Forecasting on a New Level

By J. MADELEINE NASH

Had David Thompson pursued on of the first careers he considered, he might today be a guitarist in an alternative-rock band. But Thompson, 35, became intrigued with climate and weather, and just three years after he enrolled for graduate study at the University of Washington, he and his faculty adviser, John M. Wallace, published an attention-grabbing paper that announced the discovery of the Arctic Oscillation, an important new cog in the earth's climate machine.

The Arctic Oscillation, or AO for short, is defined as the back-and-forth pattern of low and high pressure between high polar latitudes and the mid-latitudes of the northern hemisphere. The AO encircles the whole of the Arctic and also extends from the sea's surface to the stratosphere, an ethereal region of the atmosphere some seven to 30 miles above the earth that forecasters thought had little bearing on day-to-day weather. Thanks to the discovery of the AO, that view of the stratosphere is changing. Among other things, scientists studying the AO have connected sudden warmings of the stratosphere to outbreaks of wintry weather in Europe and the U.S. Somehow, scientists think, these spikes in stratospheric temperatures weaken the winds that swirl around the Arctic, thereby allowing frigid air to spill out of polar regions and envelop cities like Boston and New York, Berlin and Paris in teeth-chattering cold. Conversely, when stratospheric temperatures cool, strong winds at the surface discourage cold air from dipping so far south. Already, the AO's clear connection to the stratosphere is giving weather forecasters a predictive edge. It is also providing fresh insights into the climatological consequences of everything that affects the thermal profile of the stratosphere, from fluctuations in solar luminosity to emissions of ozone-eroding chemicals and greenhouse gases.

The stir generated among climatologists by the AO makes Thompson, an atmospheric scientist at Colorado State University, a tad uncomfortable. "I guess I have a humble tendency," he says, noting that in science, credit seldom belongs to one person alone. Thompson is broadening his focus to include other components of the climate system, notably the AO-like Antarctic Oscillation, whose behavior, he thinks, has been profoundly influenced by the leakage into the stratosphere of man-made compounds that destroy the ozone. Result: wind patterns are keeping the white continent's interior bitterly cold while allowing the outlying peninsula to warm. The young researcher may not be playing guitar for a living, but he has found new ways to rock the world. --By J. Madeleine Nash