Skip to main content

FLARES HEAT THE UPPER CHROMOSPHERE OF THE SUN


Image: Anatomy of the Sun. Credit: NASA/Jenny Mottar

The standard model of solar flares explains many observational features of flares, assuming that they are driven by magnetic reconnection. Flares release approximately 1030–1033 erg into the plasma but it is not clear, however, how that energy is partitioned between in situ heating of the corona, particle acceleration, and wave generation, nor to what extent the observable features of a flare depend on the balance between different types of coronal energy transport.


In a recent paper (Reep & Russell, 2016 ApJL), the authors have developed a numerical model of flare heating due to the dissipation of Alfvénic waves propagating from the corona to the chromosphere.

A solar flare is a sudden flash of brightness observed near the Sun's surface and it ejects clouds of electrons, ions, and atoms through the corona of the sun into space. Flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior, and they are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona.

An Alfvén wave, instead, is a type of magnetohydrodynamic wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines. The wave propagates in the direction of the magnetic field. The motion of the ions and the perturbation of the magnetic field are in the same direction and transverse to the direction of propagation.

Image: Structure of the Sun. Credit: Wikimedia Common

The paper (Reep & Russell, 2016 ApJL) presents an investigation of the key parameters of these waves on the energy transport, heating, and subsequent dynamics. For sufficiently high frequencies and perpendicular wave numbers, the waves dissipate significantly in the upper chromosphere, strongly heating it to flare temperatures. This heating can then drive strong chromospheric evaporation, bringing hot and dense plasma to the corona. The authors derive three important conclusions: (1) Alfvenic waves, propagating from the corona to the chromosphere, are capable of heating the upper chromosphere and the corona, (2) the atmospheric response to heating due to the dissipation of Alfvenic waves can be strikingly similar to heating by an electron beam, and (3) this heating can produce explosive evaporation.


Reep & Russell, 2016 (ApJL) - Alfvénic wave heating of the upper chromosphere in flares (arXiv)

 Structure of the sun --> (Nasa) (Wikipedia)
Solar flares   --> (Nasa) (Wikipedia)
Alfvén waves --> (Wikipedia)

Etichette:

Comments

Post a Comment

Popular posts from this blog

Protoplanetary disks in the hostile environment of Carina

Image: Star-forming region in the Carina Nebula. Credit: NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA) In a recent paper (Mesa-Delgado et al. 2016) [1] the authors report the first direct imaging of protoplanetary disks in the star-forming region of Carina, the most distant, massive cluster in which disks have been imaged.
Post a Comment
Read more

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...
Post a Comment
Read more

A BINARY ORIGIN FOR A CENTRAL COMPACT OBJECT (CCO)?

Figure: False-Colour X-ray and infrared emission image from the core of the infrared shell. The RGB colours correspond to Chandra X-ray 0.2-10 keV (blue), IRAC infrared 8 μm (green), and HPACS 70 μm (red) data. The intensity scale is logarithmic for all channels. Overlaid are equal brightness levels from the MIPS 24 μm band. Note that around the CCO the infrared emission is suppressed in the 70 μm band and enhanced in the 24 μm band suggesting higher dust temperature. Credit: Doroshenko et al 2016 Central compact objects (CCOs) are thought to be young isolated neutron stars that were born during the preceding core-collapse supernova explosion.
Post a Comment
Read more