The standard flare model in three dimensions, II. Upper limit on solar flare energy |
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Guillaume Aulanier Submitted: 2012-11-15 02:39
Solar flares strongly affect the Sun's atmosphere as well as the
Earth's environment. Quantifying the maximum possible energy of solar
flares of the present-day Sun, if any, is thus a key issue in
heliophysics.
The largest solar flares observed over the past few decades have reached
energies of a few times 1032 ergs, possibly up to 1033 ergs. Flares
in active Sun-like stars reach up to about 1036 ergs. In the absence
of direct observations of solar flares within this range, complementary
methods of investigation are needed to assess the probability of solar
flares beyond those in the observational record.
Using historical reports for sunspot and solar active region
properties in the photosphere we scale to observed solar values
a realistic dimensionless 3D MHD simulation for eruptive flares,
which originate from a highly sheared bipole. This enables us to
calculate the magnetic fluxes and flare energies in the model
in a wide paramater space.
Firstly, commonly observed solar conditions lead to modeled magnetic
fluxes and flare energies that are comparable to those estimated from
observations. Secondly, we evaluate from observations that 30% of the area
of sunspot groups are typically involved in flares. This is related to the
strong fragmentation of such groups, which naturally results from sub-photospheric
convection. When the model is scaled to 30% of the area of the largest
sunspot group ever reported, with its peak magnetic field being set to
the strongest value ever measured in a sunspot, it produces a flare with
a maximum energy of ~ 6x1033 ergs.
The results of the model suggest that the Sun is able to produce flares up
to about six times as energetic in TSI fluence as the strongest directly-observed
flare from Nov 4, 2003. Sunspot groups larger than historically reported would
yield superflares for spot pairs that would exceed tens of degrees in
extent. We thus conjecture that superflare-productive Sun-like stars
should have a much stronger dynamo than in the Sun.
Authors: G. Aulanier, P. Démoulin, C.J. Schrijver, M. Janvier, E. Pariat, B. Schmieder
Projects: None
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Publication Status: A&A (accepted)
Last Modified: 2012-11-20 20:25
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