scholarly journals Global Coronal Equilibria with Solar Wind Outflow

2021 ◽  
Vol 923 (1) ◽  
pp. 57
Author(s):  
Oliver E. K. Rice ◽  
Anthony R. Yeates
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Potential Field ◽  
Field Model ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Radial Magnetic Field ◽  
Similar Time ◽  
Magnetic Field Model ◽  
Magnetohydrodynamic Simulations

Abstract Given a known radial magnetic field distribution on the Sun’s photospheric surface, there exist well-established methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind models, and to initialize magneto-frictional or full magnetohydrodynamic simulations of the coronal and heliospheric magnetic fields. We describe an improved magnetic field model that calculates a magneto-frictional equilibrium with an imposed solar wind profile (which can be Parker’s solar wind solution, or any reasonable equivalent). These “outflow fields” appear to approximate the real coronal magnetic field more closely than a potential field, take a similar time to compute, and avoid the need to impose an artificial source surface. Thus they provide a practical alternative to the potential field model for initializing time-evolving simulations or modeling the heliospheric magnetic field. We give an open-source Python implementation in spherical coordinates and apply the model to data from solar cycle 24. The outflow tends to increase the open magnetic flux compared to the potential field model, reducing the well-known discrepancy with in situ observations.

Coronal magnetic-field model with non-spherical source surface

Solar Physics ◽  
1978 ◽  
Vol 60 (1) ◽  
pp. 83-104 ◽  
Author(s):  
Michael Schulz ◽  
Edward N. Frazier ◽  
Donald J. Boucher
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Spherical Source ◽  
Magnetic Field Model

scholarly journals Investigation of the Middle Corona with SWAP and a Data-Driven Non-Potential Coronal Magnetic Field Model

Solar Physics ◽  
2020 ◽  
Vol 295 (7) ◽  
Author(s):  
Karen A. Meyer ◽  
Duncan H. Mackay ◽  
Dana-Camelia Talpeanu ◽  
Lisa A. Upton ◽  
Matthew J. West
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Coronal Magnetic Field ◽  
Data Driven ◽  
Magnetic Field Model

scholarly journals An integrated data-driven solar wind - CME numerical framework for space weather forecasting

2020 ◽  
Author(s):  
Nishant M. Narechania ◽  
Ljubomir Nikolic ◽  
Lucie Freret ◽  
Hans De Sterck ◽  
Clinton P. T. Groth
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Space Weather ◽  
Weather Forecasting ◽  
Coronal Magnetic Field ◽  
Data Driven ◽  
Source Surface ◽  
Field Source ◽  
Space Weather Forecasting ◽  
Semi Empirical

The development of numerical models and tools which have operational space weather potential is an increasingly important area of research. This study presents recent Canadian efforts toward the development of a numerical framework for Sun-to-Earth simulations of solar wind disturbances. This modular three-dimensional (3D) simulation framework is based on a semi-empirical data-driven approach to describe the solar corona and an MHD-based description of the heliosphere. In the present configuration, the semi-empirical component uses the Potential Field Source Surface (PFSS) and Schatten Current Sheet (SCS) models to derive the coronal magnetic field based on observed magnetogram data. Using empirical relations, solar wind properties are associated with this coronal magnetic field. Together with a Coronal Mass Ejection (CME) model, this provides inner boundary conditions for a global MHD model which is used to describe interplanetary propagation of the solar wind and CMEs. The proposed MHD numerical approach makes use of advanced numerical techniques. The 3D MHD code employs a finite-volume discretization procedure with limited piecewise linear reconstruction to solve the governing partial-differential equations. The equations are solved on a body-fitted hexahedral multi-block cubed-sphere mesh and an efficient iterative Newton method is used for time-invariant simulations and an explicit time-marching scheme is applied for unsteady cases. Additionally, an efficient anisotropic block-based refinement technique provides significant reductions in the size of the computational mesh by locally refining the grid in selected directions as dictated by the flow physics. The capabilities of the framework for accurately capturing solar wind structures and forecasting solar wind properties at Earth are demonstrated. Furthermore, a comparison with previously reported results and future space weather forecasting challenges are discussed.

Quality assessment for objective inter-comparison of coronal models

2021 ◽  
Author(s):  
Andreas Wagner ◽  
Manuela Temmer ◽  
Eleanna Asvestari
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Weather Forecasting ◽  
Critical Factor ◽  
Coronal Magnetic Field ◽  
Space Weather Forecasting ◽  
Performance Quality ◽  
Magnetic Field Model ◽  
Benchmarking System

<p>With the increasing amount of space weather forecasting simulation codes being developed, assessing their performance becomes crucial. Especially the errors resulting from coronal magnetic field models are a critical factor, because these will get propagated further by various solar wind models. We present a first result for a benchmarking system that allows a rather easy-to-implement  assessment of the performance quality of any coronal magnetic field model. This will allow for a standardized comparison between different models. The benchmarking system is based on stepwise visual and semi-automatized comparisons between model output and EUV on-disk and coronograph white-light data. We are using various viewpoints and instrumental data provided by STEREO, SOHO and SDO. <br>In our work we exemplarily apply this scheme to the coronal model currently implemented in EUHFORIA, an adaption of the Wang-Sheeley-Arge (WSA) model, with varying input parameters. Furthermore, with this system we also show its possible usage for the derivation of an ideal parameter set. </p>

scholarly journals Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model

2019 ◽  
Vol 631 ◽  
pp. A17 ◽  
Author(s):  
Jennimari Koskela ◽  
Ilpo Virtanen ◽  
Kalevi Mursula
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Potential Field ◽  
Neutral Line ◽  
Coronal Magnetic Field ◽  
Solar Observatory ◽  
Latitudinal Variation ◽  
Source Surface ◽  
Current Parameter ◽  
Cusp Surface

Aims. We study the properties of the coronal magnetic field according to the current sheet source surface (CSSS) model in 1976–2017 for all physically reasonable values of the three model parameters (cusp surface radius Rcs, source surface radius Rss, and current parameter a), and compare the CSSS field with the potential field source surface (PFSS) model field. Methods. We used the synoptic maps of the photospheric magnetic field from the Wilcox Solar Observatory (WSO), National Solar Observatory/Kitt Peak (NSO/KP), and the NSO Synoptic Optical Long-term Investigations of the Sun Vector Spectromagnetograph (SOLIS/VSM) in order to calculate the coronal magnetic field according to the CSSS and PFSS models. We calculated the coronal field strength, its latitudinal variation and neutral line location, as well as its polarity match with the heliospheric magnetic field. Results. The CSSS model can correct the erroneous latitudinal variation of the PFSS model if the source surface is sufficiently far out with respect to the cusp surface (Rss ≥ 3 ⋅ Rcs). The topology of the neutral line only slightly depends on source surface radius or current parameter, but excludes very low values of the cusp surface (Rcs ≤ 1.5). A comparison of the polarities gives an optimum cusp surface radius that varies in time between 2 and 5; a stronger current yields a larger optimum Rcs. Interestingly, the optimum polarity match percentages and optimum radii vary very similarly in the two models over the four solar cycles we studied. Conclusions. The CSSS model can produce a stronger total coronal flux than the PFSS model and correct its latitudinal variation. However, the topology of the CSSS model is rather independent of horizontal currents and remains very similar to that of the PFSS model. Therefore, the CSSS model cannot improve the match of field polarities between corona and heliosphere.

PFSS-Based Solar Wind Forecast and the Radius of the Source-Surface

2017 ◽  
Vol 13 (S335) ◽  
pp. 307-309
Author(s):  
Ljubomir Nikolić
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Spherical Surface ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Field Source ◽  
Forecast Models ◽  
Field Lines

AbstractThe potential-field source-surface (PFSS) model of the solar corona is a widely used tool in the space weather research and operations. In particular, the PFSS model is used in solar wind forecast models which empirically associate solar wind properties with the numerically derived coronal magnetic field. In the PFSS model, the spherical surface where magnetic field lines are forced to open is typically placed at 2.5 solar radii. However, the results presented here suggest that setting this surface (the source-surface) to lower heights can provide a better agreement between observed and modelled coronal holes during the current solar cycle. Furthermore, the lower heights of the source-surface provide a better match between observed and forecasted solar wind speed.

scholarly journals An optimization principle for computing stationary MHD equilibria with solar wind flow

2020 ◽  
Author(s):  
Thomas Wiegelmann ◽  
Thomas Neukirch ◽  
Dieter Nickeler ◽  
Iulia Chifu
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Magnetic Field ◽  
Field Vector ◽  
Source Surface ◽  
Solar Chromosphere ◽  
Wind Flow ◽  
Solar Wind Flow ◽  
Nonlinear Force ◽  
The Magnetic Field

<p>Knowledge about the magnetic field and plasma environment is important<br>for almost all physical processes in the solar atmosphere. Precise<br>measurements of the magnetic field vector are done routinely only in<br>the photosphere, e.g. by SDO/HMI. These measurements are used as<br>boundary condition for modelling the solar chromosphere and corona,<br>whereas some model assumptions have to be made. In the low-plasma-beta<br>corona the Lorentz-force vanishes and the magnetic field<br>is reconstructed with a nonlinear force-free model. In the mixed-beta<br>chromosphere plasma forces have to be taken into account with the<br>help of a magnetostatic model. And finally for modelling the global<br>corona far beyond the source surface the solar wind flow has to<br>be incorporated within a stationary MHD model.<br>To do so, we generalize a nonlinear force-free and magneto-static optimization<br>code by the inclusion of a field aligned compressible plasma flow.<br>Applications are the implementation of the solar wind on<br>global scale. This allows to reconstruct the coronal magnetic field further<br>outwards than with potential field, nonlinear force-free and magneto-static models.<br>This way the model might help in future to provide the magnetic connectivity<br>for joint observations of remote sensing and in-situ instruments on Solar<br>Orbiter and Parker Solar Probe.</p>

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