Chapter 5

Circulation modelling

CHAPTER
COORDINATORS

Stefania Ciliberti

CHAPTER
AUTHORS

Nadia Ayoub, Jérôme Chanut, Mauro Cirano13, Anne Delamarche, Pierre De Mey-Frémaux, Marie Drevillon, Yann Drillet, Helene Hewitt, Simona Masina, Clemente Tanajura, Vassilios Vervatis, and Liying Wan

5.2 Circulation forecast and multi-year systems

5.2.1 Ocean-Earth system as basis for OOFS

The ocean is a system that interacts with other systems. Figure 5.1 shows a simplified representation of the Earth system interaction in weather and ocean forecasting. Focusing on the ocean, we can identify (Madec et al., 2022):

Connection with land: in particular with rivers and lakes which exchange freshwater flux with the ocean;
Connection with the atmosphere: the ocean receives precipitation and returns evaporation. The atmosphere and the ocean also exchange horizontal momentum (wind stress) and heat;
Connection with sea ice: the ocean exchanges heat, salt, freshwater and momentum with sea ice. The sea surface temperature is constrained to be at the freezing point of the interface. Sea ice salinity is very low (~4-6 PSU) compared to that of the ocean (~34 PSU). The cycle of freezing/melting is associated with freshwater and salt fluxes and cannot be neglected;
Connection with solid earth: heat and salt fluxes through the seafloor are small, hence no flux of heat and salt is considered across solid boundaries. For momentum instead, we express the kinematic boundary condition. Additionally, the ocean exchanges momentum with the Earth through friction; this needs to be parameterized in terms of turbulent fluxes using bottom and lateral boundary conditions.

These connections will be detailed along this chapter and represent the core of the OOFS architecture introduced in the next subsection.

5.2.2 Architecture singularities

An OOFS that would provide the prediction, as well as the past reconstruction of the past state of the ocean, is based on several components that are strongly linked. A general introduction to OOFS architecture singularities is provided in Chapter 4, which includes for each system component, input and output data, as well as links between some of the components, are described. Complexity of the system, components of the system, infrastructure, maintenance of the code, and monitoring of the whole data flow should be defined depending on needs, robustness and operationality. Of course, the cost of the development, maintenance and evolution of the system depends on operational constraints.

Figure 5.1. Representation of the ocean processes and connections with the Earth.

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