Typical coronal loops observed by TRACE

Coronal loops form the basic structure of the lower corona and transition region of the Sun. These highly structured and elegant loops are a direct consequence of the twisted solar magnetic flux within the solar body. The population of coronal loops can be directly linked with the solar cycle, it is for this reason coronal loops are often found with sunspots at their footpoints. The upwelling magnetic flux pushes through the photosphere, exposing the cooler plasma below. The contrast between the photosphere and solar interior gives the impression of dark spots, or sunspots. Image File history File links Download high-resolution version (768x768, 355 KB) source: http://trace. ... Image File history File links Download high-resolution version (768x768, 355 KB) source: http://trace. ... Look up Trace in Wiktionary, the free dictionary. ... In astronomy, a corona is the luminous plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... TRACE 19. ... The Sun is the star at the center of the Solar System. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... It has been suggested that this article or section be merged with Schwabe-Wolf cycle. ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ... Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water. ... The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ...

Physical features

A coronal loop is magnetic flux fixed at both ends, threading through the solar body, protruding into the solar atmosphere. They are ideal structures to observe when trying to understand the transfer of energy from the solar body, through the transition region and into the corona. In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks. ...

A Cartoon demonstrating the configuration of solar magnetic flux during the solar cycle

Many scales of coronal loops exist, neighbouring open flux tubes that give way to the solar wind and reach far into the corona and heliosphere. Anchored in the photosphere (a rigid, line-tied, anchor is assumed where the high-β; external plasma holds the loop footpoints in place), coronal loops project through the chromosphere and transition region, extending high into the corona. Image File history File links Twistedflux. ... Image File history File links Twistedflux. ... A cartoon is any of several forms of illustrations, with varied meanings that evolved from one to another. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... A stocked ships anchor. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... The chromosphere (literally, color sphere) is a thin layer of the Suns atmosphere just above the photosphere, roughly 10,000 kilometers deep. ... TRACE 19. ... In astronomy, a corona is the luminous plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ...

Also, coronal loops have a wide variety of temperatures along their lengths. Loops existing at temperatures below 1MK are generally known as cool loops, those existing at around 1MK are known as warm loops and those beyond 1MK are known as hot loops. Naturally these different categories radiate at different wavelengths.^[1]

Cartoon of the low corona and transition region, where many scales of coronal loop can be observed

A cartoon is any of several forms of illustrations, with varied meanings that evolved from one to another. ... In astronomy, a corona is the luminous plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... TRACE 19. ...

Location

Coronal loops populate both active and quiet regions of the solar surface. Active regions on the solar surface take up small areas but produce the majority of activity and are often the source of flares and Coronal Mass Ejections due to the intense magnetic field present. Active regions produce 82% of the total coronal heating energy.^[2] Coronal holes are open field lines located predominantly in the polar regions of the Sun and are known to be the source of the fast solar wind. The quiet Sun makes up the rest of the solar surface. The quiet Sun, although less active than active regions, is awash with dynamic processes and transient events (bright points, nanoflares and jets).^[3] As a general rule, the quiet Sun exists in regions of closed magnetic structures, active regions are highly dynamic sources of explosive events. It is important to note that observations suggest the whole corona is massively populated by open and closed magnetic fieldlines. A composite image showing two CMEs (at 2 oclock and 8 oclock), with the sun at center. ... Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another, changing the overall topology of a magnetic field. ... A geographical pole is either of two fixed points on the surface of a spinning body or planet, at 90 degrees from the equator, based on the axis around which a body spins. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... The word dynamics can refer to: a branch of mechanics; see dynamics (mechanics) the volume of music; see dynamics (music) When used referring to mechanics, it is referring to the study of the motion of both rigid bodies and particles. ... Transient means passing with time. ...

Coronal loops and the Coronal Heating Problem

A closed fieldline does not constitute a coronal loop however, closed flux must be filled with plasma before it can be called a coronal loop. With this in mind it becomes clear that coronal loops are a rarity on the solar surface as the majority of closed flux structures are empty. This means the mechanism that heats the corona and injects chromospheric plasma into the closed magnetic flux is highly localised.^[4] The mechanism behind plasma filling, dynamic flows and coronal heating remains a mystery. The mechanism(s) must be stable enough to continue to feed the corona with chromospheric plasma and powerful enough to accelerate and therefore heat the plasma from 6000K to well over 1MK over the short distance from chromosphere, transition region to the corona. This is the very reason coronal loops are targeted for intense study. They are anchored to the photosphere, are fed by chromospheric plasma, protrude into the transition region and exist at coronal temperatures after undergoing intensive heating.

The idea that the coronal heating problem is solely down to some coronal heating mechanism is misleading. Firstly, the plasma filling overdense loops is drained directly from the chromosphere. There is no coronal mechanism known that can compress coronal plasma and feed it into coronal loops at coronal altitudes. Secondly, observations of coronal upflows points to a chromospheric source of plasma. The plasma is therefore chromospheric in origin, there must be consideration of this when looking into coronal heating mechanisms. This is a chromospheric energization and coronal heating phenomenon possibly linked through a common mechanism.

Unsolved problems in physics: Why is the Sun's Corona so much hotter than the Sun's surface?

Image File history File links Question_dropshade. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

History of observations

1946-1975

Many strides have been made by ground-based telescopes (such as the Mauna Loa Solar Observatory, MLSO, in Hawaii) and eclipse observations of the corona, but to escape the obscuring effect of the Earth’s atmosphere, space-based observations have have become a necessary evolution for solar physics. Beginning with the short (7 minute) Aerobee rocket flights in 1946 and 1952, spectrograms measured solar EUV and Lyman-α emissions. Basic X-ray observations were attained by 1960 using such rockets. The British Skylark rocket missions from 1959-1978 also returned mainly X-ray spectrometer data.^[5] Although successful, the rocket missions were very limited in lifetime and payload. During the period of 1962-1975, the satellite series Orbiting Solar Observatory (OSO-1 to OSO-8) were able to gain extended EUV and X-ray spectrometer observations. Then in 1973, Skylab was launched and began a new multi-wavelength campaign which typified future observatories.^[6] This mission only lasted a year and was superceded by the Solar Maximum Mission which became the first observatory to last the majority of a solar cycle (from 1980-1989).^[7] A wealth of data was accumulated across the whole range of emission. The Mauna Loa Solar Observatory (MLSO) is a collection of solar imaging instruments located on the island of Hawaii, USA. General Information The MLSO is operated by the High Altitude Observatory, which is a division of the National Center for Atmospheric Research. ... Official language(s) English, Hawaiian Capital Honolulu Largest city Honolulu Area  Ranked 43rd  - Total 10,931 sq mi (29,311 km²)  - Width n/a miles (n/a km)  - Length 1,522 miles (2,450 km)  - % water 41. ... Total eclipse redirects here. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... This article is about evolution in biology. ... Year 1946 (MCMXLVI) was a common year starting on Tuesday. ... 1952 (MCMLII) was a Leap year starting on Tuesday (link will take you to calendar). ... It has been suggested that this article or section be merged with periodogram. ... In physics, the Lyman series is the series of transitions and resulting emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1 (where n is the principal quantum number referring to the energy level of the electron). ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... 1960 (MCMLX) was a leap year starting on Friday (the link is to a full 1960 calendar). ... Skylark is the name of a British elevator research sounding rocket. ... Year 1959 (MCMLIX) was a common year starting on Thursday of the Gregorian calendar. ... 1978 (MCMLXXVIII) was a common year starting on Sunday. ... // Headline text Bold text:For Acoustic uses in spectrographs of sound waves, see below. ... 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar). ... 1975 (MCMLXXV) was a common year starting on Wednesday. ... Dr. Nancy Roman, with a model of the Orbiting Solar Observatory. ... 1973 (MCMLXXIII) was a common year starting on Monday. ... Skylab was the first space station the United States launched into orbit. ... The Solar Maximum Mission satellite (or SolarMax) was designed to investigate solar phenomenon, particularly solar flares. ... It has been suggested that this article or section be merged with Schwabe-Wolf cycle. ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... 1989 (MCMLXXXIX) was a common year starting on Sunday of the Gregorian calendar. ...

1991-present day

The solar community was rocked by the launch of Yohkoh (Solar A) from Kagoshima Space Centre (Southern Japan) in August 1991 It was lost on 14th December, 2001 due to battery failure, but revolutionised X-ray observations in its decade of operations. Yohkoh (or Sunbeam) orbited the Earth in an elliptical orbit, observing X-ray and γ-ray emissions from solar phenomena such as solar flares. Yohkoh carried four instruments. The Bragg Crystal Spectrometer (BCS), the Wide Band Spectrometer (WBS), the Soft X-Ray Telescope (SXT) and the Hard X-Ray Telescope (HXT) were operated by a consortium of scientists from Japan, USA and UK. Of particular interest is the SXT instrument for observing X-ray emitting coronal loops. Yohkoh (Sunbeam in Japanese), also known as SOLAR-A, was a Japanese Institute of Space and Astronautical Science Solar mission with United States and United Kingdom collaboration. ... August is the eighth month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 1991 (MCMXCI) was a common year starting on Tuesday of the Gregorian calendar. ... (Redirected from 14th December) December 14 is the 348th day of the year (349th in leap years) in the Gregorian Calendar. ... 2001 (MMI) was a common year starting on Monday of the Gregorian calendar. ... Elliptical may refer to: Ellipse: a shape and mathematical construct Elliptical trainer: an exercise machine This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... This article is about electromagnetic radiation. ... Yohkoh (Sunbeam in Japanese), also known as SOLAR-A, was a Japanese Institute of Space and Astronautical Science Solar mission with United States and United Kingdom collaboration. ... Yohkoh (Sunbeam in Japanese), also known as SOLAR-A, was a Japanese Institute of Space and Astronautical Science Solar mission with United States and United Kingdom collaboration. ...

X-ray solar coronal loops as viewed by the Yohkoh observatory

The SXT instrument observed X-rays in the 0.25-4.0keV range, resolving solar features to 2.5 arc seconds with a temporal resolution of 0.5-2 seconds. SXT was sensitive to plasma in the 2-4MK temperature range, making it an ideal observational platform to compare with data collected from TRACE coronal loops radiating in the EUV wavelengths.^[8] Yohkoh (Sunbeam in Japanese), also known as SOLAR-A, was a Japanese Institute of Space and Astronautical Science Solar mission with United States and United Kingdom collaboration. ... The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ... Look up Trace in Wiktionary, the free dictionary. ...

The next major step in solar physics came at the launch of the Solar and Heliospheric Observatory (SOHO) in December 1995 from Cape Canaveral Air Force Station in Florida, USA. SOHO originally had an operational lifetime of two years. The mission was extended to March 2007 due to its resounding success allowing SOHO to observe a complete 11 year solar cycle. SOHO continually faces the Sun holding a slow orbit around the First Lagrangian Point (L1) where the gravitational balance between the Sun and Earth provides a stable position for SOHO to orbit. SOHO is continually eclipsing the Sun from the Earth at a distance of approximately 1.5 million kilometres. The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on 2 December 1995 to study the Sun, and began normal operations in May 1996. ... Look up December in Wiktionary, the free dictionary. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... The Bumper V-2 was the first missile launched at Cape Canaveral on July 24, 1950. ... This article or section does not cite its references or sources. ... March is the third month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD (or CE) era. ... A contour plot of the effective potential of a two-body system (the Sun and Earth here), showing the five Lagrange points. ...

A typical SOHO image of the chromosphere and magnetic structure of the Sun.

SOHO is managed by scientists from the European Space Agency (ESA) and NASA. Comprising of more instruments than both TRACE and Yohkoh, this large solar mission was designed to look at the chain from the solar interior, the solar corona to the solar wind. SOHO has 12 instruments on board including the Coronal Diagnostic Spectrometer (CDS), the Extreme ultraviolet Imaging Telescope (EIT), the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) and the UltraViolet Coronagraph Spectrometer (UVCS) which are all used extensively in the study of the transition region and corona. Image File history File links SOHO_solar_flare_sun_large_20031026_0119_eit_304. ... Image File history File links SOHO_solar_flare_sun_large_20031026_0119_eit_304. ... The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on 2 December 1995 to study the Sun, and began normal operations in May 1996. ... ESA redirects here. ...

The EIT instrument is used extensively in coronal loop observations. EIT images the transition region through to the inner corona by utilising four band passes, 171Å FeIX, 195Å FeXII, 284Å FeXV and 304Å HeII, each corresponding to different EUV temperatures, probing the chromospheric network to the lower corona.

The Transition Region And Coronal Explorer (TRACE) was launched in April, 1998 from Vandenberg Air Force Base as part of NASA’s Goddard Space Flight Center Small Explorer (SMEX) project. The small orbiting instrument has a 30×160cm, 8.66m focal length Cassegrain telescope with a 1200×1200px CCD detector. The timing of the launch was planned to coincide with the rising phase of the solar maximum. Observations of the transition region and lower corona could then be carried out in conjunction with SOHO to give an unprecedented view of the solar environment during this exciting phase of the solar cycle. Look up Trace in Wiktionary, the free dictionary. ... Look up Trace in Wiktionary, the free dictionary. ... April is the fourth month of the year in the Gregorian Calendar and one of four with the length of 30 days. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ... Vandenberg Air Force Base is a base with a spaceport, located in Santa Barbara County, California. ...

Full-disk mosaic of the million-degree Sun by TRACE

Due to the high spatial (1 arc second) and temporal resolution (1-5sec), TRACE has been able to capture highly detailed images of coronal structures, whilst SOHO provides the global (lower resolution) picture of the Sun. This campaign demonstrates the observatory’s ability to track the evolution of steady-state (or quiescent) coronal loops. TRACE utilizes filters that are sensitive to electromagnetic radiation in the 171Å FeIX, 195Å FeXII, 284Å FeXV, 1216Å HI, 1550Å CIV and 1600Å range. Of particular interest are the 171Å, 195Å and 284Å band passes as they are sensitive to the radiation emitted by quiescent coronal loops. The Sun is the star at the center of the Solar System. ... Look up Trace in Wiktionary, the free dictionary. ... In cell biology, quiescence is the state of cell when it is not dividing. ...

Dynamic flows

All of the above space missions have been highly successful in observing strong plasma flows and highly dynamic processes in coronal loops. For example, SUMER observations suggest flow velocities of 5 - 16kms^-1 in the solar disk, other joint SUMER/TRACE observations detect flows of 15-40kms^-1.^[9][10] Very high velocities have been detected by the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission where plasma velocities were found in the range of 40 - 60kms^-1.

New missions

The new solar observatory, Hinode (Solar-B), launched September 2006, will observe the magnetic structure of the corona.

SOLAR-B Hinode (ひので, Sunrise in Japanese), formerly known as Solar-B, is a Japan Aerospace Exploration Agency Solar mission with United States and United Kingdom collaboration. ...

Useful links

• The new solar observatory, Hinode (Solar-B)
• The highly successful solar X-ray mission, Yohkoh (Solar-A)
• TRACE homepage
• Solar and Heliospheric Observatory, including near-real-time images of the solar corona
• Coronal heating problem at Innovation Reports
• NASA/GSFC description of the coronal heating problem
• FAQ about coronal heating

SOLAR-B Hinode (ひので, Sunrise in Japanese), formerly known as Solar-B, is a Japan Aerospace Exploration Agency Solar mission with United States and United Kingdom collaboration. ... Yohkoh (Sunbeam in Japanese), also known as SOLAR-A, was a Japanese Institute of Space and Astronautical Science Solar mission with United States and United Kingdom collaboration. ...

References

The Sun v • d • e
Structure: Solar Core - Radiation Zone - Convection Zone
Atmosphere - Photosphere - Chromosphere - Transition region - Corona
Extended Structure: Termination Shock - Heliosphere - Heliopause - Heliosheath - Bow Shock
Solar Phenomena: Sunspots - Faculae - Granules - Supergranulation - Solar Wind - Spicules
Coronal loops - Solar Flares - Solar Prominences - Coronal Mass Ejections
Moreton Waves - Coronal Holes
Other: Solar System - Solar Variation - Solar Dynamo - Heliospheric Current Sheet - Solar Radiation - Solar Eclipse