As part of the South Carolina / Georgia High-Frequency (HF) Radar project, WERA radar stations have been established at Pritchards Island (SC) and St. Catherine's Island (GA). Each station collect 15-mintue blocks of real-time data, which are combined every half hour to form 2-D vector maps of ocean surface currents.

Sample vector map:

Two important visible phenomena:

Gulf Stream: A portion of the Gulf Stream is visible in these maps, as the fast moving currents along the right-hand side of the coverage zone. The Gulf Stream is a narrow, swift-moving current of warm water that starts in the Gulf of Mexico and travels along the eastern coast of the United States, before splitting into two branches, one heading for Europe and the other for Africa. The Gulf Stream influences weather along the eastern United States, bringing warmth and more temperate seasons to coastal regions. Although the path of the Gulf Stream varies, it is always located approximately 200 km off-shore of the GA and SC coast.

The current velocity of the Gulf Stream is the fastest at the surface, and can achieve speeds ~ 2 m/s. Note that the velocities graphed on the vector maps are given in terms of knots. Since 1 knot is approximately 0.5 m/s, a speed of 3.0 knots is about 1.5 m/s. WERA routinely records Gulf Stream velocities around 3 knots, which is consistent with expected velocities for this current.

Semidiurnal tide: A semidiurnal tide describes a system which experiences two high tides of equal magnitude and two low tides of equal magnitude each day. This is in contrast to a diurnal tide, which only has one high and low tide per day, and a mixed tide, which has two high tides of distinct magnitude and two lows tides of distinct magnitude per day. Semidiurnal tides are caused by the moon's gravitation effects on the oceans; this attraction varies due to the relative positions of the Earth and the moon. Since the moon is orbiting Earth as the Earth spins, it takes 24 hours and 50 minutes for the moon to complete a full orbit relative to a given location on Earth. Thus, a tidal day is 24 hours and 50 minutes, and the period of a semidiurnal tide is 12 hours and 25 minutes. Note that the directional arrows on the vector maps reverse direction every 6 hours, 12.5 minutes, as the tides shift. Also note that as the tides shift there are brief periods of very low currents, with neither a strong ebb nor flow direction: this period is known as a slack tide.

Background on Ocean Currents:

In general, there are two main categories of ocean currents: those that are wind-driven and those that are caused by thermohaline circulation. Thermohaline circulation refers to flow that is caused by density differences between water masses, due to variances in temperature and salinity. The Gulf Stream is a wind-driven current, powered by northeast trade winds.

Oceans are constantly circulating in ocean basins, and within a given basin currents generally flow in a clockwise direction in the northern hemisphere and in a anti-clockwise direction in the southern hemisphere. This phenomena is due to the Coriolis effect, which refers to the effect of Earth's rotation on objects in motion. In the northern hemisphere, objects are deflected to the right, setting up clockwise motion. Conversely, in the southern hemisphere, moving objects are deflected to the left, setting up anti-clockwise motion. Furthermore, ocean currents along the western boundary of an ocean basin in the northern hemisphere are stronger than those along the eastern boundary. For example, the Gulf Stream, which travels along the western boundary of the North Atlantic basin, is much stronger than the Canary current along the eastern boundary of the North Atlantic basin. The opposite holds in the southern hemisphere: currents along the eastern boundary are much stronger than those along the western boundary of an ocean basin.