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92-438: When the air that has been heated on the extensive central plateau flows down the escarpment to the coast it undergoes further warming by adiabatic processes . This accounts for the hot and dry properties of these off-shore winds, wherever they occur along South Africa's coastline. Although berg winds are often called a Föhn winds , this is probably a misnomer, as Föhn winds are rain shadow winds that result from air moving over

184-729: A n t 1 = 100 000   Pa × ( 0.001   m 3 ) 7 5 = 10 5 × 6.31 × 10 − 5   Pa m 21 / 5 = 6.31   Pa m 21 / 5 , {\displaystyle {\begin{aligned}P_{1}V_{1}^{\gamma }&=\mathrm {constant} _{1}\\&=100\,000~{\text{Pa}}\times (0.001~{\text{m}}^{3})^{\frac {7}{5}}\\&=10^{5}\times 6.31\times 10^{-5}~{\text{Pa}}\,{\text{m}}^{21/5}\\&=6.31~{\text{Pa}}\,{\text{m}}^{21/5},\end{aligned}}} so

276-466: A n t 1 = 6.31   Pa m 21 / 5 = P × ( 0.0001   m 3 ) 7 5 , {\displaystyle {\begin{aligned}P_{2}V_{2}^{\gamma }&=\mathrm {constant} _{1}\\&=6.31~{\text{Pa}}\,{\text{m}}^{21/5}\\&=P\times (0.0001~{\text{m}}^{3})^{\frac {7}{5}},\end{aligned}}} We can now solve for

368-575: A n t 2 = 10 5   Pa × 10 − 3   m 3 300   K = 0.333   Pa m 3 K − 1 . {\displaystyle {\begin{aligned}{\frac {PV}{T}}&=\mathrm {constant} _{2}\\&={\frac {10^{5}~{\text{Pa}}\times 10^{-3}~{\text{m}}^{3}}{300~{\text{K}}}}\\&=0.333~{\text{Pa}}\,{\text{m}}^{3}{\text{K}}^{-1}.\end{aligned}}} We know

460-422: A piston compressing a gas contained within a cylinder and raising the temperature where in many practical situations heat conduction through walls can be slow compared with the compression time. This finds practical application in diesel engines which rely on the lack of heat dissipation during the compression stroke to elevate the fuel vapor temperature sufficiently to ignite it. Adiabatic compression occurs in

552-413: A decrease in productivity as the waters are no longer receiving nutrient-rich water. Without these nutrients, the rest of the trophic pyramid cannot be sustained, and the rich upwelling ecosystem will collapse. Coastal upwelling has a major influence over the affected region's local climate. This effect is magnified if the ocean current is already cool. As the cold, nutrient-rich water moves upwards and

644-414: A decreasing population, especially in species that do not breed often under normal circumstances or become reproductively mature late in life. Another problem is that the decrease in the population of a species due to fisheries can lead to a decrease in genetic diversity, resulting in a decrease in biodiversity of a species. If the species diversity is decreased significantly, this could cause problems for

736-400: A delay in the reconstruction of this upwelling community. The possibility of such an ecosystem collapse is the very danger of fisheries in upwelling regions. Fisheries may target a variety of different species, and therefore they are a direct threat to many species in the ecosystem, however they pose the highest threat to the intermediate pelagic fish . Since these fish form the crux of

828-654: A few hours. This is then followed by cool onshore winds which bring low cloud, fog or drizzle to the region, but may, on occasions, produce substantial precipitation when coupled to an approaching cold front . Coastal lows are a common feature of the coastal weather in South Africa with an average of about five lows of varying intensities passing through Port Elizabeth per month. They are shallow (not more than 1,000 to 1,500 metres (3,300 to 4,900 ft) deep), mesoscale (medium-sized) systems that are generally not more than 100 to 200 kilometres (62 to 124 mi) across, trapped on

920-617: A high elevation down a slope under the force of gravity. These are thus "fall winds", which occur most typically down the coastal ice slopes of Antarctica and Greenland . Berg winds blow off the African escarpment in response to large scale weather systems in the South Atlantic Ocean , the African interior, and the Southern Indian Ocean . Berg winds are usually accompanied by coastal lows. These coastal lows owe their existence to

1012-430: A high number of commercial fishers and fisheries. On one hand, this is another benefit of the upwelling process as it serves as a viable source of food and income for so many people and nations besides marine animals. However, just as in any ecosystem, the consequences of over-fishing from a population could be detrimental to that population and the ecosystem as a whole. In upwelling ecosystems, every species present plays

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1104-469: A monatomic gas, 5 for a diatomic gas or a gas of linear molecules such as carbon dioxide). For a monatomic ideal gas, γ = ⁠ 5 / 3 ⁠ , and for a diatomic gas (such as nitrogen and oxygen , the main components of air), γ = ⁠ 7 / 5 ⁠ . Note that the above formula is only applicable to classical ideal gases (that is, gases far above absolute zero temperature) and not Bose–Einstein or Fermi gases . One can also use

1196-423: A mountain for example, can cause the water vapor pressure to exceed the saturation vapor pressure . Expansion and cooling beyond the saturation vapor pressure is often idealized as a pseudo-adiabatic process whereby excess vapor instantly precipitates into water droplets. The change in temperature of an air undergoing pseudo-adiabatic expansion differs from air undergoing adiabatic expansion because latent heat

1288-518: A mountain range, resulting in precipitation on the windward side. This releases latent heat into the atmosphere which is then warmed still further as the air descends on the leeward side (e.g., the Chinook or the original Föhn ). Berg winds do not originate in precipitation, but in the mostly dry, often arid central plateau of Southern Africa . On the other hand, katabatic winds are technically drainage winds, that carry high density, usually cold air from

1380-803: A north and south split. The split in this system occurs at Point Conception , California due to weak upwelling in the South and strong upwelling in the north. The Canary Current is an eastern boundary current of the North Atlantic Gyre and is also separated due to the presence of the Canary Islands . Finally, the Humboldt Current or the Peru Current flows west along the coast of South America from Peru to Chile and extends up to 1,000 kilometers offshore. These four eastern boundary currents comprise

1472-505: A rate of about 5–10 meters per day, but the rate and proximity of upwelling to the coast can be changed due to the strength and distance of the wind. Deep waters are rich in nutrients, including nitrate , phosphate and silicic acid , themselves the result of decomposition of sinking organic matter (dead/detrital plankton) from surface waters. When brought to the surface, these nutrients are utilized by phytoplankton , along with dissolved CO 2 ( carbon dioxide ) and light energy from

1564-430: A rise in the temperature of that mass of air. The parcel of air can only slowly dissipate the energy by conduction or radiation (heat), and to a first approximation it can be considered adiabatically isolated and the process an adiabatic process. Adiabatic expansion occurs when the pressure on an adiabatically isolated system is decreased, allowing it to expand in size, thus causing it to do work on its surroundings. When

1656-529: A significant flow of water northwards. This is actually a type of coastal upwelling. Since there are no continents in a band of open latitudes between South America and the tip of the Antarctic Peninsula, some of this water is drawn up from great depths. In many numerical models and observational syntheses, the Southern Ocean upwelling represents the primary means by which deep dense water is brought to

1748-411: A significant hazard to aircraft on landing and taking off. During the climb-out and approach phases of flight, aircraft airspeed and height are near critical values, thus rendering the aircraft especially susceptible to the adverse effects of these wind shears. The Atlantic cold fronts that move into and across the subcontinent, especially during the cooler months of the year, are frequently associated,

1840-449: A system's behaviour. For example, according to Laplace , when sound travels in a gas, there is no time for heat conduction in the medium, and so the propagation of sound is adiabatic. For such an adiabatic process, the modulus of elasticity ( Young's modulus ) can be expressed as E = γP , where γ is the ratio of specific heats at constant pressure and at constant volume ( γ = ⁠ C p / C v ⁠ ) and P

1932-445: A very high gas pressure, which ensures immediate ignition of the injected fuel. For an adiabatic free expansion of an ideal gas , the gas is contained in an insulated container and then allowed to expand in a vacuum. Because there is no external pressure for the gas to expand against, the work done by or on the system is zero. Since this process does not involve any heat transfer or work, the first law of thermodynamics then implies that

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2024-436: A vital role in the functioning of that ecosystem. If one species is significantly depleted, that will have an effect throughout the rest of the trophic levels. For example, if a popular prey species is targeted by fisheries, fishermen may collect hundreds of thousands of individuals of this species just by casting their nets into the upwelling waters. As these fish are depleted, the food source for those who preyed on these fish

2116-557: A wasp-waist richness pattern. In this type of pattern, the high and low trophic levels are well-represented by high species diversity. However, the intermediate trophic level is only represented by one or two species. This trophic layer, which consists of small, pelagic fish usually makes up about only three to four percent of the species diversity of all fish species present. The lower trophic layers are very well-represented with about 500 species of copepods , 2500 species of gastropods , and 2500 species of crustaceans on average. At

2208-469: Is diabatic . Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation". For example, the adiabatic flame temperature uses this approximation to calculate the upper limit of flame temperature by assuming combustion loses no heat to its surroundings. In meteorology , adiabatic expansion and cooling of moist air, which can be triggered by winds flowing up and over

2300-579: Is a final temperature of 753 K, or 479 °C, or 896 °F, well above the ignition point of many fuels. This is why a high-compression engine requires fuels specially formulated to not self-ignite (which would cause engine knocking when operated under these conditions of temperature and pressure), or that a supercharger with an intercooler to provide a pressure boost but with a lower temperature rise would be advantageous. A diesel engine operates under even more extreme conditions, with compression ratios of 16:1 or more being typical, in order to provide

2392-414: Is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment . Unlike an isothermal process , an adiabatic process transfers energy to the surroundings only as work . As a key concept in thermodynamics , the adiabatic process supports the theory that explains the first law of thermodynamics . The opposite term to "adiabatic"

2484-415: Is always some heat loss, as no perfect insulators exist. The mathematical equation for an ideal gas undergoing a reversible (i.e., no entropy generation) adiabatic process can be represented by the polytropic process equation P V γ = constant , {\displaystyle PV^{\gamma }={\text{constant}},} where P is pressure, V is volume, and γ

2576-430: Is depleted. Therefore, the predators of the targeted fish will begin to die off, and there will not be as many of them to feed the predators above them. This system continues throughout the entire food chain , resulting in a possible collapse of the ecosystem. It is possible that the ecosystem may be restored over time, but not all species can recover from events such as these. Even if the species can adapt, there may be

2668-415: Is desired to know how the values of dP and dV relate to each other as the adiabatic process proceeds. For an ideal gas (recall ideal gas law PV = nRT ) the internal energy is given by where α is the number of degrees of freedom divided by 2, R is the universal gas constant and n is the number of moles in the system (a constant). Differentiating equation (a3) yields Equation (a4)

2760-486: Is generally regarded as a harbinger of cold, wet weather. Coastal lows are orographically trapped weather systems that also occur in other parts of the world, where there are mountain ranges between 1,000–4,000 kilometres (620–2,490 mi) in length. Thus they occur along the coast of Chile , eastern Australia and the west coast of North America, as well as on the eastern side of the Appalachian Mountains of

2852-449: Is irreversible, with Δ S > 0 , as friction or viscosity are always present to some extent. The adiabatic compression of a gas causes a rise in temperature of the gas. Adiabatic expansion against pressure, or a spring, causes a drop in temperature. In contrast, free expansion is an isothermal process for an ideal gas. Adiabatic compression occurs when the pressure of a gas is increased by work done on it by its surroundings, e.g.,

Berg wind - Misplaced Pages Continue

2944-400: Is more than a simple 10:1 compression ratio would indicate; this is because the gas is not only compressed, but the work done to compress the gas also increases its internal energy, which manifests itself by a rise in the gas temperature and an additional rise in pressure above what would result from a simplistic calculation of 10 times the original pressure. We can solve for the temperature of

3036-505: Is often expressed as dU = nC V dT because C V = αR . Now substitute equations (a2) and (a4) into equation (a1) to obtain Upwelling Upwelling is an oceanographic phenomenon that involves wind -driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water . The nutrient-rich upwelled water stimulates

3128-423: Is produced within the system (no friction, viscous dissipation, etc.), and the work is only pressure-volume work (denoted by P d V ). In nature, this ideal kind occurs only approximately because it demands an infinitely slow process and no sources of dissipation. The other extreme kind of work is isochoric work ( d V = 0 ), for which energy is added as work solely through friction or viscous dissipation within

3220-422: Is released by precipitation. A process without transfer of heat to or from a system, so that Q = 0 , is called adiabatic, and such a system is said to be adiabatically isolated. The simplifying assumption frequently made is that a process is adiabatic. For example, the compression of a gas within a cylinder of an engine is assumed to occur so rapidly that on the time scale of the compression process, little of

3312-424: Is the adiabatic index or heat capacity ratio defined as γ = C P C V = f + 2 f . {\displaystyle \gamma ={\frac {C_{P}}{C_{V}}}={\frac {f+2}{f}}.} Here C P is the specific heat for constant pressure, C V is the specific heat for constant volume, and f is the number of degrees of freedom (3 for

3404-440: Is the absolute or thermodynamic temperature . The compression stroke in a gasoline engine can be used as an example of adiabatic compression. The model assumptions are: the uncompressed volume of the cylinder is one litre (1 L = 1000 cm = 0.001 m ); the gas within is the air consisting of molecular nitrogen and oxygen only (thus a diatomic gas with 5 degrees of freedom, and so γ = ⁠ 7 / 5 ⁠ );

3496-529: Is the eastern boundary of the South Atlantic subtropical gyre and can be divided into a northern and southern sub-system with upwelling occurring in both areas. The subsystems are divided by an area of permanent upwelling off of Luderitz , which is the strongest upwelling zone in the world. The California Current System (CCS) is an eastern boundary current of the North Pacific that is also characterized by

3588-534: Is the pressure of the gas. For a closed system, one may write the first law of thermodynamics as Δ U = Q − W , where Δ U denotes the change of the system's internal energy, Q the quantity of energy added to it as heat, and W the work done by the system on its surroundings. Naturally occurring adiabatic processes are irreversible (entropy is produced). The transfer of energy as work into an adiabatically isolated system can be imagined as being of two idealized extreme kinds. In one such kind, no entropy

3680-494: Is zero, δQ = 0 . Then, according to the first law of thermodynamics, where dU is the change in the internal energy of the system and δW is work done by the system. Any work ( δW ) done must be done at the expense of internal energy U , since no heat δQ is being supplied from the surroundings. Pressure–volume work δW done by the system is defined as However, P does not remain constant during an adiabatic process but instead changes along with V . It

3772-783: The Canary Current (off Northwest Africa ), the Benguela Current (off southern Africa ), the California Current (off California and Oregon ), the Humboldt Current (off Peru and Chile ), and the Somali Current (off Somalia and Oman ). All of these currents support major fisheries. The four major eastern boundary currents in which coastal upwelling primarily occurs are the Canary Current, Benguela Current, California Current, and Humboldt Current. The Benguela Current

Berg wind - Misplaced Pages Continue

3864-476: The Earth's atmosphere when an air mass descends, for example, in a Katabatic wind , Foehn wind , or Chinook wind flowing downhill over a mountain range. When a parcel of air descends, the pressure on the parcel increases. Because of this increase in pressure, the parcel's volume decreases and its temperature increases as work is done on the parcel of air, thus increasing its internal energy, which manifests itself by

3956-530: The El Nino-Southern Oscillation (ENSO) event. The Peruvian upwelling system is particularly vulnerable to ENSO events, and can cause extreme interannual variability in productivity. Changes in bathymetry can affect the strength of an upwelling. For example, a submarine ridge that extends out from the coast will produce more favorable upwelling conditions than neighboring regions. Upwelling typically begins at such ridges and remains strongest at

4048-514: The Sahara desert . Adiabatic expansion does not have to involve a fluid. One technique used to reach very low temperatures (thousandths and even millionths of a degree above absolute zero) is via adiabatic demagnetisation , where the change in magnetic field on a magnetic material is used to provide adiabatic expansion. Also, the contents of an expanding universe can be described (to first order) as an adiabatically expanding fluid. (See heat death of

4140-485: The cold fronts that approach the subcontinent from the South Atlantic Ocean , as well as the pressure systems on the plateau, causing air that has been warmed on the plateau by 2–3 days of sunny weather to flow down the Great Escarpment on to the coastal plain either on the west or south coasts of the country (i.e. causing a berg wind). The descending air warms up adiabatically, heating up the coastal plain, while, at

4232-410: The sun , to produce organic compounds , through the process of photosynthesis . Upwelling regions therefore result in very high levels of primary production (the amount of carbon fixed by phytoplankton ) in comparison to other areas of the ocean. They account for about 50% of global marine productivity. High primary production propagates up the food chain because phytoplankton are at the base of

4324-643: The United States. In each of these cases the weather systems are trapped vertically by stable stratifications , and laterally by Coriolis effects against the mountains. However, only the South African and the South American coastal disturbances are “coastal lows”; the remainder are generally produced by coastal ridging . Adiabatic process An adiabatic process ( adiabatic from Ancient Greek ἀδιάβατος ( adiábatos )  'impassable')

4416-430: The adiabatic constant for this example is about 6.31 Pa m . The gas is now compressed to a 0.1 L (0.0001 m ) volume, which we assume happens quickly enough that no heat enters or leaves the gas through the walls. The adiabatic constant remains the same, but with the resulting pressure unknown P 2 V 2 γ = c o n s t

4508-444: The air in this region. In addition, on reaching the escarpment the maritime air curves to the right round the low-pressure zone due to Coriolis forces (in the southern hemisphere) accentuating the cyclonic circulation of the "coastal low". The entire system is capped by an inversion consisting of a layer of warm air that has moved horizontally off the plateau at the level of the upper edge of the escarpment. This inversion layer prevents

4600-551: The apex and near-apex trophic levels, there are usually about 100 species of marine mammals and about 50 species of marine birds. The vital intermediate trophic species however are small pelagic fish that usually feed on phytoplankton . In most upwelling systems, these species are either anchovies or sardines, and usually only one is present, although two or three species may be present occasionally. These fish are an important food source for predators, such as large pelagic fish, marine mammals, and marine birds. Although they are not at

4692-405: The base of the trophic pyramid, they are the vital species that connect the entire marine ecosystem and keep the productivity of upwelling zones so high A major threat to both this crucial intermediate trophic level and the entire upwelling trophic ecosystem is the problem of commercial fishing . Since upwelling regions are the most productive and species rich areas in the world, they attract

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4784-503: The catch. Besides directly causing the collapse of the ecosystem due to their absence, this can create problems in the ecosystem through a variety of other methods as well. The animals higher in the trophic levels may not completely starve to death and die off, but the decreased food supply could still hurt the populations. If animals do not get enough food, it will decrease their reproductive viability meaning that they will not breed as often or as successfully as usual. This can lead to

4876-506: The coast from the Cederberg , 300 kilometres (190 mi) to the north of Cape Town , to Cape Hangklip on the east side of False Bay and then eastwards for 700 kilometres (430 mi) to Port Elizabeth , where they eventually peter out (see the map above). Coastal lows are initiated by the interaction of large scale weather systems such as the quasi-permanent South Atlantic and South Indian Ocean Anticyclones (high-pressure systems),

4968-529: The coastal low. The wind then changes abruptly to a strong, cold, south or south-westerly wind (called a “buster” if the change in wind speed is greater than 35 km/h). The buster coincides with the passage of the pressure minimum. The onshore wind gradually diminishes in intensity during the course of about a day, and is associated with cloudy, misty or drizzly weather. Because of the often abrupt changes in horizontal and vertical wind speeds and direction that can occur within these small weather systems they represent

5060-519: The coastal plain by the escarpment on the inland side, Coriolis effects on the oceanic side, and an inversion layer above. The pressure minima of these systems lie just off-shore. In the south-west corner of the country the coastal lows are bounded on the inland side by the Cape Fold Mountains , which tend to have a higher elevation than the escarpment, and form an almost continuous 1,000 kilometres (620 mi) mountain barrier running parallel to

5152-809: The compressed gas has V  = 0.1 L and P  = 2.51 × 10  Pa , so we can solve for temperature: T = P V c o n s t a n t 2 = 2.51 × 10 6   Pa × 10 − 4   m 3 0.333   Pa m 3 K − 1 = 753   K . {\displaystyle {\begin{aligned}T&={\frac {PV}{\mathrm {constant} _{2}}}\\&={\frac {2.51\times 10^{6}~{\text{Pa}}\times 10^{-4}~{\text{m}}^{3}}{0.333~{\text{Pa}}\,{\text{m}}^{3}{\text{K}}^{-1}}}\\&=753~{\text{K}}.\end{aligned}}} That

5244-396: The compressed gas in the engine cylinder as well, using the ideal gas law, PV  =  nRT ( n is amount of gas in moles and R the gas constant for that gas). Our initial conditions being 100 kPa of pressure, 1 L volume, and 300 K of temperature, our experimental constant ( nR ) is: P V T = c o n s t

5336-469: The compression ratio of the engine is 10:1 (that is, the 1 L volume of uncompressed gas is reduced to 0.1 L by the piston); and the uncompressed gas is at approximately room temperature and pressure (a warm room temperature of ~27 °C, or 300 K, and a pressure of 1 bar = 100 kPa, i.e. typical sea-level atmospheric pressure). P 1 V 1 γ = c o n s t

5428-505: The configuration of the plateau, escarpment and coastal plain (see diagram on the right, above), in that they are confined to the coastal areas, always below the escarpment. Though they can arise almost anywhere along the coast, they often first appear on the west coast, or even on the Namibian coast. They are then always propagated counter-clockwise along South Africa's coastline at between 30 and 60 kilometres per hour (19 and 37 mph), from

5520-514: The day before, by a coastal low that moves ahead of the front. Under these circumstances the southerly or south-westerly onshore wind of the coastal low gradually diminishes in intensity over the course of 12–20 hours, when it is replaced by a westerly wind (which may temporarily reach buster proportions) and a further drop in temperature accompanied by rain, indicative of the passage of the cold front. Thus, particularly in Cape Town , an obvious berg wind

5612-578: The direction of the wind, and the friction between that layer and the layer beneath it causes the successive layers to move in the same direction. This results in a spiral of water moving down the water column. Then, it is the Coriolis forces that dictate which way the water will move; in the Northern hemisphere, the water is transported to the right of the direction of the wind. In the Southern Hemisphere,

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5704-400: The entire trophic process of upwelling ecosystems, they are highly represented throughout the ecosystem (even if there is only one species present). Unfortunately, these fish tend to be the most popular targets of fisheries as about 64 percent of their entire catch consists of pelagic fish. Among those, the six main species that usually form the intermediate trophic layer represent over half of

5796-565: The equator, upwelling still occurs just north and south of the equator. This results in a divergence, with denser, nutrient-rich water being upwelled from below, and results in the remarkable fact that the equatorial region in the Pacific can be detected from space as a broad line of high phytoplankton concentration. Large-scale upwelling is also found in the Southern Ocean . Here, strong westerly (eastward) winds blow around Antarctica , driving

5888-612: The final pressure P 2 = P 1 ( V 1 V 2 ) γ = 100 000   Pa × 10 7 / 5 = 2.51 × 10 6   Pa {\displaystyle {\begin{aligned}P_{2}&=P_{1}\left({\frac {V_{1}}{V_{2}}}\right)^{\gamma }\\&=100\,000~{\text{Pa}}\times {\text{10}}^{7/5}\\&=2.51\times 10^{6}~{\text{Pa}}\end{aligned}}} or 25.1 bar. This pressure increase

5980-410: The general effects are the same. In the overall process of upwelling, winds blow across the sea surface at a particular direction, which causes a wind-water interaction. As a result of the wind, the water has transported a net of 90 degrees from the direction of the wind due to Coriolis forces and Ekman transport. Ekman transport causes the surface layer of water to move at about a 45-degree angle from

6072-443: The growth and reproduction of primary producers such as phytoplankton . The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll a . The increased availability of nutrients in upwelling regions results in high levels of primary production and thus fishery production. Approximately 25% of

6164-456: The ideal gas law to rewrite the above relationship between P and V as P 1 − γ T γ = constant , T V γ − 1 = constant {\displaystyle {\begin{aligned}P^{1-\gamma }T^{\gamma }&={\text{constant}},\\TV^{\gamma -1}&={\text{constant}}\end{aligned}}} where T

6256-597: The majority of coastal upwelling zones in the oceans. Upwelling at the equator is associated with the Intertropical Convergence Zone (ITCZ) which actually moves, and consequently, is often located just north or south of the equator. Easterly (westward) trade winds blow from the Northeast and Southeast and converge along the equator blowing West to form the ITCZ. Although there are no Coriolis forces present along

6348-401: The net internal energy change of the system is zero. For an ideal gas, the temperature remains constant because the internal energy only depends on temperature in that case. Since at constant temperature, the entropy is proportional to the volume, the entropy increases in this case, therefore this process is irreversible. The definition of an adiabatic process is that heat transfer to the system

6440-433: The ocean circulation suggest that broad-scale upwelling occurs in the tropics, as pressure driven flows converge water toward the low latitudes where it is diffusively warmed from above. The required diffusion coefficients, however, appear to be larger than are observed in the real ocean. Nonetheless, some diffusive upwelling does probably occur. Upwelling intensity depends on wind strength and seasonal variability, as well as

6532-476: The ocean interior, upwelling associated with eddies, topographically-associated upwelling, and broad-diffusive upwelling in the ocean interior. Coastal upwelling is the best known type of upwelling, and the most closely related to human activities as it supports some of the most productive fisheries in the world. Coastal upwelling will occur if the wind direction is parallel to the coastline and generates wind-driven currents. The wind-driven currents are diverted to

6624-495: The oceanic food chain. The food chain follows the course of: Coastal upwelling exists year-round in some regions, known as major coastal upwelling systems , and only in certain months of the year in other regions, known as seasonal coastal upwelling systems . Many of these upwelling systems are associated with relatively high carbon productivity and hence are classified as Large Marine Ecosystems . Worldwide, there are five major coastal currents associated with upwelling areas:

6716-475: The pressure applied on a parcel of gas is reduced, the gas in the parcel is allowed to expand; as the volume increases, the temperature falls as its internal energy decreases. Adiabatic expansion occurs in the Earth's atmosphere with orographic lifting and lee waves , and this can form pilei or lenticular clouds . Due in part to adiabatic expansion in mountainous areas, snowfall infrequently occurs in some parts of

6808-444: The process of upwelling. However, during El Niño events, trade winds are weaker, causing decreased upwelling in the equatorial regions as the divergence of water north and south of the equator is not as strong or as prevalent. The coastal upwelling zones diminish as well since they are wind driven systems, and the wind is no longer a very strong driving force in these areas. As a result, global upwelling drastically decreases, causing

6900-434: The ridge even after developing in other locations. The most productive and fertile ocean areas, upwelling regions are important sources of marine productivity. They attract hundreds of species throughout the trophic levels; these systems' diversity has been a focal point for marine research . While studying the trophic levels and patterns typical of upwelling regions, researchers have discovered that upwelling systems exhibit

6992-608: The right of the winds in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Coriolis effect . The result is a net movement of surface water at right angles to the direction of the wind, known as the Ekman transport (See also Ekman Spiral ). When Ekman transport is occurring away from the coast, surface waters moving away are replaced by deeper, colder, and denser water. Normally, this upwelling process occurs at

7084-415: The same time, causing an off-shore wind which blows the surface water away from the land to be replaced by cold water which wells up from the depths. This upwelling of cold subsurface water from the ocean increases the ocean-land temperature difference, causing an on-shore wind. The on-shore airflow is strengthened by the fact that the berg wind is not only hot, but it is also “stretched” vertically due to

7176-565: The sea surface temperature gets cooler, the air immediately above it also cools down and is likely to condensate, forming sea fog and stratus clouds . This also inhibits the formation of higher altitude clouds, showers and thunderstorms and results in rainfall over the ocean leaving the land dry. In year-round upwelling systems (like that of the western coasts of Southern Africa and South America), temperatures are generally cooler and precipitation scarce. Seasonal upwelling systems are often paired with seasonal downwelling systems (like that of

7268-428: The shallower the material is in the Earth. Such temperature changes can be quantified using the ideal gas law , or the hydrostatic equation for atmospheric processes. In practice, no process is truly adiabatic. Many processes rely on a large difference in time scales of the process of interest and the rate of heat dissipation across a system boundary, and thus are approximated by using an adiabatic assumption. There

7360-441: The species in an environment that is so variable and quick-changing; they may not be able to adapt, which could result in a collapse of the population or ecosystem. Another threat to the productivity and ecosystems of upwelling regions is El Niño-Southern Oscillation (ENSO) system, or more specifically El Niño events. During the normal period and La Niña events, the easterly trade winds are still strong, which continues to drive

7452-422: The sudden lowering of the floor over which it moves below the escarpment. Its low density, therefore, lowers the atmospheric pressure on the coast. This low-pressure area caused by the berg wind draws the dense moist maritime air onshore to the right of the off-shore berg wind. Shear forces between these on- and off-shore winds on the right-hand side of the berg wind tend to cause clockwise (or cyclonic ) rotation of

7544-509: The surface. In some regions of Antarctica, wind-driven upwelling near the coast pulls relatively warm Circumpolar deep water onto the continental shelf, where it can enhance ice shelf melt and influence ice sheet stability. Shallower, wind-driven upwelling is also found in off the west coasts of North and South America, northwest and southwest Africa, and southwest and south Australia , all associated with oceanic subtropical high pressure circulations (see coastal upwelling above). Some models of

7636-402: The system's energy can be transferred out as heat to the surroundings. Even though the cylinders are not insulated and are quite conductive, that process is idealized to be adiabatic. The same can be said to be true for the expansion process of such a system. The assumption of adiabatic isolation is useful and often combined with other such idealizations to calculate a good first approximation of

7728-480: The system. A stirrer that transfers energy to a viscous fluid of an adiabatically isolated system with rigid walls, without phase change, will cause a rise in temperature of the fluid, but that work is not recoverable. Isochoric work is irreversible. The second law of thermodynamics observes that a natural process, of transfer of energy as work, always consists at least of isochoric work and often both of these extreme kinds of work. Every natural process, adiabatic or not,

7820-452: The temperature contrast is greatly seasonably variable, creating periods of strong upwelling in the spring and summer, to weak or no upwelling in the winter. For example, off the coast of Oregon, there are four or five strong upwelling events separated by periods of little to no upwelling during the six-month season of upwelling. In contrast, tropical latitudes have a more constant temperature contrast, creating constant upwelling throughout

7912-447: The total global marine fish catches come from five upwellings, which occupy only 5% of the total ocean area. Upwellings that are driven by coastal currents or diverging open ocean have the greatest impact on nutrient-enriched waters and global fishery yields. The three main drivers that work together to cause upwelling are wind , Coriolis effect , and Ekman transport . They operate differently for different types of upwelling, but

8004-415: The universe .) Rising magma also undergoes adiabatic expansion before eruption, particularly significant in the case of magmas that rise quickly from great depths such as kimberlites . In the Earth's convecting mantle (the asthenosphere) beneath the lithosphere , the mantle temperature is approximately an adiabat. The slight decrease in temperature with shallowing depth is due to the decrease in pressure

8096-484: The upwardly spiraling cyclonic air of the coastal low from rising above 1000–1500 m, thus preventing it from causing significant precipitation. Along the south coast the passage of a coastal low is typically preceded by a north-easterly wind driven by the South Indian Ocean Anticyclone. The wind then backs quickly through northerly to north-westerly as its temperature rises. This is the berg wind phase of

8188-428: The vertical structure of the water , variations in the bottom bathymetry , and instabilities in the currents . In some areas, upwelling is a seasonal event leading to periodic bursts of productivity similar to spring blooms in coastal waters. Wind-induced upwelling is generated by temperature differences between the warm, light air above the land and the cooler denser air over the sea. In temperate latitudes ,

8280-417: The water is transported to the left of the wind. If this net movement of water is divergent, then upwelling of deep water occurs to replace the water that was lost. The major upwellings in the ocean are associated with the divergence of currents that bring deeper, colder, nutrient rich waters to the surface. There are at least five types of upwelling: coastal upwelling, large-scale wind-driven upwelling in

8372-591: The west coast southwards to the Cape Peninsula and then eastward along the south coast, and finally north-eastward along the KwaZulu-Natal coastline, to finally dissipate north of Durban, due to the divergence of the coastline from the plateau which disappears altogether in the vicinity of the Limpopo valley . There is always a hot off-shore berg wind ahead of a coastal low, which can blow for several days or for only for

8464-406: The year. The Peruvian upwelling, for instance, occurs throughout most of the year, resulting in one of the world's largest marine fisheries for sardines and anchovies . In anomalous years when the trade winds weaken or reverse, the water that is upwelled is much warmer and low in nutrients, resulting in a sharp reduction in the biomass and phytoplankton productivity. This event is known as

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