Applyingtheempiricalorthogonalfunction(EOF)analysistotheseasurfacetemperature(SST)fieldofthetropicalPacificandIndianOceansfordeterminationofthefirsteigenvectorfield,thecurrentworkrevealsthattherearesignificantzonalgradientsofSSTinallseasonsoftheyearinthenorthwesternandeasternIndianOceanandequatorialcentralandeasternPacificandwesternPacific.ItisalsofoundthatthevariancecontributionratesofthefirstEOFmodeofeveryseasonismorethan33%.ThisshowsthatthiskindofspatialdistributionoftheSSTisstable.ThispatternisnamedPacific-IndianOceansSSTAmode.Throughcarefulanalysisandcomparison,anindexofthemodewasdefined.