Abstract
It has been identified that there are several limitations in the Mellor–Yamada (MY) turbulence model applied to the atmospheric mixed layer, and Nakanishi and Niino proposed an improved MY model using a database for large-eddy simulations. The improved MY model (Mellor–Yamada–Nakanishi–Niino model; MYNN model) is popular in atmospheric applications; however, it is rarely used in oceanic applications. In this study, the MY model and the MYNN model are compared to identify the efficiency of the MYNN model incorporated into an ocean general circulation model. To investigate the impact of the improved MY model on the vertical mixing in the oceanic boundary layer, the response of the East/Japan Sea to Typhoon Maemi in 2003 was simulated. After the typhoon event, the sea surface temperature obtained from the MYNN model showed better agreement with the satellite measurements than those obtained from the MY model. The MY model produced an extremely shallow mixed layer, and consequently, the surface temperatures were excessively warm. Furthermore, the near-inertial component of the velocity simulated using the MY model was larger than that simulated using the MYNN model at the surface layer. However, in the MYNN model, the near-inertial waves became larger than those simulated by the MY model at all depths except the surface layer. Comparatively, the MYNN model showed enhanced vertical propagation of the near-inertial activity from the mixed layer into the deep ocean, which results in a temperature decrease at the sea surface and a deepening of the mixed layer.
Highlights
Turbulence in the oceanic boundary layer (OBL) is of paramount importance because it vertically transports heat and momentum
The impact of the MYNN model on the tropical cyclones (TCs)-induced vertical mixing in the OBL was examined by comparing the results obtained by each turbulence model before and after Typhoon Maemi passed through the EJS
Before the typhoon passed over the EJS, the sea surface temperature (SST) simulated using the two turbulence models showed a similar distribution to the observed data
Summary
Turbulence in the oceanic boundary layer (OBL) is of paramount importance because it vertically transports heat and momentum. The air–sea interaction through the SST significantly influences many atmospheric and oceanic phenomena by determining the momentum and enthalpy exchange between the atmosphere and the ocean [1,2,3,4] It plays a vital role in the occurrence and development of severe weather events originating from the ocean, such as tropical cyclones (TCs) [5]. Vincent et al [13] discussed the ocean response to TC transits by investigating the integrated impact of TCs on the seasonal ocean thermal structure and heat transport They found that the climatological ocean state is closely influenced by TC wind-driven surface heat fluxes, TC-induced oceanic vertical mixing, and advective processes
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