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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 23. — Distribution of advection in the Hawaiian 

 survey region (°C. mos.-')- A— Mean positive (cold) 

 advection; B— Mean negative (warm) advection; C— 

 Mean annual advection. 



is also true in figure 22C, except that negative 

 advection is less pronounced and occurs earlier. 



Phase differences between extremes of and 



pCpZ 



— , and changing distances between these curves 



indicate a varying advention resulting in advec- 

 tion peaks. This is best illustrated by plotting 



the difference between and — separatelv. 



pCpZ £d ^ -^ 



North of the islands, for example, advection peaks 



occur in June to July and in October to November. 



To the south of the islands, advection peaks occur 



in February, June, and November. Within the 



island area, these peaks occur during February to 



March, August, and October. 



Since both the and — curves have shapes 



PCt,Z 



At 



and times of maxima and minima typical for 



A/? 

 their location, one might call the — curve, as may 



be obtained from an island monitoring station, a 

 "characteristic heating curve." Similarly, the 

 combinations of these curves form advection 

 patterns typical for their location, so that curves, 

 such as in figure 22, may be called "characteristic 

 advection diagrams." 



In order to explore the physical meaning of 

 advection and discover its significance in the 

 vicinity of the Hawaiian Islands, the region was 

 divided into 60 three-degree squares for which 

 characteristic advection diagrams were drawn. 



First, by measuring the area between 



H ,Ad 

 and — 



pCpZ At 



of each diagram, the mean positive, the mean 

 negative, and the mean annual advection was ob- 

 tained and their distribution plotted in figure 23. 



Positive or cold advection occurs approximately 

 from May to the following Februarj' and is dis- 

 tributed as shown in figure 23A. The feature of 

 significance here is the trough of low advection 

 extending southwestward from 21° N., 150° W., 

 crossing the southern boundary of the region in 

 the vicinity of 170° W. On both sides of the 

 trough the mean advection increases to approxi- 

 mately 2° C. mos.~' in the northwest portion of 

 the region and 1° C. mos.~' in the southeast. 



Negative or warm advection occurs predomi- 

 nantly during March and April. Figure 23B 

 shows that a distinct positive advection pattern 



