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Astron. Astrophys. 351, 1139-1148 (1999)

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Temporal variability in the electron density at the solar transition region

M.E. Pérez 1, J.G. Doyle 1, E. O'Shea 2 and F.P. Keenan 2

1 Armagh Observatory, College Hill, Armagh BT61 9DG, Ireland (epp,jgd@star.arm.ac.uk)
2 Department of Pure and Applied Physics, Queen's University Belfast, Belfast BT7 1NN, Ireland (E.Oshea,F.Keenan@qub.ac.uk)

Received 23 July 1999 / Accepted 6 October 1999


The electron density as measured in the transition region of a coronal hole, a `quiet' Sun region at disk center plus an active region shows variations of up to a factor of two at Te [FORMULA] 1.5 105 K, lasting at most only a few minutes. There is remarkable agreement between the number of such variations, their temporal variability and duration in the coronal hole and `quiet' Sun datasets, consistent with an earlier bright point study. There appears to be evidence of super-granular cells, with the increases in electron density occurring along the network boundaries. At some locations, periodicities of between 8 and 16 min are visible in the electron density variations. We associate these variations with the sites of explosive events.

Key words: line: profiles – Sun: activity – Sun: corona – Sun: transition region – Sun: UV radiation

Send offprint requests to: M.E. Pérez

© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999