Coronal oscillation above a supergranular cell of the quiet Sun chromospheric network?

¹ Academy of Athens, Research Center of Astronomy and Applied Mathematics, Soranou Efessiou 4, 115 27 Athens, Greece e-mail: [cgontik;edara]@cc.uoa.gr
² Kiepenheuer-Institut fr Sonnenphysik, Schneckstr. 6, 79104 Freiburg, Germany e-mail: peter@kis.uni-freiburg.de

Received: 22 February 2005
Accepted: 24 June 2005

Abstract

We have detected an oscillation in the low corona, using a raster of the SUMER EUV spectrograph in the Ne viii, 770 Å line formed at about 700 000 K. The oscillation was found in the Ne viii Doppler map above the interior of a supergranular cell of the chromospheric network in the quiet Sun, while it is absent in line radiance. The photospheric magnetic field, extrapolated to coronal levels, was used to relate this phenomenon to the magnetic structure. This oscillation phenomenon, reported here for the first time, seems to occur only above the darkest cells of the chromospheric network. We interpret our findings as a collective non-compressible oscillation of the corona above the whole cell interior. This oscillation may originate at the chromosphere and the driving wave may undergo a mode conversion at the top chromosphere, where the magnetic pressure equals the gas pressure. Our interpretation cannot be definitive and should be verified with more data.