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| May 19 |
Tue |
Prof Anthony Yeates (Durham) |
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| 11:00 |
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SP2RC/UK-SOSS joint monthly seminar: Where do solar eruptions come from?
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Abstract:
An oft-quoted idea in solar physics is that coronal mass ejections are, fundamentally, the Sun's way of shedding the magnetic helicity that is continually generated by its interior flows. In this talk, I will show how models are helping to give us a handle on the build up of magnetic helicity in the corona (the Sun's lower atmosphere): how much is injected, where it collects, and how it is ultimately ejected. This requires time-evolving coronal magnetic field models as well as new tools for analysing the distribution of magnetic helicity.
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| May 19 |
Tue |
Giordano Cotti (Birmingham) |
Algebra / Algebraic Geometry seminar |
| 14:00 |
ONLINE |
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| May 20 |
Wed |
Didier Leibovici (SoMaS) |
Applied Mathematics Colloquium |
| 14:00 |
https://meet.google.com/rsi-pwbr-cqd |
On spatio-temporal entropy based methods for data science
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Abstract:
The entropy, as a metric to describe if a distribution tends to be uniform (high entropy) or not can be useful in data science to highlight spatio-temporal structures (low entropy). The seminar looks into complementary aspects of multiway data analysis deriving from a tensor decomposition and the use of entropy within a spatio-temporal context. Derived from practices in landscape ecology, a framework based on size and shapes of patches within a spatio-temporal context is used in conjunction with the entropy decomposition theorem or with a tensor decomposition approach. Combined with statistics, such as co-occurrences of observations or specific distance ratios instead of occurrence counts, to define pseudo-distributions to derive spatio-temporal entropies, the framework allows a range of analyses.
Along the path some examples are illustrating involved connexe methods, some of which can be found in the references below.
Leibovici DG and Claramunt C (2019) On Integrating Patch Size and Shape Distributions into a Spatio-Temporal Information Entropy Framework Entropy, 21(11):1112 (special issue)
Leibovici DG, Brosset D, Claramunt C, and Jackson M (2015 ) k-Co-occurrences Density Map Estimation. Spatial Statistics Conference: Emerging Patterns, 9-12th of June 2015, Avignon, France, Procedia Environmental Sciences, 26: 105-109.
Leibovici DG, and Birkin MH (2015) On Geocomputational Determinants of Entropic Variations for Urban Dynamic Studies. Geographical Analysis, 47 (3): 193-218
Leibovici DG, Bastin L, and Jackson M (2011) " Higher-Order Co-occurrences for Exploratory Point Pattern Analysis and Decision Tree Clustering on Spatial Data." Computers & Geosciences: 37(3): 382-389
Leibovici DG, (2010) " Spatio-temporal Multiway Decomposition using Principal Tensor Analysis on k-modes: the R package PTAk." Journal of Statistical Software, 34(10), 1-34
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| May 20 |
Wed |
Alessandra Caraceni (Oxford) |
Probability |
| 14:00 |
LT1 |
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| May 20 |
Wed |
Kieran Finn (University of Manchester) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
Frame Covariance in Quantum Gravity
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Abstract:
The laws of physics should not depend on how we choose to describe them. However, this is exactly what happens in the standard formulation of quantum field theories. The effective action receives different quantum corrections depending on how we parametrise our fields and even Feynman diagrams can yield results that depend on the definition of the fields we choose to work with. In this talk I will rectify these problems by introducing the notion of frame covariance, in which the quantum fields are treated as coordinates on a manifold, known as the field space. Field redefinitions are then simply diffeomorphisms of this manifold and thus we can impose reparametrisation invariance using well-known techniques from differential geometry. This talk is based on arXiv:1910.06661.
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| May 21 |
Thu |
Shu Sasaki (Queen Mary) |
Number Theory seminar |
| 10:00 |
Google hangout |
Serre's conjecture about weight of mod p modular forms: old conjectures,
not so old theorems and new conjectures
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Abstract:
In 1987, J.-P. Serre made a set of conjectures about weights and levels of
two-dimensional (modular) mod p Galois representations of the absolute
Galois group of Q. This conjecture of Serre has been completely proved by
C. Khare and J.-P. Wintenberger (2009) building on the work of many
mathematicians, but it has also inspired a good deal of new mathematics.
One strand of research spurred on by the development is about generalising
Serre's conjecture over to a (general) totally real number field. This was
initiated by the work (2009) of K. Buzzard, F. Diamond and F. Jarvis,
while focusing exclusively on regular weights of mod p Hilbert modular
forms. In my joint work with F. Diamond, we have improved on the
Buzzard-Diamond-Jarvis conjectures and formulated new conjectures about
general weights of (geometric) mod p Hilbert modular forms (analogous to
what B. Edixhoven did in 1992). I will explain what our conjectures say
exactly, and demonstrate some evidence that we are on the right track. In
support of our vision, I will also explain a comparatively new result
(joint work with F. Diamond and P. Kassaei) about a Jacquet-Langlands
relation between mod p geometric `Hilbert modular forms', which may well
shed some light on the problem of formulating a putative mod p Langlands
philosophy.
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| May 21 |
Thu |
Gong Show |
Topology seminar |
| 16:00 |
J11 |
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| May 21 |
Thu |
José Juan González Avilés (Laboratorio Nacional de Clima Espacial, SCiESMEX-LANCE. Morelia (Mexico)) |
Plasma Dynamics Group |
| 16:00 |
https://meet.google.com/utx-dzbb-mpf?hs=122&authuser=0 |
Numerical studies of jet formation in the solar atmosphere
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Abstract:
Using the Newtonian CAFE MHD code to perform 2.5D and 3D resistive MHD simulations in the solar atmosphere, we show that magnetic reconnection may be responsible for the formation of jets with some characteristics of Type II spicules and cool coronal jets. We numerically model the photosphere-corona region using the C7 atmosphere model. The initial magnetic configuration in the 2.5D case consists of two symmetric neighboring loops with opposite polarity, used to support reconnection. In the 3D case, the initial magnetic configuration is extrapolated up to the solar corona region from a dynamic realistic simulation of the solar photospheric magnetoconvection model that mimics the quiet-Sun.
In the 2.5D simulations, we include the effect of the thermal conduction along the magnetic field lines to study some properties of spicule jets. In this case, we find that thermal conductivity affects morphology, velocity, and temperature of the jets. Also, the heat flux maps indicate the head of the jet and corona interchange energy more efficiently than the body of the jet. In the 3D simulations, we have found that the formation of the jet depends on the Lorentz force, which helps to accelerate the plasma upward. The morphology, the upward velocity covering a range up to 130 km/s, and the timescale formation of the structure between 60 and 90 s, are similar to those expected for Type II spicules. Additionally, we analyze various properties of the jet dynamics, and find that the structure shows rotational and torsional motions which may generate torsional Alfvén waves in the corona region.
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| May 22 |
Fri |
Matthew Allcock (Sheffield) |
SP2RC seminar |
| 13:00 |
https://meet.google.com/ciq-zovu-rzm |
Breaking Symmetry: Theory and Observations of Asymmetric Solar Waveguides |
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Abstract:
50 years of solar MHD wave theory has focussed on waveguides in symmetric plasma environments. Yet the Sun’s inhomogeneous atmosphere allows for waveguides to be held in asymmetric equilibrium. We break symmetry by studying a slab model embedded in an asymmetric external plasma in three ways:
Eigenvalue problem: We derive the dispersion relation and show that asymmetric eigenmodes have mixed properties of the traditional sausage and kink modes.
Ray theory: We demonstrate how a ray theoretic approach can be used to derive this dispersion relation, giving particular insight into the nature of asymmetric leaky modes.
Initial value problem: Given an initial impulse, the time-dependence of MHD waves in these waveguides is studied.
Next, we embark on deriving a magneto-seismology technique to estimate the magnetic field strength in waveguides embedded in asymmetric external plasmas. We apply this to a series of solar chromospheric fibrils as a proof of concept and we finish by identifying ambiguities in eigenmode identification.
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| May 27 |
Wed |
Adam Butler (BIOSS) |
Statistics Seminar |
| 14:00 |
LT 6 |
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| May 27 |
Wed |
Minmin Wang (Sussex) |
Probability |
| 14:00 |
LT7 |
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| May 27 |
Wed |
Philippe Brax (Universite Paris-Saclay) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
Charged Dark matter and H0 tension |
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Abstract:
I will describe recent models of non-linear electrodynamics with charged dark matter and their cosmological consequences. In particular, I will emphasize the inhomogeneous nature of the resulting cosmology. This follows from the screening of the extra U(1) in a way akin to the K-mouflage mechanism of modified gravity. I will eventually argue that this may have some applications to the local dynamics vs large scale structure of the Universe and the H0 tension.
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| May 28 |
Thu |
Juraj Lorinčík (Astronomical Institute of the Czech Academy of Sciences, ASU (Czech Republic)) |
European Solar Physics Online Seminars (ESPOS) |
| 10:00 |
Zoom https://zoom.us/j/165498165 |
Understanding hooks of solar flare ribbons and the evolution of coronal mass ejections
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Abstract:
Solar flares and eruptions are one of the most energetic phenomena occuring in the solar system. They are typically described by the cartoon-like 2D Standard model of solar flares. This model is however not capable of describing J-shaped (hooked) solar flare ribbons, bright elongated structures typically observed in the UV part of the spectrum. Their description requires 3D MHD modelling of magnetic flux ropes, bundles of twisted field lines rooted in the hooked endings of flare ribbons. The standard flare model in three dimensions, developed in the Observatory of Paris, was recently used to find predictions on how do the field lines reconnect during solar eruptions with respect to the positions of flare ribbons (Aulanier & Dudík 2019, A&A, 621, 72). Authors of this study identified three geometries involving field lines composing and/or surrounding the erupting flux rope. With a help of high-resolution EUV data, these were identified in a series of publications focused on eruptive events. Using data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory, we will present the manifestations of the different 3D reconnection scenarios and discuss under what conditions can their constituents be observed.
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| May 28 |
Thu |
Juraj Lorinčík (Astronomical Institute of the Czech Academy of Sciences) |
SP2RC/ESPOS |
| 10:00 |
https://zoom.us/j/165498165 |
By-weekly SP2RC/ESPOS joint seminar: Understanding hooks of solar flare ribbons and the evolution of coronal mass ejections |
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| |
Abstract:
Solar flares and eruptions are one of the most energetic phenomena occuring in the solar system. They are typically described by the cartoon-like 2D Standard model of solar flares. This model is however not capable of describing J-shaped (hooked) solar flare ribbons, bright elongated structures typically observed in the UV part of the spectrum. Their description requires 3D MHD modelling of magnetic flux ropes, bundles of twisted field lines rooted in the hooked endings of flare ribbons. The standard flare model in three dimensions, developed in the Observatory of Paris, was recently used to find predictions on how do the field lines reconnect during solar eruptions with respect to the positions of flare ribbons (Aulanier & Dudík 2019, A&A, 621, 72). Authors of this study identified three geometries involving field lines composing and/or surrounding the erupting flux rope. With a help of high-resolution EUV data, these were identified in a series of publications focused on eruptive events. Using data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory, we will present the manifestations of the different 3D reconnection scenarios and discuss under what conditions can their constituents be observed.
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| Jun 3 |
Wed |
Visakan Balakumar (University of Sheffield) |
Cosmology, Relativity and Gravitation |
| 00:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
Hadamard renormalisation for a charged scalar field
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Abstract:
The Hadamard renormalisation method provides a powerful and axiomatic approach to renormalising the stress-energy tensor in the study of quantum fields in curved spacetime. This procedure has been developed by Decanini and Folacci for massive neutral scalar fields in a general spacetime of arbitrary dimension. Motivated by the study of superradiant scattering in Reissner–Nordström black holes, we extend their work to include charged scalar fields in spacetimes with a classical, background gauge field and explicitly demonstrate the Hadamard renormalisation procedure in four dimensions.
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| Jun 4 |
Thu |
Suzana de Souza e Almeida Silva (Technological Institute of Aeronautics, Sao Paulo) |
Plasma Dynamics Group |
| 16:00 |
https://meet.google.com/zgi-vauj-uhh |
Dynamics of Vortex Tubes in the Solar Atmosphere
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Abstract:
We use a state of the art vortex detection method, Instantaneous Vorticity Deviation, to define and locate three-dimensional vortices in magneto-convections simulations performed by the MURaM code. The detected vortices extend from the photosphere to the low chromosphere. The dynamics across the vortical flows at different height levels are investigated through radial profiles. We found that the vortices present similar dynamics at all height levels, with nonuniform angular rotational velocity and eddy viscosity effects. The vortices intensify the magnetic field, and in turn, the vortex dynamics are affected by the magnetic field. On the other hand, our findings hint that kinematic vortices need to present high tangential velocities at different height levels to overcome the magnetic tension and generate magnetic vortices.
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| Jun 5 |
Fri |
Peng-Fei Chen (Nanjing University, China) |
SP2RC seminar |
| 13:00 |
https://zoom.com.cn/j/169636835 |
Formation and dynamics of solar filaments
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Abstract:
Filaments, or called prominences when appearing above the solar limb, are a spectacular phenomenon in the solar atmosphere. Their formation is strongly related to chromospheric heating, their oscillations can be applied to derive the otherwise unmeasurable coronal magnetic field, and their eruptions are directly related to solar flares and coronal mass ejections (CMEs). All these explain why solar filaments have attracted wide attention in the solar community. More importantly, similar structures exist in the intergalactic medium associated with active galactic nuclei (AGN). Research on solar filaments with high resolutions can definitely shed light on the understanding of AGN filaments. In this talk, I will review our work on solar filaments formation and dynamics in the past decade, with an emphasis on our recent results.
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| Jun 11 |
Thu |
Ajay Tiwari (Northumbria University) |
European Solar Physics Online Seminars (ESPOS) |
| 10:00 |
Zoom: https://zoom.us/j/165498165 |
Study of damping of propagating kink waves in the solar corona
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Abstract:
Propagating kink waves have been reported recently and have been found to be ubiquitous in the solar corona including in the quiet Sun. It is imperative to understand the mechanisms that enable their energy to be transferred to the plasma. Carrying on the legacy of the standing kink waves, mode conversion via resonant absorption is thought to be one of the main mechanisms for damping of these propagating kink waves, and is considered to play a key role in the process of energy transfer. We use the Doppler velocity images of the Coronal Multi-channel Polarimeter (CoMP) for the study of propagating kink waves in quiescent coronal loops. A coherence-based method is used to track the Doppler velocity signal of the waves, enabling an investigation into the spatial evolution of velocity perturbations. To enable accurate estimates of these quantities, the first derivation is provided of a likelihood function suitable for fitting models to the ratio of two power spectra obtained from discrete Fourier transforms. Maximum likelihood estimation is used to fit an exponential damping model to the observed variation in power ratio as a function of frequency. This also confirms earlier indications that propagating kink waves are undergoing frequency-dependent damping. Additionally, it is found that the rate of damping decreases for longer coronal loops that reach higher in the corona. The analysis techniques are used to create a statistical sample of quiescent loops to study the statistical properties of propagating kink waves and compare it to the studies of standing kink waves. It is noted that the damping for the propagating waves appears to be significantly weaker than that found from measurements of standing kink modes. The propagating kink waves also exhibit signatures of power amplification of waves. These propagating kink waves provide a new avenue to perform coronal magneto-seismology even during the quiet Sun period and this reliable method is not limited by requiring the eruptive activity of the Sun.
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| Jun 11 |
Thu |
Ajay Tiwari (Northumbria) |
SP2RC/ESPOS |
| 10:00 |
https://zoom.us/j/165498165 |
By-weekly SP2RC/ESPOS joint seminar: Study of damping of propagating kink waves in the solar corona |
| |
| |
Abstract:
Propagating kink waves have been reported recently and have been found to be ubiquitous in the solar corona including in the quiet Sun. It is imperative to understand the mechanisms that enable their energy to be transferred to the plasma. Carrying on the legacy of the standing kink waves, mode conversion via resonant absorption is thought to be one of the main mechanisms for damping of these propagating kink waves, and is considered to play a key role in the process of energy transfer. We use the Doppler velocity images of the Coronal Multi-channel Polarimeter (CoMP) for the study of propagating kink waves in quiescent coronal loops. A coherence-based method is used to track the Doppler velocity signal of the waves, enabling an investigation into the spatial evolution of velocity perturbations. To enable accurate estimates of these quantities, the first derivation is provided of a likelihood function suitable for fitting models to the ratio of two power spectra obtained from discrete Fourier transforms. Maximum likelihood estimation is used to fit an exponential damping model to the observed variation in power ratio as a function of frequency. This also confirms earlier indications that propagating kink waves are undergoing frequency-dependent damping. Additionally, it is found that the rate of damping decreases for longer coronal loops that reach higher in the corona. The analysis techniques are used to create a statistical sample of quiescent loops to study the statistical properties of propagating kink waves and compare it to the studies of standing kink waves. It is noted that the damping for the propagating waves appears to be significantly weaker than that found from measurements of standing kink modes. The propagating kink waves also exhibit signatures of power amplification of waves. These propagating kink waves provide a new avenue to perform coronal magneto-seismology even during the quiet Sun period and this reliable method is not limited by requiring the eruptive activity of the Sun.
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| Jun 16 |
Tue |
Mitch Berger (Exeter University, UK) |
SP2RC seminar |
| 11:00 |
https://zoom.us/j/95338171418 |
UK Solar Online Seminar Series (UK-SOSS) monthly seminar: Magnetic helicity - decompositions and methods of localization
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Abstract:
Magnetic helicity is an ideal MHD invariant; it measures geometric and topological properties of a magnetic field. The talk will begin by reviewing helicity and its mathematical properties. It can be decomposed in several ways (for example, self and mutual helicity, Fourier spectra, field line helicity, linking, twist, and writhe). The talk will also review methods of measuring the helicity flux, as well as applications in solar and stellar astrophysics.
I will then discuss some new developments in measuring localized concentrations of helicity in a well-defined, gauge invariant manner, using wavelets.
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| Jun 17 |
Wed |
Hal Haggard (Bard College) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
The Black Hole Spin Puzzle, Black Hole Entropy, and Gravitational Wave Observations
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Abstract:
Black hole entropy is a robust prediction of quantum gravity with no observational test to date. This entropy can be used to determine the probability distribution of the spin of black holes at equilibrium in the microcanonical ensemble. This ensemble, relevant for black holes formed in the early universe, predicts the existence of a population of black holes with zero spin. Observations of such a population at LIGO, Virgo, and future gravitational wave observatories would elucidate the statistical nature of black hole entropy and the origin of stellar mass black holes.
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| Jun 18 |
Thu |
Matheus Aguiar-Kriginsky Silva (Universitat de les Illes Balears (Spain)) |
Plasma Dynamics Group |
| 16:00 |
https://meet.google.com/jkh-tkvn-cow?hs=122&authuser=0 |
Ubiquituous hundred-Gauss magnetic fields in solar spicules
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Abstract:
Even though they were observed for the first time in the 19th century, the nature of spicules
is not well understood because they are are thin and elongated chromospheric jets and
therefore their study is limited to the resolution of the instruments used. Every time a step
forward in the quality of the observations of the lower chromosphere is taken, the interest in
spicules sparks. Most recently, the advent of the Hinode telescope provided high-resolution
images of spicules that allowed for a better comprehension of their nature and behavior.
Studies regarding their magnetic field have been also undertaken, but most of them did not
have the ideal spatial/temporal resolution needed to give definitive results. This study is
aimed to provide a step forward in this matter, with observations in the Ca II 854.2 nm line
taken with the CRISP instrument at the Swedish 1-meter Solar Telescope in La Palma. The
sensitivity of the Ca II 854.2 nm line to the magnetic field is exploited and the Weak Field
Approximation (WFA) is used to estimate the line-of-sight component of the magnetic field
of spicules both off-limb and on the solar disk. The WFA must be used carefully, since there
are conditions that need to be met for it to be applicable. This consideration is assessed in
every pixel, and a Bayesian approach is taken to infer the line-of-sight magnetic field
component from the WFA equations. It is established that magnetic fields over 100 G are
abundant, and the reason for the failure of previous studies to conclude this is carefully
studied and is speculated to lie in the poor temporal/spatial resolution of the observations
used.
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| Jun 19 |
Fri |
David Long (Mullard Space Science Laboratory) |
SP2RC seminar |
| 13:00 |
https://meet.google.com/ciq-zovu-rzm |
Understanding the evolution of global waves in the low solar corona |
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Abstract:
Global waves in the low solar corona have been a source of significant interest and investigation since their discovery using SOHO/EIT in 1997. The advent of very high spatial and temporal resolution observations with SDO/AIA has enabled a number of significant advances in our understanding of these phenomena. In particular, the interpretation of these features are large-amplitude waves or shocks is becoming more and more accepted in the community. However, questions still remain, particularly with regard to their relationship to other associated coronal phenomena. I will present recent work looking at the techniques commonly used to identify and track these global EUV waves which shows that current techniques using wave kinematics and perturbation profiles provide a useful insight into the properties of the waves. I then show how these techniques can be used to examine the relationship between global EUV waves and Moreton-Ramsey waves typically observed using H-alpha observations.
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| Jun 24 |
Wed |
Ippocratis Saltas (CEICO) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
New tests of gravity at large and small scales in the Universe
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Abstract:
In this talk, I will explain the implications of the recent measurement of the gravitational waves’ speed for large and small scales in the Universe. I will pay special focus on how the physics of stellar structure, and in particular helioseismology, can provide us with tight constraints on the residual scalar-gravity interactions.
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| Jun 25 |
Thu |
Beatrice Popescu Braileanu (Instituto de Astrofísica de Canarias, IAC, Spain) |
European Solar Physics Online Seminars (ESPOS) |
| 10:00 |
Zoom: https://zoom.us/j/165498165 |
Two-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread: Effects of prominence magnetization and mass loading
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Abstract:
Solar prominences are formed by partially ionized plasma with inter-particle collision frequencies generally warranting magnetohydrodynamic treatment. In this work, we explore the dynamical impacts and observable signatures of two-fluid effects in the parameter regimes when ion-neutral collisions do not fully couple the neutral and charged fluids. We perform 2.5D two-fluid (charges - neutrals) simulations of the Rayleigh-Taylor instability (RTI) at a smoothly changing interface between a solar prominence thread and the corona. The purpose of this study is to deepen our understanding of the RTI and the effects of the partial ionization on the development of RTI using non-linear two-fluid numerical simulations. Our two-fluid model takes into account viscosity, thermal conductivity, and collisional interaction between neutrals and charges: ionization/recombination, energy and momentum transfer, and frictional heating. We explore the sensitivity of the RTI dynamics to the prominence equilibrium configuration, including the impact of the magnetic field strength and shear supporting the prominence thread, and the amount of prominence mass-loading. We show that, at small scales, a realistically smooth prominence-corona interface leads to qualitatively different linear RTI evolution than that expected for a discontinuous interface, while magnetic field shear has the stabilizing effect of reducing the growth rate or eliminating the instability. In the non-linear phase, we observe that in the presence of field shear the development of the instability leads to formation of coherent and interacting 2.5D magnetic structures, which, in turn, can lead to substantial plasma flow across magnetic field lines and associated decoupling of the fluid velocities of charges and neutrals.
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| Jun 25 |
Thu |
Beatrice Popescu Braileanu (Instituto de Astrofísica de Canarias) |
SP2RC/ESPOS |
| 10:00 |
https://zoom.us/j/165498165 |
By-weekly SP2RC/ESPOS joint seminar: wo-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread: Effects of prominence magnetization and mass loading |
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| Jul 1 |
Wed |
Nelson Nunes (University of Lisbon) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
Disformal couplings with a LambdaCDM background |
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| |
Abstract:
The discovery of the accelerated expansion of the Universe is now very well established and the LambdaCDM paradigm is the strongest candidate to explain it. Nonetheless, there are tensions between the relatively high level of clustering found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. A way to alleviate this issue is to consider a scalar field dark energy component conformally coupled to dark matter maintaining a LambdaCDM background cosmology. In this presentation we extend these studies to allow in addition disformal couplings which we explore by performing a dynamical system analysis.
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| Jul 2 |
Thu |
Nitin Yadav (Max Planck Institute for Solar System Research, Gottingen, Germany) |
Plasma Dynamics Group |
| 16:00 |
https://meet.google.com/dbb-drgp-tjq |
Vortex Flows in the Solar Atmosphere
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| |
Abstract:
Vortex flows exist over various spatial and temporal scales throughout the solar atmosphere
and are of great importance due to their potential in twisting the magnetic field lines and hence
facilitating Poynting flux transport. Recent advances in both, observational techniques and
numerical simulations, have enabled us to detect a multitude of small-scale vortices in the solar
atmosphere. Smaller vortices are suggested to play an important role in the solar atmospheric
heating, however, their physical properties remain poorly understood due to limited resolution
in observations. Hence, it is crucial to investigate them using high-resolution simulations
since they are more abundant and faster rotating flows than the larger vortices. Using MHD
simulations, we explored the the relationship between vortex flows at different spatial scales, analyze their physical properties, and investigate their contribution to Poynting flux transport from the lower to the upper layers of the solar atmosphere. We found that a large vortex, as
seen at low spatial resolution, consists of a large number of smaller vortices, when seen at high
spatial resolution. Statistically, they have higher densities and higher temperatures than the
average values at the same geometrical height. Their Poynting flux contribution is more than adequate to compensate for the radiative losses in the chromosphere indicating their possible role in the solar atmospheric heating.
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| Jul 3 |
Fri |
Durgesh Tripathi (IUCAA) |
SP2RC seminar |
| 13:00 |
https://us02web.zoom.us/j/82382995948?pwd=aUFzNGhQYkNMckdCdU5CekpXZHdXZz09 |
The Aditya-L1 Mission of Indian Space Research Organisation
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Abstract:
The Aditya-L1 is the first mission of the Indian Space Research Organization (ISRO) dedicated to solar observations. The spacecraft will be located at the first Lagrangian point and will provide continuous observations of the Sun using remote sensing as well as in-situ measurements. The spacecraft will carry seven payloads, including a coronagraph that will image the corona in visible and IR wavelength and will provide measurements of coronal magnetic field and will study the dynamics of coronal mass ejections; a NUV imaging telescope to study the coupling between solar photosphere and chromosphere and to measure spatially resolved solar spectral irradiance and its variation. There will be two payloads to study the soft X-ray and hard X-ray emission from the Sun, two payloads for in-situ measurements of the charged particles and a magnetometer to study the magnetic field variations during energetic events. Some of the salient features of the experiments onboard Aditya-L1 mission will be discussed.
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| Jul 8 |
Wed |
Robert Brandenberger (McGill University) |
Cosmology, Relativity and Gravitation |
| 15:00 |
https://app.vscene.net/r/KjKhl4yTE4 |
Is Inflationary Cosmology Consistent with Fundamental Physics?
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Abstract:
The inflationary scenario is currently the paradigm of early universe cosmology. However, an embedding of inflation into a fundamental theory is missing. I will first show that there are alternative early universe scenarios which are consistent with current observations. Hence, we do not require inflation to explain the data. Then I will discuss recent challenges which indicate that standard inflation is NOT consistent with fundamental physics. Specifically, I will discuss the "Swampland Criteria" and the "Trans-Planckian Censorship Conjecture".
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| Jul 17 |
Fri |
Vaibhav Pant (KU Leuven) |
SP2RC seminar |
| 13:00 |
https://meet.google.com/ciq-zovu-rzm |
MHD simulations and forward modeling of transverse MHD waves in the solar atmosphere |
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Abstract:
Several spectroscopic and imaging observations have established the ubiquity of transverse MHD waves in the solar atmosphere. Recently, an apparent discrepancy was noted in the measured wave energy flux in the transition region using SDO/AIA compared to those measured in the corona using Coronal Multi-channel Polarimeter (CoMP). Earlier studies have speculated that this discrepancy could be due to the unresolved wave amplitudes along the line-of-sight (LOS) in the solar atmosphere but they required the use of an additional, unknown source of wave energy to provide agreement with the measurements of the coronal non-thermal line widths. In this talk, I will resolve this discrepancy by presenting 3D MHD simulations of propagating transverse MHD waves in a gravitationally stratified plasma with properties similar to the coronal holes in the Sun. I will present the amount of underestimation of true energy in the MHD simulations due to the LOS superposition of different structures in the solar corona. This study could be useful in estimating the true wave energy flux using the observations of the nonthermal line widths from the upcoming solar observatories such as Solar orbiter, Aditya, UCoMP, etc.
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| Jul 30 |
Thu |
Isabell Piantschitsch (Universitat de les Illes Balears, Spain) |
Plasma Dynamics Group |
| 16:00 |
https://meet.google.com/xks-wpsx-xex |
A new method for estimating global coronal wave properties from their interaction with solar coronal holes
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Abstract:
Global coronal waves (CWs) and their interaction with coronal holes (CHs) result, among other effects, in the formation of reflected and transmitted waves. Observations of such events provide us with measurements of different CW parameters, such as phase speed and intensity amplitudes. However, several of these parameters are provided with only intermediate observational quality, other parameters, such as the phase speed of transmitted waves, can hardly be observed in general. We present a new method to estimate crucial CW parameters, such as density and phase speed of reflected as well as transmitted waves, Mach numbers and density values of the CH's interior, by using analytical expressions in combination with basic and most accessible observational measurements. The transmission and reflection coefficients are derived from linear theory and subsequently used to calculate estimations for phase speeds of incoming, reflected and transmitted waves. The obtained analytical expressions are validated by performing numerical simulations of CWs interacting with CHs. This new method enables to determine in a fast and straightforward way reliable CW and CH parameters from basic observational measurements which provides a powerful tool to better understand the observed interaction effects between CWs and CHs.
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| Jul 31 |
Fri |
William Oxley (SP2RC) |
SP2RC seminar |
| 13:00 |
https://meet.google.com/ciq-zovu-rzm |
Magnetohydrodynamic (MHD) Waves and Asymmetric Magnetic Slabs
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Abstract:
The field of solar magneto-seismology (SMS) is heavily reliant upon our understanding of magnetohydrodynamic (MHD) waves that occur in many solar features. In this talk I will discuss my two recent papers which build on previous studies of propagating MHD waves in asymmetric magnetic slabs. The new ideas in these studies are the assumptions of a line-tying boundary condition that causes standing waves to form. As with many wave studies, after setting up the model, the idea is to derive the dispersion relation which connects the wave number and the frequency of the waves supported by the waveguide. The goal is to derive expressions for observable quantities to lead order in the variables that represent the slab width and the asymmetry (which are both assumed to be small). After presenting these results I will discuss what we have learned, and how this is useful through solar magneto-seismology. The same techniques have been applied to the magnetic slab in both a magnetic and non-magnetic asymmetric environment, and comparisons between the two models will be made.
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