Preliminary Results from the Global Ocean Simulations with the Baringer-Price-Yang Marginal Sea Boundary Condition Model Wanli Wu, William Large and Gokhan Danabasoglu National Center for Atmospheric Research wanliwu@ucar.edu OUTLINE Baringer-Price-Yang Marginal Sea Boundary Condition (MSBC) model Implementation of the MSBC model into POP Preliminary Results Ongoing and Future work

The Strait of Gibraltar Geometry parameters: Location: (36N,6W) Width (W): 20km Sill depth (D): 280m Shelf-slope break (ssb) depth: 400m Slope of ssb: 0.012

The MSBC model (Baringer & Price, 1997, Price & Yang, 1997) Exchange dynamics (Bryden & Stommel, 1984; Bryden & Kinder, 1991) Outflow/inflow fluxes: Ms=-Mi = 0.07 g ’1/2 D 3/2 W, g’=g(rs-ri)/rs Entrainment & Product: (Baringer & Price, 1994; Price and Yang, 1997) Entrainment rate ~~ Froude number F=g’a/f (g’h)1/2 Product water flux is given by Mp=MsF2/3 Entrained water flux is then given by Me=-(Mp+Mi) Their steady MSBC process model requires Climatological T & S profiles from the open ocean water properties, and Climatological fresh water flux (E-P) and heat flux (Q) of the marginal sea to derive density difference (rs-ri) then --> mass transport (volume fluxes) Density difference was given by E-P, and heat fluxes over the Mediterranean Based on assumption: Mass, heat and salt conservation Observed product water ~ 900~1200m Entrained level determined by the strait geometry (~400m)

Implementation of the MSBC model into POP Implementation of the process model into POP (~3o) to simulate water transport crossing the Gibraltar Strait The strait is currently closed in the model Use instantaneous Ti, Ts, Si and Ss from model instead of climatological Ti, Si, E-P and Q, Time-varying MSBC, Based on T & S profiles to compute density difference , then volume fluxes: Ms (Mi), Me and Mp From volume fluxes --> velocity (Ui, Us, Ue, Up), then replace the zero velocity and (T&S) fluxes (UT, US) on the open ocean and marginal sea interface. Experiments: 50-year POP runs with/without MSBC

Outflow water properties model observed sources mean inflow transport (sv) 0.9 0.9~1.8 Bryden et al, 1989 seasonality: Max Min Amp March August 6% Spring Fall Bormans et al., 1986 current velocity(m/s) 0.64 0.6 Baringer et al., 1997 salinity difference(psu) 1.80 2.12 Product water depth(m) salinity (psu) potential temperature (C) 815~985 37.15 13.82 915 36.46 12.74 Price & Yang, 1997

Summary A time-dependent Marginal Sea Boundary Condition (MSBC) model was implemented to an OGCM, and applied for the Gibraltar Strait overflow. The model with MSBC simulated reasonable water properties and seasonal cycle of the water exchange through the Strait. The model with MSBC also realistically reproduced the warm and saline tongue in the North Atlantic.

Ongoing Research and Future Work (open for discussion!) Testing the same scheme in POP with higher resolution (~1o with open strait) Implement the MSBC into other places like Faroe Bank Channel, Denmark Strait. Long-term ocean alone simulation Coupled simulation for climate impact study