The proper motion of network bright points and the heating of the solar corona

Details The proper motion of network bright points and the heating of the solar corona The proper motion of network bright points and the heating of the solar corona

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283..232m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 232-240

Astronomy and Astrophysics

Astrophysics

83

Heat Transfer, Magnetic Flux, Solar Corona, Solar Granulation, Solar Magnetic Field, Histograms, Solar Atmosphere, Temperature Effects

Scientific paper

Since it has been proved that acoustic waves are inefficient, it has been widely accepted that the solar corona is heated by waves which propagate along magnetic flux tubes and are generated by the turbulent granular motions. Such motions, however, may have yet been measured nor the involved energy evaluated. We present in this paper the first measurements of the proper motion of the footprints of magnetic flux tubes, at the photospheric level, outside active regions. For this purpose, we have used a high resolution granulation movie obtained at the Pic du Midi Observatory, in which we were able to identify many network bright points (NBPs). As they are associated to the magnetic flux tubes, we have used these tiny bright points as tracers of magnetic fields. Velocity histograms have been derived. They show that NBPs proper motion is turbulent in nature and that its mean speed is 1.4 km/s. Velocities as large as 3 km/s have been measured. Using then the number density of NBPs derived by Muller & Roudier (1984) 200/100 sec x 100 sec, it has been possible to calculate the energy flux which can be carried toward the corona, using an expression recently published by Choudhuri et al. (1993a). This flux appears to be about one order of magnitude larger than is necessary. Actually, the wave flux should even be much larger than that, if we keep in mind that the magnetic flux visible as NBPs, represents only a fraction of the total magnetic flux really present in the photosphere, outside active regions. We conclude that the solar corona may really be heated by waves which propagate along magnetic flux tubes rooted in the photosphere, and shaken by granular motions. The propagation of these waves along flux tubes needed however to be understood better.

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