Microbreaking Waves on the Open Ocean
• What they are
• Why they are interesting
• How we are trying to learn more
Damon TurneyPhD Seminar, May 23, 2003
What are Microbreaking Waves?
• Microbreaking waves are on the order of 1 meter in length, and 0.1 meters tall. They are different from other small waves in that they actually “break”.
Photo credit: University of Florida
What are Microbreaking Waves?
• Microbreaking waves are formed by interaction with the wind.
Photo credit: Navy Meteorology and Oceanography Home Page
Why are Microbreaking Waves Interesting?
• Microbreaking waves, and turbulence production in general, probably play an important role in any gas-liquid exchange process where they exist.
Credit: Donnelan and Wanninkhof, Gas Transfer at Water Surfaces, 2002
Why are Microbreaking Waves Interesting?
Credit: Donnelan and Wanninkhof, Gas Transfer at Water Surfaces, 2002
Why are Microbreaking Waves Interesting?
• Carbon cycling between the atmosphere and ocean is an example of the relevance to environmental science.
Photo Credit: Australian Greenhouse Office http://www.greenhouse.gov.au/science/faq/index.html
• Microbreaking waves increase and modify the mixing of the top ~10 centimeters of the ocean.
Credits: Leifer, Piorek, Smith and Banerjee, unpublished. Period of Burst, s
0 1 2
Gen
eration
Rate, m
-2s-1s
-1
4
2
0
Lower windspeeds
Higher windspeeds
Credits: Leifer, Piorek, Smith and Banerjee, unpublished.
Why are Microbreaking Waves Interesting?
•Microbreaking waves might be the dominant surface mode on the open ocean, since the anually averaged wind speed is ~7 m/s. Since microbreakers are hard to distinguish, this statements is only a hypothesis.
•White-caps are only beginning to form at this wind speed.
•Much of the ocean experiences wind speeds which do not produce white-caps.
Why are Microbreaking Waves Interesting?
Photo Credit: NASA Winds Measurements from NSCAT http://winds.jpl.nasa.gov/index.html
• Increased mixing in the top ~10 centimeters of the open ocean will affect oxygen transport, carbon dioxide transport, nitrogen transport, etc…
• But we still have much uncertainty about how these small waves, and other small waves, affect mixing. Our empirical measurements of gas transport have a debilitating scatter.
Why are Microbreaking Waves Interesting?
• For Example: Subtropical Mode Water near Bermuda has been found to store large amounts of dissolved CO2 as a result of seasonal/decadal mixing layer oscillations. People believe this storage is dictated by interfacial gas transfer rates. Thus, uncertainties of ~400% could be “annoying”.
Why are Microbreaking Waves Interesting?
How we are Trying to Learn More
• High speed digital photographs of the mixing process in a lab, with controllable conditions.
• Gas transport measurements in a lab, with controllable conditions.
• Observations on the Santa Barbara Channel, maybe.
How we are Trying to Learn More
0 m/s wind: mean is 5.5e-6 +/- 5.4e-6 m/s1.5 m/s wind: mean is 1.1e-5 +/- 8.8e-6 m/s3.7 m/s wind: mean is 2.2e-5 +/- 9.2e-6m/s
kw =depth/( Ca/H-C)*( dC/dt + Um* dC/dx)
How we are Trying to Learn More
1.5 m/s wind: mean k is 1.0e-5 +/- 8.0e-6 m/s3.7 m/s wind: mean k is 4.7e-5 +/- 8.4e-6 m/s
Other Processes I’m Interested In
• Fluids in general.
• Lab experiments which give limnologists the better ability to model nutrient cycling.
• Understanding rivers or ocean with perturbed nutrient cycles. Relation of gas transport – or any fluid transport process -to environmental quality.