Pacific decadal oscillation
The Pacific Decadal Oscillation is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, 1977; this climate pattern affects coastal sea and continental surface air temperatures from Alaska to California. During a "warm", or "positive", the west Pacific becomes cooler and part of the eastern ocean warms; the Pacific Decadal Oscillation was named by Steven R. Hare, who noticed it while studying salmon production pattern results in 1997; the Pacific Decadal Oscillation index is the leading empirical orthogonal function of monthly sea surface temperature anomalies over the North Pacific after the global average sea surface temperature has been removed.
This PDO index is the standardized principal component time series. A PDO'signal' has been reconstructed as far back as 1661 through tree-ring chronologies in the Baja California area. Several studies have indicated that the PDO index can be reconstructed as the superimposition of tropical forcing and extra-tropical processes. Thus, unlike ENSO, the PDO is not a single physical mode of ocean variability, but rather the sum of several processes with different dynamic origins. At inter-annual time scales the PDO index is reconstructed as the sum of random and ENSO induced variability in the Aleutian low, whereas on decadal timescales ENSO teleconnections, stochastic atmospheric forcing and changes in the North Pacific oceanic gyre circulation contribute equally. Additionally sea surface temperature anomalies have some winter to winter persistence due to the reemergence mechanism. ENSO teleconnections, the atmospheric bridge ENSO can influence the global circulation pattern thousands of kilometers away from the equatorial Pacific through the "atmospheric bridge".
During El Nino events, deep convection and heat transfer to the troposphere is enhanced over the anomalously warm sea surface temperature, this ENSO-related tropical forcing generates Rossby waves that propagate poleward and eastward and are subsequently refracted back from the pole to the tropics. The planetary waves form at preferred locations both in the North and South Pacific Ocean, the teleconnection pattern is established within 2–6 weeks. ENSO driven patterns modify surface temperature, humidity and the distribution of clouds over the North Pacific that alter surface heat and freshwater fluxes and thus induce sea surface temperature and mixed layer depth anomalies; the atmospheric bridge is more effective during boreal winter when the deepened Aleutian low results in stronger and cold northwesterly winds over the central Pacific and warm/humid southerly winds along the North American west coast, the associated changes in the surface heat fluxes and to a lesser extent Ekman transport creates negative sea surface temperature anomalies and a deepened MLD in the central pacific and warm the ocean from the Hawaii to the Bering Sea.
SST reemergence Midlatitude SST anomaly patterns tend to recur from one winter to the next but not during the intervening summer, this process occurs because of the strong mixed layer seasonal cycle. The mixed layer depth over the North Pacific is deeper 100-200m, in winter than it is in summer and thus SST anomalies that form during winter and extend to the base of the mixed layer are sequestered beneath the shallow summer mixed layer when it reforms in late spring and are insulated from the air-sea heat flux; when the mixed layer deepens again in the following autumn/early winter the anomalies may again influence the surface. This process has been named "reemergence mechanism" by Alexander and Deser and is observed over much of the North Pacific Ocean although it is more effective in the west where the winter mixed layer is deeper and the seasonal cycle greater. Stochastic atmospheric forcingLong term sea surface temperature variation may be induced by random atmospheric forcings that are integrated and reddened into the ocean mixed layer.
The stochastic climate model paradigm was proposed by Frankignoul and Hasselmann, in this model a stochastic forcing represented by the passage of storms alter the ocean mixed layer temperature via surface energy fluxes and Ekman currents and the system is damped due to the enhanced heat loss to the atmosphere over the anomalously warm SST via turbulent energy and longwave radiative fluxes, in the simple case of a linear negative feedback the model can be written as the separable ordinary differential equation: d y d t = v − λ y where v is the random atmospheric forcing, λ is the damping rate and y is the response. The variance spectrum of y is: G = F w 2 + λ 2 {\displaystyle {G={\frac {w^+\la
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, the rotation of the Earth. Tide tables can be used for any given locale to find the predicted times and amplitude; the predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide, the amphidromic systems of the oceans, the shape of the coastline and near-shore bathymetry. They are however only predictions, the actual time and height of the tide is affected by wind and atmospheric pressure. Many shorelines experience low tides each day. Other locations have a diurnal tide -- one low tide each day. A "mixed tide" – two uneven magnitude tides a day – is a third regular category. Tides vary on timescales ranging from hours to years due to a number of factors, which determine the lunitidal interval. To make accurate records, tide gauges at fixed stations measure water level over time. Gauges ignore; these data are compared to the reference level called mean sea level.
While tides are the largest source of short-term sea-level fluctuations, sea levels are subject to forces such as wind and barometric pressure changes, resulting in storm surges in shallow seas and near coasts. Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field that varies in time and space is present. For example, the shape of the solid part of the Earth is affected by Earth tide, though this is not as seen as the water tidal movements. Tide changes proceed via the following stages: Sea level rises over several hours, covering the intertidal zone; the water rises to its highest level. Sea level falls over several hours; the water stops reaching low tide. Oscillating currents produced by tides are known as tidal streams; the moment that the tidal current ceases is called slack tide. The tide reverses direction and is said to be turning. Slack water occurs near high water and low water, but there are locations where the moments of slack tide differ from those of high and low water.
Tides are semi-diurnal, or diurnal. The two high waters on a given day are not the same height; the two low waters each day are the higher low water and the lower low water. The daily inequality is not consistent and is small when the Moon is over the Equator. From the highest level to the lowest: Highest astronomical tide – The highest tide which can be predicted to occur. Note that meteorological conditions may add extra height to the HAT. Mean high water springs – The average of the two high tides on the days of spring tides. Mean high water neaps – The average of the two high tides on the days of neap tides. Mean sea level – This is the average sea level; the MSL is constant for any location over a long period. Mean low water neaps – The average of the two low tides on the days of neap tides. Mean low water springs – The average of the two low tides on the days of spring tides. Lowest astronomical tide and Chart Datum – The lowest tide which can be predicted to occur. Modern charts use this as the chart datum.
Note that under certain meteorological conditions the water may fall lower than this meaning that there is less water than shown on charts. Tidal constituents are the net result of multiple influences impacting tidal changes over certain periods of time. Primary constituents include the Earth's rotation, the position of the Moon and Sun relative to the Earth, the Moon's altitude above the Earth's Equator, bathymetry. Variations with periods of less than half a day are called harmonic constituents. Conversely, cycles of days, months, or years are referred to as long period constituents. Tidal forces affect the entire earth. In contrast, the atmosphere is much more fluid and compressible so its surface moves by kilometers, in the sense of the contour level of a particular low pressure in the outer atmosphere. In most locations, the largest constituent is the "principal lunar semi-diurnal" known as the M2 tidal constituent, its period is about 12 hours and 25.2 minutes half a tidal lunar day, the average time separating one lunar zenith from the next, thus is the time required for the Earth to rotate once relative to the Moon.
Simple tide clocks track this constituent. The lunar day is longer than the Earth day because the Moon orbits in the same direction the Earth spins; this is analogous to the minute hand on a watch crossing the hour hand at 12:00 and again at about 1:05½. The Moon orbits the Earth in the same direction as the Earth rotates on its axis, so it takes more than a day—about 24 hours and 50 minutes—for the Moon to return to the same location in the sky. During this time, it has passed overhead once and underfoot once, so in many places the period of strongest tidal forcing is the above-mentioned, about 12 hours and 25 minutes; the moment of highest tide is not when the Moon is nearest to zenith or nadir, but the period of the forcing still determines the time between high tides. Because the gravitational field created by the Moon weakens
Altimeter
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, related to the term bathymetry, the measurement of depth under water. Altitude can be determined based on the measurement of atmospheric pressure; the greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft, skydivers use wrist-mounted versions for similar purposes. Hikers and mountain climbers use wrist-mounted or hand-held altimeters, in addition to other navigational tools such as a map, magnetic compass, or GPS receiver; the calibration of an altimeter follows the equation z = c T log , where c is a constant, T is the absolute temperature, P is the pressure at altitude z, Po is the pressure at sea level. The constant c depends on the molar mass of the air.
However, one must be aware that this type of altimeter relies on "density altitude" and its readings can vary by hundreds of feet owing to a sudden change in air pressure, such as from a cold front, without any actual change in altitude. A barometric altimeter, used along with a topographic map, can help to verify one's location, it is more reliable, more accurate, than a GPS receiver for measuring altitude. Because barometric pressure changes with the weather, hikers must periodically re-calibrate their altimeters when they reach a known altitude, such as a trail junction or peak marked on a topographical map. An altimeter is the most important piece of skydiving equipment, after the parachute itself. Altitude awareness is crucial at all times during the jump, determines the appropriate response to maintain safety. Since altitude awareness is so important in skydiving, there is a wide variety of altimeter designs made for use in the sport, a non-student skydiver will use two or more altimeters in a single jump: Hand, wrist or chest-mounted mechanical analogue visual altimeters.
This is the most basic and common type, is used by all student skydivers. The common design has a face marked from 0 to 4000 m, on which an arrow points to the current altitude; the face plate sports sections prominently marked with yellow and red signifying the recommended deployment altitude, as well as emergency procedure decision altitude. A mechanical altimeter has a knob that needs to be manually adjusted to make it point to 0 on the ground before jump, if the landing spot is not at the same altitude as the takeoff spot, the user needs to adjust it appropriately; some advanced electronic altimeters are available which make use of the familiar analogue display, despite internally operating digitally. Digital visual altimeters, mounted on the wrist or hand; this type always operates electronically, conveys the altitude as a number, rather than a pointer on a dial. Since these altimeters contain all the electronic circuitry necessary for altitude calculation, they are equipped with auxiliary functions such as electronic logbook, real-time jump profile replay, speed indication, simulator mode for use in ground training, etc.
An electronic altimeter is activated on the ground before the jump, calibrates automatically to point to 0. It is thus essential that the user not turn it on earlier than necessary to avoid, for example, the drive to a dropzone located at a different altitude than one's home which could cause a fatal false reading. If the intended landing zone is at a different elevation than the takeoff point, the user needs to input the appropriate offset by using a designated function. Audible altimeters; these are inserted into one's helmet, emit a warning tone at a predefined altitude. Contemporary audibles have evolved from their crude beginnings, sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched electronic logbook with data transfer to a PC for analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are auxiliary devices, do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness.
The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves. Auxiliary visual altimeters; these do not show the precise altitude, but rather help maintain a general indicator in one's peripheral vision. They might either operate in tandem with an audible equipped with an appropriate port, in which case they emit warning flashes complementing the audible tones, or be standalone and use another display mode, such as showing either green or red light depending on the altitude. Speaking al
Poseidon
Poseidon was one of the Twelve Olympians in ancient Greek religion and myth. He was god of other waters. In pre-Olympian Bronze Age Greece, he was venerated as a chief deity at Thebes, his Roman equivalent is Neptune. Poseidon was protector of seafarers, of many Hellenic cities and colonies. In Homer's Iliad, Poseidon supports the Greeks against the Trojans during the Trojan War. In the Odyssey, during the sea-voyage from Troy back home to Ithaca, the Greek hero Odysseus provokes Poseidon's fury by blinding his son, the Cyclops Polyphemus, resulting in Poseidon punishing him with storms, the complete loss of his ship and companions, a ten-year delay. Poseidon is the subject of a Homeric hymn. In Plato's Timaeus and Critias, the island of Atlantis was Poseidon's domain; the earliest attested occurrence of the name, written in Linear B, is Po-se-da-o or Po-se-da-wo-ne, which correspond to Ποσειδάων and Ποσειδάϝονος in Mycenean Greek. The form Ποτειδάϝων appears in Corinth. A common epithet of Poseidon is Ἐνοσίχθων Enosichthon, "Earth-shaker", an epithet, identified in Linear B, as, E-ne-si-da-o-ne, This recalls his epithets Ennosidas and Ennosigaios indicating the chthonic nature of Poseidon.
The origins of the name "Poseidon" are unclear. One theory breaks it down into an element meaning "husband" or "lord" and another element meaning "earth", producing something like lord or spouse of Da, i.e. of the earth. Walter Burkert finds that "the second element da- remains hopelessly ambiguous" and finds a "husband of Earth" reading "quite impossible to prove."Another theory interprets the second element as related to the word *δᾶϝον dâwon, "water". There is the possibility that the word has Pre-Greek origin. Plato in his dialogue Cratylus gives two alternative etymologies: either the sea restrained Poseidon when walking as a "foot-bond", or he "knew many things". At least a few sources deem Poseidon as a "prehellenic" word, considering an Indo-European etymology "quite pointless". If surviving Linear B clay tablets can be trusted, the name po-se-da-wo-ne occurs with greater frequency than does di-u-ja. A feminine variant, po-se-de-ia, is found, indicating a lost consort goddess, in effect the precursor of Amphitrite.
Poseidon carries the title wa-na-ka in Linear B inscriptions, as king of the underworld. The chthonic nature of Poseidon-Wanax is indicated by his title E-ne-si-da-o-ne in Mycenean Knossos and Pylos, a powerful attribute. In the cave of Amnisos Enesidaon is related with the cult of the goddess of childbirth, she was related with the annual birth of the divine child. During the Bronze Age, a goddess of nature, dominated both in Minoan and Mycenean cult, Wanax was her male companion in Mycenean cult, it is possible that Demeter appears as Da-ma-te in a Linear B inscription, however the interpretetion is still under dispute. In Linear B inscriptions found at Pylos, E-ne-si-da-o-ne is related with Poseidon, Si-to Po-tini-ja is related with Demeter. Tablets from Pylos record sacrificial goods destined for "the Two Queens and Poseidon"; the "Two Queens" may be related with Demeter and Persephone, or their precursors, goddesses who were not associated with Poseidon in periods. The illuminating exception is the archaic and localised myth of the stallion Poseidon and mare Demeter at Phigalia in isolated and conservative Arcadia, noted by Pausanias as having fallen into desuetude.
The violated Demeter was Demeter Erinys. In Arcadia, Demeter's mare-form was worshiped into historical times, her xoanon of Phigaleia shows. A Medusa type with a horse's head with snaky hair, holding a dove and a dolphin representing her power over air and water, it seems that the Arcadian myth is related with the first Greek speaking people who entered the region during the Bronze Age.. Their religious beliefs were mixed with the beliefs of the indigenous population, it is possible that the Greeks did not bring with them other gods except Zeus and the Dioskouroi. The horse was related with the liquid element, with the underworld. Poseidon appears as a beast, the river spirit of the underworld, as it happens in northern-European folklore, not unusually in Greece. Poseidon “Wanax”, is the male companion of the goddess of nature. In the relative Minoan myth, Pasiphaë is mating with the white bull, she bears the hybrid creature Minotaur; the Bull was the old pre-Olympian Poseidon. The goddess of nature and her paredros survived in the Eleusinian cult, where the following words were uttered: " Mighty Potnia bore a strong son"In the sea-dependent Mycenaean culture, there is not sufficient evidence that Poseidon was connected with the sea.
We do not know. H
Walter Munk
Walter Heinrich Munk was an American physical oceanographer. He was a professor of geophysics at the Scripps Institution of Oceanography at the University of California, San Diego in La Jolla. Born to a prominent Austrian family, in 1932 Munk was sent to school in the United States at age 14. Abandoning a New York banking career, Munk obtained a scientific education at the California Institute of Technology and his doctorate from Scripps. During World War II, Munk and his doctoral advisor Harald Sverdrup developed methods for predicting surf conditions on beaches, saving countless lives during allied landings in North Africa, the Pacific, Northern Europe. After the war, Scripps grew from a small biological station to a major research institution. Munk and his wife Judy were active in developing the Scripps campus and integrating it with the new University of California, San Diego. One of the first to bring statistical methods to the analysis of oceanographic data, Munk's work is noted for creating fruitful areas of research that continue to be explored.
These areas include surface waves, geophysical implications of variations in the Earth's rotation, internal waves, deep-ocean drilling into the sea floor, acoustical measurements of ocean properties, sea level rise, climate change. In a 1991 experiment and his collaborators tested the ability of underwater sound to propagate from the Southern Indian Ocean across all ocean basins; the aim was to use the acoustic signals to measure changes in broad-scale ocean temperatures. The experiment was criticized by environmental groups, who expected that the loud acoustic signals would adversely affect marine life. Munk was a member of the JASON think tank, he held a Secretary of the Navy/Chief of Naval Operations Oceanography Chair. Munk died at age 101 in California. Munk was born in 1917 in Austria-Hungary, to a Jewish family, his father, Dr. Hans Munk, his mother, Rega Brunner, divorced when Munk was ten years old, his maternal grandfather was Austrian politician, Lucian Brunner. His stepfather, Dr. Rudolf Engelsberg, was head of the salt mine monopoly of the Austrian government.
He was therefore a member of the Austrian governments of first Chancellor Engelbert Dollfuss and Chancellor Kurt Schuschnigg. In 1932, Munk was performing poorly in school. So, his family sent him to a boys' preparatory school in upper New York state, his family envisioned a career for Munk in finance with a New York bank connected to the family business. Munk studied at Columbia University. Munk hated banking, in 1937 he left the firm to attend the California Institute of Technology in Pasadena. While at Caltech, he took a summer job in 1939 at the Scripps Institution of Oceanography in La Jolla, California. Munk earned a B. S. in applied physics in 1939 and an M. S. in geophysics in 1940 at Caltech. Though the M. S. degree was from Caltech, the work was based on oceanographic data collected in the Gulf of California by the Norwegian oceanographer Harald Sverdrup. Sverdrup, the director of Scripps, was the thesis advisor. In 1939, Munk asked Sverdrup to take him on as a doctoral student. Sverdrup agreed, but told Munk that he did "not know of a single job in oceanography which would become available in the next decade".
However, Munk's studies were interrupted by the outbreak of World War II. He completed his doctoral degree in oceanography at Scripps under the University of California, Los Angeles in 1947. Munk applied to be a citizen of the United States in 1938, but he failed the citizenship test by giving an overly-detailed answer to a question about the Constitution. Munk obtained American citizenship in 1939. Munk married Martha Chapin in the late 1940s; the marriage ended in divorce in 1953. On June 20, 1953, Munk married Judith Horton, she was an active participant at Scripps for decades, where she made contributions to architecture, campus planning, the renovation and reuse of historical buildings. The Munks were frequent traveling companions. Judith Munk died in 2006. Munk married La Jolla community leader Mary Coakley in June 2011. Munk turned 100 in October 2017, he died of pneumonia on February 8, 2019 at La Jolla, aged 101. After the Anschluss, Munk enlisted in the ski troops of the U. S. Army as a private in 1940.
Enlistment in the Army was unusual, as all the other young men at Scripps joined the U. S. Naval Reserve. At the request of Sverdrup and Roger Revelle, Munk was discharged from military service to undertake defense-related research at Scripps, his discharge was in a week before the Japanese Attack on Pearl Harbor. He joined several of his colleagues from Scripps at the U. S. Navy Radio and Sound Laboratory, where they developed methods related to antisubmarine and amphibious warfare. In 1943, Munk and Sverdrup began working on the problem of predicting heights of ocean surface waves. Munk had observed troops in practice beach landings in the Carolinas and noted that waves larger than about five feet were dangerous to people and landing craft; the methods they developed to predict surf conditions were used during Allied landings in North Africa, the Pacific theater of war, on D-Day during the Normandy invasion. Countless lives were saved by these predictions. Munk commented in 2009: The Normandy landing is famous because weather conditions were poor and you may not realize it was postponed by General Eisenhower for 24 hours because of the prevailing wave conditions.
And he did decide, in spite of the fact that conditions were not favorable
Global Positioning System
The Global Positioning System Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Air Force. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the weak GPS signals; the GPS does not require the user to transmit any data, it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military and commercial users around the world; the United States government created the system, maintains it, makes it accessible to anyone with a GPS receiver. The GPS project was launched by the U. S. Department of Defense in 1973 for use by the United States military and became operational in 1995.
It was allowed for civilian use in the 1980s. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U. S. Congress authorized the modernization effort, GPS III. During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; the GPS system is provided by the United States government, which can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War, or degrade the service at any time. As a result, several countries have developed or are in the process of setting up other global or regional satellite navigation systems; the Russian Global Navigation Satellite System was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.
GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more and to within two meters. China's BeiDou Navigation Satellite System is due to achieve global reach in 2020. There are the European Union Galileo positioning system, India's NAVIC. Japan's Quasi-Zenith Satellite System is a GPS satellite-based augmentation system to enhance GPS's accuracy; when selective availability was lifted in 2000, GPS had about a five-meter accuracy. The latest stage of accuracy enhancement uses the L5 band and is now deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 30 centimetres or 11.8 inches. The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including classified engineering design studies from the 1960s; the U. S. Department of Defense developed the system, which used 24 satellites, it was developed for use by the United States military and became operational in 1995.
Civilian use was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it; the work of Gladys West is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS. The design of GPS is based on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator, developed in the early 1940s. Friedwardt Winterberg proposed a test of general relativity – detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth; the GPS calculated positions would drift into error, accumulating to 10 kilometers per day. This was corrected for in the design of GPS.
Winterberg, Friedwardt. “Relativistische Zeitdilatation eines künstlichen Satelliten ” When the Soviet Union launched the first artificial satellite in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit; the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem—pinpointing the user's location, given that of the satellite; this led them and APL to develop the TRANSIT system. In 1959, ARPA played a role in TRANSIT. TRANSIT was first tested in 1960, it used a constellation of five satellites and could provide a navigational fix once per hour. In 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS.
In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations
Ocean
An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean; these are, in descending order by area, the Pacific, Indian and Arctic Oceans. The word "ocean" is used interchangeably with "sea" in American English. Speaking, a sea is a body of water or enclosed by land, though "the sea" refers to the oceans. Saline water covers 361,000,000 km2 and is customarily divided into several principal oceans and smaller seas, with the ocean covering 71% of Earth's surface and 90% of the Earth's biosphere; the ocean contains 97% of Earth's water, oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, influences climate and weather patterns; the World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger over two million.
The origin of Earth's oceans is unknown. Extraterrestrial oceans may be composed of water or other compounds; the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories and Venus are theorized to have had large water oceans; the Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of natural satellites; the Solar System's giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone.
Ocean planets are a hypothetical type of planet with a surface covered with liquid. The word ocean comes from the figure in classical antiquity, the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world; the concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases. Though described as several separate oceans, the global, interconnected body of salt water is sometimes referred to as the World Ocean or global ocean; the concept of a continuous body of water with free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, other criteria.
Oceans are fringed by smaller, adjoining bodies of water such as seas, bays and straits. The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system, part of every ocean and the longest mountain range in the world; the continuous mountain range is 65,000 km long. The total mass of the hydrosphere is about 1.4 quintillion metric tons, about 0.023% of Earth's total mass. Less than 3% is freshwater; the area of the World Ocean is about 361.9 million square kilometers, which covers about 70.9% of Earth's surface, its volume is 1.335 billion cubic kilometers. This can be thought of as a cube of water with an edge length of 1,101 kilometers, its average depth is about 3,688 meters, its maximum depth is 10,994 meters at the Mariana Trench. Nearly half of the world's marine waters are over 3,000 meters deep; the vast expanses of deep ocean cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea; the bluish ocean color is a composite of several contributing agents.
Prominent contributors include dissolved organic chlorophyll. Mariners and other seafarers have reported that the ocean emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow, it is most caused by bioluminescence. Oceanographers divide the ocean into different vertical zones defined by physical and biological conditions; the pelagic zone includes all open ocean regions, can be divided into further regions categorized by depth and light abundance. The photic zone includes the oceans from the surface to a depth of
