Stratospheric Effects of ENSO-Related Tropospheric Circulation Anomalies

Using 30 years of Northern Hemisphere geopotential data, from 1000 to 10 hPa, the link between three fundamental modes of tropospheric variability [the Pacific/North America (PNA), Western Pacific Oscillation (WPO), and Tropical/Northern Hemisphere (TNH) patterns] and the extratropical wintertime northern stratospheric circulation is explored. These modes of variability are known to be influenced by El Nino/Southern Oscillation (ENSO) and may provide a mechanism for ENSO to influence interannual variability of the strato-spheric flow. Aside from any link to ENSO, these modes may be important in providing tropospheric wave forcing to the stratosphere. These modes may be characterized by three of the leading rotated empirical orthogonal functions of the wintertime 5OO-hPa height field. An index of the amplitude of each of the modes is given by time series of principal components of that mode. By examining composites of years with high-index values minus years with low-index values it is shown that ...