Nearshore Wind-Wave Forecasting at the Oregon Coast Gabriel García, H. Tuba Özkan-Haller, Peter Ruggiero November 16, 2011
What is Wave Forecasting? An attempt to predict how the ocean surface is going to look like in the future.
Ocean Representation Significant Wave Height (SWH or H 1/3 ) Wave height corresponding to the average of the highest 1/3 waves Example: We have measured these six waves [ 6 3 2 5 2 1 ] SWH = 5+6 = 5.5 units 2 This agrees (I don t know why) with what a trained observer would describe.
Ocean Representation The Wave Spectrum Waves are not all the same Different directions Different amplitudes The spectrum represents the average sea state at a finite location Courtesy of USACOE FRF
Wave Generation (Historical Perspective) Circa 350 B.C. Aristotle noted wind had an important effect on wave generation Circa 50 A.D. Pliny noted that oil calms water waves Greco-Roman Empire to XV Century Nothing Golden Age of Science (Renaissance XVI-XVII C.) Advancements on fluid mechanics Late XIX and XX Centuries Fundamental physics and some fundamental processes of ocean wave generation were understood
First Operational Forecasting Model 1944 Allied invasion of Normandy, France D-DAY
Early Operational Forecasting Models Based on relationships among: Significant Wave Height Wave Length (or other descriptive bulk parameter) Wind Duration Wind Fetch Wind Speed
Current WF Technology Numerical models based on conservation of wave action (similar to conservation of energy) N t + N = Sources + Sinks Three such models are WAve Model (WAM) European Version Wavewatch III US Version MRI III Japanese Version Multiple models mean none is perfect
Wavewatch III Developed by NOAA The WW3 model has proven to have a higher skill in the Pacific Ocean at a basin scale than other models. See: Hanson, et al. Pacific hindcast performance of three numerical wave models. Journal of Atmospheric and Oceanic Technology, A(12):1614 1633, 1973.
Wave Action Equation N t + N = 1 σ S in + S ds + S nl + S bf + S brk S in - Energy input by wind S ds - Whitecapping (Deep Water Energy Loss) S nl - Non-linear wave-wave interactions S bf - Energy dissipation due to bottom friction S brk - Energy dissipation due to wave breaking
Wavewatch III input and dissipation. Based on Tolman H. L. and Chalikov D. Source Terms in a Third-Generation wind wave model. Journal of Physical Oceanograpy, 26(11):2497-2518, 1996. S in and S ds are based on a boundary layer formulation.
S in S wind f, θ = βωf f, θ S ds Low-Frequency Dissipation S ds, l = 2u hk 2 φn k, θ High-Frequency Dissipation S ds, h = a 0 u g 2 f 3 α n B N k, θ
Sources of Ocean Data Real-time and historical measured data National Data Buoy Center (NDBC) http://www.ndbc.noaa.gov/
Interests in Pacific Northwest Region Boat Traffic Safety Coastal Hazards Wave Energy Harvesting
Our work at OSU Implementation of a wave forecasting system for the Oregon and Southwestern Washington Coast (OSUWW3)
OSUWW3 High-resolution model Approximate Resolution (spherical coordinates) Alongshore 900m Cross-shore 650m 900 times more resolved that current models
Model Validation Hindcasts This is the prediction of waves based upon the past meteorological and oceanographic data
Forecast Accuracy Many statistical metrics available Root-mean squared error is widely used RMSE = Measured Modeled 2 Modeled
Forecast Accuracy Wave Forecasting
OSUWW3 Wave Forecasting
Upcoming products Bulk and Spectral Parameters at the 25 meter contour along the PNW coast. 233 Points 2.5 kilometer (1.5 mile) spacing
Northwest Association of Networked Ocean Observing Systems (NANOOS) http://www.nanoos.org/ Select Visualization System Select View Assets Select Overlays
Experimental Wave Forecasts at the Mouth of the Columbia River Sarah Kassem, Coastal Engineering MS Student
My favorite references Ocean Surface Waves: Their Physics and Prediction by S. Massel (1996) Guide to Wave Analysis and Forecasting World Meteorological Organization (1998)
Thanks for the invitation and attention Questions? Preguntas?