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World's Tallest Structures

World's tallest structures

Until the mid 20th century the record for the world's tallest structure was relatively clearly defined (see table below.) Since that time however, more debate and confusion has been present over the criteria and definitions involved. In terms of absolute height, most of the tallest structures are the dozens of radio and television broadcasting towers that are around 2000 feet (610 meters) tall. Tall-structure enthusiasts debate:
- whether guy-wire–supported structures should be eligible to be counted
- whether only habitable height counts and if so;
- whether observation galleries on communication towers make them into habitable buildings
- whether roof-top antennas can be counted towards height of buildings (the debate over this has especially focused on the fact that things that look like spires can be either classified as an antenna or an "architectural detail")
- whether structures currently under construction can be included in the list
- whether structures rising out of water should have their below-water height included.

Tallest structures

Tallest Structure by Category spire spire The tallest currently standing structure, including those structures which are partially under water, is the Mars Platform in the Gulf of Mexico, at 990.6 m (3,250 ft). It is a tension-leg platform, meaning that it consists of a deck located atop a hull which is connected to pontoons located far below the water surface, which provide bouyancy support. The structure is connected to foundation piles on the sea floor by rigid tendons, which are analogous to guy-wires. As this oil and natural gas platform is partially supported by buoyancy, some critics argue that the below-water height should not be counted, in the same manner as the underground 'height' of buildings is not taken into account. The Mars Platform, while still standing and predominantly intact, is currently not functioning due to the effects of Hurricane Katrina in late August of 2005. The platform was engineered to withstand 22 m (72 ft) waves and 225 km/h (120 mph) winds simultaneously; however, winds alone from Katrina were estimated to be in the 265 to 280 km/h (165 to 175 mph) range in the vicinity of the platform.
- The structural height of the above-deck portion of the platform was temporarily affected by as much as 20 m (65 ft). Hurricane Katrina The tallest currently standing structure on land is the KVLY-TV mast near Mayville, North Dakota, at 629 m (2,063 ft). It is a transmission antenna, consisting of a bare metal structure supported by guy-wires. The Warsaw radio mast at Gabin-Konstantynow near Warsaw, Poland at 645 m (2,115 ft) was taller, but it collapsed on August 8, 1991. Masts such as these are generally not considered 'tall buildings', primarilly because they are not self-supporting. They require guy wires to remain upright. For greater detail on communication masts, see either List of the world's tallest structures, List of masts, or Table of masts. The Petronius Platform stands 610 m (2,001 ft) tall, making it the tallest freestanding structure in the world. However, as this oil and natural gas platform is partially supported by buoyancy, some critics argue that the below-water height should not be counted, in the same manner as the underground 'height' of buildings is not taken into account. The CN Tower in Toronto stands at 553.33 m (1,815 ft) tall, and it is the tallest freestanding structure above ground. The tallest tower built of lattice steel is Kiev TV Tower with a height of 386 metres. Built in 1934 and demolished in 1945, the tallest tower ever built of wood was the 190 metre high radio tower of the transmitter Mühlacker in Germany. The tallest tower built of wood is currently the transmission tower of the transmitter Gliwice in Poland at 118 meters.

Way of comparison

There are two ways of comparison, the CTBUH way (explained later in this article) and the AA Skyscraper way. All About Skyscrapers (AA Skyscrapers) divided the comparison of structures into seven different categories.

Tallest buildings

All About Skyscrapers Up until 1998 the tallest building status was essentially uncontested. Counting buildings as structures with floors throughout, New York City's World Trade Center was the tallest including the antennas, Sears Tower in Chicago excluding the antennas. As antennas were usually excluded, Sears Tower was counted as the tallest. When Petronas Twin Towers in Kuala Lumpur, Malaysia was built, some felt that the "spire" extending to 9 meters higher than the roof of the Sears Tower was just added to "cheat" its way into the spot as tallest building. Excluding the spire, the Petronas Towers were not taller than the Sears Tower. Therefore, before the Petronas Towers were completed, the Council on Tall Buildings and Urban Habitat defined four categories in which the "world's tallest building" can be measured: # Height to the structural or architectural top (including spires and pinnacles, but not antennas, masts or flagpoles) # Height to the highest occupied floor # Height to the top of the roof # Height to the top of antenna The height is measured from the sidewalk level of the main entrance. In all of these categories, Sears Tower had held the top spot. After Petronas was built, Sears Tower became second in the first category only. On April 20, 2004, the Taipei 101 in Taipei, Taiwan was completed. Its completion gave it the record for the first category. Today, the Taipei 101 leads in the first category with 508 m (1,667 ft); in the second category with an occupied floor at 438 m (1,437 ft); and in the third category with 448 m (1,470 ft). The first category was formerly held by the Petronas Twin Towers with 452 m (1,483 ft), and before that by Sears Tower with 443 m (1,448 ft). The second category was held by the Sears Tower, with 435 m (1,431 ft). The third category was formerly held by the Sears Tower with 442 m (1,445 ft). The Sears Tower still leads in the fourth category with 529 m (1,736 ft), previously held by the World Trade Center until its destruction in 2001; its antenna included, it measured 536 m (1,758 ft). The World Trade Center became the world's tallest buildings to be demolished–indeed, its site entered the record books twice on September 11, 2001, in that category, replacing the Singer Building, which once stood a block from the WTC site. The Ostankino Tower and the CN Tower are excluded from these categories because they are not "habitable buildings", which are defined as frame structures made with floors and walls throughout. History of Record Holders in each CTBUH category

Tallest buildings in world history

Currently-standing tallest skyscrapers

Listed by height to the architectural top. Note that this list, with the exception of the comparison section, is limited to a certain type of structure, and and is characterized by a very specific type of height measurement. Most of the tallest structures in the world are guyed broadcasting towers. The structures on this list are not sorted by the absolute highest point on the building, due to the nature of the skyscrapers. ¹ Height for inhabited buildings (with stories) does not include TV towers and antennas.
² The tallest tower in the Southern Hemisphere. Source: Council on Tall Buildings and Urban Habitat.

Proposed record-breaking structures

CTBUH CTBUH In 1956, Frank Lloyd Wright proposed a structure known as The Illinois, which would have been one mile (1609 m) high. This structure was considered by many both technically impossible, and wholly unneeded. Since that time some 4000 ft (1220 m) tall or higher skyscrapers or pyramids have been proposed as population pressures have seemed to indicate a need for them, but as of now, no structure approaching the height of The Illinois is past a planning stage. (See X-Seed 4000 and Sky City 1000) The UK architectural firm, Eric Kuhne and Associates, based in London, is in talks with the Kuwaiti Government about building a 1,001 meter tall tower in Madinat al-Hareer. The proposed solar chimney referred to as Solar Tower Buronga in Buronga, New South Wales, Australia would be 1,000 m (3,281 ft) tall. Engineering feasibility has been demonstrated to the satisfaction of consulting engineers, and construction is a matter of financial viability. The 492 m (1,614 ft; roof height) Shanghai World Financial Center in Shanghai, China has proposed completion in 2007, but has been delayed by evaluation of soil stability. A competing on-going project for the world's tallest is the 490 m (1,608 ft) Union Square Phase 7 in Hong Kong, also scheduled for completion in 2007. This would make either building the tallest under categories 2 and 3 by the CTBUH. The Freedom Tower of the new World Trade Center in New York City will reach 1,776 ft (541.3 metres) to its spire and about 1,368 ft (416.9 metres) to its roof once completed in 2011. This would make it the tallest building under categories 1 and 4 by the CTBUH, if no other record-breakers were built until then. The cornerstone was laid on July 4, 2004. Burj Dubai is a 705-metre (2,313-foot) skyscraper currently under development in Dubai, United Arab Emirates. Designed to be completed around 2008, this would put it at the number one spot in all four of CTBUH's categories, as well as make it the tallest manmade structure of any kind in history. The new Guangdong TV Tower at Guangzhou, China may also become one of the world's tallest structures. There are some plans for a 609.6 metre high free-standing TV tower at Bayonne, New Jersey. Maharishi Mahesh Yogi announced his own "world's tallest" proposal, the 677m-tall pyramid-shaped World Centre of Vedic Learning, in 1998. Serious thought and design work has been invested in a concept called the Space elevator, which could conceivably extend from ground level to past geosynchronous orbit; a height of nearly 50,000 km. Although the current state-of-the-art in technology cannot produce the materials needed for such an engineering feat, it is not too fantastic to foresee that it could someday be built, thus shattering the current record for the tallest structure by a factor of 100,000. Throughout the internet many building design proposals can be found, several of which surpass the height of Taipei 101, including Twin Towers 2.

Other proposed very tall towers

Radio masts taller than 600 metres

Towers/Skyscrapers

- TV tower of Djakarta [http://www.skyscrapercity.com/showthread.php?t=208756].

External links

- [http://www.skyscraperpage.com/ SkyscraperPage]
- [http://www.skyscrapercity.info/ SkyscraperCity]
- [http://www.skyscrapercity.com/ SkyscraperCity forum]
- [http://www.emporis.com/ Emporis]
- [http://www.guinnessworldrecords.com Guinness Book of world Records]
- [http://www.guinnessworldrecords.com/gwr5/content_pages/record.asp?recordid=50105 Guinness Entry for 'Tallest Office Building']
- [http://www.guinnessworldrecords.com/gwr5/content_pages/record.asp?recordid=49675 Guinness Entry for 'Tallest Building']
- http://www.skyscrapernews.com
- [http://www.allaboutskyscrapers.com/ All About Skyscrapers]
- http://www.infoplease.com/ipa/A0001338.html
- http://www.xs4all.nl/~hnetten/tallest.html
- http://www.civl.port.ac.uk/comp_prog/weird/tallest.html
- http://www.soyouwanna.com/site/toptens/buildings/buildings.html Category:Buildings and structures Structures
- Tallest

Antenna (electronics)

] Most simply, an antenna (U.S.) or aerial (UK) is an electronic component designed to transmit or receive radio waves. The words "antenna" and "aerial" are used throughout this article with precisely the same meaning. More specifically, an antenna is an arrangement of conductors designed to radiate (transmit) an electromagnetic field in response to an applied alternating electromotive force (EMF) and the associated alternating electric current. Alternatively, if an antenna is placed into an electromagnetic field, that field will induce an alternating current upon the antenna, and EMF between its terminals. See radio frequency induction.

Overview

There are two fundamental types of antennas. The first type is omni and the second type is directional. Omni type of antennas function in all possible directions whereas directional type of antennas work only in a single direction,i.e, "Line of Sight(LOS)". The first type couples to the electric field of an electromagnetic wave, and usually consists of a length of wire in which an electric charge moves back and forth (electric dipole). The second type couples to the magnetic field of an electromagnetic wave, and is usually a coil or loop of wire (magnetic dipole). By adding additional conducting rods or coils (called elements) and varying their length, spacing, and orientation, an antenna with specific desired properties can be created, such as a Yagi-Uda Antenna (often abbreviated to "Yagi"). Typically, antennas are designed to operate in a relatively narrow frequency range. The design criteria for receiving and transmitting antennas differ slightly, but generally an antenna can receive and transmit equally as well. This property is called reciprocity. The vast majority of antennas are simple vertical rods a quarter of a wavelength long. Such antennas are simple in construction, usually inexpensive, and both radiate in and receive from all horizontal directions (omnidirectional). One limitation of this antenna is that it does not radiate or receive in the direction in which the rod points. This region is called the antenna blind cone or null. Antennas have practical use for the transmission and reception of radio frequency signals (radio, TV, etc.), which can travel over great distances at the speed of light, and pass through nonconducting walls (although often there is a variable signal reduction depending on the type of wall, and natural rock can be very defective to radio signals).

Antenna effectiveness

Antennas may be omni and directional. There are several critical parameters that affect an antenna's performance and can be adjusted during the design process. These are resonant frequency, impedance, gain, aperture or radiation pattern, polarization, efficiency and bandwidth. Transmit antennas may also have a maximum power rating, and receive antennas differ in their noise rejection properties.

Resonant frequency

The resonant frequency is related to the electrical length of the antenna. This is usually the physical length of the wire multiplied by the ratio of the speed of wave propagation in the wire. Typically an antenna is tuned for a specific frequency, and is effective for a range of frequencies usually centered on that resonant frequency. However, the other properties of the antenna (especially radiation pattern and impedance) change with frequency, so the antenna's resonant frequency may merely be close to the center frequency of these other more important properties. Antennas can be made resonant on harmonic frequencies and with lengths that are fractions of the target frequency. Some antenna designs have multiple resonant frequencies, and some are relatively effective over a very broad range of frequencies. The most commonly known type of wide band aerial is the logarithmic or log aerial but its gain is usually much lower than that of a specific or narrower band aerial.

Impedance

Impedance is similar to refractive index in optics. As the electric wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance. At each interface, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface will reduce SWR and maximize power transfer through each part of the antenna system. Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

Gain

capacitor An antenna has gain if it radiates more strongly in one direction than in another. Gain is measured by comparing an antenna to a model antenna, typically the isotropic antenna which radiates equally in all directions. Often a dipole is also used as a practical reference as the isotropic source cannot be realised in practice, but it has 2.1 dB gain over an isotropic source. Most practical antennas radiate more than the isotropic antenna in some directions and less in others. Gain is inherently directional; the gain of an antenna is usually measured in the direction which it radiates best. Gain is one-dimensional. Gain does not mean that the antenna radiates more power than is fed to it, merely that it distributes the power more strongly in some directions than in others. Aperture, and radiation pattern are closely related to gain. Aperture is the shape of the "beam" cross section in the direction of highest gain, and is two-dimensional. (Sometimes aperture is expressed as the radius of the circle that approximates this cross section or the angle of the cone.) Radiation pattern is the three-dimensional plot of the gain, but usually only the two-dimensional horizontal and vertical cross sections of the radiation pattern are considered. Antennas with high gain typically show side lobes in the radiation pattern. Side lobes are peaks in gain other than the main lobe (the "beam"). Side lobes detract from the antenna quality whenever the system is being used to determine the direction of a signal, as in radar systems.

Efficiency

Efficiency is the ratio of power actually radiated to the power put into the antenna terminals. A dummy load may have a SWR of 1:1 but an efficiency of 0, as it absorbs all power and radiates none, showing that SWR alone is not an effective measure of an antenna's efficiency. Radiation in an antenna is caused by radiation resistance which can only be measured as part of total resistance including loss resistance.

Bandwidth

The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered around the resonant frequency. The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly and allowing the natural impedance to select the correct antenna. Small antennas are usually preferred for convenience, but there is a fundamental limit relating bandwidth, size and efficiency. Of the parameters above, SWR is most easily measured. Impedance can be measured with specialized equipment, as it relates to the complex SWR. Measuring radiation pattern requires a sophisticated setup including significant clear space (enough to get into the antenna's far field) or an anechoic chamber designed for antenna measurements, careful study of experiment geometry, and specialised measurement equipment such as robots that rotate the antenna during the measurements. Bandwidth depends on the overall effectiveness of the antenna, so all of these parameters must be understood to understand bandwidth. However, typically bandwidth is measured by only looking at SWR, i.e., by finding the frequency range over which the SWR is less than a given value. Bandwidth over which an antenna exhibits a particular radiation pattern might also be considered.

Polarization

The polarization of an antenna or orientation of the radio wave is determined by the electric field or E-plane. The ionosphere changes the polarization of signals unpredictably, so for signals which will be reflected by the ionosphere, polarization is not crucial. However, for line-of-sight communications, it can make a tremendous difference in signal quality to have the transmitter and receiver using the same polarization. Polarizations commonly considered are linear, such as vertical and horizontal, and circular, which is divided into right-hand and left-hand circular.

Transmission and receiving

All of these parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna, due to reciprocity. Impedance, however, is not applied in an obvious way; for impedance, the impedance at the load (where the power is consumed) is most critical. For a transmitting antenna, this is the antenna itself. For a receiving antenna, this is at the (radio) receiver rather than at the antenna. Antennas used for transmission have a maximum power rating, beyond which heating, arcing or sparking may occur in the components, which may cause them to be damaged or destroyed. Raising this maximum power rating usually requires larger and heavier components, which may require larger and heavier supporting structures. Of course, this is only a concern for transmitting antennas; the power received by an antenna rarely exceeds the microwatt range. If an antenna is to be used for reception at very low frequencies (below about ten megahertz), its noise rejection capabilities become important. At such frequencies, signals are reflected very effectively by the ionosphere; however, at these frequencies there are many forms of natural radio noise, including the noise produced by lightning. Successfully rejecting these forms of noise is an important antenna feature. For example, a small coil of wire with many turns is more able to reject such noise than a vertical antenna. However, the vertical will radiate much more effectively on transmit, where extraneous signals are not a concern.

Theoretical antenna types

- A dielectric resonator is a variation on the conventional antenna in which an insulator with a large dielectric constant is used to modify the electromagnetic field. It is claimed that the dielectric contains the antenna's near field and therefore prevents it from interfering with other nearby antennas or circuits, making it suitable for miniature equipment such as mobile phones.
- A feedhorn is an antenna system that handles the incoming waveform from the dish to the focal point. It usually comprises of a series of rings with decreasing radius in order to drive the signal to the polarizer.
- An isotropic radiator is an antenna that radiates equally in all directions. It is considered to be a point in space with no dimensions and no mass. Most antennas' gains are measured with reference to an isotropic radiator, and are rated in dBi (decibels with respect to an isotropic radiator). This antenna type is purely theoretical and is not achievable in real life.

Practical antenna models

There are many variations of antennas, but here are a few common models. More can be found in :Category:Radio frequency antenna types.
- The dipole antenna is simply two wires pointed in opposite directions arranged either horizontally or vertically, with one end of each wire connected to the radio and the other end hanging free in space. Variations of the dipole include the folded dipole and the whip antenna which is really just half of a dipole using a ground plane as the image of the second half. The dipole antenna is usually a multiple of a half wavelength long. For this reason, the dipole antenna is sometimes referred to as the half-wave antennna. Generally, the dipole is considered to be omnidirectional in the plane perpendicular to the axis of the antenna, but it has deep nulls in the directions of the axis. The popular J-pole antenna is a variation of the half dipole with a built in quarter wave transmission line impedance matching section.
- The yagi-Uda antenna is a directional variation of the dipole with parasitic elements added with functionality similar to adding a reflector and lenses (directors) to focus a filament lightbulb.
- The groundplane antenna takes the form of a driven vertical element 1/4 wave long in the center of a grounded plane 1/2 wave in diameter. The end of the vertical element nearest the ground plane is connected to the radio, and the far end is in hanging in free space. The ground plane can take the form of the natural Earth surface, or a network of wires and ground rods, or a solid metal sheet, or four wires arranged as two crossed dipoles and centrally connected to ground.
- The (large) loop antenna is similar to a dipole, except that the ends of the dipole are connected to form a circle, triangle (delta loop antenna) or square. Typically a loop is a multiple of a half or full wavelength in circumference. A circular loop gets higher gain (about 10%) than the other forms of large loop antenna, as gain of this antenna is directly proportional to the area enclosed by the loop, but circles can be hard to support in a flexible wire, making squares and triangles much more popular. Large loop antennas are more immune to localized noise partly due to lack of a need for a groundplane. The large loop has its strongest signal in the plane of the loop, and nulls in the axis perpendicular to the plane of the loop.
- The small loop antenna, also called the magnetic loop antenna is a loop of wire (in other words, both ends of the wire connect to the radio) less than a wavelength in circumference. Typically, the circumference is less than 1/10 for a receiving loop, and less than 1/4 for a transmitting loop. Unlike nearly all other antennas in this list, this antenna detects the magnetic component of the electromagnetic wave. As such, it is less sensitive to near field electric noise when properly shielded. The receiving aperture can be greatly increased by bringing the loop into resonance with a tuning capacitor. Due to the small size of the loop, the radiation pattern is 90 degrees from that of the large loop. The radiation pattern is perpendicular to the plane of the loop, with sharp nulls in the plane of the loop.
- The electrically short antenna is an open-end wire far less than 1/4 wavelength in length - in other words only one end of the antenna is connected to the radio, and the other end is hanging free in space. Unlike nearly all other antennas in this list, this antenna detects only the electric field of the wave instead of the electromagnetic field - think of the free end of the wire as measuring the voltage of that point in space, as opposed to measuring both the voltage and the magnetic field. Its receiving aperture can be greatly increased by increasing the voltage; by adding an inductor or resonator tuned to resonance with the signals of interest. Electrically short antennas are typically used where operating wavelength is large and space is limited, e.g. for mobile transceivers operating at long wavelengths.
- The microstrip antenna consists of a patch of metalization on a ground plane. These are low profile, light weight antennas, most suitable for aerospace and mobile applications. Because of their low power handling capability, these antennas can be used in low-power transmitting and receiving applications. Microstrip antennas are the most commonly used antennas in mobile communications, satellite links, W-LAN and so on because circuit functions can be directly integrated to the microstrip antenna to form compact tranceivers and spatial power combiners.
- The quad antenna is an array of square loops that vary in size. The quad is related to the loop in exactly the same way the yagi is related to the dipole. Typically, the quad needs fewer elements to get the same gain as a yagi. Variations of the quad include the delta loop antenna which uses a triangle instead of a square, requiring fewer supports for large wavelength antennas.
- The random wire antenna is simply a very long (greater than one wavelength) wire with one end connected to the radio and the other in free space, arranged in any way most convenient for the space available. Folding will reduce effectiveness and make theoretical analysis extremely difficult. (The added length helps more than the folding typically hurts.) Typically, a random wire antenna will also require an antenna tuner, as it might have a random impedance that varies nonlinearly with frequency.
- The Beverage antenna is a form of directional long-wire antenna which uses a resistive termination at one end and feed from the other.
- The helical antenna is a directional antenna suited for receiving signals that are either circular polarized or randomly polarized. These are usually used with satellites, and are frequently used for the driven element on a dish.
- The Phased array antenna is a group of independently fed active elements in which the relative phases of the respective signals feeding the elements are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. In plain language, this is a directional antenna that can be aimed without moving any parts.
- Synthetic aperture radar uses a series of observations separated in time and space to simulate a very large antenna. More generally, interferometry allows the combining of signals from several radio receivers or a single moving receiver.
- A trailing wire antenna is used by submarines when submerged. These antennas are designed to pick up transmissions in the low frequency (LF) and very low frequency (VLF) ranges.
- An evolved antenna refers to an antenna fully or substantially designed using a computer algorithm based on Darwinian evolution.

External links

- [http://hamradio.co.in/tcvr/antena.php Antenna] Antena for Ham / Amateur Radio
- [http://www.maxstream.net/helpdesk/article-27 dBi vs. dBd] How to measure antenna gain
- [http://www.radio-electronics.com/info/antennas/index.php Radio-Electronics.Com] Further information regarding antennas
- [http://www.dxzone.com/catalog/Antennas/ Antenna Plans] Over 400 amateur radio antenna plans and documents from [http://www.dxzone.com dxzone.com]
- [http://www.vias.org/simulations/simusoft_twoaerials.html Learning by Simulations] Interactive simulation of two coupled antennas
- [http://www.n0hr.com/total NØHR.com Best Ham Radio Links] Ham radio antenna sites sorted by band, design, and homebrew vs. commercial antenna products.
- Category:Amateur radio Category:Electrical components Category:Radio electronics ms:Antena ja:空中線

Spire

] A spire is a tapering conical or pyramidal structure on the top of a building, particularly a church tower. Etymologically, the word is derived from Anglo-Saxon, so it is related to "spear," rather than the Romance languages and "spirit." Symbolically, spires have two functions. The first is to proclaim a martial power. A spire, with its reminiscence of the spear point, gives the impression of strength. The second is to reach up toward the skies. The celestial and hopeful gesture of the spire is one reason for its association with religious buildings. As an architectural ornament, spires are most consistently found on Christian churches, where they replace the steeple. Although any denomination may choose to use a spire instead of a steeple, the lack of a cross on the structure is more common in Roman Catholic and other pre-Reformation churches. (Note, in the photo at right, that the spire serves as a platform for three bare crosses in imitation of Calvary, marking the center as Protestant (Anglican).) The battlements of cathedrals featured multiple spires in the Gothic style (in imitation of the secular military fortress). Gothic] Spires are also common and notable as solo structures. After contact with Egyptian architecture and the mania for Egyptian artifacts in the west in the 19th century, towers in the shape of obelisks enjoyed a vogue. When original obelisks could be imported, such as Cleopatra's needle in New York City, they were, but spires as memorial structures were popular in funerary architecture and public monuments (e.g. the Washington monument in Washington, DC) into the 20th century. In the Modernist movements of the 20th century, office towers in the form of free-standing spires also began to be built. Some famous buildings, such as the Space Needle in Seattle, Washington, use the spire as a testimony of civic power and hope; in the case of this example, it is also a reference to Seattle's participation in aerospace. A 1,776-foot (541-m) "Freedom Tower" is a projected feature of the 9/11 Memorial in New York City, and is to be topped by a spire. Of course, the philosophy behind a spire on one side of the Atlantic can be quite different from the interpretation in Europe. In Europe a spire on a church or cathedral is not just a symbol of piety, but cynically, also a symbol of the wealth and prestige of the order, or patron who commissioned the building. Whatever the reason for their erection, spires were an astounding architectural phenomenon during the medieval gothic period of architecture. Since that time nearly 700 years ago they have never really fallen out of fashion. In England, "spire" immediately brings to mind Salisbury Cathedral. Its 403-foot (123-m) spire, built between 1320 and 1380, is the tallest of the period anywhere in the world, and in its way is as remarkable as the Coliseum in Rome or the parthenon in Athens. A similar but slightly smaller spire was built at Leighton Buzzard in Bedfordshire, England, which indicates the popularity of the spire spreading across the country during this period. We will never know the true popularity of the medieval spire, as many more collapsed within a few years of building than ever survived to be recorded. In the United Kingdom spires generally tend to be reserved for ecclesiastical building, with the exception to this rule being the spire at Burghley House, built for Elizabeth I's Lord Chancellor in 1585. In the early Renaissance the spire was not restricted to the United Kingdom: the fashion spread across Europe. In Antwerp the 123-m spire was the tallest structure in the low countries for over five centuries. Between 1221 and 1457 richly decorated open spires were built for the Cathedral of Burgos in Spain, while at Ulm Cathedral in Germany the 529-foot (161-m) spire was built in the imported French Gothic style between 1377 and 1417. Interestingly, the Italians never really embraced the spire as an architectural feature, preferring the classical styles. The gothic style was a feature of Germanic northern Europe and was never to the Italian taste, and the few gothic buildings in Italy always seem incongruous. That is not to say that no one ever attempted to blend the classical styles with a spire, but this occurred much later. In 1822, in London, John Nash built All Souls' Church, Langham Place, a circular classical temple, with Ionic columns surmounted by a spire supported by Corinthian columns. Whether this is a happy marriage of styles or a rough admixture is a question of individual taste. Corinthian During the 19th century the Gothic revival knew no bounds. With advances in technology, steel production, and building techniques the spire enjoyed an unprecedented surge through architecture, Cologne Cathedral's famous spires, designed centuries earlier, where finally completed in this era. Later in the 19th century, Art Nouveau produced the most bizarre effects when incorporated into ecclesiastical architecture. It reached its most exaggerated point in the phenomenal spires of Sagrada Familia in Barcelona. Designed and begun by Antoni Gaudi in 1884, they were not completed until the 20th century. A cross between a stalagmite and a melting wedding cake, they cannot fail to amaze. As described earlier, the spire as an architectural form has continued to metamorphose and develop into more modern and even more fantastic forms, which in turn have inspired such sculptures the Spire of Dublin) throughout the 20th century, and will undoubtedly continue to do so in the 21st century.

Gulf of Mexico

The Gulf of Mexico is a major body of water bordered and nearly landlocked by North America. The gulf's eastern, north, and northwestern shores lie within the United States of America (specifically, the states of Florida, Alabama, Mississippi, Louisiana, and Texas); its southwestern and southern shores lie within Mexico (specifically, the states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatán, and Quintana Roo); on the southeast it is bordered by Cuba. It connects with the Atlantic Ocean via the Florida Straits between the U.S. and Cuba, and with the Caribbean Sea via the Yucatan Channel between Mexico and Cuba. (Note: In common usage, at least in the U.S., the term "Gulf Coast" usually refers to either the continuous portion of the coast running from Cape Sable, Florida, to Brownsville, Texas, or from Cape Sable, Florida, to the northern tip of the Yucatán Peninsula at Cabo Catoche, Quintana Roo. Both meanings exclude Cuba as well as the Florida Keys.) Florida Keys The total area of the Gulf of Mexico is approximately 615,000 mi² (1.6 million km²), the southern third of which lies within the tropics, and plunges to a depth of 2,080 fathoms (3804 m). This deepest part is Sigsbee Deep, an irregular trough more than 300 nautical miles (550 km) long, sometimes called the "Grand Canyon under the sea." The cooler water from the deep stimulates plankton growth, which attracts small fish, shrimp, and squid. [http://www.tsha.utexas.edu/handbook/online/articles/GG/rrg7.html 1] The Gulf Stream, a warm Atlantic Ocean current and one of the strongest ocean currents known, originates in the gulf. The gulf has been visited many times by powerful Atlantic hurricanes, some of which have caused extensive human death and other destruction (see 2005's Hurricane Katrina, for example). Tidal ranges are extremely small in the Gulf of Mexico due to the narrow connection with the ocean – much like the Mediterranean. The Bay of Campeche in Mexico constitutes a major arm of the Gulf of Mexico. Additionally, the gulf's shoreline is fringed by numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably the Mississippi River. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach. The continental shelf is quite wide at most points along the coast. The shelf is exploited for its oil by means of offshore drilling rigs, most of which are situated in the western gulf. Another important commercial activity is fishing; major catches include various fishes as well as shrimp and crabs, with oysters being harvested on a large scale from many of the bays and sounds. Other important industries along the coast include shipping, petrochemical processing and storage, paper manufacture, and tourism. Coastal cities of note include Tampa, St. Petersburg, Pensacola, Mobile, New Orleans, Beaumont, and Houston (all in the U.S.), Tampico, Tuxpam, Veracruz and Mérida (in Mexico), and Havana (in Cuba). The gulf's coastal areas were first settled by Native American groups, including those representing several of the early advanced cultures of Mexico. During the period of European exploration and colonization the entire region became a theatre of contention between the Spanish, French and English. The present-day culture of the coastal region is primarily Spanish-American (Mexico, Cuba) and Anglo-American (U.S.). English A point of interest about the Gulf is that 65 million years ago, the Chicxulub crater was formed when a large meteorite hit the earth. It is hypothesized that this impact was the asteroid that caused the extinction of the dinosaurs. [http://web.ukonline.co.uk/a.buckley/dino.htm]

Pollution

Because of the ever increasing amount of nitrogen and phosphates dissolved in the waters of the Gulf of Mexico, pollution has more than doubled since 1950. Current estimates suggest that three times as much nitrogen is being carried into the Gulf today compared with levels 30 years ago or at any time in history. Blooms of photosynthesizers die and sink, and the processes of their decay exhausts the available supplies of oxygen dissolved in the water. Every summer there is now an area south of the Louisiana coastline, larger than the U.S. state of Massachusetts at over 7,000 mi² (18,000 km²) that is hypoxic. These waters do not carry enough oxygen to sustain marine life. This annually enlarging "dead zone" is a major threat to the fishing industry and to public health. Also, there are frequent "red tide" algae blooms that kill fish and marine mammals and cause respiratory problems in humans and some domestic animals when the blooms reach close to shore. This has especially been plaguing the southwest Florida coast, from the Keys to north of Pasco County, Florida.

External links

- [http://www.epa.gov/water/yearofcleanwater/docs/Hypoxia_Factsheet.pdf EPA factsheet on hypoxia]
- [http://www.ncat.org/nutrients/hypoxia/hypoxia.html Gulf of Mexico hypoxia] Mexico ko:멕시코 만 ja:メキシコ湾

Tension-leg platform

A Tension-leg platform is a vertically moored floating structure normally used for the offshore production of oil or gas, and is particularly suited for water depths greater than 300 metres (about 1000 ft). The platform is permanently moored by means of tethers or tendons grouped at each of the structure's corners. A group of tethers is called a tension leg. A feature of the design of the tethers is that they have relatively high axial stiffness (low elasticity), such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This makes for a cheaper well completion and gives better control over the production from the oil or gas reservoir. Category:Oil platforms Category:Petroleum production

Oil

:For the heavy metal band, see Oil (band). For the language family, see Langue d'oïl. Oil is a generic term for organic liquids that are not miscible with water. The name comes from Latin oleum (olive oil). Oil is frequently used to refer to petroleum (crude oil), the type of oil that is pumped up from the ground and currently serves as a major energy source and important part of the world economy. The term foreign oil is used in the United States to refer to imported petroleum, a major point of concern since the 1973 energy crisis.

Types of oil

- Cooking oil
- Essential oil
- Fish oil
- Gear oil
- Heating oil
- Mineral oil
- Motor oil
- Painting oil
- Petroleum (crude oil)
- Stomach oil
- Synthetic oil
- Tramp oil is the unwanted oil that becomes mixed with cutting fluids
- Vegetable oil ja:油 simple:Oil

Natural gas

Natural gas (commonly refered to as gas in many countries, but note that gas is also an American and Canadian shortening of gasoline) is a gaseous fossil fuel consisting primarily of methane. It is found in oil fields and natural gas fields, as well as—in smaller quantities—in coal beds. When methane-rich gasses are produced by the anaerobic decay of non-fossil organic material, these are referred to as biogas. Sources of biogas include swamps (swamp gas), marshes (marsh gas), landfills (landfill gas), sewage sludge and manure (by way of anaerobic digesters) and flatulence (most notably in cattle.) Methane is an extremely efficient greenhouse gas which may contribute to enhanced global warming when free in the atmosphere, and such free methane, would then be considered a pollutant rather than a useful energy resource. However, methane in the atmosphere reacts with ozone, producing carbon dioxide and water, so that the greenhouse effect of released methane is relatively short-lived. Also, natural gas, when burned, produces much less greenhouse gas than more carboniferous fuel sources, such as coal. As a pollutant, significant biological sources of methane are termites, cattle (ruminants) and cultivation (estimated emissions are 15, 75 and 100 million tons per year respectively). Landfill gas, which is approximately equal parts methane and carbon dioxide, also contains trace volatile organic compounds (VOCs), many of which are known to be precursors to photochemical smog. Because landfill gas contains these trace compounds, The US Federal Clean Air Act (Part 40 of the Federal Code of Regulations) requires landfill owners to estimate the quantity of VOCs emitted. If the estimated VOC emissions exceeds 50 metric tons, then the landfill owner is required to collect the landfill gas, and treat it to remove the entrained VOCs. Usually, treatment is by combustion of the landfill gas. Because of the remoteness of landfill sites, it is sometimes not economically feasible to produce electricity from the gas.

Chemical composition and energy content

Chemical composition

The primary component of natural gas is methane (C H₄), the shortest and lightest hydrocarbon molecule. It may also contain heavier gaseous hydrocarbons such as ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀), as well as other sulphur containing gases, in varying amounts, see also natural gas condensate. Organosulfur compounds and Hydrogen sulfide (H₂S see acid gas) are common contaminants, which must be removed prior to most uses. Gas with a significant amount of sulfur impurities is termed "sour". Natural gas is tasteless and odorless. However, before gas is distributed to end-users, it is odorized by adding mercaptans, to assist in leak detection. Natrual gas is, in itself, harmless to the human body -- unlike carbon monoxide, for instance, it is not a poison. Natural gas can kill, however if it is present in large concentrations -- and thus reduces the amount of oxygen available in the air, such that the amount of oxygen remaining won't sustain life. Natural gas can also kill through an explosion. Natural gas is lighter than air, and so tends to dissipate. But when natural gas is contained, such as within a house or in a tent (perhaps put over a house for fumigation) gas concentrations can reach explosive proportions and trigger very powerful blasts that can level houses, and even neighborhoods. Methane has a Lower Explosive Limit of 5% in air, and an Upper Explosive Limit of 15%. Explosive concerns with compressed natural gas used in vehicles are almost non-existant, due the the escaping nature of the gas, and the need to maintain concentrations between 5% and 15% to trigger explosions.

Energy content and statistics

Combustion of one cubic metre of commercial quality natural gas yields 38 MJ (10.6 kWh). Equivilently, one cubic foot of natural gas produces just over 1000 British Thermal Units (BTUs). In the USA, at retail, natural gas is often sold in units of therms (th), which equals 100,000 BTU. Wholesale transactions are generally done in decatherms (DTh), or in thousand decatherms (MDth), or in million decatherms (MMDth). A million decatherms is roughly a billion cubic feet of natural gas. The US uses roughly 60,000 billion cubic feet, or 60 tera decatherms (TDth), each year.

Storage and transport

cubic metre The major difficulty in the use of natural gas is transportation and storage. Natural gas pipelines are economical, but are impractical across oceans. Many existing pipelines in North America are close to reaching their capacity prompting some politicians in colder climates to speak publicly of potential shortages. Liquefied natural gas tankers are also used, but have higher cost and safety problems. In many cases, as with oil fields the natural gas which is recovered in the course of recovering petroleum cannot be profitably sold, and is simply burned at the oil field (known as flaring). This wasteful practice is now illegal in many countries, especially since it adds greenhouse gas pollution to the earth's atmosphere, and since a profitable method may be found in the future. Instead, the gas is instead re-injected back into the formation for later recovery. This is known as Underground Gas Storage (UGS). It also assists oil pumping by keeping underground pressures higher. In Saudi Arabia, in the late 1970s, a "Master Gas System" was created, ending the need for flaring. The natural gas is used to generate electricity and heat for desalinization. Natural gas is often stored in underground caverns formed inside salt domes as Compressed Natural Gas (CNG), or in tanks as Liquefied Natural Gas (LNG).

Natural gas crisis

Many politicians and prominent figures in North America have spoken publicly about a possible natural gas crisis. This includes former Secretary of Energy Spencer Abraham, Chairman of the Federal Reserve Alan Greenspan, Ontario Minister of Energy Dwight Duncan. The natural gas crisis is typically described by the increasing price of natural gas in the U.S. over the last few years due to the decline in indigenous supply and the increase in demand for electricity generation. Indigenous supply has not truly fallen -- but it has leveled off (no matter how many new straws we put into the ground, we still get about the same amount of natural gas each year). But because of the continuing growth in demand, and the temporary but dramatic hit to production that came from Hurricanes Katrina and Rita, the price has become so high that many industrial users, mainly in the petrochemical industry, have closed their plants causing loss of jobs. Greenspan has suggested that a solution to the natural gas crisis is the importation of LNG. This solution is both capital intensive and politically charged due to the NIMBY syndrome and the public perception that LNG terminals are explosive risks, especially in the wake of the 9/11 terrorist attacks in the United States. The U.S. Department of Homeland Security is responsible for maintaining their security, and the security arrangements during the 2004 Democratic Convention in Boston, Massachusetts, home to one of only six LNG terminals in the United States, were extraordinarily tight. Infrastructure issues to establish new or expanded LNG terminals are non-trivial, to say the least, especially when taken together with high capitalization needs of each subsystem. LNG terminals require a very spacious—at least 38.5m deep—harbor, as well as being sheltered from wind and waves. These "suitable" sites are thus deep in well populated seaports, which are also burdened with right of way concerns for LNG pipelines, or conversely, required to also host the LNG expansion plant facilities and end use (petrochemical) plants amidst the high population densities of major cities (with the associated fumes, multiple serious risks to safety). Typically, to attain "well sheltered" waters, suitable harbor sites are well up rivers or estuaries, which are unlikely to be dredged deep enough. Since these very large vessels must move slowly and ponderously in restricted waters, the transit times to and from the terminal become costly, as multiple tugs and security boats shelter and safeguard the large vessels. Operationally, LNG tankers are (for example, in Boston) effectively given sole use of the harbor, forced to arrive and depart during non-peak hours, and precluded from occupying the same harbor until the first is well departed. These factors increase operating costs and make capital investment less attractive. To substantially increase the amount of LNG used to supply natural gas to North America, not only must "re-gasification" plants be built on North American shores -- difficult for the reasons stated above -- someone also must but substantial, new liquification stations in Indonesia, the Middle East, and Afreca, in order to concetrate the gas generally assoicated with oil production in those areas. A substantial explansion of the fleet of LNG tankers also must occur to move the hugh amount of fuel needed to make up for the coming shortfall in North America.

Uses

Power generation

Natural gas is important as a major source for electricity generation through the use of gas turbines and steam turbines. Particularly high efficiencies can be achieved through combining gas turbines with a steam turbine in combined cycle mode. Environmentally, natural gas burns cleaner than other fossil fuels, such as oil and coal, and produces fewer greenhouse gases. For an equivalent amount of heat, burning natural gas produces about 30% less carbon dioxide than burning petroleum and about 45% less than burning coal. [http://www.naturalgas.org/environment/naturalgas.asp#greenhouse] Combined cycle power generation using natural gas is thus the cleanest source of power available using fossil fuels, and this technology is widely used wherever gas can be obtained at a reasonable cost. Fuel cell technology may eventually provide cleaner options for converting natural gas into electricity, but as yet it is not price-competitive. Also, Natural gas is said to peak around the year 2030, 20 years after the peak of oil. It is also projected that the world's supply of natural gas should finish in the mid 2080's(2085).

Natural gas vehicles

Compressed natural gas (and LPG) is used as a clean alternative to other automobile fuels. As of 2003, the countries with the largest number of natural gas vehicles were Argentina, Brazil, Pakistan, Italy, and India. The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines, partially due to the fact that natural gas engine function using the Otto Cycle, but research is on its way to improve the process (Westport-Cycle). Here is a link to a general discription of this technology. http://www.nesea.org/greencarclub/factsheets_naturalgas.pdf#search='explosion%20ratio%20natural%20gas'

Residental domestic use

Westport-Cycle Natural gas is supplied to homes where it is used for such purposes as cooking and heating/cooling. CNG is used in rural homes without connections to piped-in public utility services, or with portable grills.

Fertilizer

Natural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production.

Other

Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, and other products.

Sources

Natural gas is commercially produced from oil fields and natural gas fields. Gas produced from oil wells is called casinghead gas or associated gas. Natural gas can also be produced by treating coal chemically, although coal gasification is not economic at current gas prices. The biggest natural gas field is located in Urengoy, Russia, with a reserve of 10.0 · 10¹² m³. See also List of natural gas fields.

Possible future sources

One experimental idea is to use the methane gas that is naturally produced from landfills to supply power to cities. Tests have shown that methane gas could be a financially sustainable power source. There are plans in Ontario to capture the biogas, methane gasses rising from the manure of cattle caged in a factory farm, and to use that gas to provide power to a small town. There is also the possibility that with the source separation of organic materials from the waste stream that by using an anaerobic digester, the methane can be used to produce useable energy. This can be improved by adding other organic material (plants as well as slaughter house waste) to the digester.

Safety

In any form, a concentrated, rotten-egg like scent (such as mercaptan/ethanethiol) is deliberately added to the otherwise colorless and odorless gas, so that leaks can be detected by smell before an explosion occurs. In mines, sensors are used and mining apparatus has been specifically developed to avoid ignition sources (e.g. the Davy lamp). Adding scent to natural gas began after the 1937 New London School explosion. The buildup of gas in the school went unnoticed, and killed three hundred students and faculty when it ignited. Explosions caused by natural gas leaks occur a few times each year. Individual homes, small businesses and boats are most frequently affected when an internal leak builds up gas inside the structure. Frequently, the blast will be enough to significantly damage a building but leave it standing. In these cases, the people inside tend to have minor to moderate injuries. Occasionally, the gas can collect in high enough quantities to cause a deadly explosion, disintegrating one or more buildings in the process. The gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if weather conditions are right. Also, considering the tens of millions of structures that use the fuel, the individual risk of using natural gas is very low. Contrary to popular belief, natural gas and the odorant that's added to it is non-toxic, though some gas fields yield 'acid gas' or 'sour gas' containing hydrogen sulfide. This untreated gas is toxic. Extraction of natural gas (or oil) leads to decrease in pressure in the reservoir. This in turn may lead to subsidence at ground level. Subsidence may affect ecosystems, waterways, sewer and water supply systems, foundations etc.

External links

Natural gas vehicles

- [http://www.iangv.org/jaytech/default.php?PageID=130 International Natural Gas Vehicle Statistics]
- [http://www.naftc.wvu.edu Alternative Fuel Vehicle Training] From the National Alternative Fuels Training Consortium.
- [http://www.iangv.org IANGV - International Association for Natural Gas Vehicles]

North America

- [http://www.energyquest.ca.gov/transportation/CNG.html What is Compressed Natural Gas?]
- [http://www.wokr13.tv/news/local/story.aspx?content_id=B841A1FA-0DAA-4EA3-88E5-EFB409DF3F38 Could CNG work in America?]
- [http://www.naturalgas.org/index.asp Natural Gas Supply Association]
- [http://www.gastechnology.org/webroot/app/xn/xd.aspx?it=enweb&xd=gtihome.xml Institute of Gas Technology]

South Asia

- India: [http://cities.expressindia.com/fullstory.php?newsid=85665 How New Delhi used CNG to ease pollution]

Pollution and allergy

- [http://www.geocities.com/RainForest/6847/#quote1 Pollutant chemical pollutant chemical that can worsen both classical allergy and chemical sensitivity]. Category:Natural gas ms:Gas asli ja:天然ガス simple:Natural gas

Hurricane Katrina

__NOEDITSECTION__ : This article is about the 2005 hurricane. For other storms with this name, see Hurricane Katrina (disambiguation). Hurricane Katrina was the eleventh named tropical storm, fourth hurricane, third major hurricane, and first Category 5 hurricane of the 2005 Atlantic hurricane season. It was the third most powerful storm of the season, behind Hurricane Wilma and Hurricane Rita, and the sixth-strongest storm ever recorded in the Atlantic basin. It first made landfall as a Category 1 hurricane just north of Miami, Florida on August 25, 2005, resulting in a dozen deaths in South Florida, spawning several tornadoes which happened not to strike any dwellings. Katrina strengthened to a 175 m.p.h. storm in the Gulf of Mexico, one of the 5 most powerful ever recorded. It weakened by the time it made landfall again on August 29 along the Central Gulf Coast near Buras-Triumph, Louisiana, as a Category 4 storm. The sheer physical size of Katrina caused devastation far from the eye of the hurricane. It was possibly the largest hurricane of its strength ever recorded. Judging the size of storms in the pre-satellite era is difficult. On August 29, its storm surge soon breached the levee system that protected New Orleans from Lake Pontchartrain and the Mississippi River. Most of the city was subsequently flooded mainly by water from the lake. Heavy damage was also inflicted onto the coasts of Mississippi and Alabama, causing Katrina to become the most destructive and costliest natural disaster in the history of the United States, and likely the deadliest since 1928. The official death toll now stands at 1,383, the third highest in US history (behind the Galveston Hurricane of 1900 and the Okeechobee Hurricane of 1928). 6,644 others remain unaccounted for, with 1,300 of them "feared dead". The damage is estimated to be from $100 to $200 billion [http://www.srh.noaa.gov/data/NHC/TWSAT], at least double from previously most expensive Hurricane Andrew making Katrina the most expensive natural disaster in U.S. history. Over a million people were displaced — a humanitarian crisis on a scale unseen in the U.S. since the Great Depression. In Louisiana, the hurricane's eye made landfall at 6:10am CDT on Monday, August 29. After 11:00 am CDT, several sections of the levee system in New Orleans collapsed. By early September, people were being forcibly evacuated, mostly by bus to neighboring states. Federal disaster declarations blanketed 90,000 square miles (233,000 km²) of the United States, an area almost as large as the United Kingdom. The hurricane left an estimated five million people without power, and it may take up to four months for all power to be restored. On September 3, Homeland Security Secretary Michael Chertoff described the aftermath of Hurricane Katrina as "probably the worst catastrophe, or set of catastrophes" in the country's history, referring to the hurricane itself plus the flooding of New Orleans. For a timeline of events leading up to Hurricane Katrina through to the aftermath of the hurricane, see Timeline of Hurricane Katrina.

Storm history

The U.S. National Hurricane Center (NHC) reported on August 23 that Tropical Depression Twelve had formed over the southeastern Bahamas. The numbering of the system was debated, as Tropical Depression Twelve formed partially from the remains of Tropical Depression Ten. The naming and numbering rules at the NHC require a system to keep the same identity if it dies, then regenerates, which would normally have caused this storm to remain number Ten. However, the NHC gave this storm a new number because a second disturbance merged with the remains of Tropical Depression Ten on August 21, and there is no way to tell whether the remnants of Tropical Depression Ten should be credited with this storm. (This is different from Hurricane Ivan in the 2004 season, when the NHC ruled that Ivan did indeed reform; the remnant of Ivan that regenerated in the Gulf of Mexico was a distinct system from the moment Ivan originally dissipated to the moment it regained tropical storm strength [http://www.nhc.noaa.gov/archive/2005/dis/al122005.discus.001.shtml].) The system was upgraded to Tropical Storm Katrina on the morning of August 24. Katrina became the fourth hurricane of the 2005 season on August 25 and made landfall later that day around 6:30 p.m. between Hallandale Beach and Aventura, Florida. Florida Katrina weakened over land on August 26, becoming a tropical storm. The initial National Hurricane Center forecasts predicted that Katrina would enter the Gulf of Mexico and begin turning northward, eventually hitting the Florida Panhandle. Katrina, however, continued a west track, eventually turning to the west-southwest. When the storm began turning to the northwest, New Orleans was its aim. On August 27, the storm was upgraded to Category 3 intensity (major hurricane) and at 12:40 a.m. CDT (0540 UTC) on August 28, Katrina was upgraded to Category 4. Later that morning, Katrina went through a period of rapid intensification, becoming a Category Five storm on the Saffir-Simpson Hurricane Scale. Katrina had maximum sustained winds of 175 mph (280 km/h), gusts of 215 mph (344 km/h) and a central pressure of 26.75 inches, or 906 mbar (hPa), by 1:00 p.m. CDT. It later reached a minimum pressure of 26.64 inches (902 mbar), making it, at the time, the fourth most intense Atlantic Basin hurricane on record (Hurricane Rita and Hurricane Wilma in 2005 would later surpass Katrina). Katrina's rapid intensification was due in part to its movement over the Gulf Loop Current. Katrina made landfall on August 29 as a Category 4 hurricane with sustained winds of 145 mph (235 km/h) with higher gusts, at 6:10 a.m. CDT near Buras-Triumph, Louisiana. Hurricane force winds extended outward 120 statute miles (190 km); pressure was 918 mbar (27.11 inHg) and forward speed 15 mph (10 km/h). Making its way up the eastern Louisiana coastline, most communities in Plaquemines and St. Bernard Parish, and Slidell in St. Tammany Parish, were severely damaged by storm surge and the strong winds of the eyewall, which also grazed eastern New Orleans. A few hours later, it made landfall for a third time near the Louisiana/Mississippi border with 125 mph (200 km/h) Category 3 sustained winds. However, because the storm was so large, extreme damaging eyewall winds and the strong northeastern quadrant of the storm, pushing record storm surges onshore, smashed the entire Mississippi Gulf Coast, including towns in Mississippi such as Waveland, Bay St. Louis, Pass Christian, Long Beach, Gulfport, Biloxi, Ocean Springs, Gautier and Pascagoula, and, in Alabama, Bayou La Batre. As Katrina moved inland diagonally over Mississippi, high winds cut a swath of damage that affected almost the entire state. Bayou La Batre (1700 UTC).]] Bayou La Batre aircraft on August 28, 2005, before the storm made landfall.]] Katrina weakened thereafter, losing hurricane strength more than 150 miles (160 km) inland, near Jackson, Mississippi. It was downgraded to a tropical depression near Clarksville, Tennessee and continued to race northward. Katrina continued to affect the central U.S. as it moved north, and was last seen in the eastern Great Lakes region on August 31. Before being absorbed by a frontal boundary, Katrina's last known position was over southeast Quebec and northern New Brunswick. On August 31, Katrina became a powerful extratropical low in the province of Quebec that gave 50 to 170 mm (1.97 to 6.69 in) of rain in 12 hours; also numerous wind gusts from 50 to 98 km/h (31 to 61 mph) were reported in southern and eastern Quebec. In the region of Saguenay and Cote-Nord, rain caused breakdown and failure in roads. The Cote-Nord region was isolated from rest of Quebec for at least 1 week. Its lowest minimum pressure at landfall was 27.108 inches (918 mbar) (hPa), making it the third strongest hurricane on record to make landfall on the United States. A 10 to 30 foot (3 to 10 m) storm surge came ashore on over 200 continuous miles of coastline, from southeast Louisiana, including Mississippi and Alabama, through to the Florida panhandle. The 30 foot (10 m) storm surge recorded at Biloxi, Mississippi is the highest ever observed in America. Record storm surges that had not occurred in at least the last 150 years, inundated the entire Mississippi coastline, destroying many historic homes. The storm surge in Mobile, Alabama was the highest in that location since 1917, besting the category 3 Hurricane Frederic which hit the city directly in 1979. At 11 p.m. EDT on August 31 (0300 UTC, September 1), U.S. government weather officials announced that the center of the remnant low of what was Katrina had been completely absorbed by a frontal boundary in southeastern Canada, with no discernible circulation. The Hydrometeorological Prediction Center's last [http://www.hpc.ncep.noaa.gov/discussions/tcpat2.html public advisory on Katrina] was at 11 p.m. EDT on August 31 and the Canadian Hurricane Centre's last [http://www.atl.ec.gc.ca/weather/hurricane/bulletins/20050831114442.Katrina.txt.en public advisory on Katrina] was at 9 a.m. EDT on August 31.

Tornadoes

There were at least 36 confirmed tornadoes associated with Hurricane Katrina, with 11 tornadoes in Mississippi, 4 tornadoes in Alabama, 15 tornadoes in Georgia, 1 tornado in Virginia, and 5 tornadoes in Pennsylvania. Most of the tornadoes were rated F0 or F1, but three tornadoes were rated F2 in Georgia, and two were rated F2 in Mississippi. Tornadoes were reported in places including Adams and Cumberland Counties in Pennsylvania, in Fauquier County, Virginia, in Carroll County, Georgia, in Carrollton, Georgia, in White County, Georgia, in Helen, Georgia, and in Fort Valley, Georgia. Several other weak tornadoes were reported by television stations in and around Mobile, Alabama, and Oktibbeha County, Lowdnes County and Harrison County in Mississippi. One death was reported from an F2 tornado near Roopville, Georgia, and 500,000 chickens were killed or set free after about 15 poultry houses were damaged. Several injuries were reported with other tornadoes across Georgia. There was major damage in Helen, Georgia by an F2 tornado, which destroyed homes and a hotel. In Fort Valley, Georgia, another tornado ripped through a credit union and destroyed local houses and trees.

Preparations and expectations before landfall

Previous short term preparations and expectations

Advance weather forecasts

Many living in the area felt that south Florida had minimal advance warning when Katrina strengthened from a tropical storm to a hurricane in one day, and struck southern Florida later that same day, on August 25. Even so, NHC forecasts showed Katrina strengthening into a hurricane well in advance of landfall, and hurricane watches and warnings were indeed issued nearly 36 and 24 hours, respectively, before hurricane conditions were felt in the area (watches and warnings are supposed to be issued at those time periods)[http://www.nhc.noaa.gov/archive/2005/pub/al122005.public.004.shtml?],[http://www.nhc.noaa.gov/archive/2005/dis/al122005.discus.006.shtml?]. By August 26 the possibility of "unprecedented cataclysm" was already being considered. Some computer models were putting New Orleans right in the center of their track probabilities, and the chances of a direct hit were forecast at nearly 90%. This scenario was considered a "potential catastrophe" because 80% of the New Orleans metropolitan area is below sea level. Louisiana governor Kathleen Babineaux Blanco declared a state of emergency for state agencies. On August 27, after Katrina crossed southern Florida and strengthened to Category 3, President George W. Bush declared a state of emergency in Louisiana, Alabama, and Mississippi two days before the hurricane made landfall[http://www.whitehouse.gov/news/releases/2005/08/20050827-1.html]. On August 28 the National Weather Service issued a [http://wikisource.org/wiki/August_28_2005_10:11_AM_CDT_NOAA_Bulletin bulletin] predicting "devastating" damage rivaling the intensity of Hurricane Camille. At a news conference, New Orleans Mayor Ray Nagin ordered a mandatory evacuation of the city with Gov. Blanco standing beside him.

Transportation and infrastructure

Ray Nagin On Sunday, August 28, Canadian National Railway (CN) suspended all rail traffic on its lines south of McComb, Mississippi (lines owned by its subsidiary Illinois Central Railroad that extend into New Orleans), in anticipation of damage from the hurricane. To help ease the resumption of services after the storm passes, CN also issued an embargo with the Association of American Railroads against all deliveries to points south of Osyka, Mississippi. CSX Transportation also suspended service south of Montgomery, Alabama until further notice. The CSX (former Louisville and Nashville Railroad) main line from Mobile to New Orleans is believed to have suffered extensive damage, especially in coastal Mississippi, but repair crews were not able to reach most parts of the line as of August 30. Amtrak, America's rail passenger carrier, announced that the southbound City of New Orleans passenger trains from Chicago, Illinois, on August 29 and through September 3 would terminate in Memphis, Tennessee, rather than their usual destination of New Orleans; the corresponding northbound trains will also originate in Memphis. The southbound Crescent from New York City, for the same period terminated in Atlanta, Georgia, with the corresponding northbound trains originating in Atlanta as well. Amtrak's westbound Sunset Limited originated in San Antonio, Texas, rather than its normal origin point of Orlando, Florida. Amtrak announced that no alternate transportation options would be made available into or out of the affected area [http://www.amtrak.com/servlet/ContentServer?pagename=Amtrak/am2Copy/Simple_Copy_Popup&c=am2Copy&cid=1093554014709]. Orlando, Florida The Waterford nuclear power plant was shut down on Sunday, August 28, before Katrina's arrival. The State Departments of Transportation in the affected area, in conjunction with the Federal Highway Administration, have a huge job to rebuild the critical highways for access to the region. Interstate 10 seems, at first glance, to be the most critical to repair, especially the twin bridges over Lake Pontchartrain, which were destroyed. These are "lifelines" to the east, but assessing the damage, there will be no quick fix. These costs could run into many billions of dollars.

Experts: Predictions, Risks and Preparations

The risk of devastation from a direct hit was well documented. The New Orleans Times-Picayune newspaper ran a series on the risk in 2002; the series predicted many of the events that happened in 2005, including the breakdown of the levee system. "It's only a matter of time before South Louisiana takes a direct hit from a major hurricane. Billions have been spent to protect us, but we grow more vulnerable every day." New Orleans Times-Picayune June 23 - 27 June 2002 [http://www.nola.com/washingaway/] National Geographic ran a feature in October 2004 [http://www3.nationalgeographic.com/ngm/0410/feature5/]. Scientific American covered the topic thoroughly in an October 2001 piece titled "Drowning New Orleans" [http://www.sciam.com/article.cfm?chanID=sa006&articleID=00060286-CB58-1315-8B5883414B7F0000]. Walter Williams did a serious short feature on it called "New Orleans: The Natural History", in which an expert said a direct hit by a hurricane could damage the city for six months [http://soundwaves.usgs.gov/2002/09/outreach3.html]. CSO magazine ran an interview with the National Weather Service's Gary Woodall in which he listed six steps that citizens and company executives can take to be prepared for hurricanes such as this. [http://www.csoonline.com/read/090105/safekeeping.html]

Evacuation and emergency shelters

"Not since the Dust Bowl of the 1930s or the end of the Civil War in the 1860s have so many Americans been on the move from a single event."[http://seattletimes.nwsource.com/html/hurricanekatrina/2002486584_katuproot11.html] At a news conference 10 a.m. on August 28, shortly after Katrina was upgraded to a Category 5 storm, New Orleans mayor Ray Nagin, calling Katrina "a storm that most of us have long feared," ordered the first ever mandatory evacuation of the city. Contraflow lane reversal on Interstate 10 leading west and Interstates 55 and 59 leading north from New Orleans was ended that afternoon. Two weeks after the storm, over half the States were involved in providing shelter for evacuees. By four weeks after the storm, evacuees had been registered in all 50 states and in almost half the Zip codes of the U.S. Three quarters of evacuees had stayed within 250 miles but tens of thousands had located more than 1000 miles away. The Louisiana State Evacuation Plan declares "The primary means of hurricane evacuation will be personal vehicles. School and municipal buses, government-owned vehicles and vehicles provided by volunteer agencies may be used to provide transportation for individuals who lack transportation and require assistance in evacuating" in Part 1 Section D. The state evacuation plan also assigns the responsibility of evacuation to each Parish with the language [the parish will] "Conduct and control local evacuation in parishes located in the risk area and manage reception and shelter operations in parishes located in the host area" in Part 1 Section D. The state evacuation plan also assigns the responsibility of evacuation of the sick and those needing assistance to the owners of the facilities with the language: "Hospitals, nursing homes, group homes, etc. will have pre-determined evacuation and/or refuge plans if evacuation becomes necessary. All facilities will have approved Multi-Hazard Emergency Operations Plans as mandated by the State of Louisiana, Dept. of Health and Hospitals (DHH). Before operating permits are given to homes/hospitals, emergency precautions are to be taken, such as the placement of emergency supplies and equipment (i.e., generators and potable water) on upper floors.." in Part 1 Section D. As many of these facilities relied on the same bus companies and ambulance services for evacuation, several were unable to evacuate before the storm hit, resulting in the deaths of their occupants. In addition to residents, many tourists were stranded. Fuel and rental cars were in short supply; also, Greyhound bus and Amtrak train service were halted well before the hurricane made landfall [http://www.burlingtonfreepress.com/apps/pbcs.dll/article?AID=/20050905/NEWS01/509050309/1009&theme=]. Future analysis of motor vehicle registration, census and Social Security Information, and death certificates may help to provide more clarity. During the Hurricane Ivan evacuation, 600,000 people remained in the city [http://www.blackpressusa.com/News/Article.asp?SID=3&Title=Hot+Stories&NewsID=4744]. Mandatory evacuations were also ordered for Assumption, Jefferson (Kenner, Metairie, as well as Grand Isle and other low lying areas), Lafourche (outside the floodgates), Plaquemines, St. Bernard, St. Charles and St. James parishes and parts of St. Tammany, Tangipahoa and Terrebonne parishes in Louisiana. In Alabama, evacuations were ordered for parts of Mobile and Baldwin counties (including Gulf Shores). In Mississippi, evacuations were ordered for parts of Hancock, Harrison and Jackson counties.

New Orleans shelters

Louisiana Superdome

Jackson Jackson On August 28, as Hurricane Katrina grew into a Category 5 storm that had yet to make landfall, Nagin established several "refuges of last resort" for citizens who could not leave the city, including the massive Louisiana Superdome. The New Orleans Times - Picayune reported that the Louisiana National Guard delivered three truckloads of water and seven truckloads of MRE's, enough to supply 15,000 people for three days according to Col. Jay Mayeaux, deputy director of the Department of Homeland Security's Office of Emergency Preparedness [http://www.nola.com/newslogs/breakingtp/index.ssf?/mtlogs/nola_Times-Picayune/archives/2005_08_