Microbreaking Waves on the Open Ocean What they are Why they are interesting How we are trying to...

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


Credit: Donnelan and Wanninkhof, Gas Transfer at Water Surfaces, 2002


• 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

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Credits: Leifer, Piorek, Smith and Banerjee, unpublished.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Credits: Leifer, Piorek, Smith and Banerjee, unpublished.


•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.


Photo Credit: NASA Winds Measurements from NSCAT http://winds.jpl.nasa.gov/index.html

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.


• 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”.


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.


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)


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.

• Ok, questions and lunch.

Microbreaking Waves on the Open Ocean What they are Why they are interesting How we are trying to...

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