410 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



data from the files of the Scripps Institution of 

 Oceanography which are scheduled for publication 

 in Oceanic Observations of the Pacific. 



TREATMENT OF DATA 



Charts I and II, the distribution of the depth of 

 the mixed layer and the surface temperature were 

 all based on bathythermograph observations which 

 were read and tabulated by 1° squares. These 

 data were then averaged for each month of each 

 year. Since in the Hawaiian region meridional 

 gradients are generally greater than zonal gradi- 

 ents, the averaged data were plotted for each 

 month in the ten meridional strips: 150° to 152° 

 W., 153° to 155° W., 156° to 158° W., 159° to 

 161° W., 162° to 164° W., 165° to 167° W., 168° to 

 170° W., 171° to 173° W., 174° to 176° W., and 

 177° to 179° W. Needless to say, data for various 

 months in different areas were missing or biased 

 toward a single year. These difficulties were in 

 part overcome by interpolation from seasonal 

 curves and from comparisons with adjacent 

 meridional distribution. The meridional surface 

 temperature and depth of mixed layer profiles were 

 then used to draw the monthly charts, where 

 smoothing was done only after re-examination of 

 the data. 



Scarcity of salinity and dynamic height data 

 prevented construction of monthly or quarterly 

 charts. In grouping the data for the construction 

 of two charts, a compromise between months of 

 maximum observations and months of oceano- 

 graphic significance had to be made. By "group- 



ing data" is meant plotting all the observations for 

 a period of months onto a single chart and then 

 drawing contours through the mean values. 



The number of salinity observations were rela- 

 tively high durmg June to September and during 

 January to March and predominated in the eastern 

 portion of the region. On the basis of the 

 seasonal salinity variation, the April to August 

 data and the November to February data were 

 grouped to draw chart III, representing the low 

 and high salmity period near Hawaii, respectively. 

 This grouping of months does not quite correspond 

 with the maximum occurrence of data, nor, as is 

 apparent from the salinity discussion in Part I, is 

 it in phase with the high or low salinity north of 

 15° N. generally, or the extremes in the southeast 

 portion of the region. 



Significant grouping of the d;\aiamic height 

 data, which were collected predominantly during 

 June to August and January to March, was more 

 difficult. In the estimation of geostrophic cur- 

 rents, gradients rather than the absolute magni- 

 tudes of geopotentials are of importance. This 

 makes grouping of several months' data, collected 

 during a number of years, questionable. In 

 addition, the dynamically significant periods as 

 reflected in the geopotential topography are not 

 known and may not correspond with any or all 

 of the advective periods discussed in the atlas. 

 Despite these shortcomings, the data from Decem- 

 ber to April and June to October were grouped to 

 draw chart IV. These, therefore, roughly bracket 

 the period of low advection during the winter and 

 high advection during the summer months. 



