2024 PDG seminars
The Solar Melting Pot: Impulsive Heating in the Solar Corona
Observations in the EUV and X-rays tell us that the solar corona is dominated by the magnetic field. The solar photosphere drags and stresses the field, thus leading to the release of magnetic energy into heat and plasma dynamics. Different scales can be involved, ranging from tiny and elusive impulsive events, called nanoflares, to large events which can even influence human activities, like flares and eruptions, but magnetic reconnection might play a major role in all cases. However, a fully realistic description would require including highly non-linear effects on several spatial and temporal scales which are unfeasible today. I will discuss MHD modeling in the light of comparison and diagnostics from present-day and forth-coming observations.
FR_2024.mp4
Hot meets cold: From eruption to post-flare rain
Erupting magnetic flux ropes (MFRs) play an important role in producing solar flares, whereas fine-scale condensed coronal rain is often found in post-flare loops. However, the formation of the MFRs in the pre-flare stage and how this leads to coronal rain in a post-eruption magnetic loop is not fully understood. In this talk, I will address how these two interdisciplinary aspects are interconnected through numerical modeling. To do this, we perform a resistive-magnetohydrodynamic simulation to explore the evolution of sheared magnetic arcades to explore the formation, and eruption of MFRs, followed by the appearance of coronal rain in the post-flare loops. The system is in mechanical imbalance at the initial state, and evolves self-consistently in a non-adiabatic atmosphere under the influence of radiative losses, thermal conduction, and background heating. The system relaxes to a semi-equilibrium state from its initial mechanical imbalance condition after a short transient temporal evolution. After this period, a series of erupting MFRs is formed due to spontaneous magnetic reconnection, and current sheets are created underneath the erupting flux ropes. Gradual development of thermal imbalance is noticed at a loop top in the post-eruption phase, which leads to catastrophic cooling and formation of cool-condensations. The dynamical and thermodynamic properties of these cool-condensations are in good agreement with observations of post-flare coronal rain. The presented simulation supports the development and eruption of multiple MFRs, and the formation of coronal rain in post-flare loops, which is one of the key aspects to reveal the coronal heating mystery in the solar atmosphere.
SSen_2024.mp4
Anemone Solar Jets: Breakthroughs from SST Observations and Numerical Simulations
Solar jets are collimated plasma flows that move along magnetic field lines and are accelerated at low altitudes following magnetic reconnection. Many of these jets originate from anemone-shaped low-lying arcades, and the most impulsive ones tend to be relatively broader, often showing untwisting motions. In this talk, I will present typical observational signatures in the lower atmosphere that correspond to the coronal evolution of these impulsive jets. In our study, we analyzed an observed solar jet associated with a circular flare ribbon using high-resolution observations from the SST, coordinated with IRIS and SDO. We specifically compared observed features with those predicted by a generic 3D line-tied numerical simulation of reconnection-driven jets, conducted using the ARMS code. Three key features were identified in the SST observations: the formation of a hook along the circular ribbon, the gradual widening of the jet through the apparent displacement of its kinked edge toward (rather than away from) the presumed reconnection site, and the falling back of some jet plasma towards a footpoint offset from that of the jet itself. These features, which emerged naturally in the 3D numerical simulation without prior assumptions, were interpreted in the context of the 3D geometry of asymmetric swirled-anemone loops and their reconnection sequences with surrounding coronal loops. Given the relatively simple conditions under which the observed jet occurred, and the generic nature of the simulation with minimal assumptions, we predict that the specific features we identified and interpreted are likely typical of all impulsive jets.
RJ_2024.mp4
Inconsistency between coronal holes and open magnetic field regions
Coronal holes (CHs) appear as the dark patches in the coronal images with weak and predominantly unipolar surface magnetic fields. They are the primary source regions for high speed solar wind streams. While the observed unipolarity of their surface magnetic fields and high-speed plasma escaping from the region have led to the belief that CHs contain field lines that are extending to infinity (i.e., open magnetic field lines), many studies have revealed significant inconsistency between CHs and the foot points of open field lines, which will be called open magnetic field (OMF) regions. The inconsistency can cause ambiguity and misunderstanding in the results of different studies, with some using CHs, some using OMF regions, and some using a combination of the two. The objective of our study is to investigate the physical reasons for the inconsistency. In this talk, the CHs without open field lines and the OMF regions not identified as coronal holes will be explained, and the results of a strategy to improve the consistency between CHs and OMF regions will be presented.
CHL_2024.mp4
An ultrasound scan of large sunspots: from birth to death
Sunspots emerge, evolve and then "die". Some sunspots can move fast, some are slow, some decay faster than others and the magnetic fragmentation proves this. I will analyse the acoustic properties of a few interesting giant sunspots. Standard local helioseismic diagnostics of large sunspots show the signature of anomalously strong compact scatterers of p-modes within about a Mm beneath their photospheres. These "strong acoustic scatterers" appear in both umbrae and inner penumbrae, but in a sunspot whose umbra is large enough to accommodate several of them, they show a decided affinity for the boundary separating the two. This work helps understanding the flux emergence of active regions, which leads to a better understanding of the development of large active regions, which produce solar flares and coronal mass ejections, all relevant for space weather processes near Earth. Also: ample discussions about other research related to flux emergence and ML
AD_2024.mp4
Analysis of Solar Spectroscopy and Imaging Data Using Machine Learning Algorithms
In the current environment of rapid technological development, data processing and analysis algorithms are required to keep pace with the increasingly large and complex observational output. In addition to more realistic theoretical models, machine learning (ML) is rapidly being integrated into solar and heliophysics research to facilitate data visualization and analysis. I would like to demonstrate the use of several supervised and unsupervised ML algorithms for the analysis of solar data, i.e. spectra and images. The first data pipeline uses t-Distributed Stochastic Neighbor Embedding (t-SNE), a nonlinear dimensionality reduction algorithm, to visualize multidimensional spectroscopic data in 2D space. The resulting embedding is subjected to cluster detection and analysis. Using a combination of ML algorithms, we aim to build a robust framework that facilitates visualization and analysis of the common physical properties of multidimensional datasets with minimal user interaction. The second project uses CNN-based variational autoencoders in combination with selected unsupervised algorithms for parameterization and classification of active region vector magnetic field maps. The results will be used as a complementary dataset to the empirical parameters in a supervised flare prediction pipeline.
ED_2024.mp4
Modelling the connection between propagating disturbances and solar spicules
Propagating (intensity) disturbances (PDs) have been reported throughout the solar atmosphere in coronal loops, plumes and recent links with spicular activity. However, despite being reported in observations, they are yet to be studied in depth from a modelling point of view. In this work, we present results from 3D MHD numerical simulations where features with striking characteristics to those of detected PDs arise as a result of the transition region dynamics. Furthermore, the PDs can be interpreted as slow magnetoacoustic pulses propagating along the magnetic field carrying sufficient energy flux to at least partially heat the lower coronal plasma. Using forward modelling, we demonstrate the similarities between the PDs in the simulations and those reported in observations from IRIS and SDO/AIA. These results may have important implications in the context of providing a source for mass and energy in powering the (fast) solar wind
SS_2024.mp4
Global MHD simulations of solar wind streams in the inner heliosphere using sunRunner3D
Understanding the large-scale three-dimensional structure of the inner heliosphere, while important in its own right, is crucial for space weather applications, such as forecasting the time of arrival and propagation of coronal mass ejections (CMEs). This study uses sunRunner3D (SR3D), a 3-D MHD model, to simulate solar wind (SW) streams and generate background states. SR3D employs the boundary conditions generated by CORHEL and the PLUTO code to compute the plasma properties of the SW with the magnetohydrodynamic (MHD) approximation up to 1.1 AU in the inner heliosphere. We demonstrate that SR3D reproduces global features of Corotating Interaction Regions (CIRs) observed by Earth-based spacecraft (OMNI) and STEREO-A for a set of Carrington rotations that cover a period that lays in the late declining phase of solar cycle 24. Additionally, we demonstrate that the model solutions are valid in the corotating and inertial frames of references. Moreover, a comparison between SR3D simulations and in-situ measurements shows reasonable agreement with the observations, and our results are comparable to those achieved by Predictive Science Inc.'s MAS code and SWASTi-SW framework.
JJGA_2024.mp4Institute for Astronomy, Astrophysics,
Space Applications and Remote Sensing (IAASARS),
National Observatory of Athens (NOA),
Greece
14 March 2024
LT6, Hicks Building and online
Swirling motions in the lower solar atmosphere: detection, statistics and profile analysis from multi-wavelength observations
Ubiquitous vortical motions in the solar atmosphere have been recently revealed by high resolution observations from both space-borne and ground-based observatories in quiet, as well as, in active regions. In chromospheric observations obtained in spectral lines, such as the Halpha and Ca II IR, they manifest themselves as swirling dark spiral- and circular-shaped patches known as “chromospheric swirls”. Their suggested contribution to the channeling of energy, mass and momentum from the sub-photospheric to the higher layers of the solar atmosphere places them amongst potential candidates for atmospheric heating. In this context, their detection and statistical information concerning their population and several significant physical parameters and properties are of vital importance. To overcome the drawbacks of the detection methods based on visual inspection or on the Local Correlation Tracking (LCT) techniques, we have developed a novel automated detection method, which is purely based on their morphological characteristics. We will be presenting a brief description of the algorithm and the results from its application on high-resolution observations obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the Swedish 1-m Solar Telescope (SST) in three chromospheric spectral lines, namely, the Halpha, Ca II IR and Ca II K lines. The results include several statistical parameters such as their number, spatial distribution and temporal evolution, as well as significant physical parameters, such as radii and lifetimes. Specifically, for the estimation of the mean lifetime, apart from the usual approaches, the statistical method of survival analysis was implemented. This approach, which estimates more accurately the mean lifetime of a population, although common in several other scientific fields, is scarcely used in solar physics/astrophysics. We will finally be focusing on co-spatially detected swirling structures in all three chromospheric lines and the profile analysis performed to derive significant physical parameters, such as line-of-sight velocities, FWHM and equivalent widths.
ID_2024.mp4Institute for Solar-Terrestrial Physics, Germany
Anchor University, Lagos, Nigeria
22 February 2024
Probing space weather effects: from the D-region to the thermosphere
The response of the lower ionosphere (D-region) to geomagnetic storms is subtle and not well developed. To understand and/or substantiate storm-induced ionospheric response in the D-region, this work explore a multi-parametric approach that combines the diagnostics of the D, E and F regions parameter, to probe the associated dynamics. By simultaneously combining observed variations of very low frequency (VLF) radio waves amplitude (in the receiver-transmitter great circle path, TRGCP) with ionosonde and GNSS data we show that geomagnetic storms can have strong and far-reaching impact on the lower ionosphere. In the thermosphere, space weather event can significantly perturb the temperature and density profile of the region, leading to enhanced atmospheric drag on satellites operating in low Earth orbit (LEO). Using a new drag model, we simulate and show aerodynamic drag effect on LEO satellites during intervals of elevated solar activity. Finally, we describe ongoing effort to advance this area of research in our region through viable collaborations and scientific cooperation.
VN_2024_1.mp4VN_2024_2.mp4
Bridging the gap between numerical simulations and experiments through computer vision and deep learning
Several physics and engineering problems require knowledge of physical properties to be completely characterized. However, such properties cannot always be easily obtained experimentally, which means that numerical simulations are often necessary to study the problem in question. In the present work, we propose to leverage data from numerical simulations to extract relevant information from experimental visualizations of the flow field using deep learning. We uniquely treat the image semantic segmentation as an image-to-image translation task that infers semantic labels of structures from the input images in a supervised way. The present methodology exploits the semantic proximity between images from the numerical and experimental domains to translate any properties of interest between them. Example applications are shown for a moving airfoil as well as for predicting forces on a sand dune. Extrapolation and interpolation for different flow regimes never seen by the neural network are discussed.
RM_2024.mp4
Identifying and Tracking Coronal Flux Ropes
To understand solar eruptions and the destabilization mechanism of the corresponding flux ropes, modelling the magnetic field in the solar corona in a time-dependent manner is commonly employed. However, identifying the field lines of solar flux ropes in simulation data is not trivial. We therefore developed a method for detecting and tracking flux ropes from modelling data. The extraction procedure uses a combination of some proxy map as input (for example the field line twist) and mathematical morphology algorithms, such as the morphological opening or the morphological gradient. The method is validated by applying it to time-dependent magnetofrictional model (TMFM) simulations of active regions AR11176 and AR12473. With full access to the flux rope field lines, we investigate the eruptivity and propagation of the flux ropes through the modelling domain. Finally, the methodology is also wrapped into a graphical user interface (GUI) to further simplify its application.
AW_2024.mp4