The influence of the Interdecadal Pacific Oscillation on Temperature and Precipitation over the Globe

The Interdecadal Pacific Oscillation (IPO) is a 40–60 year quasi-oscillation seen mostly in the Pacific basin, but its impacts on surface temperature (T) and precipitation (P) have been found over Australia, the Southwest U.S. and other regions. Here, a global analysis of IPO’s impacts on T and P and its modulation of ENSO’s influence on T and P over the globe is performed using observational and reanalysis data and model simulations. Since 1920, there are two warm (1924–1944 and 1977–1998) and two cold (1945–1976 and 1999–present) IPO phases, whose change is associated with abrupt shifts in North Pacific sea level pressure (SLP) and contrasting anomaly patterns in T and P and atmospheric circulation over the eastern and western Pacific. The IPO explains more than half of the interdecadal variations in T and P over many regions, such as northeastern Australia, western Canada and northern India. Significant correlations between the IPO and local P are observed over eastern Australia, southern Africa and the Southwest U.S. The IPO also modulates ENSO’s influence on local T and P over most of these regions. T over northern India is positively correlated with Niño3.4 ENSO index during cold IPO phases but the correlation turns negative or insignificant during IPO warm phases. Over northeastern Australia, the T versus ENSO and P versus ENSO correlations are stronger during the IPO cold phases than during the warm phases. The P versus ENSO correlation over southern Africa tends to be negative during IPO warm phases but becomes weaker or insignificant during IPO cold phases. The IPO-induced P anomalies can be explained by the associated anomaly circulation, which is characterized by a high SLP center and anti-cyclonic flows over the North Pacific, and negative SLP anomalies and increased wind convergence over the Indonesia and western Pacific region during IPO cold phases. These observed influences of the IPO on regional T and P are generally reproduced by an atmospheric model forced by observed sea surface temperatures.