1. A data-assimilated circulation model of the Northwestern Atlantic Ocean using the new mpi-version of the Princeton Ocean Model (mpiPOM) Fanghua Xu and Lie-Yauw Oey Princeton University OSM on Feb, 20, 2012

2. Goal: Present mpiPOM: to analyze loop current shedding dynamics Middle Atlantic Bight Xu & Oey, 2011: The Origin of Along-Shelf Pressure Gradient in the Middle Atlantic Bight. J. Phys. Oceanogr 41, 1720-1740 Study Region

3. mpi-Princeton Ocean Model ( http://www.imedea.uib.es/users/toni/sbpom/ ) Grids: horizontal: ~5km, vertical: 25 levels CCMP (1988-2009) & NCEP/GFS wind (after 2009) Data assimilation SSHA Highlights of Model Used in This Study ( http://www.aos.princeton.edu/WWWPUBLIC/PROFS/ )

4. A forecast experiment, 2011/07/01 SSH Black: model SSH=0; Pink: AVISO SSH=0 Eddy shedding time Forecast2011/Jul/22 Observed2011/Jul/22~29

5. 1 st order dynamics: Q i < C i = - βR o 2, (Nof 1995 JPO) can “peel” a portion of the Loop’s mass – i.e. a warm eddy – westward. Qi: Yucatan influx C i : the 1 st mode baroclinic Rossby wave velocity R o = (g’h(t)) 1/2 /f Eddy shedding time X Wind stress in Carib Sea Yucatan transport - C i Hindcast run Free model run 07/08 05/16 03/26 A free model run, starting from 2011/05/16 There exists a close connection between Yucatan transport and winds in Caribbean and in GOM: Chang & Oey, 2012, GRL, in press: Why does the Loop Current tend to shed more eddies in summer and winter? Eda’s talk on Thursday 14:30 session 30.

6. Eddy shedding time Loop Formation There is coupling with the deep layer; the coupling can be inferred from basic mass conservation as indicated in the above sketch. Chang & Oey, 2011, JPO ssh (m) Hindcast runFree model run Convergence divergence Shedding

7. If Yucatan inflow and Rossby wave dynamics alone – it will take roughly 2 months. i.e. mid-August – instead of Jul/08, for the Loop to shed – the acceleration is through baroclinic instability & upper-lower coupling The Campeche Bank 05/16 - 06/15 06/01 – 06/30 Growth rate  1/40d ~ 1/10d BCI (m 2 /s 3 ) @ z=-750m Oey, 2008, JPO

8.  The Loop Current eddy-shedding is primarily due to an imbalance between YUC influx & westward baroclinic Rossby wave, and shedding is accelerated by baroclinic instability and the upper-lower & east-west coupling.

10. ζ /f Latitude 05/1607/08 Latitude 03/2605/1607/08 SSH ζ /f : vorticity over the west Yucatan channel Latitude: edge of Loop Currents The decrease of ζ /f induces an anticyclonic circulation, which retract the loop currents

12. Total transport in YUC, FL straits, and 90w

14. Comparison of model transports in middle Atlantic with available observations

15. Comparison of 1-day average SSHA of hindcast simulation with 1-day average of tide gauge data 1994 2004 1994 2004

16. Momentum Balance: What drives the along-shelf circulation? Depth averaged currents Xu & Oey, JPO, 2011 (Lentz, JPO, 2008) Along-shelf pressure gradient (ASPG) 10 -8 ~10 -7 drives mean along-shelf flow towards the southwest (Stommel and Leetmaa,1972; Csanady, 1976; Lentz, 2008);

17. ASPG×10 8 = RIV + (7×UA+1.3)×H v (UA-UA critical ) – WIND- GS RIV=2; UA critical =1; WIND=1; GS=6 The origin of the mean along-shelf pressure gradient ( ASPG) Distance from Cape Hatteras Elevation

18. A schematic sketch of the cross-shelf section circulation illustrating 3-layer structure from mid- to outer shelves, and 2-layer from coast to mid-shelf, as well as mid-shelf near-bottom divergence, from Lentz [2008; his fig.2]. Cross-shelf circulation

19. hcastT Fig. Daily-averaged SSH (colors in m), surface currents (squiggly black lines) and wind stress vectors (blue) shown for the 15 th day of each month from Jan-Dec in 2010 for the hindcast experiment with tides. Magenta contour=AVISO SSH=0 and white contour=200m isobath.

20. (A) SSHA (B) (U g,V g ) Fig. 4 Comparison between AVISO and modeled (a) SSHA (anomaly) and (b) surface geostrophic velocity (U g,V g ). The “(a)” panels on left show top: spatial correlation coefficient between the model and AVISO SSHA’s in the region north of 23 o N and west of 84 o W, and over water region deeper than 500 m in the Gulf of Mexico for time period Jan-Dec/2010; and bottom: the corresponding RMS error for the same region. The “(b)” panels on right compare the corresponding (U g,V g ): top & middle are magnitude and angle of the complex correlation and bottom is the RMS error. In each case, the 2010-mean’s are also shown. See Table1 for experiment names.

21. Fig. 5 Comparison between modeled transport at the Straits of Florida off the eastern coast of Florida between West Palm Beach, FL to Eight Mile Rock, Grand Bahama Island and cable-estimated observed transport (http://www.aoml.noaa.gov/phod/floridacurrent/data_access.php) for the time period Jan-Dec/2010. Note that model was not forced by wind from Jan/01 through Mar/15. The Table on left shows the 2010-mean’s for observed and modeled transports, and their zero-lag correlations and 95% significances computed for the entire 2010 from Jan-Dec (3 rd column in the Table) and for Apr-Dec only (4 th column in the Table).http://www.aoml.noaa.gov/phod/floridacurrent/data_access.php Mean (Sv) R /S Jan-Dec R /S Apr-Dec Obs. 30.5-- Exp.1 31.2.32/.16.52/.17 Exp.2 30.7.34/.12.57/.12 Exp.3 30.2.39/.14.71/.19 Exp.4 30.9.38/.13.60/.13 Exp.1= hcastNoT Exp.2= hcastT Exp.3= hcast.horcon0p2 Exp.4= hcastT.horcon0p2 R=Correlation; S=95% Significance

22. Comparison of hindcast simulation with drifters

23. Comparison of hindcast simulation with ADCP currents

25. Goal: Present mpiPOM: to analyze loop current shedding dynamics Middle Atlantic Bight Xu and Oey, 2011,JPO

26. Highlights of the mpi-version of the Princeton Ocean Model mpiPOM IC BC River tides wind Data assimilation: SST, ADCP, Drf, &T/S Data assimilation: SST, ADCP, Drf, &T/S Grids output

27. Highlights of the mpi-version of the Princeton Ocean Model

28. Model engine: mpi-Princeton Ocean Model – 3D currents, T/S, SSH, turbulence KE (TKE) & length w/wave- breaking and Stokes drift TKE production; wave- enhanced BBL; 4 th -order pressure grad scheme; Grids: horizontal: ~5km, vertical: 25 levels; Topography: Etopo2+NOS digitized map on shelves; Open BC@55W: Transport and climatological T/S + radiation & FRS [Oey & Chen, 1992a,b; JGR]; Surface fluxes: CCMP wind (1987-2009); NCEP/GFS 2010-present; supplemented w/hurricane winds from AOML’s HRD; Heat & salt fluxes: monthly climatology or daily NCEP; 51 Rivers: daily, 34 in GOM, 17 east coast; Data assimilation: SSHA, SST, Drifters, bred-ensemble; Tides: M2, S2, K1 & O1; Wind-waves, w/option to couple with currents; Inundation Nesting Princeton’s Circulation & Wave Model of the Northwestern Atlantic Ocean (http://www.aos.princeton.edu/WWWPUBLIC/PROFS/)