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Astron. Astrophys. 344, 965-972 (1999)


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Average properties and temporal variations of the geometry of solar network cells

F. Berrilli 1, I. Ermolli 2, A. Florio 2 and E. Pietropaolo 3

1 Università degli Studi "Tor Vergata", Viale della Ricerca Scientifica, I-00133 Roma, Italy
2 Osservatorio Astronomico di Roma, Viale del Parco Mellini, 84, I-00136 Roma, Italy
3 Università degli Studi, Via Vetoio, Località Coppito, I-67010 L'Aquila, Italy

Received 31 March 1998 / Accepted 26 June 1998

Abstract

The average properties of the network cells geometry and their temporal variations are investigated for quiet solar regions at the center of the solar disk. These regions were extracted from the daily Ca II K full-disk observations carried out at the Rome Observatory with the PSPT telescope during one year (from July 1996 to June 1997) at the beginning of Solar Cycle 23.

We applied an automated procedure to derive the skeleton of bright Ca II K regions. By using this skeleton as representative of the chromospheric network, we identified and characterized the network cells on the images.

The results we found seemed to point out that network cells are regular in shape and slightly flat. We found an upper limit of 2% for the anisotropy of the cell orientation. By analyzing the latitudinal dependence of the cell size, we found that the cell area decreases by about 30% towards the poles.

We also characterized the network pattern by using wavelet analysis. We compared the results obtained by the different analyzes.

Finally we analyzed the temporal behaviours of the network cell geometrical properties. In particular, we found a decrease of the characteristic scale value of about 8% for the period analyzed.

Key words: techniques: image processing – Sun: activity – Sun: chromosphere

Send offprint requests to: I. Ermolli (ilaria@oarhp1.rm.astro.it)

© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999

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