On An Functional Relationship between ENSO’s Subsurface Temperature and Thermocline Depth

Abstract:

The temperature of the subsurface water entrained into the surface mixed layer plays a key role in controlling the sea surface temperature (SST) and its interannual variability in the equatorial Pacific. In this paper, we combine a hyperbolic tangent function bounded by the warm pool SST and centered at the thermocline depth with a variable sharpness parameter to describe the time-space evolution of the subsurface temperature. Under simple approximations of the sharpness parameter, this concise expression becomes remarkably efficient in capturing the observed and climate-model simulated subsurface temperature variability in terms of anomalies of the thermocline depth and SST of the El Niño-Southern Oscillation (ENSO) phenomenon. The formulations for the subsurface temperature developed in this work are useful tools for evaluating and understanding the role of the thermocline feedback in ENSO behaviors in different climates simulated in climate models.