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S. Tabata

Abstract

A variety of oceanographic data comprising mainly temperatures collected by bucket, engine-intake, reversing thermometers and thermosalinograph, and salinities obtained with bucket, seawater loop, deep-sea sampling bottles and thermosalinograph has been gathered by various Canadian weatherships dining the 20 years (1956–76) at Station P and along Line P.

The quality of sea surface temperatures and salinities observed by the oceanographic observers at Station P improved conspicuously in 1969, at which time observing techniques were altered. The accuracy of the data improved fourfold. For the period 1969–76, surface temperatures collected by the meteorological observers using specially designed bucket thermometers have been found to he correct to within ±0.1°C.

The mean difference between the bucket and the engine-intake temperatures underwent appreciable change from one cruise to another and from one ship to the other, in much the same manner as noted by Saur (1963) for U.S. Navy ships. However, unlike Saur's mean cruise standard deviation, which varied considerably for each ship from one voyage to another, that associated with the present observations remained relatively unchanged, varying between ±0.1 and ±0.2°C for all four ships. If appropriate field calibrations are made, the engine-intake method appears to provide data with the same accuracy as that obtainable by the bucket method. The mean temperature differences between the bucket and thermosalinograph temperatures also varied from one cruise to another and from one ship (instrument) to another, as did the corresponding differences between seawater-loop and thermosalinograph salinities. However, the mean cruise standard deviations of temperature and salinity were almost the same for all three ships (Vancouver, Quadra and Parizeau), that is, ±0.13°C for temperature and ±0.25% for salinity. Here again, if appropriate field calibrations are applied, the thermosalinographs appear to be capable of giving temperature to an accuracy of ±0.1°C and salinity to ±0.03%. As is the case for the engine-intake temperature recorders, the need for frequent calibration is evident.

A complete explanation for the cause of cruise-to-cruise differences between the bucket and engine- intake temperatures is not yet available. For this reason it would be advisable that this problem be resolved before the engine-intake method for acquiring temperatures is widely adapted by merchant and naval ships for scientific applications.

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S. Tabata

Abstract

An analysis of the 6 h observations of sea surface temperatures made at Station P and the eight NOAA buoy stations in the northeast Pacific Ocean indicates that the buoys appear to be providing data that are as reliable as from Station P. On the basis of the total number of observations available for each station, the mean standard deviation associated with the 3½-day average temperatures varied from ±0.1 to ±0.2°C. There are indications that the summer values of the standard deviation are somewhat higher than during the remaining months. This is attributed to the effect of diurnal heating and cooling of the surface waters. The larger values noted for autumn and winter are attributed to the effect of the rapid rate of cooling of surface waters and/or to the influence of water mass movements. A comparison has been made between the temperatures obtained at the time-series stations and by merchant ships in their vicinities. The results show that the ships' temperatures are 0.2 ± 1.5°C greater than those of the time-series stations. The quality of the ships' temperatures is not as good as it ought to be and efforts should be directed to improving it. For some locations there is some evidence that the horizontal temperature gradient present in the localities might be affecting the temperature differences between the time-series stations and ships' observations. An improvement of the quality of the ships' data by reducing the standard deviation from ¼ to ½ of the presently determined values should be sufficient to determine this at the 95% confidence level.

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S. Tabata

Abstract

Among the many mesoscale eddies found in the northeast Pacific Ocean is a well-developed, anticyclonic baroclinic eddy, situated within a few hundred kilometers of Sitka, Alaska (57°N. 138°W). It has definitely been observed during spring and summer 1958, summer 1960 and summer 1961. Observations made at other times show some evidence of its occurrence also. The trajectories of three NORPAX drifting buoys for April–May 1977 also indicated the probable presence of an eddy there. The eddy, whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m, recurs at the same location. The center of the eddy is characterized by the following features: the surface water is less saline and only somewhat warmer than at its periphery; at depths within and below the halocline it is warmer, less saline and contains more dissolved oxygen than at the periphery; and a warm core is situated within the halocline. The halocline is usually depressed by less than 100 m but the isopycnals below the halocline are depressed by as much as 185 m. The average surface speed of the eddy, at about 50 km from center, is approximately 15 cm s−1, with the maximum reaching almost 40 cm s−1 (relative to 1000 db surface) while the average baroclinic transport in the upper 1000 db layer is 5×106 m3 s−1, with maximum approaching 8×106’ m3 s−1. On the other hand, the average surface speed of the eddy at about 70 km from center, according to drifting-buoy trajectories, is 70 cm s−1 with the maximum daily speed of 110 cm s−1.

The eddy appears to have formed locally and persisted for about one-half year and there is evidence that it had persisted even longer. Attempts to relate the eddy to the distribution of wind-stress curl in the region and to the variability of mean sea levels observed along the nearby coast did not yield conclusive results. It is probable that the main generating mechanism for the eddy is the atmospherically-forced planetary waves that undergo reflection in the vicinity of the eddy. Topographic interaction may also contribute to the production of the eddy. The lack of systematic data with adequate spatial and temporal coverages does not permit drawing firm conclusions regarding generation, maintenance and dissipation of the eddy. Further studies are needed to understand the dynamics associated with the eddy.

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S. Tabata

Abstract

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S. Tabata, B. Thomas, and D. Ramsden

Abstract

Twenty-five and 22 years of hydrographic-STD casts from Station P and Line P, respectively, have been utilized to describe the annual and interannual variability of thermosteric, halosteric and total steric heights. In the offshore region beyond the continental slope thermosteric effect dominates the annual cycle of total steric height, whereas near the coast over the continental shelf halosteric effect controls the height. In between, over the slope, both temperature and salinity effect contribute almost equally to the annual cycle of height. Offshore, the annual change of steric height relative to 1000 db resembles that relative to 100 db, but as the coast is approached, the change due to the deeper water becomes more important. The heat budget within the upper 100 db of water determines most of the annual range of steric height offshore, but near the coast both dilution due to precipitation and runoff in winter and concentration due to upwelling of cool, saline water in summer govern the annual cycle of height. The annual variation of coastal, baroclinic currents appears to account for the observed annual range of adjusted mean sea level along the coast. Local currents seem to be the main factor affecting coastal sea level and not the general, large-scale oceanic circulation offshore. Considerable interannual variability of steric height is present everywhere along the Line, but it is difficult to determine any well-defined periodicity in the time-series data. “Spectral” maxima at approximately 6, 4, 3 and 2 years in addition to the strong annual period are present at various locations along the Line but only the six-year cycle at Station P can be considered reliable. Due to the limited amount of data along the Line, it is difficult to assign significance to these results. In the open ocean the interannual variability appears to be related to the time-integrated divergence of the Ekman transport.

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