1. INTRODUCTIOM 



a. Preliminary Remarks and Review of Literature 



The study of the origin and "behavior of wave motion on the open ocean 

 has received considerahle attention during the past decade. The primary 

 impetus for this work has been provided by the U.S. Navy. The Navy has a 

 continuing interest in being able to predict routinely the sea state at a 

 given location on the ocean, much the same as the Weather Bureau predicts the 

 weather. The greater part of the Navy's work has been oriented toward the 

 ice-free, non-polar areas, with little or no attention being given to the 

 nature of ocean waves in extensive areas of ice-covered oceans. 



Wave motion and wave generation do not cease in polar oceanic areas 

 because a layer of ice has been placed on the water surface, although one 

 would intuitively expect severe attenuation of wave amplitudes. This atten- 

 uation has been repeatedly reported by mariners navigating in such waters and 

 is one of the most outstanding features observed when sailing from the open 

 ocean into water with numerous ice floes. 



It was not until Robin's studies with a shipborne wave recorder in 

 the Weddell Sea were ccaipleted (I963) that any quantitative measure of the 

 attenuation of wave motion due to ice cover became available. Robin showed 

 that: (1) the ice cover, usually floes 1 to 3 meters thick, could be consid- 

 ered elastic plates for the frequencies and amplitudes encoxmtered in the ice 

 pack, (2) the waves observed in the ice field had ample energy to bend the 

 floes eind still propagate, and (3) the wave energy penetrating the pack was 

 proportional to X'*/ h' where X - wavelength, and h = ice thickness. 



The vertical component of wave motion deep within the ice pack had 

 been observed with gravimeters prior to Robin's study, although quantitative 

 discussions of the wave-producing mechanism have been attempted only recently. 

 Crary et al. (1952) made gravity observations as part of a geophysical program 

 on the pack ice of the Beaufort Sea in 1951* They reported that the optical 

 crosshair of the gravimeter oscillated about the instrioment ' s null-position, 

 usually within the range of the scale stops, with periods between 20 and hO 

 seconds. It was therefore necessary to average a series of values taken over 

 an interval of several cycles to obtain a representative value for the gravity 

 field at a given location. Further gravity observations were made by Crary 

 and Goldstein (1959) on Arctic Drift Station T-3 between 1952 and 195^. As 

 part of the geophysical program, they routinely made daily gravity measure- 

 ments, reading the gravimeter every 5 seconds for an interval of 5 to 6 

 minutes. A statistical study of these oscillations showed periods ranging 

 from 23 to 61 seconds with 70 percent of occiorrences falling between 33 and 

 U3 seconds. They found no correlation between oscillation amplitudes and 

 periods with either atmospheric pressure or surface wind speeds. They did, 

 however, observe a seasonal trend. The overall amplitude showed peaks during 

 March and November with a low in July. July, although having the least ampli- 

 tude, has the maximum occurrences of long-period energy. Hunkins (I962) made 



