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Astron. Astrophys. 330, 1136-1144 (1998)

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6. Conclusion

The important role played in the quiet sun by granules, supergranules and mesogranules has been studied and discussed extensively by Simon and Weiss (1989), Simon et al. (1991) and Brandt et al. (1994). Different kinematic approaches have been developed to match the observations to one another. More precisely, the simulation of the distribution of mesogranules and exploders has been studied with respect to supergranule cells.

For example, it has been found that the simulation of mesogranule cells centered at fixed points on a grid cannot collectively produce a supergranule velocity field (Simon et al. 1991). Proper supergranule horizontal flows are necessary in the simulations to reproduce the observations. Hence, mesogranules are considered to be independent features drifting with supergranular velocity (Simon et al. 1991) as was suggested by the Pic du Midi observations (Muller et al. 1992). Our results, with a longer time sequence (6 h 40 min) do not indicate such organized mesoscale motion over the solar surface. Indeed, our observation emphasizes to need for another approach to determine the relation between the different convection scales in the simulations.

The lifetimes and random proper motions of the mesocells analysed in the present study, have to be taken into account in the diffusion process which drags magnetics flux on the solar surface. The random walk of the magnetic flux tube,observed in the converging areas, is the result of the granular turbulence (Muller et al. 1992) but also of random, non negligible proper mesoscale motions, as described above. In particular, mesocell evolution (motions and morphology) certainly play a role in the constitution of the large-scale magnetic pattern in the quiet sun. It may also be suspected that an important role is being played by the mesoscale in the magnetic activity during the quiet sun's cycle. A precise measurement of the mesocale and flux tube transport properties provides a major challenge for the next five years.

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© European Southern Observatory (ESO) 1998

Online publication: January 27, 1998