Recent Surface Current Maps : What are they?

The maps are measured with a radio transmitter and receiver. Radio waves sent from a land station are scattered from ocean waves, and received again on land. The current is determined from the radio-wave Doppler shift induced by the motion of the ocean waves, considered with other information about the waves (technical details ). Pioneering papers on this technique are Stewart and Joy, 1974 (Deep-Sea Res., 21: 1039-1049) and Barrick, Evans and Weber, 1977 (Science, vol 198, p138-144). A collection of papers from investigators using this measurement can be found in the Oceanography, v10, n2.

The length and direction of the arrows indicate the current speed and direction. The current speed is also shown by the color, keyed by a color bar at the bottom of the map. Current speeds are in centimeters per second (1 knot = 51.4 centimeters/second).

Daily averages are used to help filter out tidal variations.

Please note: these are research, rather than routine, measurements. These near-real-time measurements have not been subjected to thorough data checking. Their accuracy is not guaranteed; in fact, some errors are to be expected. Treat them skeptically, and use at your own risk.