scholarly journals Coronal magnetic fields from the inversion of linear polarization measurements

2009 ◽  
Vol 5 (S264) ◽  
pp. 96-98
Author(s):  
Yu Liu ◽  
Haosheng Lin ◽  
Jeff Kuhn
Keyword(s):  
Linear Polarization ◽  
Spatial Relation ◽  
Coronal Magnetic Field ◽  
Surface Model ◽  
Source Surface ◽  
Coronal Emission ◽  
Field Source ◽  
Close Relationship ◽  
The Difference ◽  
Ir Emission

AbstractReal 3-D coronal magnetic field reconstruction is expected to be made based on the technologies of IR spectrometry and tomography, in which the data from other wavelengths can be used as critical reference. Our recent studies focused on this issue are briefly reviewed in this paper. Liu & Lin (2008) first evaluated the validity of potential field source surface model applied to one of five limb regions in the corona by comparing the theoretical polarization maps with SOLARC observations in the IR Fe XIII 10747 Å forbidden coronal emission line (CEL). The five limb coronal regions were then studied together in order to study the spatial relation between the bright EUV features on the solar disk and the inferred IR emission sources, which were obtained from the inversion of the SOLARC linear polarization (LP) measurements (Liu 2009). The inversion for each fiber data in the field of view was made by finding the best location where the difference between the synthesized and the observed polarizations reaches the minimum in the integration path along the line of sight. We found a close relationship between the inferred IR emission source locations and the EUV strong emission positions.

scholarly journals An elliptic expansion of the potential field source surface model

2020 ◽  
Vol 638 ◽  
pp. A109
Author(s):  
M. Kruse ◽  
V. Heidrich-Meisner ◽  
R. F. Wimmer-Schweingruber ◽  
M. Hauptmann
Keyword(s):  
Magnetic Field ◽  
Potential Field ◽  
Three Dimensional ◽  
Coronal Magnetic Field ◽  
Magnetic Configuration ◽  
Surface Model ◽  
Source Surface ◽  
Field Source ◽  
Numerical Solver ◽  
Elliptical Models

Context. The potential field source surface model is frequently used as a basis for further scientific investigations where a comprehensive coronal magnetic field is of importance. Its parameters, especially the position and shape of the source surface, are crucial for the interpretation of the state of the interplanetary medium. Improvements have been suggested that introduce one or more additional free parameters to the model, for example, the current sheet source surface model. Aims. Relaxing the spherical constraint of the source surface and allowing it to be elliptical gives modelers the option of deforming it to more accurately match the physical environment of the specific period or location to be analyzed. Methods. A numerical solver is presented that solves Laplace’s equation on a three-dimensional grid using finite differences. The solver is capable of working on structured spherical grids that can be deformed to create elliptical source surfaces. Results. The configurations of the coronal magnetic field are presented using this new solver. Three-dimensional renderings are complemented by Carrington-like synoptic maps of the magnetic configuration at different heights in the solar corona. Differences in the magnetic configuration computed by the spherical and elliptical models are illustrated.

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.

scholarly journals Low Brightness Temperature in Microwaves at Periphery of Some Solar Active Regions

2017 ◽  
Vol 54 (3) ◽  
pp. 58-67
Author(s):  
B. I. Ryabov ◽  
D. A. Bezrukov ◽  
J. Kallunki
Keyword(s):  
Brightness Temperature ◽  
Open Field ◽  
Active Regions ◽  
Source Surface ◽  
The Sun ◽  
Coronal Emission ◽  
Field Source ◽  
Wavelet Space ◽  
Solar Active Regions ◽  
Field Lines

AbstractThe microwave regions with low brightness temperature are found to overlap the regions of the depressed coronal emission and open field lines at the periphery of two solar active regions (ARs). The imaging microwave observations of the Sun with the Nobeyama Radio heliograph at 1.76 cm, the MRO-14 radio telescope of Metsähovi Radio Observatory at 0.8 cm, and the RT-32 of Ventspils International Radio Astronomy Centre in the range 3.2-4.7 cm are used. To reduce the noise in the intensity distribution of the RT-32 maps of the Sun, one wavelet plane of “à trous” wavelet space decomposition is subtracted from each map. To locate the open-field regions, the full-Sun coronal magnetic fields with the potential field source surface (PFSS) model for RSS= 1.8 Rʘare simulated. We conclude that the revealed LTRs present narrow coronal hole-like regions near two ARs and imply an extra investigation on the plasma outflow.

Three-dimensional reconstruction of an expanding shock associated with a Solar particle event

2021 ◽  
Author(s):  
Federica Frassati ◽  
Monica Laurenza ◽  
Alessandro Bemporad ◽  
Matthew J. West ◽  
Salvatore Mancuso ◽  
...  
Keyword(s):  
Magnetic Field ◽  
3D Reconstruction ◽  
Ultra Violet ◽  
Coronal Magnetic Field ◽  
Release Time ◽  
Shock Acceleration ◽  
Source Surface ◽  
Type Ii ◽  
Field Source ◽  
The Magnetic Field

<p><span>On 2013 June 21st an eruption occurred in the active region NOAA 1177 (14S73E), </span><span>giving rise to</span> <span>a M2.9 class flare starting at 02:30 UT, a fast partial halo coronal mass ejection (CME), and a type II radio burst. The concomitant emission of solar energetic particles (SEPs) produced a significant increase in the proton fluxes measured by LET and HET aboard STEREO-B. By using stereoscopic observations in extreme ultra violet (EUV) and white light (WL) spectral intervals, we performed a 3D reconstruction of the expanding front by processing SDO/AIA, STEREO/EUVI, COR1 and COR2, and SOHO/LASCO data assuming a spheroidal model. By using the 3D reconstruction, we estimated the temporal evolution of θ</span><span><sub>Bn,</sub></span><span> </span><span>i.e.,</span> <span>the angle between the normal to the expanding front and the coronal magnetic field computed by the Potential-Field Source-Surface (PFSS) approximation, within 2.5 R</span><span><sub>ʘ</sub></span><span>. The front </span><span>of the CME</span><span>was found to be quasi-parallel to the magnetic field almost everywhere</span><span><sub>.</sub></span><span> Above 2.5 R</span><span><sub>ʘ</sub></span><span>, where the front was identified as a shock, we projected the 3D expanding surface </span><span>reconstructed for </span><span>different times on the ecliptic plane and</span><span> </span><span>we calculated the θ</span><span><sub>Bn </sub></span><span>between the normal to the front and Parker spiral arms. In this case the shock was almost perpendicular to the magnetic field (quasi-parallel shock). During the expansion the region located between the nose and the eastern flank of the shock was magnetically connected with ST-B in agreement with the significant SEP flux measured on-board this spacecraft.</span> <span>W</span><span>hile</span> <span>the shock was only marginally connected with ST-A and GOES-15. </span><span>T</span><span>he SEP release time was estimated to be 10 minutes after the Type II onset, when the shock front was already above 2.5 R</span><span><sub>ʘ</sub></span><span> with a quasi-parallel configuration. Our results are discussed in the framework of the shock acceleration scenario, even if quasi-parallel shocks are expected to have a reduced acceleration efficiency.</span></p>

scholarly journals The spatial relation between EUV cavities and linear polarization signatures

2013 ◽  
Vol 8 (S300) ◽  
pp. 395-396 ◽  
Author(s):  
Urszula Bak-Stȩślicka ◽  
Sarah E. Gibson ◽  
Yuhong Fan ◽  
Christian Bethge ◽  
Blake Forland ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Cross Section ◽  
Linear Polarization ◽  
Flux Rope ◽  
Spatial Relation ◽  
Coronal Magnetic Field ◽  
Systematic Analysis ◽  
Elliptical Cross ◽  
Magnetic Flux Rope

AbstractSolar coronal cavities are regions of rarefied density and elliptical cross-section. The Coronal Multi-channel Polarimeter (CoMP) obtains daily full-Sun coronal observations in linear polarization, allowing a systematic analysis of the coronal magnetic field in polar-crown prominence cavities. These cavities commonly possess a characteristic “lagomorphic” signature in linear polarization that may be explained by a magnetic flux-rope model. We analyze the spatial relation between the EUV cavity and the CoMP linear polarization signature.

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 Non-spherical source-surface model of the heliosphere: a scalar formulation

1997 ◽  
Vol 15 (11) ◽  
pp. 1379-1387 ◽  
Author(s):  
M. Schulz
Keyword(s):  
Neutral Line ◽  
Scalar Potential ◽  
Coronal Magnetic Field ◽  
Tangential Component ◽  
Good Choice ◽  
Surface Model ◽  
Source Surface ◽  
Spherical Source ◽  
Actual Application ◽  
Time Required

Abstract. The source-surface method offers an alternative to full MHD simulation of the heliosphere. It entails specification of a surface from which the solar wind flows normally outward along straight lines. Compatibility with MHD results requires this (source) surface to be non-spherical in general and prolate (aligned with the solar dipole axis) in prototypical axisymmetric cases. Mid-latitude features on the source surface thus map to significantly lower latitudes in the heliosphere. The model is usually implemented by deriving the B field (in the region surrounded by the source surface) from a scalar potential formally expanded in spherical harmonics, with coefficients chosen so as to minimize the mean-square tangential component of B over this surface. In the simplified (scalar) version the quantity minimized is instead the variance of the scalar potential over the source surface. The scalar formulation greatly reduces the time required to compute required matrix elements, while imposing essentially the same physical boundary condition as the vector formulation (viz., that the coronal magnetic field be, as nearly as possible, normal to the source surface for continuity with the heliosphere). The source surface proposed for actual application is a surface of constant F̃ ≡ r-kB̃, where r is the heliocentric distance and B̃ is the scalar magnitude of the B field produced by currents inside the Sun. Comparison with MHD simulations suggests that k ≈ 1.4 is a good choice for the adjustable exponent. This value has been shown to map the neutral line on the source surface during Carrington Rotation 1869 (May–June 1993) to a range of latitudes that would have just grazed the position of Ulysses during that month in which sector structure disappeared from Ulysses' magnetometer observations.

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