CONTINENTAL SHELF WAVES 



L. A. Mysak 



Harvard University 



Cambridge, Massachusetts 



INTRODUCTION 



When a static, normal stress distribution acts upon the sea surface, it 

 reacts as an inverse barometer. In the literature such a response is often 

 termed "isostatic"; however, in this paper we shall call such a response 'Taaro- 

 metric." In the past it has also been assumed that the sea surface responds 

 barometrically when the distribution is time-dependent, such as in ordinary, 

 moving weather systems, provided the fluctuations are of sufficiently low fre- 

 quency (considerably less than the Coriolis parameter). Recently, however, 

 Hamon (1-3) and Hamon and Hannan (4) have observed that the daily mean sea 

 level fluctuations at the Australian coast are not barometric: At four stations 

 on the east coast the behavior is appreciably less than barometric (that is, the 

 magnitude of the "barometric factor," the ratio of daily mean sea level changes 

 to atmospheric pressure changes, is appreciably less than the expected value of 

 1.0 cm/mb), and at two stations on the west coast the behavior is appreciably 

 greater than barometric. An analysis of a simultaneous record of the daily 

 mean sea level fluctuations at Lord Howe Island, on the other hand, indicates a 

 barometric behavior. 



Another unexpected phenomenon Hamon (2,3) observed is the existence of 

 adjusted sea level phase lags between neighboring coastal stations whose dis- 

 tance separation is of the order 100 km. (The adjusted sea level is defined as 

 the observed sea level with the atmospheric pressure eliminated according to 

 the hydrostatic relation 1-cm decrease in sea level for 1-mb increase in pres- 

 sure.) More specifically, for a series of six east coast stations between Eden 

 (37 °S) and Urangan (25 °S), the lags between adjacent stations are related in a 

 manner which suggests the presence of a northward-traveling wave with a speed 

 of 400 cm/sec (3). The lagged correlations between adjusted sea levels at (west 

 coast stations) Geraldton, Fremantle, and Bunbary, on the other hand, suggest 

 the presence of a southward traveling wave. In this case the wave speed has not 

 been determined accurately, but it is estimated to lie in the range 300 to 600 

 cm/sec (3). 



Robinson (5) attributed the nonbarometric behavior at the east coast to a 

 resonant response of the sea surface to a plane-wave pressure distribution 

 which travels northward along a sloping sheK which sharply drops off to water 

 at constant depth. His solution also predicts the existence of a northward- 

 traveling shelf wave with a speed of 250 cm/sec, which is of the order of the 



477 



