GLOBAL-SCALE MODES OF SURFACE-TEMPERATURE VARIABILITY ON INTERANNUAL TO CENTURY TIMESCALES

Using 100 years of global temperature anomaly data, we have performed a singular value decomposition of temperature variations in narrow fre quency bands to isolate coherent spatio-temporal ''modes'' of global c limate variability. Statistical significance is determined from confid ence limits obtained by Monte Carlo simulations. Secular variance is d ominated by a globally coherent trend, with nearly all grid points war ming in phase at varying amplitude. A smaller, but significant, share of the secular variance corresponds to a pattern dominated by warming and subsequent cooling in the high latitude North Atlantic with a roug hly centennial timescale. Spatial patterns associated with significant peaks in variance within a broad period range from 2.8 to 5.7 years e xhibit characteristic El Nino-Southern Oscillation (ENSO) patterns. A recent transition to a regime of higher ENSO frequency is suggested by our analysis. An interdecadal mode in the 15-to-18 years period range appears to represent long-term ENSO variability. This mode has a size able projection onto global-average temperature, and accounts for much of the anomalous global warmth of the 1980s. A quasi-biennial mode ce ntered near 2.2-years period and a mode centered at 7-to-8 years perio d both exhibit predominantly a North Atlantic Oscillation (NAG) temper ature pattern. A potentially significant ''decadal'' mode centered on 11-to-12 years period also exhibits an NAG temperature pattern and may be modulated by the century-scale North Atlantic variability.