Association of Interannual and Interdecadal Variations of Global-Mean Temperature with Tropical Pacific SST Appearing in a Model and Observations

Abstract

Long-term variations of global-mean air temperature at the surface are investigated using data from a GFDL coupled ocean-atmosphere model 139-year simulation and the observed datasets of surface air temperature over the globe for 139 years and tropical Pacific SST for 42 years. The global-mean surface air temperatures of both the model and observation are characterized by interdecadal oscillations with timescales of about 20 years and 10 years and interannual fluctuations with timescales of 3?6 years. The global-mean temperature anomaly (GMTA) is related to the first empirical orthogonal function mode of surface air temperature over the globe, which, in turn, is associated with the first eigenmode of SST over the tropical Pacific. The first eigenmode of tropical Pacific SST has a spatial pattern similar to that during a mature phase of El Niño, and its associated time series is characterized by the 3?6-yr interannual and interdecadal timescales. It is demonstrated that both interannual and interdecadal variations of the GMTA are associated with the corresponding variations of tropical Pacific SST. Comparisons of the model results with observed counterparts show that the coupled model has a capability of simulating many important features of surface air temperature variations over the globe and SST fluctuations over the tropical Pacific, except that the interannual variations of the model with timescales of 3?6 years are relatively weak. The sampling error of the observed GMTA for the 139 years 1854?1992 due to inhomogenous spatial distribution of the data over the globe is examined by using the coupled model data. Although the sampling error of monthly mean GMTA is not small even for recent years, the long-term variations of GMTA with timescales longer than few years are not much affected by the sampling problem.