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result(s) for
"Sun, Evolution"
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GARSTEC—the Garching Stellar Evolution Code
We describe the Garching Stellar Evolution Code. General features, treatment of the microphysics, details of the numerical solution, handling and particularities are discussed. The standard solar model serves as the most basic benchmark to test the accurateness of the code and is presented, too.
Journal Article
CESAM: a free code for stellar evolution calculations
The
cesam
code is a consistent set of programs and routines which perform calculations of 1D quasi-hydrostatic stellar evolution including microscopic diffusion of chemical species and diffusion of angular momentum. The solution of the quasi-static equilibrium is performed by a collocation method based on piecewise polynomials approximations projected on a B-spline basis; that allows stable and robust calculations, and the exact restitution of the solution, not only at grid points, even for the discontinuous variables. Other advantages are the monitoring by only one parameter of the accuracy and its improvement by super-convergence. An automatic mesh refinement has been designed for adjusting the localisations of grid points according to the changes of unknowns. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; in the convection zones mixing and evolution of chemical are simultaneous. The solution of the diffusion equation employs the Galerkin finite elements scheme; the mixing of chemicals is then performed by a strong turbulent diffusion. A precise restoration of the atmosphere is allowed for.
Journal Article
Sunspot data collection of Specola Solare Ticinese in Locarno
Sunspot observations and counting are carried out at the Specola Solare Ticinese in Locarno since 1957 when it was built as an external observing station of the Zurich observatory. When in 1980 the data center responsibility was transferred from ETH Zurich to the Royal Observatory of Belgium in Brussels, the observations in Locarno continued and Specola Solare Ticinese got the role of pilot station. The data collected at Specola cover now the last 6 solar cycles. The aim of this presentation is to discuss and give an overview about the Specola data collection, the applied counting method and the future archiving projects. The latter includes the publication of all data and drawings in digital form in collaboration with the ETH Zurich University Archives, where a parallel digitization project is ongoing for the document of the former Swiss Federal Observatory in Zurich collected since the time of Rudolph Wolf.
Journal Article
A Magnetofrictional model for the solar corona
Regular reconstruction of global solar corona constrained by observational data is required to monitor the space weather variations. We develop a model for simulating the global coronal magnetic field using magnetofrictional approach. Here we perform simulations to study the evolution of the magnetic field associated with a bipolar active region in response to photospheric flows.
Journal Article
Multivariate analysis of intermediate periodicities of the green corona
Solar activity is observed to fluctuate with time, undergoing a wide range of periodicities from minutes up to thousands of years as evinced from proxies based on cosmogenic isotopes. In this work, we apply Multichannel Singular Spectrum Analysis (MSSA), a data-adaptive, multivariate technique that simultaneously exploits the spatial and temporal correlations of the input data to extract common modes of variability to investigate the intermediate quasi-periodicities of the green coronal emission line at 530.3 nm for the period between 1944 and 2008. A preliminary MSSA analysis confirms the presence of significant quasi-biennial oscillations in the data with amplitude varying significantly with time and latitude. On the other hand, a clear North-South asymmetry is observed both in their intensity and period distribution.
Journal Article
Evolution of solar-type activity: acoustic and magnetic energy generation and propagation in β Hydri (G2 IV)
We examine the acoustic and magnetic energy generation and propagation in β Hydri (G2 IV). The underlying motivation for this work is based on the solar, stellar, and galactic relevance of β Hyi (a star in the Southern hemisphere), which is readily understood as a prime example and proxy of the future Sun – thus allowing assessments and analyses of the secular decay of solar activity. Regarding the magnetic energy generation, we consider longitudinal flux tube waves. We also assess acoustic waves. For the acoustic wave energy flux, the difference between the results obtained for β Hyi and the Sun is significantly smaller than typically attained for main-sequence stars, which is largely due to the gravity-dependence of the acoustic energy generation. Furthermore, we study the height-dependent behavior of the magnetic energy flux for different magnetic filling factors corresponding to different flux tube spreadings. Finally, we comment on possible directions of future research.
Journal Article
A prediction of the solar cycle 25
Here we report our recent prediction of the solar cycle 25 based on a newly developed scheme, which is used to investigate the predictability of the solar cycle over one cycle. The scheme is a combination of the empirical properties of solar cycles and a surface flux transport model to get the possible axial dipole moment evolution at a few years before cycle minimum, by which to get the subsequent cycle strength based on the correlation between the axial dipole moment at cycle minimum and the subsequent cycle strength. We apply this scheme to predict the large-scale field evolution since 2018 onwards. The results show that the northern polar field will keep on increasing, while the southern polar field almost keeps flat by the end of cycle 24. This leads to the cycle 25 strength of 125 ± 32, which is about 10% stronger than cycle 24 according to the mean value.
Journal Article
State-of-the-art of kinematic modeling the solar cycle
The kinematic modeling of the solar convection zone remains the workhorse of the solar dynamo to understand the solar cycle. During the past several years, the major progress in understanding the solar cycle using kinematic models is as follows. (1). The Babcock-Leighton (BL) mechanism was confirmed to be at the essence of the solar cycle. (2). The scatter of sunspot tilt angles is identified as a major cause of solar cycle irregularities. (3). The important roles of the magnetic pumping in the dynamo process are recognized. (4). Some 3D kinematic BL type dynamo models have been developed. As a key part of the solar dynamo loop, the surface observable part of the BL mechanism makes the physics-based solar cycle prediction feasible. Including the effects of the tilt scatter on the polar field generation, the possible strength of the subsequent cycle can be predicted when a cycle starts for a few years.
Journal Article
The Evolution of Barbs of a Polar Crown Filament Observed by SDO
From 16 to 21 August 2010, a northern (∼ N60) polar crown filament was observed by
Solar Dynamics Observatory
(SDO). Employing the six-day SDO/AIA data, we identify 69 barbs, and select 58 of them, which appeared away from the western solar limb (≤ W60), as our sample. We systematically investigate the evolution of filament barbs. Three different types of apparent formation of barbs are detected, including i) the convergence of surrounding moving plasma condensations, comprised 55.2 % of our sample, ii) the flows of plasma condensations from the filament, comprised 37.9 %, and iii) the plasma injections from the neighboring brightening regions, comprised 6.9 %. We also find three different ways that barb disappear, involving: i) bi-lateral movements (44.8 %), and ii) outflowing of barb plasma (27.6 %) results in the disappearance of a barb, as well as iii) disappearance of a barb is associated with a neighboring brightening (27.6 %). The evolution of the magnetic fields,
e.g.
emergence and cancellation of magnetic flux, may cause the formation or disappearance of the barb magnetic structures. Barbs exchange plasma condensations with the surrounding atmosphere, filament, and nearby brightenings, leading to the increase or drainage of barb material. Furthermore, we find that all the barbs undergo oscillations. The average oscillation period, amplitude, and velocity are 30 min, 2.4 Mm, and 5.7 km s
−1
, respectively. Besides the oscillations, 21 (36 %) barbs manifested sideward motions having an average speed of 0.45 km s
−1
. Small-scale wave-like propagating disturbances caused by small-scale brightenings are detected, and the barb oscillations associated with these disturbances are also found. We propose that the kinematics of barbs are influenced or even caused by the evolution of the neighboring photospheric magnetic fields.
Journal Article