Scientists hope to glimpse
the secret life of clouds

(page 2 of 3)

Researchers use a geodesic grid of data points distributed around the Earth to portray clouds and climate. (Click image to enlarge and for more information.)

Modelers predict weather by solving partial differential equations representing physical conservation laws for mass, energy and momentum. The 10-second time steps enable the GCRM to simulate individual clouds’ growth and death. The equations describe how things change with time and how properties of the air evolve as it moves and the sun rises and sets.

Randall elaborates: “If you have, for instance, a little chunk of air moving around and you have some humidity there, an equation in the model says the humidity of that air will stay the same” – unless one or more of several variables change the outcome.

“Basically, the equation says that humidity doesn’t change except when one of these things happens, and then it changes this way. Then we have to write more equations to tell how these humidity-changers work. The model ends up being a system of equations that are all coupled and have to be solved simultaneously.”

The equation set, developed by UCLA’s Akio Arakawa and Colorado State’s Celal Konor, eliminates sound waves. “The atmosphere can make lots of different kinds of waves, but in choosing equations we knew we wanted to avoid those that include sound waves because sound waves are completely irrelevant to weather and climate,” Randall says.

Rather, Randall’s team has selected equations that directly describe the evolution of vorticity in clouds, or their “spinning motion,” Randall says. Vorticity ‘is really at the core of much of the important fluid dynamics in the atmosphere. Vortices move around and maintain their identities and live a life, like little animals. Sometimes two vortices will merge and make a bigger one.”

This vorticity approach, developed by Arakawa and Colorado State’s Joon-Hee Jung, will be particularly useful for simulating large thunderstorms, which are important for global atmospheric circulation.

These storms pack a lot of energy in the form of updrafts that move, in extreme cases, 30 to 40 meters a second – “scary fast,” Randall says. They “lift air from near Earth’s surface to way up near the stratosphere in just a few minutes.”

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