Nearshore Wind-Wave
Forecasting at the Oregon Coast
Gabriel García, H. Tuba Özkan-Haller,
Peter Ruggiero
November 16, 2011
Wave Forecasting
• What is Wave Forecasting?
– An attempt to predict how the ocean surface is
going to look like in the future.
Wave Forecasting
Wave Forecasting
• Ocean Representation
– Significant Wave Height (SWH or H1/3)
• 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
2
= 5.5 units
• This agrees (I don’t know why) with what a trained
observer would describe.
Wave Forecasting
• 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 Forecasting
• 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
Wave Forecasting
• First Operational Forecasting Model
– 1944 Allied invasion of Normandy, France
“D-DAY”
Wave Forecasting
• Early Operational Forecasting Models
– Based on relationships among:
•
•
•
•
•
Significant Wave Height
Wave Length (or other descriptive bulk parameter)
Wind Duration
Wind Fetch
Wind Speed
Wave Forecasting
• 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
Wave Forecasting
• 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 Forecasting
• Wave Action Equation
•
𝜕𝑁
𝜕𝑡
1
𝜎
+𝛻∙𝑁 =
•
•
•
•
𝑆𝑖𝑛 - Energy input by wind
𝑆𝑑𝑠 - Whitecapping (Deep Water Energy Loss)
𝑆𝑛𝑙 - Non-linear wave-wave interactions
𝑆𝑏𝑓 - Energy dissipation due to bottom friction
𝑆𝑖𝑛 + 𝑆𝑑𝑠 + 𝑆𝑛𝑙 + 𝑆𝑏𝑓 + 𝑆𝑏𝑟𝑘
• 𝑆𝑏𝑟𝑘 - Energy dissipation due to wave breaking
Wave Forecasting
• 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.
– 𝑆𝑖𝑛 and 𝑆𝑑𝑠 are based on a boundary layer
formulation.
Wave Forecasting
• 𝑆𝑖𝑛
– 𝑆𝑤𝑖𝑛𝑑 𝑓, 𝜃 = 𝛽𝜔𝐹 𝑓, 𝜃
• 𝑆𝑑𝑠
– Low-Frequency Dissipation
• 𝑆𝑑𝑠 , 𝑙 = −2𝑢∗ ℎ𝑘 2 𝜑𝑁 𝑘, 𝜃
– High-Frequency Dissipation
• 𝑆𝑑𝑠 , ℎ =
𝑢∗ 2 3 𝐵
−𝑎0
𝑓 𝛼𝑛 𝑁
𝑔
𝑘, 𝜃
Wave Forecasting
• Sources of Ocean Data
– Real-time and historical measured data
• National Data Buoy Center (NDBC)
• http://www.ndbc.noaa.gov/
Wave Forecasting
• Interests in Pacific Northwest
Region
– Boat Traffic Safety
– Coastal Hazards
– Wave Energy Harvesting
Wave Forecasting
• Our work at OSU
• Implementation of a wave forecasting system
for the Oregon and Southwestern Washington
Coast (OSUWW3)
Wave Forecasting
• OSUWW3
• High-resolution model
– Approximate Resolution (spherical coordinates)
• Alongshore 900m
• Cross-shore 650m
• 900 times more resolved that current models
Wave Forecasting
Wave Forecasting
• Model Validation
– Hindcasts
– This is the prediction of waves based upon the
past meteorological and oceanographic data
Wave Forecasting
Wave Forecasting
• Forecast Accuracy
– Many statistical metrics available
– Root-mean squared error is widely used
– 𝑅𝑀𝑆𝐸 =
𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑−𝑀𝑜𝑑𝑒𝑙𝑒𝑑 2
𝑀𝑜𝑑𝑒𝑙𝑒𝑑
Wave Forecasting
• Forecast Accuracy
Wave Forecasting
• OSUWW3
Wave Forecasting
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
Wave Forecasting
Wave Forecasting
Wave Forecasting
• Northwest Association of Networked Ocean
Observing Systems (NANOOS)
– http://www.nanoos.org/
– Select Visualization System
– Select View Assets
– Select Overlays
Wave Forecasting
• Experimental Wave Forecasts at the Mouth of
the Columbia River
– Sarah Kassem, Coastal Engineering MS Student
Wave Forecasting
• My favorite references
– Ocean Surface Waves: Their Physics and
Prediction by S. Massel (1996)
– Guide to Wave Analysis and Forecasting
World Meteorological Organization (1998)
Wave Forecasting
• Thanks for the invitation and attention
• Questions? ¿Preguntas?