pattern is not discernible. The 6-yr series of the depth of 

 a, 26 is shown in the lower panel indicating that the fluc- 

 tuations in depth of the lower boundary of the layer are 

 coherent with those in heat content: high heat content 

 corresponds to greater thickness of the layer and lower 

 heat content with reduced thickness. The coherence is 

 clearly shown by the dashed line in Figure 16, repre- 

 senting the heat content variability due to changes in 

 thickness {SAz) only. The values were obtained by se- 

 quentially adding the monthly changes {SAz) to the in- 

 itial heat content on day 1, 1966. (The series was re- 

 initialized on day 61, 1968.) 



The seasonal aspects of the change of heat content per 

 month due to change in the mean temperature in the 

 layer above ct, 26.0 izAd), and the monthly heat ex- 

 change across the sea surface are shown in Figure 17. 

 The two quantities plotted are of equivalent magnitude 

 although the month to month variability of the change 

 of heat content is greater than that of the heat ex- 

 change. If one assumes that the magnitude of the heat 

 exchange is correct, then a greater decline in heat con- 

 tent than expected from heat exchange tends to occur 

 during fall and winter. Heat content increases, greater 

 than those expected from heat exchange, tend to occur 

 during spring and summer. According to our estimates 

 the heat exchange across the sea surface contributes 

 only 47?o to the variance in the rate of change of heat 

 content due to mean temperature change. The remain- 

 der must be attributed to advection and diffusion of 

 which the former is probably the dominant process. 



Another opportunity to examine the effect of total 

 heat exchange across the sea surface occurred during the 

 time from the fall of 1969 to the spring of 1970 when both 

 the surface temperature and the mean temperature in 

 the layer above a, 26 were below the 6-yr average. Cool- 

 ing began in August, 2 mo earlier than average, and con- 

 tinued until March 1970 (Fig. 18). A greater than 

 average increase in temperature occurred in April 1970 

 (1.1°C instead of 0.1°C). Throughout this time there is 

 no indication of anomalous heat exchange across the sea 

 surface (Fig. 17). It is interesting to note that in April 

 1970 there was an increase in the surface salinity that 

 subsequently persisted as a shallow subsurface salinity 

 maximum (Fig. 14). There was no significant change in 

 depth of the thermal structure {a^ 26) during this month 

 of relatively large surface temperature and salinity 

 changes. 



In summary, anomalous heat content changes in the 

 6-yr series cannot be attributed exclusively to 

 anomalous heat exchange across the sea surface. Pos- 

 sibly, effects of processes >1,(XX) km upstream in the 

 principal heat loss area of the North Pacific Ocean play 

 an important role in the temperature variability. Unfor- 

 tunately, heat advection cannot be calculated from the 

 properties that were measured at OWS-V. 



The salinity and salt content are important prop- 

 erties in isentropic analysis. Salt budget analyses, 

 however, suffer from the lack of reliable precipitation 

 data. The association of a shallow salinity maximum 

 with the depth of tr, 26 has already been described. In 



addition, there appears to be a seasonal trend in the 6-yr 

 average of the surface salinity with the maximum occur- 

 ring in late winter and spring and the minimum in late 

 summer and early fall. Departures during individual 

 years are large so that the average of only 6 yr may 

 depart significantly from a long-term mean. 



Reed and Elliott (1973) have estimated the precipita- 

 tion at OWS-V from the present weather code in the 

 standard marine weather repwrts. Although absolute 

 magnitudes of these estimates may be in doubt, the 

 seasonal trend is probably correct. The mean monthly 

 values are listed in Table 4 together with the estimates 

 of mean evaporation at OWS-V (Husby and Seckel 

 1975). The evaporation minus precipitation values indi- 

 cate excess evaporation over precipitation during most 

 of the year with lowest values occurring from April to 

 August when the average salinities are also declining at 

 OWS-V. 



As in the case of the surface temperature the effect of 

 advection on the surface salinity may be pronounced. 



Table 4.— Estimates of mean evaporation rates (E)', mean precipita- 

 tion rates (P)", and evaporation minus precipitation (E-P), (in milli- 

 meters per month) at Ocean Weather Station V. 



'Husby and Seckel (1975). 

 'Reed and Elliot (1973). 



SUMMARY AND CONCLUSIONS 



In this report the oceanographic station data obtained 

 at OWS-V from 1966 to 1971 have been presented in a 

 form that lends itself to an examination of the effects of 

 atmospheric forcing on the water structure. The report 

 complements a previous report on large-scale air-sea 

 interactions at OWS-V (Husby and Seckel 1975). The 

 data processing and analysis procedures have been de- 

 scribed. In order to facilitate future analysis of ocean 

 structure, the principal features in the ocean variability 

 have been described and heat budget estimates have 

 been made that point to the important processes af- 

 fecting the temperature in the upper layer at OWS-V. 



Rather than presenting the temperature, salinity, and 

 o; as a function of depth, the temperature, salinity, and 

 depth were presented as a function of ct, which we call 

 the isentropic format. Harmonic analysis was used as a 

 curve-fitting procedure to summarize the isentropic 

 data with a relatively small number of coefficients and 

 to provide smoothed estimates of daily observations. 

 Large gaps in the sampling record in 1966 and 1967 limit 

 the usefulness of the harmonic coefficients during these 

 time periods. Results of the harmonic analyses are 

 presented in the appendix showing the harmonic coef- 

 ficients for the temperature, salinity, and depth at inter- 

 vals of 0.2 a, 



Presentation of the oceanographic station data in 

 isentropic format shows that the apparently complex 



26 



