OCEANOGRAPHIC CLIMATE OF HAWAIIAN ISLANDS REGION 



373 



Although reasons for the occurrence of skipjack 

 in Hawaiian waters are not known, the seasonal 

 and annual variations in tlieir abundance, as 

 reflected by catch statistics, are associated with 

 climatic features such as the seasonal movement 

 of different types of water through the island 

 area. These climatic changes can be monitored 

 with the aid of surface temperatures and salinities 

 as obtained at Koko Head, Oahu. 



I would like to express my appreciation to the 

 members of the faculty of the Department of 

 Oceanography, University of Washington, for 



making their facilities available during a portion 

 of the work and for providing encouragement and 

 valuable suggestions. 1 would also like to thank 

 Drs. C. A. Barnes, N. P. Fofonoff, and M. Rattray 

 for reading the manuscript and for their valuable 

 suggestions — T. S. Austin, J. C. Marr, and K. D. 

 Waldron for reviewing the manuscript, Mrs. M. 

 K. Robinson for supplying the bathythermograms 

 from the Scripps Institution of Oceanographj- 

 deck, and T. Nakata for drawing the figures and 

 charts. 



PART I. DISTRIBUTION OF SURFACE VARIABLES 



1. DEPTH OF THE MIXED SURFACE LAYER 



A. Definition and Practical Means of Determination 



In this paper an attempt will be made to relate 

 the space and time distribution of a surface vari- 

 able, such as temperature, to physical processes 

 such as heat exchange and advection. Although 

 these processes will be discussed in part II, one 

 of the parameters entering into budget considera- 

 tions is the depth to which the processes at the 

 sea surface are effective. For example, the change 

 of temperature due to a certain amount of net 

 lieat exchange across the sea surface depends on 

 the volume of water through which this heat 

 has been distributed. Thus, the depth of this 



effective layer must be defined and its distribution 

 must be determined. 



Since the processes at the sea surface involve 

 energy changes, it is appropriate to consider the 

 stability generally encountered in the upper 300 

 meters of the Hawaii region. The stabihty 



1 J* 



E=- -J- has been discussed by Sverdrup et 



al. (1942) and is a function of the vertical 

 density gradient. It is also proportional to the 

 force required to displace a parcel of water verti- 

 cally by a unit length. 



Figure 1 illustrates the vertical winter and 

 summer density (<r,) distribution at 10° N., 20° 

 N., and 30° N., appro .ximately along a meridian 



100 



Figure 1. — Temperature, salinity, and density (ff() depth curves. Panel A, winter and summer near 10° N'., 

 158° W.; panel B, winter and summer near 21° N., 158° W.; panel C, winter and summer 30° N., 160° W. 

 (158° W.). 



