solar magnetism

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

whawkins — Thu, 01 Aug 2024 15:39:00 +0000

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance whawkins Thu, 08/01/2024 - 09:39

Author:

whawkins

Aug 1, 2024

Corrected Figure 7 of Paper I, showing the polarimetric errors for a stepped waveplate with 150◦ retardance (8-state modulation scheme), with dual-beam analysis, and 10 s integration. For this example, we adopted a non-optimal demodulation scheme consisting of simple additions and subtractions of individual modulated signals.

The Astrophysical Journal: (Published 2012 September 4; submitting a "corrected" Figure 7 of Paper I) We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.

New Book! The Problem of Coronal Heating: A Rosetta Stone for Electrodynamic Coupling in Cosmic Plasmas

kolinski — Mon, 25 Mar 2024 15:28:28 +0000

New Book! The Problem of Coronal Heating: A Rosetta Stone for Electrodynamic Coupling in Cosmic Plasmas kolinski Mon, 03/25/2024 - 09:28

By Philip Judge and James A. Ionson

Author:

kolinski

Mar 25, 2024

HAO is pleased to announce the publication of a new and timely book written for young and open-minded scientists just prior to the total eclipse over the USA in April. Senior scientist Philip Judge and co-author James A. Ionson ask why, 8 decades after Bengt Edlen published his seminal article, we still do not have a clear answer to one of the longest-lasting puzzles in all of astronomy. Why is the solar corona so hot?

Cover of Phil Judge's book, The Problem of Coronal Heating

The book offers deep insights during the modern era of major advances in experimentation, with new telescopes on the ground and multiple novel spacecraft -- some orbiting within the corona itself. It serves as a needed new resource for all of astronomy concerned with the coupling of gravitationally-bound objects such as stars, black holes, and galaxies to their environment, through electromagnetic forces.

The publisher's web page contains further information about the text and the authors: https://link.springer.com/book/10.1007/978-3-031-46273-3

Anyone interested can also watch Phil's colloqiuium video that presents just a few nuggets, including such things as radio jets, chocolate cake, and the Rolling Stones.

MLSO UCoMP Science Data Now Available

kolinski — Tue, 19 Dec 2023 20:31:47 +0000

MLSO UCoMP Science Data Now Available kolinski Tue, 12/19/2023 - 13:31

Author:

kolinski

Dec 19, 2023

The Mauna Loa Solar Observatory Upgraded Coronal Multi-Channel Polarimeter (UCoMP) coronagraph science data (version 1.0.1) have now been released to the community via the Mauna Loa web page.

Sample of UCoMP data on the MLSO website.

These data cover the period from July 18, 2021 through Nov 9, 2022. UCoMP observes the solar corona from 1.04 to ~2 solar radii in 9 coronal emission lines. Data have been released for 5 coronal emission lines: FeXIII 1074.7 and 1079.8 nm; FeXI 789.4 nm; FeX 637.4 nm; and FeXV 706.2 nm. Science products are in fits format and include: Level 1 observations of Stokes I, Q, U, and V at multiple wavelengths across each emission line; Level 2 products: Intensity [center wavelength, enhanced and peak]; line-of-sight Doppler velocity; FWHM Line Width; weighted average Stokes I, Q, U, V and linear polarization; plane-of-sky magnetic field azimuth and radial azimuth; and a noise mask. Quicklook images and movies are also provided.

The UCoMP Data User Guide is provided with every fits tar download and quicklook zip download. Please see the user guide for more information.

This is the first release of the data and some problems remain. The most significant are stray light, wavelength tuning drift and image alignment. The stray light and wavelength drift impact the line width and Doppler images. We are working to solve these issues for the next release in 2024. The guide includes the link to the GitHub system where you can read details about all UCoMP issues.

Please report any problems or questions about UCoMP data to mlso_data_requests@ucar.edu

Derivation of Instrument Requirements for Polarimetry using Mg, Fe, and Mn lines between 250 and 290 nm

whawkins — Tue, 14 Feb 2023 18:45:32 +0000

Derivation of Instrument Requirements for Polarimetry using Mg, Fe, and Mn lines between 250 and 290 nm whawkins Tue, 02/14/2023 - 11:45

Author:

whawkins

Feb 14, 2023

Judge et al. (2021) recently argued that a region of the solar spectrum in the near-UV between about 250 and 290 nm is optimal for studying magnetism in the solar chromosphere due to an abundance of Mg II, Fe II, and Fe I lines that sample various heights in the solar atmosphere. In this paper we derive requirements for spectropolarimetric instruments to observe these lines. We derive a relationship between the desired sensitivity to magnetic field and the signal-to-noise of the measurement from the weak-field approximation of the Zeeman effect. We find that many lines will exhibit observable polarization signals for both longitudinal and transverse magnetic field with reasonable amplitudes.

IRIS map used to calculate the longitudinal and transverse sensitivity factors for Mg II and Mn I lines. Left panel: intensity in the core of the Mg II k line. Center panel: longitudinal field sensitivity factor Γ. Right panel: transverse field sensitivity factor X.

Designing a New Coronal Magnetic Field Energy Diagnostic

whawkins — Wed, 31 Aug 2022 19:43:18 +0000

Designing a New Coronal Magnetic Field Energy Diagnostic whawkins Wed, 08/31/2022 - 13:43

Author:

whawkins

Aug 31, 2022

In the solar corona, the free energy, i.e., the excess in magnetic energy over a ground-state potential field, forms the reservoir of energy that can be released during solar flares and coronal mass ejections. Such a free energy further provides a measure of non-potentiality of the magnetic field. Recent theoretical studies indicate that the presence of non-potential magnetic fields is imprinted into the structures of infrared, off-limb, coronal polarization. Thanks to the Coronal Multichannel Polarimeter, coronal linear polarization observations are now available on a daily basis and have been demonstrated to be useful for diagnosing properties of the coronal magnetic field. Future telescopes such as the Daniel K. Inouye Solar Telescope and the proposed Coronal Solar Magnetism Observatory Large Coronagraph will yield circular polarization measurements in the corona. In this paper, we investigate the possibility of exploiting such observations for mapping and studying the accumulation and release of coronal free magnetic energy, with the goal of developing a new tool for identifying "hot spots" of coronal free energy such as those associated with twisted and/or sheared coronal magnetic fields. We applied forward modeling of infrared coronal polarimetry to three-dimensional models of non-potential and potential magnetic fields. From these we defined a diagnostic of non-potentiality that in future could be calculated from a comparison of infrared, o-limb, coronal polarization observations and the corresponding polarization signal forward-modeled from a potential field extrapolated from photospheric magnetograms. We considered the relative diagnostic potential of linear and circular polarization, and the sensitivities of these diagnostics to coronal density distributions and assumed boundary conditions of the potential field. Our work confirms the capacity of polarization measurements for diagnosing non-potentiality and free energy in the solar corona.

Non-potentiality diagnostics of the energized flux-rope simulation at time step 89, computed from the fraction of circular polarization, V/I, using a potential field source surface simulation as reference. First column: V/I two-dimensional map forward modeled from the flux-rope simulation. Second column: V/I map forward modeled from the potential field. Third column: non-potentiality map (squared difference between energized flux-rope simulation V/I and potential field V/I). Fourth column: two-dimensional map column density integral of non-potential energy calculated from difference of the ground-truth simulation magnetic energy and the potential field magnetic energy. Green lines represent. the POS direction of the magnetic field. Solid yellow line indicates the surface of the Sun.

The Astrophysical Journal (abstract)

Solar Transition Region UltraViolet Explorer (STRUVE) requirements flow down to design

whawkins — Tue, 23 Aug 2022 19:11:52 +0000

Solar Transition Region UltraViolet Explorer (STRUVE) requirements flow down to design whawkins Tue, 08/23/2022 - 13:11

Author:

whawkins

Aug 23, 2022

Graph showing the flow-down of requirements from the three science questions (SQ 1.A, SQ 1.B, and SQ 2.A) to Level 1 requirements, and to selected Level 2 requirements.

The Solar Transition Region UltraViolet Explorer (STRUVE) is a proposed miniature satellite (CubeSat) conceived to study the magnetic field in the solar atmosphere currently funded by NASA for a concept study. Magnetism in the solar atmosphere is responsible for "space weather" through explosive processes called flares and coronal mass ejections. Our ability to understand these processes is limited by a lack of observations. STRUVE is designed to observe magnetic field in the solar atmosphere from the deepest observable layers up to the base of the heliosphere that connects the magnetic field of the sun to the earth. To do this, the STRUVE instrument measures polarization in spectral lines in a region of the near-UV that contains the well-known Mg II h and k lines as well as a number of Fe I and Fe II lines that sample many heights in the atmosphere. This paper aims to illustrate the flow down of requirements from the mission science objectives to design requirements while also giving an overview of the design developed from the concept study. The derived requirements from the science objectives are the primary functions STRUVE will need to perform to capture the needed data for the mission. The overview of the mission design will delve into the mission operations and give an overview of the STRUVE instrument and spacecraft. Links between the requirements and mission design are made, pointing out how critical requirements are being met. Throughout the paper, trade studies are presented showing the rationale behind many of the critical design choices made in developing STRUVE for the concept study.

On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions

kolinski — Mon, 11 Jul 2022 20:45:28 +0000

On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions kolinski Mon, 07/11/2022 - 14:45

Publication Name: The Astrophysical Journal; Author's names: Centeno, R., de la Cruz Rodriguez, J., del Pino Aleman, T.

Author:

kolinski

Jul 11, 2022

Scattering polarization tends to dominate the linear polarization signals of the Ca II 8542 A line in weakly magnetized areas (B ~ 100 G), especially when the observing geometry is close to the limb. In this paper we evaluate the degree of applicability of existing non-LTE spectral line inversion codes (which assume that the spectral line polarization is due to the Zeeman effect only) at inferring the magnetic field vector and, particularly, its transverse component. To this end, we use the inversion code STiC to extract the strength and orientation of the magnetic field from synthetic spectropolarimetric data generated with the Hanle-RT code. The latter accounts for the generation of polarization through scattering processes as well as the joint actions of the Hanle and the Zeeman effects. We find that, when the transverse component of the field is stronger than ~80 G, the inversion code is able to retrieve accurate estimates of the transverse field strength as well as its azimuth in the plane of the sky. Below this threshold, the scattering polarization signatures become the major contributors to the linear polarization signals and often mislead the inversion code into severely over- or under-estimating the field strength. Since the line-of-sight component of the field is derived from the circular polarization signal, which is not affected by atomic alignment, the corresponding inferences are always good.

Inversion results for observing geometries away from the disk center. The panels show the relative (percent) differences between the magnetic field values retrieved by the STiC inversions and those in the model atmospheres used for the Hanle-RT syntheses. Left and right correspond, respectively, to the Zeeman-only and the full calculation with atomic polarization cases. The top two rows show the results for the strength and the azimuth of the transverse component of the magnetic field, while the bottom panels present the results for the LOS magnetic field.

Optimal spectral lines for measuring chromospheric magnetic fields

kolinski — Mon, 11 Jul 2022 20:33:01 +0000

Optimal spectral lines for measuring chromospheric magnetic fields kolinski Mon, 07/11/2022 - 14:33

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm

kolinski — Mon, 11 Jul 2022 20:24:06 +0000

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm kolinski Mon, 07/11/2022 - 14:24

Author:

kolinski

Jul 11, 2022

Alin Paraschiv and Philip Judge present CLEDB, a single point inversion algorithm for determining magnetic parameters using spectro-polarimetric measurements of emission lines formed in the solar corona. We select lines of interest and construct databases for combinations of plasma thermal and magnetic configurations. The method is intended to be applied to two or more lines observed simultaneously. The solutions initially yield magnetic orientation, thermal properties, and the spatial position of the emitting plasma in three dimensions. Multiple possible solutions for each observation are returned, including irreducible degeneracies. The magnetic field strength is separately derived from the simple ratio of observed to database polarization data, after the thermal properties and scattering geometry solutions have been determined.

CLEDB 2-line magnetic inversion algorithm flowchart. An important aspect is the delivery of multiple possible solutions for each observation at the last step. Note that the x-coordinate of the point in space, as well as nearest electron density, are returned along with B. The figure uses the notation Vobs and Vdb for observed and computed values of the amplitudes of the Stokes parameters corresponding to O3 and S3 (B = 1) in the text.

The Coronal Veil

kolinski — Mon, 11 Jul 2022 20:15:00 +0000

The Coronal Veil kolinski Mon, 07/11/2022 - 14:15

Publication: Astrophysical Journal; Authors: Malanushenko, A.; Cheung, M. C. M.; DeForest, C. E.; Klimchuk, J. A.; Rempel, M.

Author:

kolinski

Jul 11, 2022

3D view of the simulated corona; bottom panel: magnetogram; back panel: synthetic AIA 211A coronal image; middle vertical plane: volumetric emissivity. Field lines are included for reference.

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 active region in a radiative magnetohydrodynamic simulation to locate volume counterparts for coronal loops. In many cases, a loop cannot be linked to an individual thin strand in the volume. While many thin loops are present in the synthetic images, the bright structures in the volume are fewer and of complex shape. We demonstrate that this complexity can form impressions of thin bright loops, even in the absence of thin bright plasma strands. We demonstrate the difficulty of discerning from observations whether a particular loop corresponds to a strand in the volume, or a projection artifact. We demonstrate how apparently isolated loops could deceive observers, even when observations from multiple viewing angles are available. While we base our analysis on a simulation, the main findings are independent from a particular simulation setup and illustrate the intrinsic complexity involved in interpreting observations resulting from line-of-sight integration in an optically thin plasma. We propose alternative interpretation for strands seen in Extreme Ultraviolet images of the corona. The "coronal veil" hypothesis is mathematically more generic, and naturally explains properties of loops that are difficult to address otherwise-such as their constant cross section and anomalously high density scale height. We challenge the paradigm of coronal loops as thin magnetic flux tubes, offering new understanding of solar corona, and by extension, of other magnetically confined bright hot plasmas.

solar magnetism

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

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New Book! The Problem of Coronal Heating: A Rosetta Stone for Electrodynamic Coupling in Cosmic Plasmas

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MLSO UCoMP Science Data Now Available

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Derivation of Instrument Requirements for Polarimetry using Mg, Fe, and Mn lines between 250 and 290 nm

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Designing a New Coronal Magnetic Field Energy Diagnostic

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Solar Transition Region UltraViolet Explorer (STRUVE) requirements flow down to design

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On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions

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Optimal spectral lines for measuring chromospheric magnetic fields

Recent News

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm

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The Coronal Veil

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