394 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



APRIL 



AUGUST 



15° 20° 25° 



NORTH LATITUDE 



30° 10° 15° 20° 25° 



NORTH LATITUDE 



15° 20° 25° 



NORTH LATITUDE 



30° 



Figure 21. — Meridional profiles at 160° W. of evaporation, precipitation, evaporation minus precipitation, and equivalent 

 salinity changes per month (upper panel) during April, August, and December. 



It is also difficult to explain the sudden drop of 



salinity at 13° N. during October and November 



(fig. 9) in terms of evaporation minus precipitation. 



Here the decline of salinity occurs at the very time 



when there is a change from excess precipitation 



to excess evaporation. As at 21° N., this indicates 



the movement of a boundary, possibly due to the 



same forces which are involved in the rapid change 



of {E-P). 



3. ADVECTION 



A. Characteristic Advection Diagram 



The simplified heat (temperature) budget equa- 

 tion (equation 6) contains only three terms. 

 Therefore, by using the temperature data from 

 part I and the net heat exchange across the sea 

 surface from the previous section, one can obtain 

 a measure of the advection. This is best accom- 



plished by drawing 



and — - versus time lor any 



pCpZ At 



one location. Then, as the approximate tempera - 

 = V-Vd shows, the difference 



ture budget 



H Ad 



pCpZ M 



between the two curves indicates the magnitude of 

 advection. 



Figure 22 shows the and — curves for the 



^ pCpZ At 



three-degree squares 14° to 17° N., 156° to 159° 

 W., 20° to 23° N., 156° to 159° W., and 26° to 

 29° N., 156° to 159° W. One notes that the shape 

 of the curves changes with location. For example, 

 to the south of the islands the heat exchange across 

 the sea surface, as it affects the surface tempera- 

 ture, reaches its maximum during September and 

 October and its minimum during January. In the 

 vicinity of the islands, the maximum occurs during 

 July and the minimum during December. Finally, 

 to the north of the islands the maxinium heat 

 exchange occurs in Jmie and the minimum occurs 



