The Space Physics seminars take place once a month, generally on Thursday at 14:00, and are held in hybrid format.
The events are organised by Lucile Turc. If you are interested in giving a presentation, have a suggestion for a speaker (for example a collaborator visiting the University of Helsinki), or for any other enquiries, please contact Lucile Turc (lucile.turc at helsinki.fi).
Note for PAPU students: Attendance to the Space Physics seminar can be counted towards completing the PAPU seminar course, please bring your card for the organiser to sign at the end of the presentation, or arrange with them to sign your card at another time if you are attending remotely.
- 19th October at 14:00: Abiyot Workayehu (University of Helsinki) – High-latitude ionospheric currents from the Swarm satellites (Exactum A114 and on Zoom Meeting ID 645 0675 3475 – Passcode 568758)
High-latitude ionospheric currents have been studied for over a century, primarily using ground-based magnetic field measurements. However, significant progress in their investigation was started recently with the advent of magnetic field vector observations by low-earth orbiting satellites. These early studies primarily focused on qualitatively determining the latitude/local-time patterns of ionospheric currents. More quantitative investigations have become possible with the availability of continuous time series of high-precision magnetic data measured by satellites such as Ørsted, CHAMP, and ESA’s Swarm satellite constellation.
It has been traditionally assumed that the coupling between the magnetosphere and ionosphere is symmetrical in the north and south hemispheres, but recent observations have suggested that coupling, as manifested by magnetic field aligned currents (FACs), is stronger in the north than in the south. However, the role of data coverage and data analysis methods in obtaining some of the results has been questioned.
We have made a very comprehensive analysis of several years of magnetic field data recorded by the ESA’s Swarm-A and -C satellites to yield ionospheric horizontal and field-aligned currents both in the north and south hemispheres using the spherical elementary current system (SECS) method. The main objective of our study has been to statistically investigate the effect of geomagnetic activity, local season and IMF directions on the currents, giving special emphasis on hemispheric asymmetry.
Our results confirm the existence of hemispheric asymmetry in the high-latitude current systems and provide substantial new insights into the seasonal, geomagnetic activity, and IMF-dependence of the asymmetry. In this seminar, I will provide a general overview of the SECS/Swarm method we used for magnetic analysis and present our key research findings, along with potential physical mechanisms that could account for the observed hemispheric asymmetry.
- 5th October at 14:00: Seth Dorfman (UCLA) – “Investigations of fundamental Alfvénic wave physics in the laboratory and in space” (Exactum A114 and on Zoom Meeting ID 645 0675 3475 – Passcode 568758)
Low frequency Alfvénic waves are are ubiquitous throughout ourheliosphere. The linear and non-linear properties of these waves may play key roles in the turbulent solar wind, heating of the solar corona, and the environment near the Earth’s bow shock. The use of multiple tools together can help us gain insight into the behavior of the waves in these contexts; spacecraft measurements provide the ground truth while laboratory experiments allow us to isolate the key physical processes for detailed study in a real plasma. In this seminar, I will present examples of experimental work on the Large Plasma Device (LAPD) at UCLA as well as observational studies in space. One focus of our work is Alfvén wave parametric instabilities, which bound the solar wind parameter space [Bowen, et. al. 2018]. LAPD experiments show the first lab observation of an Alfvén wave parametric instability, including features not yet predicted by theory [Dorfman and Carter, PRL 2016]. We also recently conducted a proof-of-principle experiment to measure the growth rate of the standard Parametric Decay Instability (PDI) in the laboratory. Current work also includes the first observation of residual energy in a non-linear Alfvén wave interaction — this is important because the inertial range of the turbulent cascade in the solar wind has residual energy (more energy in the magnetic than the velocity fluctuations), but an MHD Alfvén wave has equal amounts of energy in fluctuations of each type.
In contrast to laboratory experiments, wave measurements in spacetypically use a small number of datapoints due to limited available spacecraft. Common single-spacecraft wave vector analysis techniques built around these limitations are widely used, even in regions where the wave amplitude profile may have a strong spatial dependence. We show that in these gradient regions, the divergence-free condition of the magnetic field requires a local modification to the plane of polarization that is incorrectly interpreted by single-spacecraft techniques. This result is explored in the context of the Earth’s ion foreshock and forms the basis of a new technique for determining the edge of the Ultra Low Frequency (ULF) wave region. However, our results also have broad implications for wave measurements in other contexts [Dorfman et. al. JGR 2023]. After examining these various examples, I will discuss the prospects of a new Solar Wind Machine aimed at producing magnetized plasma turbulence in the laboratory for detailed study to complement spacecraft observations [Dorfman, et. al, NASA Decadal White Paper 2022].
- 21st September at 14:00: Manon Jarry (IRAP, France) – Exploring the role of coronal shock waves in the acceleration of particles (Exactum A114 and on Zoom, Meeting ID: 631 4919 0344 – Passcode: 937882)
The mechanisms that produce solar energetic particles (SEPs) are still highly debated but shock waves in the solar corona have been proposed as efficient particle accelerators that may be implicated in the production of SEPs.An analysis of 32 Coronal Mass Ejections (CMEs) that produced strong pressure waves in the solar corona during their eruption has been done. For each event Kouloumvakos et al. (2019) exploited remote-sensing observations from multiple vantage points to reconstruct their 3-D ellipsoidal shapes. This catalogue of shock waves provides important statistical information on their kinematic evolution that we report in Jarry et al. (2023) together with their relation to X-ray flaring activitiy. Different SEPs exhibit significant spectral and compositional variability. We looked for links between the composition of SEPs and shock parameters (Mach number, shock geometry, ..) that typically evolves rapidly along the magnetic field lines connected to the spacecraft recording SEPs.
- 31st August at 10:15 (note the unusual time!): Brian Walsh (Boston University) – “The importance of boundaries – advancing space sciences through large-scale probing of Earth’s magnetosphere” (Exactum A114 and on Zoom Meeting ID: 630 0721 4373 – Passcode: 887862)
- 25th May 2023: Stephan Heinemann (University of Helsinki) – “On the evolutionary aspects of solar coronal holes: A fast rotating and decaying coronal hole” (Exactum A114 and Zoom Meeting ID 696 0194 9621 – Passcode: 343376)
The topology and dynamics of the solar atmosphere are governed by the complex interplay of open and closed magnetic fields. Open fields link the solar surface to interplanetary space, allowing outflowing plasma to be accelerated to supersonic speeds and are the source of the heliospheric open flux (see review by Cranmer & Winebarger 2019). The open field structure leads to the formation of large scale low-density, low-temperature regions in the solar corona that can be observed as structures of reduced emission in EUV and X-ray (on-disk) and white-light (off-limb), the so-called coronal holes (see review by Cranmer 2009, and references therein). And as the source regions of the fast solar wind streams, that are the major cause for weak to moderate geomagnetic activity at Earth (see, e.g., Alves et al. 2006; Richardson 2018), the evolution of coronal holes is of great interest to the field of solar terrestrial physics and space weather.In this seminar I will given an introduction to coronal hole evolution and present our recent study that focuses on the evolution of a well observed decaying coronal hole during its last days. Using EUV observations as well as LOS magnetic field remote sensing observations we tracked and analyzed the coronal hole’s morphological and magnetic evolution from April 23rd to May 4th. The coronal hole showed a tilting motion that can be linked to different rotation speed at different latitudes on the Sun. During its last days, the coronal holes tilting rate is significantly faster than one expected by differential rotation, which we believe is caused by non-potential process in the corona, first and foremost interchange reconnection. The interaction with a newly emerging ephemeral region in the northern part of the coronal hole may play a major role. While the area of the coronal hole decays by more than a factor of 3 in around 4 days (from ≈ 12.8 × 10^9 km^2 to ≈3.9 × 10^9 km^2), its open flux remains conserved at a value of (1.82 ± 0.43) × 10^20 Mx. This suggests that the majority of the morphological evolution of the coronal hole is driven by interchange reconnection at the boundary and changes in the underlying photospheric magnetic field like flux emergence and cancellation only play a minor part. Also, the observed structure of reduced emission in the corona and its evolution cannot be reproduced as open field areas modeled using PFSS. This further indicates that (1) there are no significant changes visible in the photospheric magnetic field during this time period and (2) that the magnetic structure of this coronal hole is highly non-potential.
- 18th April 2023 (Note the unusual day: Tuesday!): Shannon Hill (University of Michigan) – “When the Earth’s heavenly fires reach the north pole: simulation study of the theta aurora” (Exactum A114 and Zoom Meeting ID 699 6544 0543 – Passcode: 576284
The theta aurora is a fascinating phenomenon during which a sun-aligned auroral arc spans across the typically empty polar cap to connect the nightside and dayside auroral oval in a shape that resembles the Greek letter theta. Theta auroras, also referred to as transpolar auroral arcs (TPAs), are generated during periods of northward IMF. The specific TPA formation mechanisms are highly debated. However, it is generally agreed that nightside reconnection and magnetotail twisting play a role in TPA generation, which indicates an active magnetosphere during periods of northward IMF. Therefore, the study of theta auroras offers insight into the solar wind-magnetosphere-ionosphere coupling and global energy transfer that occurs during northward IMF quiet periods. In this seminar, we present simulation results of an observed theta aurora event on 15 May 2005. We simulate the theta aurora observations with the University of Michigan’s Space Weather Modeling Framework in the Geospace configuration. We compare the simulation and observations and identify dayside and nightside TPA features produced by the simulation. We map the ionospheric TPA features to their multiple source regions in the magnetosphere. Our study provides the first simulation evidence that the TPA is formed from multiple magnetospheric sources that connect as a single structure in the ionosphere.
- 6th April 2023: Chaitanya Sishtla (University of Helsinki) – “Magnetohydrodynamic modelling of Alfvén waves in the solar corona” (Exactum A114 and Zoom Meeting ID: 630 9625 5164 – Passcode: 326311)
Alfvén waves are ubiquitous in the solar wind. Their nonlinear interactions and eventual turbulent cascade result in an important heating mechanism that accelerates the solar wind. These waves are generated at the photosphere and propagate throughout the heliosphere. They are processed and interact with plasma structures like shocks and coronal mass ejections (CME). However, the non-linear nature of the wave-wave and wave-plasma interactions makes studying the propagation of these waves challenging and complex to assess. In this seminar, I will present a magnetohydrodynamic approach to modelling Alfvén waves and studying their interactions with CMEs in the solar corona. I will discuss the results in the context of modelling solar wind heating through Alfvén wave turbulence, emphasising the limitations of existing turbulent heating models.
- 23rd March 2023: Karmen Martinic (University of Zagreb) – “Understanding the dynamics of coronal mass ejection in the heliosphere in terms of its orientation” (Exactum A114 and Zoom Meeting ID: 675 6393 3368 – Passcode: 062888)
In the scope of space-weather forecast, it is crucial to more reliably predict the arrival time, speed, and magnetic field configuration of the coronal mass ejection (CME). From the time the CME is launched, the dominant factor influencing all of the above is the interaction of the CME with the ambient plasma and interplanetary magnetic field (IMF). Due to the generally anisotropic heliosphere, differently oriented CMEs may interact differently with the ambient plasma and IMF, even though initial eruption conditions could be similar. For this we examined the possible link between the orientation of a CME and its propagation in the heliosphere (up to 1 AU) based on a sample of 31 CME-ICME associations in the period 1997-2018. We determined the CME orientation in the near-Sun environment using an ellipse fitting technique applied to single spacecraft data from SOHO/LASCO C2 and C3 coronagraphs. In the near-Earth environment, we obtained the orientation of the corresponding ICME using in situ plasma and magnetic field data. We investigated shock orientation and non-radial flows (NRF) in the sheath region for differently oriented CMEs. In addition, we calculate the CME transit time to Earth and drag parameter to probe the overall drag force for differently oriented CMEs. We found a significant difference in NRF for differently oriented CMEs, whereas the significant difference in drag for differently oriented CMEs was not found.
- 2nd March 2023: Peijin Zhang (University of Helsinki) – “Low-frequency radio view of the Sun” (Exactum D340 and Zoom Meeting ID: 658 5754 7318 – Passcode: 910060)
Low-frequency radio observation provides a unique viewing point for solar and spaceweather studies, including the inspection of solar energetic particles and the diagnostics for background plasmas. Solar radio bursts are generated from high energy particles pacing through the solar atmosphere and inner heliosphere interacting with the background plasma. The Low-frequency array (LOFAR) is a radio telescope composed of massive numbers of antennas spreading all over Europe, it is currently the largest radio telescope in the frequency range of 10-240MHz. In this talk, I present the recent proceedings in solar and spaceweather radio observations with LOFAR’s high resolution and sensitivity, including the imaging and spectroscopy of solar radio bursts, using bright quasar to perform sounding detection for the inner-heliosphere, and imaging of the quiet Sun.
- 9th February 2023: Eleanna Asvestari (University of Helsinki) – “Modelling coronal mass ejections as spheromaks with EUHFORIA: a game of forces” (Exactum A114 and Zoom Meeting ID: 675 7355 6433 – Passcode: 749566)
Coronal mass ejections (CMEs) are primary drivers of space weather related phenomena that impact human life and activity in space and on ground. Being able to predict how they evolve from the moment they erupt and throughout their journey across the solar system is essential both from a scientific and a socioeconomic perspective. Consequently, the development of space weather models that accurately reconstruct the kinematic and magnetic field evolution of CMEs is at the heart of space weather research efforts. A prime example of such models is EUHFORIA, a state-of-the-art magnetohydrodynamic (MHD) model simulating CMEs from 0.1AU to the Earth and beyond. In EUHFORIA CMEs are at the time of insertion modelled as spheromaks, which are axisymmetric, force-free configurations where twisted magnetic fields fill a spherical volume of constant density and temperature. The spheromak implementation in EUHFORIA brought to light different manifestations of a phenomenon called the spheromak tilting instability in the heliospheric simulation domain. According to this instability, when the magnetic moment of a spheromak is at an angle with the ambient magnetic field in which it is inserted, then the structure experiences a torque, causing it to tilt – rotate – to reduce its magnetic potential energy. The result of the tilting is a change in the spheromak’s orientation, compared to how it was inserted. In addition, the spheromak can also experience a magnetic net-force, which causes it to undergo additional drift from its original direction of propagation. The extent to which these affect the evolution of the spheromak-CMEs is a matter of a game of forces. Join me for this seminar, to embark on a journey from discovery to quantification and visualization. And let us discuss the questions that this “discovery” opened and what future research and observations we need to address them.
- 19th January 2023: Leo Kotipalo (University of Helsinki) – “Adaptive Mesh Refinement in Vlasiator” (Exactum A114 and Zoom Meeting ID: 613 4037 3261 – Passcode: 535497)
Simulating space plasma in a global scale is computationally demanding due to the system size involved. Modeling regions with variable resolution depending on physical behavior can save computational resources without compromising too much on simulation accuracy. This presentation examines adaptive mesh refinement as a method of optimizing Vlasiator, a global hybrid-Vlasov plasma simulator. Behavior of plasma near the Earth’s magnetosphere and different characteristic scales that need to be factored in simulation are introduced. Kinetic models using statistical methods and fluid methods are examined. Modeling electrons kinetically requires resolution orders of magnitude finer than ions, so in Vlasiator ions are modeled kinetically and electrons as a fluid. This allows for lighter simulation while preserving some kinetic effects. Mesh refinement used in Vlasiator is introduced as a method to save memory and computational work. Due to the structure of the magnetosphere, resolution isn’t uniform in the simulation domain, with particularly the tail regions and magnetopause having rapid spatial changes compared to the relatively uniform solar wind. The area to refine is parametrized and static throughout a simulation run. Adaptive mesh refinement based on the simulation data is introduced as an evolution of this method. This provides several benefits: more rigorous optimization of refinement regions, easier reparametrization for different conditions, following dynamic structures and saving computation time in initialization. Refinement is done based on two indices measuring the spatial rate of change of relevant variables and reconnection respectively. The grid is re-refined at set intervals as the simulation runs. Tests similar to production runs show adaptive refinement to be an efficient replacement for static refinement. Refinement parameters produce results similar to the static method, while giving somewhat different refinement regions. Performance is in line with static refinement, and refinement overhead is minor. Further avenues of development are presented, including dynamic refinement intervals
- 24th October 2022: Simon Good (University of Helsinki) – “Turbulence in coronal mass ejections and the solar wind” (Exactum A114 & Zoom Meeting ID: 612 3838 5777 – Passcode: 858468)
The solar wind contains broadband fluctuations with power spectra that take power-law forms. From the scale at which energy is injected via large-amplitude, low-frequency Alfvén waves originating at the Sun (kdi ~ 10-5), down to ion length scales in the plasma (kdi ~ 1), the fluctuations display the properties of a magnetohydrodynamic turbulent cascade. In the collisionless environment of the solar wind, the cascade plays a central role in transferring energy from injection to sub-ion scales, where kinetic effects become dominant and heating occurs. The seminar will include a general introduction to the nature of solar wind turbulence as seen in spacecraft observations, followed by a presentation of relevant work currently being performed in the group, which aims to fit coronal mass ejections and their sheaths into the framework of solar wind turbulence.
- 29 September 2022: Maxime Dubart (University of Helsinki) – “Vlasiator & the sub-grid model of pitch-angle diffusion in hybrid-Vlasov simulations” (Exactum A114 & Zoom Meeting ID: 697 1134 1148 – Passcode: 462869)
Numerical simulations have grown to play a central role in modern sciences over the years. The ever improving technology of supercomputers has made large and precise models available. However, this accuracy is often limited by the cost of computational resources. Lowering the simulation’s spatial resolution in order to conserve resources can lead to key processes being unresolved. We show here how insufficient spatial resolution of the proton cyclotron instability leads to a misrepresentation of ion dynamics in hybrid-Vlasov simulations. This leads to larger than expected temperature anisotropy and loss-cone shaped velocity distribution functions. We also present a sub-grid numerical model to introduce pitch-angle diffusion in a 3D Cartesian velocity space, at a spatial resolution where the relevant wave-particle interactions were previously not correctly resolved. We show that the method is successfully able to isotropize loss-cone shaped velocity distribution functions, and that this method could be applied to simulations in order to save computational resources and still correctly model wave-particle interactions.
- 5 May 2022: Mikko Savola (University of Helsinki) – “Mutual information and applying it to plasma physics” (Zoom Meeting ID: 664 1909 1276 – Passcode: 189697)
Geomagnetic storms, originating from the Sun, cause disturbances in the Earth’s magnetic field, e.g. by increasing the flux of highly energetic electrons at the outer Van Allen radiation belts, located some 3-10 Earth radii from Earth. The occurrence of such “killer electrons” is not only problematic due to their ability to break satellites but also not completely understood. The connection between geomagnetic storms and highly energetic (>1 MeV) electrons has been studied at least since the 1980s, and multiple mechanisms have been proposed and shown to have an effect on the electron flux. One often mentioned factor is ultra-low frequency (ULF) waves, which are thought to be able to accelerate electrons from lower to higher energy levels, and this relationship has been investigated quite extensively using linear regression. However, the equations describing the phenomena in the Earth’s magnetic field are non-linear, so that methods using linear models might not well capture a dependence between the variables.By studying the mutual information between two random variables one can find out the strength of the dependence between the variables regardless of its functional form. Mutual information is a statistical measure that, heuristically speaking, tells how much information can be obtained from the random variable X when the value of the random variable Y is known. Related to mutual information is conditional mutual information (CMI), which is mutual information between X and Y, conditioned on a third variable Z. CMI can be used to extract a dependence between X and Y that is stronger during some conditions.In the present work we use mutual information and conditional mutual information to evaluate the dependence between ULF wave power and low-energy (130 keV) and high-energy (1.2 MeV) electron fluxes. Based on the results there exists a statistically significant dependence, which is stronger during conditions with high solar wind speed.
- 14 April 2022: Harriet George (University of Helsinki) – “Radial diffusion of outer radiation belt electrons” (Kvantti, Physicum C208 – Zoom Meeting ID: 641 8820 6224 – Passcode: 570600)
The Earth’s radiation belts are a highly complex and dynamic environment. Electrons in the outer radiation belt can reach extremely high energies, which can damage satellites that pass through radiation belts and present hazards to humans in space. Radial diffusion is a major transport process acting on electrons in the outer belt, and understanding this process is key to understanding the radiation belt response to geomagnetic storms and thus predicting the space weather impacts. In this seminar, I will give a theoretical overview of radial diffusion and discuss some of the radial diffusion models that have been developed in the literature. One key factor for the accuracy of radial diffusion models is their treatment of the Earth’s geomagnetic field. I will compare the different responses to a geomagnetic storm that triggered an intense dropout of high-energy electrons predicted with the Brautigam & Albert (2000) model that assumes a dipole field and the Cunningham (2016) model that allows for a non-dipolar field. I will also present a novel methodology to evaluate radial diffusion that is based on fundamental particle properties and global electromagnetic fluctuations provided by the Vlasiator simulation.
- 24 March 2022: Fasil Tesema Kebede (University of Helsinki) – “Energetic electron precipitation of pulsating aurorae and their mesospheric effects” (Room TBC – Zoom Meeting ID: 651 3637 3900 – Passcode: 543138)
The major (about 75%) auroral energy input in the nightside atmosphere is from diffuse auroral precipitation driven by wave-particle interactions. Pulsating aurorae, the dynamic auroral structures embedded in the diffuse aurora, are one of the most common types associated with precipitating energetic electrons. It is often observed after local midnight, at the equatorial boundary of the auroral oval, and during the recovery phase of substorms. It switches on and off with a quasi-periodic oscillation period from a few to 10 seconds. The general definition of pulsating aurora structures consists of auroral arcs, arc segments, and irregularly shaped patches with a variable area having a scale size from 10 to 200 km. Precipitating electrons that cause pulsating aurora are originated from outer radiation belts and plasma sheet and are energetic enough to reach below 100km altitude, sometimes down to 70 km. This makes the pulsating aurora electrons vital in the magnetosphere-ionosphere dynamics and the dynamics and chemistry of the mesosphere. In this presentation, I will discuss the energy range and characteristics of precipitating pulsating aurora electrons and their effect in the mesosphere. The energy distribution of different structures (types) of pulsating aurora will also be discussed.
- 24 February 2022 at 14:00: Milla Kalliokoski (University of Helsinki): “Outer radiation belt electron response to sheath regions of coronal mass ejections” (Zoom Meeting ID: 689 6927 0264 – Passcode: 566298)
The Earth’s magnetic field traps charged particles in the Van Allen radiation belts where they pose a hazard for satellites. Electrons dominate the outer radiation belt where the electron fluxes can vary dramatically on timescales from minutes to days in response to solar wind driving. In this talk, I focus on how the outer belt electrons respond to the impact of sheath regions of interplanetary coronal mass ejections, especially investigating changes on short timescales of a few hours or less. Predicting changes in the outer belt is difficult as various competing acceleration, transport, and loss processes govern the electron dynamics. I will discuss the typical electron flux response to sheath events based on the results of statistical studies and show how detailed case studies of electron phase space density shed more light into the dominant processes occurring in the outer belt depending on the solar wind properties and the associated wave activity in the inner magnetosphere. Additionally, measurements from the Global Positioning System (GPS) constellation complement the Van Allen Probes data largely used in this research, providing a broader coverage which allows for investigation of outer belt electron dynamics at even shorter timescales.
- 20 January 2022 at 14:00: Giulia Cozzani (University of Helsinki) – “Microphysics of magnetic reconnection beyond the laminar, 2D, steady-state picture” (Zoom Meeting ID: 690 1115 9300 – Passcode: 771640)
Magnetic reconnection is a fundamental process that naturally occurs in a diverse variety of environments in space and astrophysical plasmas and it underlies physical phenomena such as coronal mass ejections and aurora. Magnetic reconnection efficiently converts the energy stored in the magnetic field to the particles of the plasmas, resulting in particle acceleration and plasma heating. The explosive energy conversion associated with reconnection affects large volumes but the reconnection process is initiated in a minuscule region called the electron diffusion region (EDR). The magnetosphere is the best laboratory at our disposal to investigate magnetic reconnection and the Magnetospheric Multiscale (MMS) mission has been launched in 2015 with the primary goal to study this process at the kinetic scales. The high-resolution particle measurements provided by MMS have allowed for the first time the investigation of the small and elusive – yet critical – electron diffusion region. Indeed, the understanding of the EDR has made large strides forward. However, the considered reconnection picture is in most cases two-dimensional and steady and the EDRs analyzed in previous studies are laminar. In the last years, the synergy between MMS in situ observations and fully kinetic numerical simulations shed light on the complexity of the EDR and magnetic reconnection. In particular, recent studies show that the EDR can be non-homogeneous and that the interplay between reconnection and other current sheet instabilities as well as turbulence can perturb the 2D steady-state picture of reconnection. This seminar will present recent studies focused on this faceted topic and discusses the complexity of the reconnection process that emerges from these works.
- 2 December 2021 at 14:00: Ivan Zaitsev (University of Helsinki) – “Ion dynamic in kinetic simulations of magnetotail reconnection” (Zoom Meeting ID: 629 5883 7606 – Passcode: 328833)
Being the major driver of the Earth’s magnetosphere dynamic, magnetic reconnection energizes plasma particles by a variety of kinetic mechanisms. Initiated on spatial scales close to the electron inertial length, magnetic reconnection leads to energy conversion and changes the magnetic topology of the large-scale system. In the MHD framework, it is assumed that energy dissipation is provided by the appearance of finite conductivity in the region where frozen-in conditions are violated, while in the kinetic approximation these dissipation sources may be established. The results of fully kinetic simulations performed with particle-in-cell code iPIC3D code will give us insight into the electron-to-ion energy exchange mechanisms during collisionless symmetric reconnection that mimic magnetotail current sheet disruption. In particular, the impact of the Hall electric fields onto ion populations having different thermal spread will be discussed. Special attention will be paid to ion velocity distributions peculiar to distinguished reconnection regions.
- 11 November 2021 at 14:00: Ranadeep Sarkar (University of Helsinki) – “Origin, evolution, and space weather consequences of coronal mass ejections” (Zoom Meeting ID: 676 9823 2690 – Passcode: 755740)
Coronal mass ejections (CMEs), the most violent eruptive phenomena occurring in the heliosphere, are the major driver of space weather disturbances. CMEs erupt in the form of gigantic clouds of magnetized plasma from the Sun and can reach Earth within several hours to days. If an Earth-directed CME or its associated sheath region carries a strong southward interplanetary magnetic field (IMF) Bz, then it interacts with the Earth’s magnetosphere, leading to severe geomagnetic storms. Therefore, in the context of space-weather forecasting, it is crucial to understand the conditions on the Sun leading to CME initiation and the Sun-to-Earth evolution of its magnetic properties. Since magnetic field cannot be measured reliably remotely in solar eruptions, and direct continuous measurements of the Earth impacting solar transients are available only very close to our planet, modelling of CME magnetic properties based on its source region characteristics is paramount.
In this talk, I will briefly discuss our studies on the physical conditions leading to CME initiation and their nature of evolution close to Sun which provide the crucial inputs for the space weather forecasting models. I will further discuss our recent work on modelling the CME magnetic properties from Sun to Earth using both analytical and numerical modelling framework. Our studies advance the current knowledge on constraining the CME flux rope properties in heliospheric models, which provide the steppingstones towards building an operational space weather forecasting tool.
- 14 October 2021 at 14:00: Sanchita Pal (University of Helsinki) – “On the Geoeffective Properties of Coronal Mass Ejections” (Zoom Meeting ID: 616 2264 5762 – Passcode: 360472)
The Sun often ejects large-scale magnetized plasma known as Coronal Mass Ejections (CMEs) that drive the space weather. Depending on intrinsic properties, CMEs may inject energetic particles and large amounts of energy into the Earth’s magnetosphere, resulting in geomagnetic storms. The geoeffectiveness of CMEs depends on their kinematics and magnetic properties, which might evolve in their interplanetary propagation. Forecasting space weather through prior estimation of the geoeffectiveness of CMEs is quite a challenging task as it has to be made in a dynamic and complex solar-terrestrial system with considerable accuracy, reliability, and timeliness. My research investigates and thereby improves the current understanding of the probable origin and Sun-Earth evolution of the CME intrinsic properties determining their geoeffectiveness. With an intention to predict the geoeffectiveness of CMEs, we attempt to constrain their magnetic structures before they arrive at Earth. Therefore, this study provides important implications for the origin, evolution, and prediction of geoeffectiveness in CMEs.
- 9 September 2021 at 14:15: Angelica M. Castillo (GFZ – University of Potsdam) – “Reconstructing the dynamics of the outer electron radiation belt by means of the standard and ensemble Kalman filter with the VERB-3D code”
Reconstruction and prediction of the state of the near-Earth space environment is important for anomaly analysis, development of empirical models and understanding of physical processes. Accurate reanalysis or predictions that account for uncertainties in the associated model and the observations, can be obtained by means of data assimilation. The ensemble Kalman filter (EnKF) is one of the most promising filtering tools for non-linear and high dimensional systems in the context of terrestrial weather prediction. In this study, we adapt traditional ensemble based filtering methods to perform data assimilation in the radiation belts. We use a one-dimensional radial diffusion model with a standard Kalman filter (KF) to assess the convergence of the EnKF. Furthermore, with24the split-operator technique, we develop two new three-dimensional EnKF approaches for electron phase space density that account for radial and local processes, and allow for reconstruction of the full 3D radiation belt space. The capabilities and properties of the proposed filter approximations are verified using Van Allen Probe and GOES data. Additionally, we validate the two 3D split-operator Ensemble Kalman filters against the 3D split-operator KF. We show how the use of the split-operator technique allows us to include more physical processes in our simulations and offers computationally efficient data assimilation tools that deliver accurate approximations to the optimal solution of the KF and are suitable for real-time forecasting. Future applications of the EnKF to direct assimilation of fluxes and non-linear estimation of electron lifetimes are discussed.
- 2 September 2021 at 11:15: Felix Spanier (Universität Heidelberg) – “The mass of the neutrino – why plasma matters” (Zoom Meeting ID: 648 6154 8067 – Passcode: 248621)
Neutrinos are everywhere – we are bombarded by solar neutrinos
all day long, astrophysical neutrinos traverse the universe at extreme
energies. But we still can only guess the mass of the neutrino. The
KATRIN experiment aims at finding better limits for the neutrino mass.
Since the interaction of neutrinos with matter has a very small
cross-section, direct measurements are impossible. The KATRIN experiment
uses the electron spectrum of the tritium decay to calculate the
neutrino mass. Unfortunately a large vessel filled with tritium emits
enough electrons to ionize the gas leading ultimately to a plasma.
Within this talk I will highlight, which effect a plasma has on the
measurements and what kind of simulations is necessary to understand the
plasma physics within the KATRIN source.
- 17 June 2021 at 14:00: Kosta Horaites (previously at LASP, Boulder, now at University of Helsinki) – “Kinetic Physics of Electrons from the Inner Heliosphere to Mars” (Zoom Meeting ID: 647 9881 6048 – Passcode: 442035)
In this introductory talk, I’ll describe my work on the kinetic physics of electrons in interplanetary space and at Mars. First, I’ll discuss the field-aligned beam of electrons known as the ‘strahl’, which comes from a competition between magnetic focusing and pitch-angle scattering (due to the weak-but-present Coulomb collisions). The physics of the strahl can be formalized in kinetic theory, which yields predictions for the velocity distribution. These predictions compare well with observations, as will be shown with data from the Wind satellite. Following the path of my own research career, I will finally discuss how electrons behave when they enter Mars’s magnetosphere, again from a kinetic perspective. In the Martian magnetosheath downstream of the bow shock, particle collisions may be neglected and Liouville’s theorem may be applied. As shown by electron data from the MAVEN satellite, observations of electron energization can then provide information on the planet’s global electric field. As the physics of shocks is more or less universal, these results may have applications at other planets such as Earth
- 20 May 2021 at 14:00: Maxime Grandin (University of Helsinki) – “Dune aurora, citizen science, mesospheric bore – 2021: An Ignorosphere Odyssey” (Zoom Meeting ID: 661 7872 3184 – Passcode: 639924)
A year ago, citizen scientist photographs led to the discovery of a new auroral form called “the dune aurora” which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. I will present the results of our new study published this month, which investigates a large-scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1500 km for at least four hours. Spacecraft observations indicate that the dunes are associated with particle precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west-southwest direction at about 200 m/s, presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least-known region of near-Earth space at altitudes near 100 km.
- 15 Apr 2021 at 14:00: Theodoros Sarris (Democritus University of Thrace, Greece) – “Radial Diffusion of Relativistic Electrons in the Radiation Belts and potential contributions from Vlasiator” (Zoom Meeting ID: 681 8653 0755 – Passcode: 686048)
The Earth’s magnetosphere often undergoes oscillations in the Ultra Low Frequency (ULF) range, roughly 1 mHz to 1 Hz (periods 1 to 1000 sec), which are a fundamental response of the magnetosphere to various external or internal drivers. ULF waves can have significant effects, such as enhancing the radial diffusion of radiation belt relativistic energetic electrons, which have drift periods within that range. However the quantification of the radial diffusion coefficients, which are greatly needed in predictive and assimilative models of the radiation belts, is a subject of ongoing debate, with numerous derivations, often with contradicting results and/or offsets by large factors. Among a few of the reasons underlying such discrepancies are the differentiation between electrostatic and electromagnetic contributions, the role of azimuthal wavenumbers of ULF waves, the divergence from the underlying assumption of linear diffusion and the mix between large-scale radial transport and radial diffusion. In this talk we will briefly introduce the status of understanding, we will outline key factors for the above discrepancies between estimating diffusion coefficients, we will present recent advances in calculating azimuthal wavenumbers that are needed in diffusion coefficient estimates and we will open a discussion on the potential of using global simulations of the magnetosphere, such as Vlasiator, for addressing open issues of radial diffusion.
- 18 Mar 2021 at 14:00: Markku Alho (University of Helsinki) – “A global survey of geospace electrons with eVlasiator: first results” (Zoom Meeting ID: 656 6238 4338 – Passcode: 569868)
Models of the geospace plasma environment have been proceeding towards
more realistic descriptions of the solar wind—magnetosphere
interaction, from gas-dynamic to MHD and hybrid ion-kinetic models such
as the state-of-the-art Vlasiator model. Advances in computational
capabilities have enabled global simulations of detailed physics, but
the electron scale has so far been out of reach in a truly global
In this work we present results from eVlasiator, an offshoot of the
Vlasiator model, showing first results from a global 2D+3V kinetic
electron geospace simulation. Despite truncation of some electron
physics and use of ion-scale spatial resolution, we show that realistic
electron distribution functions are obtainable within the magnetosphere
and describe these in relation to MMS observations.
- 18 Feb 2021 at 14:00: Farhad Daei (University of Helsinki) – “Complex network of solar active regions” (Zoom Meeting ID: 649 2612 8206 – Passcode: 103417)
In my presentation, I will review my PhD research about solar active regions system in which I applied graph theory and complex network approach.
Aim: The goal of this study was to prove that the system of ARs can be considered as a system of self-organized criticality (SOC).
Method: We constructed a network (graph) for ARs based on their location, occurrence time, and life duration, studying the local and global properties of the growing graph. The network then was categorized based on these parameters.
Results: The complex network of ARs is scale-free, so it is a SOC. In addition to that, the occurrence probability of flares on the network hubs is higher other nodes.
- 14 Jan 2021 at 14:00: Hongyang Zhou (University of Helsinki) – “From Macro to Micro: Simulating Ganymede’s Magnetosphere” (Zoom Meeting ID: 653 2623 0893 – Passcode: 408496)
To capture the local kinetic processes within a global magnetosphere simulation, the implicit kinetic particle-in-cell (PIC) model is embedded in the MHD model. We applied the coupled MHD-EPIC model to the magnetosphere of Ganymede, the third Galilean moon of Jupiter and the only moon known to possess an intrinsic magnetic field in the solar system. The model has been improved gradually over the years with higher resolutions, better schemes and more physics.
In this talk, I will present our development and recent progress in studying the reconnection related processes with the numerical model. By analyzing the reconnection sites, the relation between spatiotemporal variations in plasma and field properties across the magnetopause, the flux rope generation, and the reconnection rate will be discussed. I will show the comparison on the direct and indirect reconnection rate calculation from several numerical models and give insights into the flux transfer events (FTEs) and the responses from Ganymede’s magnetosphere.
- 3 Dec 2020 at 14:00: Anshu Kumari (University of Helsinki) – “Radio Polarimetric Studies of the Solar Corona at Low Frequencies” (Zoom Meeting ID: 663 3202 4009 – Passcode: 359423)
Measurements of the coronal magnetic field strength particularly in the radial distance range ~ 1.1 – 2.0 R, (where R is the radius of the solar photosphere) is presently difficult because of practical reasons. Polarization observations, by measuring the Stokes-V parameter of the received radio signal, are generally used as a tool to measure the magnetic field strength associated with the radio emission; the latter is one of the widely pursued areas of research in the solar coronal physics, in addition to the currently available but limited methods of estimating the magnetic field strength using simultaneous radio imaging and spectral observations. In this talk, I will be talking about: i) design of a new wideband, low frequency antennas, ii) design, development and characterization of a high temporal and spectral resolution multi frequency polarimeteric receiver system for solar observations at low radio frequencies, iii) studies of the solar radio bursts observed with these instruments and their counterparts as observed in multi frequencies with other space and ground-based instruments.
- 12 Nov 2020 at 14:00: Maarja Bussov (University of Helsinki) – “Clustering analysis for astrophysical structures (Zoom Meeting ID: 633 6072 3014 – Passcode: 456417)
“I will cover the techniques of analysis I have been doing in my PhD studies and the datasets I have been working with. Most emphasis will be put on the particle-in-cell turbulent plasma for the detection of current sheets with ensemble unsupervised learning. Additionally, I will briefly cover spatial statistics and cosmological datasets as well. To give a broader perspective of the techniques and relation between seemingly different datasets.“