Benguela Current - Wikipedia
May 12, Two major ocean currents collide at Cape Hatteras. Here, the Gulf Stream, bringing warm water from the South, meets the Slope Sea Gyre, also A second swimming fatality occurs on Outer BanksJuly 22, In "News". The Benguela Current /bɛŋˈɡweɪlə/ is the broad, northward flowing ocean current that forms 1 Boundaries; 2 Upwelling and primary production; 3 Benguela Niño; 4 See also; 5 References; 6 External links The icy Benguela and the warm, south-flowing Agulhas current do not meet off the Cape of Good Hope (see. Major ocean current systems of the world. A characteristic surface speed is about 5 to 50 cm (about 2 to 20 inches) per second. . not often met, though deflection of a wind-driven surface current at somewhat smaller than 45° warmest surface water is found, there occurs the eastward-flowing Equatorial Counter Current.
Thirty-five foot waves are forecast for the Gulf Stream. Or perhaps it is a morale-boosting decision by the captain and chief scientist? The familiar hum of the engines was absent when I woke up.
After two weeks on the ship, you become attuned to every sound and motion. The hum and whir of the propellers started up again. The sound of waves slamming into the side of the ship resumed, as did our wild rolls from side to side. Hmm, we must have just finished a CTD cast and are moving on to another station.
The last thing you want in rough weather is for the CTD to become a wrecking ball. It made for a long night, but the constant activity made time go faster. He replied that the ingredients would slide off in the oven.
Our definition of bad weather has changed. No pizza for us tonight. I was heading up to the main lab today when I heard a series of faint whistles and clicks. I watched them until sunset. They seemed delighted to find something to play with out in the cold dark ocean.
Winds have increased to storm force—again. Too rough for Scanfish, too rough for CTDs, too rough for pizza, and too rough for reading in my bunk. As the ship rolled heavily in the swell, portholes in the main lab alternated between views of the sky and views beneath the waves.
As the water swirled around the round porthole, I had an uncanny feeling like I was in a giant steel washing machine. With just the right pillow placement, I have managed to wedge myself into my bunk. The sounds of waves crashing into the hull are far from soothing. This evening we steamed past the moorings to check that they were still there.
The anemometer on the guard buoy is dangling from a single mounting bracket—the other one must have broken off. We are hoping it lasts the night. The forecast for tomorrow looks a little better: And then who knows when we would be able to get our precious data? In the Southern Hemisphere, this deflection would be toward the left.
It can be shown that the Coriolis force always acts perpendicular to motion. Frictional forces Movement of water through the oceans is slowed by friction, with surrounding fluid moving at a different velocity. A faster-moving fluid layer tends to drag along a slower-moving layer, and a slower-moving layer will tend to reduce the speed of a faster-moving layer.
This momentum transfer between the layers is referred to as frictional forces. The wind blowing over the sea surface transfers momentum to the water.
This frictional force at the sea surface i. Currents moving along the ocean floor and the sides of the ocean also are subject to the influence of boundary-layer friction. The motionless ocean floor removes momentum from the circulation of the ocean waters.
Geostrophic currents For most of the ocean volume away from the boundary layers, which have a characteristic thickness of metres about feetfrictional forces are of minor importance, and the equation of motion for horizontal forces can be expressed as a simple balance of horizontal pressure gradient and Coriolis force.
This is called geostrophic balance. On a nonrotating Earth, water would be accelerated by a horizontal pressure gradient and would flow from high to low pressure. On the rotating Earth, however, the Coriolis force deflects the motion, and the acceleration ceases only when the speed, U, of the current is just fast enough to produce a Coriolis force that can exactly balance the horizontal pressure-gradient force.
Scientists studying the ocean currents that collide at Hatteras - francinebavay.info
From this balance it follows that the current direction must be perpendicular to the pressure gradient because the Coriolis force always acts perpendicular to the motion. In the Northern Hemisphere this direction is such that the high pressure is to the right when looking in current direction, while in the Southern Hemisphere it is to the left.
This type of current is called a geostrophic current. The simple equation given above provides the basis for an indirect method of computing ocean currents.
The relief of the sea surface also defines the streamlines paths of the geostrophic current at the surface relative to the deep reference level. The hills represent high pressure, and the valleys stand for low pressure. Clockwise rotation in the Northern Hemisphere with higher pressure in the centre of rotation is called anticyclonic motion.
Counterclockwise rotation with lower pressure in its centre is cyclonic motion. In the Southern Hemisphere the sense of rotation is the opposite, because the effect of the Coriolis force has changed its sign of deflection. Ekman layer The wind exerts stress on the ocean surface proportional to the square of the wind speed and in the direction of the wind, setting the surface water in motion.
This motion extends to a depth of about metres in what is called the Ekman layer, after the Swedish oceanographer V. Walfrid Ekmanwho in deduced these results in a theoretical model constructed to help explain observations of wind drift in the Arctic. Within the oceanic Ekman layer the wind stress is balanced by the Coriolis force and frictional forces. This phenomenon is called Ekman transportand its effects are widely observed in the oceans.
Since the wind varies from place to place, so does the Ekman transport, forming convergence and divergence zones of surface water. A region of convergence forces surface water downward in a process called downwellingwhile a region of divergence draws water from below into the surface Ekman layer in a process known as upwelling. Upwelling and downwelling also occur where the wind blows parallel to a coastline. The principal upwelling regions of the world are along the eastern boundary of the subtropical ocean waters, as, for example, the coastal region of Peru and northwestern Africa.
Upwelling in these regions cools the surface water and brings nutrient-rich subsurface water into the sunlit layer of the ocean, resulting in a biologically productive region. Upwelling and high productivity also are found along divergence zones at the Equator and around Antarctica. The primary downwelling regions are in the subtropical ocean waters—e. Such areas are devoid of nutrients and are poor in marine life. The vertical movements of ocean waters into or out of the base of the Ekman layer amount to less than 1 metre about 3.
Within an upwelling region, the water column below the Ekman layer is drawn upward. This process, with conservation of angular momentum on the rotating Earth, induces the water column to drift toward the poles. Conversely, downwelling forces water into the water column below the Ekman layer, inducing drift toward the Equator. An additional consequence of upwelling and downwelling for stratified waters is to create a baroclinic field of mass.
Surface water is less dense than deeper water. Ekman convergences have the effect of accumulating less dense surface water. This water floats above the surrounding water, forming a hill in sea level and driving an anticyclonic geostrophic current that extends well below the Ekman layer. Divergences do the opposite: This induces a depression in sea level with a cyclonic geostrophic current. The ocean current pattern produced by the wind-induced Ekman transport is called the Sverdrup transportafter the Norwegian oceanographer H.
Sverdrupwho formulated the basic theory in Several years later the American geophysicist and oceanographer Walter H. Two types of ocean circulation Ocean circulation derives its energy at the sea surface from two sources that define two circulation types: These two circulation types are not fully independent, since the sea-air buoyancy and momentum exchange are dependent on wind speed.
The wind-driven circulation is the more vigorous of the two and is configured as gyres that dominate an ocean region. The wind-driven circulation is strongest in the surface layer. The thermohaline circulation is more sluggish, with a typical speed of 1 cm 0. Wind-driven circulation Wind stress induces a circulation pattern that is similar for each ocean.
Ocean current | francinebavay.info
In each case, the wind-driven circulation is divided into gyres that stretch across the entire ocean: The depth penetration of the wind-driven currents depends on the intensity of ocean stratification: Near the thermal equator, where the warmest surface water is found, there occurs the eastward-flowing Equatorial Counter Current. At the geographic Equator a jetlike current is found just below the sea surface, flowing toward the east counter to the surface current.
This is called the Equatorial Undercurrent. It attains speeds of more than 1 metre per second at a depth of nearly metres.
It is driven by higher sea level in the western margins of the tropical ocean, producing a pressure gradient, which in the absence of a horizontal Coriolis force drives a west-to-east current along the Equator. The wind field reverses the flow within the surface layer, inducing the South Equatorial Current.
Equatorial circulation undergoes variations following the irregular periods of roughly three to eight years of the Southern Oscillation i. Weakening of the east-to-west wind during a phase of the Southern Oscillation allows warm water in the western margin to slip back to the east by increasing the flow of the Equatorial Counter Current. Surface water temperatures and sea level decrease in the west and increase in the east. In the tropical Indian Ocean the strong seasonal winds of the monsoons induce a similarly strong seasonal circulation pattern.
The subtropical gyres The subtropical gyres are anticyclonic circulation features. The centre of the subtropical gyre is shifted to the west.
This westward intensification of ocean currents was explained by the American meteorologist and oceanographer Henry M. Stommel as resulting from the fact that the horizontal Coriolis force increases with latitude. This causes the poleward-flowing western boundary current to be a jetlike current that attains speeds of 2 to 4 metres 6.
Informally called PEACH Processes driving Exchange at Cape Hatterasthe project will study the ocean currents to determine what causes the exchange between offshore and inshore waters. The waters being studied have often been called the Graveyard of the Atlantic, home to many shipwrecks.
This research project will help explain why. PEACH will focus primarily on the physics of the ocean, according to Savidge, but the information gathered will also help scientists understand the chemistry and biology, and may cast light on issues like carbon cycling, global climate change and the feasibility of offshore drilling.
Field work will continue until the fall of A variety of tracking systems will be used, including radar, buoys, moorings and gliders. Monitoring stations have been set up in the airport offices at Ocracoke and north of Frisco, and the data will be checked once a month The cables I had observed are connected to poles which contain high-frequency radar equipment, situated on sand dunes overlooking the ocean.