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WAVE PARAMETERS

 
  
 
Sea   conditions   are   critical   to   carrier   flight operations,  replenishment  operations,  undersea  warfare operations, amphibious operations, and search and rescue missions. Your observations of sea conditions are vitally important. They must be accurate so that forecaster  and  operations  personnel  may  predict  the success of planned operations. The majority of waves are disturbances on the surface of the water produced by blowing  winds.  Although  there  is  some  net displacement of water in waves, the majority of the movement of water in a wave is in a circular motion beneath the surface. Waves move across the surface of the water by transferring energy—not matter. Waves move in a sine wave pattern, as shown in figure 1-31. WAVE PARAMETERS The success of any operation conducted in the ocean environment may depend on the height of the seas, the direction of the seas, and the wave period. Waves, in general, are described by wave height, wave length,  and  wave  period.  Wave  direction  is  another important aspect used to describe waves. Wave Height In oceanography, wave height (fig. l-31) is the vertical distance, usually measured in feet, from the crest of a wave (the highest portion of a wave) to the trough of the wave (the lowest portion of the wave). This  differs  from  the  "wave  height"  or  "amplitude" normally used in physics, in which the distance is measured from the "at rest" or midline position to the crests and troughs. When waves are generated by the force of wind acting on the water, the wind speed determines the maximum height of the wave. For a given  wind  speed,  many  different  wave  lengths (frequencies) are produced, and for each wave length (frequency),  many  different  wave  heights  are developed. Although the general relationship that higher waves tend to have longer wave lengths (lower frequencies) is true, there is no specific relationship between  wave  height  and  wave  length. The primary factor that determines the maximum wave height is the wind speed. But the duration of the wind (length of time the wind has been blowing at a certain wind speed) and the fetch, (distance over the water the winds have been blowing) also limit the maximum wave height. When the highest theoretical wave height based on the wind speed cannot be attained because the winds have not blown for a sufficient period of time, the sea heights are said to be duration limited. When the sea heights cannot be attained because the straight line area the winds have been blowing over the water is too short, the sea heights are said to be fetch limited. The tables in Appendix V provide a breakdown of wind speeds in relation to wave heights and a wind and sea scale for a fully arisen sea. The table in Appendix V also refers to the 10 states- of-the-sea,  or  sea-states.  Although  not  used extensively,  sea-states  may  be  mentioned  in  literature  or messages. Sea-states refers to general descriptions of wave heights and the appearance of the water surface. They range from "calm" and "sea like a mirror," as in sea-state 0, to "exceptionally high waves" with the "air filled with foam and spray" as in sea-state 9. Accurate observations of wave height are the most difficult  determination  in  an  observation,  especially from the catwalk on an aircraft carrier. Typically, observers on large ships, such as an aircraft carrier, significantly underestimate the wave height, while observers on smaller ships and in small boats provide Figure 1-31.—Sine wave pattern and associated parameters in ocean waves. 1-46


   


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