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Title:
Some implications of the nanoflare concept
Authors:
Cargill, Peter J.
Affiliation:
AA(Naval Research Lab., Washington, DC, US)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 422, no. 1, p. 381-393 (ApJ Homepage)
Publication Date:
02/1994
Category:
Solar Physics
Origin:
STI
NASA/STI Keywords:
CORONAL LOOPS, SOLAR COOLING, SOLAR CORONA, SOLAR FLARES, SOLAR PHYSICS, SOLAR TEMPERATURE, MAGNETOHYDRODYNAMICS, NUMERICAL ANALYSIS, STELLAR MODELS
DOI:
10.1086/173733
Bibliographic Code:
1994ApJ...422..381C

Abstract

The concept that the corona is heated by small flares (named 'nanoflares' by Parker) is examined. A model in which the closed, active region corona is comprised of many hundred of small elemental flux loops randomly heated by nanoflares is presentd. The cooling of these flux loops is examined using analytic techniques. It is assumed that the heated loops cool initially by conduction and at later times by radiation. Radiative cooling with and without downward mass flows are discussed, the experimental signature of such a coronal model are predicted. The distribution of temperatures in these loops peaks at around 2 x 106 K, while the distribution of densities peaks above 1010/cu cm. For 2 x 105 K less than T less than 106 K, radiative cooling with mass flows gives an emission measure that scales as T1.5, in agreement with existing observations. For T greater than 106 K, the emission measure increases more steeply, scaling as T4.5. These scalings are entirely due to the temperature dependence of the radiative loss function. It is shown that such a loop model has filling factors (defined as the ratio of the volume of hot plasma to the total volume) of order unity for subarcsecond energy release scales. A brief survey of the dependence of the results on the parameters of the system is presented. The temperature distribution function and emission measure are relatively insensitive to the loop length, coronal energy loss, number of elemental loops, and nanoflare energy, but the filling factor is dependent on these quantities. A simple scaling for this dependence is presented.

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