Modeling the Gulf of Alaska using theROMS three-dimensional ocean circulation model
Yi Chao1,2,3, John D. Farrara2, Zhijin Li1,2, Xiaochun Wang2, Peggy Li1, Xin Jin3
1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA 911092Joint Institute for Regional Earth System Science and Engineering, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095
3Department of Atmospheric and Oceanic Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA, USA 90095
L0 10km, 40 layersL1 3.6km, 40 layersL2 1.2km, 40 layers
Atmospheric Forcing:L2: UAA, 4km WRF
L1, L0: 0.5o GFS
Tides forced on lateral boundaryof L0 domain byOSU global tide model output.
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
Seward Line Transect, 4-6 May 2009
Seward Line Transect, 15-19 Sept 2009
USCG Cruise South of Copper River
USCG Cruise South of Copper River Transect 27-29 July 2010
USCG Cruise South of Copper River Transect 8-9 April 2010
Effects of Horizontal Resolution
L1(3km)
L0(9km)
USCG Cruise South of Copper River Transect 27-29 July 2010
L0(9km)
L1(3km)
Effects of Horizontal Resolution
USCG Cruise South of Copper River Transect 27-29 July 2010
Seasonal Evolution ROMS L1
● 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)
ROMS L2 results
Sound Predictions 2009 Observations
July 20 - 26, 2009Strong SE winds,
strong north to northwestward flow in the central Sound
WRF Surface WindsSurface Currents
HF radar observed (Red), ROMS (Black)
July 27 – 30, 2009Moderate SE winds,
weak central Sound eddy
WRF Surface WindsSurface Currents
HF radar observed (Red), ROMS (Black)
July 31 – Aug 3, 2009Weak SW winds, central Sound eddy
WRF Surface WindsSurface Currents
HF radar observed (Red), ROMS (Black)
ROMS vs. HF Radar,Current Speed
Bias: -0.01 CRMS: 0.67 C
Bias: +0.27 PSURMS: 0.74 PSU
Bias: +0.08 CRMS: 0.69 CCorr: 0.71
Bias: +0.12 CRMS: 0.91 CCorr: 0.56
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
Seasonal Evolution ROMS L1
ROMS Analysis
ROMS Analysis
ROMS 3-level nested GOA configuration9, 3, and 1 km horizontal resolution(from the largest to the smallest domains)40 levels in the vertical
ROMS 3DVAR Data Assimilation and Forecast Cycle
2 or 3 day forecast
Aug.100Z
Time
Aug.118Z
Aug.112Z
Aug.106Z
Initialcondition
6-hour forecast
Aug.200Z
xa
xf
6-hour assimilation cycle
xa =x f
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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
ROMS vs. HF Radar,Current Speed
ROMS vs. HF Radar,Current Direction
Bias: -0.01 CRMS: 0.67 C
Bias: +0.27 PSURMS: 0.74 PSU
Bias: +0.11 CRMS: 0.96 C
Bias: +0.39 PSURMS: 0.82 PSU