Structural Feature Analysis Ofthe Variability Of Tropical Pacific Sea Surface Temperature Anomalies

Based on the observed monthly mean sea suface temperature (SST) data setsduring 1958-2008 from Hadley center, seasonal joint empirical orthogonal function(SEOF) decomposition is employed to extract the first two dominant modes of detrended tropical Pacific SST anomaly.(SSTA) variability with seasonal evolution. The first seasonal-varying mode of SEOF, the most dominant feature of cyclic climate variability on interannual timescales, presents the conventional El Nino events and its evolution from boreal summer to following spring. The second mode of SEOF, characterized by warming from the central equatorial to the northeastern subtropical Pacific associated with a colder SSTA in the cold tongue, is an interdecadal mode with roughly 10-12 years period, which we define as the tropical Pacific interdecadal mode (TPDM). We compare global climatic teleconnections between these two modes and find that differing from ENSO’s global effect, teleconnections to TPDM is local, much confined in the tropical and north Pacific, indeed, some is opposite to ENSO’s.We investigate the structural feature of TPDM from overall point of view. By means of correlation and linear regression analysis, we find that the variability of SSTA in the northeastern subtropical Pacific and difference between central and eastern equatorial Pacific which all are anomaly centers of TPDM are nearly independent on each other and ENSO. What is more, they both solely could regressed a part of TPDM which is approximately equal to arithmetic mean of those two regressed patterns, the former simulating almost entire warming in the northeastern subtropical and central equatorial Pacific, the latter nearly entire cooling in the cold tongue and a little of warming in the central Pacific, implicating that TPDM could probably be further decomposited into two independent simpler modes.Using the filtered SSTA by a fourier filter to removed interannual variability below 8yr, SEOF is employed once more attempting a further decomposition to TPDM based on the above conclusion. As expected, the first mode of interdecadal SEOF, explaining 35.7 percent of interdecadal variability, is similar to the pattern that variability of SSTA in the northeastern subtropical Paicifc regressed, warming in the most central and eastern Pacific with two warming centers locating in the central equatioral and northeastern subtropical Pacific, which we define as tropical Pacifci interdecadal meridional mode (TPDMM) besed on its meridional structure of double warming centers. The second mode of interdecadal SEOF, explaining 13.8 percent of interdecadal variability, is also likely to the pattern that difference between central and eastern equatorial Pacific regressed, cooling in the cold tongue and warming in the central Pacific, which we call after tropical Pacific interdecadal zonal mode (TPDZM), correspondingly, based on its zonal out-of-phase structure. Further study implicates that TPDMM maybe modulation of ENSO at interdecadal timescales on account of their similiar global climate telleconnection pattern, as well as to a certain extent coordinate variation of timeserises, while TPDZM may represent the change of SST mean state. However, further research is necessary for the sake of deep understanding.