Large- Scale Air- Sea Interactions at Ocean Weather 



Station V, 1951-71 



DAVID M. HUSBY and GUNTER R. SECKEL' 



ABSTRACT 



The meteorological observations at OWSV (Ocean Weather SUtion V, lat. 34''N, long. 164°EI were 

 used to compute large-scale air-sea heat exchange processes and wind stresses for each month from 

 September 1951 to March 1971. The monthly values are tabulated as anomalies from the 1955 to 1971 

 means. The quality of the data record and the accuracy of the derived heat exchange components are 

 discussed. 



The air-sea interaction climatology at OWS-V, which lies in the net annual heat loss area of the 

 western North Pacific, is described. At this station the average monthly heat exchange across the sea 

 surface is estimated to range from a gain during July of 307 cal cm'' day"' to a loss during December of 

 388 cal cm"' day"' with an annual loss of 32 cal cm"' day"'. The principal process causing monthly and 

 seasonal variations in the net heat exchange across the sea surface, besides the radiation from sun and sky, 

 is the heat used for evaporation. The average monthly heat lost through evaporation is estimated to range 

 from 86 cal cm"' day' during July to 374 cal cm "'day' during December with an annual average of 234 cal 

 cm"' day"'. Anomalous evaporation rates are caused by anomalous "Vapor pressure differences" 

 (saturation vapor pressure at the sea-surface temperature minus the vapor pressure of air) and/or 

 anomalous wind speeds. 



INTRODUCTION 



Air-sea interactions in the western North Pacific Ocean 

 play an important role in conditioning the waters that 

 eventually reach the eastern North Pacific with its rich 

 living resources. In mid-latitudes the ocean loses heat 

 across the sea surface in fall and winter and gains heat in 

 spring and summer, thus producing seasonal changes in 

 surface temperature as well as affecting the vertical 

 density structure. 



The heat exchange across the sea surface is not uniform 

 over the ocean as illustrated in Figure 1, reproduced from 

 Wyrtki (1965). In a large region extending eastward from 

 Japan to the central Pacific, the ocean loses more heat than 

 it gains annually. In the mid-latitude eastern portion of the 

 North Pacific, a small annual net heat gain across the sea 

 surface indicates that most of the heat gained during spring 

 and summer is lost during fall and winter. The excess heat 

 lost in the west is that which was stored in the ocean at 

 lower latitudes. The distribution of heat exchange across 

 the sea surface indicates that the reduction of heat content 

 in the northeastward flowing Kuroshio Current occurs 

 primarily off Japan. When the water reaches the central 

 Pacific heat loss on an annual average basis ceases so that 

 the heat content of the water will not change as it continues 

 to drift eastward. One can also postulate on the basis of the 

 distribution of heat exchange across the sea surface, that 

 anomalies in heat content produced or found in the western 

 Pacific would persist after the water reaches the central 

 Pacific and drifts eastward. Favorite and McLain (1973) 



'Pacific Environmental Group, National Marine Fisheries Service, 

 NOAA. Monterey. CA 93940. 



have described such an event. Anomalous sea-surface 

 temperatures were found in the western North Pacific that 

 moved eastward across the ocean in a coherent fashion in 2 

 to 3 yr. This discussion illustrates that for an understand- 

 ing and the prediction of interseason and interyear changes 

 in water properties reaching the eastern North Pacific, 

 monitoring of air-sea interaction processes, and determin- 

 ing their effect on the water structure, must begin in the 

 upstream area on the western side of the ocean. 



Ocean Weather Station V (OWS-V) lies within, albeit 

 near the periphery, of the net annual heat loss region of the 

 North Pacific (Fig. 1). The station was operated by the 

 U.S. Coast Guard at lat. 31°N, long. 164°E from 29 

 September 1951 to 12 March 1955 and then at lat. 34°N, 

 long. 164°E until its discontinuance in January 1972. 

 Surface meteorological observations were made throughout 

 this time. Beginning in 1965 oceanographic station data 

 were also collected. The meteorological and oceanographic 

 data will permit a number of investigations leading toward 

 the objective of predicting the surface properties of the 

 water flowing toward the eastern Pacific. 



Because such predictions will be based primarily on 

 surface marine meteorological observations obtained from 

 merchant vessels, air-sea interactions computed from 

 OWS-V data will provide a reliable reference. Air-sea 

 interactions computed from OWS-V data will also permit 

 studies of their effect on the water structure for the years 

 when oceanographic station data are available. Finally, 

 these studies will permit extrapolation of results to the net 

 annual heat loss area where only merchant vessel 

 meteorological data are available reg^ularly. 



The initial phase of this work, namely bringing the 

 meteorological data of OWS-V into useable form, is 

 reported here. 



