R. Arlt
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View article: Gravity’s role in taming the Tayler instability in red giant cores
Gravity’s role in taming the Tayler instability in red giant cores Open
The stability of toroidal magnetic fields in radiative stellar interiors remains a key open problem in astrophysics. We investigate the Tayler instability of purely toroidal fields, B ϕ , in a nonrotating stellar region with stable thermal…
View article: Data-Driven Reconstruction of a Low-Order Dynamo Model from Sunspot Data
Data-Driven Reconstruction of a Low-Order Dynamo Model from Sunspot Data Open
Understanding the long-term variability of the solar dynamo remains a key challenge in solar physics. In this work, we apply the Sparse Identification of Nonlinear Dynamical Systems (SINDy) framework to reconstruct a low-order dynamo model…
View article: Gravity's role in taming the Tayler instability in red giant cores
Gravity's role in taming the Tayler instability in red giant cores Open
The stability of toroidal magnetic fields in radiative stellar interiors is a key open problem in astrophysics. We investigate the Tayler instability of purely toroidal fields $B_ϕ$ in a nonrotating, thermally stably stratified stellar reg…
View article: Evaluating solar-like behavior in turbulent alpha and Babcock–Leighton mechanisms using non-kinematic nonlinear flux-transport solar dynamos
Evaluating solar-like behavior in turbulent alpha and Babcock–Leighton mechanisms using non-kinematic nonlinear flux-transport solar dynamos Open
In this study, we simulate 30,000 years of solar activity using turbulent-alpha (TA) and Babcock-Leighton (BL) mechanisms in a non-kinematic, nonlinear mean field flux-transport solar dynamo model. We evaluate their performances against ob…
View article: Sunspot positions from observations by Flaugergues in the Dalton Minimum
Sunspot positions from observations by Flaugergues in the Dalton Minimum Open
French astronomer Honoré Flaugergues compiled astronomical observations in a series of handwritten notebooks for 1782–1830, which are preserved at Paris Observatory. We reviewed these manuscripts and encoded the records that contain sunspo…
View article: Sunspot positions from observations by Flaugergues in the Dalton Minimum
Sunspot positions from observations by Flaugergues in the Dalton Minimum Open
French astronomer Honoré Flaugergues compiled astronomical observations in a series of hand-written notebooks for 1782$\unicode{x2013}$1830, which are preserved at Paris Observatory. We reviewed these manuscripts and encoded the records th…
View article: Recalibration of the Sunspot-Number: Status Report
Recalibration of the Sunspot-Number: Status Report Open
We report progress on the ongoing recalibration of the Wolf sunspot number ( $S_{\mathrm{N}}$ ) and group-sunspot number ( $G_{\mathrm{N}}$ ) following the release of version 2.0 of $S_{\mathrm{N}}$ in 2015. This report constitutes both…
View article: Auroral oval reconstruction for historical geomagnetic storms in the 18th and 19th century
Auroral oval reconstruction for historical geomagnetic storms in the 18th and 19th century Open
The investigation of extreme space weather events can yield important information about the solar activity. Here, we present the reconstruction of the auroral oval position and size based on Bayesian inference for nine historical geomagnet…
View article: Karl von Lindener’s sunspot observations during 1800–1827: Another long-term dataset for the Dalton Minimum
Karl von Lindener’s sunspot observations during 1800–1827: Another long-term dataset for the Dalton Minimum Open
On a centennial timescale, solar activity oscillates quasi-periodically and also tends to occasionally get into a low-activity period. The Dalton Minimum (circa 1790s–1820s) was one of such low-activity periods that had been captured in te…
View article: Tau Herculids 2022: Rate, number density, population index and geometrical effects from visual data
Tau Herculids 2022: Rate, number density, population index and geometrical effects from visual data Open
We analysed visual observation data of the Tau Herculids collected between 2022 May 28 and June 1. The population index for the entire sample is 2.4. For the pre-peak period we find r=2.57+-0.23, the peak period yields r=2.38+-0.06. The ZH…
View article: Reconstruction of the Solar Activity from the Catalogs of the Zurich\n Observatory
Reconstruction of the Solar Activity from the Catalogs of the Zurich\n Observatory Open
Catalogs of the Zurich Observatory contain positional information on\nsunspots, prominences and faculae in late 19th and early 20th centuries. This\ndatabase is given in handwritten tabular form and was not systematically\nanalysed earlier…
View article: Bayesian approach for auroral oval reconstruction from ground-based observations
Bayesian approach for auroral oval reconstruction from ground-based observations Open
Naked eye observations of aurorae might be used to obtain information on the large-scale magnetic field of the Earth at historic times. Their abundance may also help bridge gaps in observational time-series of proxies for solar activity su…
View article: SOLAR ACTIVITY ACCORDING TO THE ARCHIVES OF GEORG CHRISTOPH EIMMART
SOLAR ACTIVITY ACCORDING TO THE ARCHIVES OF GEORG CHRISTOPH EIMMART Open
The period of the Maunder minimum is well known due to the observations of astronomers at the Paris Observatory: Picard, father and son La Hire, Cassini and their students.Thanks to their drawings of the solar disk, we know the pattern of …
View article: IAU volume 15 issue 354 Cover and Front matter
IAU volume 15 issue 354 Cover and Front matter Open
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View article: Comparison of telescopic and naked‐eye sunspots for the very small spots on February 15, 1900 and January 30, 1911
Comparison of telescopic and naked‐eye sunspots for the very small spots on February 15, 1900 and January 30, 1911 Open
In a recent discussion of the Maunder Minimum, two sunspot observations by Chinese court astronomers on February 15, 1900 and January 30, 1911 (±1 day) – presumably made with the unaided eye – were considered false detections because the s…
View article: Historical sunspot records
Historical sunspot records Open
Sunspot observations are available in fairly good numbers since 1610, after the invention of the telescope. This review is concerned with those sunspot observations of which longer records and drawings in particular are available. Those re…
View article: SOLAR ACTIVITY ACCORDING TO OBSERVATION DATA BY CIGOLI, GALILEI, COLONNA, COLOGNA, AND SCHEINER IN 1612–1614
SOLAR ACTIVITY ACCORDING TO OBSERVATION DATA BY CIGOLI, GALILEI, COLONNA, COLOGNA, AND SCHEINER IN 1612–1614 Open
The paper presents the results of reconstruction of the parameters of solar activity from the drawings of observers at the beginning of the seventeenth century.We analyse the drawings of the solar disk obtained by different methods and acc…
View article: Sunspot Characteristics at the Onset of the Maunder Minimum Based on the Observations of Hevelius
Sunspot Characteristics at the Onset of the Maunder Minimum Based on the Observations of Hevelius Open
An analysis of the sunspot observations made by Hevelius during 1642–1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum (MM). We have studied different phenomena meticulously recor…
View article: Various scenarios for the equatorward migration of sunspots
Various scenarios for the equatorward migration of sunspots Open
The profile of the differential rotation together with the sign of the alpha-effect determine the dynamo wave direction. In early models of the solar dynamo the dynamo wave often leads to a poleward migration of the activity belts. Flux tr…
View article: Constraining non-linear dynamo models using quasi-biennial oscillations from sunspot area data
Constraining non-linear dynamo models using quasi-biennial oscillations from sunspot area data Open
Context . Solar magnetic activity exhibits variations with periods between 1.5 and 4 years, the so-called quasi-biennial oscillations (QBOs), in addition to the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the mechanism…
View article: Delayed Babcock-Leighton dynamos in the diffusion-dominated regime
Delayed Babcock-Leighton dynamos in the diffusion-dominated regime Open
Context . Solar dynamo models of Babcock-Leighton type typically assume the rise of magnetic flux tubes to be instantaneous. The periods of solutions with high magnetic diffusivity are too short, and their active belts do not migrate corre…
View article: Reconstructed sunspot positions in the Maunder minimum based on the correspondence of Gottfried Kirch
Reconstructed sunspot positions in the Maunder minimum based on the correspondence of Gottfried Kirch Open
We present reconstructed sunspot positions based on observations reported in letters between Gottfried Kirch and other contemporary astronomers from AD 1680 to 1709, that is in the last decades of the Maunder minimum. The letters to and fr…
View article: 3D simulations of rising magnetic flux tubes in a compressible rotating interior: The effect of magnetic tension
3D simulations of rising magnetic flux tubes in a compressible rotating interior: The effect of magnetic tension Open
\n Context. Long-term variability in solar cycles represents a challenging constraint for theoretical models. Mean-field Babcock-Leighton dynamos that consider non-instantaneous rising flux tubes have been shown to exhibit long-term variab…
View article: Extended Subadiabatic Layer in Simulations of Overshooting Convection
Extended Subadiabatic Layer in Simulations of Overshooting Convection Open
We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. We find that a substantial fraction of the lower part of the convection zone (CZ) is stably stratified according to the Schwarzschild crit…
View article: Magnetic field dynamos and magnetically triggered flow instabilities
Magnetic field dynamos and magnetically triggered flow instabilities Open
The project A2 of the LIMTECH Alliance aimed at a better understanding of those magnetohydrodynamic instabilities that are relevant for the generation and the action of cosmic magnetic fields. These comprise the hydromagnetic dynamo effect…
View article: Wings of the butterfly: Sunspot groups for 1826–2015
Wings of the butterfly: Sunspot groups for 1826–2015 Open
\n The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we pre…
View article: Sunspot positions, areas, and group tilt angles for 1611−1631 from observations by Christoph Scheiner
Sunspot positions, areas, and group tilt angles for 1611−1631 from observations by Christoph Scheiner Open
Digital images of the observations printed in the books "Rosa Ursina sive\nsolis" and "Prodromus pro sole mobili" by Christoph Scheiner as well as the\ndrawings from Scheiner's letters to Marcus Welser are analysed in order to\nobtain info…
View article: Properties of sunspot cycles and hemispheric wings since the 19th century
Properties of sunspot cycles and hemispheric wings since the 19th century Open
\n Aims. The latitudinal evolution of sunspot emergence over the course of\n the solar cycle, the so-called butterfly diagram, is a fundamental property of the solar\n dynamo. Here we present a study of the butterfly diagram of sunspot gro…