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Figure 7.— Time series of monthly sea level anomalies for selected west coast tide stations. Inserts show mean annual cycle with standard 



deviations as vertical bars and monthly extremes as dots. 



of 25 cm occurred at Manzanillo in December 1972. where the occur- 

 rence of high sea levels preceeded those observed at more northern sta- 

 tions by a month or more. At Monterey, sea levels were higher than 

 average during the winter of 1972-73 (see also Fig. 7). During the El 

 Nino period (see time-series plots in Appendix B). atmospheric pres- 

 sures at Monterey were less than average and wind stress was negligi- 

 ble except during February 1973 when anomalous southerly winds 

 resulted in onshore transport of surface waters and downwelling. 



The strong alongcoast correlation of monthly sea level anomalies 

 shows that sea level changes at Monterey are related to large-scale 

 influences rather than to strictly local events. Table 1 shows that the 

 anomalies at Monterey are correlated, at the 5% level of significance, 

 with anomalies recorded at stations from Prince Rupert, Canada, to 

 Callao, Pern, but are more closely related to events affecting sea levels 

 in the group of stations from Crescent City to Quepos, Costa Rica. 

 Processes producing the El Nino phenomenon in the eastern tropical 

 Pacific also apparently affect sea level at Monterey. Recent theories 

 (e.g., McCreary 1976; predict a deepening of the thermocline associ- 



ated with the El Niiio, which propagates northward along the coast as a 

 Kelvin wave, and that northward geostrophic currents are produced 

 behind the Kelvin wave fronts. Such currents cause changes in the 

 cross shelf sea surface slope and northward advection of warm water. 

 Both processes would cause anomalous increases in sea level at stations 

 along the coast. 



CAUSES OF SEA LEVEL VARIATIONS 

 AT MONTEREY 



The effects on sea level of changes in atmospheric pressure, 

 changes in sea surface slopes due to changes in alongcoast currents, 

 and changes in average density of the water column are all interre- 

 lated. A change in the distribution of atmospheric pressure over the 

 ocean surface will generally change the horizontal gradient of pres- 

 sure, resulting in a change in the geostrophic and other wind compo- 



