616 



GROEN AND GROVES 



[chap. 17 



variation. The wind stress is so much more effective in shallow water (see 

 section 3 of this Chapter) that the local wind in the vicinity of the port is 

 usually more important than the integrated effect over a large region of ad- 

 jacent ocean. The effect of even steady winds is difficult to evaluate owing to 

 the importance of the local topograj^hy. But some general conclusions can be 

 drawn from comparison of wind and sea-level records. Onshore winds raise sea- 

 level. Longshore winds raise sea-level if the land lies on the right of the wind 

 vector (in the Northern Hemisphere). On the edge of continents the corrected 

 sea-level does not appear to be in equilibrium with the wind, but rather reflects 



CORRECTED SEA LEVEL 

 TG ond AP - Son Francisco 



Fig. 4. Simultaneous plots of corrected sea-level along the California coast. "TG" and 

 "AP" indicate the stations from which the tide data and the atmospheric pressure 

 data were taken. (After Groves, 1957. By courtesy of the American Meteorological 

 Society.) 



a time-integrated wind effect. That is, the sea-level extremes tend to coincide 

 with the wind reversals, and not with the wind extremes. A possible explanation 

 for this is that the response to the wind stress may have a time constant 

 appreciably longer than a day. This is true in the case of response to longshore 

 winds, and also if the response to onshore and offshore winds is mainly 

 baroclinic ; i.e. reflects changes in the density structure of the water rather 

 than a direct wind set-up (see Groves, 1954). Longard and Banks (1952) have 

 observed such wind-induced changes of density structure along an open coast. 

 At islands there is apparently no obvious relation between sea-level and the 

 local wind. Sea-level may be related in a simple manner to the divergence or 

 curl of the wind stress, but these cannot be inferred from wind observations at 

 a single station. It may be useful to consider variation of sea-level at islands in 



