Speaker
Sara Esteban Pozuelo
(Instituto de Astrofísica de Andalucía (IAA-CSIC))
Description
We study the evolution of small-scale convective motions in
a sunspot located close to disk center using a temporal
sequence of high resolution observations acquired at the
SST. We calculate Dopplergrams in photospheric layers and
filter them for subsonic oscillations. Lateral downflows
appear everywhere in the center side penumbra as small,
weak, redshifted patches next to blueshifted flow channels.
These patches merge and fragment frequently and have an
intermittent life. They show median LOS velocities of 210
m/s, widths of 0.16”, lifetimes of 3.2 minutes and move
together with the hosting filaments reacting to their shape
variations. The evolution of the penumbral velocity field is
surprisingly similar to that of the quiet Sun, except for
the shape of the structures. We conclude that penumbral
filaments can be understood as elongated convective cells
with upflows along their length, weak downflows at the edges
and a strong downflow at the end. These results support the
existence of overturning convection in the penumbra
(Scharmer et al. 2008), which seems to be backed up by the
latest 3D numerical simulations (Rempel et al. 2009, Rempel
2011, 2012). However, from a kinematical point of view, the
velocity field is also compatible with other theoretical
scenarios, such as convective rolls (Danielson 1961) or
twisted horizontal magnetic flux tubes (Borrero 2007).
Primary author
Sara Esteban Pozuelo
(Instituto de Astrofísica de Andalucía (IAA-CSIC))
