Amplitude Distribution of Storm Microseisms 



51 



matched with those on record "A". In addition 

 to pointing to a direct meteorologic origin for 

 the microseisms, this case also suggests that 

 bearings or azimuths computed by any of the 

 procedures in use should not be expected to 

 give a direction to the center of an extra-trop- 

 ical cyclone, but rather to the center of the 

 most turbulent zone or the cold air mass. 



Case 2. Calm seas existed in the same 

 area from March 4 at 2000 to March 6 at 1200 

 according to wave records of the Beach Erosion 

 Board. Figure 12 D is a simplified surface 

 weather chart for 0030, March 5, 1952 (Pali- 

 sades is shown by the dot to the right of "P"). 

 A vigorous cold front is seen approaching Pali- 

 sades. The sensitive microbarograph and hot- 

 wire microphone records show short-period 



pressure fluctuations prior to and during fron- 

 tal passage at Palisades, culminating in very 

 severe variations. The latter, between 0200 and 

 0300, March 5, was attended by heavy showers 

 and high winds which backed from NE to NW 

 establishing frontal passage. During this time 

 no short-period microseisms occurred, although 

 long-period microseisms are present which can 

 be correlated with a more distant storm present 

 for some time prior to this record. However 

 between 0400 and 0500 on March 5 the begin- 

 ning of a new microseism storm was recorded 

 showing fairly regular 2.5 second microseisms. 

 This would just allow time for the atmospheric 

 pressure disturbances recorded at Palisades to 

 travel to local offshore waters. It would appear 

 that the pressure disturbances recorded on the 

 upper halfs of records "A" and "B" generated 



Figure 11. Atmospheric pressure, and microseisms at Palisades for February 11- 12, 1952 together 

 with related weather data. A - record of seismically compensated microbarograph (T o -10.5, 

 Tg=76); B - record of hot-wire microphone; C- record from vertical seismograph, drum speeds 15mm 

 per minute (T o :10; Tg = 75); D - record from Columbia vertical component electronic seismograph 

 (T : 12), drum speed=30mm per minute. 



