The meridional mode of global tropospheric–stratospheric circulation

The spatio–temporal variations of major meridional modes are studied by using the ECMWF and NCEP/NCAR reanalyzed geopotential data between 70 and 10hPa during 1979 and 2001. The variance contribution rates from the first and second modes are 56–69% and 14–22%, respectively, for ECMWF, but 76–85% and 9–10% for NCEP/NCAR. The climatic trend coefficients are positive and negative in the troposphere and stratosphere, respectively. The reversal is remarkably correlated with the AO/NAM, AAO/SAM and polar vortex, suggesting their important role in connecting the mid-low and upper circulation and the interaction between SH and NH.