by Jeffrey Graf

Created on: August 27, 2008

To understand the forces that drive a hurricane, we must first understand the forces that drive a heat engine. An engine can be abstracted as a heat source, a conversion mechanism and a heat sink. For example, if we consider a steam locomotive, the heat source is the fuel and the firebox, the conversion mechanism is the piston and cylinder, and the heat sink is the environment into which the exhaust steam escapes. Likewise, a power generation plant has a heat source such as a gas or oil burner, converter such as a steam turbine, and a heat sink such as a cooling tower. In fact, the characteristic tower shape associated with the cooling process of a nuclear power plant is the "heat" sink associated with this type of power generation process.

To apply our "engine" abstraction to the process of a hurricane, we must first identify the heat sources and sinks. To do this, we consider the now familiar satellite view of the hurricane. We will notice that at the center of the hurricane, we see the white of the clouds as viewed from space. This implies that at the core of the hurricane, the storm is reflecting the sun's energy back into space. ( and thus the clouds appear white, the color of all the wavelengths in the color spectrum.

But outside the body of the storm, we see the blue of the ocean. This implies that the sun's energy is entering the sea water, it is being absorbed, and consequently heating the ocean, and only a small amount of blue light is being reflected back into space. Thus, the blue water, absorbing the suns energy will be considered as our heat source, much like the firebox on our previously considered steam engine. And just as a firebox causes water in the liquid state to change into water in the gaseous state in an engine's boiler, the heating of the sea water by the sun causes water vapor to leave the ocean and go into the atmosphere. This causes a rather familiar process we all know as cloud formation, and equally familiar is the process of condensation and rain. Thus, we know have identified and hopefully understand the heat source of our engine and the heat sink, or condensation phase of our heat engine.

Lets turn our attention to the actual mechanism of the hurricane's engine. As water vapor cools and causes cloud and rain formation, it causes a drop in pressure. As we know from our high school physics class, pressure is dependent upon temperature. ( remember pv=nrt ? ) As temperature drops, air pressure drops. But as a more sophisticated principle,

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