Earth's magnetic field , also known as the geomagnetic field , is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind , a stream of charged particles emanating from the Sun . The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core : these convection currents are caused by heat escaping from the core, a natural process called a geodynamo .
158-400: A nuclear electromagnetic pulse ( nuclear EMP or NEMP ) is a burst of electromagnetic radiation created by a nuclear explosion . The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges . The specific characteristics of a particular nuclear EMP event vary according to a number of factors,
316-529: A current density of tens of amperes per square metre. Because of the downward tilt of the Earth's magnetic field at high latitudes , the area of peak field strength is a U-shaped region to the equatorial side of the detonation. As shown in the diagram, for nuclear detonations in the Northern Hemisphere , this U-shaped region is south of the detonation point. Near the equator , where the Earth's magnetic field
474-566: A geomagnetic storm . Like a geomagnetic storm, E3 can produce geomagnetically induced currents in long electrical conductors, damaging components such as power line transformers . Because of the similarity between solar-induced geomagnetic storms and nuclear E3, it has become common to refer to solar-induced geomagnetic storms as "Solar EMP". "Solar EMP" does not include E1 or E2 components. Factors that control weapon effectiveness include altitude, yield , construction details, target distance, intervening geographical features, and local strength of
632-435: A magnetic-dipole –type that dies out with distance from the current. In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential (such as in an antenna) produce an electric-dipole –type electrical field, but this also declines with distance. These fields make up the near field. Neither of these behaviours is responsible for EM radiation. Instead, they only efficiently transfer energy to
790-422: A microwave oven . These interactions produce either electric currents or heat, or both. Like radio and microwave, infrared (IR) also is reflected by metals (and also most EMR, well into the ultraviolet range). However, unlike lower-frequency radio and microwave radiation, Infrared EMR commonly interacts with dipoles present in single molecules, which change as atoms vibrate at the ends of a single chemical bond. It
948-404: A ring current . This current reduces the magnetic field at the Earth's surface. Particles that penetrate the ionosphere and collide with the atoms there give rise to the lights of the aurorae while also emitting X-rays . The varying conditions in the magnetosphere, known as space weather , are largely driven by solar activity. If the solar wind is weak, the magnetosphere expands; while if it
1106-461: A transverse wave , where the electric field E and the magnetic field B are both perpendicular to the direction of wave propagation. The electric and magnetic parts of the field in an electromagnetic wave stand in a fixed ratio of strengths to satisfy the two Maxwell equations that specify how one is produced from the other. In dissipation-less (lossless) media, these E and B fields are also in phase, with both reaching maxima and minima at
1264-611: A wave form of the electric and magnetic equations , thus uncovering the wave-like nature of electric and magnetic fields and their symmetry . Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light , Maxwell concluded that light itself is an EM wave. Maxwell's equations were confirmed by Heinrich Hertz through experiments with radio waves. Maxwell's equations established that some charges and currents ( sources ) produce local electromagnetic fields near them that do not radiate. Currents directly produce magnetic fields, but such fields of
1422-545: A 1.44 Mt (6.0 PJ ) bomb 400 kilometres (250 mi; 1,300,000 ft) above the mid-Pacific Ocean. This demonstrated that the effects of a high-altitude nuclear explosion were much larger than had been previously calculated. Starfish Prime made those effects known to the public by causing electrical damage in Hawaii , about 1,445 kilometres (898 mi) away from the detonation point, disabling approximately 300 streetlights, triggering numerous burglar alarms and damaging
1580-575: A bulk collection of charges which are spread out over large numbers of affected atoms. In electrical conductors , such induced bulk movement of charges ( electric currents ) results in absorption of the EMR, or else separations of charges that cause generation of new EMR (effective reflection of the EMR). An example is absorption or emission of radio waves by antennas, or absorption of microwaves by water or other molecules with an electric dipole moment, as for example inside
1738-411: A certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations appeared to contradict the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein explained this puzzle by resurrecting the particle theory of light to explain the observed effect. Because of the preponderance of evidence in favor of
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#17328594665171896-605: A component wave is said to be monochromatic . A monochromatic electromagnetic wave can be characterized by its frequency or wavelength, its peak amplitude, its phase relative to some reference phase, its direction of propagation, and its polarization. Interference is the superposition of two or more waves resulting in a new wave pattern. If the fields have components in the same direction, they constructively interfere, while opposite directions cause destructive interference. Additionally, multiple polarization signals can be combined (i.e. interfered) to form new states of polarization, which
2054-487: A fission explosion is 3.5% of the yield, but in a 10 kt (42 TJ) detonation the triggering explosive around the bomb core absorbs about 85% of the prompt gamma rays, so the output is only about 0.5% of the yield. In the thermonuclear Starfish Prime the fission yield was less than 100% and the thicker outer casing absorbed about 95% of the prompt gamma rays from the pusher around the fusion stage. Thermonuclear weapons are also less efficient at producing EMP because
2212-496: A fluorescence on a nearby plate of coated glass. In one month, he discovered X-rays' main properties. The last portion of the EM spectrum to be discovered was associated with radioactivity . Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate through a covering paper in a manner similar to X-rays, and Marie Curie discovered that only certain elements gave off these rays of energy, soon discovering
2370-576: A higher energy (and hence shorter wavelength) than gamma rays and vice versa. The origin of the ray differentiates them, gamma rays tend to be natural phenomena originating from the unstable nucleus of an atom and X-rays are electrically generated (and hence man-made) unless they are as a result of bremsstrahlung X-radiation caused by the interaction of fast moving particles (such as beta particles) colliding with certain materials, usually of higher atomic numbers. EM radiation (the designation 'radiation' excludes static electric and magnetic and near fields )
2528-418: A large, radial pulse of electric current propagating outward from the burst location confined to the source region (the region over which the gamma photons are attenuated). The Earth's magnetic field exerts a force on the electron flow at a right angle to both the field and the particles' original vector, which deflects the electrons and leads to synchrotron radiation . Because the outward traveling gamma pulse
2686-519: A linear medium such as a vacuum. However, in nonlinear media, such as some crystals , interactions can occur between light and static electric and magnetic fields—these interactions include the Faraday effect and the Kerr effect . In refraction , a wave crossing from one medium to another of different density alters its speed and direction upon entering the new medium. The ratio of the refractive indices of
2844-585: A long underground power line that caused a fire in the power plant in the city of Karaganda . After the dissolution of the Soviet Union , the level of this damage was communicated informally to US scientists. For a few years US and Russian scientists collaborated on the HEMP phenomenon. Funding was secured to enable Russian scientists to report on some of the Soviet EMP results in international scientific journals. As
3002-539: A lower energy level, it emits a photon of light at a frequency corresponding to the energy difference. Since the energy levels of electrons in atoms are discrete, each element and each molecule emits and absorbs its own characteristic frequencies. Immediate photon emission is called fluorescence , a type of photoluminescence . An example is visible light emitted from fluorescent paints, in response to ultraviolet ( blacklight ). Many other fluorescent emissions are known in spectral bands other than visible light. Delayed emission
3160-492: A microwave link. Starfish Prime was the first success in the series of United States high-altitude nuclear tests in 1962 known as Operation Fishbowl . Subsequent tests gathered more data on the high-altitude EMP phenomenon. The Bluegill Triple Prime and Kingfish high-altitude nuclear tests of October and November 1962 in Operation Fishbowl provided data that was clear enough to enable physicists to accurately identify
3318-417: A particular star. Spectroscopy is also used in the determination of the distance of a star, using the red shift . When any wire (or other conducting object such as an antenna ) conducts alternating current , electromagnetic radiation is propagated at the same frequency as the current. As a wave, light is characterized by a velocity (the speed of light ), wavelength , and frequency . As particles, light
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#17328594665173476-413: A permanent magnetic moment. This remanent magnetization , or remanence , can be acquired in more than one way. In lava flows , the direction of the field is "frozen" in small minerals as they cool, giving rise to a thermoremanent magnetization . In sediments, the orientation of magnetic particles acquires a slight bias towards the magnetic field as they are deposited on an ocean floor or lake bottom. This
3634-400: A presently accelerating rate—10 kilometres (6.2 mi) per year at the beginning of the 1900s, up to 40 kilometres (25 mi) per year in 2003, and since then has only accelerated. The Earth's magnetic field is believed to be generated by electric currents in the conductive iron alloys of its core, created by convection currents due to heat escaping from the core. The Earth and most of
3792-417: A receiver very close to the source, such as inside a transformer . The near field has strong effects its source, with any energy withdrawn by a receiver causing increased load (decreased electrical reactance ) on the source. The near field does not propagate freely into space, carrying energy away without a distance limit, but rather oscillates, returning its energy to the transmitter if it is not absorbed by
3950-467: A receiver. By contrast, the far field is composed of radiation that is free of the transmitter, in the sense that the transmitter requires the same power to send changes in the field out regardless of whether anything absorbs the signal, e.g. a radio station does not need to increase its power when more receivers use the signal. This far part of the electromagnetic field is electromagnetic radiation. The far fields propagate (radiate) without allowing
4108-490: A region can be represented by a chart with isogonic lines (contour lines with each line representing a fixed declination). Components of the Earth's magnetic field at the surface from the World Magnetic Model for 2020. Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of the Earth and tilted at an angle of about 11° with respect to
4266-572: A result, formal documentation of some of the EMP damage in Kazakhstan exists, although it is still sparse in the open-scientific literature. For one of the K Project tests, Soviet scientists instrumented a 570-kilometer (350 mi) section of telephone line in the area that they expected to be affected by the pulse. The monitored telephone line was divided into sub-lines of 40 to 80 kilometres (25 to 50 mi) in length, separated by repeaters . Each sub-line
4424-456: A simple compass can remain useful for navigation. Using magnetoreception , various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation. At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North
4582-425: A surface burst, absorption of gamma rays by air would limit the range of gamma-ray deposition to approximately 16 kilometres (10 mi), while for a burst in the lower-density air at high altitudes, the range of deposition would be far greater. Typical nuclear weapon yields used during Cold War planning for EMP attacks were in the range of 1 to 10 Mt (4.2 to 41.8 PJ ). This is roughly 50 to 500 times
4740-588: A third of NASA's satellites. The largest documented storm, the Carrington Event , occurred in 1859. It induced currents strong enough to disrupt telegraph lines, and aurorae were reported as far south as Hawaii. The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the ionosphere ( ionospheric dynamo region ) and magnetosphere, and some changes can be traced to geomagnetic storms or daily variations in currents. Changes over time scales of
4898-445: A third type of radiation, which in 1903 Rutherford named gamma rays . In 1910 British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914 Rutherford and Edward Andrade measured their wavelengths, finding that they were similar to X-rays but with shorter wavelengths and higher frequency, although a 'cross-over' between X and gamma rays makes it possible to have X-rays with
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5056-420: A typical case of E1 pulse produced by a second-generation nuclear weapon such as those of Operation Fishbowl . The typical gamma rays given off by the weapon have an energy of about 2 MeV ( mega electron-volts). The gamma rays transfer about half of their energy to the ejected free electrons, giving an energy of about 1 MeV. In a vacuum and absent a magnetic field, the electrons would travel with
5214-431: A very large (ideally infinite) distance from the source. Both types of waves can have a waveform which is an arbitrary time function (so long as it is sufficiently differentiable to conform to the wave equation). As with any time function, this can be decomposed by means of Fourier analysis into its frequency spectrum , or individual sinusoidal components, each of which contains a single frequency, amplitude and phase. Such
5372-464: A wave is its rate of oscillation and is measured in hertz , the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion . A monochromatic wave (a wave of a single frequency) consists of successive troughs and crests, and
5530-506: A year or more mostly reflect changes in the Earth's interior , particularly the iron-rich core . Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index . Data from THEMIS show that the magnetic field, which interacts with the solar wind, is reduced when
5688-518: Is quantized and proportional to frequency according to Planck's equation E = hf , where E is the energy per photon, f is the frequency of the photon, and h is the Planck constant . Thus, higher frequency photons have more energy. For example, a 10 Hz gamma ray photon has 10 times the energy of a 10 Hz extremely low frequency radio wave photon. The effects of EMR upon chemical compounds and biological organisms depend both upon
5846-457: Is 1–2 Earth radii out while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity. As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays , high-energy charged particles that are mostly from outside the Solar System . Many cosmic rays are kept out of
6004-428: Is a brief but intense electromagnetic field that induces high voltages in electrical conductors. E1 causes most of its damage by causing electrical breakdown voltages to be exceeded. E1 can destroy computers and communications equipment and it changes too quickly (nanoseconds) for ordinary surge protectors to provide effective protection from it. Fast-acting surge protectors (such as those using TVS diodes ) will block
6162-472: Is a more subtle affair. Some experiments display both the wave and particle natures of electromagnetic waves, such as the self-interference of a single photon . When a single photon is sent through an interferometer , it passes through both paths, interfering with itself, as waves do, yet is detected by a photomultiplier or other sensitive detector only once. A quantum theory of the interaction between electromagnetic radiation and matter such as electrons
6320-438: Is a much lower intensity "intermediate time" EMP, which is further divided into E2A (scattered gamma EMP) and E2B (neutron gamma EMP). E3 is a very long-duration "late time" pulse, which is extremely slow in rise and fall times compared to the other components of EMP. E3 is further divided into E3A (blast wave) and E3B (heave). E3 is also called magnetohydrodynamic EMP. The E1 pulse is a very fast component of nuclear EMP. E1
6478-404: Is a stream of photons . Each has an energy related to the frequency of the wave given by Planck's relation E = hf , where E is the energy of the photon, h is the Planck constant , 6.626 × 10 J·s, and f is the frequency of the wave. In a medium (other than vacuum), velocity factor or refractive index are considered, depending on frequency and application. Both of these are ratios of
Nuclear electromagnetic pulse - Misplaced Pages Continue
6636-544: Is approximately dipolar, with an axis that is nearly aligned with the rotational axis, occasionally the North and South geomagnetic poles trade places. Evidence for these geomagnetic reversals can be found in basalts , sediment cores taken from the ocean floors, and seafloor magnetic anomalies. Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.1 million years to as much as 50 million years. The most recent geomagnetic reversal, called
6794-523: Is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field , while the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena. In quantum mechanics , an alternate way of viewing EMR
6952-450: Is called compositional convection . A Coriolis effect , caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north–south polar axis. A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which
7110-431: Is called detrital remanent magnetization . Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle , cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field. When the Earth's field reverses, new basalt records
7268-422: Is called phosphorescence . The modern theory that explains the nature of light includes the notion of wave–particle duality. Together, wave and particle effects fully explain the emission and absorption spectra of EM radiation. The matter-composition of the medium through which the light travels determines the nature of the absorption and emission spectrum. These bands correspond to the allowed energy levels in
7426-563: Is classified by wavelength into radio , microwave , infrared , visible , ultraviolet , X-rays and gamma rays . Arbitrary electromagnetic waves can be expressed by Fourier analysis in terms of sinusoidal waves ( monochromatic radiation ), which in turn can each be classified into these regions of the EMR spectrum. For certain classes of EM waves, the waveform is most usefully treated as random , and then spectral analysis must be done by slightly different mathematical techniques appropriate to random or stochastic processes . In such cases,
7584-774: Is consequently absorbed by a wide range of substances, causing them to increase in temperature as the vibrations dissipate as heat. The same process, run in reverse, causes bulk substances to radiate in the infrared spontaneously (see thermal radiation section below). Infrared radiation is divided into spectral subregions. While different subdivision schemes exist, the spectrum is commonly divided as near-infrared (0.75–1.4 μm), short-wavelength infrared (1.4–3 μm), mid-wavelength infrared (3–8 μm), long-wavelength infrared (8–15 μm) and far infrared (15–1000 μm). Earth%27s magnetic field The magnitude of Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 G). As an approximation, it
7742-729: Is described by the theory of quantum electrodynamics . Electromagnetic waves can be polarized , reflected, refracted, or diffracted , and can interfere with each other. In homogeneous, isotropic media, electromagnetic radiation is a transverse wave , meaning that its oscillations are perpendicular to the direction of energy transfer and travel. It comes from the following equations : ∇ ⋅ E = 0 ∇ ⋅ B = 0 {\displaystyle {\begin{aligned}\nabla \cdot \mathbf {E} &=0\\\nabla \cdot \mathbf {B} &=0\end{aligned}}} These equations predicate that any electromagnetic wave must be
7900-447: Is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF). The solar wind exerts a pressure, and if it could reach Earth's atmosphere it would erode it. However, it is kept away by the pressure of
8058-408: Is generally reported in microteslas (μT), with 1 G = 100 μT. A nanotesla is also referred to as a gamma (γ). The Earth's field ranges between approximately 22 and 67 μT (0.22 and 0.67 G). By comparison, a strong refrigerator magnet has a field of about 10,000 μT (100 G). A map of intensity contours is called an isodynamic chart . As the World Magnetic Model shows,
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#17328594665178216-453: Is known as parallel polarization state generation . The energy in electromagnetic waves is sometimes called radiant energy . An anomaly arose in the late 19th century involving a contradiction between the wave theory of light and measurements of the electromagnetic spectra that were being emitted by thermal radiators known as black bodies . Physicists struggled with this problem unsuccessfully for many years, and it later became known as
8374-403: Is more closely proportional to the total energy yield of the weapon. In nuclear EMP all of the components of the electromagnetic pulse are generated outside of the weapon. For high-altitude nuclear explosions , much of the EMP is generated far from the detonation (where the gamma radiation from the explosion hits the upper atmosphere). This electric field from the EMP is remarkably uniform over
8532-480: Is more nearly horizontal, the E1 field strength is more nearly symmetrical around the burst location. At geomagnetic field strengths typical of the mid-latitudes, these initial electrons spiral around the magnetic field lines with a typical radius of about 85 metres (280 ft). These initial electrons are stopped by collisions with air molecules at an average distance of about 170 metres (560 ft). This means that most of
8690-537: Is propagating at the speed of light, the synchrotron radiation of the Compton electrons adds coherently , leading to a radiated electromagnetic signal. This interaction produces a large, brief, pulse. Several physicists worked on the problem of identifying the mechanism of the HEMP E1 pulse. The mechanism was finally identified by Conrad Longmire of Los Alamos National Laboratory in 1963. Longmire gives numerical values for
8848-510: Is represented by a field of a magnetic dipole currently tilted at an angle of about 11° with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through the center of Earth. The North geomagnetic pole ( Ellesmere Island , Nunavut , Canada) actually represents the South pole of Earth's magnetic field, and conversely the South geomagnetic pole corresponds to
9006-407: Is shown below . Declination is positive for an eastward deviation of the field relative to true north. It can be estimated by comparing the magnetic north–south heading on a compass with the direction of a celestial pole . Maps typically include information on the declination as an angle or a small diagram showing the relationship between magnetic north and true north. Information on declination for
9164-589: Is shown in the image. This forms the basis of magnetostratigraphy , a geophysical correlation technique that can be used to date both sedimentary and volcanic sequences as well as the seafloor magnetic anomalies. Paleomagnetic studies of Paleoarchean lava in Australia and conglomerate in South Africa have concluded that the magnetic field has been present since at least about 3,450 million years ago . In 2024 researchers published evidence from Greenland for
9322-458: Is strong, it compresses the magnetosphere and more of it gets in. Periods of particularly intense activity, called geomagnetic storms , can occur when a coronal mass ejection erupts above the Sun and sends a shock wave through the Solar System. Such a wave can take just two days to reach the Earth. Geomagnetic storms can cause a lot of disruption; the "Halloween" storm of 2003 damaged more than
9480-477: Is that it consists of photons , uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field , responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation . The energy of an individual photon
9638-420: Is the declination ( D ) or variation . Facing magnetic North, the angle the field makes with the horizontal is the inclination ( I ) or magnetic dip . The intensity ( F ) of the field is proportional to the force it exerts on a magnet. Another common representation is in X (North), Y (East) and Z (Down) coordinates. The intensity of the field is often measured in gauss (G) , but
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#17328594665179796-486: Is the emission spectrum of nebulae . Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature. These phenomena can aid various chemical determinations for the composition of gases lit from behind (absorption spectra) and for glowing gases (emission spectra). Spectroscopy (for example) determines what chemical elements comprise
9954-482: The Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001. The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal). The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects
10112-505: The Brunhes–Matuyama reversal , occurred about 780,000 years ago. A related phenomenon, a geomagnetic excursion , takes the dipole axis across the equator and then back to the original polarity. The Laschamp event is an example of an excursion, occurring during the last ice age (41,000 years ago). The past magnetic field is recorded mostly by strongly magnetic minerals , particularly iron oxides such as magnetite , that can carry
10270-466: The North and South Magnetic Poles abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors. The magnetosphere is defined by the extent of Earth's magnetic field in space or geospace . It extends above
10428-648: The Planck energy or exceeding it (far too high to have ever been observed) will require new physical theories to describe. When radio waves impinge upon a conductor , they couple to the conductor, travel along it and induce an electric current on the conductor surface by moving the electrons of the conducting material in correlated bunches of charge. Electromagnetic radiation phenomena with wavelengths ranging from as long as one meter to as short as one millimeter are called microwaves; with frequencies between 300 MHz (0.3 GHz) and 300 GHz. At radio and microwave frequencies, EMR interacts with matter largely as
10586-473: The Planck–Einstein equation . In quantum theory (see first quantization ) the energy of the photons is thus directly proportional to the frequency of the EMR wave. Likewise, the momentum p of a photon is also proportional to its frequency and inversely proportional to its wavelength: The source of Einstein's proposal that light was composed of particles (or could act as particles in some circumstances)
10744-538: The Starfish Prime nuclear test, most damage was to the satellites' solar panels while passing through radiation belts created by the explosion. For detonations within the atmosphere, the situation is more complex. Within the range of gamma ray deposition, simple laws no longer hold as the air is ionized and there are other EMP effects, such as a radial electric field due to the separation of Compton electrons from air molecules, together with other complex phenomena. For
10902-478: The electrical conductivity σ and the permeability μ . The term ∂ B /∂ t is the partial derivative of the field with respect to time; ∇ is the Laplace operator , ∇× is the curl operator , and × is the vector product . The first term on the right hand side of the induction equation is a diffusion term. In a stationary fluid, the magnetic field declines and any concentrations of field spread out. If
11060-523: The electromagnetic (EM) field , which propagate through space and carry momentum and electromagnetic radiant energy . Classically , electromagnetic radiation consists of electromagnetic waves , which are synchronized oscillations of electric and magnetic fields . In a vacuum , electromagnetic waves travel at the speed of light , commonly denoted c . There, depending on the frequency of oscillation, different wavelengths of electromagnetic spectrum are produced. In homogeneous, isotropic media,
11218-402: The ionosphere , several tens of thousands of kilometres into space , protecting Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects Earth from harmful ultraviolet radiation . Earth's magnetic field deflects most of the solar wind, whose charged particles would otherwise strip away
11376-418: The ultraviolet catastrophe . In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum. Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta . In 1905, Albert Einstein proposed that light quanta be regarded as real particles. Later
11534-432: The 50,000 volts per metre limit by unspecified mechanisms. The reality and possible construction details of these weapons are classified and are, therefore, unconfirmed in the open scientific literature The E2 component is generated by scattered gamma rays and inelastic gammas produced by neutrons . This E2 component is an "intermediate time" pulse that, by IEC definition, lasts from about one microsecond to one second after
11692-473: The E1 pulse. E1 is produced when gamma radiation from the nuclear detonation ionizes (strips electrons from) atoms in the upper atmosphere. This is known as the Compton effect and the resulting current is called the "Compton current". The electrons travel in a generally downward direction at relativistic speeds (more than 90 percent of the speed of light). In the absence of a magnetic field, this would produce
11850-562: The EMP would have been much larger (22 to 30 kV/m) because of the greater strength of the Earth's magnetic field over the United States, as well as its different orientation at high latitudes. These calculations, combined with the accelerating reliance on EMP-sensitive microelectronics, heightened awareness that EMP could be a significant problem. In 1962, the Soviet Union performed three EMP-producing nuclear tests in space over Kazakhstan,
12008-402: The Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years. In a perfect conductor ( σ = ∞ {\displaystyle \sigma =\infty \;} ), there would be no diffusion. By Lenz's law , any change in the magnetic field would be immediately opposed by currents, so the flux through a given volume of fluid could not change. As
12166-420: The Earth's magnetic field cycles with intensity every 200 million years. The lead author stated that "Our findings, when considered alongside the existing datasets, support the existence of an approximately 200-million-year-long cycle in the strength of the Earth's magnetic field related to deep Earth processes." The inclination is given by an angle that can assume values between −90° (up) to 90° (down). In
12324-675: The Earth's magnetic field. According to an internet primer published by the Federation of American Scientists : Thus, for equipment to be affected, the weapon needs to be above the visual horizon . The altitude indicated above is greater than that of the International Space Station and many low Earth orbit satellites. Large weapons could have a dramatic impact on satellite operations and communications such as occurred during Operation Fishbowl. The damaging effects on orbiting satellites are usually due to factors other than EMP. In
12482-434: The Earth's magnetic field. The magnetopause , the area where the pressures balance, is the boundary of the magnetosphere. Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 Earth radii out but the other side stretching out in a magnetotail that extends beyond 200 Earth radii. Sunward of the magnetopause is the bow shock , the area where the solar wind slows abruptly. Inside
12640-437: The Earth's surface are called the North and South geomagnetic poles. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either. Earth's magnetic field, predominantly dipolar at its surface,
12798-481: The IEC, are called "E1", "E2", and "E3". The three categories of high-altitude EMP are divided according to the time duration and occurrence of each pulse. E1 is the fastest or "early time" high-altitude EMP. Traditionally, the term "EMP" often refers specifically to this E1 component of high-altitude electromagnetic pulse. The E2 and E3 pulses are often further subdivided into additional divisions according to causation. E2
12956-567: The Solar System by the Sun's magnetosphere, or heliosphere . By contrast, astronauts on the Moon risk exposure to radiation. Anyone who had been on the Moon's surface during a particularly violent solar eruption in 2005 would have received a lethal dose. Some of the charged particles do get into the magnetosphere. These spiral around field lines, bouncing back and forth between the poles several times per second. In addition, positive ions slowly drift westward and negative ions drift eastward, giving rise to
13114-579: The Starfish Prime EMP in Hawaii (about 5.6 kilovolts/metre) and the relatively small amount of damage (for example, only 1% to 3% of streetlights extinguished) led some scientists to believe, in the early days of EMP research, that the problem might not be significant. Later calculations showed that if the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of
13272-414: The ability to impair or destroy many protective and control features. The energy associated with the second component thus may be allowed to pass into and damage systems." The E3 component is different from E1 and E2. E3 is a much slower pulse, lasting tens to hundreds of seconds. It is caused by the nuclear detonation's temporary distortion of the Earth's magnetic field. The E3 component has similarities to
13430-471: The altitude of the detonation, energy yield , gamma ray output, interactions with the Earth's magnetic field and electromagnetic shielding of targets. The fact that an electromagnetic pulse is produced by a nuclear explosion was known in the earliest days of nuclear weapons testing. The magnitude of the EMP and the significance of its effects were not immediately realized. During the first United States nuclear test on 16 July 1945, electronic equipment
13588-432: The atoms in the star's atmosphere. A similar phenomenon occurs for emission , which is seen when an emitting gas glows due to excitation of the atoms from any mechanism, including heat. As electrons descend to lower energy levels, a spectrum is emitted that represents the jumps between the energy levels of the electrons, but lines are seen because again emission happens only at particular energies after excitation. An example
13746-413: The atoms. Dark bands in the absorption spectrum are due to the atoms in an intervening medium between source and observer. The atoms absorb certain frequencies of the light between emitter and detector/eye, then emit them in all directions. A dark band appears to the detector, due to the radiation scattered out of the light beam . For instance, dark bands in the light emitted by a distant star are due to
13904-403: The average number of photons in the cube of the relevant wavelength is much smaller than 1. It is not so difficult to experimentally observe non-uniform deposition of energy when light is absorbed, however this alone is not evidence of "particulate" behavior. Rather, it reflects the quantum nature of matter . Demonstrating that the light itself is quantized, not merely its interaction with matter,
14062-407: The basis for magnetostratigraphy , a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores . Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that
14220-408: The combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are ionizing – individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds . Ionizing radiation can cause chemical reactions and damage living cells beyond simply heating, and can be a health hazard and dangerous. James Clerk Maxwell derived
14378-435: The current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks. The nature of Earth's magnetic field is one of heteroscedastic (seemingly random) fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in
14536-468: The devices that would normally protect against E2. The EMP Commission Executive Report of 2004 states, "In general, it would not be an issue for critical infrastructure systems since they have existing protective measures for defense against occasional lightning strikes. The most significant risk is synergistic because the E2 component follows a small fraction of a second after the first component's insult, which has
14694-400: The distance between two adjacent crests or troughs is called the wavelength . Waves of the electromagnetic spectrum vary in size, from very long radio waves longer than a continent to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength, according to the equation: where v is the speed of the wave ( c in a vacuum or less in other media), f is
14852-460: The electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force ). These effects can be combined in a partial differential equation for the magnetic field called the magnetic induction equation , where u is the velocity of the fluid; B is the magnetic B-field; and η = 1/σμ is the magnetic diffusivity , which is the reciprocal of the product of
15010-524: The electromagnetic spectrum includes: radio waves , microwaves , infrared , visible light , ultraviolet , X-rays , and gamma rays . Electromagnetic waves are emitted by electrically charged particles undergoing acceleration , and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum , and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation
15168-447: The electromagnetic vacuum. The behavior of EM radiation and its interaction with matter depends on its frequency, and changes qualitatively as the frequency changes. Lower frequencies have longer wavelengths, and higher frequencies have shorter wavelengths, and are associated with photons of higher energy. There is no fundamental limit known to these wavelengths or energies, at either end of the spectrum, although photons with energies near
15326-539: The electrons are stopped by collisions with air molecules before completing a full spiral around the field lines. This interaction of the negatively charged electrons with the magnetic field radiates a pulse of electromagnetic energy. The pulse typically rises to its peak value in some five nanoseconds. Its magnitude typically decays by half within 200 nanoseconds. (By the IEC definition, this E1 pulse ends 1000 nanoseconds after it begins.) This process occurs simultaneously on about 10 electrons. The simultaneous action of
15484-563: The electrons causes the resulting pulse from each electron to radiate coherently, adding to produce a single large-amplitude, short-duration, radiated pulse. Secondary collisions cause subsequent electrons to lose energy before they reach ground level. The electrons generated by these subsequent collisions have so little energy that they do not contribute significantly to the E1 pulse. These 2 MeV gamma rays typically produce an E1 pulse near ground level at moderately high latitudes that peaks at about 50,000 volts per metre. The ionization process in
15642-495: The energy release of the 1.44 Mt (6.0 PJ) Starfish Prime test, the EMP will be at least 8% as powerful. Since the E1 component of nuclear EMP depends on the prompt gamma-ray output, which was only 0.1% of yield in Starfish Prime but can be 0.5% of yield in low-yield pure nuclear fission weapons, a 10 kt (42 TJ) bomb can easily be 5 * 8% = 40% as powerful as the 1.44 Mt (6.0 PJ) Starfish Prime at producing EMP. The total prompt gamma-ray energy in
15800-429: The existence of the magnetic field as early as 3,700 million years ago. Starting in the late 1800s and throughout the 1900s and later, the overall geomagnetic field has become weaker; the present strong deterioration corresponds to a 10–15% decline and has accelerated since 2000; geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value, from circa year 1 AD. The rate of decrease and
15958-486: The explosion. E2 has many similarities to lightning , although lightning-induced E2 may be considerably larger than a nuclear E2. Because of the similarities and the widespread use of lightning protection technology, E2 is generally considered to be the easiest to protect against. According to the United States EMP Commission, the main problem with E2 is that it immediately follows E1, which may have damaged
16116-479: The field strength may be expected to be tens of kilovolts per metre over most of the area receiving the EMP radiation." The text also states that, "... over most of the area affected by the EMP the electric field strength on the ground would exceed 0.5 E max . For yields of less than a few hundred kilotons, this would not necessarily be true because the field strength at the Earth's tangent could be substantially less than 0.5 E max ." ( E max refers to
16274-527: The fields present in the same space due to other causes. Further, as they are vector fields, all magnetic and electric field vectors add together according to vector addition . For example, in optics two or more coherent light waves may interact and by constructive or destructive interference yield a resultant irradiance deviating from the sum of the component irradiances of the individual light waves. The electromagnetic fields of light are not affected by traveling through static electric or magnetic fields in
16432-406: The first stage can pre-ionize the air which becomes conductive and hence rapidly shorts out the Compton currents generated by the fusion stage. Hence, small pure fission weapons with thin cases are far more efficient at causing EMP than most megaton bombs. This analysis, however, only applies to the fast E1 and E2 components of nuclear EMP. The geomagnetic storm -like E3 component of nuclear EMP
16590-420: The fluid is sustained by convection , motion driven by buoyancy . The temperature increases towards the center of the Earth, and the higher temperature of the fluid lower down makes it buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten iron solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making it lighter. This
16748-429: The fluid moved, the magnetic field would go with it. The theorem describing this effect is called the frozen-in-field theorem . Even in a fluid with a finite conductivity, new field is generated by stretching field lines as the fluid moves in ways that deform it. This process could go on generating new field indefinitely, were it not that as the magnetic field increases in strength, it resists fluid motion. The motion of
16906-406: The frequency and λ is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant. Electromagnetic waves in free space must be solutions of Maxwell's electromagnetic wave equation . Two main classes of solutions are known, namely plane waves and spherical waves. The plane waves may be viewed as the limiting case of spherical waves at
17064-583: The inclination. The inclination of the Earth's field is 90° (downwards) at the North Magnetic Pole and –90° (upwards) at the South Magnetic Pole. The two poles wander independently of each other and are not directly opposite each other on the globe. Movements of up to 40 kilometres (25 mi) per year have been observed for the North Magnetic Pole. Over the last 180 years, the North Magnetic Pole has been migrating northwestward, from Cape Adelaide in
17222-473: The individual frequency components are represented in terms of their power content, and the phase information is not preserved. Such a representation is called the power spectral density of the random process. Random electromagnetic radiation requiring this kind of analysis is, for example, encountered in the interior of stars, and in certain other very wideband forms of radiation such as the Zero point wave field of
17380-540: The intense radiation of radium . The radiation from pitchblende was differentiated into alpha rays ( alpha particles ) and beta rays ( beta particles ) by Ernest Rutherford through simple experimentation in 1899, but these proved to be charged particulate types of radiation. However, in 1900 the French scientist Paul Villard discovered a third neutrally charged and especially penetrating type of radiation from radium, and after he described it, Rutherford realized it must be yet
17538-538: The intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada, Siberia, and the coast of Antarctica south of Australia. The intensity of the magnetic field is subject to change over time. A 2021 paleomagnetic study from the University of Liverpool contributed to a growing body of evidence that
17696-405: The interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core. The mechanism by which the Earth generates a magnetic field is known as a geodynamo . The magnetic field is generated by a feedback loop: current loops generate magnetic fields ( Ampère's circuital law ); a changing magnetic field generates an electric field ( Faraday's law ); and
17854-800: The known speed of light. Maxwell therefore suggested that visible light (as well as invisible infrared and ultraviolet rays by inference) all consisted of propagating disturbances (or radiation) in the electromagnetic field. Radio waves were first produced deliberately by Heinrich Hertz in 1887, using electrical circuits calculated to produce oscillations at a much lower frequency than that of visible light, following recipes for producing oscillating charges and currents suggested by Maxwell's equations. Hertz also developed ways to detect these waves, and produced and characterized what were later termed radio waves and microwaves . Wilhelm Röntgen discovered and named X-rays . After experimenting with high voltages applied to an evacuated tube on 8 November 1895, he noticed
18012-416: The large area affected. According to the standard reference text on nuclear weapons effects published by the U.S. Department of Defense, "The peak electric field (and its amplitude) at the Earth's surface from a high-altitude burst will depend upon the explosion yield, the height of the burst, the location of the observer, and the orientation with respect to the geomagnetic field . As a general rule, however,
18170-414: The last few centuries. The direction and intensity of the dipole change over time. Over the last two centuries the dipole strength has been decreasing at a rate of about 6.3% per century. At this rate of decrease, the field would be negligible in about 1600 years. However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual. A prominent feature in
18328-415: The last in the " Soviet Project K nuclear tests ". Although these weapons were much smaller (300 kiloton ) than the Starfish Prime test, they were over a populated, large landmass and at a location where the Earth's magnetic field was greater. The damage caused by the resulting EMP was reportedly much greater than in Starfish Prime. The geomagnetic storm –like E3 pulse from Test 184 induced a current surge in
18486-514: The limits to which the oscilloscopes were set. The Yucca EMP was initially positive-going, whereas low-altitude bursts were negative-going pulses. Also, the polarization of the Yucca EMP signal was horizontal, whereas low-altitude nuclear EMP was vertically polarized. In spite of these many differences, the unique EMP results were dismissed as a possible wave propagation anomaly. The high-altitude nuclear tests of 1962, as discussed below, confirmed
18644-422: The liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 °C; 10,340 °F), to the core-mantle boundary , which is about 3,800 K (3,530 °C; 6,380 °F). The heat is generated by potential energy released by heavier materials sinking toward the core ( planetary differentiation , the iron catastrophe ) as well as decay of radioactive elements in
18802-483: The magnet is suspended so it can turn freely. Since opposite poles attract, the North Magnetic Pole of the Earth is really the south pole of its magnetic field (the place where the field is directed downward into the Earth). The positions of the magnetic poles can be defined in at least two ways: locally or globally. The local definition is the point where the magnetic field is vertical. This can be determined by measuring
18960-643: The magnetic field once shifted at a rate of up to 6° per day at some time in Earth's history, a surprising result. However, in 2014 one of the original authors published a new study which found the results were actually due to the continuous thermal demagnitization of the lava, not to a shift in the magnetic field. In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached ~10° per year – almost 100 times faster than current changes and 10 times faster than previously thought. Although generally Earth's field
19118-467: The magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in blackouts and disruptions in artificial satellites . Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation . Over hundreds of years, magnetic declination is observed to vary over tens of degrees. The animation shows how global declinations have changed over
19276-479: The magnetosphere is the plasmasphere , a donut-shaped region containing low-energy charged particles, or plasma . This region begins at a height of 60 km, extends up to 3 or 4 Earth radii, and includes the ionosphere. This region rotates with the Earth. There are also two concentric tire-shaped regions, called the Van Allen radiation belts , with high-energy ions (energies from 0.1 to 10 MeV ). The inner belt
19434-417: The maximum electric field strength in the affected area.) In other words, the electric field strength in the entire area that is affected by the EMP will be fairly uniform for weapons with a large gamma-ray output. For smaller weapons, the electric field may fall at a faster rate as distance increases. Electromagnetic radiation In physics , electromagnetic radiation ( EMR ) consists of waves of
19592-447: The media determines the degree of refraction, and is summarized by Snell's law . Light of composite wavelengths (natural sunlight) disperses into a visible spectrum passing through a prism, because of the wavelength-dependent refractive index of the prism material ( dispersion ); that is, each component wave within the composite light is bent a different amount. EM radiation exhibits both wave properties and particle properties at
19750-480: The mid- stratosphere causes this region to become an electrical conductor, a process that blocks the production of further electromagnetic signals and causes the field strength to saturate at about 50,000 volts per metre. The strength of the E1 pulse depends upon the number and intensity of the gamma rays and upon the rapidity of the gamma-ray burst. Strength is also somewhat dependent upon altitude. There are reports of "super-EMP" nuclear weapons that are able to exceed
19908-439: The most important of which is the altitude of the detonation. The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges. In military terminology, a nuclear warhead detonated tens to hundreds of miles above the Earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on factors including
20066-407: The nearby violet light. Ritter's experiments were an early precursor to what would become photography. Ritter noted that the ultraviolet rays (which at first were called "chemical rays") were capable of causing chemical reactions. In 1862–64 James Clerk Maxwell developed equations for the electromagnetic field which suggested that waves in the field would travel with a speed that was very close to
20224-704: The non-dipolar part of the secular variation is a westward drift at a rate of about 0.2° per year. This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD. Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as paleomagnetic secular variation or paleosecular variation (PSV) . The records typically include long periods of small change with occasional large changes reflecting geomagnetic excursions and reversals. A 1995 study of lava flows on Steens Mountain , Oregon appeared to suggest
20382-519: The north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward Earth's South magnetic field. While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, Earth's field reverses and
20540-435: The north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations. Historically, the north and south poles of a magnet were first defined by the Earth's magnetic field, not vice versa, since one of the first uses for a magnet was as a compass needle. A magnet's North pole is defined as the pole that is attracted by the Earth's North Magnetic Pole when
20698-477: The northern hemisphere, the field points downwards. It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator. It continues to rotate upwards until it is straight up at the South Magnetic Pole. Inclination can be measured with a dip circle . An isoclinic chart (map of inclination contours) for the Earth's magnetic field
20856-626: The oscillations of the two fields are on average perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave . Electromagnetic radiation is commonly referred to as "light", EM, EMR, or electromagnetic waves. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength,
21014-446: The ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of the magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars , resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere . The study of
21172-401: The particle of light was given the name photon , to correspond with other particles being described around this time, such as the electron and proton . A photon has an energy, E , proportional to its frequency, f , by where h is the Planck constant , λ {\displaystyle \lambda } is the wavelength and c is the speed of light . This is sometimes known as
21330-418: The past for unknown reasons. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases. The Earth's magnetic north pole is drifting from northern Canada towards Siberia with
21488-422: The past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth's magnetic field is recorded in igneous rocks , and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetism to track the past motion of continents. Reversals also provide
21646-417: The physical mechanisms behind the electromagnetic pulses. The EMP damage of the Starfish Prime test was quickly repaired due, in part, to the fact that the EMP over Hawaii was relatively weak compared to what could be produced with a more intense pulse, and in part due to the relative ruggedness (compared to today) of Hawaii's electrical and electronic infrastructure in 1962. The relatively small magnitude of
21804-417: The planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids. The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core , with a radius of 1220 km, and a liquid outer core . The motion of
21962-428: The radiation's power and its frequency. EMR of lower energy ultraviolet or lower frequencies (i.e., near ultraviolet , visible light, infrared, microwaves, and radio waves) is non-ionizing because its photons do not individually have enough energy to ionize atoms or molecules or to break chemical bonds . The effect of non-ionizing radiation on chemical systems and living tissue is primarily simply heating, through
22120-470: The red part of the spectrum, through an increase in the temperature recorded with a thermometer . These "calorific rays" were later termed infrared. In 1801, German physicist Johann Wilhelm Ritter discovered ultraviolet in an experiment similar to Herschel's, using sunlight and a glass prism. Ritter noted that invisible rays near the violet edge of a solar spectrum dispersed by a triangular prism darkened silver chloride preparations more quickly than did
22278-415: The reversed direction. The result is a series of stripes that are symmetric about the ridge. A ship towing a magnetometer on the surface of the ocean can detect these stripes and infer the age of the ocean floor below. This provides information on the rate at which seafloor has spread in the past. Radiometric dating of lava flows has been used to establish a geomagnetic polarity time scale , part of which
22436-411: The rotational axis of the Earth. The dipole is roughly equivalent to a powerful bar magnet , with its south pole pointing towards the geomagnetic North Pole. This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels
22594-412: The same points in space (see illustrations). In the far-field EM radiation which is described by the two source-free Maxwell curl operator equations, a time-change in one type of field is proportional to the curl of the other. These derivatives require that the E and B fields in EMR are in-phase (see mathematics section below). An important aspect of light's nature is its frequency . The frequency of
22752-464: The same time (see wave-particle duality ). Both wave and particle characteristics have been confirmed in many experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances. For example, when electromagnetic radiation is absorbed by matter, particle-like properties will be more obvious when
22910-459: The size of the Hiroshima and Nagasaki bombs. Physicists have testified at United States Congressional hearings that weapons with yields of 10 kt (42 TJ) or less can produce a large EMP. The EMP at a fixed distance from an explosion increases at most as the square root of the yield (see the illustration to the right). This means that although a 10 kt (42 TJ) weapon has only 0.7% of
23068-411: The solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for
23226-472: The source, the power density of EM radiation from an isotropic source decreases with the inverse square of the distance from the source; this is called the inverse-square law . This is in contrast to dipole parts of the EM field, the near field, which varies in intensity according to an inverse cube power law, and thus does not transport a conserved amount of energy over distances but instead fades with distance, with its energy (as noted) rapidly returning to
23384-494: The speed in a medium to speed in a vacuum. Electromagnetic radiation of wavelengths other than those of visible light were discovered in the early 19th century. The discovery of infrared radiation is ascribed to astronomer William Herschel , who published his results in 1800 before the Royal Society of London . Herschel used a glass prism to refract light from the Sun and detected invisible rays that caused heating beyond
23542-410: The term associated with the changing static electric field of the particle and the magnetic term that results from the particle's uniform velocity are both associated with the near field, and do not comprise electromagnetic radiation. Electric and magnetic fields obey the properties of superposition . Thus, a field due to any particular particle or time-varying electric or magnetic field contributes to
23700-529: The tests. A 2010 technical report written for Oak Ridge National Laboratory stated that "Power line insulators were damaged, resulting in a short circuit on the line and some lines detaching from the poles and falling to the ground". Nuclear EMP is a complex multi-pulse, usually described in terms of three components, as defined by the International Electrotechnical Commission (IEC). The three components of nuclear EMP, as defined by
23858-475: The transmitter or absorbed by a nearby receiver (such as a transformer secondary coil). In the Liénard–Wiechert potential formulation of the electric and magnetic fields due to motion of a single particle (according to Maxwell's equations), the terms associated with acceleration of the particle are those that are responsible for the part of the field that is regarded as electromagnetic radiation. By contrast,
24016-427: The transmitter to affect them. This causes them to be independent in the sense that their existence and their energy, after they have left the transmitter, is completely independent of both transmitter and receiver. Due to conservation of energy , the amount of power passing through any spherical surface drawn around the source is the same. Because such a surface has an area proportional to the square of its distance from
24174-557: The unique results of the Yucca high-altitude test and increased the awareness of high-altitude nuclear EMP beyond the original group of defense scientists. The larger scientific community became aware of the significance of the EMP problem after a three-article series on nuclear EMP was published in 1981 by William J. Broad in Science . In July 1962, the US carried out the Starfish Prime test, exploding
24332-470: The wave theory, however, Einstein's ideas were met initially with great skepticism among established physicists. Eventually Einstein's explanation was accepted as new particle-like behavior of light was observed, such as the Compton effect . As a photon is absorbed by an atom , it excites the atom, elevating an electron to a higher energy level (one that is on average farther from the nucleus). When an electron in an excited molecule or atom descends to
24490-422: Was an experimental anomaly not explained by the wave theory: the photoelectric effect , in which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage . Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the frequency , rather than the intensity , of the light. Furthermore, below
24648-402: Was protected by fuses and by gas-filled overvoltage protectors. The EMP from the 22 October (K-3) nuclear test (also known as Test 184) blew all of the fuses and destroyed all of the overvoltage protectors in all of the sub-lines. Published reports, including a 1998 IEEE article, have stated that there were significant problems with ceramic insulators on overhead electrical power lines during
24806-463: Was shielded because Enrico Fermi expected the electromagnetic pulse. The official technical history for that first nuclear test states, "All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment." During British nuclear testing in 1952–53, instrumentation failures were attributed to " radioflash ", which
24964-450: Was their term for EMP. The first openly reported observation of the unique aspects of high-altitude nuclear EMP occurred during the helium balloon -lofted Yucca nuclear test of the Hardtack I series on 28 April 1958. In that test, the electric field measurements from the 1.7 kiloton weapon exceeded the range to which the test instruments were adjusted and was estimated to be about five times
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