What Are Surface Currents Caused By? | Sciencing
The first reasonable theory of how the wind affects surface currents was derived by The result is a map showing how the height of the sea surface at any given point The trade winds set up two westward-flowing currents north and south of the . trying to find information about this topic for it is related to ocean currents. Ocean circulation, coupled with trade wind changes, efficiently limits . Schematic of the atmosphere–ocean circulation: Image (a) shows the. Episodic shifts in winds and water currents across the equatorial Pacific can cause floods in Easterly trade winds (which blow from the Americas toward Asia) falter and can even Chart showing increased rainfall during El Niño years . .. up along the coast of Chile, likely the result of El Niño related changes in the ocean.
As along California coast e. Because the prevailing winds circle the Atlantic in a clock-wise gyre, the Ekman Transport of near-surface seawater makes currents flow into the center of the gyre. The sea level of the Sargasso Sea is almost 3 feet higher than that along the coast of North America. Geostrophic Flow - In the Northern Hemisphere the right-hand Coriolis deflection results in the accumulation of light surface waters on the right side of major surface currents.
This causes the buildup of a mound of water on the right side of the current flow i. This buildup continues until the downhill force of gravity, tending to pull the water back off the mound, is equal and opposite to the Coriolis deflection of the flowing water up into the mound.
When this happens the two forces balance and the current flows sideways along the mound in the wind direction. This type of current, which results from the balancing of gravity and the Coriolis deflection, is called geostrophic flow. Most ocean surface currents are a combination of wind-driven and geostrophic currents.
The winds are the basic driving force, but inertia and geostrophic effects ensure that the currents continue to flow even during periods when the wind stops. Oceanographers have long observed that the so-called western boundary currents flowing along the western edges of the major ocean basins, are especially fast-moving and narrow compared to ocean currents elsewhere in the ocean basins.
The Gulf Stream is an example of one of these western boundary currents. There are a number of reasons for this all related to the Earth's rotation and atmospheric circulation. I'll mention two just to give you an idea of the processes at work here. The Trade Winds blow equatorial surface water to the west causing it to pile up i. Here this excess water flows downhill to the north and south along the edge of the continents.
As I mentioned earlier the Coriolis deflection increases with increasing latitude i. Therefore, the eastward return flow of the major currents at higher latitudes is strongly deflected southwards towards the equator. This compresses Equatorial currents and concentrates the westward-flowing water in a narrow band that squirts out forcefully when it reaches the western continental boundaries.
Warmed by the sun in the Gulf of Mexico, where seawater pumped in by the North Equatorial Current circulates, water must exit the Gulf by way of the narrow Straits of Florida. This crystal clear, azure-blue, warm, nutrient-poor water from the tropics moves up along the coast of North America gradually slowing down as it approaches Cape Hatteras and turns farther eastward into the Atlantic. The temperature change can be impressive.
The two currents are sometimes so close that the bow of a boat may be in one while the stern is in the other. One boat reported a 22o temperature difference between its bow and stern. Along the NC coast the Gulf Stream is a dependable source of fish of all kinds and tropical seabirds often follow their food supply north along its path. Charter boat captains and commercial fishermen keep careful track of its position as it meanders around the western North Atlantic.
Changes in position of the Gulf Stream often generate meanders that become cut off from the main flow of the current. These can trap within them cold or warm core rings of cold, nutrient-rich shelf water or warm, nutrient-poor Sargasso Sea water, respectively.
Ocean Circulations | North Carolina Climate Office
Cold core rings move southeastward from the Gulf Stream into the waters of the Sargasso Sea. Warm core rings move northwestward up over the continental slope and shelf. Many people were talking about the unusual weather conditions of such as: At the same time New England had such warm temperatures that they had very little snow and ski resorts were suffering.
Temperatures in the USA were, on average, 6o above normal making it the warmest January on record. Australia, the Caribbean, and parts of Central America experienced severe drought. In the Pacific Ocean, where these effects are most pronounced, they are usually first observed around Christmas time.
This results when the normal patterns of surface winds and currents is disrupted because the relatively constant Trade Winds decrease significantly in intensity for significant periods of time. The change in the Trade Winds is a result of changes in atmospheric pressures on either side of the Pacific Ocean.
This is called the Southern Oscillation. This in turn diminishes flow of the Peru Current northward along the western coast of South America thus allowing warm, tropical Pacific Ocean water to drift back eastward. As the warm, tropical water flows back eastward it suppresses the normal coastal upwelling observed off of western South America.
It is this coastal upwelling of cold, deep, nutrient-rich water that supports a flourishing fishing industry off of Peru by supporting a thriving plant population. Floods and landslides in northwestern South America b.
Significant declines in the number of anchovies found in coastal waters of northwestern S. Anchovies are not a popular foodfish also called table fish. However, they are widely used as a protein supplement in chicken and livestock feed. So when the price of anchovies goes up, the price of beef, pork, chicken, etc. Seabirds in the area starve because their food supply dwindles.
Organisms that transmit disease also respond to such changes in climate. Copepods tiny shrimp-like creatures which are the most abundant marine animals gorged on the algae and their population surged. Cholera bacteria live on the surface of copepods and when the populations of these carriers rose, so did the incidence of cholera.
What direction are Polar winds generally and why? How are winds named? What is the relationship between wind and surface ocean currents?
What are oceanic gyres and what causes them? Explain how and where ocean currents transport heat to higher latitudes. BOX 2 Now apply the same reasoning to the winds between the subtropical highs and the polar front, or subpolar lows. Westerly winds tend to shift direction much more than the trades and also tend to be more blustery.
In the southern hemisphere, they blow with such ferocity that mariners named these latitudes the Roaring Forties, Furious Fifties, and Screaming Sixties. That's average wind speed. Cold Polar Easterlies cover the highest latitudes for the same reason easterly trade winds prevail in the tropics. Finally, one should note that the diagram shows a very idealized version of the global winds.
Heating and cooling of land surfaces causes much variation, such as seasonal monsoons in tropical Asia. Nonetheless, it generally holds true, especially over the oceans. For testing purposes, memorizing the yellow global wind and pressure belt diagram will be quite helpful.
Ocean Surface Currents Friction from surface winds drives the global ocean surface currents. These huge flows of water have an enormous impact on regional climates as they transport heat poleward, and return cool water back to the tropics. The largest ocean circulations are huge gyres in the major ocean basins centered on sub-tropical High pressure centers as shown below. The surface current map shows this same phenomenon in more detail. An enormous gyre in the South Pacific sends warm water poleward near Australia and cool water equatorward along South America.
So why is the deeper, colder water saltier than the warmer, surface-based seawater? It is due to freshwater runoff. As a result, the water at the ocean surface is less salty than the water below it. In the northern Atlantic and Pacific Oceans, when the air gets cold enough for ice to form on the surface of the ocean, the dissolved salt is excluded from the ice that forms, leading to cold and extra salty water forming at these latitudes as the fresh water becomes ice.
This very dense water sinks to deep levels in the ocean and spreads out from there.
The bottom topography of the ocean and the arrangement of the continents helps steer this deep salty water around the globe. From this, we can get underwater currents that can be thousands of feet below the surface of the ocean. In a way, the thermohaline circulation can work together with wind-driven circulations and create a conveyer belt that circulates all around the world.
How does this relate to public health?