A Concise and Effective Expression Relating Subsurface Temperature to the Thermocline in the Equatorial Pacific

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 evolutions 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 and thermocline sharpness developed in this work should be useful tools for evaluating and understanding the role of the thermocline feedback in ENSO behaviors in both theoretical and comprehensive climate models.

ENSO Diversity Simulated in a Revised Cane-Zebiak Model

“…The primary difference of the mixed-layer model between RCZ and the CZ model is in the formulation of subsurface temperature parameterization. Yuan et al (2020) found that the parameterization scheme in the CZ model 1) artificially introduces an over-strong El Niño/La Niña asymmetry and 2) underestimates subsurface temperature anomalies in the central Pacific (also see Figure 1). Inspired by ZC87 and Yuan et al (2020), a subsurface temperature parameterization is proposed as…”

On the Breakdown of ENSO's Relationship With Thermocline Depth in the Central‐Equatorial Pacific

“…Zhang et al., 2003, 2005; Zheng et al., 2006). However, accurately describing T d using solely knowledge of thermocline depth is problematic and additional considerations including mixing processes appear to be needed (Dewitte et al., 2009; Yuan et al., 2020).…”

“…Several more empirical local and nonlocal parameterized relationships have been established between T d anomalies and thermocline depth anomalies or SSH anomalies (Kang & Kug, 2000;R.-H. Zhang et al, 2003R.-H. Zhang et al, , 2005Zheng et al, 2006). However, accurately describing T d using solely knowledge of thermocline depth is problematic and additional considerations including mixing processes appear to be needed (Dewitte et al, 2009;Yuan et al, 2020).…”