tropical storm -- too lengthy to explain here -- but needless to say, it is a direct circulation with inflow at low levels at about the temperature of the SST, rising motion near the center of the storm (slantwise moist ascent), moist outflow aloft, followed by moist and then dry descent at outer radii. It doesn't take into account the eye or the eyewall -- the features of which I've explained in a current post in the News Talkbacks -- but does a pretty good job of capturing the environmental factors affecting a single hurricane's intensity. The global circulation deals more with the exchange of energy between the midlatitudes, polar regions, and tropics; some of these factors may work their way down to the fine-scale and impact SSTs and the like, but they aren't directly related. |