90- -m 



IjillllHlJi 



ilii 



,il.illlii.illi.l.ii.iii..ijiill 



"*' tn^i^f 



period in days 



Figure 15. — Absolute magnitude of the amplitudes of the harmonic function for the S-yr series of the depth of 

 o, 26.0. Procedure was identical to that used in the annual analyses. 



depth of (Tj 26 was also shallow. The high salinity indi- 

 cates the presence of Kuroshio water at OWS-V al- 

 though the shallow depth of a, 26 did not indicate a 

 northward shift of the Kuroshio Extension. An explana- 

 tion may be a weakened baroclinic flow during 1970 or a 

 residual consequence of processes upstream of the sta- 

 tion that also caused the lower surface temperatures at 

 OWS-V during the first half of 1970. 



The Water Structure and Air-Sea Interaction 



A study of the effects of atmospheric forcing on ocean 

 variability at OWS-V is not within the scope of this 

 report. Nevertheless, some inferences can be made 

 about the changes described above in the light of the air- 

 sea interactions previously published (Husby and 

 Seckel 1975). For example, principal heat loss from the 

 sea surface occurs during the 6 mo from 1 October to 1 

 April, and one can inquire about the change in heat con- 

 tent of the water column between these dates. 



Consider the layer above ct, 26 in which temperature 

 and salinity show seasonal changes. The heat content of 

 this layer is pc^ dz where p is the density of the water, Cp 

 is the specific heat at constant pressure, S is the mean 

 temperature of the layer and z is the depth of the layer. 

 With p and Cp assumed constant, the heat content of the 

 layer changes because of changes in the thickness of the 

 layer (divergence) and because of changes in the mean 

 temperature. 



AH = PC Mdz) = pc [eiz + zse]. 



(7) 



Changes in the last term are caused by the heat ex- 

 change across the sea surface, advection, and diffusion. 

 In Table 3, the heat content change, the heat content 

 change due to the mean temperature change, and the 

 total heat exchange across the sea surface are listed for 



the fall and winter cooling seasons from 1966 to 1971. 

 Note the large interannual variability in the heat con- 

 tent changes with the layer actually gaining heat during 

 the 1967-68 season when the total heat loss across the 

 sea surface was anomalously high. Not only are these 

 changes much larger than can be accounted for by the 

 total heat exchange, they also bear no resemblance to 

 the year to year changes of this atmospheric forcing 

 process. The heat content change due to the change of 

 mean temperature has the same order of magnitude as 

 the total heat exchange but again, the interannual vari- 

 ability does not resemble that of the atmospheric forcing 

 process. For example, the total heat exchange in the 

 1968-69 season was less than half that of the previous 

 year, and yet the difference in the heat content change 

 due to change in mean temperature was only 8 kcal 

 cm"^. Evidently other processes such as heat advection, 

 play an important part in the change of mean 

 temperature. 



The 6-yr series of heat content of the layer to the o; 26 

 level (Fig. 16) shows that during 1966 the heat content 

 was high, and during 1970 it was relatively low with ir- 

 regular fluctuations between these years. A seasonal 



Table 3. — Heat budget estimates at Ocean Water Station V for the 

 6-mos cooling portion of the year, 1 October to 1 April. 



'Heat content change in the layer from surface to (t^26. 

 •Heat content change due to the change in mean temperature in layer 

 from the surface to 0^26 (see text). 



'Total heat exchange across sea surface. 



24 



