Based on the NCEP (National Centers for Environmental Prediction) data,the relationship between the Sea Surface Temperature Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study.The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited a basin-wide horseshoe pattern with a warm center in November 2007.This persistent SSTA pattern would induce positive GHAs in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area,leading to the occurence of the circumpolar trough-ridge wave train anomaly in January 2008.
Mechanisms for the spatio-temporal development of the Tropical Pacific Meridional Mode （TPMM） are investigated using a coupled ocean-atmosphere model and observations. In both observations and the model, this meridional mode displays decadal variations and is most pronounced in spring and early summer. The model simulation suggests that once SST anomalies in the subtropical northeastern Pacific are initiated, say by northeasterly trade wind variability, perturbations evolve into a merdional dipole in 2 -3 months. A wind-evaporative-SST feedback causes a southwestward propagation of initial subtropical SST anomalies, while anomalous equatorial upwelling helps form the southern lobe of the meridional dipole. The TPMM development is a fast process （a few months） and depends on the seasonal cycle.
