Modeling the Gulf of Alaska using the ROMS three-dimensional ocean circulation model Yi Chao 1,2,3,...

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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

Freshwater input to ROMS from point sources (rivers)

and line sources (runoff)

Copper River Discharge

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)

L1(3km)

Effects of Horizontal Resolution

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

July 31 – Aug 3, 2009Weak SW winds, central Sound eddy

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 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

Aug.118Z

Aug.112Z

Aug.106Z

Initialcondition

6-hour forecast

Aug.200Z

6-hour assimilation cycle

xa =x f

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: +0.11 CRMS: 0.96 C

Modeling the Gulf of Alaska using the ROMS three-dimensional ocean circulation model Yi Chao 1,2,3,...

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