Letter to the Editor

Sunspot seismic halos generated by fast MHD wave refraction

¹ Instituto de Astrofísica de Canarias, C/ vía Láctea, s/n, 38205 Tenerife, Spain e-mail: khomenko@iac.es
² Main Astronomical Observatory, NAS, 03680 Kyiv, Ukraine

Received: 30 July 2009
Accepted: 8 September 2009

Abstract

Aims. We suggest an explanation for the high-frequency power excess surrounding active regions known as seismic halos.

Methods. We use numerical simulations of magneto-acoustic wave propagation in a magnetostatic sunspot model.

Results. We propose that seismic halos can be caused by the additional energy injected by high-frequency fast mode waves refracted in the higher atmosphere due to the rapid increase of the Alfvén speed. Our model qualitatively explains the magnitude of the halo and allows us to make predictions of its behavior that can be checked in future observations.