Symposium on Microseisms Held at Arden House, Harriman, N.Y. 4-6 September 1952, Sponsored by the Office of Naval Research, and the Geophysical Research Directorate of the U.S. Air Force. (1953) / Chapter Skim
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Storm and Surf Microseisms
Storm and Surf Microseisms
Pages 94-108
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From page 94... ...
W van Straten Office of the Chief of Naval Operations The practical meteorologist is interested in the so-called microseismic phenomenon because it may provide a potential for giving early warning of the existence of large destructive storms and because it may permit a type of direction-finding which will track such storms once they have formed.
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From page 95... ...
Lower wind velocities behind the front did not apparently affect the microseisms adversely. Kammer and Dinger, on the other hand, indicate that microseisms occur when the storm affects shallow water and that the magnitude of response to such "surf action" is such as to mask any direct storm response.
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From page 96... ...
While nothing definitive is established by this analysis, it would appear that the question of what produces the microseismic phenomenon is still completely unresolved and that some hope still remains that the meteorologist may find a tool for studying hurricanes. It would seem that the first test for determining whether microseisms originate in or near a storm is to seek a case when it is wellestablished that no surf action is occurring but when microseismic activity is marked.
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From page 97... ...
Table 3 Typhoon Ruby -- October 1950 Table 6 Typhoon Ruth -- October 1951 Date Distance Center Swell at Micro Time from Intensity Guam Amplitude (GCT)
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From page 98... ...
One such attempt involved plotting central wind intensity against microseismic response for the three storms which showed WIND IN CENTER (KTS) RANGE CIRCLES CENTERED ON GUAM Figure 1
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From page 99... ...
This rather pleasing result is somewhat soured by the fact that an attempt to subtract the amplitude of the microseism produced by the storm as shown by Figure 7 from the total effect on a storm-surf microseismic record did not produce any relationship between swell amplitude and microseismic activity. This may be the result of incorrect hypothesis, poor swell forecasting or the result of the fact that the microseismic amplitude as measured is not a simple additive function of the two disturbances.
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From page 100... ...
RANGE CIRCLES . CENTERED ON GUAM Figure 3
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From page 101... ...
van Straten in her careful investigation came to the conclusion that hurricane microseisms are partly generated within the storm area, partly by surf effects, and that the latter are dominant. As a result of a recent investigation of microseisms connected with non-tropical storms approaching the Pacific coast of the United States, the present author has reached the similar conclusion that these microseisms derived their energy mainly from RANGE CIRCLES CENTERED ON GUAM Figure 4
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From page 102... ...
More detailed results of this investigation which was sponsored by the Geophysical Research Division of the Air Force Cambridge Research Center, are to be published in the Transactions of the American Geophysical Union. In several microseismic storms recorded at stations in California, the State of Washington and in British Columbia during NovemberDecember, 1951, the increase and decrease of the microseismic amplitudes were more and more delayed with increasing distance of the recording station from the storm center.
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From page 103... ...
IB) ; to the contrary, the microseisms usually reached their largest periods at about the time of the maximum amplitudes, while the ocean waves frequently exhibited relatively short periods when their amplitudes were large.
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From page 104... ...
van Straten has presented a thought provoking paper. She has courageously attempted to reconcile two schools of thought on the origin of group microseisms -- the school that holds that microseisms originate at the center of a storm and the school that holds that microseisms cannot originate at the center of a storm over deep water but rather at some distance from the center in shallow water, as a Figure 7
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From page 105... ...
van Straten refers to the indifferent results that he obtained. It is not quite clear whether she is classifying all of Gilmore's results as indifferent or whether she is criticizing those which he admitted were not too successful.
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From page 106... ...
(A) Amplitudes of regular microseisms with periods of 5-8 seconds recorded at Santa Clara University, California, during November-December, 1951, and highest recorded ocean waves at Ellwood, California.
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From page 107... ...
Dr. van Straten states that "Kammer and Dinger demonstrate that microseisms occur only if surf action is appreciable and that the magnitude of response to surf action is such as to mask any direct storm response." I think that is a fair statement of the conclusion of Kammer and Dinger, but I emphasize that it is their conclusion from their data and not merely a statement of their data.
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From page 108... ...
Our work with cold front microseisms has convinced us that these frontal microseisms originate in the Great Lakes, possibly, as Dr. van Straten suggests as the result of interfering swells.
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