54 



Symposium on Microseisms 



seism-period band, and permits discrimination 

 between microseisms from different generating 

 areas, or different parts of one generating area. 

 Further use of this new method of microseism 

 study seems promising. 



3. Empirical studies of the intensity and 

 times of beginning and termination of ampli- 

 tude changes during microseism storms re- 

 corded at east-coastal stations together with 

 simultaneous weather and ocean wave data for 

 east-coastal waters permit discrimination 

 among suggested mechanisms of microseism 

 origin. The only unique method of origin 

 seems to lie in excitation within the area of an 

 atmospheric disturbance and by direct coupling 

 of the energy of some impulsive air disturb- 

 ances to the sea surface. At lower than hurri- 

 cane wind velocities, cold air is a much more 

 efficient microseism source than warm air. All 

 of the observations made on the east coast ne- 

 gate ocean waves or swell (whether progressive 

 or standing) as being transitional in the gener- 

 ation of microseisms from an original energy 



source in the air. This appears to conflict with 

 observations and interpretations made on the 

 western coasts of Europe and North America. 

 Since these coasts are the targets for both 

 storms and their associated ocean waves which 

 generally travel westward in the latitudes of 

 microseism study a clear possibility of ambigu- 

 ity exists. Even here it has been interpreted 

 that ocean waves produced by the cold sectors 

 of storms are especially efficient in microseism 

 generation. On the east coast, where storms 

 move offshore, it is possible to distinguish be- 

 tween these factors as shown in this paper. 



Acknowledgments — The study and instrumen- 

 tation involved in this research was supported 

 by Contract N6-onr-27133 and Contract AF19 

 (122)441 between Columbia University and 

 the Office of Naval Research and the Geophysi- 

 cal Research Division of the Air Force Cam- 

 bridge Research Center, respectively. Weath- 

 er data was supplied by the United States 

 Weather Bureau Office at La Guardia Field. 



Figure 14. Marine weather charts showing development and positions of the cyclone related to 

 the microseism storm shown in Figure 13. 



