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Blobrana


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Sun's Atmosphere
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NASA Spacecraft Provides New Information About Sun's Atmosphere

NASA's Interface Region Imaging Spectrograph (IRIS) has provided scientists with five new findings into how the sun's atmosphere, or corona, is heated far hotter than its surface, what causes the sun's constant outflow of particles called the solar wind, and what mechanisms accelerate particles that power solar flares.
The new information will help researchers better understand how our nearest star transfers energy through its atmosphere and track the dynamic solar activity that can impact technological infrastructure in space and on Earth. Details of the findings appear in the current edition of Science.
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Blobrana


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RE: Corona
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Best Evidence Yet For Coronal Heating Theory Detected by NASA Sounding Rocket

Scientists have recently gathered some of the strongest evidence to date to explain what makes the sun's outer atmosphere so much hotter than its surface. The new observations of the small-scale extremely hot temperatures are consistent with only one current theory: something called nanoflares - a constant peppering of impulsive bursts of heating, none of which can be individually detected -- provide the mysterious extra heat.
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Blobrana


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Posts: 131433
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Solar corona
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Title: Fine strand-like structure in the solar corona from MHD transverse oscillations
Author: P. Antolin, T. Yokoyama, T. Van Doorsselaere

Current analytical and numerical modelling suggest the existence of ubiquitous thin current sheets in the corona that could explain the observed heating requirements. On the other hand, new high resolution observations of the corona indicate that its magnetic field may tend to organise itself in fine strand-like structures of few hundred kilometres widths. The link between small structure in models and the observed widths of strand-like structure several orders of magnitude larger is still not clear. A popular theoretical scenario is the nanoflare model, in which each strand is the product of an ensemble of heating events. Here, we suggest an alternative mechanism for strand generation. Through forward modelling of 3D MHD simulations we show that small amplitude transverse MHD waves can lead in a few periods time to strand-like structure in loops in EUV intensity images. Our model is based on previous numerical work showing that transverse MHD oscillations can lead to Kelvin-Helmholtz instabilities that deform the cross-sectional area of loops. While previous work has focused on large amplitude oscillations, here we show that the instability can occur even for low wave amplitudes for long and thin loops, matching those presently observed in the corona. We show that the vortices generated from the instability are velocity sheared regions with enhanced emissivity hosting current sheets. Strands result as a complex combination of the vortices and the line-of-sight angle, last for timescales of a period and can be observed for spatial resolutions of a tenth of loop radius.

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Blobrana


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Posts: 131433
Date:
RE: Corona
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Space Instrument Adds Big Piece to the Solar Corona Puzzle

How can the solar atmosphere get hotter, rather than colder, the farther you go from the Sun's surface? This mystery has puzzled solar astronomers for decades. A suborbital rocket mission that launched in July 2012 has just provided a major piece of the puzzle.
The High-resolution Coronal Imager, or Hi-C, revealed one of the mechanisms that pumps energy into the corona, heating it to temperatures up to 7 million degrees F. The secret is a complex process known as magnetic reconnection.
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Blobrana


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NASA's Solar Fleet Peers Into Coronal Cavities

The sun's atmosphere dances. Giant columns of solar material - made of gas so hot that many of the electrons have been scorched off the atoms, turning it into a form of magnetized matter we call plasma - leap off the sun's surface, jumping and twisting. Sometimes these prominences of solar material, shoot off, escaping completely into space, other times they fall back down under their own weight.
The prominences are sometimes also the inner structure of a larger formation, appearing from the side almost as the filament inside a large light bulb. The bright structure around and above that light bulb is called a streamer, and the inside "empty" area is called a coronal prominence cavity.
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