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Astron. Astrophys. 318, 947-956 (1997)

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7. Conclusions

The consideration of the motion of each the three fluids made of neutrals, ions and electrons, is not simple but leads to a physical description of the formation and structure of thin magnetic flux tubes (see also Paper I) that explains several observational facts:

1. At deep photospheric levels, flux tubes are presumably cooler than their surroundings. 2. In the chromosphere, above the temperature minimum region, flux tubes are presumably hotter than surroundings.

3. The coronal abundances of elements are different from the photospheric abundances and depend on the FIP.

4. Matter is ejected with high upwards velocities in spicules.

It is worth noticing that electric currents in flux tubes explain at least qualitatively these four items including both the formation of the solar chromosphere, coronal abondance anomalies and spicules generation. The first item was treated in Paper I. The second and third item result from the possible fast outflow of neutrals across the lines of force, that leads to a separation between highly ionized magnetic flux-tubes, enriched in elements of low first ionization potential, and a more extended region with a weaker degree of ionization and therefore with a lower temperature. Our model indicates also that plasma must be ejected to high altitude like as observed in spicules. Consequently, electric currents play a significant rôle in the physics of thin flux tubes that cannot be treated without taking into account the not small deviation from ideal MHD.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998