12 
Sy, A. et al. (2002): Upper Ocean Climate Ship-of-Opportunity Programme of BSH - A Status Report 
Line AX-11 intersects the eastern margin of the subtropical gyre. The mean temperature field 
(Fig. 8 top) represents the main water masses such as the Tropical Surface Water (0 > 20 °C), 
the Central Water, and the northward spreading Antarctic Intermediate Water (AAIW). The 
dominant feature is the bowl of warm water of the subtropical gyre which limits the northward 
spreading of AAIW north of 24°N. RMS values (Fig. 8 bottom) are highest in the surface layer 
down to 150 m, especially in the equatorial region from 5°S to 15°N. This high variability of the 
temperature field is associated with seasonal changes in the wind field and migration of the 
intertropical convergence zone from its southernmost position in north spring to its northernmost 
position in north fall. These atmospheric variations induce changes in the currents, like the 
weakening or even reversal of the North Equatorial Countercurrent from north spring to north 
fall. 
Fig. 8: Mean temperature field (top) and RMS values (bottom) along line AX-11