Impulsive wave excitation by rapidly changing granules. (arXiv:2008.12779v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kwak_H/0/1/0/all/0/1">Hannah Kwak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chae_J/0/1/0/all/0/1">Jongchul Chae</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Madjarska_M/0/1/0/all/0/1">Maria S. Madjarska</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cho_K/0/1/0/all/0/1">Kyuhyoun Cho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Song_D/0/1/0/all/0/1">Donguk Song</a>
It is not yet fully understood how magnetohydrodynamic waves in the interior
and atmosphere of the Sun are excited. Traditionally, turbulent convection in
the interior is considered to be the source of wave excitation in the quiet
Sun. Over the last few decades, acoustic events observed in the intergranular
lanes in the photosphere have emerged as a strong candidate for a wave
excitation source. Here we report our observations of wave excitation by a new
type of event: rapidly changing granules. Our observations were carried out
with the Fast Imaging Solar Spectrograph in the H$alpha$ and Ca II 8542
$unicode{xC5}$ lines and the TiO 7057 $unicode{xC5}$ broadband filter imager
of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. We
identify granules in the internetwork region that undergo rapid dynamic changes
such as collapse (event 1), fragmentation (event 2), or submergence (event 3).
In the photospheric images, these granules become significantly darker than
neighboring granules. Following the granules’ rapid changes, transient
oscillations are detected in the photospheric and chromospheric layers. In the
case of event 1, the dominant period of the oscillations is close to 4.2 min in
the photosphere and 3.8 min in the chromosphere. Moreover, in the Ca II$-$0.5
$unicode{xC5}$ raster image, we observe repetitive brightenings in the
location of the rapidly changing granules that are considered the manifestation
of shock waves. Based on our results, we suggest that dynamic changes of
granules can generate upward-propagating acoustic waves in the quiet Sun that
ultimately develop into shocks.
It is not yet fully understood how magnetohydrodynamic waves in the interior
and atmosphere of the Sun are excited. Traditionally, turbulent convection in
the interior is considered to be the source of wave excitation in the quiet
Sun. Over the last few decades, acoustic events observed in the intergranular
lanes in the photosphere have emerged as a strong candidate for a wave
excitation source. Here we report our observations of wave excitation by a new
type of event: rapidly changing granules. Our observations were carried out
with the Fast Imaging Solar Spectrograph in the H$alpha$ and Ca II 8542
$unicode{xC5}$ lines and the TiO 7057 $unicode{xC5}$ broadband filter imager
of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. We
identify granules in the internetwork region that undergo rapid dynamic changes
such as collapse (event 1), fragmentation (event 2), or submergence (event 3).
In the photospheric images, these granules become significantly darker than
neighboring granules. Following the granules’ rapid changes, transient
oscillations are detected in the photospheric and chromospheric layers. In the
case of event 1, the dominant period of the oscillations is close to 4.2 min in
the photosphere and 3.8 min in the chromosphere. Moreover, in the Ca II$-$0.5
$unicode{xC5}$ raster image, we observe repetitive brightenings in the
location of the rapidly changing granules that are considered the manifestation
of shock waves. Based on our results, we suggest that dynamic changes of
granules can generate upward-propagating acoustic waves in the quiet Sun that
ultimately develop into shocks.
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