Vertical mixing in the ROMS model
发布日期: 2019/03/01

报告人:Robin Robertson, Professor, Xiamen University

时间:14:00-15:00 Monday 11/03/2019

地点:IOO Meeting Room, Xuhui Campus

摘要:

Vertical mixing is important in the ocean for maintaining its stratification, redistributing temperature and salinity, distributing nutrients and pollutants, and the energy cascade. It plays a key role in ocean energy transport, climate change, and marine ecosystems. Getting the mixing right in ocean circulation and climate models is critical in reproducing ocean and climate physics. Ocean models, like the Regional Ocean Modeling System (ROMS 3.4), provide several options for determining vertical mixing through the vertical mixing parameterization schemes. In order to evaluate which of these methods best reproduces realistic vertical mixing by internal tides, simulations of baroclinic tides generated by a seamount were performed using eight different vertical mixing parameterizations: Mellor-Yamada 2.5 (MY), Large-McWilliams-Doney’s Kpp (LMD), Nakanishi-Niino’s modification of Mellor-Yamada (NN), the Generic Ocean Mixing (GOM), and four versions of the Generic Length Scale (GLS). The GLS versions in ROMS 3.4 severely overmixed the water column within a day and were not considered realistic. GOM performance was also unrealistic with all values near the molecular level, 10-6 m2 s-1. We suspect a coding error has been introduced for them. We focused on the performance of the MY, LMD, and NN vertical mixing parameterizations. LMD was found to overmix the water column. The performance of MY and NN were nearly equivalent and both well reproduced the observed velocity and diffusivity fields. NN performed slightly better by having a lower rms for M2 and K1, less benthic mixing, more mid-water column mixing, less overmixing, and fewer extremely high diffusivities (> 1 m2 s-1).

 

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