Relationship Between North Pacific SST Anomalies and the Atmospheric Circulation Anomalies in January 2008

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.

Traditional El Nio and El Ni o Modoki Revisited:Is El Nio Modoki Linearly Independent of Traditional El Nio?

The present study revisited the first two leading modes of tropical Pacific sea surface temperature anomalies （SSTA） during the period of 1979-2008. It is suggested that the so-called El Nino Modoki, which is captured by the second mode, exists objectively and exhibits obvious differences from traditional El Nifio, which is captured by the first mode, in terms of its spatial characteristics. Furthermore, the authors found that El Nino Modoki is linearly independent of traditional El Nino; hence, it cannot be described as part of the traditional El Nino evolution, and vice versa.

Occurrences of Wintertime Tropical Cyclones in the Western North Pacific under the Background of Global Warming

Using tropical cyclone （TC） observations over a 58-yr period （1949-2006） from the China Meteorological Administration, the 40-year ECMWF Reanalysis （ERA-40）, NCEP-NCAR reanalysis, and the Hadley Centre sea ice and sea surface temperature （HadISST） datasets, the authors have examined the behaviors of tropical cyclones （TCs） in the western north Pacific （WNP） in boreal winter （November-December-January-February）. The results demonstrate that the occurrences of wintertime TCs, including super typhoons, have decreased over the 58 years. More TCs are found to move westward than northeastward, and the annual total number of parabolic-track-type TCs is found to be decreasing. It is shown that negative sea surface temperature anomalies （SSTAs） related to La Nifia events in the equatorial central Pacific facilitate more TC genesis in the WNP region. Large-scale anomalous cyclonic circulations in the tropical WNP in the lower troposphere are observed to be favorable for cyclogenesis in this area. On the contrary, the positive SSTAs and anomalous anticyclonic circulations that related to E1 Nifio events responsible for fewer TC genesis. Under the background of global warming, the western Pacific subtropical high tends to intensify and to expand more westward in the WNP, and the SSTAs display an increasing trend in the equatorial eastern-central Pacific. These climate trends of both atmospheric circulation and SSTAs affect wintertime TCs, inducing fewer TC occurrences and causing more TCs to move westward.

Characteristics of Tropical Sea Surface Temperature Anomalies and Their Influences on the Onset of South China Sea Summer Monsoon

The characteristics of sea surface temperature anomalies （SSTAs） in the tropical oceans and their influences on the onset of South China Sea summer monsoon （SCSSM） have been studied.The anomaly of SST in tropical Pacific Ocean exerts persistence impact for one to three months on atmospheric circulations.If the warm pool becomes anomalously warmer during an earlier period from February to April,the SCSSM breaks out earlier,and vice versa.Singular value decomposition （SVD） and composite analysis have shown that,in La Ni（n）a pattern,the convection over Western Pacific will occur earlier and be stronger than normal,which favors the convergence at a lower layer over Western Pacific,as well as the strengthening of upwelling branch of Walker circulation,leading to an earlier burst of westerly in the southern South China Sea.Moreover,the convection in Sumatra appears earlier than normal and favors the westerly evolution in eastern Indian Ocean,resulting in the splitting of the subtropical high belt and an early onset of SCSSM.However,the atmospheric circulation anomaly is reversed in El Ni（n）o pattern.