Water Structure at Ocean Weather Station V, 

 Northwestern Pacific Ocean, 1966-71 



D. M. HUSBY and G. R. SECKEL' 



ABSTRACT 



The oceanographic station data obtained at Ocean Weather Station V from 1966 to 1972 by the 

 U.S. Coast Guard have been analyzed and are presented in a form suitable for water structure studies. 

 Temperatures, salinities, and depths are given as a function of density (sigma-f). We used harmonic 

 analysis as a curve-fitting technique, to obtain parameters for these properties as a function of time. 

 The harmonic coefficients and interpolated values at the first of each month for the 6-year series are 

 tabulated in an appendix. 



We describe the temporal distributions of salinity and depth in terms of the oceanographic setting. 

 At depths greater than sigma-f 26, temperature-salinity relationships remain relatively constant in 

 time. Depth variations at these levels are attributed primarily to meanders of the Kuroshio Extension. 

 The surface divergence, as reflected by changes in the depth of sigma-( 26, has no annual periodicity. 

 The 6-year record shows that large baroclinic variability occurs at time scales of more than 35 days 

 with largest variability occurring at the interannual scale. 



Heat budget estimates show that the effects of local ocean-atmosphere exchange processes are ob- 

 scured by advected properties. For example, the heat content of the layer above sigma-(26is primarily 

 determined by the divergence of this layer and anomalies in the mean temperature are produced by 

 heat advection rather than heat exchange across the sea surface. 



INTRODUCTION 



Monitoring and predicting ocean variability in the 

 fishing areas of the eastern North Pacific are important 

 problems facing the fishery oceanographer. In contrast 

 to the global monitoring of the atmosphere at a network 

 of stations every 6 h, there is no network of monitoring 

 stations in the oceans. Oceanographers are therefore at- 

 tempting to infer ocean variability from atmospheric 

 forcing, i.e., the exchange of momentum, moisture, and 

 heat between the atmosphere and ocean, that can be 

 calculated from the regularly observed meteorological 

 properties. The temperature structure in the upper 

 layers of the ocean, for example, is affected by heat ex- 

 change and wind stress as well as by the changing cur- 

 rent field and diffusion. Inferring ocean variability from 

 atmospheric forcing, therefore, is not a trivial problem. 



Conditioning of the water reaching the eastern North 

 Pacific Ocean begins in the western North Pacific, an 

 area characterized by a net annual heat loss across the 

 sea surface (Husby and Seckel 1975). Thus, studies of 

 the effects of heat exchange across the sea surface and 

 wind stress on ocean properties and structure must be 

 undertaken upstream of the fishing areas if predictions 

 of anomalous water conditions are to be made. The only 

 time series of concurrent meteorological and oceano- 

 graphic data for use in such studies are those that were 

 obtained at ocean weather stations. One of these, Ocean 

 Weather Station V (OWS-V) was located at lat. 34°N, 



'Pacific Environmental Group, National Marine Fisheries Service, 

 NOAA, c/o Fleet Numerical Oceanography Center, Monterey, CA 93940. 



long. 164°E within the net annual heat loss area that is 

 of concern to us. 



At OWS-V meteorological observations were obtained 

 from 1951 to 1972 and oceanographic station data from 

 1966 to 1972. The large-scale air-sea interaction pro- 

 cesses derived from the station's meteorological data 

 were described by Husby and Seckel (1975). Our work is 

 a companion paper in which the oceanographic station 

 data are presented in a form suitable for studies of the 

 water structure. Temperatures, salinities, and depths at 

 selected density (sigma-t) levels are analyzed and 

 presented as a function of time. Harmonic analysis is 

 used as a curve-fitting technique, to obtain parameters 

 for these properties as a function of time. Results of the 

 analyses are presented in Appendices I and H. Finally, 

 the time variations in the distribution of properties, the 

 water structure, are described in terms of the oceano- 

 graphic setting at OWS-V. 



PROCESSING PROCEDURES AND 

 ANALYSIS 



The Data 



Oceanographic sampling at OWS-V began in January 

 1966 with daily Nansen bottle casts by the U.S. Coast 

 Guard on alternate 3-wk patrols. In March 1968 the 

 program was expanded to daily observations on each 

 patrol. The temperature and salinity were sampled at 

 the sea surface and at the depths of 10, 30, 50, 75, 100, 

 150, 200, 300, 400, 600, 800, 1,000, and 1,500 m. The 

 observations and initial data processing methods were 

 described by Husby (1968). 



