David E. Steitz<br />Headquarters, Washington August 1, 2003<br />(Phone: 202/358-1730)<br /><br /><br />Jana Goldman<br />National Oceanic and Atmospheric Administration, Silver <br />Spring, Md.<br />(Phone: 301/713-2483)<br /><br /><br />RELEASE: 03-255<br /><br /><br />WHITHER COMES WEATHER? SCIENTISTS SUGGEST STRATOSPHERE'S <br />ROLE<br /><br /><br /> What happens in the stratosphere, the atmospheric layer <br />just above where commercial airplanes fly, may have a larger <br />influence on our climate and weather than previously <br />thought, according to research funded by NASA, the National <br />Oceanic and Atmospheric Administration (NOAA), and the <br />National Science Foundation.<br /><br /><br />"The stratosphere is an active player in providing memory to <br />the climate system," said Dr. Mark P. Baldwin, Senior <br />Research Scientist at NorthWest Research Associates, <br />Bellevue, Wash. He is lead author of a paper in the August 1 <br />issue of Science. <br /><br /><br />Baldwin and his co-authors suggest, although the <br />stratosphere is mostly clear and weather free, it appears <br />changes to the stratospheric circulation can affect weather <br />patterns for a month or more. Wind patterns in the lower <br />stratosphere tend to change much more slowly than those near <br />the surface. <br /><br /><br />Once the winds in the lower stratosphere become unusually <br />strong or weak, they tend to stay that way for at least a <br />month. "This is the key," Baldwin said, "to understanding <br />how the stratosphere can affect our weather." Large-scale <br />waves that originate in the troposphere, the level of the <br />atmosphere closest to the Earth's surface, appear to be <br />sensitive to the slowly shifting winds in the stratosphere. <br />The waves allow stratospheric changes to feed back, <br />affecting weather and climate on the Earth's surface.<br /><br /><br />Knowing the stratosphere plays this role could be helpful in <br />predicting weather patterns well beyond the seven-to-10-day <br />limit of current weather prediction models. The <br />stratospheric effect could be compared to the effects of El <br />Nino in that they both provide predictability of average <br />weather patterns. However, the stratospheric effects last <br />only two months at most, and the effects only occur from <br />late fall to early spring. <br /><br /><br />A better understanding of the stratosphere's effect on the <br />troposphere could also be useful in gaining additional <br />insight into the climatic effects of stratospheric ozone <br />depletion, solar changes and variations in aerosol amounts <br />associated with major volcanic eruptions.<br /><br /><br />The stratospheric wind shifts can be thought of as changes <br />to the strength of the belt of westerly winds that circulate <br />around the globe at high latitudes. Scientists call these <br />winds the "stratospheric polar vortex." The waves from the <br />troposphere first create fluctuations in the strength of the <br />polar vortex, and then the changes in the vortex strength <br />feed back to affect a hemispheric-scale weather pattern <br />known as the Arctic Oscillation.<br /><br /><br />When the Arctic Oscillation, also known as the North <br />Atlantic Oscillation, is in its positive phase, there are <br />stronger westerly winds at mid-latitudes, especially across <br />the Atlantic. Northern Europe and much of the United States <br />are warmer and wetter than average, while Southern Europe is <br />drier than average, according to Baldwin. "In effect, the <br />stratosphere can act as a predictor of the state of the <br />Arctic Oscillation," he said.<br /><br /><br />NASA funds this research through its Earth Science <br />Enterprise, a program dedicated to understanding the Earth <br />as an integrated system and applying Earth System Science to <br />improve prediction of weather and natural hazards using the <br />unique vantage point of space.<br /><br /><br />For information about NASA on the Internet, visit:<br /><br /><br />http://www.nasa.gov<br /><br /><br />For information about NASA's Earth Science Enterprise on the <br />Internet, visit:<br /><br /><br />www.earth.nasa.gov<br /><br /><br />For information about NOAA on the Internet, visit:<br /><br /><br />www.noaa.gov