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Stellar corona

A corona (: coronas or coronae) is the outermost layer of a star's atmosphere. It is a hot but relatively dim region of plasma populated by intermittent coronal structures known as solar prominences or filaments.

The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. Coronal light is typically obscured by diffuse sky radiation and glare from the solar disk, but can be easily seen by the naked eye during a total solar eclipse or with a specialized coronagraph. Spectroscopic measurements indicate strong ionization in the corona and a plasma temperature in excess of 1 000  000 kelvins, much hotter than the surface of the Sun, known as the photosphere.

is, in turn, derived.

History
In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that the aura visible during a solar eclipse belongs to the Sun, not to the Moon. In 1809, Spanish astronomer José Joaquín de Ferrer coined the term 'corona'. Based in his own observations of the 1806 solar eclipse at Kinderhook (New York), de Ferrer also proposed that the corona was part of the Sun and not of the Moon. English astronomer Norman Lockyer identified the first element unknown on Earth in the Sun's chromosphere, which was called helium (from Greek helios 'sun'). French astronomer Jules Jenssen noted, after comparing his readings between the 1871 and 1878 eclipses, that the size and shape of the corona changes with the sunspot cycle. In 1930, Bernard Lyot invented the "coronograph" (now "coronagraph"), which allows viewing the corona without a total eclipse. In 1952, American astronomer Eugene Parker proposed that the solar corona might be heated by myriad tiny 'nanoflares', miniature brightenings resembling solar flares that would occur all over the surface of the Sun.

Historical theories
The high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a previously unknown element, "coronium". Instead, these spectral features have since been explained by highly ionized iron (Fe-XIV, or Fe13+). Bengt Edlén, following the work of Walter Grotrian in 1939, first identified the coronal spectral lines in 1940 (observed since 1869) as transitions from low-lying metastable levels of the ground configuration of highly ionised metals (the green Fe-XIV line from Fe13+ at 5 303  Å, but also the red Fe-X line from Fe9+ at 6  374  Å).

Observable components
The solar corona has three recognized, and distinct, sources of light that occupy the same volume: the "F-corona" (for "Fraunhofer"), the "K-corona" (for "kontinuierlich"), and the "E-corona" (for "emission").

The "F-corona" is named for the Fraunhofer spectrum of absorption lines in ordinary sunlight, which are preserved by reflection off small material objects. The F-corona is faint near the Sun itself, but drops in brightness only gradually far from the Sun, extending far across the sky and becoming the zodiacal light. The F-corona is recognized to arise from small dust grains orbiting the Sun; these form a tenuous cloud that extends through much of the solar system.

The "K-corona" is named for the fact that its spectrum is a continuum, with no major spectral features. It is sunlight light that is Thomson-scattered by free electrons in the hot plasma of the Sun's outer atmosphere. The continuum nature of the spectrum arises from Doppler broadening of the Sun's Fraunhofer absorption lines in the reference frame of the (hot and therefore fast-moving) electrons. Although the K-corona is a phenomenon of the electrons in the plasma, the term is frequently used to describe the plasma itself (as distinct from the dust that gives rise to the F-corona).

The "E-corona" is the component of the corona with an emission-line spectrum, either inside or outside the wavelength band of visible light. It is a phenomenon of the ion component of the plasma, as individual ions are excited by collision with other ions or electrons, or by absorption of ultraviolet light from the Sun.

Physical features

The Sun's corona is much hotter (by a factor from 150 to 450) than the visible surface of the Sun: the corona's temperature is 1 to 3 million kelvin compared to the photosphere's average temperature – around 5 800  kelvin. The corona is far less dense than the photosphere, and produces about one-millionth as much visible light. The corona is separated from the photosphere by the relatively shallow chromosphere. The exact mechanism by which the corona is heated is still the subject of some debate, but likely possibilities include episodic energy releases from the pervasive magnetic field and magnetohydrodynamic waves from below. The outer edges of the Sun's corona are constantly being transported away, creating the "open" magnetic flux entrained in the solar wind.

The corona is not always evenly distributed across the surface of the Sun. During periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions. However, during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity. The solar cycle spans approximately 11 years, from one solar minimum to the following minimum. Since the solar magnetic field is continually wound up due to the faster rotation of mass at the Sun's equator (differential rotation), sunspot activity will be more pronounced at solar maximum where the magnetic field is more twisted. Associated with sunspots are coronal loops, loops of magnetic flux, upwelling from the solar interior. The magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the relatively dark sun spots.

Since the corona has been photographed at high resolution in the X-ray range of the spectrum by the satellite Skylab in 1973, and then later by Yohkoh and the other following space instruments, it has been seen that the structure of the corona is quite varied and complex: different zones have been immediately classified on the coronal disc. The astronomers usually distinguish several regions, as described below.

Active regions
Active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops. They generally distribute in two zones of activity, which are parallel to the solar equator. The average temperature is between two and four million kelvin, while the density goes from 109 to 1010 particles per cubic centimetre.

Active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights above the Sun's surface: sunspots and faculae occur in the photosphere; spicules, Hα filaments and plages in the chromosphere; prominences in the chromosphere and transition region; and flares and coronal mass ejections (CME) happen in the corona and chromosphere. If flares are very violent, they can also perturb the photosphere and generate a Moreton wave. On the contrary, quiescent prominences are large, cool, dense structures which are observed as dark, "snake-like" Hα ribbons (appearing like filaments) on the solar disc. Their temperature is about 5 000–8  000  K, and so they are usually considered as chromospheric features.

In 2013, images from the High Resolution Coronal Imager revealed never-before-seen "magnetic braids" of plasma within the outer layers of these active regions.

Coronal loops
Coronal loops are the basic structures of the magnetic solar corona. These loops are the closed-magnetic flux cousins of the open-magnetic flux that can be found in coronal holes and the solar wind. Loops of magnetic flux well up from the solar body and fill with hot solar plasma. Due to the heightened magnetic activity in these coronal loop regions, coronal loops can often be the precursor to solar flares and CMEs.

The solar plasma that feeds these structures is heated from under 6 000  K to well over 106 K from the photosphere, through the transition region, and into the corona. Often, the solar plasma will fill these loops from one point and drain to another, called foot points (siphon flow due to a pressure difference, or asymmetric flow due to some other driver).

When the plasma rises from the foot points towards the loop top, as always occurs during the initial phase of a compact flare, it is defined as chromospheric evaporation. When the plasma rapidly cools and falls toward the photosphere, it is called chromospheric condensation. There may also be symmetric flow from both loop foot points, causing a build-up of mass in the loop structure. The plasma may cool rapidly in this region (for a thermal instability), its dark filaments obvious against the solar disk or prominences off the Sun's limb.

Coronal loops may have lifetimes in the order of seconds (in the case of flare events), minutes, hours or days. Where there is a balance in loop energy sources and sinks, coronal loops can last for long periods of time and are known as steady state or quiescent coronal loops (example).

Coronal loops are very important to our understanding of the current coronal heating problem. Coronal loops are highly radiating sources of plasma and are therefore easy to observe by instruments such as TRACE. An explanation of the coronal heating problem remains as these structures are being observed remotely, where many ambiguities are present (i.e., radiation contributions along the line-of-sight propagation). In-situ measurements are required before a definitive answer can be determined, but due to the high plasma temperatures in the corona, in-situ measurements are, at present, impossible. The next mission of the NASA Parker Solar Probe will approach the Sun very closely, allowing more direct observations.

Large-scale structures
Large-scale structures are very long arcs which can cover over a quarter of the solar disk but contain plasma less dense than in the coronal loops of the active regions.

They were first detected in the June 8, 1968, flare observation during a rocket flight.

The large-scale structure of the corona changes over the 11-year solar cycle and becomes particularly simple during the minimum period, when the magnetic field of the Sun is almost similar to a dipolar configuration (plus a quadrupolar component).

Interconnections of active regions
The interconnections of active regions are arcs connecting zones of opposite magnetic field, of different active regions. Significant variations of these structures are often seen after a flare.

Some other features of this kind are helmet streamers – large, cap-like coronal structures with long, pointed peaks that usually overlie sunspots and active regions. Coronal streamers are considered to be sources of the slow solar wind.

Filament cavities

Filament cavities are zones which look dark in the X-rays and are above the regions where Hα filaments are observed in the chromosphere. They were first observed in the two 1970 rocket flights which also detected coronal holes.

Filament cavities are cooler clouds of plasma suspended above the Sun's surface by magnetic forces. The regions of intense magnetic field look dark in images because they are empty of hot plasma. In fact, the sum of the magnetic pressure and plasma pressure must be constant everywhere on the heliosphere in order to have an equilibrium configuration: where the magnetic field is higher, the plasma must be cooler or less dense. The plasma pressure $$p$$ can be calculated by the state equation of a perfect gas: $$ p = n k_B T$$, where $$n$$ is the particle number density, $$k_B$$ the Boltzmann constant and $$T$$ the plasma temperature. It is evident from the equation that the plasma pressure lowers when the plasma temperature decreases with respect to the surrounding regions or when the zone of intense magnetic field empties. The same physical effect renders sunspots apparently dark in the photosphere.

Bright points
Bright points are small active regions found on the solar disk. X-ray bright points were first detected on April 8, 1969, during a rocket flight.

The fraction of the solar surface covered by bright points varies with the solar cycle. They are associated with small bipolar regions of the magnetic field. Their average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in the X-ray emission.

Coronal holes
Coronal holes are unipolar regions which look dark in the X-rays since they do not emit much radiation. These are wide zones of the Sun where the magnetic field is unipolar and opens towards the interplanetary space. The high speed solar wind arises mainly from these regions.

In the UV images of the coronal holes, some small structures, similar to elongated bubbles, are often seen as they were suspended in the solar wind. These are the coronal plumes. More precisely, they are long thin streamers that project outward from the Sun's north and south poles.

The quiet Sun
The solar regions which are not part of active regions and coronal holes are commonly identified as the quiet Sun.

The equatorial region has a faster rotation speed than the polar zones. The result of the Sun's differential rotation is that the active regions always arise in two bands parallel to the equator and their extension increases during the periods of maximum of the solar cycle, while they almost disappear during each minimum. Therefore, the quiet Sun always coincides with the equatorial zone and its surface is less active during the maximum of the solar cycle. Approaching the minimum of the solar cycle (also named butterfly cycle), the extension of the quiet Sun increases until it covers the whole disk surface excluding some bright points on the hemisphere and the poles, where there are coronal holes.

Alfvén surface
The Alfvén surface is the boundary separating the corona from the solar wind defined as where the coronal plasma's Alfvén speed and the large-scale solar wind speed are equal.

Researchers were unsure exactly where the Alfvén critical surface of the Sun lay. Based on remote images of the corona, estimates had put it somewhere between 10 and 20 solar radii from the surface of the Sun. On April 28, 2021, during its eighth flyby of the Sun, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated the Alfvén surface.

Variability of the corona
A portrait, as diversified as the one already pointed out for the coronal features, is emphasized by the analysis of the dynamics of the main structures of the corona, which evolve at differential times. Studying coronal variability in its complexity is not easy because the times of evolution of the different structures can vary considerably: from seconds to several months. The typical sizes of the regions where coronal events take place vary in the same way, as it is shown in the following table.

Flares

Flares take place in active regions and are characterized by a sudden increase of the radiative flux emitted from small regions of the corona. They are very complex phenomena, visible at different wavelengths; they involve several zones of the solar atmosphere and many physical effects, thermal and not thermal, and sometimes wide reconnections of the magnetic field lines with material expulsion.

Flares are impulsive phenomena, of average duration of 15 minutes, and the most energetic events can last several hours. Flares produce a high and rapid increase of the density and temperature.

An emission in white light is only seldom observed: usually, flares are only seen at extreme UV wavelengths and into the X-rays, typical of the chromospheric and coronal emission.

In the corona, the morphology of flares is described by observations in the UV, soft and hard X-rays, and in Hα wavelengths, and is very complex. However, two kinds of basic structures can be distinguished:
 * Compact flares, when each of the two arches where the event is happening maintains its morphology: only an increase of the emission is observed without significant structural variations. The emitted energy is of the order of 1022 – 1023 J.
 * Flares of long duration, associated with eruptions of prominences, transients in white light and two-ribbon flares: in this case the magnetic loops change their configuration during the event. The energies emitted during these flares are of such great proportion they can reach 1025 J.

As for temporal dynamics, three different phases are generally distinguished, whose duration are not comparable. The durations of those periods depend on the range of wavelengths used to observe the event: Sometimes also a phase preceding the flare can be observed, usually called as "pre-flare" phase.
 * An initial impulsive phase, whose duration is on the order of minutes, strong emissions of energy are often observed even in the microwaves, EUV wavelengths and in the hard X-ray frequencies.
 * A maximum phase
 * A decay phase, which can last several hours.

Coronal mass ejections
Often accompanying large solar flares and prominences are coronal mass ejections (CME). These are enormous emissions of coronal material and magnetic field that travel outward from the Sun at up to 3000 km/s, containing roughly 10 times the energy of the solar flare or prominence that accompanies them. Some larger CMEs can propel hundreds of millions of tons of material into interplanetary space at roughly 1.5 million kilometers an hour.

Stellar coronae
Coronal stars are ubiquitous among the stars in the cool half of the Hertzsprung–Russell diagram. These coronae can be detected using X-ray telescopes. Some stellar coronae, particularly in young stars, are much more luminous than the Sun's. For example, FK Comae Berenices is the prototype for the FK Com class of variable star. These are giants of spectral types G and K with an unusually rapid rotation and signs of extreme activity. Their X-ray coronae are among the most luminous (Lx ≥ 1032 erg·s−1 or 1025W) and the hottest known with dominant temperatures up to 40 MK.

The astronomical observations planned with the Einstein Observatory by Giuseppe Vaiana and his group showed that F-, G-, K- and M-stars have chromospheres and often coronae much like the Sun. The O-B stars, which do not have surface convection zones, have a strong X-ray emission. However these stars do not have coronae, but the outer stellar envelopes emit this radiation during shocks due to thermal instabilities in rapidly moving gas blobs. Also A-stars do not have convection zones but they do not emit at the UV and X-ray wavelengths. Thus they appear to have neither chromospheres nor coronae.

Physics of the corona
The matter in the external part of the solar atmosphere is in the state of plasma, at very high temperature (a few million kelvin) and at very low density (of the order of 1015 particles/m3). According to the definition of plasma, it is a quasi-neutral ensemble of particles which exhibits a collective behaviour.

The composition is similar to that in the Sun's interior, mainly hydrogen, but with much greater ionization of its heavier elements than that found in the photosphere. Heavier metals, such as iron, are partially ionized and have lost most of the external electrons. The ionization state of a chemical element depends strictly on the temperature and is regulated by the Saha equation in the lowest atmosphere, but by collisional equilibrium in the optically thin corona. Historically, the presence of the spectral lines emitted from highly ionized states of iron allowed determination of the high temperature of the coronal plasma, revealing that the corona is much hotter than the internal layers of the chromosphere.

The corona behaves like a gas which is very hot but very light at the same time: the pressure in the corona is usually only 0.1 to 0.6 Pa in active regions, while on the Earth the atmospheric pressure is about 100 kPa, approximately a million times higher than on the solar surface. However it is not properly a gas, because it is made of charged particles, basically protons and electrons, moving at different velocities. Supposing that they have the same kinetic energy on average (for the equipartition theorem), electrons have a mass roughly 1 800 times smaller than protons, therefore they acquire more velocity. Metal ions are always slower. This fact has relevant physical consequences either on radiative processes (that are very different from the photospheric radiative processes), or on thermal conduction. Furthermore, the presence of electric charges induces the generation of electric currents and high magnetic fields. Magnetohydrodynamic waves (MHD waves) can also propagate in this plasma, even though it is still not clear how they can be transmitted or generated in the corona.

Radiation
Coronal plasma is optically thin and therefore transparent to the electromagnetic radiation that it emits and to that coming from lower layers. The plasma is very rarefied and the photon mean free path overcomes by far all the other length-scales, including the typical sizes of common coronal features.

Electromagnetic radiation from the corona has been identified coming from three main sources, located in the same volume of space:
 * The K-corona (K for kontinuierlich, "continuous" in German) is created by sunlight Thomson scattering off free electrons; doppler broadening of the reflected photospheric absorption lines spreads them so greatly as to completely obscure them, giving the spectral appearance of a continuum with no absorption lines.
 * The F-corona (F for Fraunhofer) is created by sunlight bouncing off dust particles, and is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the F-corona extends to very high elongation angles from the Sun, where it is called the zodiacal light.
 * The E-corona (E for emission) is due to spectral emission lines produced by ions that are present in the coronal plasma; it may be observed in broad or forbidden or hot spectral emission lines and is the main source of information about the corona's composition.

Thermal conduction
In the corona thermal conduction occurs from the external hotter atmosphere towards the inner cooler layers. Responsible for the diffusion process of the heat are the electrons, which are much lighter than ions and move faster, as explained above.

When there is a magnetic field the thermal conductivity of the plasma becomes higher in the direction which is parallel to the field lines rather than in the perpendicular direction. A charged particle moving in the direction perpendicular to the magnetic field line is subject to the Lorentz force which is normal to the plane individuated by the velocity and the magnetic field. This force bends the path of the particle. In general, since particles also have a velocity component along the magnetic field line, the Lorentz force constrains them to bend and move along spirals around the field lines at the cyclotron frequency.

If collisions between the particles are very frequent, they are scattered in every direction. This happens in the photosphere, where the plasma carries the magnetic field in its motion. In the corona, on the contrary, the mean free-path of the electrons is of the order of kilometres and even more, so each electron can do a helicoidal motion long before being scattered after a collision. Therefore, the heat transfer is enhanced along the magnetic field lines and inhibited in the perpendicular direction.

In the direction longitudinal to the magnetic field, the thermal conductivity of the corona is $$ k = 20 \left(\frac{2}{\pi}\right)^{3/2}\frac{\left(k_\text{B} T \right)^{5/2}k_\text{B}}{m_e^{1/2} e^4 \ln \Lambda} \approx \frac{T^{5/2}}{\ln \Lambda} \times 1.8 \times 10^{-10}~ \mathrm{W m^{-1}K^{-1}} $$ where $$k_\text{B}$$ is the Boltzmann constant, $$T$$ is the temperature in kelvin, $$m_e$$ is the electron mass, $$e$$ is the electric charge of the electron, $$ \ln \Lambda = \ln \left(12\pi n \lambda_D^3 \right) $$ is the Coulomb logarithm, and $$\lambda_D = \sqrt{ \frac{k_\text{B} T }{4 \pi n e^2 }}$$ is the Debye length of the plasma with particle density $$n$$. The Coulomb logarithm $$ \ln \Lambda $$ is roughly 20 in the corona, with a mean temperature of 1 MK and a density of 1015 particles/m3, and about 10 in the chromosphere, where the temperature is approximately 10kK and the particle density is of the order of 1018 particles/m3, and in practice it can be assumed constant.

Thence, if we indicate with $$q$$ the heat for a volume unit, expressed in J m−3, the Fourier equation of heat transfer, to be computed only along the direction $$x$$ of the field line, becomes $$ \frac{\partial q}{\partial t} = 0.9 \times 10^{-11}~ \frac{\partial^2 T^{7/2}}{\partial x ^2 }.$$

Numerical calculations have shown that the thermal conductivity of the corona is comparable to that of copper.

Coronal seismology
Coronal seismology is a method of studying the plasma of the solar corona with the use of magnetohydrodynamic (MHD) waves. MHD studies the dynamics of electrically conducting fluids – in this case, the fluid is the coronal plasma. Philosophically, coronal seismology is similar to the Earth's seismology, the Sun's helioseismology, and MHD spectroscopy of laboratory plasma devices. In all these approaches, waves of various kinds are used to probe a medium. The potential of coronal seismology in the estimation of the coronal magnetic field, density scale height, fine structure and heating has been demonstrated by different research groups.

Coronal heating problem
The coronal heating problem in solar physics relates to the question of why the temperature of the Sun's corona is millions of kelvins versus the thousands of kelvins of the surface. Several theories have been proposed to explain this phenomenon, but it is still challenging to determine which is correct. The problem first emerged after the identification of unknown spectral lines in the solar spectrum with highly ionized iron and calcium atoms. The comparison of the coronal and the photospheric temperatures of 6 000  K, leads to the question of how the 200-times-hotter coronal temperature can be maintained. The problem is primarily concerned with how the energy is transported up into the corona and then converted into heat within a few solar radii.

The high temperatures require energy to be carried from the solar interior to the corona by non-thermal processes, because the second law of thermodynamics prevents heat from flowing directly from the solar photosphere (surface), which is at about 5 800  K, to the much hotter corona at about 1 to 3 MK (parts of the corona can even reach 10  MK).

Between the photosphere and the corona, the thin region through which the temperature increases is known as the transition region. It ranges from only tens to hundreds of kilometers thick. Energy cannot be transferred from the cooler photosphere to the corona by conventional heat transfer as this would violate the second law of thermodynamics. An analogy of this would be a light bulb raising the temperature of the air surrounding it to something greater than its glass surface. Hence, some other manner of energy transfer must be involved in the heating of the corona.

The amount of power required to heat the solar corona can easily be calculated as the difference between coronal radiative losses and heating by thermal conduction toward the chromosphere through the transition region. It is about 1 kilowatt for every square meter of surface area on the Sun's chromosphere, or 1/40 000 of the amount of light energy that escapes the Sun.

Many coronal heating theories have been proposed, but two theories have remained as the most likely candidates: wave heating and magnetic reconnection (or nanoflares). Through most of the past 50 years, neither theory has been able to account for the extreme coronal temperatures.

In 2012, high resolution (<0.2″) soft X-ray imaging with the High Resolution Coronal Imager aboard a sounding rocket revealed tightly wound braids in the corona. It is hypothesized that the reconnection and unravelling of braids can act as primary sources of heating of the active solar corona to temperatures of up to 4 million kelvin. The main heat source in the quiescent corona (about 1.5 million kelvin) is assumed to originate from MHD waves.

NASA's Parker Solar Probe is intended to approach the Sun to a distance of approximately 9.5 solar radii to investigate coronal heating and the origin of the solar wind. It was successfully launched on August 12, 2018 and as of fall 2022 has completed the first 13 of more than 20 planned close approaches to the Sun.

Wave heating theory
The wave heating theory, proposed in 1949 by Évry Schatzman, proposes that waves carry energy from the solar interior to the solar chromosphere and corona. The Sun is made of plasma rather than ordinary gas, so it supports several types of waves analogous to sound waves in air. The most important types of wave are magneto-acoustic waves and Alfvén waves. Magneto-acoustic waves are sound waves that have been modified by the presence of a magnetic field, and Alfvén waves are similar to ultra low frequency radio waves that have been modified by interaction with matter in the plasma. Both types of waves can be launched by the turbulence of granulation and super granulation at the solar photosphere, and both types of waves can carry energy for some distance through the solar atmosphere before turning into shock waves that dissipate their energy as heat.

One problem with wave heating is delivery of the heat to the appropriate place. Magneto-acoustic waves cannot carry sufficient energy upward through the chromosphere to the corona, both because of the low pressure present in the chromosphere and because they tend to be reflected back to the photosphere. Alfvén waves can carry enough energy, but do not dissipate that energy rapidly enough once they enter the corona. Waves in plasmas are notoriously difficult to understand and describe analytically, but computer simulations, carried out by Thomas Bogdan and colleagues in 2003, seem to show that Alfvén waves can transmute into other wave modes at the base of the corona, providing a pathway that can carry large amounts of energy from the photosphere through the chromosphere and transition region and finally into the corona where it dissipates it as heat.

Another problem with wave heating has been the complete absence, until the late 1990s, of any direct evidence of waves propagating through the solar corona. The first direct observation of waves propagating into and through the solar corona was made in 1997 with the Solar and Heliospheric Observatory space-borne solar observatory, the first platform capable of observing the Sun in the extreme ultraviolet (EUV) for long periods of time with stable photometry. Those were magneto-acoustic waves with a frequency of about 1 millihertz (mHz, corresponding to a 1 000  second wave period), that carry only about 10% of the energy required to heat the corona. Many observations exist of localized wave phenomena, such as Alfvén waves launched by solar flares, but those events are transient and cannot explain the uniform coronal heat.

It is not yet known exactly how much wave energy is available to heat the corona. Results published in 2004 using data from the TRACE spacecraft seem to indicate that there are waves in the solar atmosphere at frequencies as high as 100 mHz (10 second period). Measurements of the temperature of different ions in the solar wind with the UVCS instrument aboard SOHO give strong indirect evidence that there are waves at frequencies as high as 200 Hz, well into the range of human hearing. These waves are very difficult to detect under normal circumstances, but evidence collected during solar eclipses by teams from Williams College suggest the presences of such waves in the 1–10 Hz range.

Recently, Alfvénic motions have been found in the lower solar atmosphere and also in the quiet Sun, in coronal holes and in active regions using observations with AIA on board the Solar Dynamics Observatory. These Alfvénic oscillations have significant power, and seem to be connected to the chromospheric Alfvénic oscillations previously reported with the Hinode spacecraft.

Solar wind observations with the Wind spacecraft have recently shown evidence to support theories of Alfvén-cyclotron dissipation, leading to local ion heating.

Magnetic reconnection theory

The magnetic reconnection theory relies on the solar magnetic field to induce electric currents in the solar corona. The currents then collapse suddenly, releasing energy as heat and wave energy in the corona. This process is called "reconnection" because of the peculiar way that magnetic fields behave in plasma (or any electrically conductive fluid such as mercury or seawater). In a plasma, magnetic field lines are normally tied to individual pieces of matter, so that the topology of the magnetic field remains the same: if a particular north and south magnetic pole are connected by a single field line, then even if the plasma is stirred or if the magnets are moved around, that field line will continue to connect those particular poles. The connection is maintained by electric currents that are induced in the plasma. Under certain conditions, the electric currents can collapse, allowing the magnetic field to "reconnect" to other magnetic poles and release heat and wave energy in the process.

Magnetic reconnection is hypothesized to be the mechanism behind solar flares, the largest explosions in the Solar System. Furthermore, the surface of the Sun is covered with millions of small magnetized regions 50–1 000  km across. These small magnetic poles are buffeted and churned by the constant granulation. The magnetic field in the solar corona must undergo nearly constant reconnection to match the motion of this "magnetic carpet", so the energy released by the reconnection is a natural candidate for the coronal heat, perhaps as a series of "microflares" that individually provide very little energy but together account for the required energy.

The idea that nanoflares might heat the corona was proposed by Eugene Parker in the 1980s but is still controversial. In particular, ultraviolet telescopes such as TRACE and SOHO/EIT can observe individual micro-flares as small brightenings in extreme ultraviolet light, but there seem to be too few of these small events to account for the energy released into the corona. The additional energy not accounted for could be made up by wave energy, or by gradual magnetic reconnection that releases energy more smoothly than micro-flares and therefore does not appear well in the TRACE data. Variations on the micro-flare hypothesis use other mechanisms to stress the magnetic field or to release the energy, and are a subject of active research in 2005.

Spicules (type II)
For decades, researchers believed spicules could send heat into the corona. However, following observational research in the 1980s, it was found that spicule plasma did not reach coronal temperatures, and so the theory was discounted.

As per studies performed in 2010 at the National Center for Atmospheric Research in Colorado, in collaboration with the Lockheed Martin's Solar and Astrophysics Laboratory (LMSAL) and the Institute of Theoretical Astrophysics of the University of Oslo, a new class of spicules (TYPE II) discovered in 2007, which travel faster (up to 100 km/s) and have shorter lifespans, can account for the problem. These jets insert heated plasma into the Sun's outer atmosphere.

Thus, a much greater understanding of the corona and improvement in the knowledge of the Sun's subtle influence on the Earth's upper atmosphere can be expected henceforth. The Atmospheric Imaging Assembly on NASA's recently launched Solar Dynamics Observatory and NASA's Focal Plane Package for the Solar Optical Telescope on the Japanese Hinode satellite which was used to test this hypothesis. The high spatial and temporal resolutions of the newer instruments reveal this coronal mass supply.

These observations reveal a one-to-one connection between plasma that is heated to millions of degrees and the spicules that insert this plasma into the corona.

title: Stellar corona


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Chrono Cross

Chrono Cross (クロノ・クロス) is a 1999 role-playing video game developed and published by Square for the PlayStation video game console. It is set in the same world as Chrono Trigger, which was released in 1995 for the Super Nintendo Entertainment System. Chrono Cross was designed primarily by scenarist and director Masato Kato, who had help from other designers who also worked on Chrono Trigger, including art director Yasuyuki Honne and composer Yasunori Mitsuda. Nobuteru Yūki designed the characters of the game.

The story of Chrono Cross focuses on a teenage boy named Serge and a theme of parallel worlds. Faced with an alternate reality in which he died as a child, Serge endeavors to discover the truth of the two worlds' divergence. The flashy thief Kid and many other characters assist him in his travels around the tropical archipelago El Nido. Struggling to uncover his past and find the mysterious Frozen Flame, Serge is chiefly challenged by Lynx, a shadowy antagonist working to apprehend him.

Upon its release in Japan in 1999 and North America in 2000, Chrono Cross received critical acclaim, earning a perfect 10.0 score from GameSpot. The game shipped 1.5 million copies worldwide by 2003, leading to a Greatest Hits re-release and continued life in Japan as part of the Ultimate Hits series. Chrono Cross was later re-released for the PlayStation Network in Japan in July 2011, and in North America four months later. A remaster of the game, titled Chrono Cross: The Radical Dreamers Edition (クロノ・クロス ： ラジカル・ドリーマーズ エディション) was released on April 7, 2022, for Nintendo Switch, PlayStation 4, Windows, and Xbox One.

Gameplay
Chrono Cross features standard role-playing video game gameplay with some differences. Players advance the game by controlling the protagonist Serge through the game's world, primarily by foot and boat. Navigation between areas is conducted via an overworld map, much like Chrono Trigger's, depicting the landscape from a scaled-down overhead view. Around the island world are villages, outdoor areas, and dungeons, through which the player moves in three dimensions. Locations such as cities and forests are represented by more realistically scaled field maps, in which players can converse with locals to procure items and services, solve puzzles and challenges, or encounter enemies. Like Chrono Trigger, the game features no random encounters; enemies are openly visible on field maps or lie in wait to ambush the party. Touching the monster switches perspectives to a battle screen, in which players can physically attack, use "Elements", defend, or run away from the enemy. Battles are turn-based, allowing the player unlimited time to select an action from the available menu. For both the playable characters and the computer-controlled enemies, each attack reduces their number of hit points (a numerically based life bar), which can be restored through some Elements. When a playable character loses all hit points, he or she faints. If all the player's characters fall in battle, the game ends and must be restored from a previously saved chapter—except for specific storyline-related battles that allow the player to lose. Chrono Cross ' s developers aimed to break new ground in the genre, and the game features several innovations. For example, players can run away from all conflicts, including boss fights and the final battle.

Battle and Elements
The Element system of Chrono Cross handles all magic, consumable items, and character-specific abilities. Elements unleash magic effects upon the enemy or party and must be equipped for use, much like the materia of 1997's Final Fantasy VII. Elements can be purchased from shops or found in treasure chests littered throughout areas. Once acquired, they are allocated to a grid whose size and shape are unique to each character. They are ranked according to eight tiers; certain high level Elements can only be assigned on equivalent tiers in a character's grid. As the game progresses, the grid expands, allowing more Elements to be equipped and higher tiers to be accessed. Elements are divided into six paired oppositional types, or "colors," each with a natural effect. Red (fire/magma) opposes Blue (water/ice), Green (wind/flora) opposes Yellow (earth/lightning), and White (light/cosmos) opposes Black (darkness/gravity). Each character and enemy has an innate color, enhancing the power of using same-color Elements while also making them weak against elements of the opposite color. Chrono Cross also features a "field effect", which keeps track of Element color used in the upper corner of the battle screen. If the field is purely one color, characters are able to unleash a powerful summon element at the cost of one of the player's stars. The field will also enhance the power of Elements of the colors present, while weakening Elements of the opposite colors. Characters also innately learn some special techniques ("Techs") that are unique to each character but otherwise act like Elements. Like Chrono Trigger, characters can combine certain Techs to make more powerful Double or Triple Techs. Consumable Elements may be used to restore hit points or heal status ailments during or after battle.

Another innovative aspect of Chrono Cross is its stamina bar. At the beginning of a battle, each character has seven points of stamina. When a character attacks or uses an Element, stamina is decreased proportionally to the potency of the attack. Stamina slowly recovers when the character defends or when other characters perform actions in battle. Characters with stamina below one point must wait to take action. Use of an Element reduces the user's stamina bar by seven stamina points; this often means that the user's stamina gauge falls into the negative and the character must wait longer than usual to recover. With each battle, players can enhance statistics such as strength and defense. However, no system of experience points exists; after four or five upgrades, statistics remain static until players defeat a boss. This adds a star to a running count shown on the status screen, which allows for another few rounds of statistical increases. Players can equip characters with weapons, armor, helmets, and accessories for use in battle; for example, the "Power Seal" upgrades attack power. Items and equipment may be purchased or found on field maps, often in treasure chests. Unlike Elements, weapons and armor cannot merely be purchased with money; instead, the player must obtain base materials—such as copper, bronze, or bone—for a blacksmith to forge for a fee. The items can later be disassembled into their original components at no cost.

Parallel dimensions
The existence of two major parallel dimensions, like time periods in Chrono Trigger, plays a significant role in the game. Players must go back and forth between the worlds to recruit party members, obtain items, and advance the plot. Much of the population of either world have counterparts in the other; some party members can even visit their other versions. The player must often search for items or places found exclusively in one world. Events in one dimension sometimes have an impact in the other—for instance, cooling scorched ground on an island in one world allows vegetation to grow in the other world. This system assists the presentation of certain themes, including the questioning of the importance of one's past decisions and humanity's role in destroying the environment. Rounding out the notable facets of Chrono Cross ' s gameplay are the New Game+ option and multiple endings. As in Chrono Trigger, players who have completed the game may choose to start the game over using data from the previous session. Character levels, learned techniques, equipment, and items gathered copy over, while acquired money and some story-related items are discarded. On a New Game+, players can access twelve endings. Scenes viewed depend on players' progress in the game before the final battle, which can be fought at any time in a New Game+ file.

Characters
Chrono Cross features a diverse cast of 45 party members. Each character is outfitted with an innate Element affinity and three unique special abilities that are learned over time. If taken to the world opposite their own, characters react to their counterparts (if available). Many characters tie in to crucial plot events. Since it is impossible to obtain all 45 characters in one playthrough, players must replay the game to witness everything. Through use of the New Game+ feature, players can ultimately obtain all characters on one save file.

Serge, the game's protagonist, is a 17-year-old boy who lives in the fishing village of Arni. One day, he slips into an alternate world in which he drowned ten years before. Determined to find the truth behind the incident, he follows a predestined course that leads him to save the world. He is assisted by Kid, a feisty, skilled thief who seeks the mythical Frozen Flame. Portrayed as willful and tomboyish due to her rough, thieving past, she helps Serge sneak into Viper Manor in order to obtain the Frozen Flame. Kid vows to find and defeat Lynx, an anthropomorphic panther who burned down her adopted mother's orphanage.

Lynx, a cruel agent of the supercomputer FATE, is bent on finding Serge and using his body as part of a greater plan involving the Frozen Flame. Lynx travels with Harle, a mysterious, playful girl dressed like a harlequin. Harle was sent by the Dragon God to shadow Lynx and one day steal the Frozen Flame from Chronopolis, a task she painfully fulfills despite being smitten with Serge.

To accomplish this goal, Harle helps Lynx manipulate the Acacia Dragoons, the powerful militia governing the islands of El Nido. As the Dragoons maintain order, they contend with Fargo, a former Dragoon turned pirate captain who holds a grudge against their leader, General Viper. Though tussling with Serge initially, the Acacia Dragoons—whose ranks include the fierce warriors Karsh, Zoah, Marcy, and Glenn—later assist him when the militaristic nation of Porre invades the archipelago. The invasion brings Norris and Grobyc to the islands, a heartful commander of an elite force and a prototype cyborg soldier, respectively, as they too seek the Frozen Flame.

Story
The game begins with Serge located in El Nido, a tropical archipelago inhabited by ancient natives, mainland colonists, and beings called Demi-humans. Serge slips into an alternate dimension in which he drowned on the beach ten years prior, and meets the thief, "Kid". As his adventure proceeds from here, Serge is able to recruit a multitude of allies to his cause. While assisting Kid in a heist at Viper Manor to steal the Frozen Flame, he learns that ten years before the present, the universe split into two dimensions—one in which Serge lived, and one in which he perished. Through Kid's Astral Amulet charm, Serge travels between the dimensions. At Fort Dragonia, with the use of a Dragonian artifact called the Dragon Tear, Lynx switches bodies with Serge. Unaware of the switch, Kid confides in Lynx, who stabs her as the real Serge helplessly watches. Lynx boasts of his victory and banishes Serge to a strange realm called the Temporal Vortex. He takes Kid under his wing, brainwashing her to believe the real Serge (in Lynx's body) is her enemy. Serge escapes with help from Harle, although his new body turns him into a stranger in his own world, with all the allies he had gained up to that point abandoning him due to his new appearance. Discovering that his new body prevents him from traveling across the dimensions, he sets out to regain his former body and learn more of the universal split that occurred ten years earlier, gaining a new band of allies along the way. He travels to a forbidden lagoon known as the Dead Sea—a wasteland frozen in time, dotted with futuristic ruins. At the center, he locates a man named Miguel and presumably Home world's Frozen Flame. Charged with guarding the Dead Sea by an entity named FATE, Miguel and three visions of Crono, Marle, and Lucca from Chrono Trigger explain that Serge's existence dooms Home world's future to destruction at the hands of Lavos. To prevent Serge from obtaining the Frozen Flame, FATE destroys the Dead Sea.

Able to return to Another world, Serge allies with the Acacia Dragoons against Porre and locates that dimension's Dragon Tear, allowing him to return to his human form. He then enters the Sea of Eden, Another world's physical equivalent of the Dead Sea, finding a temporal research facility from the distant future called Chronopolis. Lynx and Kid are inside; Serge defeats Lynx and the supercomputer FATE, allowing the six Dragons of El Nido to steal the Frozen Flame and retire to Terra Tower, a massive structure raised from the sea floor. Kid falls into a coma, and Harle bids the party goodbye to fly with the Dragons. Serge regroups his party and tends to Kid, who remains comatose. Continuing his adventure, he obtains and cleanses the corrupted Masamune sword from Chrono Trigger. He then uses the Dragon relics and shards of the Dragon Tears to create the mythic Element Chrono Cross. The spiritual power of the Masamune later allows him to lift Kid from her coma. At Terra Tower, the prophet of time, revealed to be Belthasar from Chrono Trigger, visits him with visions of Crono, Marle, and Lucca. Serge learns that the time research facility Chronopolis created El Nido thousands of years ago after a catastrophic experimental failure drew it to the past. The introduction of a temporally foreign object in history caused the planet to pull in a counterbalance from a different dimension. This was Dinopolis, a city of Dragonians—parallel universe descendants of Chrono Trigger ' s Reptites. The institutions warred and Chronopolis subjugated the Dragonians. Humans captured their chief creation—the Dragon God, an entity capable of controlling nature.

Chronopolis divided this entity into six pieces and created an Elements system. FATE then terraformed an archipelago, erased the memories of most of Chronopolis's staff, and sent them to inhabit and populate its new paradise. Thousands of years later, a panther demon attacked a three-year-old Serge. His father took him to find assistance at Marbule, but Serge's boat blew off course due to a raging magnetic storm caused by Schala. Schala, the princess of the Kingdom of Zeal, had long ago accidentally fallen to a place known as the Darkness Beyond Time and began merging with Lavos, the chief antagonist of Chrono Trigger. Schala's storm nullified Chronopolis's defenses and allowed Serge to contact the Frozen Flame; approaching it healed Serge but corrupted his father, turning him into Lynx. A circuit in Chronopolis then designated Serge "Arbiter", simultaneously preventing FATE from using the Frozen Flame by extension. The Dragons were aware of this situation, creating a seventh Dragon under the storm's cover named Harle, who manipulated Lynx to steal the Frozen Flame for the Dragons.

After Serge returned home, FATE sent Lynx to kill Serge, hoping that it would release the Arbiter lock. Ten years after Serge drowned, the thief Kid—presumably on Belthasar's orders—went back in time to save Serge and split the dimensions. FATE, locked out of the Frozen Flame again, knew that Serge would one day cross to Another world and prepared to apprehend him. Lynx switched bodies with Serge to dupe the biological check of Chronopolis on the Frozen Flame. Belthasar then reveals that these events were part of a plan he had orchestrated named Project Kid. Serge continues to the top of Terra Tower and defeats the Dragon God. Continuing to the beach where the split in dimensions had occurred, Serge finds apparitions of Crono, Marle, and Lucca once more. They reveal that Belthasar's plan was to empower Serge to free Schala from melding with Lavos, lest they evolve into the "Time Devourer", a creature capable of destroying spacetime. Lucca explains that Kid is Schala's clone, sent to the modern age to take part in Project Kid. Serge uses a Time Egg—given to him by Belthasar—to enter the Darkness Beyond Time and vanquish the Time Devourer, separating Schala from Lavos and restoring the dimensions to one. Thankful, Schala muses on evolution and the struggle of life and returns Serge to his home, noting that he will forget the entire adventure. She then seemingly records the experience in her diary, noting she will always be searching for Serge in this life and beyond, signing the entry as Schala "Kid" Zeal, implying that she and Kid have merged and became whole again. A wedding photo of Kid and an obscured male sits on the diary's desk. Scenes then depict a real-life Kid searching for someone in a modern city, intending to make players entertain the possibility that their own Kid is searching for them. The ambiguous ending leaves the events of the characters' lives following the game up to interpretation.

Relation to Radical Dreamers
Chrono Cross employs story arcs, characters, and themes from Radical Dreamers, a Satellaview side story to Chrono Trigger released in Japan. Radical Dreamers is an illustrated text adventure which was created to wrap up an unresolved plot line of Chrono Trigger. Though it borrows from Radical Dreamers in its exposition, Chrono Cross is not a remake of Radical Dreamers, but a larger effort to fulfill that game's purpose; the plots of the games are irreconcilable. To resolve continuity issues and acknowledge Radical Dreamers, the developers of Chrono Cross suggested the game happened in a parallel dimension. A notable difference between the two games is that Magus—present in Radical Dreamers as Gil—is absent from Chrono Cross. Director Masato Kato originally planned for Magus to appear in disguise as Guile, but scrapped the idea due to plot difficulties. Kato specifically felt that the game's large number of characters, as well as the difficult production schedule, did not allow him to develop the relationship between Magus and Kid. In the DS version of Chrono Trigger, Kato teases the possibility of an amnesiac Magus.

Development
Square began planning Chrono Cross immediately after the release of Xenogears in 1998 (which itself was originally conceived as a sequel to the SNES game). Chrono Trigger ' s scenario director Masato Kato had brainstormed ideas for a sequel as early as 1996, following the release of Radical Dreamers. Square's managers selected a team, appointed Hiromichi Tanaka producer, and asked Kato to direct and develop a new Chrono game in the spirit of Radical Dreamers. Kato thought Dreamers was released in a "half-finished state", and wanted to continue the story of the character Kid. Kato and Tanaka decided to produce an indirect sequel. They acknowledged that Square would soon re-release Chrono Trigger as part of Final Fantasy Chronicles, which would give players a chance to catch up on the story of Trigger before playing Cross. Kato thought that using a different setting and cast for Chrono Cross would allow players unfamiliar with Chrono Trigger to play Cross without becoming confused. The Chrono Cross team decided against integrating heavy use of time travel into the game, as they thought it would be "rehashing and cranking up the volume of the last game". Masato Kato cited the belief, "there's no use in making something similar to before [sic]", and noted, "we're not so weak nor cheap as to try to make something exactly the same as Trigger ... Accordingly, Chrono Cross is not Chrono Trigger 2. It doesn't simply follow on from Trigger, but is another, different Chrono that interlaces with Trigger." Kato and Tanaka further explained their intentions after the game's release:

"We didn't want to directly extend Chrono Trigger into a sequel, but create a new Chrono with links to the original. Yes, the platform changed; and yes, there were many parts that changed dramatically from the previous work. But in my view, the whole point in making Chrono Cross was to make a new Chrono with the best available skills and technologies of today. I never had any intentions of just taking the system from Trigger and moving it onto the PlayStation console. That's why I believe that Cross is Cross, and NOT Trigger 2."

"When creating a series, one method is to carry over a basic system, improving upon it as the series progresses, but our stance has been to create a completely new and different world from the ground up, and to restructure the former style. Therefore, Chrono Cross is not a sequel to Chrono Trigger. Had it been, it would have been called Chrono Trigger 2. Our main objective for Chrono Cross was to share a little bit of the Chrono Trigger worldview, while creating a completely different game as a means of providing new entertainment to the player. This is mainly due to the transition in platform generation from the SNES to the PS. The method I mentioned above, about improving upon a basic system, has inefficiencies, in that it's impossible to maximize the console's performance as the console continues to make improvements in leaps and bounds. Although essentially an RPG, at its core, it is a computer game, and I believe that games should be expressed with a close connection to the console's performance. Therefore, in regards to game development, our goal has always been to 'express the game utilizing the maximum performance of the console at that time.' I strongly believe that anything created in this way will continue to be innovative."

Full production began on Chrono Cross in mid-1998. The Chrono Cross team reached 80 members at its peak, with additional personnel of 10–20 cut-scene artists and 100 quality assurance testers. The team felt pressure to live up to the work of Chrono Trigger ' s "Dream Team" development group, which included famous Japanese manga artist Akira Toriyama. Kato and Tanaka hired Nobuteru Yūki for character design and Yasuyuki Honne for art direction and concept art. The event team originally envisioned a short game, and planned a system by which players would befriend any person in a town for alliance in battle. Developers brainstormed traits and archetypes during the character-creation process, originally planning 64 characters with unique endings that could vary in three different ways per character. Kato described the character creation process: "Take Pierre, for example: we started off by saying we wanted a wacko fake hero like Tata from Trigger. We also said things like 'we need at least one powerful mom', 'no way we're gonna go without a twisted brat', and so on so forth."

As production continued, the length of Cross increased, leading the event team to reduce the number of characters to 45 and scrap most of the alternate endings. Developers humorously named the character Pip "Tsumaru" in Japanese (which means "packed") as a pun on their attempts to pack as much content into the game as possible. To avoid the burden of writing unique, accented dialogue for several characters, team member Kiyoshi Yoshii coded a system that produces accents by modifying basic text for certain characters. Art director Nobuteru Yuuki initially wanted the characters to appear in a more chibi format with diminutive proportions. The game world's fusion of high technology and ethnic, tribal atmospheres proved challenging at first. He later recalled striving to harmonize the time period's level of technology, especially as reflected in characters' garb. The demands of the art style led to Square merging the Final Fantasy VIII team into that of Chrono Cross two months before the Japanese release.

The Chrono Cross team devised an original battle system using a stamina bar and Elements. Kato planned the system around allowing players to avoid repetitive gameplay (also known as "grinding") to gain combat experience. Elements were developed while planning the final battle (during which a sequence of specific Elements must be triggered), and then applied in reverse to the rest of the game. Hiromichi Tanaka likened the Elements system to card games, hoping players would feel a sense of complete control in battle. The team programmed each battle motion manually instead of performing motion capture. Developers strove to include tongue-in-cheek humor in the battle system's techniques and animations to distance the game from the Final Fantasy franchise. Masato Kato planned for the game's setting to feature a small archipelago, for fear that players would become confused traveling in large areas with respect to parallel worlds. He hoped El Nido would still impart a sense of grand scale, and the development team pushed hardware limitations in creating the game's world. To create field maps, the team modeled locations in 3D, then chose the best angle for 2D rendering. The programmers of Chrono Cross did not use any existing Square programs or routines to code the game, instead writing new, proprietary systems. Other innovations included variable-frame rate code for fast-forward and slow-motion gameplay (awarded as a bonus for completing the game) and a "CD-read swap" system to allow quick data retrieval.

Masato Kato directed and wrote the main story, leaving sub-plots and minor character events to other staff. The event team sometimes struggled to mesh their work on the plot due to the complexity of the parallel worlds concept. Masato Kato confirmed that Cross featured a central theme of parallel worlds, as well as the fate of Schala, which he was previously unable to expound upon in Chrono Trigger. Concerning the ending sequences showing Kid searching for someone in a modern city, he hoped to make players realize that alternate futures and possibilities may exist in their own lives, and that this realization would "not ... stop with the game". He later added, "Paraphrasing one novelist's favorite words, what's important is not the message or theme, but how it is portrayed as a game. Even in Cross, it was intentionally made so that the most important question was left unanswered." Kato described the finished story as "ole' boy-meets-girl type of story" with sometimes-shocking twists. Kato rode his motorcycle to relieve the stress of the game's release schedule. He continued refining event data during the final stages of development while the rest of the team undertook debugging and quality control work. Square advertised the game by releasing a short demo of the first chapter with purchases of Legend of Mana. The North American version of Cross required three months of translation and two months of debugging before release. Richard Honeywood translated, working with Kato to rewrite certain dialogue for ease of comprehension in English. He also added instances of wordplay and alliteration to compensate for difficult Japanese jokes. To streamline translation for all 45 playable characters, Honeywood created his own version of the accent generator which needed to be more robust than the simple verbal tics of the Japanese cast. Although the trademark Chrono Cross was registered in the European Union, the game was not released in Europe.

After the game was done, the team was merged with those behind Parasite Eve II, Brave Fencer Musashi and Mana to make Final Fantasy XI. The programming for the game endured as the basis for the engine of Final Fantasy XI.

Music
Chrono Cross was scored by freelance video game music composer Yasunori Mitsuda, who previously worked on Chrono Trigger. Director Masato Kato personally commissioned Mitsuda's involvement, citing a need for the "Chrono sound". Kato envisioned a "Southeast Asian feel, mixed with the foreign tastes and the tones of countries such as Greece"; Mitsuda centered his work around old world cultural influences, including Mediterranean, Fado, Celtic, and percussive African music. Mitsuda cited visual inspiration for songs: "All of my subjects are taken from scenery. I love artwork." To complement the theme of parallel worlds, he gave Another and Home respectively dark and bright moods, and hoped players would feel the emotions of "'burning soul,' 'lonely world,' and 'unforgettable memories'". Mitsuda and Kato planned music samples and sound effects with the philosophy of "a few sounds with a lot of content".

Xenogears contributor Tomohiko Kira played guitar on the beginning and ending themes. Noriko Mitose, as selected by Masato Kato, sang the ending song—"Radical Dreamers – The Unstolen Jewel". Ryo Yamazaki, a synthesizer programmer for Square Enix, helped Mitsuda transfer his ideas to the PlayStation's sound capabilities; Mitsuda was happy to accomplish even half of what he envisioned. Certain songs were ported from the score of Radical Dreamers, such as "Gale", "Frozen Flame", and "Viper Mansion". Other entries in the soundtrack contain leitmotifs from Chrono Trigger and Radical Dreamers. The melody of "Far Promise ~ Dream Shore" features prominently in "Dreams of the Ages" and "Sailing (Another World)". Masato Kato faced internal opposition in hiring Noriko Mitose:

"Personally, for me, the biggest pressure was coming from the ending theme song. From the start of the project, I had already planned to make the ending into a Japanese song, but the problem was now 'who was going to sing the song?' There was a lot of pressure from the people in the PR division to get someone big and famous to sing it, but I was totally against the idea. And as usual, I didn't heed to the surrounding complaints, but this time, there was a pretty tough struggle."

Production required six months of work. After wrapping, Mitsuda and Kato played Chrono Cross to record their impressions and observe how the tracks intermingled with scenes; the ending theme brought Kato to tears. Players who preordered the game received a sampler disc of five songs, and Square released a three-CD official soundtrack in Japan after the game's debut. The soundtrack won the Gold Prize for the PlayStation Awards of 2000. In 2005, Square Enix reissued the soundtrack due to popular demand. Earlier that year, Mitsuda announced a new arranged Chrono Cross album, scheduled for release in July 2005. Mitsuda's contract with Square gave him ownership and full rights to the soundtrack of Chrono Cross. It was delayed, and at a Play! A Video Game Symphony concert in May 2006, he revealed it would feature acoustic music and would be "out within the year", later backtracking and alleging a 2007 release date. Mitsuda posted a streaming sample of a finished track on his personal website in January 2009, and has stated the album will be released to coincide with the 10th anniversary of the Japanese debut of Cross. Music from Chrono Cross has been featured in the September 2009 Symphonic Fantasies concerts, part of the Symphonic Game Music Concert series conducted by Arnie Roth. That same year, the Chrono Cross theme "Scars of Time" was voted first place in Hardcore Gaming 101's "Best Video Game Music of All Time" poll. "Scars of Time" was also featured in 2012 by NPR in a program about classically arranged video game scores.

Release and reception
Chrono Cross shipped 850,000 units in Japan and 650,000 abroad by 2003. It was re-released once in the United States as a Sony Greatest Hits title and again as part of the Japanese Ultimate Hits series. Chrono Cross was also released on the PlayStation Network in Japan on July 6, 2011, and in North America on November 8, 2011, but a PAL region release has not been announced. Critics praised the game's complex plot, innovative battle system, varied characters, moving score, vibrant graphics, and success in breaking convention with its predecessor. Electronic Gaming Monthly gave Chrono Cross a Gold Award, scoring it 10/10/9.5 in their three reviewer format with the first review declaring the game to be "a masterpiece, plain and simple". GameSpot awarded the game a perfect 10, one of only sixteen games in the 40,000 games listed on GameSpot to have been given the score, and its Console Game of the Year Award for 2000. It also received the annual Best Role-Playing Game, Best Game Music and Best PlayStation Game awards, and nominations for Best Game Story and Best Graphics, Artistic. IGN gave the game a score of 9.7, and Cross appeared 89th in its 2008 Top 100 games list. Famitsu rated the game 36 out of 40 from four reviewers.

Fan reaction was largely positive, though certain fans complained that the game was a far departure from its predecessor, Chrono Trigger; Chrono Cross broke convention by featuring more characters, fewer double and triple techs, fewer instances of time travel, and few appearances of Trigger characters and locations. Producer Hiromichi Tanaka and director Masato Kato were aware of the changes in development, specifically intending to provide an experience different from Chrono Trigger. Kato anticipated and rebuffed this discontent before the game's release, wondering what the Chrono title meant to these fans and whether his messages ever "really got through to them". He continued, "Cross is undoubtedly the highest quality Chrono that we can create right now. (I won't say the 'best' Chrono, but) If you can't accept that, then I'm sorry to say this but I guess your Chrono and my Chrono have taken totally different paths. But I would like to say, thank you for falling in love with Trigger so much." Tanaka added, "Of course, the fans of the original are very important, but what innovation can come about when you're bound to the past? I believe that gameplay should evolve with the hardware." Kato later acknowledged that he could have "shown more empathy to the player" by making the story less complex, and acknowledged fans who felt the game was a departure from Chrono Trigger, noting that one can still "equally enjoy the game." He later reflected in 2015 that "the bashing was terrible" in reference to fans' push-back on featuring so many playable characters, acknowledging the complaint that recruiting all characters required several playthroughs.

During the 4th Annual Interactive Achievement Awards, the Academy of Interactive Arts & Sciences nominated Chrono Cross for the "Game of the Year", "Console Game of the Year", and "Console Role-Playing" awards.

Legacy
On December 9, 2021, a cross-over event between Chrono Cross and the free-to-play RPG Another Eden was released. A collaborative effort between Chrono writer Kato and composer Mitsuda, the game features elements similar to the Chrono series, such as talking frog protagonists and time-travel elements. Titled Complex Dream, the event introduces several Chrono Cross characters, including Serge, Kid, and Harle, as well as gameplay elements from the series such as element magic and combo techs.

Remaster
Publications began discussion of a possible remastered version of Chrono Cross in September 2021, when a security flaw allowed for a web developer to see an internal listing of current and upcoming video games in Nvidia's GeForce Now database, which included a never-announced Chrono Cross Remastered. Nvidia later confirmed that the list was real, but that the games listed were speculative, and may or may not end up getting a final release. A second Nvidia leak occurred the following November, which again listed Chrono Cross Remastered, this time with a December 2021 release date. Further comments on the game's existence also arose in November; Video Games Chronicle reported Nick Baker of the XboxEra podcast could confirm prior reports of its existence, and game website Gematsu separately confirmed the game's existence. On December 4, 2021, Square Enix announced a cross over event between Chrono Cross and mobile game Another Eden; the announcement spurred more discussion on a remaster, considering Square was reviving the game for the first time in 20 years, and writer Masato Kato worked on both games.

A remaster of the game, titled Chrono Cross: The Radical Dreamers Edition, was announced on February 9, 2022, during a Nintendo Direct presentation, being slated for release on April 7, 2022, for Nintendo Switch, PlayStation 4, Windows, and Xbox One. The remaster of the title includes quality-of-life updates such as the ability to disable encounters, in addition to an enhanced OST. The remaster is also bundled with the text adventure game Radical Dreamers, previously only available to Japanese players through the Satellaview peripheral for the Super Famicom. Masato Kato, Yasunori Mitsuda, Nobuteru Yuuki, and Hiromichi Tanaka were brought in to lightly polish the game's dialogue, music, character art, and mechanics, respectively. Tanaka revealed that the game's assets, stored on magnetic tape after development ceased in 1999, were lost in the intervening years, causing him to rely on a personal backup he had maintained for certain aspects of his polishing work. Producer Koichiro Sakamoto further explained that creating the remaster required teams to painstakingly upscale the game's original location art and remap each 3D field map, sometimes relying on AI to improve the resolution. The work demanded close scrutiny to ensure no original details were missed.

While Chrono Cross: The Radical Dreamers Edition was received well by critics, it received a negative reaction from players in part due to how it performed as compared to its PlayStation 1 counterpart. Analysis showed that the remastered version had its frame rate dropping quite frequently, and was also unable to cross the threshold of 30 FPS. This issue has been noticed across all the platforms it was released on. On February 22, 2023, Square-Enix released an update patch for the remaster on all systems it released for which has fixed some of the various gameplay issues with the remaster, as well as updating several performance aspects of the game including increasing the game's framerate to 60fps.

Sequel
In 2001, Hironobu Sakaguchi revealed the company's staff wanted to develop a new game and were discussing script ideas. Although Kato was interested in a new title, the project had not been greenlighted. Square then registered a trademark for Chrono Break worldwide, causing speculation concerning a new sequel. Nothing materialized, and the trademark was dropped in the United States on November 13, 2003, though it still stands in Japan and the European Union. Kato later returned to Square Enix as a freelancer to work on Children of Mana and Dawn of Mana. Mitsuda also expressed interest in scoring a new Chrono series game. In 2005, Kato and Mitsuda teamed up to do a game called Deep Labyrinth, and again in 2008 for Sands of Destruction, both for the Nintendo DS. The February 2008 issue of Game Informer ranked the Chrono series eighth among the "Top Ten Sequels in Demand", naming the games "steadfast legacies in the Square Enix catalogue" and asking "what's the damn holdup?!" In Electronic Gaming Monthly ' s June 2008 "Retro Issue", writer Jeremy Parish cited Chrono as the franchise video game fans would be most thrilled to see a sequel to. In the May 1, 2009, issue of Famitsu, Chrono Trigger placed 14th out of 50 in a vote of most-wanted sequels by the magazine's readers. At E3 2009, SE Senior Vice President Shinji Hashimoto remarked, "If people want a sequel, they should buy more!"

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Chrono Cross


text:
Planned economy

A planned economy is a type of economic system where the distribution of goods and services or the investment, production and the allocation of capital goods takes place according to economic plans that are either economy-wide or limited to a category of goods and services. A planned economy may use centralized, decentralized, participatory, or Soviet-type forms of economic planning. The level of centralization or decentralization in decision-making and participation depends on the specific type of planning mechanism employed.

Socialist states based on the Soviet model have used central planning, although a minority such as the former Socialist Federal Republic of Yugoslavia have adopted some degree of market socialism. Market abolitionist socialism replaces factor markets with direct calculation as the means to coordinate the activities of the various socially owned economic enterprises that make up the economy. More recent approaches to socialist planning and allocation have come from some economists and computer scientists proposing planning mechanisms based on advances in computer science and information technology.

Planned economies contrast with unplanned economies, specifically market economies, where autonomous firms operating in markets make decisions about production, distribution, pricing and investment. Market economies that use indicative planning are variously referred to as planned market economies, mixed economies and mixed market economies. A command economy follows an administrative-command system and uses Soviet-type economic planning which was characteristic of the former Soviet Union and Eastern Bloc before most of these countries converted to market economies. This highlights the central role of hierarchical administration and public ownership of production in guiding the allocation of resources in these economic systems.

Overview
In the Hellenistic and post-Hellenistic world, "compulsory state planning was the most characteristic trade condition for the Egyptian countryside, for Hellenistic India, and to a lesser degree the more barbaric regions of the Seleucid, the Pergamenian, the southern Arabian, and the Parthian empires". Scholars have argued that the Incan economy was a flexible type of command economy, centered around the movement and utilization of labor instead of goods. One view of mercantilism sees it as involving planned economies.

The Soviet-style planned economy in Soviet Russia evolved in the wake of a continuing existing World War I war-economy as well as other policies, known as war communism (1918–1921), shaped to the requirements of the Russian Civil War of 1917–1923. These policies began their formal consolidation under an official organ of government in 1921, when the Soviet government founded Gosplan. However, the period of the New Economic Policy (c. 1921 to c. 1928) intervened before the planned system of regular five-year plans started in 1928. Leon Trotsky was one of the earliest proponents of economic planning during the NEP period. Trotsky argued that specialization, the concentration of production and the use of planning could "raise in the near future the coefficient of industrial growth not only two, but even three times higher than the pre-war rate of 6% and, perhaps, even higher". According to historian Sheila Fitzpatrick, the scholarly consensus was that Stalin appropriated the position of the Left Opposition on such matters as industrialisation and collectivisation.

After World War II (1939–1945) France and Great Britain practiced dirigisme – government direction of the economy through non-coercive means. The Swedish government planned public-housing models in a similar fashion as urban planning in a project called Million Programme, implemented from 1965 to 1974. Some decentralized participation in economic planning occurred across Revolutionary Spain, most notably in Catalonia, during the Spanish Revolution of 1936.

Relationship with socialism

In the May 1949 issue of the Monthly Review titled "Why Socialism?", Albert Einstein wrote: "I am convinced there is only one way to eliminate these grave evils, namely through the establishment of a socialist economy, accompanied by an educational system which would be oriented toward social goals. In such an economy, the means of production are owned by society itself and are utilized in a planned fashion. A planned economy, which adjusts production to the needs of the community, would distribute the work to be done among all those able to work and would guarantee a livelihood to every man, woman, and child. The education of the individual, in addition to promoting his own innate abilities, would attempt to develop in him a sense of responsibility for his fellow-men in place of the glorification of power and success in our present society."

While socialism is not equivalent to economic planning or to the concept of a planned economy, an influential conception of socialism involves the replacement of capital markets with some form of economic planning in order to achieve ex-ante coordination of the economy. The goal of such an economic system would be to achieve conscious control over the economy by the population, specifically so that the use of the surplus product is controlled by the producers. The specific forms of planning proposed for socialism and their feasibility are subjects of the socialist calculation debate.

Computational economic planning
In 1959 Anatoly Kitov proposed a distributed computing system (Project "Red Book", Красная книга) with a focus on the management of the Soviet economy. Opposition from the Defence Ministry killed Kitov's plan.

In 1971 the socialist Allende administration of Chile launched Project Cybersyn to install a telex machine in every corporation and organization in the economy for the communication of economic data between firms and the government. The data was also fed into a computer-simulated economy for forecasting. A control room was built for real-time observation and management of the overall economy. The prototype-stage of the project showed promise when it was used to redirect supplies around a trucker's strike, but after CIA-backed Augusto Pinochet led a coup in 1973 that established a military dictatorship under his rule the program was abolished and Pinochet moved Chile towards a more liberalized market economy.

In their book Towards a New Socialism (1993), the computer scientist Paul Cockshott from the University of Glasgow and the economist Allin Cottrell from Wake Forest University claim to demonstrate how a democratically planned economy built on modern computer technology is possible and drives the thesis that it would be both economically more stable than the free-market economies and also morally desirable.

Cybernetics

The use of computers to coordinate production in an optimal fashion has been variously proposed for socialist economies. The Polish economist Oskar Lange (1904–1965) argued that the computer is more efficient than the market process at solving the multitude of simultaneous equations required for allocating economic inputs efficiently (either in terms of physical quantities or monetary prices).

In the Soviet Union, Anatoly Kitov had proposed to the Central Committee of the Communist Party of the Soviet Union a detailed plan for the re-organization of the control of the Soviet armed forces and of the Soviet economy on the basis of a network of computing centers in 1959. Kitov's proposal was rejected, as later was the 1962 OGAS economy management network project. Soviet cybernetician, Viktor Glushkov argued that his OGAS information network would have delivered a fivefold savings return for the Soviet economy over the first fifteen-year investment.

Salvador Allende's socialist government pioneered the 1970 Chilean distributed decision support system Project Cybersyn in an attempt to move towards a decentralized planned economy with the experimental viable system model of computed organisational structure of autonomous operative units through an algedonic feedback setting and bottom-up participative decision-making in the form of participative democracy by the Cyberfolk component.

Fictional portrayals
The 1888 novel Looking Backward by Edward Bellamy depicts a fictional planned economy in a United States around the year 2000 which has become a socialist utopia.

The World State in Aldous Huxley's Brave New World (1932) and Airstrip One in George Orwell's Nineteen Eighty-Four (1949) provide fictional depictions of command economies, albeit with diametrically opposed aims. The former is a consumer economy designed to engender productivity while the latter is a shortage economy designed as an agent of totalitarian social control. Airstrip One is organized by the euphemistically named Ministry of Plenty.

Other literary portrayals of planned economies include Yevgeny Zamyatin's We (1924), which influenced Orwell's work. Like Nineteen Eighty-Four, Ayn Rand's dystopian 1938 story Anthem offered an artistic portrayal of a command economy that was influenced by We. The difference is that it was a primitivist planned economy as opposed to the advanced technology of We or Brave New World.

Advantages
The government can harness land, labor, and capital to serve the economic objectives of the state. Consumer demand can be restrained in favor of greater capital investment for economic development in a desired pattern. In international comparisons, state-socialist nations have compared favorably with capitalist nations in health indicators such as infant mortality and life expectancy. However, according to Michael Ellman, the reality of this, at least regarding infant mortality, varies depending on whether official Soviet or WHO definitions are used.

The state can begin building massive heavy industries at once in an underdeveloped economy without waiting years for capital to accumulate through the expansion of light industry and without reliance on external financing. This is what happened in the Soviet Union during the 1930s when the government forced the share of gross national income dedicated to private consumption down from 80% to 50%. As a result of this development, the Soviet Union experienced massive growth in heavy industry, with a concurrent massive contraction of its agricultural sector due to the labor shortage.

Economic instability
Studies of command economies of the Eastern Bloc in the 1950s and 1960s by both American and Eastern European economists found that contrary to the expectations of both groups they showed greater fluctuations in output than market economies during the same period.

Inefficient resource distribution
Critics of planned economies argue that planners cannot detect consumer preferences, shortages and surpluses with sufficient accuracy and therefore cannot efficiently co-ordinate production (in a market economy, a free price system is intended to serve this purpose). This difficulty was notably written about by economists Ludwig von Mises and Friedrich Hayek, who referred to subtly distinct aspects of the problem as the economic calculation problem and local knowledge problem, respectively. These distinct aspects were also present in the economic thought of Michael Polanyi.

Whereas the former stressed the theoretical underpinnings of a market economy to subjective value theory while attacking the labor theory of value, the latter argued that the only way to satisfy individuals who have a constantly changing hierarchy of needs and are the only ones to possess their particular individual's circumstances is by allowing those with the most knowledge of their needs to have it in their power to use their resources in a competing marketplace to meet the needs of the most consumers most efficiently. This phenomenon is recognized as spontaneous order. Additionally, misallocation of resources would naturally ensue by redirecting capital away from individuals with direct knowledge and circumventing it into markets where a coercive monopoly influences behavior, ignoring market signals. According to Tibor Machan, "[w]ithout a market in which allocations can be made in obedience to the law of supply and demand, it is difficult or impossible to funnel resources with respect to actual human preferences and goals".

Historian Robert Vincent Daniels regarded the Stalinist period to represent an abrupt break with Lenin's government in terms of economic planning in which an deliberated, scientific system of planning that featured former Menshevik economists at Gosplan had been replaced with a hasty version of planning with unrealistic targets, bureaucratic waste, bottlenecks and shortages. Stalin's formulations of national plans in terms of physical quantity of output was also attributed by Daniels as a source for the stagnant levels of efficiency and quality.

Suppression of economic democracy and self-management
Economist Robin Hahnel, who supports participatory economics, a form of socialist decentralized planned economy, notes that even if central planning overcame its inherent inhibitions of incentives and innovation, it would nevertheless be unable to maximize economic democracy and self-management, which he believes are concepts that are more intellectually coherent, consistent and just than mainstream notions of economic freedom. Furthermore, Hahnel states: "Combined with a more democratic political system, and redone to closer approximate a best case version, centrally planned economies no doubt would have performed better. But they could never have delivered economic self-management, they would always have been slow to innovate as apathy and frustration took their inevitable toll, and they would always have been susceptible to growing inequities and inefficiencies as the effects of differential economic power grew. Under central planning neither planners, managers, nor workers had incentives to promote the social economic interest. Nor did impeding markets for final goods to the planning system enfranchise consumers in meaningful ways. But central planning would have been incompatible with economic democracy even if it had overcome its information and incentive liabilities. And the truth is that it survived as long as it did only because it was propped up by unprecedented totalitarian political power."

Command economy
Planned economies contrast with command economies in that a planned economy is "an economic system in which the government controls and regulates production, distribution, prices, etc." whereas a command economy necessarily has substantial public ownership of industry while also having this type of regulation. In command economies, important allocation decisions are made by government authorities and are imposed by law.

This is contested by some Marxists. Decentralized planning has been proposed as a basis for socialism and has been variously advocated by anarchists, council communists, libertarian Marxists and other democratic and libertarian socialists who advocate a non-market form of socialism, in total rejection of the type of planning adopted in the economy of the Soviet Union.

Most of a command economy is organized in a top-down administrative model by a central authority, where decisions regarding investment and production output requirements are decided upon at the top in the chain of command, with little input from lower levels. Advocates of economic planning have sometimes been staunch critics of these command economies. Leon Trotsky believed that those at the top of the chain of command, regardless of their intellectual capacity, operated without the input and participation of the millions of people who participate in the economy and who understand/respond to local conditions and changes in the economy. Therefore, they would be unable to effectively coordinate all economic activity.

Historians have associated planned economies with Marxist–Leninist states and the Soviet economic model. Since the 1980s, it has been contested that the Soviet economic model did not actually constitute a planned economy in that a comprehensive and binding plan did not guide production and investment. The further distinction of an administrative-command system emerged as a new designation in some academic circles for the economic system that existed in the former Soviet Union and Eastern Bloc, highlighting the role of centralized hierarchical decision-making in the absence of popular control over the economy. The possibility of a digital planned economy was explored in Chile between 1971 and 1973 with the development of Project Cybersyn and by Aleksandr Aleksandrovich Kharkevich, head of the Department of Technical Physics in Kiev in 1962.

While both economic planning and a planned economy can be either authoritarian or democratic and participatory, democratic socialist critics argue that command economies under modern-day communism is highly undemocratic and totalitarian in practice. Indicative planning is a form of economic planning in market economies that directs the economy through incentive-based methods. Economic planning can be practiced in a decentralized manner through different government authorities. In some predominantly market-oriented and Western mixed economies, the state utilizes economic planning in strategic industries such as the aerospace industry. Mixed economies usually employ macroeconomic planning while micro-economic affairs are left to the market and price system.

Decentralized planning
A decentralized-planned economy, occasionally called horizontally planned economy due to its horizontalism, is a type of planned economy in which the investment and allocation of consumer and capital goods is explicated accordingly to an economy-wide plan built and operatively coordinated through a distributed network of disparate economic agents or even production units itself. Decentralized planning is usually held in contrast to centralized planning, in particular the Soviet-type economic planning of the Soviet Union's command economy, where economic information is aggregated and used to formulate a plan for production, investment and resource allocation by a single central authority. Decentralized planning can take shape both in the context of a mixed economy as well as in a post-capitalist economic system. This form of economic planning implies some process of democratic and participatory decision-making within the economy and within firms itself in the form of industrial democracy. Computer-based forms of democratic economic planning and coordination between economic enterprises have also been proposed by various computer scientists and radical economists. Proponents present decentralized and participatory economic planning as an alternative to market socialism for a post-capitalist society.

Decentralized planning has been a feature of anarchist and socialist economics. Variations of decentralized planning such as economic democracy, industrial democracy and participatory economics have been promoted by various political groups, most notably anarchists, democratic socialists, guild socialists, libertarian Marxists, libertarian socialists, revolutionary syndicalists and Trotskyists. During the Spanish Revolution, some areas where anarchist and libertarian socialist influence through the CNT and UGT was extensive, particularly rural regions, were run on the basis of decentralized planning resembling the principles laid out by anarcho-syndicalist Diego Abad de Santillan in the book After the Revolution. Trotsky had urged economic decentralisation between the state, oblast regions and factories during the NEP period to counter structural inefficiency and the problem of bureaucracy.

Negotiated coordination
Economist Pat Devine has created a model of decentralized economic planning called "negotiated coordination" which is based upon social ownership of the means of production by those affected by the use of the assets involved, with the allocation of consumer and capital goods made through a participatory form of decision-making by those at the most localized level of production. Moreover, organizations that utilize modularity in their production processes may distribute problem solving and decision making.

Participatory planning
The planning structure of a decentralized planned economy is generally based on a consumers council and producer council (or jointly, a distributive cooperative) which is sometimes called a consumers' cooperative. Producers and consumers, or their representatives, negotiate the quality and quantity of what is to be produced. This structure is central to guild socialism, participatory economics and the economic theories related to anarchism.

Kerala
Some decentralized participation in economic planning has been implemented in various regions and states in India, most notably in Kerala. Local level planning agencies assess the needs of people who are able to give their direct input through the Gram Sabhas (village-based institutions) and the planners subsequently seek to plan accordingly.

Revolutionary Catalonia
Some decentralized participation in economic planning has been implemented across Revolutionary Spain, most notably in Catalonia, during the Spanish Revolution of 1936.

Community participatory planning
The United Nations has developed local projects that promote participatory planning on a community level. Members of communities make decisions regarding community development directly.

title: Planned economy