Chromospheric impact of an exploding solar granule^⋆

¹ Kiepenheuer Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg Germany
e-mail: cfischer@kis.uni-freiburg.de
² Instituto de Astrofísica de Canarias, Avda Vía Láctea S/N, La Laguna 38200, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna ( Tenerife), Spain

Received: 6 May 2017
Accepted: 24 May 2017

Abstract

Context. Observations of multi-wavelength and therefore height-dependent information following events throughout the solar atmosphere and unambiguously assigning a relation between these rapidly evolving layers are rare and difficult to obtain. Yet, they are crucial for our understanding of the physical processes that couple the different regimes in the solar atmosphere.

Aims. We characterize the exploding granule event with simultaneous observations of Hinode spectroplarimetric data in the solar photosphere and Hinode broadband Ca ii H images combined with Interface Region Imaging Spectrograph (IRIS) slit spectra. We follow the evolution of an exploding granule and its connectivity throughout the atmosphere and analyze the dynamics of a magnetic element that has been affected by the abnormal granule.

Methods. In addition to magnetic flux maps we use a local correlation tracking method to infer the horizontal velocity flows in the photosphere and apply a wavelet analysis on several IRIS chromospheric emission features such as Mg ii k2v and Mg ii k3 to detect oscillatory phenomena indicating wave propagation.

Results. During the vigorous expansion of the abnormal granule we detect radially outward horizontal flows, causing, together with the horizontal flows from the surrounding granules, the magnetic elements in the bordering intergranular lanes to be squeezed and elongated. In reaction to the squeezing, we detect a chromospheric intensity and velocity oscillation pulse which we identify as an upward traveling hot shock front propagating clearly through the IRIS spectral line diagnostics of Mg ii h&k.

Conclusions. Exploding granules can trigger upward-propagating shock fronts that dissipate in the chromosphere.