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Astron. Astrophys. 362, 371-378 (2000)

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Characteristics of quiet Sun cell and network brightenings

L.K. Harra 1, P.T. Gallagher 2 and K.J.H. Phillips 3

1 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
2 Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, CA 92314-9672, USA
3 Department of Space Science and Technology, Rutherford Appleton Laboratory, Chilton, DIDCOT, Oxon OX11 0QX, UK

Received 10 April 2000 / Accepted 16 August 2000

Abstract

Extreme ultraviolet observations of the quiet Sun are made with the Coronal Diagnostic Spectrometer (CDS ) on board the Solar and Heliospheric Observatory (SOHO ). It has been previously noted that frequent transition region brightenings occur in both the bright network and dark cell regions. Analysing 1125 events, we determined the characteristics of the brightenings in the cell and network regions which include the duration, energy, and intensity increase above the background. Network brightenings are found to be larger than cell events occurring with a mean duration of 150 s and releasing an average of [FORMULA] ergs per event. Cell brightenings, on the other hand, last for an average of 96 s and release [FORMULA] ergs per event. It has also been found that the distribution of energy is a power-law which is different in the cell ([FORMULA]=2.5) and network ([FORMULA]=1.5) regions. When the entire quiet Sun region is analysed the value of [FORMULA] is 1.7. The number of events per CDS pixel is approximately the same, and a histogram of the ratio ([peak value - background]/background) shows similar values for both the cell and network. It is important to analyse the cell and network regions separately in the context of coronal heating by such small flare-like events.

Key words: Sun: corona – Sun: transition region – Sun: UV radiation

Send offprint requests to: L.K. Harra (lkh@mssl.ucl.ac.uk)

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100
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