La Palma observations of umbral flashes

¹ The Institute for Solar Physics of the Royal Swedish Academy of Sciences, AlbaNova University Center, 10691 Stockholm, Sweden
² Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: R.J.Rutten,P.Suetterlin,P.J.Sloover,J.M.Krijger@astro.uu.nl
³ Institute of Theoretical Astrophysics, Oslo University, PO Box 1029 Blindern, 0315 Oslo, Norway

Corresponding author: L. Rouppe van der Voort, rouppe@astro.su.se

Received: 23 December 2002
Accepted: 13 February 2003

Abstract

We present high-quality Ca ii H & K data showing chromospheric flashes in sunspot umbrae collected with the Swedish Vacuum Solar Telescope, the Dutch Open Telescope, and the Swedish 1-m Solar Telescope at the Roque de los Muchachos Observatory on La Palma. Differential movies, time slices, spectrograms, and Fourier power maps demonstrate that umbral flashes and running penumbral waves are closely related oscillatory phenomena, combining upward shock propagation with coherent wave spreading over the entire spot. We attribute the flash brightening to large redshift by post-shock material higher up. We find no obvious relation between umbral dots and umbral flashes.