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

A UNIVERSE WITHOUT A CENTER?

Image Credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb. According to the standard theories of cosmology, there is no center of the universe. In a conventional explosion, material expand out from a central point and the instinct suggests that with the Big Bang happened something similar. But the Big Bang was not an explosion like that at all: it was an explosion of space, not an explosion in space . The Big Bang happened everywhere in the Universe.
Post a Comment
Read more

UNIVERSE IS FINITE OR INFINITE?

Art by Moonrunner Design   At present there is no answer to this question. However I will try to list the hypothesys currently on the table with related issues.
Post a Comment
Read more

New research looks at how ‘cosmic web’ of filaments alters star formation in galaxies

Cosmic Web. Credit: NASA Astronomer Gregory Rudnick sees the universe crisscrossed by something like an interstellar superhighway system. Filaments — the strands of aggregated matter that stretch millions of light years across the universe to connect galaxy clusters — are the freeways. “Galaxies will flow along filaments from less dense parts of the universe to more dense parts of the universe, kind of like cars flowing down a highway to the big city. In this case, they are going toward big clusters, being pulled by the gravity of those large concentrations of matter,” he said. “I’m interested in how galaxies are affected by the regions in which they live,” Rudnick said. “Filaments are the first place where galaxies come into contact with higher density regions of the universe. If a galaxy in a ‘rural’ part of the universe enters a dense part, I want to know how its properties change — for example, does it change the number of stars it forms, or does its shape get altered? Us...
Post a Comment
Read more