based on long-term mean meteorological data. 

 Differences resulting from the use of a constant 

 instead of a variable drag coefficient in the 

 evaporation equation also become apparent. 



Results from two locations were chosen for 

 comparisons: (1) lat. 17° N., long. 152° W., in 

 the trade wind region. (2) lat. 2°N., long. 157° 

 W., in the equatorial region. The heat of evap- 

 oration and the net heat exchange across the 

 sea surface from the trade wind region are 

 shown in figure 5 and those from the equatorial 

 region are shown in figure 6. 



In the trade wind zone (fig. 5), the large fluc- 

 tuations in Q(E), which change from year to 

 year, make it difficult to discern a seasonal 

 trend. A seasonal trend in the variation of Q(N), 

 however, is not obscured even though the effects 

 of the large fluctuations of Q(E) are apparent. 

 The relatively large amplitude in the seasonal 

 cycle of Q(S) must, therefore, be a dominant 

 factor in the net heat exchange across the sea 

 surface at lat. 17° N. 



In view of the large variability in the heat of 

 evaporation, the month-to-month trend of Wyrt- 

 ki's Q(E) values is not expected to correspond 

 with those during either of the 2 years from 



1963 to 1965. As was true for the results of 

 table B, Wyrtki's 0(E) fluctuations do not ob- 

 scure the seasonal trend of Q(N). 



Comparison of Q(E) and Q(N) averages shows 

 good agreement. The 1963 to 1965 average Q(E) 

 is about 260 cal. cmr^day-' and Wyrtki's annual 

 average 0(E) is about 270 cal. cmT^day"'. Sim- 

 ilar mean values of Q(N) are about 30 cal. 

 cmT^ day"' and 50 cal. cmT^day"', respectively. 



In the equatorial example (fig. 6), fluctua- 

 tions in Q(E) during 1963 to 1965 are less pro- 

 nounced than in the trade wind zone and a sea- 

 sonal trend is apparent; evaporation is high 

 during summer and autumn and low during win- 

 ter and spring. Year-to-year changes inQ(N), 

 however, are larger than expected from the dif- 

 ferences in Q(E), particularly from November 

 to February. In the equatorial region the ampli- 

 tude of the seasonal variations in the clear sky 

 radiation, Qq, is relatively small so that year- 

 to-year differences in cloudiness must play an 

 important role in the net heat exchange across 

 the sea surface. This variability in Q(S) also 

 obscures the seasonal trend of the heat of evap- 

 oration in 0(N). 



N D J F 

 MONTHS 



N J F 

 MONTHS 



M A M J 



Figure 5. — The heat of evaporation, Q(E), and the net heat exchange across 

 the sea surface, Q(N), at lat. 17° N. , long. 152° W. , July 1963 to June 

 1965 (from table B) , and interpolated values from climatic charts by 

 Wyrtki (1966). 



lA 



