52 



Symposium on Microseisms 



the microseisms shown on the middle and lower 

 parts of record "C". 



This is consistent with earlier findings of 

 microseisms associated with fronts and cold air 

 masses (Donn 1951, Jones 1949). It may be 

 interesting to compare these quotations from 

 the studies of Donn in December 1951 and Feb- 

 ruary 1952 with that of Roschke in June 1952: 

 Donn — "Microseism intensity may be main- 

 tained at a high level by fresh to strong winds 

 (in the cold air) which may follow a cold front. 

 It seems significant that winds of similar 

 strength in the warm air preceding a cold front 

 have no noticeable effect in the production of 

 microseism storms. This suggests the effect of 

 gustiness or turbulence as being of special 

 significance in microseism origin." "It is sug- 

 gested that pulsations or oscillations in the air 

 striking the water resulting from instability or 

 turbulence in the cold air are coupled to the sea 

 surface by some mechanism." Roschke — "It 

 is shown that high-velocity flows of cold air are 



much more efficient mechanisms for producing 

 extended intervals of maximum-amplitude 

 micro-oscillations in the air than corresponding 

 warm air flows." 



Lee (1934) observed that although micro- 

 seism storms can always be associated with 

 some atmospheric disturbance, the intensity of 

 the microseisms varied despite similar condi- 

 tions of pressure gradient and winds within the 

 atmospheric disturbance. This effect is more 

 explainable on the basis of pressure oscillations 

 in the air which will depend on factors of tem- 

 perature, density, stability, etc. in addition to 

 pressure gradient and wind force. The follow- 

 ing observations given by Roschke are again 

 applicable: "Extended intervals of maximum- 

 amplitude micro-oscillations occur concurrently 

 with the combination of a tight horizontal sur- 

 face pressure gradient and a very cold polar air 

 mass ; however, the occurrence of either a tight 

 pressure gradient or a particular air mass does 

 not, of itself, signify a particular characteristic 



Figure 12. Palisades pressure and microseism data for March 4-5, 1952: A - record from micro- 

 barograph; B - record from hot-wire microphone, C - microseism record from Columbia vertical, 

 D - weather data. 



