Issue |
A&A
Volume 437, Number 1, July I 2005
|
|
---|---|---|
Page(s) | 311 - 317 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20042405 | |
Published online | 10 June 2005 |
The cooling of coronal plasmas
II. Properties of the radiative phase
Space and Atmospheric Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2BZ, UK e-mail: s.bradshaw@imperial.ac.uk
Received:
22
November
2004
Accepted:
16
March
2005
The robust power-law relationship between the
temperature (T) and the density (n) that arises during the
radiative cooling phase of a solar coronal loop is investigated. Using
an analytical model and numerical hydrodynamic simulations, we
demonstrate that radiative energy loss from the transition region is
the dominant physical process. It governs the down-flow by which mass
is lost from the corona and hence controls the evolution of the entire
loop.
We also show that the down-flow is initiated by a weakening of the
pressure gradient between the corona and the transition region, such
that the plasma can no longer be supported in hydrostatic
equilibrium. Rather than driving the down-flow, the pressure gradient
actually regulates it and acts as a brake against gravitational
acceleration.
Key words: Sun: corona / Sun: transition region / Sun: UV radiation
© ESO, 2005
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