1. Modeling the Gulf of Alaska using the ROMS three-dimensional ocean circulation model Yi Chao 1,2,3, John D. Farrara 2, Zhijin Li 1,2, Xiaochun Wang 2, Peggy Li 1, Xin Jin 3 1 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA 91109 2 Joint Institute for Regional Earth System Science and Engineering, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095 3 Department of Atmospheric and Oceanic Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA, USA 90095 L0 10km, 40 layers L1 3.6km, 40 layers L2 1.2km, 40 layers Atmospheric Forcing: L2: UAA, 4km WRF L1, L0: 0.5 o GFS Tides forced on lateral boundary of L0 domain by OSU global tide model output.

2. 2009 Freshwater discharge produced by a Digital Elevation Model (DEM) vs. Copper River observations WRF/GFS Precipitation DEM Freshwater input to ROMS from point sources (rivers) and line sources (runoff) Copper River Discharge 2009

4. Seward Line Transect, 4-6 May 2009

6. Seward Line Transect, 15-19 Sept 2009

8. USCG Cruise South of Copper River

9. USCG Cruise South of Copper River Transect 27-29 July 2010

10. USCG Cruise South of Copper River Transect 8-9 April 2010

11. Effects of Horizontal Resolution L1 (3km) L0 (9km) USCG Cruise South of Copper River Transect 27-29 July 2010

12. L0 (9km) L1 (3km) Effects of Horizontal Resolution USCG Cruise South of Copper River Transect 27-29 July 2010

13. Seasonal Evolution ROMS L1

16. ● ROMS L1 (3km horizontal resolution) realistically reproduces the vertical structure and seasonal changes from spring to summer in temperature and salinity observed along the Seward Line and south of the Copper River. ● ROMS L1 realistically reproduces the nearshore Alaska coastal current and the Alaskan stream at the shelf break. ● Thus, ROMS L1 is well suited for use in process studies in the northern Gulf of Alaska. ● ROMS L0 (9km horizontal resolution) results are less realistic, in particular, the Alaskan stream is weaker and more diffuse. http://ourocean.jpl.nasa.gov/PWS Summary (ROMS L1)

17. ROMS L2 results

18. Sound Predictions 2009 Observations

19. July 20 - 26, 2009 Strong SE winds, strong north to northwestward flow in the central Sound WRF Surface Winds Surface Currents HF radar observed (Red), ROMS (Black)

20. July 27 – 30, 2009 Moderate SE winds, weak central Sound eddy WRF Surface Winds Surface Currents HF radar observed (Red), ROMS (Black)

21. July 31 – Aug 3, 2009 Weak SW winds, central Sound eddy WRF Surface Winds Surface Currents HF radar observed (Red), ROMS (Black)

22. ROMS vs. HF Radar, Current Speed

23. Bias: -0.01 C RMS: 0.67 C Bias: +0.27 PSU RMS: 0.74 PSU

25. Bias: +0.08 C RMS: 0.69 C Corr: 0.71 Bias: +0.12 C RMS: 0.91 C Corr: 0.56

26. Summary (ROMS L2) During the Prince William Sound Predictions Field Experiment 2009, the ROMS ocean modeling system was run daily in real-time to support operations. http://ourocean.jpl.nasa.gov/PWS09 The broad-scale temperature and salinity patterns within the PWS were reproduced in ROMS nowcasts/forecasts, though in general horizontal and vertical gradients were weaker than observed and there was a near surface salty bias. The overall flow pattern, as well as individual drifter trajectories, were well simulated. In addition, the time evolution through the following 3 distinct phases was reproduced: 1) Strong SE winds, rain, low light conditions; strong north to northwestward flow in the central Sound 2) Moderate SE winds, weak central Sound eddy 3) Weak SW winds, central Sound eddy

27. Seasonal Evolution ROMS L1

31. ROMS Analysis

32. ROMS Analysis

33. ROMS 3-level nested GOA configuration 9, 3, and 1 km horizontal resolution (from the largest to the smallest domains) 40 levels in the vertical

34. ROMS 3DVAR Data Assimilation and Forecast Cycle 2 or 3 day forecast Aug.1 00Z Time Aug.1 18Z Aug.1 12Z Aug.1 06Z Initial condition 6-hour forecast Aug.2 00Z xaxa xfxf 6-hour assimilation cycle 34 Satellite Observations (MODIS SSTs) In-situ Observations (e.g., Gliders) 1) Multi-scale 3DVAR Data assimilation scheme --> Nowcast every 6 hours 2) Ensemble of sixteen 48-hour forecasts each day

38. ROMS vs. HF Radar, Current Speed

39. ROMS vs. HF Radar, Current Direction

40. Bias: -0.01 C RMS: 0.67 C Bias: +0.27 PSU RMS: 0.74 PSU

41. Bias: +0.11 C RMS: 0.96 C Bias: +0.39 PSU RMS: 0.82 PSU