thirty years of operational ocean wave forecasting at fleet numerical meteorology and oceanography...

Thirty Years of Operational Ocean Wave Forecasting at Fleet Numerical

Meteorology and Oceanography Center

Paul Wittmann and Mike Clancy

Fleet Numerical Meteorology and Oceanography CenterMonterey, CA 93943

Singular Wave Model

• Developed by W.E. Hubert and B.R. Mendenhall.

• Used empirical growth curves to compute significant wave height and average wave periods from winds.

• Used simple time decay of swell to simulate wave dissipation.

• Used ray tracing techniques to propagate a single swell component along great circle paths.

• Became operational at Fleet Numerical for the Northern Hemisphere in 1964.

The Spectral Ocean Wave Model (SOWM)

• Developed by W.J. Pierson, T. Inoue, V.J. Cardone. • Implemented at Fleet Numerical by S.M. Lazanoff and

N.M. Stevenson.• Used a spectral resolution of 15 frequency and 12

directional bin.• Used a combined and modified Phillips/Miles wave

growth mechanism for wave growth.• Included wave dissipation due to opposing winds.

SOWM (Continued)

• Wave propagation was accomplished using a “jump” technique, where the wave energy is propagated to the surrounding grid points after sufficient time has passed.

• The Mediterranean SOWM became operational at Fleet Numerical in 1973.

• The Northern Hemisphere SOWM became operational at Fleet Numerical in 1975.

Global Spectral Ocean Wave Model (GSOWM)

• GSOWM built upon the success of the first-generation SOWM models.

• Contained essentially the same growth and dissipation formulations as SOWM.

• Increased the directional resolution to 24 bins (15 degrees).

• Used a new wave propagation method that ran on a spherical 2.5º x 2.5º global grid, forced by NOGAPS.

• GSOWM became operational at Fleet Numerical in 1984.

Third Generation Wave Model (WAM)

• Developed by the WAM Development and Implementation Group, an international an international group led by Klaus Hasselmann.

• Included explicit parameterization of non-linear wave interactions.

• Used Snyder wind growth formulation (later changed to Janssen growth term).

• Used wave dissipation developed by Hasselmann and Komen.

WAM (Continued)

• Initially implemented in 1990 for the Mediterranean basin on a 0.25º x 0.25º grid, forced by NORAPS.

• Implemented globally in 1994 on a 1º x 1º grid, forced by NOGAPS.

• Many high resolution nested regional areas were added and driven by mesoscale NWP models (NORAPS and later COAMPS).

Third-Generation Wave Model (WAM)

Wave Heights Predicted byCOAMPS/WAM During Hurricane Floyd

WaveWatch III

• Third-generation wave model similar to WAM, developed by Hendrik Tolman of NCEP.

• Uses Tolman/Chalikov wave growth equations.

• Improved third-order accurate wave propagation scheme.

• Uses the Message Passing Interface (MPI) routines to achieve efficient operation on distributed memory computer architectures.

• Implemented at Fleet Numerical in partnership with NCEP.

WaveWatch III (Continued)• Became operational at Fleet Numerical for global and

nested regional application, fully replacing WAM, in 2001.

• Initial global implementation in 2001 on a 1º x 1º grid; upgraded to a 0.5º x 0.5º global grid in the fall of 2002 to coincide with a comparable upgrade in NOGAPS resolution.

• Regional implementations forced by COAMPS for each COAMPS region.

Published Validation Studies of Wave Models at Fleet Numerical

Model RMSE Date Measurement Reference

----- ---- ---- ----------- ---------

SOWM 1.92 Jan 1985 Buoys Clancy et al. 1986

GSOWM 1.36 Jan 1985 Buoys Clancy et al. 1986

GSOWM 0.94 Mar 1992 Buoys Wittmann et al. 1994

WAM 0.74 Mar 1992 Buoys Wittmann et al. 1994

WAM 0.65 Jan/Feb 2000 Buoys Wittmann, 2002

WW3 0.67 Jan/Feb 2000 Buoys Wittmann, 2002

WAM 0.63 Jan/Feb 2000 ERS-2 Wittmann, 2002

WW3 0.58 Jan/Feb 2000 ERS-2 Wittmann, 2002

Quick Overview of Wave Model Historyat Fleet Numerical

• Singular Wave Model 1964 -1974

• Mediterranean SOWM 1972 -1990

• Northern Hemisphere SOWM 1974 - 1984

• Global SOWM 1984 - 1994

• Mediterranean WAM 1990 - 2001

• Global WAM 1994 -2001

• Nested Regional WAMs 1994 - 2001

• Global and Regional Wavewatch III 2001- present

Summary and Outlook

• Fleet Numerical has pioneered operational wave forecasting for over 30 years.

• The combined effect of improvements in ocean wave model and NWP models has improved forecast error significantly.

• Fleet Numerical will continue to partner with NCEP to achieve ongoing upgrades to WaveWatch III

• In addition to the traditional support provided for hazard avoidance, optimum track ship routing, and surf forecasting, Fleet Numerical wave models will play a new and important role supporting the Sea Basing component of the Navy’s Sea Power 21 doctrine.

This presentation is dedicated to the late Willard J. Pierson, whose

groundbreaking development of spectral ocean wave models laid the foundation

for practical ocean wave predictions and operational ocean wave models.