Contact: Dane Konop FOR IMMEDIATE RELEASE
1/13/97
NOAA-FUNDED STUDY INDICATES "PREDICTABILITY" OF NORTH
ATLANTIC CLIMATE
Scientists funded by the Commerce Department's National Oceanic and Atmospheric Administration have taken a small but necessary first step toward demonstrating the feasibility of predicting Eurasian climate conditions a year or more in advance -- such as the likely general severity of winters.
Writing in the current issue of the journal Science, Stephen M. Griffies of NOAA's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., and Kirk Bryan of Princeton University say that their supercomputer simulations show that with sufficient monitoring of oceanic conditions such as sea surface heights, salinity and temperatures by satellites and ships, scientists could make accurate long-term predictions of North Atlantic Ocean conditions that, along with the overlying atmosphere, are a major influence on the climate of Europe and western Asia.
Both oceanic and atmospheric conditions affect climate. Although it is not possible to predict weather conditions more than a few days in advance because of the chaotic nature of the atmosphere, earlier studies had indicated that the oceans react much more slowly to changing influences and thus retain a greater memory of climate trends.
According to Griffies, "Our study does not directly show that the Eurasian climate can be predicted since we only looked at oceanic climate conditions of the North Atlantic, and not the equally important overlying atmospheric climate conditions. But these results provide intriguing possibilities for forecasting the climate of Europe and western Asia, which are the land regions most affected by variability in the North Atlantic, since they suggest that indeed the oceanic climate component could be predicted."
Their supercomputer-derived results point to three physical properties of the North Atlantic Ocean that could be used for Eurasian climate predictions.
First, the upper layers of the North Atlantic are well "stirred" by the atmosphere, retaining a memory of atmospheric conditions over a period of months to years.
Second, variations in the temperature and salinity of North Atlantic seawater produce rhythmic changes in ocean circulation patterns that affect the climate of even broader areas of the Atlantic Ocean over many years.
Third, strong variations in sea surface temperatures in high latitudes near Greenland influence the atmosphere in a "downstream," or eastward, direction.
Because there is only a short historical record of oceanic conditions, Griffies and Bryan used the GFDL coupled ocean-atmosphere numerical model run on the laboratory's supercomputer to simulate a suite of possible climate scenarios in the North Atlantic. To quantify the North Atlantic's predictability, Griffies and Bryan made four separate ensemble runs of the GFDL model, each starting with identical initial oceanic conditions, but with varying atmospheric conditions chosen randomly from many possibilities.
The North Atlantic Ocean observational system required would likely be at least as broad-ranging as NOAA's new El Nino observing network, which includes a string of 80 fixed climate-sensing buoys that span the western Pacific.
Griffies and Bryan say their results should particularly encourage scientists to continue monitoring sea surface heights by both ships and satellites since it is this oceanic feature that appears to provide the clearest signal of climate-inducing changes in the North Atlantic. Their work is part of a larger NOAA-funded effort by government and university scientists, called the North Atlantic Climate Change Program, to assess the role of the Atlantic Ocean in the regional and global climate system and provide the necessary foundations for forecasting climate variability.
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