On the fine structure of the quiet solar Ca II K atmosphere

¹ Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, CA-92314, USA e-mail: ali@bbso.njit.edu, ali@kis.uni-freiburg.de, ali@nso.edu
² Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany e-mail: [wolfgang;wedemeyer]@kis.uni-freiburg.de
³ National Solar Observatory/Sacramento Peak (Operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for the National Science Foundation.) , PO Box 62, Sunspot, NM-88349, USA e-mail: huitenbroek@nso.edu

Received: 29 August 2005
Accepted: 23 October 2006

Abstract

Aims.We investigate the morphological, dynamical, and evolutionary properties of the internetwork and network fine structure of the quiet sun at disk centre.

Methods.The analysis is based on a ~6 h time sequence of narrow-band filtergrams centred on the inner-wing  K_2v reversal at 393.3 nm. To examine the temporal evolution of network and internetwork areas separately we employ a double-Gaussian decomposition of the mean intensity distribution. An autocorrelation analysis is performed to determine the respective characteristic time scales. In order to analyse statistical properties of the fine structure we apply image segmentation techniques.

Results. The results for the internetwork are related to predictions derived from numerical simulations of the quiet sun. The average evolutionary time scale of the internetwork in our observations is 52 s. Internetwork grains show a tendency to appear on a mesh-like pattern with a mean cell size of ~4–5 arcsec. Based on this size and the spatial organisation of the mesh we speculate that this pattern is related to the existence of photospheric downdrafts as predicted by convection simulations. The image segmentation shows that typical sizes of both network and internetwork grains are in the order of 1.6 arcsec.