Decadal change in the relationship between the oceanic entrainment temperature and thermocline depth in the far western tropical Pacific

The interaction between the thermocline and mixed layer is a key process important to the El Niño-Southern Oscillation (ENSO) in the tropical Pacific climate system. Decadal changes in the relationships between the depth of 20°C isotherm (D_20C) and the temperature of subsurface water entrained into the mixed layer (T_e) are analyzed using observed temperature data during the periods 1955-2003 in association with the 1976-77 climate shift. The thermocline in the western tropical Pacific is anomalously deep before the shift, but shallow after the shift. It is found that the relationship has undergone decadal change in the far western tropical Pacific (west of 160°E). The effects of the decadal changes in the D_20C-T_e relationships on ENSO properties are further examined using an intermediate coupled model (ICM). It is demonstrated that ENSO properties are sensitive to the decadal changes in the D_20C-T_e relationship in the far western tropical Pacific.