where /, the Coriolis parameter, is evaluated for 

 present purposes at lat. 45° N. The zonal com- 

 ponent was computed for each degree of latitude 

 from 39.5° N. to 48.5° N. along long. 124.5° W., 

 and then averaged to give mean zonal transport 

 in g. cm."i sec."i for June and July 1962-64. The 

 results indicated that the intensity of upwelling 

 was highest in June and July of 1962, when the 

 offshore transport across 124.5° W. was largest, 

 and lowest in June and July of 1964, when offshore 

 transport was least (table 1). Wind data are not 

 available for June and July of 1961. 



T.\BLE 1. — Average zonal component of Ekman transport, 

 M^(g. cm.-' sec.-'XiO -'), westward across long. 124.5° 

 W. from lat. 39.5° N. to 48.6° N., for June and July 

 1962-64 



Correspondingly, oceanographic evidence indi- 

 cates greater upwelling in 1962 than in 1963 or 

 1964. Local heating of upwelled water, as pointed 

 out previously, precludes use of near-surface 

 temperature and density for assessment of up- 

 welling. Salinity, however, is little changed by 

 processes other than diffusion and upwelling, and 

 thus provides the best available estimator of up- 

 welling effects. The extent of the nearshore 

 province and, therefore, July development of up- 

 welling may be compared between years by noting 

 the distance from the coast at which the 32.5 °/oo 

 isohaline is first encountered at the sea surface. 

 The mean distance of this isohaline from the coast 

 was about 50 nautical miles (90 km.) in 1962, but 

 less than 20 nautical mUes (35 km.) in' 1961, 1963, 

 and 1964. These distances indicate a significant 

 seaward extension of the nearshore province in 

 1962. The rather precise nearshore coincidence of 

 the 32.5°/oo isohalines in 1961, 1963, and 1964 

 suggests close similarity of upwelling in these years 

 and further heightens the contrast of 1962 condi- 

 tions. Similar checks on the near-siu-face distri- 

 butions of other less conservative properties 

 (temperature, density, oxygen concentration) con- 

 firm qualitatively that upwelling effects were 

 markedly pronounced in Jidy 1962. Secondary 

 effects of differences were not apparent; extremes 

 were observed in the plume in years when intensity 



of upwelling in the nearshore province was similar. 



Closer correspondence of June transport than of 

 Jidy transport to the JiJy distributions of prop- 

 erties suggests an appreciable time lag in the re- 

 sponse of the nearshore province to changes in 

 wind field. Prediction of upwelling conditions by 

 computations from coastal wind field of the pre- 

 vious month may thus be possible. 



The extent and character of the pliune province 

 have exhibited the greatest variation from year 

 to year. Differences in size and intensity of the 

 plimie itself, shown by comparison of values and 

 gradients in near-surface salinity distributions 

 (fig. 4), suggest large year-to-year differences in 

 the balance of processes that determine plume 

 distribution — volume of discharge from land, 

 diffusion, and advection.^ For the period 1961-64, 

 summer conditions in 1963 and 1964 displayed 

 maximum contrast. The plume in July 1963 

 showed the weakest development; though the 

 area was large the salinity was high and the hori- 

 zontal gradients were exceedingly small. In spite 

 of less than normal June discharge of fresh water 

 into the province, the depth of the secondary 

 halocline in the plume was not notably less in 

 1963 than in other years (fig. 8). The small 

 horizontal gradients and large values of salinity 

 in the upper layers of the plume thus show that 

 lateral diffusion and zonal advection were rela- 

 tively more effective than meridional advection 

 in distributing plume water. Indeed, the smaller 

 zonal gradients of dynamic height of July 1963 

 (fig. 11) indicate diminished southward transport 

 by the geostrophic component of motion, whereas 

 wind-velocity fields in June and July 1963 indicate 

 large offshore displacements by the Ekman com- 

 ponent of motion (fig. 12), particularly to the 

 south of lat. 44° N. 



The July 1964 plume, at the other extreme, was 

 highly constrained and was characterized by low 

 salinities (<^ 27°/oo at one offshore station) and by 

 large horizontal gradients of salinity. The meridi- 

 onal constraint of the 1964 plume, together with 

 the observation that the discharge in June 1964 

 from the Columbia River was largest of the years 

 considered (table 2, last column), indicates domi- 

 nance of meridional advection over zonal advection 



< The eSects of time-dependent hydraulic mixing near fresh- water sources, 

 which presumably would determine the characteristics of water in the plume 

 province, are here considered to have been "averaged out" in the time re- 

 quired for water to transit the nearshore province and enter the plume 

 province. 



OOEANOGKAPHIO CONDITIONS IN NORTHEAST PACIFIC OCEAN 



519 



319-171 O - 68 - 6 



