SECKEL : 



SKIPJACK AND ENVIRONMENT 

 MONTH 



CVJ 



I 

 o 



CO 



^ - 9 

 -10 



-I.I 



-1.2 



-r.3 



-1.4 

 -1.5 



JAN 



FEB 



MAR 



APR 



MAY 



JUN 



JUL 



AUG 



SEP 



OCT 



NOV 



DEC 



EAST-WEST COMPONENT 



MONTH 



5 -3 

 o 



CO -4 



UJ 



^ -.5 

 -.6 

 -.7 

 -.8 



-.9^ 



FEB MAR APR MAY JUN 

 I I I I ll I I I I 



JAN FEB 



JUL 



AUG SEP OCT NOV 



DEC 



\ 



NORTH-SOUTH COMPONENT 



Figure 11. — Zonal and meridional components of wind stress in latitude bands 10°-14°N, 15°-19°N, 20°-24°N av- 

 eraged between long 120° and 160°W (University of California, 1948). Stress is positive if directed to the east 

 and north, respectively. 



of lat 15°N rapidly drift northward. Objects ap- 

 pear to concentrate on the southern and northern 

 edge of their distribution and then merge west 

 of long 150°W in a relatively narrow band be- 

 tween lat 18° and 22°N. Lost in the presenta- 

 tion are a few objects that drifted across the 

 northern edge of the equatorial current in the 

 western portion of the model ocean and those 

 that drifted west beyond long 160°W. In the 

 western part of the model area considerable 

 mingling of objects introduced in different sea- 

 sons takes place. In some 1-degree units of area 

 are found objects that were introduced during 

 3 seasons. 



The concentration of drifting objects at the 

 southern edge of their distribution is caused by 

 the seasonal difference in the convergence of the 

 meridional wind-driven current. The zonal com- 

 ponent of the trades is stronger from November 

 to June at lat 10° to 14°N then at lat 15° to 



19°N but weaker from June to November 

 (Figure 11). Consequently, the meridional 

 component of wind-driven current is strongly 

 convergent from November to June but weakly 

 convergent or divergent during the remainder 

 of the year. The effect of this seasonal differ- 

 ence is illustrated in Figure 14. Note that in 

 the first case with a high meridional wind-driven 

 current only 4 objects are left south of lat 15°N 

 but 11 objects are left in the second case. Again, 

 in the first case with strong meridional conver- 

 gence there were 14 objects between lat 15° and 

 17° but 8 objects for the second case. 



The seasonal variation of meridional wind- 

 driven current inferred from the lat 15° to 19° 

 and 20° to 24°N curves in Figure 11 is smaller 

 than it is south of lat 15 °N. Consequently the 

 northward drift near lat 20°N is not as large 

 as in the example given above. Near this lati- 

 tude, however, the southward component of the 



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