Yu-Heng Tseng 1 *, Chia-Ping Chiang 1 , Sen Jan 2 , David E. Dietrich 3

1. Modeling Deep Circulation System in the Western North Pacific Yu-Heng Tseng1*, Chia-Ping Chiang1, Sen Jan2, David E. Dietrich3 1Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan 2Institute of Hydrological and Oceanic Sciences, National Central University, Taipei, Taiwan 3AcuSea Inc., San Diego, USA

2. Major Currents of the World Ocean But, how much do we understand the deep part?

3. Global Thermohaline Circulation: 1, thermal forcing, when water is cooled and sinks, and 2, haline forcing, when excess precipitation makes water less dense, and thus resistant to sinking. Driven by the sinking of cold, saline water No deep water formation The heat transport associated with “Atlantic deep circulation” plays an important role in the present climate. http://science.howstuffworks.com/ocean-current3.htm

4. Motivations and objectives Great Ocean Conveyor Belt in North Pacific? Deep Western Boundary Current (DWBC) in North Pacific (is weak but exists) Western boundary undercurrent (WBUC) east of Taiwan, Philippines and Ryuku island chain (resulting from the shifting of NEC, i.e. Qu and Lukas (2002)? similar to CUC?) Model descriptions Results: Overview of the northward transport DWBC in North Pacific WBUC east of Taiwan and Philippines Summary and future work

5. 1/8Ox1/8O 1/4Ox1/4O Extended to 30OS Dual-grids Pacific Ocean Model (DUPOM) Japan Sea East China Sea South China Sea NPB (North Pacific Basin) Domain: 30°S to 60°N and 150°E to 80°W TAI Domain: 0° to 50°N and 100°E to 150°E

6. Greenland 1/8ox1/8o 1/16ox1/16o 1/4ox1/4o 1/8ox1/8o 1/24ox1/24o MEDiNA model: Bathymetry (km) and sub-domains Six domain: GOM (1/8o) 304x336 NAB (1/4o) 162x398 IBE (1/8o) 100x794 VIS (1/16o) 60x158 GIB (1/24o) 125x107 MED (1/8o) 316x157 1/8ox1/8o 30 vertical layers; top layer 11 m thick; bottom layer 750 m thick Dietrich et al. (2008) 'Accurate Mediterranean overflow water (MOW) simulation using a coupled multiple-grid Mediterranean Sea/North Atlantic Ocean model on a PC', J. Geophys. Res.-Ocean, 113, C07027, doi:10.1029/2006JC003914, 2008

7. MOW deep penetration Strait of Gibraltar domain velocity vectors (1000m) Tseng and Dietrich (2006) 'Entrainment and transport in the three-dimensional idealized gravity current simulation', J. Atmos. Oceanic Technol., 23, 1249-1269 velocity maximum is 48.9 cm/s

8. Salinity at different longitudes MOW deep penetration

9. Vertical/longitudinal salinity section at 43°N Annual averaged model results U. S. Navy’s GDEM climatology

10. Based on the 4th order accurate, collocated Arakawa “a” grid DieCAST (Dietrich/Center for Air Sea Technology) model. The control volume equations include fluxes of the conservation of momentum, heat and salt across control volume faces. Bathymetry: Interpolated from unfiltered ETOPO5 depth data Supplemented with NCOR’s 1-minute high accuracy depth archive. The vertical resolution ~ linear-exponential stretched grid, 26 layers - Z=6, 20, 36, 54, 75, 98, 126, 159, 198, 244, 298, 364, 442, 537, 652, 790, 958, 1161, 1408, 1709, 2075, 2520, 3063, 3725, 4532 m. Varying latitude and uniform longitude grid (Mercator grid).

11. Surface forcing: Use interpolated monthly Hellerman and Rosentstein winds (Hellerman and Rosenstein, 1983). Use Levitus’94 climatology (Levitus and Boyer, 1994) to initialize the model and determine its surface sources of heat and fresh water. Other details: The northern boundary is closed. The southern boundary condition (30°S) is slow nudging toward climatology in a sponge layer. The bottom is insulated, with non-slip conditions parameterized by a nonlinear bottom drag. Sub-grid scale vertical mixing is parameterized by eddy diffusivity (for temperature and salinity) and viscosity (for momentum) using a modified Richardson number based approach based on Pacanowski and Philander. Background lateral viscosity (diffusivity) is 100 (20) m²/s in both domains.

12. Northward heat transport Low latitude: cyclonic Middle-high latitude: anti-cyclonic Ganachaud (2003) Fig. 4 , , Model results during Year 36-37

13. Global Thermohaline Circulation: 1, thermal forcing, when water is cooled and sinks, and 2, haline forcing, when excess precipitation makes water less dense, and thus resistant to sinking. Driven by the sinking of cold, saline water No deep water formation The heat transport associated with “Atlantic deep circulation” plays an important role in the present climate. http://science.howstuffworks.com/ocean-current3.htm

14. Mid latitudes Deep currents carry the Lower Circumpolar Water (LCPW)and oxygen-rich water ~2000–3000m above the LCPW eastern branch Yanagimotoet al.,2007 Low latitudes Eastern branch western branch

15. TAI bathymetry and observations km

16. Deep current at 38°N east of Japan A pair of opposite flows From：Deep current measurements at 38N east of Japan (Fujio and Yanagimoto, 2005)

17. Izu-Ogasawara Trench Vertical current structure normal to 34°N (Day 201 Year 36) 2 pairs of opposite current cores which flow above 1000 and below 1500 m. Deep current at 34°N east of Japan Geostrophic veloctiy relative to 2000 db (Fujio et al., 2000)

18. Deep current at 34°N east of Japan Velocity out of phase From：Deep current structure above the Izu-Ogasawara Trench (Fujio et al., 2000)

19. Deep countercurrent beneath the Kuroshio Obs. <520m DUPOM Consistent with Feng et al., 2000 <625m Model (1998-2006) 2.5 m 526.9 m Nakamura et al., 2008

20. WBUC east of the Philippine Vertical current structure east of Philippine (Qu et al., 1997) Southward flow underneath the Kuroshio east of Luzon

21. Impact of North Equatorial Current (NEC) NEC NEC NEC Northward shifting of NEC with increasing depth. • Geostrophic velocity at 100, 300, and 500 m relative to 1500 db calculated from WOA94. (Qu et al., 1997)

22. WBUC east of Taiwan 4 1 WBUC resulting from NEC?? Guan (1990)

23. Possible Explanation: • Mix layer • Middle Layer (thermocline layer) • Deep Layer If h’‧h’>0 (same direction), V increases with depth, will not reverse. If h’‧h’<0 (opposite direction), V decreases with depth, could reverse. Without stratification V is determined by h’ Independent of Z V varies with depth V0 equals at the bottom of the middle layer Independent of Z

24. Thermohaline circulation in North Pacific Deep circulation in lower and middle latitudes contributes to the heat transport in the North Pacific DWBC shows consistent southward flow along the western boundary of the Pacific DWUC is the countercurrent beneath Kuroshio and is commonly found from Philippine to South of Japan Future work The mechanisms for DWUC (causes?) Formation of cold dome and its variability in the northeast of Taiwan South China Sea throughflows Summary and future work

25. A summary of interior flow (Schmitz, 1995)

26. 1st term: Relative veloctiy thermal wind equation 2nd term: Relative veloctiy thermal wind equation

27. . Cold air from the Canadian arctic forms the most plentiful source of deep water – the North Atlantic Deep Water Warm surface water of the conveyor moves north in the Atlantic until it hits a region near Iceland where it is cooled by cold arctic air. Effective transfer of heat to the atmosphere occurs, thus keeping northern Europe usually warm for it’s latitude. The surface water cools due to this heat transfer and, as a result becomes more dense and sinks. This sinking is aided by the extra salinity of the Arctic Ocean. Thermohahaline Circulation

28. The second method of deepwater formation is by freezing out When ice freezes, salt is excluded. This raises the salinity of the underlying water, making it more dense. The densest water on the ocean bottom is formed by freezing out in Antartica – but this water is not a plentiful source, compared to North Atlantic Deep Water.

29. Ocean currents in the GIN Seas Saline water transport West spitsbergen Current East Greenland Current Greenland Deep convection Norwegian Atlantic Current Iceland Saline water transport Saline water is transported from the Atlantic Ocean to the GIN Seas and the Arctic Ocean through the Iceland-Scotland passage and the Fram Strait. ・ How much does the model resolution affect the representation of such current system in the GIN Seas and the formation of the Atlantic deep circulation ?

30. Contents OGCM experiment under SSS restoring boundary condition 1, Control ( 2 x 2 resolution ) 2, Increased resolution in the GIN Seas ( 1 ~ 0.25 degrees) → It is shown that increased resolution leads to more realistic representation of oceanic salinity transport in the GIN Seas. OGCM experiment forced by climatological freshwater flux → How much model resolution affect the strength of the Atlantic deep circulation ?

31. 2, Model CCSR Ocean Component model(COCO) ・Bottom Boundary Layer Parameterization(Nakano and Suginohara 2002) ・The model horizontal coordinate is rotated so that the North Pole is on Greenland. Sea ice model ・Dynamical part is EVP rheology (Hunke and Dukowicz 1997). ・Thermodynamical part is Semtner 0 layer model. Surface boundary conditions ・Heat : calculated from bulk formula using sea surface heat flux climatology of NCEP ・Salinity ： 1, restored to monthly climatology of PHC (Steele et al.2001). 2, forced by climatological E-P-R without SSS restoring

32. Control ( 2x2 resolution ) with SSS restoring Temperature Atlantic Ocean Meridional streamfunction Salinity

33. Salinity forcing in the North Atlantic (Broecker, 1997)

34. Sea ice formation: A salinity forcing (Open Univ, 2005)

35. Salinity forcing around Antarctica (Open Univ., 2005)

36. Nutrient distribution and deep circulation ２５００ｍ

37. Meridional sections Pacific Atlantic PT S

38. Objectively mapped WOCE Natural D14C on 3500 m level surface

39. Objectively mapped WOCE Natural D14C “age” on 3500 m level surface

40. (Stewart, 2008 Introduction of Physical Oceanography, p71) 1PW=10^15W Global heat transport in 1988