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THE ROLE OF THE NAO IN NEW ENGLAND'S CLIMATE
Citation:
Walker, H A. THE ROLE OF THE NAO IN NEW ENGLAND'S CLIMATE. Presented at New England Regional Assessment Meeting, University of New Hampshire, Durham, NH, January 8, 2001.
Description:
We are currently in a period of rapid climate change. The global surface temperature is rising with the greatest warming during the 20th century occurring over land masses in the Northern Hemisphere during winter. Stratospheric temperatures have cooled, which is another predicted consequence of increased concentrations of greenhouse gases which absorb outgoing infrared radiation in the lower atmosphere. Based on recent results from three stratospheric models and two tropospheric models from the Goddard Institute of Space Sciences, greenhouse gas induced cooling in the stratosphere has affected stratospheric pressure gradients and is related to observed strengthening of stratospheric wind vortices around both poles. This polar vortex strengthening is associated with changes in the characteristics of the winter North Atlantic Oscillation (NAO), including a shift into a relatively persistent positive NAO index phase, and shifts in regional climate around the North Atlantic. To the north, recently declassified data from the Arctic indicates sea ice thickness from the ocean surface to the bottom of the ice pack has declined by 4.3 feet (40 %) since the first measurements were made in 1958. To the south, between 1960 and 1990 the winter sea water temperature of Narragansett Bay has warmed by 3 degrees centigrade in a shift from negative to positive winter NAO index phases. NAO variability is also associated with variability in storminess over the North Atlantic, and regional shifts in moisture flux, affecting both terrestrial and marine ecosystems. A shift into more persistent positive NAO index phase in recent decades is associated with generally wetter conditions along much of the U.S. Atlantic coast. Persistent negative NAO index phases such as in the 1960s are associated with regional drought in the Northeastern U.S. Future regional shifts in climate are not yet predictable, but could include more persistent positive or negative NAO index phases. Hence, it may be prudent to plan to minimize environmental and health risks associated with both wet and dry extremes of regional climate.