An eddy is a rotating parcel of fluid. As such, the eddy concept can be applied to phenomena ranging from momentary vortices in the sea-surface flow to the steady circulation of a basin-wide gyre. For ASW application, however, mesoscale features of 100 to 400 km (55 -215 nmi) are most important. These eddies are rotating masses of water that have broken off from a strong front such as the Gulf Stream. They can be considered circular fronts with water trapped inside having different physical properties from the surrounding water.

Surface winds cause vertical water movements. Upwelling can be caused by winds blowing across the ocean surface. Coastal upwelling occurs where prevailing winds blow parallel to the coast. Winds cause surface water to move, but the presence of land or a shallow bottom restricts water movements. When the wind-induced water movement is off-shore, subsurface water flows to the surface near the coast. This slow, upward flow, from 100 to 200 meters (300 to 600 feet) deep, replaces surface waters blown seaward. Coastal upwelling is common along the west coast of continents. Upwelling also occurs in the equatorial open oceans. This wind-induced upwelling is caused by the change indirection of the Coriolis effect at the equator. Westward flowing, wind-driven surface currents near the equator flow northward on the north side and southward on the south side of the equator.

TYPICAL LOCATIONS OF PACIFIC AND ATLANTIC OCEAN FRONTS

Figures 9-15 and 9-16 show approximate locations of Pacific and Atlantic Ocean fronts. The dashed lines are weak fronts, which may not be significant to ASW operations. The solid lines represent the moderate fronts which, under certain conditions, may be important operationaly. The heavy lines are the strong fronts, which usually have a significant effect on ASW tactics.

Although it is not possible to show typical locations of large ocean eddies due to their constant motion, they are generally found on either side of strong fronts such as the Gulf Stream or the Kuroshio. Smaller eddies, such as those formed by upwelling can be found in any part of the ocean.

Figure 9-15.-Mean position of Pacific fronts.

Figure 9-16.-Mean position of Atlantic fronts.

This information is now available on CD in Adobe PDF Printable Format

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing