Math Model Warns of Intense Weather Ahead

July 22, 2008

A new mathematical model is sounding the alarm. Hurricanes and cyclones, which are born of the same mechanism, may greatly intensify because of climate change.

The model indicates that for every increase in Earth's surface temperature of 3.6 degrees Fahrenheit, the intensity of a storm could grow by as much as 10 percent.

The model, which is based on a generalization of Daniel Bernoulli's equation relating wind speed and pressure, incorporates such variables as friction and energy source. The new equation allows researchers to calculate more accurately than before the maximum expected intensity of a spiraling system, based on the depth of the troposphere and the temperature and humidity of the air in the storm's path.

"This model allows us to relate changes in storms' intensity to environmental conditions," atmospheric scientist Nilton Renno of the University of Michigan said. It shows "that climate change could lead to increases in how efficient convective vortices are and how much energy they transform into wind," he noted. "Fueled by warmer and moister air, there will be stronger and deeper storms in the future that reach higher into the atmosphere."

The work by Renno and researcher Natalia Andronova bolsters other studies saying that hurricanes have grown stronger over the last half century because of increases in ocean temperatures. It also helps explain the formation of spiral bands and wall clouds, the first clouds that descend during a tornado. They result from a pressure drop where the air speed has increased.

"This is the first thermodynamic model that unifies all these vortices," Renno said. "When you unify them, you can see the big picture and you can really understand what makes them form and change."

Renno's paper, called "A Thermodynamically General Theory for Convective Vortices," can be found online in the journal Tellus A.

Source: University of Michigan, July 8, 2008.