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Astrophysics and Astrononmy
Sunspot MHD simulations: subsurface structure and penumbral filament formation | Mayukh Panja
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
19.05.2021
Caption:
Penumbral filaments do not form naturally in MHD simulations of sunspots. This is typically circumvented by modifying the top boundary: the field is made 2-3 times more horizontal than a potential field configuration. In this talk, I will explore the possibility that penumbral filament formation is governed by the subsurface structure of sunspots. We conducted a series of numerical experiments where we used flux tubes with different initial curvatures to study the effect of the fluting instability on the subsurface structure of spots using the MURaM code. We find that the curvature of a flux tube indeed determines the degree of fluting the flux tube will undergo—the more curved a flux tube is, the more fluted it becomes. In addition, sunspots with strong curvature have strong horizontal fi
Mode coupling at the transition region and the validity of line-tied boundary conditions | Alex Prokopyszyn
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
19.05.2021
Caption:
In this seminar, we aim to show why Fast/Alfvén waves couple at the solar surface. We will also show that the polarisation of the waves changes upon reflection at the solar surface. Finally, we will test the validity of line-tied boundary conditions for highly phase-mixed Alfvén waves. For most parameters, line-tied boundary conditions provide a good approximation. However, for highly phase-mixed waves, the coronal transverse length scales can be shorter than the corresponding parallel length scales in the chromosphere. In that case, we find that the line-tied model produces unphysically large boundary layers. Hence, we have the counter-intuitive result that the length scales parallel to the solar surface play a key role in determining the validity of line-tied boundary conditions.
The Kelvin-Helmholtz Instability in the Fan-spine Magnetic Topology in the Solar Corona | Sudheer K. Mishra
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
20.05.2021
Caption:
Using multi-wavelength imaging observation obtained from the Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO), we study the evolution of Kelvin-Helmholtz (K-H) instability in a fan-spine magnetic topology. This fan-spine configuration is situated near the Active Region 12297 and is rooted in a nearby sunspot. The two layers of the cool plasma flows lift up from the fan plane in parallel and interact with each other at the maximum height of the elongated spine in the lower corona. The first layer of the plasma flow (F1) moving with a slow velocity (5 km/s) reflected from the spine’s field lines. Subsequently second layer of plasma flow (F2) with impulsive velocity (114-144 km/s) interacts with the first layer at the maximum height and generating the shear motion ,
Magnetic Perturbations in a Sunspot Chromosphere Linked to Plasma Fractionation in the Corona | Deborah Baker
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
28.06.2021
Caption:
Element abundance signatures have long been used as tracers of physical processes throughout astrophysics. Understanding the spatial and temporal variations in the composition of the solar corona provides insight into how matter and energy flow from the solar chromosphere out into the heliosphere as well as from the chromospheres of solar-type stars into their astrospheres. In this work, we investigate the spatial distribution of highly varying plasma composition around one of the largest sunspots of solar cycle 24. Observations of the photosphere, chromosphere, and corona are brought together with magnetic field modeling of the sunspot in order to probe the conditions that regulate the degree of plasma fractionation within loop populations of differing connectivities. We find that, in the
The Dynamic and Magnetic Evolution of Arch Filament Systems | Sergio J. González Manrique
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
19.05.2021
Caption:
We study the dynamics of plasma along the legs of an arch filament system (AFS) observed with relatively high-cadence spectropolarimetric data from the ground-based solar GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He I 10830 Å range. The temporal evolution of the plasma of an AFS was followed using the chromospheric He I 10830 Å triplet and Si I 10827 Å. Measurements of vector magnetic fields in the solar chromosphere, especially in AFS, are extremely scarce, but very important. The magnetic field configuration reveals how AFSs are sustained in the chromosphere and hints at their formation, evolution, and disappearance. The magnetic field in the AFS follows loop-like structures traced by chromospheric absorption lines. However, if magnetic field lines follow
Upflows in the quiet Sun and coronal holes | Conrad Schwanitz
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
28.02.2022
Caption:
Recent observations from Solar Orbiter have emphasised the importance of small and short-lived phenomena in the solar atmosphere. They have shown small extreme-ultraviolet brightenings in the solar corona, which appear very frequently. Previously, Parker Solar Probe has revealed a highly dynamic structure in the solar wind’s magnetic field, which are referred to as switchbacks. Those results raise the question of the importance of small-scale phenomena and their potential contribution to the solar wind. We have analysed 14 coronal upflows, which were derived as blue shifts in spectroscopic data and examined the potential sources for each upflow. This was done by using Hinode/EIS rasters and calculating the Doppler velocities for the Fe XII line. Events, which are stronger blue-shifted than
Small-scale MHD waves in the solar chromosphere with ALMA | Juan Camilo Guevara Gómez
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
31.03.2022
Caption:
Magnetohydrodynamic (MHD) waves are thought to be one of the key mechanisms for transferring energy and momentum through the Sun’s atmosphere, hence maintaining the temperature profile of the outer atmospheric layers. Here, we have studied small-scale chromospheric bright features, exhibiting oscillations in brightness temperature, size, and horizontal velocity, in Bands 3 (∼3 mm) and 6 (∼1.2 mm) of 2 seconds cadence solar observations with ALMA, as well as in associated synthetic lines from a Bifrost simulation, degraded to match the ALMA’s spatial and temporal resolutions. In total, 486 and 235 features were analysed in the observations and simulations, respectively.
See more at https://espos.stream/2022/03/17/Guevara-Gomez/
Multiline Spectropolarimetric Observation of a C2-Class Solar Flare | Rahul Yadav
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
28.09.2021
Caption:
We present high-resolution and multiline spectropolarimetric observations of a C2-class solar flare (SOL2019-05-06T08:47). The rise, peak, and decay phases of the flare were recorded continuously and simultaneously in the Ca II K, Ca II 8542 Å, and Fe I 6173 Å lines with the CRISP and CHROMIS instruments at the Swedish Solar Telescope (SST). At the flare footpoints, a non-LTE multiline inversion code (STiC) was employed to infer the temperature, magnetic field, line-of-sight (LOS) velocity, and microturbulent velocity. The temporal analysis of the inferred temperature at the flare footpoints shows that the flaring atmosphere from log τ500 ∼ −2.5 to −3.5 is heated up to 7 kK, whereas from log τ500 ∼ −3.5 to −5 the inferred temperature ranges between ∼7.5 kK and ∼11 kK.
See more at https:/
Shock-wave radio probing of solar wind sources in coronal magnetic fields | Artem Koval
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
08.10.2021
Caption:
The Space Weather effects in the near-Earth environment as well as in atmospheres of other terrestrial planets arise by corpuscular radiation from the Sun, known as the solar wind. The solar magnetic fields govern the solar corona structure. Magnetic-field strength values in the solar wind sources - key information for modeling and forecasting the Space Weather climate - are derived from various solar space- and ground-based observations, but, so far not accounting for specific types of radio bursts. These are “fractured” type II radio bursts attributed to collisions of shock waves with coronal structures emitting the solar wind. Here, we report about radio observations of two “fractured” type II bursts to demonstrate a novel tool for probing of magnetic field variations in the solar wind
Classification of High-resolution Solar Hα Spectra using t-distributed Stochastic Neighbor Embedding | Meetu Verma
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
17.08.2021
Caption:
The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. The presented work is based on high-spectral resolution Hα spectra obtained with the echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide (ODT), Tenerife, Spain. The number of spectra accumulated at VTT over one observing day easily reaches up to millions. Hence, we require tools to identify and classify spectra with minimal human intervention. I will present exploratory work, which provides the framework and some ideas on how to tailor a classification scheme towards specific spectral data and science questions.
Read more at https://espos.stream/2020/12/03/Verma/
Collisional ionisation and recombination effects on coalescence instability in chromospheric partially ionised plasmas | Giulia Murtas
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
16.05.2022
Caption:
Plasmoid-mediated fast magnetic reconnection plays a fundamental role in driving explosive dynamics and heating in the solar atmosphere, but relatively little is known about how it develops in partially ionised plasmas (PIP) of the chromosphere. Partial ionisation can largely alter the dynamics of the coalescence instability, which promotes fast reconnection and forms a turbulent reconnecting current sheet through plasmoid interaction, but it is still unclear to what extent PIP effects influence this process. In this talk, I investigate the role of collisional ionisation and recombination in the development of plasmoid coalescence: I will present 1D and 2.5D simulations of a two-fluid model of a partially ionised plasma (PIP) and show how the dynamics change in the presence and absence of
On the formation of solar wind & switchbacks, and quiet Sun heating | Vishal Upendran
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
22.12.2021
Caption:
The solar coronal heating in quiet Sun (QS) and coronal holes (CH), including solar wind formation, are intimately tied by magnetic field dynamics. Thus, a detailed comparative study of these regions is needed to understand the underlying physical processes. CHs are known to have subdued intensity and larger blueshifts in the corona. This work investigates the similarities and differences between CHs and QS in the chromosphere using the Mg II h & k, C II lines, and transition region using Si IV line, for regions with identical absolute magnetic flux density (|B|). See more info at https://espos.stream/2021/12/16/Upendran/.
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