Submitted by Anonymous on Wed, 03/12/2008 - 06:01
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Bering Ecosystem Change

Here is wishing you a smooth departure, Mr K!  Considering the conditions that The Healy  might encounter in the Bearing Sea, you do not seem to have over-packed-- you are prepared!  My science class in Durham NC is interested in the wave action that you encounter-- how do you measure and describe the swells? Can you see a relatioship between local wind speed and wave height?  Or are these waves genersted somewhere else?  How do they affect you on the boat? 

Smooth Sailing!

 Mrs Ward

 

Thu, 03/13/2008 - 02:10

Craig Kasemodel

How do we measure sea swells? First, lets consider waves. Waves are measured from the wave crest (the wave top) to the wave trough (the wave bottom). Wave length is measured as the horizontal distance between two successive wave crests or wave troughs. The unit of measure is typically meters (m). During storms, wave height increases as wave length decreases. Waves are created by the wind as it pushes it, transfering some of it's energy to the water. A simple demo is to lay a pencil on a table and gentle roll or "wave" your hand over the pencil. The pencil will move in the direction of your hand movement. Just as you increase the speed of your hand, the speed of the pencil will increase. The same holds true for wind generated waves.
However, there are many other variables to consider out in large bodies of water. As an example, what happens when a rock is thrown out in a lake? The ripples move out from the orgin. The waves move out in a circular motion. What happens when there are many rocks thrown at the same time? Waves are generated from every point where the rocks landed. It creates a 'confused sea' which means that the waves are generated without any one point of origin. 
In a body of water with a large surface area or fetch, the waves begin to increase in energy and create what are called wave trains. With a large fetch,  wave swells are created as they move long distances away from the point of orgin. A large group of swells are called a wave train. Wave trains are influenced by the wind energy recieved and the fetch distance. 
Other factors in swells are the 'confused sea' and the depth of the water. Wave height does not have a linear relationship with wind speed due to these factors and the fact that wind speed is a local measurement and wave height is a global measurement.
I hope this helps - the winds have been relatively calm in Dutch Harbor. The Healy finally arrives tomorrow and we board in the early am. I will keep you posted for more information regarding the waves and swells we'll encounter in the Bering Sea. I do not expect that the seas will rough for very long as we expect to encounter the sea ice within a day of travel.
 Mr. K