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

Astrophysics collection (March 11, 2016)

Latest astrophysics news Rotation curves of galaxies as a test of MOND? Galaxies are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together. In a recent paper ( Haghi et al. 2016 ) the authors test the Modified Newtonian Dynamics (MOND).    Read>> A binary origin for a central compact object (CCO)? Doroshenko et al. 2016 investigate the possible binary origin of the CCO XMMUJ173203.3-344518 .   Read>> Rapidly rotating pulsars as possible sources of fast radio bursts (FRB) In a recent paper ( Lyutikov et al. 2016 ) the authors discuss possible association of fast radio bursts (FRBs) with supergiant pulses emitted by young pulsars.   Read>> Supernovae from WD-WD direct collisions In recent years it was suggested that WD-WD direct collisions (probably extremely rare and occurring only in dense stellar clusters) provide an additional channel for supernova...
Post a Comment
Read more

Dark Neutron Stars

Illustration of a neutron star. Credit: NASA/Dana Berry There is good evidence that electron-positron pair formation is not present in that section of the pulsar open magnetosphere which is the source of coherent radio emission, but the possibility of two-photon pair creation in an outer gap remains. Calculation of transition rates for this process based on measured whole-surface temperatures, combined with a survey of gamma-ray, X-ray and optical luminosities, expressed per primary beam lepton, shows that few Fermi LAT pulsars have significant outer-gap pair creation. For radio-loud pulsars with positive polar-cap corotational charge density and an ion-proton plasma there must be an outward flow of electrons from some other part of the magnetosphere to maintain a constant net charge on the star. In the absence of pair creation, it is likely that this current is the source of GeV gamma-emission observed by the Fermi LAT and its origin is in the region of the outer gap. With n...
Post a Comment
Read more

A METHOD TO TEST THE EXISTENCE OF REGULAR BLACK HOLES

Illustration of a black hole. Image Credit & Copyright: Alain Riazuelo The existence of the singularity is an intrinsic problem of the General Relativity (GR). At the fundamentally level, the resolution of the problem of the singularity lies with the expectation that under situations where quantum effects become strong, the behavior of gravity could possibly greatly deviate from that predicted by the classical theory of GR. Regular black hole solution are proposed with the same spacetime geometry outside the horizon as the traditional black hole, but bears no singularity inside. Whether or not black hole singularities should exist, they would be covered by the black hole horizon. The black hole horizon serves as an information curtain hindering outside observers from directly observing the interior structure of the black hole, and determining that whether or not the black hole singularity does really exist. A method is needed to check the correctness of the new constructions ...
Post a Comment
Read more