A5036037675- Solar and Space Plasma Dynamics
- Geomagnetism and Paleomagnetism Studies
- Astro and Planetary Science
- Ionosphere and magnetosphere dynamics
- Geophysics and Gravity Measurements
- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Magnetic and Electromagnetic Effects
- Astrophysics and Star Formation Studies
- Meteorological Phenomena and Simulations
- Fluid dynamics and aerodynamics studies
- Oceanographic and Atmospheric Processes
- Tropical and Extratropical Cyclones Research
- Computational Fluid Dynamics and Aerodynamics
- Spacecraft Design and Technology
- History and Developments in Astronomy
- Galaxies: Formation, Evolution, Phenomena
- Astronomical Observations and Instrumentation
- Characterization and Applications of Magnetic Nanoparticles
- Spacecraft Dynamics and Control
- Atomic and Molecular Physics
- Magnetic Field Sensors Techniques
- Inertial Sensor and Navigation
- Non-Destructive Testing Techniques
- Advanced Thermodynamics and Statistical Mechanics
Max Planck Institute for Solar System Research
2014-2023
Max Planck Society
2014-2021
KTH Royal Institute of Technology
2012-2018
Stockholm University
2010-2018
Aalto University
2014-2018
AlbaNova
2010-2013
Nordic Institute for Theoretical Physics
2010-2013
University of California, Los Angeles
1996-1998
Planetary Science Institute
1996-1997
Context. Chromospheric activity monitoring of a wide range cool stars can provide valuable information on stellar magnetic and its dependence fundamental parameters such as effective temperature rotation. Aims. We compile chromospheric catalogue 4454 from combination archival HARPS spectra multiple other surveys, including the Mount Wilson data that have recently been released by NSO. explore variation in along main sequence for with different temperatures. Additionally, we also perform an...
We present results from simulations of rotating magnetized turbulent convection in spherical wedge geometry representing parts the latitudinal and longitudinal extents a star. Here we consider set runs for which density stratification is varied, keeping Reynolds Coriolis numbers at similar values. In case weak stratification, find quasi-steady dynamo solutions moderate rotation oscillatory ones with poleward migration activity belts more rapid rotation. For stronger growth rate tends to...
Galileo magnetometer data at 0.22-second resolution reveal a complex interaction between Io and the flowing plasma of torus. The highly structured magnetic field depression across downstream wake, although consistent with magnetized Io, is modified by sources currents within that introduce ambiguity into interpretation signature. Highly monochromatic ion cyclotron waves appear to be correlated local neutral particle density. power peaks in range molecular gyrofrequencies, suggesting...
Within Jupiter's magnetosphere, Ganymede's magnetic field creates a mini‐magnetosphere. We show that the measured during Galileo‧s second pass by Ganymede, with closest approach at low altitude almost directly over moon's polar cap, can be understood to large measure in terms of structure vacuum superposition model uniform and Ganymede‐centered dipole field. Departures from simple attributed principally magnetopause currents. orientation observed normal is qualitatively consistent...
Solar magnetic activity shows both smooth secular changes, such as the Grand Modern Maximum, and quite abrupt drops that are denoted Minima. Direct numerical simulations (DNS) of convection driven dynamos offer one way examining mechanisms behind these events. In this work, we analyze a solution solar-like DNS has been evolved for roughly 80 cycles 4.9 years, during which epochs irregular behavior detected. The emphasis our analysis is to find physical causes behavior. employed semi-global...
We investigate dynamo action in global compressible solar-like convective dynamos the framework of mean-field theory. simulate a solar-type star wedge-shaped spherical shell, where interplay between convection and rotation self-consistently drives large-scale dynamo. To analyze mechanism we apply test-field method for azimuthally ($\phi$) averaged fields to determine 27 turbulent transport coefficients electromotive force, which six are related $\alpha$ tensor. This has previously been used...
We seek to understand the transition from nearly axisymmetric configurations at solar rotation rates nonaxisymmetric for rapid using 3D numerical simulations of turbulent convection and considering between 1 30 times value. find a axi- solutions around 1.8 rate. This coincides with change in profile antisolar- solar-like differential faster equator slow poles. In regime, field configuration consists an oscillatory accompanied by m=1 azimuthal mode (two active longitudes), which also shows...
Collaboration et al., (2021). The Pencil Code, a modular MPI code for partial differential equations and particles: multipurpose multiuser-maintained. Journal of Open Source Software, 6(58), 2807, https://doi.org/10.21105/joss.02807
Ganymede presents a unique example of an internally magnetized moon whose intrinsic magnetic field excludes the plasma present at its orbit, thereby forming magnetospheric cavity. We describe some properties this mini‐magnetosphere, embedded in sub‐Alfvénic flow and formed within planetary magnetosphere. A vacuum superposition model (obtained by adding internal to imposed Jupiter) organizes data acquired Galileo magnetometer on four close passes useful, intuitive fashion. The last line that...
We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. find that a substantial fraction the lower part zone (CZ) is stably stratified according to Schwarzschild criterion while enthalpy flux outward directed. This occurs when heat conduction profile at bottom CZ smoothly varying, based either on Kramers-like opacity prescription as function temperature and density or static similar shape. show subadiabatic layer arises due nonlocal energy...
Several solar-like stars exhibit cyclic magnetic activity similar to the Sun as found in photospheric and chromospheric emission. We want understand physical mechanism involved rotational dependence of these cycle periods. use three-dimensional magnetohydrodynamical simulations global convective dynamos models investigate dependency dynamos. further apply test-field method determine $\alpha$ effect simulations. find dynamo with clear oscillating mean fields for moderately rapidly rotating...
Introduces an algorithm which allows under certain assumptions to estimate the current density distribution along track from single spacecraft magnetic field measurements. The are chosen that they meet at least partly conditions encountered by Freja satellite on its northernmost orbital segment, namely all currents field-aligned, ionospheric do not contribute significantly measurements, and velocity component perpendicular direction is large (>5 km/s). Problems arise in case of moving or...
We present results from four convectively-driven stellar dynamo simulations in spherical wedge geometry. All of these produce cyclic and migrating mean magnetic fields. Through detailed comparisons we show that the migration direction can be explained by an $\alpha\Omega$ wave following Parker--Yoshimura rule. conclude equatorward this previous work is due to a positive (negative) $\alpha$ effect northern (southern) hemisphere negative radial gradient $\Omega$ outside inner tangent cylinder...
(abidged) Context: Stellar convection zones are characterized by vigorous high-Reynolds number turbulence at low Prandtl numbers. Aims: We study the dynamo and differential rotation regimes varying levels of viscous, thermal, magnetic diffusion. Methods: perform three-dimensional simulations stratified fully compressible magnetohydrodynamic in rotating spherical wedges various thermal numbers (from 0.25 to 2 5, respectively). Results: find that profiles for high diffusivity show a...
Magnetic fields on small scales are ubiquitous in the universe. Though they can often be observed detail, their generation mechanisms not fully understood. One possibility is so-called small-scale dynamo (SSD). Prevailing numerical evidence, however, appears to indicate that an SSD unlikely exist at very low magnetic Prandtl numbers ($Pr_M$) such as present Sun and other cool stars. We have performed high-resolution simulations of isothermal forced turbulence employing lowest $Pr_M$ values...
During the Galileo‐Io flyby, nearly field‐aligned, left‐hand circularly polarized ion cyclotron waves were observed in a band near sulfur‐dioxide gyrofrequency. We have performed warm plasma dispersion analysis using nominal Io torus composition ratios, pickup “ring”‐type velocity‐space distributions, and thermal background of typical temperature. Analysis shows that SO 2 + wave is dominant, particularly as ring begins to broaden. The spectral peak indicates distribution highly unstable...
As the Galileo spacecraft passed through Io torus, ion cyclotron waves were observed near sulfur dioxide gyrofrequency. The torus plasma is continually replenished by ionization of neutral particles from Io. It well known that dissociates rapidly, so corotating consists predominantly and oxygen ions. However, for small fraction molecules become ionized before dissociation, appearance SO 2 + gyroresonant indicates wave growth timescale (or wave‐particle scattering time) short compared with...
We report the spontaneous formation of bipolar magnetic structures in direct numerical simulations stratified forced turbulence with an outer coronal envelope. The is transverse random waves only lower (turbulent) part domain. Our initial field either uniform entire domain or confined to turbulent layer. After about 1–2 diffusion times, a region vertical develops two coherent circular that live during one time, and then decay 0.5 times. resulting strengths inside are comparable equipartition...
We report on the results of four convective dynamo simulations with an outer coronal layer. The magnetic field is self-consistently generated by motions beneath surface. Above convection zone, we include a polytropic layer that extends to 1.6 solar radii. temperature increases in this region $\approx8$ times value at surface, corresponding $\approx1.2$ bottom spherical shell. associate corona. find solar-like differential rotation radial contours constant rate, together near-surface shear...
We explore the effects of an outer stably stratified coronal envelope on rotating turbulent convection, differential rotation, and large-scale dynamo action in spherical wedge models Sun. solve compressible magnetohydrodynamic equations a two-layer model with unstable stratification below surface, representing convection zone, above. The interface represents free surface. compare our to that have no envelope. presence is found modify Reynolds stress $\Lambda$ effect resulting weaker...
We aim to reproduce the structure of corona above a solar active region as seen in extreme ultraviolet (EUV) using three-dimensional magnetohydrodynamic (3D MHD) model. The 3D MHD data-driven model solves induction equation and mass, momentum, energy balance. To drive system, we feed observed evolution magnetic field photosphere AR 12139 into bottom boundary. This creates hot cool self-consistent way. synthesize coronal EUV emission from densities temperatures compare this actual...
Force-free extrapolations are widely used to study the magnetic field in solar corona based on surface measurements. The assume that ratio of internal energy plasma energy, plasma-beta is negligible. Despite widespread use this assumption observations, models, and theoretical considerations show beta order a few percent more than 10%, thus not small. We investigate what consequences has for reliability extrapolation results. basic concepts starting with force balance infer relations between...
It has recently been shown numerically that a small-scale dynamo (SSD) instability might be possible in solar-like low magnetic Prandtl number plasmas. was proposed the presence of SSD have significant effect on dynamics large-scale (LSD) stellar convection zones. The simultaneous study these two dynamos, and LSD, global magnetoconvection model requires high-resolution simulations large amounts computational resources. Starting from well-studied convective produces cyclic fields, we...