Spatial and Temporal Variability in Thickness Fields of the Western Pacific Warm Pool Thermohaline Structure

Based on the monthly temperature and salinity data during 1950-2011, the mixed layer thickness (MLT), barrier layer thickness (BLT) and deep layer thickness (DLT) in the western Pacific warm pool area (20ºN-15ºS,120ºE-140ºW) are calculated with 28℃ isotherm as the boundary of the western Pacific warm pool (WPWP). The spatial and temporal variability of MLT, BLT and DLT anomaly fields are further analyzed using an empirical orthogonal function (EOF) analysis method. In addition, the relationships between the leading EOF modes of these fields and El Niño-Southern Oscillation (ENSO) are also discussed. Moreover, the influences of the temperature and salinity at each layer, zonal winds stress, zonal currents, sea surface net heat fluxes and precipitation in the WPWP on the leading modes of the thickness anomaly fields of three layers are examined by cross correlation analysis and composite analysis methods. The analysis results show that the MLT, BLT and DLT anomaly fields are mainly composed by two leading modes with similar temporal periods and different spatial patterns. Of them, the first modes of thickness anomaly fields suggest a coincident oscillation in the whole area, while the second modes have an anti-phase oscillation, which are almost associated with central Pacific ENSO (CP-ENSO). It is interesting that the mechanisms for these leading modes are different from each other. As for the MLT anomaly field, the first mode is primarily controlled by zonal winds, South Equatorial Current (SEC), net heat fluxes and precipitation altogether, while the second mode is mainly affected by zonal winds in the northwest WPWP and SEC. In regard to the BLT anomaly field, the first mode primarily results from zonal winds, SEC and precipitation, while the second mode is primarily controlled by the zonal winds and precipitation. And as to the DLT anomaly field, the two leading modes are primarily controlled by SEC.