Coronal loops form the basic structure of the lower corona and transition region of the Sun. TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The solar transition region is a region of the Sun 's atmosphere between the Chromosphere and Corona. The Sun (Sol is the Star at the center of the Solar System. These highly structured and elegant loops are a direct consequence of the twisted solar magnetic flux within the solar body. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. 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 solar cycle, or the solar magnetic activity cycle, is the main source of periodic variation of all solar phenomena driving variations in Space weather. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming The upwelling magnetic flux pushes through the photosphere, exposing the cooler plasma below. 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 The contrast between the photosphere and solar interior gives the impression of dark spots, or sunspots. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming
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Physical features
A coronal loop is magnetic flux fixed at both ends, threading through the solar body, protruding into the solar atmosphere. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks 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.
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. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. 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. Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically An anchor is an object often made out of metal that is used to attach a ship to the bottom of a body of water at a specific point Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically The chromosphere (literally "colour sphere" is a thin layer of the Sun 's atmosphere just above the Photosphere, roughly 10000 kilometres deep The solar transition region is a region of the Sun 's atmosphere between the Chromosphere and Corona. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily
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]
Location
Coronal loops populate both active and quiet regions of the solar surface. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The solar transition region is a region of the Sun 's atmosphere between the Chromosphere and Corona. 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. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the 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. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. 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.
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 1 MK 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.
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. This is a list of some of the major unsolved problems in Physics. The Mauna Loa Solar Observatory (MLSO is a collection of Solar imaging instruments located on the island of Hawaii, USA at an elevation of 11000 feet The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 eVolution is the third Album by eLDee, it was due to be released in 2008 Beginning with the short (7 minute) Aerobee rocket flights in 1946 and 1952, spectrograms measured solar EUV and Lyman-α emissions. The Aerobee rocket was a small (8 m unguided suborbital Sounding rocket used for high atmospheric and Cosmic radiation research in the United States Year 1946 ( MCMXLVI) was a Common year starting on Tuesday (link will display full 1946 calendar of the Gregorian calendar. Year 1952 ( MCMLII) was a Leap year starting on Tuesday (link will display full calendar of the Gregorian calendar. The spectrogram is the result of calculating the Frequency spectrum of Windowed frames of a compound signal. In Physics, the Lyman series is the series of transitions and resulting Emission lines of the Hydrogen Atom as an Electron goes from Basic X-ray observations were attained by 1960 using such rockets. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Year 1960 ( MCMLX) was a Leap year starting on Friday (link will display full calendar of the Gregorian calendar. The British Skylark rocket missions from 1959-1978 also returned mainly X-ray spectrometer data. Skylark was a British Sounding rocket design The Skylark was first launched in 1957 from Woomera, Australia and its The year 1959 ( MCMLIX) was a Common year starting on Thursday (link will display full calendar of the Gregorian calendar. Year 1978 ( MCMLXXVIII) was a Common year starting on Sunday (link displays the 1978 Gregorian calendar) A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used [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. Year 1962 ( MCMLXII) was a Common year starting on Monday (the link is to a full 1962 calendar of the Gregorian calendar. Year 1975 ( MCMLXXV) was a Common year starting on Wednesday (link will display full calendar of the Gregorian calendar. The Orbiting Solar Observatory (abbreviated OSO) was the name of a series of nine NASA Satellites built by Ball Aerospace to study the Sun Then in 1973, Skylab was launched and began a new multi-wavelength campaign which typified future observatories. Year 1973 ( MCMLXXIII) was a Common year starting on Monday (link will display full calendar of the 1973 Gregorian calendar. Skylab was the first Space station the United States launched into orbit and the second space station ever visited by a human crew [6] This mission lasted only a year and was superseded by the Solar Maximum Mission which became the first observatory to last the majority of a solar cycle (from 1980-1989). The Solar Maximum Mission Satellite (or SolarMax was designed to investigate solar phenomenon particularly Solar flares. The solar cycle, or the solar magnetic activity cycle, is the main source of periodic variation of all solar phenomena driving variations in Space weather. Year 1980 ( MCMLXXX) was a Leap year starting on Tuesday (link displays the 1980 Gregorian calendar) Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) [7] A wealth of data was accumulated across the whole range of emission.
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 ( Sunbeam in Japanese) also known as Solar-A, was a Japanese Institute of Space and Astronautical Science Solar mission The is a space launch facility close to the Japanese city of Uchinoura, in Kagoshima Prefecture. Other names In Arabic, the month is called أغسطسص ʾUġusṭuṣ or آب ʾĀb; usage varies from place to place and Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Yohkoh (or Sunbeam) orbited the Earth in an elliptical orbit, observing X-ray and γ-ray emissions from solar phenomena such as solar flares. In Mathematics, an ellipse (from the Greek ἔλλειψις literally absence) is a Conic section, the locus of points in a In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions 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. Yohkoh ( Sunbeam in Japanese) also known as Solar-A, was a Japanese Institute of Space and Astronautical Science Solar mission For a topic outline on this subject see List of basic Japan topics. The United States of America —commonly referred to as the The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located 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
The SXT instrument observed X-rays in the 0. Yohkoh ( Sunbeam in Japanese) also known as Solar-A, was a Japanese Institute of Space and Astronautical Science Solar mission 25-4. 0 keV 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 2-4 MK temperature range, making it an ideal observational platform to compare with data collected from TRACE coronal loops radiating in the EUV wavelengths. TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and [8]
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. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December Events in December Union Day of Romania (1 December World AIDS Day ( December 1) National Day of Year 1995 ( MCMXCV) was a Common year starting on Sunday. Events of 1995 The Cape Canaveral Air Force Station (CCAFS is a detachment of the 45th Space Wing (45 SW Patrick AFB provides headquarters functions from the 45 SW a major airfield Florida ( is a state located in the southeastern region of the United States, bordering Alabama to the northwest and Georgia to the 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. Events in March American Red Cross Month Fire Prevention month ( The Philippines) Women's History Month ( United Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. 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.
SOHO is managed by scientists from the European Space Agency (ESA) and NASA. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member 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.
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, 171 Å FeIX, 195 Å FeXII, 284 Å FeXV and 304 Å 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. TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and April holidays and events National Poetry Month - in United States National Sexual Assault Awareness Month - in United Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar) Vandenberg Air Force Base is a United States military installation with a Spaceport, in Santa Barbara County, California, United States. The small orbiting instrument has a 30×160 cm, 8. 66 m 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.
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. The Sun (Sol is the Star at the center of the Solar System. TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and 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 171 Å FeIX, 195 Å FeXII, 284 Å FeXV, 1216 Å HI, 1550 Å CIV and 1600 Å range. Of particular interest are the 171 Å, 195 Å and 284 Å band passes as they are sensitive to the radiation emitted by quiescent coronal loops.
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 - 16 km s-1 in the solar disk, other joint SUMER/TRACE observations detect flows of 15-40 km s-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 - 60 km s-1.
New missions
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
References
- ^ Vourlidas, A. Hinode (ひので Japanese: "Sunrise" formerly known as Solar-B, is a Japan Aerospace Exploration Agency Solar mission with Yohkoh ( Sunbeam in Japanese) also known as Solar-A, was a Japanese Institute of Space and Astronautical Science Solar mission ; J. A. Klimchuk, C. M. Korendyke, T. D. Tarbell, B. N. Handy (2001). "On the correlation between coronal and lower transition region structures at arcsecond scales". Astrophysical Journal 563: 374–380. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Aschwanden, M. J. (2001). "An evaluation of coronal heating models for Active Regions based on Yohkoh, SOHO, and TRACE observations". Astrophysical Journal 560: 1035–1044. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Aschwanden, M. J. (2004). Physics of the Solar Corona. An Introduction. Praxis Publishing Ltd. . ISBN 3-540-22321-5.
- ^ Litwin, C. (1993). "On the structure of solar and stellar coronae - Loops and loop heat transport". ApJ 412: 375–385. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Boland, B. C. (1975). "Further measurements of emission line profiles in the solar ultraviolet spectrum". MNRAS 171: 697–724.
- ^ Vaiana, G. S. (1973). "X-Ray Observations of Characteristic Structures and Time Variations from the Solar Corona: Preliminary Results from SKYLAB". Astrophysical Journal Letters 185: L47–L51. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Strong, K. T. (1999). The many faces of the Sun: a summary of the results from NASA’s Solar Maximum Mission. New York: Springer.
- ^ Aschwanden, M. J. (2002). "Observations and models of coronal loops: From Yohkoh to TRACE, in Magnetic coupling of the solar atmosphere" 188: 1–9.
- ^ Spadaro, D. ; A. C. Lanzafame, L. Consoli, E. Marsch, D. H. Brooks, J. Lang (2000). "Structure and dynamics of an active region loop system observed on the solar disc with SUMER on SOHO". Astronomy & Astrophysics 359: 716–728.
- ^ Winebarger, A. R. ; H. Warren, A. van Ballegooijen, E. E. DeLuca, L. Golub (2002). "Steady flows detected in extreme-ultraviolet loops". Astrophysical Journal Letters 567: L89–L92. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
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