Parameterization of vertical mixing in the Weddell Sea

• Published in: Ocean Modelling
• Main Authors: Timmermann, R., Beckmann, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2004
• Subjects: Weddell Sea; Weddell; Mellor; Sea ice
• Online Access: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=211392

A series of vertical mixing schemes implemented in a circumpolar Coupled ice-ocean model of the BRIOS family is validated against observations of hydrography and sea ice coverage in the Weddell Sea. Assessed parameterizations include the Richardson number-dependent Pacanowski-Philander scheme, the Mellor-Yamada turbulent closure scheme, the K-profile parameterization, a bulk mixed layer model and the ocean penetrative plume scheme (OPPS). Combinations of the Pacanowski-Philander parameterization or the OPPS with a simple diagnostic model depending on the Monin-Obukhov length yield particularly good results. In contrast, experiments using a constant diffusivity and the traditional convective adjustment cannot reproduce the observations. An underestimation of wind-driven mixing in summer leads to an accumulation of salt in the winter water layer, inducing deep convection in the central Weddell Sea and a homogenization of the water column. Large upward heat fluxes in these simulations lead to the formation of unrealistic, large polynyas in the central Weddell Sea after only a few years of integration. Furthermore, spurious open-ocean convection affects the basin-scale circulation and leads to a significant overestimation of meridional overturning rates. We conclude that an adequate parameterization of both wind-induced mixing and buoyancy-driven convection is crucial for realistic simulations of processes in seasonally ice-covered seas.