Issue |
A&A
Volume 462, Number 1, January IV 2007
|
|
---|---|---|
Page(s) | 311 - 322 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20065152 | |
Published online | 24 October 2006 |
A nanoflare model of quiet Sun EUV emission
1
Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany e-mail: anuschka.pauluhn@psi.ch
2
now at Paul Scherrer Institut, 5232 Villigen, Switzerland
Received:
7
March
2006
Accepted:
19
October
2006
Nanoflares have been proposed as the main source of heating of the solar
corona. However, detecting them directly has so far proved elusive, and
extrapolating to them from the properties of larger brightenings
gives unreliable estimates of the power-law exponent α characterising their
distribution.
Here we take the approach of statistically
modelling light curves representative of the quiet Sun as seen in
EUV radiation.
The basic assumption is that all quiet-Sun EUV emission is due to
micro- and nanoflares, whose radiative energies display a power-law
distribution.
Radiance values in the quiet Sun follow a lognormal distribution.
This is irrespective of whether the distribution is made over a spatial
scan or over a time series.
We show that these distributions can be reproduced by our simple model.
By simultaneously fitting the radiance distribution function and the power
spectrum obtained from the light curves emitted by transition region
and coronal lines
the power-law distribution of micro- and nanoflare brightenings
is constrained.
A good statistical match to the measurements is obtained
for a steep power-law distribution of nanoflare energies,
with power-law exponent . This is consistent with the
dominant heat input to the corona being provided by nanoflares, i.e.,
by events with energies around 1023 erg.
In order to reproduce the observed SUMER time series approximately
103 to 104 nanoflares are needed per second throughout
the atmosphere of the quiet Sun (assuming the nanoflares to cover an
average area of 1013 m2).
Key words: Sun: flares / Sun: transition region / Sun: corona
© ESO, 2007
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