The K-profile Parameterization augmented by Deep Neural Networks
(KPP_DNN) in the General Ocean Turbulence Model (GOTM)
Abstract
This study utilizes Deep Neural Networks (DNN) to improve the K-Profile
Parameterization (KPP) for the vertical mixing effects in the ocean’s
surface boundary layer turbulence. The DNNs were trained using 11-year
turbulence-resolving solutions, obtained by running a large eddy
simulation model for Ocean Station Papa, to predict the turbulence
velocity scale coefficient and unresolved shear coefficient in the KPP.
The DNN-augmented KPP schemes (KPP_DNN) have been implemented in the
General Ocean Turbulence Model (GOTM). This implementation is stable for
long-term integration and as efficient as existing variants of KPP
schemes. Three different KPP_DNN schemes, varying in input and output
variables, have been developed and trained. The performance of models
using the KPP_DNN schemes is compared with that of those using popular
deterministic first-order and second-moment closure turbulent mixing
parameterizations. Solution comparisons show that the simulated mixed
layer is cooler and deeper, aligning closely with observations when wave
effects are included in parameterizations. In the KPP framework, changes
to the velocity scale of unresolved shear, which is used to calculate
mixed layer depth, have a larger impact on the simulated mixed layer
than do changes to the magnitude of diffusivity. In the KPP_DNN,
changes to unresolved shear depend on not only on wave forcing, but also
on the mixed layer depth and buoyancy forcing.