Helmet streamers

Helmet Streamers and the Magnetic Structure of the Corona. Magnetic field lines from a computer simulation performed in advance of the October 24, solar eclipseto predict the structure of the solar corona, helmet streamers.

A three-dimensional axisymmetric time-dependent magnetohydrodynamic model has been used to obtain quasi-static helmet-streamer solutions that contain a cavity flux rope in their closed field region. The dynamical equilibrium of the cavity flux rope inside the closed region of the streamer can be described as the partial balance between the outward acting magnetic force and the pressure and gravity forces inside the flux rope, which, in addition, is held down by the helmet dome above. Our solutions indicate that the helmet streamer containing a cavity flux rope has more magnetic energy than the corresponding open field configuration, which means that the state transition from the former to the latter is permitted energetically. These solutions may serve as pre-event coronae for studying the initiation of coronal mass ejections. Subject headings: MHD Sun: corona. Coronal helmet streamers are large-scale, quasi-static structures in the solar corona.

Helmet streamers

Coronal Features. Click on image for larger version. Helmet Streamers Helmet streamers are large cap-like coronal structures with long pointed peaks that usually overlie sunspots and active regions. We often find a prominence or filament lying at the base of these structures. Helmet streamers are formed by a network of magnetic loops that connect the sunspots in active regions and help suspend the prominence material above the solar surface. The closed magnetic field lines trap the electrically charged coronal gases to form these relatively dense structures. The pointed peaks are formed by the action of the solar wind blowing away from the Sun in the spaces between the streamers. Polar Plumes Polar plumes are long thin streamers that project outward from the Sun's north and south poles. We often find bright areas at the footpoints of these features that are associated with small magnetic regions on the solar surface. These structures are associated with the "open" magnetic field lines at the Sun's poles. The plumes are formed by the action of the solar wind in much the same way as the peaks on the helmet streamers. Coronal Loops Coronal loops are found around sunspots and in active regions. These structures are associated with the closed magnetic field lines that connect magnetic regions on the solar surface. Some loops, however, are associated with solar flares and are visible for much shorter periods.

In the present paper, we actually obtain two self-consistent MHD solutions of a helmet streamer containing a cavity flux rope with background solar wind, helmet streamers.

A large-scale structure seen in white-light images of the Sun's corona. Streamers are brighter than the surrounding corona because they are of higher density, and are often bottle-shaped, narrowing away from the Sun. They are also referred to as helmet streamers because of their resemblance to a helmet with a spike on top. The broad base of the streamer is where coronal plasma is trapped along closed magnetic field lines, but at larger distances the magnetic field weakens and the plasma is able to break free from the Sun, producing the narrow spike. Streamers are principally found above active regions and prominences, but also occur at solar minimum when there are few or no active regions. In the latter case, two streamers are seen on opposite sides of the Sun, close to the equator.

Helmet streamers , also known as coronal streamers , are elongated cusp-like structures in the Sun 's corona which are often visible in white-light coronagraphs and during solar eclipses. They are closed magnetic loops which lie above divisions between regions of opposite magnetic polarity on the Sun's surface. The solar wind elongates these loops to pointed tips which can extend a solar radius or more into the corona. During solar minimum , helmet streamers are found closer to the heliographic equator, whereas during solar maximum they are found more symmetrically distributed around the Sun. Helmet streamers have cusp-like bases that taper radially outward away from the Sun forming long stalks. The base typically extends up to 1. Helmet streamers are structured by closed magnetic fields and lie above boundaries separating opposite magnetic polarity in the Sun's photosphere. Their thin stalks consist of oppositely directed magnetic fields which form current sheets. The white-light emissions of helmet streamers is due to the high electron density of the confined plasma relative to the surrounding corona. Light from the photosphere is Thompson scattered off of these electrons with the intensity of scattered light depending on the number of electrons along the observer's line of sight.

Helmet streamers

During any total solar eclipse, you are guaranteed to see the magnificent solar corona extending far from the obscured solar disk. In general, the corona will not look like a smooth halo of light, but will have structure to it both big and small. The most dramatic large structures are the helmet streamers that look like their namesake and have been recorded in eclipse drawings since the s. During the Eclipse of Sept. The story of Eclipses, G. Chambers He identified an extended, smooth component onto which he superposed large, conical features along with some indication of prominences. This astronomical drawing during the July 28, total solar eclipse was published in Thierry Moreux's 'Les Eclipses' and also shows pronounced conical-shaped features in a remarkably regular pattern. By the eclipse of July 29, Ettiene Trouvelot rendered this artist-quality painting of coronal details.

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Streamers are brighter than the surrounding corona because they are of higher density, and are often bottle-shaped, narrowing away from the Sun. The base typically extends up to 1. Click on image for larger version. The helmet streamer containing a cavity flux rope has more magnetic energy than the corresponding streamer containing a flux rope with density enhancement. Living Reviews in Solar Physics. An optional semi-implicit operator similar to the one used by Miki et al. Oxford Reference. Our test results suggest that the cavity must contain enough magnetic strength for its existence. The radius, pressure, magnetic field, and currents are normalized, as follows: with R , p , and B being solar radius, plasma pressure, and magnetic field strength on the solar surface, respectively. All Rights Reserved.

For five months in mid , Emily Mason did the same thing every day. Then, in October , she stopped.

Prominences are often situated beneath helmet streamers, and active regions occur beneath streamers near the equator sometimes called active regions streamers. Plage Spicule Moreton wave. Coronal Loops Coronal loops are found around sunspots and in active regions. Comparing with the corresponding configuration before mass draining, we see that after mass draining, the whole configuration is still in equilibrium, although the flux rope expands a little. Our results also indicate that the helmet streamer containing a cavity flux rope may have more magnetic energy than the corresponding open field configuration, which makes the state transition of the streamer possible without an external energy source. For convenience, constants J and J p are replaced by 1 and 2 which have clearer physical meaning. Current sheet Termination shock Heliosheath Heliopause Bow shock. Advances in Space Research. Delete Cancel Save. The second phenomena is that the streamers eventually become sculpted by outflowing gas in the expanding corona or the solar wind, which draws them out into linear, radial features at a few million km from the solar surface. In our simulation, we also tested the cases in which only mass draining takes place in the flux rope without increasing the magnetic field strength. Small blobs of plasma, or "plasmoids" are sometimes released from the tips of helmet streamers, and this is one source of the slow component of the solar wind. Personal Profile.