Monday, 14 January 2002: 11:45 AM
Evidences of Dominant Atmospheric Circulation Variability in the Context of Global Warming
Recent studies show dramatic changes of atmospheric circulation during last decades. For example, the recognized Annular Mode or Arctic Oscillation and Antarctic Oscillation by Thompson and Wallace (1998) and Gong and Wang (1998) indicate persistent negative anomalies of sea level pressure (SLP) since late 1980s up to present. In terms of zonal symmetry of these leading modes and their similarity in both hemispheres, we investigated coherent variability of zonal mean geopotential height extending from north pole to south pole and from 1000mb to 100mb, its seasonality, associated mid-latitude westerlies and their correlation with global warming, with NCAR/NCEP reanalysis data from 1948 to 2001 and long-term observation of global temperature and SLP (e.g. Jones, et al. 1999). EOF 1 of zonal mean geopotential height explains almost 70% of total variance in annual mean, revealing opposite pattern between tropical and high latitudes in both hemispheres. This leading mode is characterized by geopotential height decreasing in both polar area and increasing over the tropics. When seasonal and monthly data are applied for analyses, the leading modes are also robust and their contributions to total variances range from 46% to 62% with maximum for summer data. Correlations show strong relationship of above leading mode to global warming. Correlation efficient can arrive at -0.84 in winter. Westerlies in both hemispheres measured by the SLP/geopotential height difference between 60°N and 40°N and 60°S and 45°S intensify in troposphere and weaken in stratosphere since 1980s.