Publications (51)
Rapid Blue- and Red-shifted Excursions in H line profiles synthesized from realistic 3D MHD simulations
S. Danilovic, J. P. Bjørgen, J. Leenaarts +1
Rapid blue- and red-shifted events (RBEs/RREs) may have an important role in mass-loading and heating the solar corona, but their nature and origin are still debatable. We aim to m…
The dynamical disconnection of sunspots from their magnetic roots
M. Schuessler, M. Rempel
After a dynamically active emergence phase, magnetic flux at the solar surface soon ceases to show strong signs of the subsurface dynamics of its parent magnetic structure. This in…
Numerical simulations of active region scale flux emergence: From spot formation to decay
M. Rempel, M. C. M Cheung
We present numerical simulations of active region scale flux emergence covering a time span of up to 6 days. Flux emergence is driven by a bottom boundary condition that advects a…
Acoustic-gravity wave propagation characteristics in 3D radiation hydrodynamic simulations of the solar atmosphere
B. Fleck, M. Carlsson, E. Khomenko +3
There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the…
Simulation of the Formation of a Solar Active Region
M. C. M. Cheung, M. Rempel, A. M. Title +1
We present a radiative magnetohydrodynamics simulation of the formation of an Active Region on the solar surface. The simulation models the rise of a buoyant magnetic flux bundle f…
A study of the capabilities for inferring atmospheric information from high-spatial-resolution simulations
C. Quintero Noda, E. Khomenko, M. Collados +8
In this work, we study the accuracy that can be achieved when inferring the atmospheric information from realistic numerical magneto-hydrodynamic simulations that reproduce the spa…
Activity Cycles of Southern Asteroseismic Targets
T. S. Metcalfe, P. G. Judge, S. Basu +4
The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle pe…
High-resolution calculations of the solar global convection with the reduced speed of sound technique: I. The structure of the convection and the magnetic field without the rotation
H. Hotta, M. Rempel, T. Yokoyama
We carry out non-rotating high-resolution calculations of the solar global convection, which resolve convective scales of less than 10 Mm. To cope with the low Mach number conditio…
Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations
A. Kilcik, V. B. Yurchyshyn, M. Rempel +5
We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high resolution data r…
Modeling the Subsurface Structure of Sunspots
H. Moradi, C. Baldner, A. C. Birch +19
While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspo…
Comparison of inversion codes for polarized line formation in MHD simulations. I. Milne-Eddington codes
J. M. Borrero, B. W. Lites, A. Lagg +2
Milne-Eddington (M-E) inversion codes for the radiative transfer equation are the most widely used tools to infer the magnetic field from observations of the polarization signals i…
Validating Time-Distance Helioseismology With Realistic Quiet Sun Simulations
K. DeGrave, J. Jackiewicz, M. Rempel
Linear time-distance helioseismic inversions are carried out for vector flow velocities using travel times measured from two realistic m…
A solar coronal loop in a box: Energy generation and heating
C. Breu, H. Peter, R. Cameron +4
Coronal loops are the basic building block of the upper solar atmosphere. Comprehending how these are energized, structured, and evolve is key to understanding stellar coronae. Her…
High-resolution calculation of the solar global convection with the reduced speed of sound technique: II. Near surface shear layer with the rotation
H. Hotta, M. Rempel, T. Yokoyama
We present a high-resolution, highly stratified numerical simulation of rotating thermal convection in a spherical shell. Our aim is to study in detail the processes that can maint…
The uncombed penumbra
J. M. Borrero, M. Rempel, S. K. Solanki
The uncombed penumbral model explains the structure of the sunspot penumbra in terms of thick magnetic fibrils embedded in a magnetic surrounding atmosphere. This model has been su…
Penumbral structure and outflows in simulated sunspots
M. Rempel, M. Schüssler, R. H. Cameron +1
Sunspots are concentrations of magnetic field on the visible solar surface that strongly affect the convective energy transport in their interior and surroundings. The filamentary…
Structure and dynamics of the internetwork solar chromosphere: results of a small-scale dynamo simulation
D. Przybylski, R. Cameron, S. K. Solanki +3
The heating and structure of the solar chromosphere depends on the underlying magnetic field, among other parameters. The lowest magnetic flux of the solar atmosphere is found in t…
The Coronal Veil
A. Malanushenko, M. C. M. Cheung, C. E. DeForest +2
Coronal loops, seen in solar coronal images, are believed to represent emission from magnetic flux tubes with compact cross-sections. We examine the 3D structure of plasma above an…
Evershed and counter-Evershed flows in sunspot MHD simulations
A. L. Siu-Tapia, M. Rempel, A. Lagg +1
There have been a few reports in the literature of counter-Evershed flows observed in well developed sunspot penumbrae, i.e. flows directed towards the umbra along penumbral filame…
Observed and Simulated Power Spectra of Kinetic and Magnetic Energy retrieved with 2D inversions
S. Danilovic, M. Rempel, M. van Noort +1
We try to retrieve the power spectra with certainty to the highest spatial frequencies allowed by current instrumentation. For this, we use 2D inversion code that were able to reco…
Constraints on Acoustic Wave Energy Fluxes and Radiative Losses in the Solar Chromosphere from Non-LTE Inversions
J. M. da Silva Santos, M. Molnar, I. MiliÄ +3
Accurately assessing the balance between acoustic wave energy fluxes and radiative losses is critical for understanding how the solar chromosphere is thermally regulated. We invest…
Efficient numerical treatment of ambipolar and Hall drift as hyperbolic system
M. Rempel, D. Przybylski
Partially ionized plasmas, such as the solar chromosphere, require a generalized Ohm's law including the effects of ambipolar and Hall drift. While both describe transport processe…
Heating of the solar chromosphere through current dissipation
J. M. da Silva Santos, S. Danilovic, J. Leenaarts +5
The solar chromosphere is heated to temperatures higher than predicted by radiative equilibrium. This excess heating is greater in active regions where the magnetic field is strong…
Major Scientific Challenges and Opportunities in Understanding Magnetic Reconnection and Related Explosive Phenomena throughout the Universe
H. Ji, A. Alt, S. Antiochos +97
This white paper summarizes major scientific challenges and opportunities in understanding magnetic reconnection and related explosive phenomena as a fundamental plasma process.
The Role of Subsurface Flows in Solar Surface Convection: Modeling the Spectrum of Supergranular and Larger Scale Flows
J. W. Lord, R. H. Cameron, M. P. Rast +2
We model the solar horizontal velocity power spectrum at scales larger than granulation using a two-component approximation to the mass continuity equation. The model takes four ti…
Characterization of magneto-convection in sunspots -- The Gough & Tayler stability criterion in MURaM sunspot simulations
M. Schmassmann, M. Rempel, N. Bello González +2
We analyse a sunspot simulation in an effort to understand the origin of the convective instabilities giving rise to the penumbral and umbral distinct regimes. We applied the crite…
Combining magneto-hydrostatic constraints with Stokes profiles inversions
J. M. Borrero, A. Pastor Yabar, M. Rempel +1
Inversion codes for the polarized radiative transfer equation can be used to infer the temperature , line-of-sight velocity , and magnetic field as a f…
Magnetic field intensification by three-dimensional explosion process
H. Hotta, M. Rempel, T. Yokoyama
We investigate an intensification mechanism for the magnetic field near the base of the solar convection zone that does not rely on differential rotation. Such mechanism in additio…
Observation and Modeling of the Solar-Cycle Variation of the Meridional Flow
L. Gizon, M. Rempel
We present independent observations of the solar-cycle variation of flows near the solar surface and at a depth of about 60 Mm, in the latitude range . We show that th…
Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo
M. Rempel
We present a series of radiative MHD simulations addressing the origin and distribution of mixed polarity magnetic field in the solar photosphere. To this end we consider numerical…
Towards data-driven modeling and real-time prediction of solar flares and coronal mass ejections
M. Rempel, Y. Fan, M. Dikpati +7
Modeling of transient events in the solar atmosphere requires the confluence of 3 critical elements: (1) model sophistication, (2) data availability, and (3) data assimilation. Thi…
Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota Horologii
T. S. Metcalfe, S. Basu, T. J. Henry +5
The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle pe…
Superstrong photospheric magnetic fields in sunspot penumbrae
A. Siu-Tapia, A. Lagg, M. van Noort +2
Recently, there have been some reports of unusually strong photospheric magnetic fields (which can reach values of over 7 kG) inferred from Hinode SOT/SP sunspot observations withi…
Chromospheric Extension of the MURaM Code
D. Przybylski, R. Cameron, S. K. Solanki +5
Detailed numerical models of chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated…
Time-Distance Helioseismology of Two Realistic Sunspot Simulations
K. DeGrave, J. Jackiewicz, M. Rempel
Linear time-distance helioseismic inversions are carried out using several filtering schemes to determine vector flow velocities within two $\sim100^2\,{\rm Mm^2}\times 20\,{\rm Mm…
Radiative MHD simulation of sunspot structure
M. Rempel, M. Schuessler, M. Knoelker
Results of a 3D MHD simulation of a sunspot with a photospheric size of about 20 Mm are presented. The simulation has been carried out with the MURaM code, which includes a realist…
Numerical Calculation of Convection with Reduced Speed of Sound Technique
H. Hotta, M. Rempel, T. Yokoyama +2
Context. The anelastic approximation is often adopted in numerical calculation with low Mach number, such as stellar internal convection. This approximation requires frequent globa…
Solar Atmosphere Radiative Transfer Model Comparison based on 3D MHD simulations
M. Haberreiter, S. Criscuoli, M. Rempel +1
The reconstruction of the solar spectral irradiance (SSI) on various time scales is essential for the understanding of the Earth's climate response to the SSI variability. The driv…
The role of the Lorentz force in sunspot equilibrium
J. M. Borrero, A. Pastor Yabar, M. Schmassmann +3
Sunspots survive on the solar surface for time-scales ranging from days to months. This requires them to be in an equilibrium involving magnetic fields and hydrodynamic forces. Unf…
Efficient small-scale dynamo in solar convection zone
H. Hotta, M. Rempel, T. Yokoyama
We investigate small-scale dynamo action in the solar convection zone through a series of high resolution MHD simulations in a local Cartesian domain with 1 (solar radius)…
Small-scale loops heated to transition region temperatures and their chromospheric signatures in the simulated solar atmosphere
M. Skan, S. Danilovic, J. Leenaarts +2
Recent observations revealed loop-like structures at very small scales visible in observables that sample transition region (TR) and coronal temperatures. Their formation remains u…
Solar convection zone dynamics
M. Rempel
A comprehensive understanding of the solar magnetic cycle requires detailed modeling of the solar interior including the maintenance and variation of large scale flows (differentia…
The Dimmest State of the Sun
K. L. Yeo, S. K. Solanki, N. A. Krivova +5
How the solar electromagnetic energy entering the Earth's atmosphere varied since pre-industrial times is an important consideration in the climate change debate. Detrimental to th…
Nature of grand minima and maxima from fully non-linear Flux-Transport Dynamos
F. Inceoglu, R. Arlt, M. Rempel
We aim to investigate the nature and occurrence characteristics of grand solar minimum and maximum periods, which are observed in the solar proxy records such as 10Be and 14C, usin…
Numerical simulations of sunspot decay: On the penumbra -- Evershed flow -- moat flow connection
M. Rempel
We present a series of high-resolution sunspot simulations that cover a time span of up to 100 hours. The simulation domain extends about 18 Mm in depth beneath the photosphere and…
Operating the Fabry-Pérot systems of the European Solar Telescope in multi-aperture mode
G. B. Scharmer, M. G. Löfdahl, J. de la Cruz RodrÃguez +5
We discuss how to optimise the science output of the European Solar Telescope (EST), when used without the wide-field compensation for high-altitude seeing that the EST multi conju…
Internetwork magnetic field as revealed by 2D inversions
S. Danilovic, M. van Noort, M. Rempel
Properties of magnetic field in the internetwork regions are still fairly unknown due to rather weak spectropolarimetric signals. We address the matter by using the 2D inversion co…
The striated solar photosphere observed at 0."03, resolution
D. Kuridze, F. Wöger, H. Uitenbroek +5
Striated granular edges observed in the solar photosphere represent one of the smallest-scale phenomena on the Sun. They arise from the interaction of strongly coupled hydrodynamic…
Major Scientific Challenges and Opportunities in Understanding Magnetic Reconnection and Related Explosive Phenomena in Solar and Heliospheric Plasmas
H. Ji, J. Karpen, A. Alt +105
Magnetic reconnection underlies many explosive phenomena in the heliosphere and in laboratory plasmas. The new research capabilities in theory/simulations, observations, and labora…
On the contribution of quiet Sun magnetism to solar irradiance variations: Constraints on quiet Sun variability and grand minimum scenarios
M. Rempel
While the quiet Sun magnetic field shows only little variation with the solar cycle, long-term variations cannot be completely ruled out from first principles. We investigate the p…
Waves as the source of apparent twisting motions in sunspot penumbrae
L. Bharti, R. H. Cameron, M. Rempel +2
The motion of dark striations across bright filaments in a sunspot penumbra has become an important new diagnostic of convective gas flows in penumbral filaments. The nature of the…