Kavli Affiliate: Robert Cameron
| First 5 Authors: Sanghita Chandra, Sanghita Chandra, , ,
| Summary:
H$alpha$ observations of the solar chromosphere reveal dynamic small-scale
structures known as spicules at the limb and rapid blue and red shifted
excursions (RBEs/RREs) on-disk. We want to understand what drives these dynamic
features, their magnetohydrodynamic (MHD) properties and their role in energy
and heat transport to the upper solar atmosphere. To do this, we aim to develop
a proxy for synthetic H$alpha$ observations in radiative-MHD simulations to
help identify these features. We use the chromospheric extension to the MURaM
code (MURaM-ChE) to simulate an enhanced network region. We develop a proxy for
H$alpha$ based on a photon escape probability. This is a Doppler-shifted proxy
that we use to identify fine structures in the line wings. We study on-disk
features in 3D, obtaining their 3D structure from the absorption coefficient.
We validate the H$alpha$ proxy by comparing it against features detected in
the wings of H$alpha$ synthesized using MULTI3D. We detect numerous
small-scale structures rooted at the network patches, similar to observations
in H$alpha$. The dynamics of an example feature (RBE) at a Doppler shift of 37
km/s show that flux emergence and consequent reconnection drive the formation
of this feature. Pressure gradient forces build up to drive a flow along the
field line carrying the feature, making it a jet. There is strong viscous and
resistive heating at the first appearance of the feature associated with the
flux emergence. At the same time and location, a heating front appears and
propagates along the field lines at speeds comparable to the Alfven velocity.
We show that a synthetic observable based on an escape probability is able to
reliably identify features observed with the H$alpha$ spectral line. We
demonstrate its applicability by studying the formation, dynamics and
properties of an RBE.
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