The North Atlantic Drift Current The North Atlantic drift as represented by the Mariano Global Surface Velocity Analysis (MGSVA). The N. Atlantic drift is the broad, northward flow of surface waters that replaces the sinking waters in the N. Atlantic polar seas. Click here for example plots of seasonal averages . Aptly named, the North Atlantic Drift Current (NADC) is a slow-moving body of water located between about 50°-64°N and 10°-30°W. NADC is also considered to be an extension of the North Atlantic Current. It is recognized as a shallow, widespread and variable wind-driven surface movement of warm water that covers a large part of the eastern subpolar North Atlantic and slowly spills into the Nordic Seas. It is also sometimes included as the Subarctic or Subpolar Front as it is thought of as the boundary between the cold, subpolar region and the warm, subtropical gyre of the Northeastern Atlantic. Generally, the NADC originates from the Gulf Stream-North Atlantic Current system and from the northern Sargasso Sea.

These waters then slowly flow northward into the Labrador and European basins (Veron, et.al, 1999), eventually becoming the NADC as it enters the Iceland Basin. The current is unique in that it transports warm waters to latitudes higher than in any other ocean, thereby producing the moderate climate of Europe and western Scandinavia. Because of the rapid advection of the North Atlantic gyre, the temperature of the surface waters of the NADC almost always exceeds that of both surrounding waters and the overlying atmosphere (Rossby, 1996). Water temperatures in March are at around 8degC in the NADC while ranging from 2°C to 6°C in surrounding waters (Rossby, et. al., 1998). Several authors define the region that is occupied by the lethargic NADC as bounded by the cool Irminger current to its west, while its southern and eastern border is weakly constrained by the extension of the North Atlantic Current that bends northeastward, flanking the western edge of the Rockall Plateau. Eventually, the NADC feeds into the Norwegian Current to the north, past Iceland.

The loop of the East Iceland Current acts as a boundary along the northern extent of the NADC (Rossby, 1996). Mostly warm surface water trapped between cooler, faster flowing subpolar currents to its east, and the Rockall Plateau to its west, the NADC in the Iceland Basin can extend to a depth of about 1000 meters (Bower et. al., 2002). The NADC is generally a slow-moving body of water that transports between 2 - 5 Sv (Krauss, 1986) Although other authors have estimated volumes of 16 Sv (Bacon, 1997), the exact values remain unknown. Unlike the currents that surround it, the flow of the NADC current is obscure, evident mainly through decadal-scale observations of drifter data. Its northward speed averages about 3 cm s-1 (Otto & van Aken, 1996) along the western edge of the Rockall Plateau.

According to Krauss and Käse (1984), the North Atlantic Current, and not interference with the Mid-Atlantic Ridge, is the main source of eddy energy in the North Atlantic. In the upper ocean, eddy kinetic energy decreases from about 1000 cm2s-2 (near Newfoundland) to about 300 cm2s-2 in the NAD near western Scotland. East of the Mid-Atlantic Ridge, kinetic energy tapers off to less than 100 cm2s-2 in the form of a homogenous pool of low-kinetic energy (Krauss and Käse, 1984). As far as it is known, the NADC exists as a "swath" or region, rather than an actual stream-like current, where the main thermocline shoals to the surface along which a stronger baroclinic transport is sustained than either the north or the south. A quiet, warm pool of water at the surface, its salinity can range between 35.2 and 35.7 ppt (Rossby et. al., 1998).

The NADC feeds two well-defined currents, transporting warm, saline water to both the northward-flowing Norwegian Current and to the southward-flowing Canary Current (Rossby, 1996). The southern-most extent of the NADC is marked by the northernmost boundary of the subtropical circulation system, i.e. the eastward flowing NAC along ~52°N. The zonal flow across the Mid-Atlantic Ridge seem to occur in the form of various branches (Krauss, 1996), some of which turn northwards into the subpolar region, feeding the thermohaline circulation; and others turning south and entering the recirculation of the wind-driven subtropical gyre (Rossby et. al., 1998). Veron, et. al. (1999) determined that spatial gradients in the ratios of 206Pb/207Pb are consistent with thermohaline circulation of the different water masses in the North Atlantic, each having relatively discrete lead isotope signatures.

Based on parallels between the initial isotopic data and temperature and salinity measurements, these authors proposed that stable lead isotope compositions may be employed as complimentary tracers of the mixing of source waters in the Nordic seas, particularly the NADC waters and flanking currents (Veron, 1999). The isotopic ratios and a salinity maximum (>35.2) measured in the Faroe Bank Channel, indicates a core of NADC between 130 and 430 m, and that this water mixes with cooler, fresher deeper water to form the Iceland-Scotland Overflow Waters. Although the more distinct properties of the NADC waters themselves are poorly defined in the literature, the influences this current has on climate are well-documented. It is the contribution of warm waters from the North Atlantic Drift current that is now understood to be the main moderating force of the climate over western Scandinavia, the UK and western Europe (Bigg, 1996; Johnson, 1997; Little et. al., 1997; Moron et. al., 1998; Giraudeau et. al., 2000).

And, based on diatom records, the NADC is thought to have been established as early as 13,400 years ago, although with periods of decadal-scale variations of heating and cooling (Koc et. al., 1993). The path of the NADC is clearly seen in the warming of the air over the western North Atlantic extending eastwards-and intensifying-into the Norwegian Sea (Rossby, 1996). Blindheim et. al. (2000) have shown that a positive link exists between the NADC penetration into the Norwegian Sea and the North Atlantic Ocean (NAO) index, defined as the difference in sea-level pressure between two stations close to the low over Iceland and the high over the Azores. High NAO indices imply that only a narrow flow extends northward of the Faeroe-Iceland Strait, resulting in a sea-surface temperature (SST) cooling at the scale of the Greenland and Norwegian basins, owing to the spread of polar waters eastward. During these conditions, flow is simultaneously intensified in the narrow band along the Norwegian shelf, northwards towards Svarlbad.

The strong westerlies caused by the high winter/spring indices bring in warm, moist air over the European continent and leads to a rather mild, maritime winter. Conversely, a low winter/spring index reflects weaker mean westerlies over the NAO, which in turn corresponds to colder European winters (Eynaud, et. al., 2002). Movement of the NADC because of anomalous winds, will cause a significant latitudinal alteration in the climate zones of western Europe (Bigg 1996). So important, in fact, is the transport of warm water to this region, that a decadal-scale shift in the flow of the NADC can initiate an ice age (Johnson, 1997). A study was conducted by Moron et al. (1998) aimed at giving a global description of climactic phenomena that exhibited some regularity during the twentieth century. They first analyzed multi-channel singular spectrum data, which was then used to extract long-term trends and quasi-regular oscillations of global SST fields since 1901.

From 1910 to about 1940, the authors observed a general warming trend with a short cooling before another brief warming trend. Substantial cooling occurred in the North Atlantic, from about 1950-1980, and continues today. Overall, a 13-15 year see-saw pattern oscillation between the Gulf Stream and the NADC was observed, and also found to affect the tropical Atlantic (Moron et. al., 1998). At times of increased trade wind strength, tropical and subtropical waters are forced across the equator, enhancing the pool of warm water to be transferred to the high latitudes of the North Atlantic via the Gulf Stream and North Atlantic Drift, thereby increasing the pull of the thermohaline convective conveyor. The increased supply of warm water to the polar regions of the northern hemisphere increases the ice-ocean moisture gradient and can accelerate ice sheet growth (Little et. al., 1997). References Bacon, S., 1997: Circulation and Fluxes in the North Atlantic between Greenland and Ireland, Journal of Oceanography, 27, 1420-1435.

Blindheim, J., Borovkov, V., Hansen, B., Malmberg, S. A., Turrell, W. R., Osterhus, S., 2000: Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing, Deep-Sea Research I, 47, 655-680. Bigg, Grant R., 1996: The Oceans and Climate, Cambridge University Press, UK, 266p. Bower, A. S., B. LeCann, T. Rossby, W. Zenk, J. Gould, K. Speer, P. L. Richardson, M. D. Prater and H. M. Zhang, 2002: Directly measured mid-depth circulation in the northeastern North Atlantic Ocean, Nature, 419, 603-607. Eynaud, F., Turon, J. L., Mattheissen, J., Kissel, C., Peypouquet, J.

P., De Vernal, A., and Henry, M., 2002: Norwegian sea-surface paleoenvironments of marine oxygen-isotope stage 3: the paradoxical response of dinoflagellate cysts, Journal of Quaternary Science, 17, 349-359. Giraudeau J., Cremer M., Manthe S., Labeyrie L., Bond G., 2000: Coccolith evidence for instabilities in surface circulation south of Iceland during the Holocene times, Earth and Planetary Science Letters, 179, 257-268. Iselin, C. O., 1936: A study of the circulation of the western North Atlantic, Pap. Phys. Oceanogr. Meteorol., 4, 101 pp. Johnson, R. G., 1997: Ice age initiation by an ocean-atmospheric circulation change in the Labrador Sea, Earth And Planetary Science Letters, 148, 367-379.

Koc, N., Jansen E., and Haflidason, H., 1993: Paleoceanographic reconstructions of the surface ocean conditions in the Greenland, Iceland and Norwegian Seas through the last 14-Ka based on diatoms, Quaternary Science Reviews, 12, 115-140. Krauss, W., 1996: The warm water sphere of the North Atlantic Ocean, Gebruder Borntraeger, 466p. Krauss, W., and Käs, R. H., 1984: Mean circulation and eddy kinetic energy in the Eastern North Atlantic, Journal of Geophysical Research, 89(C3), 3407-3415. Little, M. G., Schneider, R. R. , Kroon, D., Price B, Summerhayes CP, Segl M., 1997: Trade wind forcing of upwelling, seasonality, and Heinrich events as a response to sub-Milankovitch climate variability, Paleoceanography, 12, 568-576.

Moron, V., Vautard R., Ghil M., 1998: Trends, inderdecadal and interannual oscillations in global sea surface temperatures, Climate Dynamics, 14, 545-569. Otto, L, and H. M. van Aken, 1996: Surface circulation in the Northeast Atlantic as observed with drifters, Deep Sea Research I, 43, 467-499. Rossby, T., Mark Prater, Huai-Min Zhang, Peter Lazarevich and Paula Pérez-Bunius, 1998: Isopycnal Float Studies of the Subpolar Front: Preliminary Results, Presented at the WOCE Conference in Halifax, Nova Scotia, Canada, May 25-29. Rossby, T., 1996: The North Atlantic Current and Surrounding Waters: At the Crossroads, Review of Geophysics, 34, 463-481. Veron, A.J., Church, T.M., Rivera-Duarte, I., and Flegal, A.

R., 1999: Stable lead isotopic ratios trace thermohaline circulation in the subarctic North Atlantic, Deep-Sea Research II, 46, 919-935. North Atlantic Ocean | Article about North Atlantic Ocean by The Free Dictionary North Atlantic Ocean | Article about North Atlantic Ocean by The Free Dictionary Related to North Atlantic Ocean: North Pacific Ocean Atlantic Ocean [Lat.,=of Atlas], second largest ocean (c.31,800,000 sq mi/82,362,000 sq km; c.36,000,000 sq mi/93,240,000 sq km with marginal seas). Physical Geography Extent and Seas The Atlantic Ocean extends in an S shape from the arctic to the antarctic regions between North and South America on the west and Europe and Africa on the east. It is connected with the Arctic Ocean by the Greenland Sea and Smith Sound; with the Pacific Ocean by Drake Passage, the Straits of Magellan, and the Panama Canal; and with the Indian Ocean by the Suez Canal and the expanse between Africa and Antarctica.

The shortest distance across the Atlantic Ocean (c.1,600 mi/2,575 km) is between SW Senegal, W Africa, and NE Brazil, E South America. The principal arms of the Atlantic Ocean are Hudson and Baffin bays, the Gulf of Mexico, and the Caribbean Sea in the west; the Baltic, North, Mediterranean, and Black seas in the east; and the Weddell Sea in the south. More large rivers, including the Mississippi, the Congo, and the Amazon, drain into the Atlantic than into any other ocean. Islands The Atlantic has relatively few islands, with the greatest concentration found in the Caribbean region. Most of the islands are structurally part of the continents, such as the British Isles, Falkland Islands, Canary Islands, and Newfoundland. Iceland, the Azores, the islands of Cape Verde, Ascension, the South Sandwich Islands, the West Indies, and Bermuda are exposed tops of submarine ridges. The Bahamas are low coral islands that sit on the Blake Plateau, while the Madeiras are high volcanic islands. Ocean Floor The floor of the Atlantic has an average depth of c.12,000 ft (3,660 m).

It is separated from that of the Arctic Ocean by a submarine ridge extending from SE Greenland to N Scotland; part of the floor (c.3,000 ft/910 m deep) is known as "telegraph plateau" because of the network of cables laid there. A shallow submarine ridge across the Strait of Gibraltar separates the Mediterranean basin from the Atlantic and limits the exchange of water between the two bodies. The Mid-Atlantic Ridge (c.300–600 mi/480–970 km wide), a submarine mountain range extending c.10,000 mi (16,100 km) from Iceland to near the Antarctic Circle, generally follows the trend of the coastlines of the continents. It rises to an average height of c.10,000 ft (3,050 m), and a few peaks emerge as islands. The ridge, which is the center of volcanic activity and earthquakes, has a great rift that is constantly widening (see seafloor spreading seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges.

First proposed in the early 1960s by the American geologist Harry H. ..... Click the link for more information. ) and filling with molten rock from the earth's interior. As a result the Western Hemisphere and Europe and Africa are moving away from each other. The Mid-Atlantic Ridge divides the floor of the Atlantic Ocean into eastern and western sections that are composed of a series of deep-sea basins (abyssal plains). The greatest depth (c.28,000 ft/8,530 m) is the Milwaukee Deep, in the Puerto Rico Trench, N of Puerto Rico. Scientific knowledge of the ocean floor dates from the Challenger expedition Challenger expedition, British oceanographic expedition under the direction of the Scottish professor Charles Wyville Thompson and the British naturalist Sir John Murray. Taking place from 1872 to 1876, it opened the era of descriptive oceanography. ..... Click the link for more information. (1872–76). Currents Because of its shape, the Atlantic may be divided into two basins—North Atlantic Ocean and South Atlantic Ocean—each with a distinct circulation system.

The clockwise-moving currents of the North Atlantic (North Equatorial Current, Antilles Current, Gulf Stream, North Atlantic Drift, Canaries Current) and the counterclockwise-moving currents of the South Atlantic (South Equatorial Current, Brazil Current, West Wind Drift, Benguela Current) are separated from each other by the Equatorial Counter Current; the Guinea Current off W Africa is a link between the two systems. At the Grand Banks off Newfoundland heavy fogs form along the front where the warm Gulf Stream meets the cold Labrador Current. The surface waters in the Atlantic's trade wind belts attain the highest salinity known in ocean water. Commerce and Shipping The North Atlantic Ocean has some of the world's busiest shipping lanes; the northern lanes are patrolled for icebergs. Commerce between the Mediterranean Sea and the NE Atlantic Ocean was initiated by the Carthaginians. From the 7th cent. A.D., Scandinavians navigated the Atlantic; they probably reached North America c.1000. Trade routes along the coast of Africa were opened by Portugal in the 15th cent. and to the Western Hemisphere by Spain after the voyages of Columbus.

The Grand Banks have traditionally contained some of the world's best commercial fishing grounds, but by the early 1990s the area had been overfished, and many species were depleted. Bibliography See V. H. Cassidy, The Sea around Them: The Atlantic Ocean, A.D. 1250 (1968); K. F. George, The Atlantic Ocean (1977); K. O. Emery and E. Uchupi, The Geology of the Atlantic Ocean (1984); S. Winchester, Atlantic (2010). Atlantic Ocean (the Latin name Mare Atlanticum and Greek name Atlantis designated the stretch between the Strait of Gibraltar and the Canary Islands; the entire ocean was called Oceanus Occidentalis—Western Ocean). Islands. The main island groups originated as part of the mainland and are located off coasts (such as Great Britain, Ireland, Newfoundland, the Greater Antilles and, partially, the Lesser Antilles, the Canary Islands, Cape Verde, and the Falklands). There are few islands in the open part of the ocean; they are all of volcanic origin (the Azores, St.

Helena, Tristan de Cunha, and others). Coasts. The coastal line is strongly dissected in the northern part of the Atlantic Ocean. Almost all the internal seas and large gulfs (Biscay, Guinea, Fundy, and others) are located here. The coasts are weakly dissected in the southern part of the Atlantic Ocean; only the outlying Weddell Sea (off Antarctica) and small gulfs off the coasts of South America (La Plata, San Matías, and others) are found here. To the east, the coasts are predominantly original; alluvial coasts predominate to the west, and glacial coasts in the antarctic region. Relief and geological structure of the floor. The characterist; element of the relief of the floor of the Atlantic Ocean is the vast meridional Mid-Atlantic Ridge, which divides the ocean into eastern and western sections. Underwater plateaus (Bermuda, Rio Grande), ridges (Southern Antilles, Kitovyi), and elevations (Rockall and Sierra Leone) are located to the west and east of the Mid-Atlantic Ridge in the region of the ocean bed.

Elevations of the floor demarcate vast basins: the Labrador, North America, Guiana, Brazil, Argentine, and other basins in the west; the West Europe, North Africa, Guinea, Angola, Cape, and Agulhas basins in the east; and the African-Antarctic Basin in the south. The depth of the basins ranges from 3,000 to 7,200–7,300 m. The maximum depths of the Atlantic Ocean are linked to deepwater trenches which border on mountain systems of island arcs—the Greater Antilles (the Puerto Rico Trench, 8,385 m) and the South Sandwich Islands (South Sandwich Trench, 8,428 m). The Greater and Lesser Antilles island arcs separate the Mexican, Yucatan (with Cayman Trench), Colombian, and Venezuelan basins from open portions of the Atlantic Ocean; the threshold of the Strait of Gibraltar separates the Mediterranean Sea. The basin floors are composed of hilly or virtually flat abyssal plains; only here and there are they complicated by underwater mountains.

Occasionally, mountain peaks project above the water in the form of volcanic islands (Bermuda, Azores, Canary, Cape Verde, Fernando de Noronha, Martin Vaz, St. Helena, Tristan de Cunha, Gough, and other islands). The largest seamounts include Altair, Anti-Altair, Milne, Kelvin, San Pablo, Rehoboth, Ronkevei, Yakutat, Atlantis, Plateau, Cruizer, Great Meteor, Josephine, Amper, Davis, Columbia, Discovery, Schmitt-Ott Bank, Meteor, and Alfred Mers. The underwater outskirts of the continents surrounding the basin of the Atlantic Ocean are characterized by gently inclined plains of continental embankments and steep continental slopes. The latter are cut by underwater canyons, which are situated, for the most part, along extensions of river valleys of the land mass. The width of continental embankments ranges from several dozen kilometers (off the coasts of Argentina and North America) to several hundred (the North, Baltic, and other seas). The depth of the external region of the continental shelves ranges from 100 to 500 m.

The bottom deposits of the Atlantic Ocean, which attain maximum thicknesses of 800–1,000 m at the bottoms of basins, can be divided into several types according to their origin. Terrigenous sediments (gravelly-pebbly, sandy, and oozy material) are distributed primarily on the underwater outskirts of the continents. Biogenous sediments are represented by calcareous (more than 30 percent CaCO3) and siliceous (more than 10 percent amorphous SiO2) deposits. Calcareous deposits (65 percent of the area of the bottom) cover the slopes of the Mid-Atlantic Ridge, sizable extents of the floor of basins, and slopes of submarine elevations within the basins. Siliceous deposits (about 10 percent of the area of the bottom) are prevalent only in the southern part of the ocean, near Antarctica. Polygenous deposits (about 26 percent of the area of the bottom) are of mixed origin; they are represented by red deepwater clays which cover the deepest parts of the basins. Volcanogenic deposits—deposits with admixtures of volcanic ashes—are prevalent in regions of volcanic islands.

The so-called rift deposits are related to rift ravines of the axial zone of the Mid-Atlantic Ridge; they represent the products of the disintegration of plutonic rocks. Chemogenic deposits are developed in the form of glauconites and phosphate nodules in the region of the underwater outskirts of continents and in the form of ferrous manganese nodules on the floor of deep basins. In the northern and southern parts of the Atlantic Ocean, the dispersion of coarsely fragmented material by floating ice and icebergs has an important influence on the composition of bottom deposits. Deposits of suspended currents play an important role among the sediments of deep basins. Outcrops of indigenous rocks are encountered on continental slopes in the form of sedimentary and metamorphic formations of different ages up to the Cretaceous. Tholeiitic and alkali basalts are found on volcanic mountains and islands; on the summits of chains of the Mid-Atlantic Ridge are basalts and plutonic rocks of basic composition (gabbro) and ultrabasic composition (dunites, peridotites).

Serpentin-ites developing on peridotites are evident, as are greenstone rocks, which formed as a result of regional metamor-phism of basalts and gabbro at the bottom of the crust. Rocks of ultrabasic composition compose the island of Sao Paolo. It is conjectured that they are of plutonic (mantle) origin and that their age is on the order of 4.5 billion years (nearly the age of the earth). Tectonic structure. Characteristic of the submarine outskirts of the continents are the continental type of crust and continental platform structures which, as a rule, are broken by the continental slopes. The extension of these continental features into the domain of the ocean has been traced only in the gulfs of Biscay and Mexico; in other places, this extension is unknown.

The bottom of a basin is covered over with a crust of the oceanic type which consists of three strata: the stratum of porous deposits; the so-called second stratum, which is characterized by seismic waves of velocities around 5.0 km/sec and which may be made up of sedimentary volcanogenic or magmatic rocks; and the “basaltic” stratum, which is characterized by velocities of seismic waves on the order of 6.7 km/sec and which is probably composed of basic rocks of the gabbro-basaltic type and serpentinized ultrabasic rocks. Lower down, rocks of the upper mantle are deposited; they are characterized by velocities of seismic waves on the order of 8.3 km/sec and are represented by peridotites and dunites. The sedimentary stratum is virtually absent in the structure of the Mid-Atlantic Ridge, while the second and basaltic strata are thinned and ^occasionally faulted in the rift zone, so that ultrabasic rocks are exposed on the bottom. Here, according to seismic data, decompressed rocks of the upper mantle, characterized by velocities of waves on the order of 7.3–7.6 km/sec, are deposited.

G. B. U DINTSEV Climate. The great longitudinal stretch of the Atlantic Ocean determines the diversity of climatic conditions on its surface. The ocean is located in all climatic belts, from the equatorial to the subarctic in the north and the antarctic in the south. The great area of the Atlantic Ocean, between approximately 40° N lat. and 40° S lat., is located in the equatorial, tropical, and subtropical climate belts. Four main centers of action of the atmosphere are developed over the Atlantic Ocean—the Icelandic and Antarctic minimums and the North Atlantic and South Atlantic maximums, divided at the equator by a zone of depressed atmospheric pressure. Interacting with the regions of pressure which develop over adjacent continents, these centers produce the dominance of strong west winds in temperate latitudes and of northeast and southeast winds (trade winds) in subtropical and tropical latitudes in the northern and southern hemispheres respectively. Winds attain their maximum strength in the temperate latitudes, especially in the southern part of the Atlantic Ocean. Storms are so frequent here that the southern temperate latitudes got the name the Roaring Forties. Strong winds are also characteristic of the Bay of Biscay.

In northern tropical latitudes, tropical (so-called West Indies) hurricanes, which traverse the ocean from east to west, are characteristic from June to October-November. They achieve their maximum force over the Caribbean Sea and the Gulf of Mexico. The air temperature in winter, in February (August in the southern part of the Atlantic Ocean), varies from 25° C at the equator to 0° C at 60° N lat. and from -8° C to -10° C at 60° S lat. In the extreme northwest and the south, the temperature drops to -25° C and below. In summer, in August (in February in the southern part of the Atlantic Ocean), the temperature is 26°-28° C at the equator, 8°-12° C at 60° N lat. and 0°-2° C at 60° S lat. In the south, the temperature of the Weddell Sea is between -4° and -6° C.

There is a perceptible difference between the air temperature of the eastern and western parts of the ocean throughout the area situated to the north of 40° S lat.; it is caused by the dominance of warm or cold currents. North of 30° N lat. the temperature in the west is 10° C lower than in the east, whereas between 30° N lat. and 40° S lat. the temperature in the west is 5° C higher than in the east. The average annual cloudiness in regions of low atmospheric pressure is 60–80 percent in northern temperate, high southern, and equatorial latitudes; in regions of high pressure in the sub-tropics, the figure decreases to 30–40 percent.

The mean annual precipitation on the equator is more than 2,000 mm; in the temperate latitudes, it is 1,000–1,500 mm; in subtropical latitudes and in the antarctic, it decreases to 250–500 mm; in regions adjoining the desert shores of Africa, it decreases to 100 mm; and in the southern part of the ocean, it is less than 100 mm. Fogs are characteristic of regions where warm and cold waters meet (such as the Grand Banks of Newfoundland and near the mouth of the gulf of the Rio de la Plata); fog is also characteristic of southern temperate latitudes, where warm air passes over the cool surface of the ocean. Dusty hazes, borne by the northeast trade wind from the Sahara, are recorded in the region of the Cape Verde Islands. The hydrologic conditions of the Atlantic Ocean form under the influence of climatic conditions, water exchange with adjoining oceans and the Mediterranean Sea, and peculiarities of the configuration of the surrounding land.

Under the influence of atmospheric circulation, the surface currents of the Atlantic Ocean form anticyclonal cycles in subtropical and tropical latitudes and cyclonal cycles in northern temperate and high southern latitudes. A characteristic feature of the Atlantic Ocean is the powerful system of warm currents—the so-called Gulf Stream system—which develops in its northern part. The Gulf Stream and its extension, the North Atlantic current, form respectively the western and northern peripheries of the northern anticyclonal cycle. The eastern periphery of this cycle is formed by the cold Canaries Current, the southern periphery by the warm North Equatorial Current. The northern cyclonal cycle is formed by the warm North Atlantic and Irminger currents and the cold Labrador Current, which enters from Baffin Bay. In the southern part of the Atlantic Ocean, the anticyclonal cycle is formed by the warm South Equatorial and Brazil currents on the north and west respectively and the cold Southern Ocean and Benguela currents in the south and east. Cyclonic circulation develops south of 50° S lat. with its center in the Weddell Sea.

In summer, anticyclonal circulations of the northern and southern parts of the Atlantic Ocean are divided, north of the equator, by the Equatorial (Inter-trade-wind) Countercurrent; in the winter, these circulations are replaced by the general western transfer of surface waters. The subsurface Lomonosov Countercurrent is a more permanent boundary at the equator. Currents are the primary redistributors of the solar heat absorbed by the surface of the ocean. The thermal balance of the Atlantic Ocean is formed from the radiation balance, heat loss by evaporation, and turbulent heat exchange with the atmosphere. The greatest positive thermal balance, amounting to 2.5–3.3 gigajoules /(m2-yr), equivalent to 60–80 kilocalories /(cm2-yr), is recorded at the equator; it approaches 0 at 30° N lat. and S lat. As the latitude increases, the thermal balance becomes negative. Thus, the surface of the Atlantic Ocean absorbs heat primarily between latitudes 30° N and S; over the rest of its area, the ocean gives off heat to the atmosphere.

The water temperature on the surface of the Atlantic Ocean in winter (February; August in the southern part of the ocean) is 27°-28° C at the equator, 6° C at 60° N lat., and -1° C at 60° S lat. In the summer (August; February in the southern part of the ocean) the temperature is 26° C at the equator, 10° C at 60° N lat., and about 0° C at 60° S lat. Under the influence of warm and cold currents, great differences in temperature are created within latitudinal zones. North of 30° N lat., the temperature in the west is about 10° C lower than in the east. Between 30° N lat. and 40° S lat., on the other hand, the temperature in the west is 5° C higher than in the east. South of 40° S lat., where a zonal current of surface water predominates, this difference disappears.

The salinity of the water depends on the water balance, which on the average forms as follows for the surface of the Atlantic Ocean: evaporation of 1,040 mm per year, precipitation of 780 mm per year, and continental drainage of 200 mm per year. The continental drainage is of importance primarily in the narrow coastal strip off estuarine sections of the ocean. In the open ocean, salinity is determined by the correlation of evaporation and precipitation. Maximum evaporation (1,640–1,660 mm per year) is in tropical and subtropical latitudes; at the equator, it decreases to 1,400 mm per year; at 60° N lat., 780 mm per year; and at 60° S lat., 320 mm per year. The greatest quantity of precipitation—about 1,770 mm per year—occurs at the equator; at 20° N lat. the quantity decreases to 640 mm per year, and at 20° S lat. to 270 mm.

In the temperate latitudes, precipitation increases again up to 1,100–1,200 mm per year. Correspondingly, the maximum salinity, 37.25 parts per thousand (‰), is recorded in tropical and subtropical latitudes; at the equator, salinity decreases to 35‰, in southern temperate latitudes, to 34‰, and in the Antarctic region, to 33.6–33.8‰; in northern temperate latitudes it is 32‰ in the west and 35.5‰ in the east. The greatest density of water is observed in the northeast and south of the ocean, where it exceeds 1,027 kg/m3; the figure decreases to 1,022.5 kg/m3 toward the equator. The oxygen content in the surface stratum of the Atlantic Ocean changes from 4 liters /m3 at the equator to 5 liters/m3 in high latitudes. The water color in subtropical and tropical latitudes is dark blue and blue; in temperate and high latitudes, green shades predominate.

The greatest transparency of the water is 66 m, in the Sargasso Sea. Tides are primarily semidiurnal. Their greatest magnitude (for the entire world ocean) of 18 m is recorded in the Bay of Fundy. In the open part of the Atlantic Ocean, the height of tides is about 1 m (the island of St. Helena, 0.8 m; Ascension Island, 0.6 m). In various regions, tides are compound and diurnal; their magnitudes range from 0.5 to 2.2 m. In the northern part of the Atlantic Ocean, ice forms only in internal seas of temperate latitudes (the Baltic, Azov, and Black seas, the Gulf of St. Lawrence, and others); the ice forms yearly. In the open ocean, a great quantity of ice and many icebergs are carried from the Arctic Ocean (Baffin Bay and Greenland Sea). The average boundary of ice and icebergs passes approximately along 40° N lat., but in certain cases icebergs are encountered in the western part of the Atlantic Ocean at 31° N lat.

In the southern part of the ocean, marine ice and icebergs form off the continent of Antarctica and in the Weddell Sea. Icebergs are most prevalent during November and December, when their boundary passes along 40° S lat. in the middle part of the ocean and 35° S lat. in the west and the east. The greatest prevalence of marine ice is observed during August and September, when it is carried by winds and currents approximately to 55° S lat. During February and March (summer in the southern hemisphere) it is encountered only in the narrow coastal zone of Antarctica and in the Weddell Sea. Deep-sea circulation and the vertical structure of the Atlantic Ocean are formed by waters that sink as a result of their density increase occurring in zones of convergence of surface currents in antarctic latitudes, as well as by deep waters which enter from the Mediterranean Sea and Arctic Ocean. Densification occurs in zones of convergence as a result of the mixing of waters of different temperatures and salinity. The greater the temperature and salinity difference of the mixed waters and the lower their temperature, the greater the increase in the density of the water.

Accordingly, waters which sink in higher latitudes occupy lower strata in the ocean. Subsurface waters sink in subtropical latitudes and occupy the layer below surface waters in the ocean (from depths of 100–150 m to 400–500 m). Their temperature is between 10° and 22° C; they have high salinity of 34.8–36.0°/oo and are characterized in different places by low oxygen content (toward the east in the southern subtropical latitudes, 1.0–1.5 liters [/] per m3). Over the remaining area of the ocean, the quantity of oxygen is 4.0–5.5 //m3; it reaches 7.0 //m3 in the south. Intermediate waters sink in subpolar zones of convergence and are located at depths of 400–500 m to 1,000 -1,500 m.

Their temperature is between 3° and 7° C; their salinity has the lowest value in the vertical distribution (of 34.0–34.9*/oo), and their oxygen content is 3.0–6.2 //m3, which decreases at the continental slope of Africa to 1–2.5 //m3. Subsurface and intermediate waters complete an-ticyclonic circulations, along whose eastern peripheries the characteristics of these waters are transferred toward the equator. In the northern part of the Atlantic Ocean, a role in the formation of deep waters is played by the deep water of the Mediterranean Sea—which determines the high salinity of the Atlantic waters—and the deep water of the Greenland Sea, the influence of which is limited, however, to the extreme northern part of the ocean. Deep waters are distributed in the stratum from 1,000–1,500 m to 3,500 m in the southern direction.

Their temperature is between 2.5° and 3° C, their salinity 34.71–34.99°/oo, and their oxygen content 4.5–6.4 Urn3.The densest waters form in antarctic latitudes, where they sink to the bottom and follow in the level adjacent to the bottom in a northerly direction. They are characterized by temperatures of 1° C-2.5° C (below 0° C in high southern latitudes), salinity of 34.64–34.89°/oo and oxygen content of 4.5–5.9 //m3. Thus, in the vertical structure of the Atlantic Ocean, subsurface and deep-sea maximums and intermediate minimums of salinity and intermediate minimums of oxygen are recorded. A. M. M UROMTSEV Flora. The vegetable life of the Atlantic Ocean is very diverse.

Bottom vegetation (phytobenthos), which occupies the coastal zone down to depths of 100 m (about 2 percent of the total area of the ocean bottom), includes brown, green, and red algae; flowering vegetation (phyllospadix, Zostera, poseidonia) also inhabits the salt water. There are similarities between the bottom vegetation of the northern and southern parts of the Atlantic Ocean, but the leading forms are represented by different species and sometimes different genuses. Similarities are expressed more clearly among the vegetation of the western and eastern shores. A clear geographic succession of the main forms of phytobenthos is observed with variation in latitude. In high arctic latitudes of the Atlantic Ocean, where the surface is covered with ice for much of the time, the littoral is devoid of vegetation. The bulk of phytobenthos in the sublittoral is made up of Laminaria with an admixture of red algae. In the temperate zone, along the American and European shores of the northern Atlantic, brown development of phytobenthos is characteristic.

Brown algae (Fucus and Ascophyllum) predominate sharply on the littoral; in the sublittoral they are replaced by forms of Laminaria, Alaria, Desmarestia, and red algae (such as Furtselliaria, Ahnfeltia, Lithothamnion, and Rhodimenia). Zostera is prevalent on soft bottoms. Brown algae, Laminaria in particular, predominate in the temperate and cold zones of the southern hemisphere. Vegetation is virtually absent on the littoral and in the upper strata of the sublittoral in the tropical zone because of strong heating and intensive insolation. The so-called Sargasso Sea is situated between 20° N lat. and 40° N lat. and 30° W long, and 60° W long, in the Atlantic Ocean. It is characterized by the constant presence of a mass of floating brown algae—Sargassum.

As distinct from phytobenthos, phytoplankton is developed over the entire area of the ocean in the upper 100-meter stratum; it achieves its maximum concentration, however, in the upper 40- to 50-meter layer. Phytoplankton consists of small one-celled algae (diatoms, dinoflagellates, blue-green algae, Silicoflagellatae, coccolith-ophores). The mass of phytoplankton varies between I and 100 mg/m3, and in the high latitudes (50°-60° lat.) of the northern and southern hemispheres it reaches 10 g/m3 and above during the period of mass development (blooming). In the cold and temperate zones of the northern and southern parts of the Atlantic Ocean, diatoms predominate, forming the bulk of phytoplankton. The mass development of phaeosystis (from brown algae) in the spring is characteristic of the coastal regions of the North Atlantic. In the tropics, different species of coccolithophores and blue-green Trichodesmium are very widespread.

The greatest quantitative development of phytoplankton in the high latitudes of the Atlantic Ocean is observed in the summer during the period of most intensive solar radiation. Two peaks are characteristic of the development of phytoplankton in the temperate region. The spring blooming has the maximum biomass. During the autumn blooming, the biomass is considerably less than in the spring. In the tropical region the development of phytoplankton proceeds year round, but the biomass is small throughout the year. The floral world of the tropical region of the Atlantic Ocean is marked by great diversity in kind but smaller quantitative development than the floral world of the temperate and cold zones. Fauna. Animal organisms inhabit the entire depth of the water of the Atlantic Ocean. The diversity in fauna increases in the direction of the tropics. In the cold and temperate belts, the fauna includes thousands of species; in the tropics, tens of thousands. Characteristic animals of the cold and temperate belts are whales, seals, and walruses, among mammals; and among fish, herring, cod, perch, and flounder. Among zooplankton, a sharp predominance of Copepoda crustaceans and sometimes Pteropoda mollusks is noted.

Great similarity is evident among the fauna of the moderate belts of both hemispheres. Not fewer than 100 species of animals are of the bipolar variety—that is, they are characteristic of cold and temperate belts and are absent in the tropics. These include hair seals, northern fur seals, whales, sprats, sardines, anchovies, and many invertebrates, including mussels. Characteristic of the tropical belts of the Atlantic Ocean are sperm whales, sea turtles, crustaceans, sharks, flying fish, crabs, coral polyps, jellyfish, Siphonophora, and Radiolaria. The fauna of the Sargasso Sea is distinctive. This area is inhabited both by free-swimming animals (such as mackerel, flying fish, pipe fish, and crabs) and by animals which attach to seaweeds (sea anemones, Bryozoa). The deep-sea fauna of the Atlantic Ocean is richly represented by sponges, corals, echinoderms, crustaceans, fish, and others. This fauna stands out in the independent Atlantic deep-sea region.

REFERENCES NOAA's National Ocean Service Education: Currents: Winds Drive Surface Ocean Currents Surface Ocean Currents 1 2 3 4 Winds Drive Surface Ocean Currents Global winds drag on the water’s surface, causing it to move and build up in the direction that the wind is blowing. And just as the Coriolis effect deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, it also results in the deflection of major surface ocean currents to the right in the Northern Hemisphere (in a clockwise spiral) and to the left in the Southern Hemisphere (in a counter-clockwise spiral). These major spirals of ocean-circling currents are called “gyres” and occur north and south of the equator. They do not occur at the equator, where the Coriolis effect is not present (Ross, 1995). There are five major ocean-wide gyres—the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres. Each is flanked by a strong and narrow “western boundary current,” and a weak and broad “eastern boundary current” (Ross, 1995).

The Gulf Stream is a powerful western boundary current in the North Atlantic Ocean that strongly influences the climate of the East Coast of the United States and many Western European countries. Click the image for a larger view. One particularly powerful western boundary current is the Gulf Stream. The Gulf Stream, paired with the eastern boundary Canary Current, flanks the North Atlantic gyre. The Gulf Stream, also called the North Atlantic Drift, originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastline of the United States and Newfoundland. It travels at speeds of 25 to 75 miles per day at about one to three knots (1.15-3.45 miles per hour or 1.85-5.55 kilometers per hour). It influences the climate of the east coast of Florida, keeping temperatures warmer in the winter and cooler than the other southeastern states in the summer. Since it also extends toward Europe, it warms western European countries as well. Ocean Currents and Climate Ocean Currents and Climate There are two type of Ocean Currents: 1. Surface Currents--Surface Circulation These waters make up about 10% of all the water in the ocean.

These waters are the upper 400 meters of the ocean. 2. Deep Water Currents--Thermohaline Circulation These waters make up the other 90% of the ocean These waters move around the ocean basins by density driven forces and gravity. The density difference is a function of different temperatures and salinity These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase. Ocean Currents are influenced by two types of forces 1. Primary Forces--start the water moving The primary forces are: 2. Secondary Forces--influence where the currents flow 1. Surface Circulation Solar heating cause water to expand. Near the equator the water is about 8 centimeters high than in middle latitudes. This cause a very slight slope and water wants to flow down the slope. Winds blowing on the surface of the ocean push the water. Friction is the coupling between the wind and the water's surface. A wind blowing for 10 hours across the ocean will cause the surface waters to flow at about 2% of the wind speed. Water will pile up in the direction the wind is blowing.

Gravity will tend to pull the water down the "hill" or pile of water against the pressure gradient. But the Coriolis Force intervenes and cause the water to move to the right (in the northern hemisphere) around the mound of water. These large mounds of water and the flow around them are called Gyres. The produce large circular currents in all the ocean basins. Gyres North Atlantic Gyre Note how the North Atlantic Gyre is separated into four distinct Currents, The North Equatorial Current, the Gulf Stream, the North Atlantic Current, and the Canary Current. But why doesn't the water spin towards the center of the ocean? Why does it flow around the hill in this circular motion. Remember the hill of water-- This hill is formed by the inward push of water through a process call Ekman Transport Remember the Coriolis Force move objects to the right in the northern hemisphere Ekman Transport Wind blowing on the surface of the ocean has the greatest effect on the surface. However, for the lower layers of the ocean to move they must be pushed by the friction between the layers of water above. Consequently, the lower layer moves slower than the layer above. With each successive layer down in the water column the speed is reduce.

This leads to the spiral affect seen in the above diagram. The net movement of water (averaged over the entire upper 330 meters of the ocean) is 90o to the right of the wind direction (in the northern hemisphere). When the water is pushed to the right it forms the hill we described above. So, when water is pushed along by the wind it wants to be turned to the right by the Coriolis force (in the northern hemisphere) but it must fight against gravity (trying to move up the hill of water formed by Ekman transport). A balance is met between the Coriolis and the gravity (pressure gradient force). This balance produces a balanced flow called a Geostrophic current. Eastern and Western Boundary Currents Boundary Currents are the major geostrophic currents around the gyre Note the difference is strength (Sv) between the western and eastern boundary currents.

This is caused by the effect of the rotating Earth which tends to move the "hill" of water to the western sides of the ocean basins The Gulf Stream is an example of a Western Boundary Current Ocean Motion : Impact : Ocean Conveyor Belt Ocean Conveyor Belt Weakening Current By Edwin Schiele Ocean surface currents redistribute heat around the world and have a profound effect on the world’s climate. Nowhere is this clearer than in the North Atlantic Ocean. The Gulf Stream and the North Atlantic Current ferry huge volumes of warm salty tropical water north to the Greenland coast and to the Nordic Seas. Heat radiating off of this water helps keep the countries of northwest Europe, which are at the same latitude as Labrador and Greenland, relatively comfortable places to live. Many scientists, however, are warning that the North Atlantic might cool down, perhaps by the turn of the century. Paradoxically, global warming would be to blame. Rising temperatures may trigger events that could not only slow the supply of tropical water flowing north, it could disrupt the entire ocean circulation pattern. This scenario has led to wild talk of the start of a new ice age, a notion that climate scientists universally dismiss. Still the impact on the world’s climate could be profound.

Scientists are therefore scrambling to gather data on ocean circulation and the forces that drive it. Ocean circulation is comprised of a global network of interconnected currents, counter-currents, deepwater currents, and turbulent eddies. From this complex circulation, an underlying transport pattern emerges. Water cycles from surface currents to deepwater currents then back to the surface again in what scientists liken to a giant conveyor belt. Scientists call this global conveyor belt the meridional overturning circulation. There are two major forces driving the meridional overturning circulation. First there is the wind. The wind, in combination with the Earth’s rotation, generates the gyres that circle the major ocean basins. Turbulent swirling packets of water called eddies, many of which are hundreds of kilometers in diameter, spin out of these wind-driven currents and carry the water trapped inside them to other parts of the ocean. The second force is tied to differences in the density of water. Temperature and salinity independently affect water’s density. The colder and saltier the water, the denser it becomes. As water becomes denser, it sinks. This is where the Atlantic Ocean plays a pivotal role.

Again, the Gulf Stream and the North Atlantic Current carry warm salty tropical water up into the Labrador and Greenland Seas. Frigid Arctic winds cool this water, increasing its density. The water then sinks, feeding deepwater currents. This same density driven creation of deepwater also takes place in the frigid Ross and Weddell Seas off the coast of Antarctica, and to a lesser extent in the salty Mediterranean Sea. Scientists call this density-driven component of the meridional overturning circulation the thermohaline circulation; thermo meaning heat and saline meaning salt. Without this density-driven process, deepwater currents would no longer be created. The global conveyor belt would grind to a halt. Scientists are using observations and models to trace the complex pathways of the meridional overturning circulation and determine its strength. It’s an overwhelming task. Maps charting the circulation’s course are still evolving. Deeper currents and upwelling in particular are extremely difficult to measure. But some patterns are becoming clearer. Starting off the Greenland coast, the newly created deepwater slowly drifts south along the western margin of the Atlantic basin. It then crosses the equator and mixes with the deepwater currents circling Antarctica. Models suggest that some of this water resurfaces in this area.

Much of it, however, spreads north into Indian and Pacific Oceans where it mixes with warmer water and resurfaces. To close the loop of the conveyor belt, surface water flows from the Pacific and Indian Oceans back into the South Atlantic then heads north. Some cold water enters the South Atlantic from the Pacific around the southern tip of South America. The Agulhas Current in the Indian Ocean is another important source. This fast-moving current, the Indian Ocean’s equivalent of the Gulf Stream, flows down the southeast coast of Africa and past the tip of South Africa then takes a sharp turn to the east. Large eddies called Agulhas Rings spin off this bend and carry huge bundles of warm salty Indian Ocean water west into the South Atlantic. Currents carry much of this Indian Ocean water north to the equator where the sun heats it further. Eventually this water enters the Caribbean and is swept into the Gulf Stream. Scientists believe that these Agulhas Rings are critical sources of the salty water that drives the formation of deep water up north. Eddies spinning out of the Mediterranean Sea and net evaporation in the tropical Atlantic also contribute salty water. Despite its enormous scope, the meridional overturning circulation is vulnerable.

Places where deepwater currents are created comprise less than one percent of the ocean’s surface area. Should the temperature or salinity in these limited areas change, the creation of deep water could slow or even stop. There is strong evidence that such a shutdown has happened in the past, drastically altering the world’s climate in just a matter of years. Eleven thousand years ago, ice age glaciers were retreating. In central Canada, an immense glacial lake called Lake Agassiz occupied an area larger than all the Great Lakes. Suddenly the dams holding Lake Agassiz collapsed. The contents of the entire lake rushed into the North Atlantic by way of the St. Lawrence River. This massive infusion of fresh water diluted the polar seas to the point where the water was no longer dense enough to sink. The meridional overturning circulation likely ground to a stop. Called the Younger Dryas, this one thousand year period saw the temporary return of the ice age. We may soon face a similar although far less drastic situation. Scientists are predicting that rising temperatures will melt the Greenland ice sheet.

Models suggest that the resulting influx of fresh melt water into the polar sea could weaken the meridional overturning circulation, although not as drastically as the events thought to have triggered the Younger Dryas period. Still it could slow enough to reduce the flow of warm tropical water north into the polar seas. Temperatures over northwestern Europe could drop as much five degrees Celsius. Predictably, talk of such a scenario has led to some big misconceptions. First, a slowdown or even a stoppage of the meridional overturning circulation would NOT spell the end to the Gulf Stream. Wind and large-scale turbulence drive the bulk of the Atlantic Subtropical Gyre, of which the Gulf Stream is a part. The Gulf Stream would, however, draw significantly less water from the tropics. Second, unlike during the Younger Dryas, a weakening of the meridional overturning circulation will NOT trigger another ice age. Rising temperatures due to global warming would offset most of the temperature drop. Armadas of icebergs floating off the New Jersey coast are just Hollywood fantasies. But even in the absence of these most extreme scenarios, any disruption of the meridional overturning circulation can have far-reaching consequences.

Models and paleoclimate data suggest that as less warm water flows north across the equator, the southern oceans will warm. The thermal equator (band of highest temperatures) would therefore likely shift south. The tropical rain belts would follow, altering rainfall patterns. Decreased downwelling would deliver less oxygen to the deep ocean, and decreased upwelling would carry fewer nutrients up from the bottom, potentially devastating ocean ecosystems. Monitoring the meridional overturning circulation and identifying changes in the thermohaline circulation is daunting. To separate real trends in ocean circulation from natural variability, scientists require huge volumes of data gathered over a long period of time. A global network of surface and deep profiling ARGO drifters that measure currents, water temperature, and salinity form the backbone of this effort. Moored buoys measure the southbound deepwater currents at strategic locations in the Atlantic. Satellites measure wind, sea surface temperatures, and sea surface height, and programs such as OSCAR calculate surface currents based on these measurements. In 2010, a new satellite, Aquarius, will begin to measure surface salinity throughout the ocean.

These observations already form the foundation for global ocean circulation and climate models that are helping scientists predict how the oceans and climate will respond as the Earth warms. Global Ocean Surface Currents Geology Final - Geology 211 with Zintambila at Illinois State University - StudyBlue Transports cool northern water toward equator. 2nd current in North Atlantic drift North Equatorial Current Moves west. Derives energy from northeast trades Kuroshio Current Gulf Stream's counterpart. Ocean circulation in North Pacific. Warm water flowing north. Merges with North Pacific Drift North Pacific Drift A portion of it flows south along western coast of US as California Current How do ocean currents influence weather? Warm & moisture from currents help develop cyclonic storms Warm air over cold water creates fog Warm water helps keep winter temps warmer Distinct temp gradients exist along boundaries of surface ocean currents When warm water meets cold water, sharp temp contrasts are present El Nino Warming of tropical Pacific Ocean between South America & Australia/Indonesia in equator region. Occurs around Christmas every 2-7 years. Warm waters pile up along coasts of Ecuador & Peru.

Warm water blocks upwelling of colder nutrient filled water which is devastating to fishing industry La Nina Continental tropical: High temp.,low humidity, dry air. Northern Mexico & southwest US Continental polar air mass Low temp. and dry air. Cold and stable. Dew point temps less than -30oC/-22oF. Originate over ice and snow covered regions of northern Canada & Alaska and moves south which causes it to warm up Continental arctic air mass Same as continental polar but colder. Travels in shallow but large dome of extremely cold air. The leading edge of it is marked by a cold front. Maritime polar air mass Low temp. & high humidity. Cool, moist, & conditionally unstable. 40-50oF. Causes light snow, freezing rain, and light drizzle during winter and spring in mid Atlantic and New England states.. Cumulus clouds form. After it crosses the Rockies, the cool moist air descends as relatively dry air. Stationary front. Maritime tropical air mass Produces heavy precipitation. High temp. & high humidity. Warm and moist. Sometimes called "pineapple express".

Produced heavy rain and extensive flooding in northern and central California on January 1, 1997 Continental tropical High temp.,low relative humidity (less than 10% during afternoon, Hot, dry, and conditionally unstable air at low levels. Frequent dust devils form during the day. Air must rise 3000m before condensation. Clear skies, hot weather, no rainfall.. If it moves to Great Plains a severe drought may result. What are fronts? Transition zone between 2 air masses of different densities Stationary fronts Nearly stationary. Winds blow almost parallel and from opposite directions on each side of the front. Clear to partly cloudy with colder air lying on east side. No precipitation unless warm air rides over cold air which causes light precipitation. (circle on top and triangle on bottom) Cold fronts Cooler air replaces warmer air. Continental polar replaces maritime tropical. Cold, dense air lifts warm air up steeply forming a steepers slope. Cumulonimbus cloud forms on a steep slope. Brings heavy rainfall and floods. Move faster than warm fronts. Rainfall occurs where cold front touches the surface (triangles at top) Warm fronts Warmer air replaces cooler air. Maritime tropical replaces continental polar.

Warm air glides over retreating cooler air(overrunning) Warm air forms a gentle slope. Different clouds including nimbostratus rain cloud develop on front. Brings light rainfall (circles at top) Occluded fronts Formed when a cold front catches up with a warm front. Has cold type(cold occlusion) where air behind it is colder than air in front and a warm type(warm occlusion) where air ahead of it is colder than air behind it. Heavy, showery precipitation with winds shifting to west or northwest. (circles and triangles on the top) Upper-air fronts Present aloft. Forms when the tropopause dips downward and folds under the polar jet stream. Impacts surface weather Maritime polar pathway Originates over Asia and moves east and south over the Pacific Ocean into California. After crossing several mountain ranges, it descends the eastern side of the Rockies. Originates in North Atlantic along the East Coast over eastern Canada and US Continental arctic pathway Originates near Antartica and travels southeast across upper plains through continental polar into northern Canada. Travels in shallow but large dome of extremely cold air.

Continental polar pathway Originates in northern Canada and travels south and southeast through Canada into US Maritime tropical pathway Wintertime source is the east Pacific Ocean and it travels northeast to southern California coast. In the summer it originates over Gulf of Mexico and Caribbean Sea and travels north into southern US states Continental tropical pathway Summer only. Originates in southern US and Mexico. Travels northeast and northwest in US Cold outbreak temperature on 12/22/90 -28oF Cold outbreak temp. on 12/22/89 -23oF Cold temp outbreak on 12/23/89 5oF In which regions of the US cold winter air masses take over Eastern and Midwest What is temperature range of a winter continental polar air mass? -4oF-14oF (-30o- -20oC) Starts at -4, gets warmer, and then gets colder as it gets higher What is the temperature range of a summer continental polar air mass?

14oF - 68oF Starts at 68o then gets colder as it gets higher Polar front Cold frontal boundary that separates colder air from warmer air at the surface and aloft Arctic front Separates cold air from extremely cold air. More shallow Where do mid-latitude cyclones tend to form? Regions of North America including Gulf of Mexico, Atlantic Ocean east of the Carolinas, and eastern slope of high mountain ranges such as the Rockies and Sierra Nevada. Idealized cycle of a mid-latitude cyclone 1. polar front separates warm and cold easterlies 2.cyclogenisis begins 5. both air masses continue to move and low pressure center forms 6. warm + cold fronts become established 7. fronts occlude and cyclone dies What are tropical cyclones? All hurricane-type storms that originate over tropical waters like Pacific, Indian, & Atlantic Ocean about 22o-5o from equator Where do tropical cyclones form? Over the warm northern Atlantic and eastern North Pacific oceans. How do tropical cyclones (hurricanes) compare with Mid-Latitude Cyclones?

Both move counterclockwise in Northern Hemisphere & clockwise in Southern Hemisphere Strongest winds in H are near surface around the eye. Aloft near jet stream for MLC Surface pressure is lowest at center for both Vertical structure weakens with height, high pressure aloft, & warm core low for H. Strengthens with height, low pressure aloft, & old core low with MLC Air in center sinks for H and rises for MLC Weather fronts for MLC but none for H Energy source for H is warm water & release of latent heat. Horizontal temp. contrasts for MLC How do tropical cyclones form? Wavelike disturbance called easterly wave develops Cloudy weather forms from east side of dashed line surface winds converging and rising Sunny weather forms from west side of dashed line surface winds diverging and sinking Tropical waters, light winds, high humidity, surface water temp is warm Stages of development of tropical cyclones Tropical Disturbance: Disorganized cluster of tropical thunderstorms.

Have slight to no circulation Tropical Depression: Organized cluster of tropical thunderstorms w/ weak cyclonic circulation of less than 39mph Tropical Storm: Tropical cyclone w/ highest sustained cyclonic winds at center between 39 and 47mph Hurricane: Tropical cyclone with winds at center of at least 74mph Anatomy of Tropical Cyclones Eye: Center. Has broken clouds which swirl around eye. Sinking air & calm. Light winds. Surface air pressure is low Eye wall: Ring of strong storms. Region of high winds & heavy rainfall. Whirl around storm's center & may extend upward. Damage-potential scale of Tropical Cyclones Saffir-Simpson scale. Category 1: 74-95 mph minimal damage Category 2: 96-110 mph moderate damage Category 3: 111-130 mph extensive damage Category 4: 131-155 mph extreme damage Category 5: more than 155 mph catastrophic What atmospheric conditions lead to the formation of thunderstorms? Warm moist air rises in a conditionally unstable environment. Rising air is warmer than air surrounding it.

Where does the highest frequency of thunderstorms occur in the United States? Why there? Florida. Combination of warmth and moisture. Low level of convergence of air helps initiate uplift. Close proximity to water source. Stages of development of ordinary thunderstorms Cumulus stage: growth stage. Rising, warm, humid air develops into a cumulus cloud Mature stage: downdraft and updraft appear. Most intense. Turbulence, lightning, and thunder. Heavy rain and sometimes small hail. Dissipating stage: Downdrafts exist throughout the cumulonimbus cloud. Updrafts weaken as gust front moves away. Light precipitation Ordinary cell thunderstorms

Question: The North Atlantic Drift ocean current over NW Europe starts as what at the US Florida Strait?
Answer: Gulf Stream