OCEANOGRAPHIC CLIMATE OF HAWAIIAN ISLANDS REGION 



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Figure 3. — Minimum and maximum mean depth of mixed 

 layer 10° to 30° N. Panel A, 153°-161° W.; panel B, 

 168°-176° W. 



mum and minimum depth of mixed layer has been 

 indicated in figures 3A and B, together with the 

 month of occurrence. These figures also indicate 

 the annual depth range both in the eastern and 

 western portion of the survey region between 10° 

 and 30° N. 



In figure 3 A, for the eastern section, one notes 

 that south of 14° N. the extremes in depth of the 

 mixed layer occur in spring and autumn, whereas 

 north of 15° N. they occur at the beginning of 

 winter and summer. This suggests that the area 

 south of about 14° N. belongs to a region with a 

 diflFerent oceanographic climate, where extremes 

 in the depth of the mixed layer follow those to the 

 north of 14° N. by approximately three months. 



Figure 3A also shows that the maximum difi"er- 

 ence in the average depth of the mixed laj'er be- 

 tween summer and winter is 220 feet (67 m.) and 

 occurs at 23° N. The minimum difference occurs, 

 as might be expected, at the nodal point, 15° N., 

 where it is about 60 feet (18 m.). At 10° N. the 

 seasonal range is again 200 feet (61 m.). 



In the western section, figure 3B, the boundary 

 between the two cUmatic regions lies at approxi- 

 mately 13° N. during the minimum depth of the 

 mixed layer period. South of this latitude the 



minimum occurs in October (one month later than 

 in the eastern section) and north of this latitude 

 in June. During the maximum depth of the 

 mixed layer period, the boundary is less distinct. 

 At 10° N. the ma.ximum occurs during February- 

 March, between 11° and 15° N. in February, and 

 north of 15° N. it occurs in January. This sug- 

 gests that the boundary which separates the two 

 climatic regions at 13° N. during the minimum 

 depth of the mixed layer period, has shifted south- 

 ward during the maximum depth of the mixed 

 layer period. That is, in winter the western por- 

 tion of the region between 10° and 30° N. Ues 

 within the same oceanographic climate. 



Figure 3B also shows that the maximum differ- 

 ence in the average depth of the mixed layer be- 

 tween summer and winter is about 260 feet (79 

 m.) at 23° N., as in the eastern section. The 

 minimum difference is about 90 feet (27 m.) at 

 10° N. Although a node is indicated between 12° 

 and 13° N. in figure 2B, the minimum difference in 

 the summer and winter depth of mixed layer did 

 not occur at this latitude because of the apparent 

 seasonal motion of the chmatic boundary. 



The mean seasonal variation in the depth of the 

 mixed layer at 12°, 18°, 20°, and 22° N. in the 

 meridinal storip between 153° and 161° W., is 

 illustrated in figure 4. Comparison of the data 

 for 12° N. with those to the north indicates the 

 phase difference in extremes. It also shows that 

 in the vicinity of the high islands of the Hawaiian 

 archipelago the seasonal range in the depth of the 

 mixed layer is less than that to either the north or 

 south. Finally, figure 4 shows the seasonal vari- 

 ation in the depth of the mixed layer for the vi- 

 cinity of 27° N. and 175° W. Here the depth 

 decreases at a time (Dec. and Jan.) when it ap- 

 proaches the maximum throughout the northern 

 portion of the region. 



2. SURFACE TEMPERATURE 



In oceanography as well as in weather analysis, 

 temperature has long been recognized as an im- 

 portant climatic character. Surface temperature 

 charts of the oceans, such as the U.S. Navy Hy- 

 drographic Office, Monthlj' Surface Temperature 

 Charts of the North Pacific Ocean, (Misc. No. 

 10577), are readily available. A standard refer- 

 ence in oceanography is the temperature charts 

 of Schott (1935). A new set of monthlj' tempera- 

 ture charts (appendix B, chart II) have been pre- 



