quinta-feira, 8 de setembro de 2011
terça-feira, 6 de setembro de 2011
Why, "environment" is a matter of global security?
For more than two years, when no one has yet had the courage to say that the environment is a matter of global security, I have been writing through my blog: "Environment is a matter of global security."
All the intelligence services, government, public and private institutions, organized society, everyone must mobilize itself in addressing the climate and geological consequences in progress before the foreshadowing serious environmental disaster of major proportions, which can affect drastically, modern society, entirely dependent on modern technology, highly vulnerable, as evidenced in Japan
Because it can affect nuclear power plants, and it happened in Japan, a country well prepared, imagine what will happen when an earthquake occurs in a country unprepared for earthquakes and tsunamis, but that has nuclear power plants, and I quote the example of Brazil.
Brazil does not have any preparation for earthquakes, but it has nuclear power plants.Imagine an earthquake, in Angra dos Reis, with the precarious location of our nuclear power plant!
Angra dos Reis is at sea level, near the sea, built in an area of difficult access, no evacuation areas, a dormant volcanic region, fearful of a close one of the most populated cities in Brazil, which is the city of "Rio de Janeiro."
The nuclear contamination occurs in the wind currents, directly affecting the neighboring countries, and spreading across the earth.
Grain production is another sensitive issue that can cause global consequences.
Oil refinery plants exploding, or leaking oil, is another matter of global security.
Earthquakes in the areas of storage silos for nuclear weapons.
Drastic sea level rise in large port cities of the world, another issue of global security.
Disappearance of countries and peoples located on islands, another problem of global security.
Uncontrollable environmental disasters caused financial crises in the affected countries, reflected in its economic partners, another issue of global security.
Lack of clean water ...
Unable to land communication ...
Lack of fuel ...
Diseases from environmental disasters can contaminate the whole planet ...
Lack of medicines, in cases of great public calamity, globally affect all nations ...
Health issues, public safety, lack of infrastructure, as occurred in Haiti, there are localized problems, but that cause global consequences.
I do not think there's still time to reverse the situation, I cite the example of two news today, released by Twitter, which clearly demonstrate that passed the point of return:
01 - @AP Waves of earthquakes detected at Iceland's Katla volcano; scientists watching out for eruption: http://apne.ws/qfoERs –CJ
02 - Pics of Greenland glacier melt shocksexpert -http://www.physorg.com/news/2011-09-pics-greenland-glacier-shocksexpert.html via @TopicfireNews
In the event of the eruption of Katla volcano, and I suspect that scientists are not certain in his optimistic predictions, the modern world will be faced with a situation of chaos unknown air, just check what happened in 1893 when there was no global dependency planes, roads, and economic interdependencies.
The second story, about the accelerated melting of glaciers could raise sea levels, with catastrophic consequences in port facilities, affecting the transport of products globally, sea.
Not to mention the quality of air we breathe, food contamination, breakdown of communication networks, the ozone layer, opportunistic attacks of the situation, and countless other possibilities.
Anyway, the picture is disturbing, and seriously undermines global security.
RUI SANTOS DE SOUZA
Brazil, Curitiba, September 6, 2011 - 22h: 08
All the intelligence services, government, public and private institutions, organized society, everyone must mobilize itself in addressing the climate and geological consequences in progress before the foreshadowing serious environmental disaster of major proportions, which can affect drastically, modern society, entirely dependent on modern technology, highly vulnerable, as evidenced in Japan
Because it can affect nuclear power plants, and it happened in Japan, a country well prepared, imagine what will happen when an earthquake occurs in a country unprepared for earthquakes and tsunamis, but that has nuclear power plants, and I quote the example of Brazil.
Brazil does not have any preparation for earthquakes, but it has nuclear power plants.Imagine an earthquake, in Angra dos Reis, with the precarious location of our nuclear power plant!
Angra dos Reis is at sea level, near the sea, built in an area of difficult access, no evacuation areas, a dormant volcanic region, fearful of a close one of the most populated cities in Brazil, which is the city of "Rio de Janeiro."
The nuclear contamination occurs in the wind currents, directly affecting the neighboring countries, and spreading across the earth.
Grain production is another sensitive issue that can cause global consequences.
Oil refinery plants exploding, or leaking oil, is another matter of global security.
Earthquakes in the areas of storage silos for nuclear weapons.
Drastic sea level rise in large port cities of the world, another issue of global security.
Disappearance of countries and peoples located on islands, another problem of global security.
Uncontrollable environmental disasters caused financial crises in the affected countries, reflected in its economic partners, another issue of global security.
Lack of clean water ...
Unable to land communication ...
Lack of fuel ...
Diseases from environmental disasters can contaminate the whole planet ...
Lack of medicines, in cases of great public calamity, globally affect all nations ...
Health issues, public safety, lack of infrastructure, as occurred in Haiti, there are localized problems, but that cause global consequences.
I do not think there's still time to reverse the situation, I cite the example of two news today, released by Twitter, which clearly demonstrate that passed the point of return:
01 - @AP Waves of earthquakes detected at Iceland's Katla volcano; scientists watching out for eruption: http://apne.ws/qfoERs –CJ
02 - Pics of Greenland glacier melt shocksexpert -http://www.physorg.com/news/2011-09-pics-greenland-glacier-shocksexpert.html via @TopicfireNews
In the event of the eruption of Katla volcano, and I suspect that scientists are not certain in his optimistic predictions, the modern world will be faced with a situation of chaos unknown air, just check what happened in 1893 when there was no global dependency planes, roads, and economic interdependencies.
The second story, about the accelerated melting of glaciers could raise sea levels, with catastrophic consequences in port facilities, affecting the transport of products globally, sea.
Not to mention the quality of air we breathe, food contamination, breakdown of communication networks, the ozone layer, opportunistic attacks of the situation, and countless other possibilities.
Anyway, the picture is disturbing, and seriously undermines global security.
RUI SANTOS DE SOUZA
Brazil, Curitiba, September 6, 2011 - 22h: 08
Por quê, "meio-ambiente" é questão de segurança global?
Há mais de dois anos, quando ninguém ainda tinha a coragem de dizer que meio-ambiente é uma questão de segurança global, que venho escrevendo através do meu blog: "Meio-ambiente é uma questão de segurança global."
Todos os serviços de inteligência, governos, instituições públicas e privadas, sociedade organizada, todos devem mobilizar-se na abordagem das consequências climáticas e geológicas em curso, diante dos prenúncios sérios, de desastres ambientais de grandes proporções, que podem afetar de maneira drástica, a sociedade moderna, inteiramente dependente da tecnologia moderna, altamente vulnerável, como ficou evidente no Japão.
Porque pode afetar as usinas nucleares, e aconteceu no Japão, um país bem preparado, imaginem o que acontecerá quando ocorrer um terremoto num país despreparado para terremotos e tsunamis, mas que possua usinas nucleares, e cito como exemplo o Brasil.
O Brasil não tem nenhum preparo para terremotos, mas tem usinas nucleares. Imaginem um terremoto, em Angra dos Reis, com a localização precária da nossa usina nuclear!
Angra dos Reis está no nível do mar, próxima do mar, construída numa região de difícil acesso, sem áreas de evacuação, numa região vulcânica adormecida, numa proximidade temerosa de umas das mais povoadas cidades do Brasil, que é a cidade do "Rio de Janeiro".
A contaminação nuclear ocorre nas correntes de ventos, afetando diretamente os países vizinhos, e espalhando-se por toda a Terra.
Produção de grãos, é outro ponto sensível que pode causar consequências globais.
Usinas de refinaria de petróleo explodindo, ou vazando óleo, é outra questão de segurança global.
Terremotos em áreas de silos de armazenamento de armas nucleares.
Drástica elevação do nível do mar em grandes cidades portuárias do Mundo, outra questão de segurança global.
Desaparecimento de Países e povos situados sobre ilhas, outro problema de segurança global.
Desastres ambientais provocando incontroláveis crises financeiras nos países afetados, com reflexos em seus parceiros econômicos,outra questão de segurança global.
Falta de água potável...
Impossibilidade de comunicação terrestre...
Falta de combustível...
Doenças provenientes de desastres ambientais podem contaminar todo o Planeta...
Falta de medicamentos, em casos de grandes calamidades públicas, afetam globalmente todas as nações...
As questões sanitárias, de segurança pública, falta de infra-estrutura, como ocorreu no Haiti, não são problemas localizados, mas que causam consequências globais.
Não creio que ainda exista tempo de reverter o quadro, cito o exemplo de duas notícias de hoje, divulgadas pelo Twitter, que demonstram claramente que ultrapassamos o ponto de retorno:
01 - @AP Waves of earthquakes detected at Iceland
02 - Pics of Greenland glacier melt shocksexpert - http://www.physorg.com/news/2011-09-pics-greenland-glacier-shocksexpert.html via @TopicfireNews
Caso ocorra a erupção do vulcão Katla, e desconfio que os cientistas não estejam certos em suas previsões otimistas, o Mundo moderno vai depara-se com uma situação de caos aéreo desconhecida, basta verificar o que aconteceu em 1893, quando não havia dependência global de aviões, estradas, e interdependências econômicas.
A segunda notícia, sobre o acelerado derretimento das geleiras, poderá elevar o nível dos oceanos, com consequências catastróficas nas instalações portuárias, afetando globalmente o transporte de produtos, via marítima.
Sem falar na qualidade do ar que respiramos, contaminação de alimentos, quebra das redes de comunicação, camada de ozônio, ataques terroristas oportunistas da situação, e outras inúmeras possibilidades.
Enfim, o quadro é preocupante, e compromete seriamente a segurança global.
RUI SANTOS DE SOUZA
Brasil, Curitiba, 06 de setembro de 2011 - 22h:08
#Katla #volcano #earthquakes #Iceland's via @AP
@AP Waves of earthquakes detected at Iceland's Katla volcano; scientists watching out for eruption: > http://apne.ws/qfoERs –CJ
Sea level
Sea level
From Wikipedia, the free encyclopedia
For the sea level change associated with the current episode of global warming, see current sea level rise.
For other uses, see Sea level (disambiguation).
Mean sea level (MSL) is a measure of the average height of the ocean's surface (such as the halfway point between the mean high tide and the mean low tide); used as a standard in reckoning land elevation.[1] MSL also plays an extremely important role inaviation, where standard sea level pressure is used as the measurement datum of altitude at flight levels.
To an operator of a tide gauge, MSL means the "still water level"—the level of the sea with motions such as wind waves averaged out—averaged over a period of time such that changes in sea level, e.g., due to thetides, also get averaged out. One measures the values of MSL in respect to the land. Hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates.
In the UK, mean sea level has been measured atNewlyn in Cornwall and Liverpool for decades, by tide gauges to provide Ordnance Datum for the zerometres height on UK maps.
Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA andCNES, TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Missionon the Jason-2 satellite in 2008.
[edit]Difficulties in utilization
To extend this definition far from the sea means comparing the local height of the mean sea surface with a "level" reference surface, or datum, called the geoid. In a state of rest or absence of external forces, the mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field. In reality, due to currents, air pressure variations, temperature and salinity variations, etc., this does not occur, not even as a long term average. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as (stationary)ocean surface topography. It varies globally in a range of ± 2 m.
Traditionally, one had to process sea-level measurements to take into account the effect of the 228-month Metonic cycle and the 223-month eclipse cycle on the tides. Mean sea level is not constant over the surface of the Earth. For instance, mean sea level at the Pacific end of the Panama Canalstands 20 cm (7.9 in) higher than at the Atlantic end.
[edit]Sea level and dry land
Several terms are used to describe the changing relationships between sea level and dry land. When the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps. The term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in the level of the land relative to a fixed point in the earth, possibly due to thermal buoyancy or tectonic effects; it implies no change in the volume of water in the oceans. The melting of glaciers at the end of ice ages is one example of eustatic sea level rise. The subsidence of land due to the withdrawal ofgroundwater is an isostatic cause of relative sea level rise.Paleoclimatologists can track sea level by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America. Areas like volcanic islands are experiencing relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink.
On other planets that lack a liquid ocean, planetologists can calculate a "mean altitude" by averaging the heights of all points on the surface. This altitude, sometimes referred to as a "sea level", serves equivalently as a reference for the height of planetary features.
[edit]Sea level change
[edit]Local and eustatic sea level
Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes. Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. Changes in ground-based ice volume also affect local and regional sea levels by the readjustment of the geoid and true polar wander. Atmospheric pressure, ocean currents and local ocean temperaturechanges can affect LMSL as well.
Eustatic change (as opposed to local change) results in an alteration to the global sea levels due to changes in either the volume of water in the world oceans or net changes in the volume of the ocean basins.[2]
[edit]Short term and periodic changes
There are many factors which can produce short-term (a few minutes to 14 months) changes in sea level.
| Periodic sea level changes | ||
|---|---|---|
| Diurnal and semidiurnal astronomical tides | 12–24 h P | 0.2–10+ m |
| Long-period tides | ||
| Rotational variations (Chandler wobble) | 14 month P | |
| Meteorological and oceanographic fluctuations | ||
| Atmospheric pressure | Hours to months | –0.7 to 1.3 m |
| Winds (storm surges) | 1–5 days | Up to 5 m |
| Evaporation and precipitation (may also follow long-term pattern) | Days to weeks | |
| Ocean surface topography (changes in water density and currents) | Days to weeks | Up to 1 m |
| El Niño/southern oscillation | 6 mo every 5–10 yr | Up to 0.6 m |
| Seasonal variations | ||
| Seasonal water balance among oceans (Atlantic, Pacific, Indian) | ||
| Seasonal variations in slope of water surface | ||
| River runoff/floods | 2 months | 1 m |
| Seasonal water density changes (temperature and salinity) | 6 months | 0.2 m |
| Seiches | ||
| Seiches (standing waves) | Minutes to hours | Up to 2 m |
| Earthquakes | ||
| Tsunamis (generate catastrophic long-period waves) | Hours | Up to 10 m |
| Abrupt change in land level | Minutes | Up to 10 m |
[edit]Long term changes
Various factors affect the volume or mass of the ocean, leading to long-term changes in eustatic sea level. The two primary influences are temperature (because the volume of waterdepends on temperature), and the mass of water locked up on land and sea as fresh water in rivers, lakes, glaciers, polar ice caps, and sea ice. Over much longer geological timescales, changes in the shape of the oceanic basins and in land/sea distribution will affect sea level.
Observational and modelling studies of mass loss from glaciers and ice caps indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century.
[edit]Glaciers and ice caps
Each year about 8 mm (0.3 inch) of water from the entire surface of the oceans falls into the Antarcticaand Greenland ice sheets as snowfall. If no ice returned to the oceans, sea level would drop 8 mm every year. To a first approximation, the same amount of water appeared to return to the ocean inicebergs and from ice melting at the edges. Scientists previously had estimated which is greater, ice going in or coming out, called the mass balance, important because it causes changes in global sea level. High-precision gravimetry from satellites in low-noise flight has since determined Greenland is losing billions of tons per year, in accordance with loss estimates from ground measurement.
Ice shelves float on the surface of the sea and, if they melt, to first order they do not change sea level. Likewise, the melting of the northern polar ice cap which is composed of floating pack ice would not significantly contribute to rising sea levels. Because they are lower in salinity, however, their melting would cause a very small increase in sea levels, so small that it is generally neglected.
- Scientists previously lacked knowledge of changes in terrestrial storage of water. Surveying of water retention by soil absorption and by reservoirs outright ("impoundment") at just under the volume of Lake Superior agreed with a dam-building peak in the 1930s-1970s timespan. Such impoundment masked tens of millimetres of sea level rise in that span. ( Impact of Artificial Reservoir Water Impoundment on Global Sea Level. B. F. Chao,* Y. H. Wu, Y. S. Li).
- If small glaciers and polar ice caps on the margins of Greenland and the Antarctic Peninsula melt, the projected rise in sea level will be around 0.5 m. Melting of the Greenland ice sheet would produce 7.2 m of sea-level rise, and melting of the Antarctic ice sheet would produce 61.1 m of sea level rise.[3] The collapse of the grounded interior reservoir of the West Antarctic Ice Sheet would raise sea level by 5–6 m.[4]
- The snowline altitude is the altitude of the lowest elevation interval in which minimum annual snow cover exceeds 50%. This ranges from about 5,500 metres above sea-level at the equator down to sea level at about 70° N&S latitude, depending on regional temperature amelioration effects.Permafrost then appears at sea level and extends deeper below sea level polewards.
- As most of the Greenland and Antarctic ice sheets lie above the snowline and/or base of the permafrost zone, they cannot melt in a timeframe much less than several millennia; therefore it is likely that they will not, through melting, contribute significantly to sea level rise in the coming century. They can, however, do so through acceleration in flow and enhanced iceberg calving.
- Climate changes during the 20th century are estimated from modelling studies to have led to contributions of between –0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and runoff).
- Estimates suggest that Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long-term adjustment to the end of the last ice age.
The current rise in sea level observed from tide gauges, of about 1.8 mm/yr, is within the estimate range from the combination of factors above[5] but active research continues in this field. The terrestrial storage term, thought to be highly uncertain, is no longer positive, and shown to be quite large.
[edit]Geological influences
At times during Earth's long history, the configuration of the continents and seafloor have changed due to plate tectonics. This affects global sea level by determining the depths of the ocean basins and how glacial-interglacial cycles distribute ice across the Earth.
The depth of the ocean basins is a function of the age of oceanic lithosphere: as lithosphere becomes older, it becomes denser and sinks. Therefore, a configuration with many smalloceanic plates that rapidly recycle lithosphere will produce shallower ocean basins and (all other things being equal) higher sea levels. A configuration with fewer plates and more cold, dense oceanic lithosphere, on the other hand, will result in deeper ocean basins and lower sea levels.
When there were large amounts of continental crust near the poles, the rock record shows unusually low sea levels during ice ages, because there was lots of polar land mass upon which snow and ice could accumulate. During times when the land masses clustered around the equator, ice ages had much less effect on sea level.
Over most of geologic time, long-term sea level has been higher than today (see graph above). Only at the Permian-Triassic boundary ~250 million years ago was long-term sea level lower than today. Long term changes in sea level are the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term.[6]
During the glacial/interglacial cycles over the past few million years, sea level has varied by somewhat more than a hundred metres. This is primarily due to the growth and decay of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea.
The Mediterranean Basin's gradual growth as the Neotethys basin, begun in the Jurassic, did not suddenly affect ocean levels. While the Mediterranean was forming during the past 100 million years, the average ocean level was generally 200 metres above current levels. However, the largest known example of marine flooding was when the Atlantic breached the Strait of Gibraltar at the end of theMessinian Salinity Crisis about 5.2 million years ago. This restored Mediterranean sea levels at the sudden end of the period when that basin had dried up, apparently due to geologic forces in the area of the Strait.
| Long-term causes | Range of effect | Vertical effect |
|---|---|---|
| Change in volume of ocean basins | ||
| Plate tectonics and seafloor spreading (plate divergence/convergence) and change in seafloor elevation (mid-ocean volcanism) | Eustatic | 0.01 mm/yr |
| Marine sedimentation | Eustatic | < 0.01 mm/yr |
| Change in mass of ocean water | ||
| Melting or accumulation of continental ice | Eustatic | 10 mm/yr |
| • Climate changes during the 20th century | ||
| •• Antarctica (the results of increasing precipitation) | Eustatic | -0.2 to 0.0 mm/yr |
| •• Greenland (from changes in both precipitation and runoff) | Eustatic | 0.0 to 0.1 mm/yr |
| • Long-term adjustment to the end of the last ice age | ||
| •• Greenland and Antarctica contribution over 20th century | Eustatic | 0.0 to 0.5 mm/yr |
| Release of water from earth's interior | Eustatic | |
| Release or accumulation of continental hydrologic reservoirs | Eustatic | |
| Uplift or subsidence of Earth's surface (Isostasy) | ||
| Thermal-isostasy (temperature/density changes in earth's interior) | Local effect | |
| Glacio-isostasy (loading or unloading of ice) | Local effect | 10 mm/yr |
| Hydro-isostasy (loading or unloading of water) | Local effect | |
| Volcano-isostasy (magmatic extrusions) | Local effect | |
| Sediment-isostasy (deposition and erosion of sediments) | Local effect | < 4 mm/yr |
| Tectonic uplift/subsidence | ||
| Vertical and horizontal motions of crust (in response to fault motions) | Local effect | 1–3 mm/yr |
| Sediment compaction | ||
| Sediment compression into denser matrix (particularly significant in and near river deltas) | Local effect | |
| Loss of interstitial fluids (withdrawal of groundwater or oil) | Local effect | ≤ 55 mm/yr |
| Earthquake-induced vibration | Local effect | |
| Departure from geoid | ||
| Shifts in hydrosphere, aesthenosphere, core-mantle interface | Local effect | |
| Shifts in earth's rotation, axis of spin, and precession of equinox | Eustatic | |
| External gravitational changes | Eustatic | |
| Evaporation and precipitation (if due to a long-term pattern) | Local effect | |
[edit]Changes through geologic time
Sea level has changed over geologic time. As the graph shows, sea level today is very near the lowest level ever attained (the lowest level occurred at thePermian-Triassic boundary about 250 million years ago).
During the most recent ice age (at its maximum about 20,000 years ago) the world's sea level was about 130 m lower than today, due to the large amount ofsea water that had evaporated and been deposited assnow and ice, mostly in the Laurentide ice sheet. The majority of this had melted by about 10,000 years ago.
Hundreds of similar glacial cycles have occurred throughout the Earth's history. Geologists who study the positions of coastal sediment deposits through time have noted dozens of similar basinward shifts of shorelines associated with a later recovery. This results in sedimentary cycles which in some cases can be correlated around the world with great confidence. This relatively new branch of geological science linking eustatic sea level to sedimentary deposits is called sequence stratigraphy.
The most up-to-date chronology of sea level change during the Phanerozoic shows the following long term trends:[7]
- Gradually rising sea level through the Cambrian
- Relatively stable sea level in the Ordovician, with a large drop associated with the end-Ordovician glaciation
- Relative stability at the lower level during the Silurian
- A gradual fall through the Devonian, continuing through the Mississippian to long-term low at the Mississippian/Pennsylvanian boundary
- A gradual rise until the start of the Permian, followed by a gentle decrease lasting until theMesozoic.
[edit]Recent changes
Main article: Current sea level rise
For at least the last 100 years, sea level has been rising at an average rate of about 1.8 mm per year.[8] The majority of this rise can be attributed to the increase in temperature of the sea and the resulting thermal expansion of sea water. Additional contributions come from water sources on land such as melting snow and glaciers (see global warming).[9]
[edit]Aviation
Using pressure to measure altitude results in two other types of altitude. Distance above true or MSL(mean sea level) is the next best measurement to absolute. MSL altitude is the distance above where sea level would be if there were no land. If one knows the elevation of terrain, the distance above theground is calculated by a simple subtraction.
An MSL altitude—called pressure altitude by pilots—is useful for predicting physiological responses in unpressurized aircraft (see hypoxia). It also correlates with engine, propeller, and wing performance, which all decrease in thinner air.
Pilots can estimate height above terrain with an altimeter set to a defined barometric pressure. Generally, the pressure used to set the altimeter is the barometric pressure that would exist at MSL in the region being flown over. This pressure is referred to as either QNH or "altimeter" and is transmitted to the pilot by radio from air traffic control (ATC) or an Automatic Terminal Information Service (ATIS). Since the terrain elevation is also referenced to MSL, the pilot can estimate height above ground by subtracting the terrain altitude from the altimeter reading. Aviation charts are divided into boxes and the maximum terrain altitude from MSL in each box is clearly indicated. Once above the transition altitude (see below), the altimeter is set to the international standard atmosphere (ISA) pressure at MSL which is 1013.2 HPa or 29.92 inHg.[10]
[edit]Flight level
MSL is useful for aircraft to avoid terrain, but at high enough altitudes, there is no terrain to avoid. Above that level, pilots are primarily interested in avoiding each other, so adjust their altimeter to standard temperature and pressure conditions (average sea level pressure and temperature) and disregard actual barometric pressure—until descending below transition level. To distinguish from MSL, such altitudes are called flight levels. Standard pilot shorthand is to express flight level as hundreds of feet, so FL 240 is 24,000 feet (7,300 m). Pilots use the international standard pressure setting of 1013.25 hPa (29.92 inHg) when referring to Flight Levels. The altitude at which aircraft are mandated to set their altimeter to flight levels is called "transition altitude". It varies from country to country. For example in the U.S. it is 18,000 feet, in many European countries it is 3,000 or 5,000 feet.
[edit]See also
- Above mean sea level
- Flood myth
- Geopotential height
- List of places on land with elevations below sea level
- Marine terrace
- Normal height
- Normaal Amsterdams Peil
- Normalhöhennull
- North West Shelf Operational Oceanographic System
- Orthometric height
- Sea level rise
- Standard sea level
- World Geodetic System
- Meltwater pulse 1A
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