corona

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.

HAO flew observers to MLSO to observe the Sun during the solar eclipse

whawkins — Tue, 12 Mar 2024 17:35:55 +0000

HAO flew observers to MLSO to observe the Sun during the solar eclipse whawkins Tue, 03/12/2024 - 11:35

Author:

whawkins

Mar 12, 2024

Helicopter flying in batteries and solar panels to MLSO located at 11,200 feet on Mauna Loa. The observatory domes are visible at left.

On April 8, 2024, the day of the total solar eclipse, HAO observers Ben Berkey (site manager) and Lisa Perez-Gonzalez flew by helicopter (the road is still closed due to the volcanic eruption of 2022) to the Mauna Loa Solar Observatory (MLSO) located at 11,200 feet on the north face of Mauna Loa to observe the Sun’s corona using the MLSO coronagraphs. During an eclipse the moon blocks out the bright disk of the Sun making the faint pearly corona visible. Coronagraphs are instruments that create ‘artificial’ eclipse images, using a disk inside the telescope to block the bright disk of the Sun. Unfortunately, clouds prevented observations on April 8, but Ben and Lisa were able to return on April 9 to capture beautiful observations of the corona with both coronagraphs.

The Corona on April 9, 2024

An image of the corona from the MLSO K-Coronagraph (K-Cor) in ‘white light’, similar to what is visible with the naked eye.

The MLSO UCoMP coronagraph image of the iron emission line of Fe XIII at a wavelength of 1074.7 nm. This emission line captures plasma with temperatures of ~1.6 million degrees. That is hot enough to strip 12 of the electrons from these iron atoms.

About 4 hours of coronal observations were acquired on April 9 with K-Cor and UCoMP. There are different types of data products available online from UCoMP and from K-Cor.

The Solar Cycle

Royal Observatory of Belgium

The April 8, 2024 eclipse occurred very close to solar maximum activity, when the corona tends to be at its brightest. This plot above shows the ’11-year sunspot cycle’. The Sun goes through peaks and lulls in solar activity that last ~11 years. The plot shows the rise and fall in the number of sunspots. Sunspots are regions of very strong magnetic field. Solar activity, such as flares and explosive events known as coronal mass ejections (CMEs), derive their energy from the Sun’s magnetic field. Solar activity rises, on average, with the number of sunspots.

Don Kolinski

The April 8, 2024 eclipse showed a beautiful ‘solar maximum’ corona, with bright structures all around the Sun. Cool, dense structures known as prominences were also visible during the eclipse. This is a photo of the April 8th eclipse by HAO’s Don Kolinski. The reddish-colored structures seen around the corona are prominences. These are often seen erupting as part of a CME. The best chance to see a prominence during an eclipse is at solar maximum.

By contrast, the solar corona during solar minimum activity looks very different, as shown in this image, taken by the MLSO K-Cor instrument in 2019 when sunspots were near zero. There are very few bright prominences present at solar minimum.

Scientists are using the April 2024 observations of the corona from MLSO, eclipse experiments, and other ground- and space-based data to study the coronal magnetic field and plasma conditions during solar maximum.

For information on the MLSO observing plan and other eclipse-day experiments and modeling efforts please see the WHPI 2024 eclipse campaign.

A Comprehensive Radiative Magnetohydrodynamics Simulation of Active Region Scale Flux Emergence from the Convection Zone to the Corona

whawkins — Thu, 22 Jun 2023 22:10:31 +0000

A Comprehensive Radiative Magnetohydrodynamics Simulation of Active Region Scale Flux Emergence from the Convection Zone to the Corona whawkins Thu, 06/22/2023 - 16:10

Author:

whawkins

Jun 22, 2023

ApJ: Feng Chen, Matthias Rempel, and Yuhong Fan present a comprehensive radiative magnetohydrodynamic simulation of the quiet Sun and large solar active regions. The 197 Mm wide simulation domain spans from 18(10) Mm beneath the photosphere to 113 Mm in the solar corona. Radiative transfer assuming local thermal equilibrium, optically thin radiative losses, and anisotropic conduction transport provide the necessary realism for synthesizing observables to compare with remote-sensing observations of the photosphere and corona. This model self-consistently reproduces observed features of the quiet Sun, emerging and developed active regions, and solar flares up to M class. Here, we report an overview of the first results. The surface magneto-convection yields an upward Poynting flux that is dissipated in the corona and heats the plasma to over 1 MK. The quiescent corona also presents ubiquitous propagating waves, jets, and bright points with sizes down to 2 Mm. Magnetic flux bundles emerge into the photosphere and give rise to strong and complex active regions with over 1023 Mx magnetic flux. The coronal free magnetic energy, which is approximately 18% of the total magnetic energy, accumulates to approximately 1033 erg. The coronal magnetic field is clearly non-force-free, as the Lorentz force needs to balance the pressure force and viscous stress as well as drive magnetic field evolution. The emission measure from log10T=4.5 to log10T>7 provides a comprehensive view of the active region corona, such as coronal loops of various lengths and temperatures, mass circulation by evaporation and condensation, and eruptions from jets to large-scale mass ejections.

Coronal dimming created in the quiet Sun by an emerging active region. Panel (a): Bz at the photosphere, before the active region emerges. Panel (b): Bz as in panel (a), but when a flux concentration (at (x,y) = (120,50)) starts to form. Panels (c) and (d): synthetic AIA 193 channel images from the top view. The time stamps are the same as in panels (a) and (b), respectively. The dimming region is visible in the lower half of the field of view. Panels (e) and (f): synthetic AIA 193 channel images from a side view along the y-axis. The time stamps are the same as in panels (a) and (b), respectively.

Thermal and Non-thermal Properties of Active Region Recurrent Coronal Jets Publication Name

whawkins — Wed, 21 Sep 2022 17:06:04 +0000

Thermal and Non-thermal Properties of Active Region Recurrent Coronal Jets Publication Name whawkins Wed, 09/21/2022 - 11:06

Author:

whawkins

Sep 21, 2022

The Astrophysical Journal: Alin R. Paraschiv, Alina C. Donea, and Philip G. Judge present comprehensive observations of recurrent active region coronal jets, and derive their thermal and non-thermal properties. We discuss a peculiar penumbral magnetic reconnection site, which we previously identified as a "Coronal Geyser". This analysis of geysers provides new information and observational constraints applicable to theoretical modeling of solar jets. The main thermal plasma physical parameters, such as temperature, density, energy flux contributions, etc., are calculated using multiple inversion techniques. The underlying models are assessed, and their limitations and applicability are debated. Additionally, we perform source reconstruction and spectral analysis of higher energy observations to further assess the thermal structure and identify non-thermal plasma emission properties. Cool and hot thermal emission are found. These jets are found to be energetically stronger than polar jets, but we find their potential influence on heliospheric energetics and dynamics to be limited. We additionally found that our observations can only be explained by a combination of thermal and non-thermal emission models.

A multi-wavelength view of a coronal geyser jet.

Study of Coronal Hole Lifetimes

whawkins — Wed, 31 Aug 2022 20:29:27 +0000

Study of Coronal Hole Lifetimes whawkins Wed, 08/31/2022 - 14:29

Author:

whawkins

Aug 31, 2022

Coronal hole centroid latitude vs. Carrington Rotation (bottom) and year (top) for almost three solar cycles (SC21-23). Red represents negative polarity and blue represents positive polarity, with the darker shades representing longer lifetimes, i.e., the number of rotations a given coronal hole or grouping of coronal holes recurs (assuming a rigid 27.3 day rotation rate). Note that coronal holes that last for more than one rotation are plotted for each rotation at the location of their centroid position for that rotation. The 11-year magnetic polarity change at the poles as seen with coronal holes is clear as is the slight asymmetry of the evolution of coronal holes at each pole – i.e., the new polarity coronal hole appears at the north poleslightly before the south pole. The beginning of the solar cycles are marked with a vertical dashed line and based on Sunspot Index and Long-term Solar Observations (SILSO) sunspot numbers.

Version 2; SILSO data available from Royal Observatory of Belgium, Brussels

Ian Hewins, Sarah Gibson, David Webb, Bob McFadden, Thomas Kuchar, and Barbara Emery-Geiger

Using the McIntosh Archive of solar features, we analyze the evolution of coronal holes over more than three solar cycles. We demonstrate that coronal hole positions and lifetimes change dramatically on time scales from months to yrs, and that the pattern of these changes is clearly linked to the solar activity cycle. We demonstrate that the lifetimes of low-latitude coronal holes are usually less than one rotation but may extend to as long as three years. When plotted over time, the positions of low latitude coronal holes that remain visible for over one rotation track the sunspot butterfly diagram in terms of their positions on the sun over a solar cycle. Finally, we confirm that coronal holes do not in general rigidly rotate.

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.

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX

kolinski — Mon, 11 Jul 2022 18:57:40 +0000

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX kolinski Mon, 07/11/2022 - 12:57

Publication: The Astrophysical Journal; Authors: Aatiya Ali, Alin Razvan Paraschiv, Kevin Reardon, and Philip Judge

Author:

kolinski

Jul 11, 2022

The infrared solar spectrum contains a wealth of physical data about the Sun and is being explored using modern detectors and technology with new ground-based solar telescopes. One such instrument will be the ground-based Cryogenic Near-IR Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope (DKIST), which will be capable of sensitive imaging of the faint infrared solar coronal spectra with full Stokes polarization states. Highly ionized emission lines have been observed in galaxies and the solar corona. Quantifying the accuracy of spectral inversion procedures requires a precise spectroscopic calibration of observations. A careful interpretation of the spectra around prominent magnetic dipole lines is essential for deriving physical parameters and particularly for quantifying the off-limb solar coronal observations from DKIST. In this work, we aim to provide an analysis of the spectral regions around the infrared coronal emission lines of Fe xiii 1074.68 nm, Fe xiii 1079.79 nm, Si x 1430.10 nm, and Si ix 3934.34 nm, aligning with the goal of identifying solar photospheric and telluric lines that will help facilitate production of reliable inversions and data products from four sets of solar coronal observations.

Fe XIII 1074.68 nm emission over atmospheric absorption (normalized) in the He I Cryo-NIRSP wavelength range with all labeled candidate lines. The green curve represents the atmospheric spectra that are convolved with a Gaussian function correspondent to the Cryo-NIRSP 0"5 slit spectral resolution of 0.027 nm.

A New Coronagraph for Mauna Loa

kolinski — Wed, 01 Dec 2021 21:36:31 +0000

A New Coronagraph for Mauna Loa kolinski Wed, 12/01/2021 - 14:36

Author:

kolinski

Dec 1, 2021

NCAR's High Altitude Observatory (HAO) will be installing a new white light coronagraph at the Mauna Loa Solar Observatory (MLSO) in Hawaii in August of this year (2013). A coronagraph is an instrument designed to mimic a total solar eclipse, which occurs when the moon completely occults the solar disk. The new coronagraph, known as K-cor, was designed by HAO engineers and scientists, along with two engineering consultants. K-cor will replace the 1-D scanning coronameter at Mauna Loa known as the Mk4. K-cor will provide a factor of ten improvement in speed and signal-to-noise as well as significant advancements in calibration accuracy and reliability.

It is specially designed to acquire images of the lowest region of the very faint, hot solar atmosphere known as the corona. With a field-of-view of 1.05 to 3.0 solar radii, and a time cadence of 15 seconds, the K-cor will provide unprecedented white light imaging for studying the birth and evolution of coronal mass ejections (CMEs). CMEs are dramatic eruptions in the solar atmosphere that hurl millions of tons of magnetized plasma into the solar wind that can create severe space weather at Earth and throughout the heliosphere. High time cadence images of the low corona provide crucial observations for understanding the formation of CMEs and CME-driven shocks in the solar wind.

A sequence of coronal images from Mk4 showing a CME erupting through the corona in May 2001.

Electrical engineer, Brandon Larson, and Technician Rob Graves install the K-cor center section onto the solar spar at the NCAR Mesa Lab in Boulder.

K-cor has been successfully deployed to the HAO solar spar in Boulder, Colorado. The deployment required careful alignment of the optical systems beginning with the installation of the primary objective lens near the front of the telescope. The objective lens is bombarded by light from the solar surface, which is a million times brighter than the faint corona. The lens must be nearly free of scratches, striations and any blemishes that will cause light to scatter and overwhelm the faint signal coming from the corona.

K-cor occulter

The back end of the K-cor instrument contains the occulter, filters, polarization modulator, lenses and cameras. The system is carefully designed to filter out all unwanted light and capture the all-important polarized light scattered by the electrons in the Sun’s corona. If the corona were not polarized it would not be possible with current technologies to observe it in white light from the ground except during a total solar eclipse. The white object at center left in the image is the K-cor occulter, illuminated by, and blocking, the bright light from the solar surface.

K-cor system testing at the Mesa spar by project manager Scott Sewell and electrical engineer Brandon Larson.

K-cor is undergoing spar testing before it is fully deployed to the Mauna Loa spar in August. The pristine skies at MLSO provide the ideal sky conditions needed to observe the faint corona. HAO engineers and scientists will work with the Mauna Loa observers (Allen Stueben, Ben Berkey, Greg Rose and Lisa Waters) to complete the installation at MLSO by September.

K-cor instrument scientist Alfred de Wijn inspects the calibration optics at the Mesa spar in Boulder.

Following installation at the Mauna Loa spar, K-cor will begin routine observations of the corona. Final checks on data calibration by HAO scientists, led by Alfred deWijn (pictured at left,) will be completed and cross-checked to space-based coronagraph observations to ensure the community receives highest quality dataset. All K-cor observations will be provided via the Mauna Loa website.

K-Cor H-alpha image

An image of the solar corona taken with the K-cor in a neutral emission line of hydrogen known as H-alpha. The dark circle is the projection of the occulter obscuring the solar disk. The two bright features are dense, cool objects known as prominences which may play a key role in the dynamical processes that result in CME formation.

Thermal Properties of Coronal Cavities

kolinski — Thu, 18 Nov 2021 17:29:30 +0000

Thermal Properties of Coronal Cavities kolinski Thu, 11/18/2021 - 10:29

Publication Name: Astronomy and Astrophysics; First HAO Author's Name: Sarah Gibson

Author:

kolinski

Nov 18, 2021

We have analyzed 33 cavities observed between 2012 and 2018, from solar activity maximum to minimum. For each cavity we applied a differential emission measure method to obtain both a temperature distribution and a value of the average temperature.

Average temperature of 35 cavities (black) and their surrounding streamers (red).

We find that cavities are filled with material hotter than the surrounding streamer, with temperatures in the range of 1.67 - 2.15 MK. Differences between temperatures of cavities and surrounding streamers are in the range of 0.11 - 0.32 MK with an average value of 0.21 MK. We found that temperatures of both, cavities and streamers, vary as a function of different phases of solar activity. During solar maximum the structures are slightly hotter than those observed during solar minimum (1.85 - 2.15 MK vs. 1.67 - 1.88 MK for cavities and streamers, respectively).

Link to paper: Thermal Properties of Coronal Cavities

corona

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

Recent News

HAO flew observers to MLSO to observe the Sun during the solar eclipse

Recent News

A Comprehensive Radiative Magnetohydrodynamics Simulation of Active Region Scale Flux Emergence from the Convection Zone to the Corona

Recent News

Thermal and Non-thermal Properties of Active Region Recurrent Coronal Jets Publication Name

Recent News

Study of Coronal Hole Lifetimes

Recent News

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

Recent News

The Coronal Veil

Recent News

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX

Recent News

A New Coronagraph for Mauna Loa

Recent News

Thermal Properties of Coronal Cavities

Recent News