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| solar corona | |
|---|---|
| Name | Solar corona |
| Type | Stellar atmosphere |
solar corona
The solar corona is the outermost layer of the Sun's atmosphere, visible as a pearly halo during total Solar eclipse and studied across wavelengths by space missions like Solar and Heliospheric Observatory and Parker Solar Probe. It exhibits temperatures of order 1–3 million kelvin despite originating above the much cooler photosphere observed by instruments on International Solar-Terrestrial Physics and ground facilities such as the Mauna Loa Solar Observatory. Coronal behavior drives phenomena that affect Earth and the heliosphere, motivating observations from observatories like SOHO and agencies including NASA and European Space Agency.
The corona overlays the photosphere and chromosphere and extends outward into the heliosphere observed by probes such as Ulysses (spacecraft), Wind (spacecraft), and Voyager program. It is composed of highly ionized plasma threaded by magnetic fields originating from active regions monitored by the National Solar Observatory and modeled by centers such as NASA Goddard Space Flight Center. Coronal emission lines, first noted in spectra from eclipses and early spectrographs developed by teams affiliated with the Royal Observatory Greenwich and the Yerkes Observatory, revealed forbidden lines later explained by highly ionized elements.
The corona's plasma density and temperature vary with height; densities near the base are measured by instruments on Hinode (solar mission) and inferred from eclipse coronagraphy used by Large Angle and Spectrometric Coronagraph teams. Coronal abundances show fractionation relative to the photosphere, studied in work by researchers at University of Cambridge and Stanford University. Magnetic pressure dominates gas pressure in many coronal regions, a balance explored in theoretical studies by groups associated with Princeton University and Harvard-Smithsonian Center for Astrophysics. Spectroscopic diagnostics from observatories like TRACE and IRIS (spacecraft) provide charge-state and density measurements used in coronal seismology developed by scientists at Max Planck Institute for Solar System Research.
Leading explanations for coronal heating include wave dissipation and magnetic reconnection, theories advanced by investigators at Perkins Observatory and teams including members of Lockheed Martin Solar and Astrophysics Laboratory. Alfvén waves generated in the convection zone and chromosphere, studied by researchers at University of Chicago and University of Oslo, may transport energy upward; dissipation mechanisms were explored in analyses published by groups at Columbia University and University of California, Berkeley. Nanoflare heating, a model proposed in work influenced by Eugene Parker and advanced by collaborators from University of Hawaii, invokes small-scale reconnection events quantified in studies from Los Alamos National Laboratory and CERN-affiliated plasma physics groups. Competing models are tested with data from missions such as Solar Dynamics Observatory and experimental facilities including National Center for Atmospheric Research laboratories.
Coronal structures include streamers, coronal holes, plumes, and active-region loops first cataloged in imagery from observatories like Mt. Wilson Observatory and later from Yohkoh (satellite). Coronal loops anchored in sunspots and active regions monitored by the Royal Observatory of Belgium evolve through magnetic flux emergence studied by teams at Caltech and University of Tokyo. Dynamic processes such as magnetic reconnection events and flares are correlated with phenomena observed by GOES satellites and analyzed by groups at Los Alamos National Laboratory and University of Colorado Boulder. Coronal seismology uses oscillations detected by instruments developed at Johns Hopkins University and Leibniz Institute for Astrophysics Potsdam to infer field strengths and plasma parameters.
The corona is the source of the solar wind observed by Parker Solar Probe and historical missions like Mariner 2. Fast and slow solar wind streams originate in coronal holes and streamer belts studied by teams at NASA Ames Research Center and Jet Propulsion Laboratory. Coronal mass ejections (CMEs), first identified in coronagraph data from Naval Research Laboratory and characterized by studies at Catholic University of America, expel plasma and magnetic flux driving geomagnetic storms observed by agencies including NOAA and research centers such as Space Weather Prediction Center. CME initiation, propagation, and interaction with planetary magnetospheres are modeled by consortia including Community Coordinated Modeling Center investigators.
Techniques include white-light coronagraphy pioneered by inventors affiliated with American Optical Company and spaceborne instruments like SOHO/LASCO and imagers on STEREO (mission). Extreme ultraviolet and X-ray imaging from missions such as Hinode, SDO, and RHESSI reveal high-temperature structures; spectrometers on SUMER and EIS provide plasma diagnostics developed by instrument teams at ESA and JAXA. In situ sampling of coronal-origin plasma by Parker Solar Probe and Solar Orbiter complements remote sensing performed by ground-based telescopes including Daniel K. Inouye Solar Telescope and networks coordinated by International Astronomical Union working groups.
Magnetohydrodynamic (MHD) models of the corona are developed at institutions like Princeton Plasma Physics Laboratory and University of Michigan using codes validated against observations from SDO and SOHO. Global heliospheric models coupling corona to solar wind are produced by teams at Institute of Space and Astronautical Science and Los Alamos National Laboratory for space weather forecasting used by European Space Agency and NOAA. High-resolution kinetic and particle-in-cell simulations from research groups at Max Planck Institute for Plasma Physics and Lawrence Livermore National Laboratory explore microphysical heating and reconnection processes.