Enhanced Turbulent Mixing in the Equatorial Thermocline

Kelvin John Richards, University of Hawai’i at Mānoa, International Pacific Research Center, Honolulu, HI, United States, Andrei Natarov, IPRC/SOEST Univ Hawaii, Honolulu, HI, United States and Yanli Jia, International Pacific Research Center, Honolulu, HI, United States
Enhanced mixing caused by small vertical scale features (SVSs) in the equatorial thermocline are known to impact the state of the ocean and its interaction with the atmosphere, in particular the sea surface temperature of the Pacific cold tongue and ENSO variability. The SVSs are produced by wind variability and instabilities. The good news is that with enough resolution these features can be captured in both observations and models. From observations we show that the vertical distribution of turbulent activity in the thermocline is very dependent on the turbulent length scale. From models we show that inertial and parametric subharmonic instability play a role and that wind driven inertia-gravity waves lead to an enhancement in mixing by a combination of a number of factors that include: a stronger superinertial component of the wind forcing close to the equator, wave action convergence at turning latitudes for equatorially trapped waves, nonlinear wave-wave interactions between equatorially trapped waves, and critical layer absorption. Using a combination of idealized models and an OGCM we investigate the properties of SVS activity and its impact on mixing. Of particular interest is the dependency on stratification, the spatial and temporal variability of wind forcing and model resolution (both vertical and horizontal). The impact of the spatially and temporally varying mixing on the seasonal and interannual variability of the tropical Pacific with be discussed. Such knowledge is invaluable in the planning of future observational studies and the design of the next generation climate models.