according to eq.uation (1), vhere p = ice density (0.90gm/cm3), p\ = water 

 density (1.025gm/ctn3), and g = gravity (983cm/sec2) . 



For ice 20 meters thick (the estimated thickness of ARLIS II), T = 

 6.5 seconds; T increases to ih,"] seconds for ice thickness of 60 meters. Short- 

 period spectral peaks of all curves in figure 1? lie between 10 and l4 seconds. 

 To exanine this period range more closely, a portion of the 03U5 to 0515Z wave 

 record was used to recompute the power spectrum using a AT of 2.5 seconds 

 (figure 18}. This permits the extension of the short -period end of the spectrun 



1000 



1 1 1 1 1 1 1 1 1 1 1 



/^ 



\^_^ 



-— ^ 











CMGAL f 



-cps- 



/ 









\ 



^— 



^^X 





/ 6 JULY 1961 

 / 0345-0406 i 

 / AT=2.6 SEC 













95% 1 



CONFIDENCE + 



LIMITS T 





1 1 1 



12.5 



1 



11.1 



10 

 1 



9.1 



1 



-< PERIOD (SEC) 



.. -1 1 



FIGURE 18 Power spectrum of o portion of tfie 0345 — 0515Z gravimeter record empfiosizing short-period energy. 



from a minimum of 

 real and probably 

 \Th.en simultaneous 

 this short-period 

 while long-period 

 these records and 



10 seconds to 5 seconds. The peak at 11.1 seconds appears 

 is the natural oscillation of the island excited by the wind, 

 wave recordings were made on ARLIS II and the adjacent pack, 

 resonant energy was notably lacking in the pack ice record, 

 energy levels were more nearly alike. Spectra computed frcsn 

 corrected for instrument response are compared in figure 19. 



Further evidence of this natural bobbing is obtained by close exami- 

 nation of the high amplitude arrivals in the long wave record shown in figure 

 20, The three such arrivals shown have average periods of 9.7* 10. 9> and 12.5 

 seconds. The increased energy at 2035tlO is shown on an expanded scale in 

 figvire 21. It was assumed that this energy was imparted by collision of the 

 island with adjacent floes. The comparatively slow decay of this energy sug- 

 gests that there is little damping action in this ice-water system. 



