Seasonal and Regional Variability in North Pacific Upper-Ocean Turbulence

Turbulent diffusion at ocean mixed layer base (MLB) plays a fundamental role in the transport of energy between the upper and abyssal ocean. Recent investigations of North Pacific mooring data at Ocean Climate Stations (OCS) Papa (50.1N,144.9W) and KEO (32.3N,144.6E) suggest seasonal and regional variability in thermal diffusivity (κ_T). In this investigation, it is hypothesized that these observed differences in κ_T are directly associated with synoptic variability in net surface heat flux (Q₀), surface wind stress (τ), mixed layer depth (h), and density stratification at MLB (∂_zσ|_-h). To test this hypothesis, daily-averaged time series of κ_T are regressed against those of Q₀, τ, h, and ∂_zσ|_-h at both Papa and KEO over a six year time period (2007-2013). Seasonality of each time series is removed before regression to capture synoptic variability of each variable. Preliminary results of the regression analysis suggest statistically significant correlations between κ_T and all forcing parameters at both mooring sites. Corresponding regression coefficients have well-determined orders of magnitude and signs consistent with the hypothesis. As a result, differences in κ_T between Papa and KEO may be recast in terms of differences in their regression coefficients. In order to continue investigation of these parameters and their effects on mean seasonal differences between the two regions, these results are compared with turbulence predicted by the K-Profile Parameterization ocean turbulence model.