Atlantic Equatorial Undercurrent (Buchanan Undercurrent, Lomonosov 
Undercurrent ) 
The Atlantic Equatorial Undercurrent was discovered in 1886 by the 
British oceanographer J. Y. Buchanan. From limited direct observations 
the undercurrent appears to be a permanent phenomenon, flowing east at 
the Equator during all seasons for a distance at least between 37° and 
h°w. Speed of the current has been measured by drogues and anchored 
current meters during northern spring and winter, and little seasonal 
variation is indicated. Drogue measurements at the Equator near 41°W 
showed no undercurrent; however, at 37°, 35°, and 33°W, an east set at 
1.5 knots was recorded at depths between 75 and 100 meters (246 and 
328 feet). The surface currents observed at these three locations were 
moderate westward during northern summer, and weak eastward in winter. 
Detailed current measurements obtained at various locations along 
the Equator from 30° to }°W disclose a strong deep current with speeds 
at times exceeding 2 knots; a remarkable similarity to the Pacific 
Equatorial (Cromwell) Undercurrent is indicated. The core of highest 
speeds (Figure 4) is at a depth between 40 and 90 meters (131 and 295 feet), 
but its limits have not been reliably defined to date. 
At O°O09'N, 30°00'W, current meter measurements showed an east set 
from the surface to 150 meters (492 feet); at 50 meters (164 feet) the 
speed was 1.7 knots, at 100 meters (328 feet) 1.7 mots, and at 150 
meters (492 feet) 0.8 knot. The east flow at the surface probably 
resulted from surfacing of the undercurrent during a period of weak 
winds, not unusual at this latitude. Other observations taken in 
February and March 1963 between 30.0° and 27.5°W show the undercurrent 
to be strongest and most constant between 0.0° and 0.5°N. Near the 
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