College of LAS « Illinois

Atmospheric Sciences

Discovery of Stratosphere's Influence on Spring May Lead to More Accurate Forecasts

stratosphere

A new study suggests that the interplay between two layers of the Earth's atmosphere plays a major role in the arrival of spring—a discovery that has the potential of improved weather and climate forecasting. Co-authors of the study, which include LAS atmospheric sciences professor Walter Robinson, have also discovered that spring arrives earlier and more abruptly than previously thought.

Until recently, scientists believed that the lowest region of atmosphere where weather occurs—the troposphere—drove changes in the stratosphere, the atmospheric layer directly above the troposphere. Yet, in the late 1990s, new studies found that the stratosphere can affect tropospheric circulation.

These studies, however, focused on individual seasons. Robinson and scientists from Georgia Institute of Technology were interested in the transitions between seasons because of their profound influence on the hydrological cycle, the growing season, and ecosystems. They gathered observational data derived from a variety of sources and constructed a composite picture of spring's arrival over a 40-year period.

When winter draws to a close, the westerly jet stream in the troposphere begins to weaken. At the same time, the westerly jet stream in the stratosphere above not only weakens, but eventually reverses direction to become easterly. Robinson and his colleagues discovered that stratospheric final warming accelerates the weakening of the tropospheric winds from several weeks to just about one. "It's as if someone flipped a switch," says Robinson.

Other factors influence the arrival of spring. However, stratospheric warming explains a significant part of warming, especially in the Arctic.

The researchers have received a three-year grant from the National Science Foundation to continue their work.

Fall/Winter 2005–06