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2025-01-02T14:11:57Z

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Template:Infobox Nugget

2025-01-02T13:51:05Z

Dbarrous:

<noinclude>
This is the "RHESSI Nugget Infobox" template.
It should be called in the following format:
<pre>
{{Infobox Nugget
|name = Nugget
|title = Nugget Title
|number = Nugget Number
|first_author = First Author Name
|second_author = Second Author (if any)
|publish_date = 15 Nov 2010
|next_nugget = [Next Article Name]
|previous_nugget = [Previous Article Name]
}}
</pre>
Edit the page to see the template text.
</noinclude>

{| class="infobox" style="width:24em; text-align:left;"
|-
!colspan="2" style="background-color:#00394a; text-align:center; color:#ffff42; font-size:110%;"|{{{name}}}
|-
! Number:
| [[RHESSI Nugget Index::{{{number|}}}]]
|-
! 1st Author:
| [[RHESSI Nugget First Author::{{{first_author|}}}]]
|-
! 2nd Author:
| [[RHESSI Nugget Second Author::{{{second_author|}}}]]
|-
! Published:
| [[RHESSI Nugget Date::{{{publish_date|}}}]]
|-
! Next [[:Category:Nugget|Nugget]]:
| {{{next_nugget}}}
|-
! Previous [[:Category:Nugget|Nugget]]:
| {{{previous_nugget}}}
|-
|}

[[Category:Nugget]]
__SHOWFACTBOX__

<noinclude>
[[Category:Infobox templates|Nugget]]
</noinclude>

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2024-11-21T09:33:27Z

Dbarrous:

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Dbarrous:

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Dbarrous:

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Dbarrous:

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2024-11-21T09:32:53Z

Dbarrous:

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2024-11-21T09:32:43Z

Dbarrous:

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2024-11-21T09:32:33Z

Dbarrous:

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Dbarrous:

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2024-11-21T09:32:05Z

Dbarrous:

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2024-11-21T09:31:43Z

Dbarrous: Dbarrous uploaded a new version of File:476f1.png

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2024-11-21T09:29:34Z

Dbarrous:

Revised Point-Spread Functions of AIA and their effect on DEM analyses

2024-11-21T09:29:12Z

Dbarrous: Created page with "{{Infobox Nugget |name = Nugget |title = Revised Point-Spread Functions of AIA and their effect on DEM analyses |number = 478 |first_author = Stefan HOFMEISTER, |second_author = Daniel Wolf SAVIN, and Michael HAHN |next_nugget = Unrequited currents |previous_nugget = {{#ask: Category:Nugget RHESSI Nugget Index::477}} }} == Introduction == Since 2010, the Atmospheric Imaging Assembly [https://aia.lmsal.com AIA] has been imaging the Sun in the extreme-ultravio..."

{{Infobox Nugget
|name = Nugget
|title = Revised Point-Spread Functions of AIA and their effect on DEM analyses
|number = 478
|first_author = Stefan HOFMEISTER,
|second_author = Daniel Wolf SAVIN, and Michael HAHN
|next_nugget = Unrequited currents
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::477]]}}
}}

== Introduction ==

Since 2010, the Atmospheric Imaging Assembly
[https://aia.lmsal.com AIA] has been imaging
the Sun in the extreme-ultraviolet
([https://en.wikipedia.org/wiki/Extreme_ultraviolet EUV]) range,
providing valuable
insights into the structure and dynamics of the solar corona.
These data have had an enormous influence across many branches of
solar physics.

However, EUV imaging presents a unique challenge: the imaging
wavelength is rather close to the scale of the mirror's roughness,
which leads to significant long-distance instrumental
[https://en.wikipedia.org/wiki/Scattering_from_rough_surfaces scattering].
This scattering can artificially increase observed intensities in
darker regions, such as the off-limb corona and coronal holes, while
reducing intensities in brighter areas, like active regions and
flares.
Scattering obviously can lead to a serious systematic bias in any quantitative
analysis of the beautiful AIA images.

== A new treatment of scattering ==

Previously, it was difficult to quantify this scattering accurately,
limiting our ability to correct AIA images for these effects.
To address this we have revised AIA's point-spread
functions
([https://en.wikipedia.org/wiki/Point_spread_function PSFs]), which
describe the imaging function of the optics, including its scattering behavior
(Ref. [1]).

Using partially
lunar-occulted AIA images, we refined the PSF tails and recalibrated
the diffraction patterns that arise from the meshes that support
the filters.
We demonstrate this in Figure 1 for the AIA 171 Â channel.
By comparing the scattered-light intensity in lunar-occulted areas
to the solar disk's intensity distribution, we first estimate the PSF.
Then, we test the accuracy of the PSF by predicting scattered light
in other lunar-occulted images, where a well-fitted PSF allows us to
accurately predict the observed scattered-light intensity in
the occulted regions.
In this example, our PSF follows the observed intensity profile well,
showing that the PSF is robust.

[[File: 478f1.png|thumb|center|700px|Figure 1: 
The 2016 Oct 30 eclipse. Left, an AIA 171 Â image of the eclipse.
Right, the measured and simulated intensity profiles in the occulted region
along the grey dashed line in the image.
The yellow line shows the measured
intensities; the red line the simulated intensities using our new
PSF; the green line using the AIA team PSF; and the blue line using
the commonly used PSF from Ref. [2].

]]

We applied this method across all AIA channels simultaneously, using
10 lunar-occulted images from 2010-2014 as input to increase the
robustness against calibration errors.
Each PSF and its uncertainty
were calculated by bootstrapping the lunar-occulted images 100 times
and then validated on lunar-occulted images from 2015-2023 and on
flare images.
Our findings reveals that AIA scatters and diffracts
approximately 37-55% of light over medium-to-long distances, depending
on the AIA channel (see Figure 2).
The uncertainties in each AIA
channel primarily stem from the dark-current calibration uncertainties.

[[File: 478f2.png|thumb|center|700px|Figure 2: 
(a) Amount of diffracted and scattered light by the AIA channels.
For each channel, the black vertical bar markes the median value,
the dark grey box the 1 sigma uncertainty, the light gray box the
2 sigma uncertainty, and the color-shaded areas the associated
probability distribution.
Each of the vertical gray and white stripes
mark AIA channels that are on the same of the four AIA telescopes.
(b) Cylindrically averaged AIA 171 PSF weights as a function of
distance to the PSF center.
(c) Amount of light that is scattered and diffracted farther than
a given distance.

]]

We further evaluated the impact of the updated PSFs on the image
quality and subsequent analysis (illustrated in Figure 3).
As expected, dark regions become significantly darker, with up to 90%
of the observed intensity in coronal holes (at 193 Â) found to be
instrumental scatter (not shown here).
Bright regions, such as
active regions and flares, increase in brightness by about 30%.
When applying a differential emission measure (DEM) analysis using
the Hannah-Kontar method (Ref. [3]) to the corrected images, off-limb regions
showed a faster decreases in emission measure (EM) with distance
to the solar disk and slight shifts in the DEM-averaged temperature.
For flares, the low-temperature DEM peak remains largely unchanged,
but the flare DEM peak increases by about 50% in height, suggesting
that PSF corrections do not just increase the image brightness but
also lead the DEM algorithm to converge on a solution with a higher
plasma content.

[[File: 478f3.png|thumb|center|700px|Figure 3: 

Comparison of DEM results for solar regions using different PSF
deconvolutions.
(a) AIA 193 Â quiet Sun off-limb region.
(b) EM and
DEM-averaged temperature along the green box marked in (a).
(g) AIA 94 Â flare image.
(h) DEM of the flaring region marked in green in (g).
In (b) and (h), the blue lines give the DEM results using the
original AIA images as input; the orange line using our new PSF;
the green line using the AIA team PSF; and the PSF from Ref. [2].

]]

== Conclusion ==

EUV imagers like AIA scatter a significant fraction of photons over
large angular distances.
Correcting for these effects is often important.
With PSF deconvolution, dark regions such as coronal holes and
off-limb areas appear significantly darker, while bright regions
like active regions, flares, and coronal bright points become notably
brighter.
The improvements described here should have a quantitative impact on
analyses of AIA data, especially including DEM studies.

The revised PSFs for AIA, including a description how to use them correctly,
can be found [https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/DYT4ZL here].
For full details, see Ref. [1].

== References ==

[1] [https://ui.adsabs.harvard.edu/abs/2024arXiv241008967H "Revised Point-Spread Functions for the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory"]

[2] [https://ui.adsabs.harvard.edu/abs/2013ApJ...765..144P "Point-spread Functions for the Extreme-ultraviolet Channels of SDO/AIA Telescopes"]

[3] [https://ui.adsabs.harvard.edu/abs/2012A&A...539A.146H "Differential emission measures from the regularized inversion of Hinode and SDO data"]

How much of the energy in flare-accelerated electrons reaches the chromosphere?

2024-11-21T09:28:47Z

Dbarrous: Created page with "{{Infobox Nugget |name = Nugget |title = How much of the energy in flare-accelerated electrons reaches the chromosphere? |number = 477 |first_author = M. ALAOUI |second_author = G. HOLMAN |next_nugget = AIA point-spread function and DEM |previous_nugget = {{#ask: Category:Nugget RHESSI Nugget Index::476}} }} == Introduction == Weakly relativistic electrons play an important role in [https://en.wikipedia.org/wiki/Solar_flare solar flares] as a mechanism for e..."

{{Infobox Nugget
|name = Nugget
|title = How much of the energy in flare-accelerated electrons reaches the chromosphere?
|number = 477
|first_author = M. ALAOUI
|second_author = G. HOLMAN
|next_nugget = AIA point-spread function and DEM
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::476]]}}
}}

== Introduction ==

Weakly relativistic electrons play an important role in
[https://en.wikipedia.org/wiki/Solar_flare solar flares]
as a mechanism for energy transport.
We often treat these electrons as in a thick-target laboratory
X-ray source, in which the fast electrons come to a complete stop as
they radiate
[https://en.wikipedia.org/wiki/Bremsstrahlung bremsstrahlung] photons.

In both the standard (cold) collisional thick target model (CTTM)
and the warm-CTTM, Coulomb collisions between the flare-accelerated
energetic electron beam and ambient plasma electrons are the
primary energy loss mechanism from the injection site down to the
chromosphere.
However, since these energetic electrons must typically
have very large fluxes (on the order of
1034-1036 electrons/s)
and propagate from their acceleration site at the looptop to the lower solar
atmosphere, they must be accompanied by an oppositely directed
return current which is generated as a result of the large
charge displacement in the solar corona.
The impact of the return current on
the beams energy losses has been studied extensively assuming that
[https://en.wikipedia.org/wiki/Ohm%27s_law Ohm's law] governs the
dynamics of the interaction.
Our work (Ref. [1],[2]) examines the conditions
under which this is a good assumption and conditions where collisionless
effects, especially the acceleration of runaway electrons out of
the ambient RC plasma, need to be taken into account.

== Energy deposition in the corona vs. the chromosphere ==

Our earlier work (Ref. [1]) calculates the steady-state field-aligned energy losses in a 1D
model, considering Coulomb collisions and return-current deceleration.
We include runaway electrons accelerated out of the ambient plasma, in a
"warm-target" approximation (see
[https://research.ssl.berkeley.edu/~tohban/wiki/index.php/How_to_better_determine_the_power_in_non-thermal_electrons_from_observed_X-ray_spectra
Nugget No. 264], for example).
This warm-target capability is especially important for lower (and higher)
values of the low-energy cutoff (and injected
electron power-law spectral index).
The calculations not only show the energy deposition in the corona
but also the total potential drop in the corona, which can be observed as
a flattening in hard X-ray spectra at lower photon energies.
We also discuss regions where the return-current losses can be
neglected altogether, and alternatively where RC losses are significant
and where runaway electrons also need to be included.

Additionally, in Ref. [2], we find

* Implications for initial conditions in atmospheric response calculations: Notice that at lower coronal temperatures and/or densities, collisionless effects are increasingly significant with the injected flux density.

* The conclusion that injected electron flux densities are inconsistent with negligible return current losses at the HXR peak times for two X-class RHESSI flares: SOL2002-Jul-23T00:20 and SOL2006-Dec-06T18:30.

Figure 1 summarizes this work.

[[File: 477f1.png|thumb|center|600px|Figure 1: 
Ratio of the nonthermal energy flux density at the transition region
to the injected energy flux density at the looptop.
Each panel shows calculations using the same low-energy cutoff,
spectral index, loop length and coronal density as coronal temperature
vs. injected electron energy flux.
The various curves represent the conditions for which: (1) the
fraction of the return current carried by runaway electrons at the
looptop is 1% and 30% (solid gray curves), (2) the maximum return-current
electric field magnitude normalized to the
[https://en.wikipedia.org/wiki/Dreicer_field Dreicer field]
is equal
to 0.15 (solid red); above this value even our quasi-collisional
model is insufficient to account for the dynamics.
The vertical dashed lines show the conditions for the energetic electron
density to be 10% of the ambient return-current density.
]]

== What is the dominant collisionless effect? ==

Collisionless effects include acceleration of runaway electrons
which are included in the model and current-driven instabilities,
which are not included so far.
However, we show the conditions where these do need to be taken into
account.
The return-current drift speed varies along the legs of the loop, but
comparing its maximum value to the
local electron thermal speed is sufficient to test whether the flux
density threshold for generating a current-driven instability is
met.
Figure 2 shows that accelerating runaway electrons occurs for
lower injected electron flux densities compared to the lowest threshold
for a current-driven instability if the electron and ion temperatures
are equal. Our results must be used to check for self-consistency
of the assumptions used in the interpretation of HXR spectra and
of the atmospheric response to the electron injection into the solar
plasma.

[[File: 477f2.png|thumb|center|400px|Figure 2: 

The ratio of maximum drift speed to electron thermal speed for a
range of injected energy flux densities (x-axis) and co- spatial
coronal temperatures (y-axis) and for two coronal density values
(3 x 109 and 3 1x 1010 cm-3, on
the left and right panels, respectively.
Various curves are also overplotted that show (1) the conditions
for the return current to be carried by 1% runaway electrons.
This is a somewhat arbitrary number showing the limit between purely
collisional and quasi-collisionless propagation.
(2) The threshold for a current driven instability to be generated
if the electron and ion temperatures are equal.
Note that contrary to the runaway
acceleration, this threshold is not calculated self-consistently.
(3) The threshold for the quasi-collisionless model in our paper
to be a valid approximation for energy losses at a normalized RC
electric field of 0.15.
]]

== Conclusions ==

Return currents are non-negligible under the conditions defined in
this paper.
Specifically, for sufficiently large injected flux
densities and/or sufficiently low temperatures, the return current
is a drifting Maxwellian or a Maxwellian with a runaway tail with
significant energy losses.
Additional work needs to be done to build
self-consistent models of the beam/return-current propagation especially at the
highest injected flux densities and/or sufficiently low co-spatial
temperatures and densities.

== References ==

[1] [https://ui.adsabs.harvard.edu/abs/2021ApJ...917...74A "Role of Suprathermal Runaway Electrons Returning to the Acceleration Region in Solar Flares"]

[2] [https://ui.adsabs.harvard.edu/abs/2024ApJ...974..177A/abstract "Reduction of the Downward Energy Flux of Nonthermal Electrons in the Solar Flare Corona due to Cospatial Return-current Losses"]

SolarNuggets

2024-11-21T09:28:20Z

Dbarrous:

Welcome to the [[RHESSI Science Nuggets]]: science notes from [[RHESSI]]. The following is a time-ordered list of the latest Nuggets added to the wiki. An [[:Category:Nugget|alphabetical list of wiki Nuggets]] is also available as well as [[:Category:RHESSI Nugget List|yearly lists]]. We welcome volunteer authors - please see our page of [[Help:For_Authors| help for authors]]

{{Nugget Badge
|title = Revised Point-Spread Functions of AIA and their effect on DEM analyses
|number = 478
|first_author =Stefan HOFMEISTER,
|second_author = Daniel Wolf SAVIN, and Michael HAHN
|publish_date = 18 November 2024
|description = Substantial revisions of the AIA point-response functions
|image=Icon478.png}}

{{Nugget Badge
|title = How much of the energy in flare-accelerated electrons reaches the chromosphere?
|number = 477
|first_author = Meriem ALAOUI
|second_author = and Gordon HOLMAN
|publish_date = 11 November 2024
|description = Keeping flare-accelerated electrons out of the chromosphere
|image=Icon477.png}}

{{Nugget Badge
|title = Spatially resolved plasma composition evolution in a solar flare
|number = 476
|first_author = Andy S. H. TO
|publish_date = 4 November 2024
|description = Reconnection outflow feeds abundance variations
|image=Icon476.png}}

{{Nugget Badge
|title = HOPE during high activity
|number = 475
|first_author = Hugh HUDSON
|second_author = and Alphonse STERLING
|publish_date = 28 October 2024
|description = Hot onsets appear even in the most active solar conditions
|image=Icon475.png}}

{{Nugget Badge
|title = Simulated heliospheric electron spectra show sensitivity to plasma properties of a source region in the flaring corona
|number = 474
|first_author = Ross PALLISTER
|second_author = and Natasha JEFFREY
|publish_date = 21 October 2024
|description = Getting closer to an understanding of how solar energetic particles "escape"
|image=Icon474.png}}

{{Nugget Badge
|title = An extremely complex active region with very strong non-neutralized electric currents
|number = 473
|first_author = Ioannis KONTOGIANNIS
|publish_date = 14 October 2024
|description = Large non-neutralized electric currents flow through the active-region corona
|image=Icon473.png}}

{{Nugget Badge
|title = An X9 flare and its huge crochet (SFE)
|number = 472
|first_author = Hugh HUDSON
|publish_date = 7 October 2024
|description = The geomagnetic effect (SFE/crochet) that will calibrate the Carrington flare
|image=Icon472.png}}

{{Nugget Badge
|title = All microflares that accelerate electrons to high energies are rooted in sunspots
|number = 471
|first_author = Andrea Francesco BATTAGLIA
|publish_date = 30 September 2024
|description = Microflares with hard X-ray spectra are a well-defined class, and invariably have one footpoint embedded in a sunspot
|image=Icon471.png}}

{{Nugget Badge
|title = The warm-target model and kappa distributions
|number = 470
|first_author = Yingjie LUO
|publish_date = 16 September 2024
|description = A self-consistent treatment of non-thermal electron spectra points to kappa distributions
|image=Icon470.png}}

{{Nugget Badge
|title = Is there HOPE for Hyder flares...
|number = 468
|first_author = Hugh HUDSON
|publish_date = 15 March 2024
|description = Filament eruptions/Hyder flares/disparitions brusques may all show HOPE
|image=Icon468.png}}

{{Nugget Badge
|title = Sun-as-a-star Analysis of the M8.7 Flare on 2022 October 2 Using H-alpha and EUV Spectra Taken by SMART/SDDI and SDO/EVE
|number = 467
|first_author = Takato OTSU
|publish_date = 19 February 2024
|description = Whole-Sun spectroscopic observations can readily detect ejecta
|image=Icon467.png}}

{{Nugget Badge
|title = Unexpected Asymmetry in GeV Emission
|number = 466
|first_author = Bruno ARSIOLI and Elena ORLANDO
|publish_date = 15 January 2024
|description = The high-energy solar gamma radiation shows inexplicable but fascinating properties
|image=Icon466.png}}

{{Nugget Badge
|title = When it rippled in one place and exploded in another
|number = 465
|first_author = Ivan ZIMOVETS
|publish_date = 25 December 2023
|description = Pulsations precede a flare, but seem unrelated
|image=Icon465.png}}

{{Nugget Badge
|title = Solar flares: evaporation and simulation‎
|number = 464
|first_author = Malcolm DRUETT
|publish_date = 18 December 2023
|description = Fitting beam electrons into multi-dimensional models
|image=Icon464.png}}

{{Nugget Badge
|title = Pre-impulsive and Impulsive Phases of the March 28, 2022 Sub-Terahertz Flare
|number = 463
|first_author = Galina G. MOTORINA
|publish_date = 11 December 2023
|description = A flare with an increasing sub-THz spectrum and sub-THZ precursor information
|image=Icon463.png}}

{{Nugget Badge
|title = Coronal Bright Points
|number = 462
|first_author = Daniel NÓBREGA-SIVERIO
|publish_date = 27 November 2023
|description = Bright EUV rowel-like structures can result from null-point reconnection
|image=Icon462.png}}

{{Nugget Badge
|title = Aurora-like Radio Emission from a Sunspot
|number = 461
|first_author = Sijie YU
|publish_date = 20 November 2023
|description = Maser action above a sunspot
|image=Icon461.png}}

{{Nugget Badge
|title = Search for a Flare Anticipation Index (FAI)
|number = 460
|first_author = Hugh HUDSON
|second_author = and Jim McTiernan
|publish_date = 13 November 2023
|description = Quantifying flare precursors on a few-minute time scale
|image=Icon460.png}}

{{Nugget Badge
|title = Bouncing motions of fast electrons using Nobeyama Radioheliograph
|number = 459
|first_author = Keitarou MATSUMOTO
|publish_date = 6 November 2023
|description = Solar evidence for conservation of second adiabatic invariant in particle motion
|image=Icon459.png}}

{{Nugget Badge
|title = Impact of nanoflare heating in the lower solar atmosphere
|number = 458
|first_author = Helle BAKKE
|publish_date = 30 October 2023
|description = The behavior of nanoflare fast electrons in Bifrost models
|image=Icon458.png}}

{{Nugget Badge
|title = Precise timing of flare footpoint sources from mid-infrared observations‎
|number = 457
|first_author = Paulo SIMÕES et al.
|publish_date = 23 October 2023
|description = Mid-IR observations at high spatial and high temporal resolution: Conjugacy
|image=Icon457.png}}

{{Nugget Badge
|title = The Greatest GOES Flares‎
|number = 456
|first_author = Hugh HUDSON
|second_author = and Ed CLIVER
|publish_date = 25 September 2023
|description = The greatest GOES events, re-analyzed, fall short of expectations
|image=Icon456.png}}

{{Nugget Badge
|title = Introducing SunSketcher
|number = 455
|first_author = Hugh HUDSON
|second_author = and Gordon EMSLIE
|publish_date = 11 September 2023
|description = Galloping towards roundup in the 2024 total solar eclipse
|image=Icon455.png}}

{{Nugget Badge
|title = TeV Gamma rays from the Quiescent Sun
|number = 454
|first_author = Mehr Un NISA
|second_author = and John BEACOM
|publish_date = 21 August 2023
|description = Solar photons at unprecedented high energies
|image=Icon454.png}}

{{Nugget Badge
|title = Temporal and Spatial Characteristics of Hard X-Ray Sources in Flare Model with Vertical Current Sheet
|number = 453
|first_author = Alexander SHABALIN, Eugenia OVCHINNIKOVA,
|second_author = and Yuri CHARIKOV
|publish_date = 7 August 2023
|description = Modeling betatron acceleration in current-sheet development.
|image=Icon453.png}}

{{Nugget Badge
|title = Spatial Distribution of Magnetic Reconnection Rate in an M6.5 Solar Flare
|number = 452
|first_author = Ju JING
|publish_date = 12 June 2023
|description = Linking hard X-rays to high-resolution images that show reconnection rates.
|image=Icon452.png}}

{{Nugget Badge
|title = Statistical study of Type III bursts and associated HXR emissions
|number = 451
|first_author = Nicole VILMER and Tomin JAMES
|publish_date = 29 May 2023
|description = Linking electron populations escaping from the Sun with those that RHESSI detects.
|image=Icon451.png}}

{{Nugget Badge
|title = Solar flare hard X-rays from the anchor points of an eruptive filament
|number = 450
|first_author = Muriel STIEFEL
|publish_date = 15 May 2023
|description = A rare "four-ribbon" flare has been detected in hard X-rays.
|image=Icon450.png}}

{{Nugget Badge
|title = Did a Solar Flare Accelerate all the Ambient Electrons in the Coronal Acceleration Region?...
|number = 449
|first_author = Gordon EMSLIE, Eduard KONTAR,
|second_author = Galina MOTORINA, and Brian DENNIS
|publish_date = 1 May 2023
|description = Considering SOL2017-09-10, probably not.
|image=Icon449.png}}

{{Nugget Badge
|title = Diagnostics of Spatially-Extended Turbulent Acceleration and Transport
|number = 448
|first_author = Morgan STORES
|publish_date = 24 April 2023
|description = Drilling down into the detailed structure of solar-flare energy release by including turbulence with particle acceleration.
|image=Icon448.png}}

{{Nugget Badge
|title = RHESSI's Re-entry
|number = 447
|first_author = Pascal SAINT-HILAIRE and
|second_author = Hugh HUDSON
|publish_date = 17 April 2023
|description = The final demise of RHESSI is this week
|image=Icon447.png}}

{{Nugget Badge
|title = A Glasgow geomagnetic observation of a solar flare
|number = 446
|first_author = Hugh HUDSON, John MALONE-LEIGH,
|second_author = Graham WOAN, and Chris OSBORNE
|publish_date = 13 March 2023
|description = Irish and Scottish geomagnetic observatories see a crochet much like that of the Carrington event
|image=Icon_446.png}}

{{{Nugget Badge
|title = Particle Acceleration in Two Coronal Jets
|number = 445
|first_author = Yixian ZHANG
|publish_date = 27 February 2023
|description = Coronal jets with hard X-ray sources at disjoint locations
|image=Icon445.png}}

{{Nugget Badge
|title = The Curious First Sunquake of Solar Cycle 25‎
|number = 444
|first_author = Alexander KOSOVICHEV
|publish_date = 13 February 2023
|description = A double whammy: two distinct sunquakes from SOL2022-05-10.
|image=Icon444.png}}

{{Nugget Badge
|title = Hard X-ray Pulsations via Gaussian Decomposition
|number = 443
|first_author = Hannah COLLIER and Laura HAYES
|publish_date = 30 January 2023
|description = Flare hard X-ray time variations decomposed objectively
|image=Icon443.png}}

{{Nugget Badge
|title = A possible coronal magnetic flare precursor
|number = 442
|first_author = Enrico LANDI
|publish_date = 16 January 2023
|description = Novel measurements of the coronal magnetic field may help with flare prediction
|image=Icon442.png}}

{{Nugget Badge
|title = A slow HOPE with microwave context
|number = 441
|first_author = Hugh HUDSON
|publish_date = 12 December 2022
|description = A new microwave facility at Chashan Observatory, and a prototypical HOPE
|image=Icon441.png}}

{{Nugget Badge
|title = Rapid variations of Si IV spectra in a flare observed by IRIS at a sub-second cadence
|number = 440
|first_author = Juraj LÖRINČÍK
|publish_date = 14 November 2022
|description = Transition-region lines in a flare have a Doppler component revealing quasi-periodic pulsations
|image=Icon440.png}}

{{Nugget Badge
|title = A Significant Sudden Ionospheric Disturbance Associated with a Massive Gamma-ray Burst
|number = 439
|first_author = Laura HAYES and Peter GALLAGHER
|publish_date = 31 October 2022
|description = A first SID observed in broad daylight, from a source far far away
|image=Icon439.png}}

{{Nugget Badge
|title = Effects of Coronal Structures on the Dynamics of the Global Coronal Wave of SOL2017-09-10‎
|number = 438
|first_author = Huidong HU, Ying D. LIU, and Bei ZHU
|publish_date = 17 October 2022
|description = The amazing global coronal wave of SOL2017-09-10 wrapped around the whole Sun, and displayed transmission and reflection at both polar coronal holes
|image=Icon438.png}}

{{Nugget Badge
|title = KW-Sun: The Konus-Wind Solar Flare Database in Hard X-Ray and Soft Gamma-Ray Ranges
|number = 437
|first_author = Alexandra LYSENKO
|publish_date = 26 September 2022
|description = An unrivaled hard X-ray and gamma-ray database is entering its third activity maximum
|image=Icon437.png}}

{{Nugget Badge
|title = First Detection of Kink Oscillations with Solar Orbiter
|number = 436
|first_author = Sihui ZHONG et al.
|publish_date = 19 September 2022
|description = SolO sees coronal oscillations as well as AIA can, and even better
|image=Icon436.png}}

{{Nugget Badge
|title = Energetic Neutral Hydrogen from Large Solar Flares
|number = 435
|first_author = Glenn MASON
|publish_date = 6 September 2022
|description = A rediscovered data treasury reveals the occurrence of many flare/CME events producing solar high-energy neutral atoms
|image=Icon435.png}}

{{Nugget Badge
|title = Fifty-year Anniversary of the First Detection of Gamma rays from a Solar Flare
|number = 434
|first_author = Jim Ryan,
|second_author = Brian Dennis, and Phil Dunphy
|publish_date = 8 August 2022
|description = The rich astrophysics of gamma-ray astronomy began with solar observations fifty years ago
|image=Icon434.png}}

{{Nugget Badge
|title = Fast Prograde Flows in Solar Active Regions
|number = 433
|first_author = Hugh HUDSON
|publish_date = 25 July 2022
|description = Unexpected, unpredicted, and not modeled yet - weird flows in hot active-region loops
|image=Icon433.png}}

{{Nugget Badge
|title = Undetected Minority-polarity Flux, Moss, and Coronal Heating
|number = 432
|first_author = Yi-Ming WANG
|publish_date = 11 July 2022
|description = There's plenty of room in "unipolar" active regions for both polarities, and there is good evidence for them
|image=Icon432.png}}

{{Nugget Badge
|title = Thermal/Nonthermal with MinXSS and RHESSI
|number = 431
|first_author = Shunsaku NAGASAWA
|publish_date = 13 June 2022
|description = Time-domain studies of improved X-ray spectra reveal a "super-hot' component
|image=Icon431.png}}

{{Nugget Badge
|title = Sun-as-a-star spectroscopic observations of the line-of-sight velocity of a solar eruption on October 28, 2021
|number = 430
|first_author = Yu XU
|second_author = and Hui TIAN
|publish_date = 30 May 2022
|description = The observation of the full 3d velocity of a CME, for an anniversary event
|image=Icon430.png}}

{{Nugget Badge
|title = Carl Størmer
|number = 429
|first_author = Hugh HUDSON
|second_author = and Lyndsay FLETCHER
|publish_date = 15 April 2022
|description = Størmer and the theory of trapping in loops
|image=Icon429.png}}

{{Nugget Badge
|title = Solar Hard X-rays with Insight
|number = 428
|first_author = Wei WANG
|second_author = and Ping ZHANG
|publish_date = 21 March 2022
|description = A spectacular limb flare introduces Insight/HXMT, a new observational resource
|image=Icon428.png}}

{{Nugget Badge
|title = Probing chromospheric current sheets using SST and ALMA co-observations
|number = 427
|first_author = João da SILVA SANTOS
|publish_date = 21 February 2022
|description = Emerging magnetic flux appears in ALMA images reflecting coronal current sheets
|image=Icon427.png}}

{{Nugget Badge
|title = A demonstration of STIX hard X-ray imaging spectroscopy capabilities for an X-class flare (SOL2021-10-28)
|number = 426
|first_author = Andrea BATTAGLIA, Hannah COLLIER,
|second_author = and Säm KRUCKER
|publish_date = 7 February 2022
|description = STIX imaging of an X-class flare marks its success
|image=Icon426.png}}

{{Nugget Badge
|title = A solar flare driven by thermal conduction observed in mid-infrared
|number = 425
|first_author = Guillermo GIMÉNEZ de CASTRO
|publish_date = 24 January 2022
|description = Strong 10-micron emission from a GOES C2 flare suggests conductive heating
|image=Icon425.png}}

{{Nugget Badge
|title = Disk Occultation of a Lopsided Sun‎
|number = 424
|first_author = Hugh HUDSON,
|second_author = Stephen WHITE and Säm KRUCKER
|publish_date = 10 January 2022
|description = Observing a spotless Sun can enable observations of the faint corona.
|image=Icon424.png}}

{{Nugget Badge
|title = Resolving two distinct thermal X-ray components in a compound solar flare
|number = 423
|first_author = Zhenjun ZHOU
|second_author = and Rui LIU
|publish_date = 28 December 2021
|description = Superhot coronal sources may be independent loop systems
|image=Icon423.png}}

{{Nugget Badge
|title = Bridging solar flares to coronal mass ejections
|number = 422
|first_author = Markus ASCHWANDEN
|publish_date = 14 December 2021
|description = The Neupert effect allows us to trace coronal mass ejections seamlessly
|image=Icon422.png}}

{{Nugget Badge
|title = The Jakimiec Diagnostic Diagram
|number = 421
|first_author = Hugh HUDSON
|publish_date = 29 November 2021
|description = The joint variation of GOES temperature and emission measure discloses new features via an old tool
|image=Icon421.png}}

{{Nugget Badge
|title = First look at ALMA/HInode/IRIS microflares
|number = 420
|first_author = Toshifumi SHIMIZU
|second_author = et al.
|publish_date = 8 November 2021
|description = High-resolution ALMA and multiwavelength observations of microflaring
|image=Icon420.png}}

{{Nugget Badge
|title = Thomson scattering near sunspots
|number = 419
|first_author = Pascal Saint-Hilaire
|second_author = et al.
|publish_date = 25 October 2021
|description = Completing the modeling of low-coronal Thomson polarimetry
|image=Icon419.png}}

{{Nugget Badge
|title = A Non-PFSS Global Coronal Model
|number = 418
|first_author = Oliver RICE
|second_author = and Anthony YEATES
|publish_date = 11 October 2021
|description = Modeling as convenient as PFSS but much more realistic
|image=Icon418.png}}

{{Nugget Badge
|title = Manifold Nonthermality
|number = 417
|first_author = Marina BATTAGLIA
|second_author = et al.
|publish_date = 27 September 2021
|description = Even weak flares involve multiple sites of non thermal activity
|image=Icon417.png}}

{{Nugget Badge
|title = X-Rays from a Type I Radio Burst
|number = 416
|first_author = R. RAMESH
|publish_date = 20 September 2021
|description = A first identification of type I radio emission with hot plasma
|image=Icon416.png}}

{{Nugget Badge
|title = Do Hot Onsets Predict Flare Magnitudes?
|number = 415
|first_author = Hugh HUDSON
|publish_date = 30 August 2021
|description = Maybe we can tell how big a flare is going to be from its initial development...
|image=Icon415.png}}

{{Nugget Badge
|title = Confined or Eruptive?
|number = 414
|first_author = Ting LI et al.
|publish_date = 16 August 2021
|description = Increased magnetic flux reduces CME eruptivity
|image=Icon414.png}}

{{Nugget Badge
|title = Impulsive and Gradual Eruptive Gamma Flares and Associated CMEs
|number = 413
|first_author = Alexey STRUMINSKY,
|second_author = Irina GRIGORIEVA and Andrei SADOVSKI
|publish_date = 19 July 2021
|description = Extreme behavior of flare/CME events explained by environment
|image=Icon373.png}}

{{Nugget Badge
|title = The Morphology of Flare Time Profiles
|number = 412
|first_author = Larisa KASHAPOVA
|second_author = et al.
|publish_date = 12 July 2021
|description = Systematic comparison of solar and stellar flaring time profiles
|image=Icon412.png}}

{{Nugget Badge
|title = Flare Pulsation and the Heliosphere
|number = 411
|first_author = Brendan CLARKE
|second_author = et al.
|publish_date = 5 July 2021
|description = Flare pulsations link closely to the distant heliosphere
|image=Icon411.png}}

{{Nugget Badge
|title = STIX, the Hard X-Ray Telescope on board Solar Orbiter
|number = 410
|first_author = Andrea Francesco BATTAGLIA
|second_author = and Säm KRUCKER
|publish_date = 28 June 2021
|description = STIX is operational and producing great data
|image=Icon410.png}}

{{Nugget Badge
|title = Nonequilibrium Ionization of Flare Plasma Observed by Hinode/EIS
|number = 409
|first_author = Shinsuke IMADA
|second_author =
|publish_date = 14 June 2021
|description = Evidence for non-equilibrium ionization in the current sheet of SOL2017-09-10
|image=Icon409.png}}

{{Nugget Badge
|title = Effects of Flares on Solar p-modes
|number = 408
|first_author = Maria-Cristina RABELLO SOARES
|second_author = and Frederic BAUDIN
|publish_date = 26 April 2021
|description = No detectable p-mode amplitude changes due to solar flares
|image=Icon408.png}}

{{Nugget Badge
|title = Subsecond Spikes in Solar Flare X-ray Flux as Seen by Fermi GBM
|number = 407
|first_author =Trevor KNUTH
|second_author = and Lindsay GLESENER
|publish_date = 19 April 2021
|description = A new analysis technique pushes hard X-ray time scales to 0.1 sec or faster
|image=Icon407.png}}

{{Nugget Badge
|title = Negative He 10830 Flare Ribbons and Non-thermal Electrons
|number = 406
|first_author = Graham KERR
|second_author =
|publish_date = 12 April 2021
|description = A 1D radiation hydrodynamics model can explain the dark leading edges of He I flare ribbons
|image=Icon406.png}}

{{Nugget Badge
|title = Tracing the sources of gradual solar energetic particle events
|number = 405
|first_author = David H. BROOKS
|second_author = and Stephanie L. YARDLEY
|publish_date = 29 March 2021
|description = Chemical abundances in SEPs suggest an origin in flare-related moss regions
|image=Icon405.png}}

{{Nugget Badge
|title = The Superflare SOL2017-09-06: from submm to mid-IR
|number = 404
|first_author = Guillermo (Guigue) GIMÉNEZ DE CASTRO
|second_author =
|publish_date = 15 March 2021
|description = Glimpsing the "missing decades" of the flare emission spectrum
|image=Icon404.png}}

{{Nugget Badge
|title = The Neupert Effect Revisited
|number = 403
|first_author = Jiong QIU
|second_author =
|publish_date = 8 March 2021
|description = Two time scales for heating individual flare strands
|image=Icon403.png}}

{{Nugget Badge
|title = FLUKA as a tool for interpreting flare gamma-rays
|number = 402
|first_author = Alec MACKINNON
|second_author =
|publish_date = 1 March 2021
|description = The nuclear physics of solar flares captured in a detailed model
|image=Icon402.png}}

{{Nugget Badge
|title = A Collective Study of 11 NuSTAR Microflares
|number = 401
|first_author = Jessie DUNCAN and
|second_author = Lindsay GLESENER
|publish_date = 22 February 2021
|description = Swarms of NuSTAR micro flares
|image=Icon401.png}}

{{{{Nugget Badge
|title = A Solar FRB
|number = 400
|first_author = Dale GARY and
|second_author = Hugh HUDSON
|publish_date = 15 February 2021
|description = A new frontier in the solar time domain
|image=Icon400.png}}

{{Nugget Badge
|title = Richard Schwartz
|number = 399
|first_author = Brian DENNIS and
|second_author = Hugh HUDSON
|publish_date = 25 January 2021
|description = Remembering a friend and colleague
|image=Icon399.jpg}}

{{Nugget Badge
|title = Observing Solar Flare X-ray Polarization with Prospective CubeSat Missions
|number = 398
|first_author = Natasha JEFFREY
|publish_date = 4 January 2021
|description = The polarization of the solar X-ray spectrum generally remains to be observed
|image=Icon398.png}}

{{Nugget Badge
|title = Solar effects in the local interstellar medium
|number = 397
|first_author = Don GURNETT and
|second_author = Hugh HUDSON
|publish_date = 14 December 2020
|description = Relativistic particle events observed _in situ_ in the interstellar medium
|image=Icon397.png}}

{{Nugget Badge
|title = Investigation of Small-Scale Energy Releases in Hard X-rays with FOXSI
|number = 396
|first_author = Subramania ATHIRAY and
|second_author = Juliana VIEVERING
|publish_date = 7 December 2020
|description = Hard X-rays and high temperatures from the feeblest microflares
|image=Icon396.png}}

{{Nugget Badge
|title = What drives impulsive coronal heating?
|number = 395
|first_author = Pradeep CHITTA
|second_author = et al.
|publish_date = 30 November 2020
|description = Impulsive footpoint emissions suggest magnetic reconnection in the chromosphere
|image=Icon395.png}}

{{Nugget Badge
|title = Probing the solar coronal heating function with slow magnetoacoustic waves
|number = 394
|first_author = Dmitrii KOLOTKOV
|second_author = et al.
|publish_date = 16 November 2020
|description = Coronal heating models meet damped slow magnetoacoustic waves
|image=Icon394.png}}

{{Nugget Badge
|title = Self-Consistent Flare Model
|number = 393
|first_author = Wenzhi RUAN
|second_author = and Rony KEPPENS
|publish_date = 2 November 2020
|description = Energy transport by fast particles made self-consistent with MHD flare modeling
|image=Icon393.png}}

{{Nugget Badge
|title = Hot Flare Onsets
|number = 392
|first_author = Hugh HUDSON
|second_author = et al.
|publish_date = 26 October 2020
|description = The initial soft X-ray temperatures of solar flares tend to be in the 10-15 MK range
|image=Icon392.png}}

{{Nugget Badge
|title = Electric Current Neutralization and Eruption
|number = 391
|first_author = Ellis AVALLONE
|second_author = and Xudong SUN
|publish_date = 19 October 2020
|description = Coronal currents without neutralizing return currents appear to
|image=Icon391.png}}

{{Nugget Badge
|title = Prediction of Solar Cycle 25
|number = 390
|first_author = Leif SVALGAARD
|second_author =
|publish_date = 5 October 2020
|description = Now we know how big the next solar maximum will be
|image=Icon390.png}}

{{Nugget Badge
|title = Flare/CME Cartoon Archive
|number = 389
|first_author = Hugh HUDSON
|second_author =
|publish_date = 27 September 2020
|description = A new edition of the Flare/CME archive, nearly a half kilotoon now
|image=Icon389.png}}

{{Nugget Badge
|title = Submerged Flare Acoustic Sources
|number = 388
|first_author = Juan Camilo BUITRAGO CASAS
|second_author = and Angel MARTÍNEZ
|publish_date = 13 September 2020
|description = Flare acoustic radiation emanates from a source _inside_ the Sun
|image=Icon388.png}}

{{Nugget Badge
|title = Circular Ribbon Flare at Microwaves
|number = 387
|first_author = Jeongwoo LEE
|second_author =
|publish_date = 31 August 2020
|description = Breakout reconnection reveals itself via microwave polarization measurements.
|image=Icon387.png}}

{{Nugget Badge
|title = Relation of Non-neutralized electric currents and the activity in active regions
|number = 386
|first_author = P. VEMAREDDY
|second_author =
|publish_date = 24 August 2020
|description = Non-neutralized coronal current systems contribute to CME eruptions
|image=Icon386.png}}

{{Nugget Badge
|title = White-light emission and photospheric magnetic field changes in flares
|number = 385
|first_author = J. Sebastián CASTELLANOS DURÁN
|second_author = and Lucia KLEINT
|publish_date = 17 August 2020
|description = There are strong correlations between white-light flare emissions and line-of-sight magnetic field changes
|image=Icon385.png}}

{{Nugget Badge
|title = Sunspot Differential Rotation in an X-class Flare
|number = 384
|first_author = Richard GRIMES,
|second_author = Balázs PINTÉR and Huw MORGAN
|publish_date = 10 August 2020
|description = Observations suggesting how the coronal tail can wag the photospheric dog
|image=Icon384.png}}

{{Nugget Badge
|title = Energy Partitioning in a Nonthermally Dominated Two-loop Solar Flare
|number = 383
|first_author = Galina MOTORINA
|second_author = et al.
|publish_date = 3 August 2020
|description = Modeling the propagation of energy via GX Simulator in an early-impulsive flare
|image=Icon383.png}}

{{Nugget Badge
|title = SOL2013-11-10 Eruptive Circular-ribbon Flare with Extended Remote Brightenings
|number = 382
|first_author = Chang LIU
|second_author = et al.
|publish_date = 31 July 2020
|description = A circular-ribbon event can launch an eruption by breaking through its separatrix dome
|image=Icon382.png}}

{{Nugget Badge
|title = Extreme-Ultraviolet Late Phase of Solar Flares
|number = 381
|first_author = Rui LIU
|second_author =
|publish_date = 22 June 2020
|description = Both arcade and circular-ribbon flares may sometimes spawn EUV late phase emission
|image=Icon381.png}}

{{Nugget Badge
|title = Energy transport by accelerated particles in the quiet solar atmosphere
|number = 380
|first_author = Lars FROGNER,
|second_author = Boris GUDIKSEN and Helle BAKKE
|publish_date = 15 June 2020
|description = A first study of non-thermal particles integrated into an MHD simulation of the solar atmosphere
|image=Icon380.png}}

{{Nugget Badge
|title = Quasi-periodic pulsations as indicators of oscillatory processes in solar flares
|number = 379
|first_author = Elena KUPRIYANOVA
|second_author = et al.
|publish_date = 11 May 2020
|description = Many, many QPPs
|image=Icon379.png}}

{{Nugget Badge
|title = Rejuvenating Solar Flare Termination Shocks as Particle Accelerators
|number = 378
|first_author = Bin CHEN
|second_author =
|publish_date = 4 May 2020
|description = At last, clear evidence for a long-predicted phenomenon
|image=Icon378.png}}

{{Nugget Badge
|title = Broad symmetrical Doppler-shifted Fe XXI line profiles
|number = 377
|first_author = Vanessa POLITO
|second_author =
|publish_date = 20 April 2020
|description = It is difficult to explain "evaporation" line profiles by superposition of unresolved flows
|image=Icon377.png}}

{{Nugget Badge
|title = Phenomena in the unusually long pre-impulsive phase of SOL2011-06-07
|number = 376
|first_author = Marian KARLICKÝ,
|second_author = Jana KA&Scaron;PAROVÁ, and Robert SYCH
|publish_date = 13 April 2020
|description = A massive and slowly-rising filament eruption reveals important new signatures of the physics
|image=Icon376.png}}

{{Nugget Badge
|title = Evidence for a Coronal Shock Wave Origin for Relativistic Protons Producing Solar Gamma-Rays and Observed by Neutron Monitors at Earth‎
|number = 375
|first_author = Athanasios KOULOUMVAKOS
|second_author = and Gerry SHARE
|publish_date = 6 April 2020
|description = Successful modeling of prolonged solar gamma-ray emissions and terrestrial ground-level cosmic-ray events
|image=Icon375.png}}

{{Nugget Badge
|title = Using overlappogram data to find hot flare plasma
|number = 374
|first_author = Louise HARRA
|
|publish_date = 23 March 2020
|description = Imaging Fe XXIV at high resolution with the EIS slot data
|image=Icon374.png}}

{{Nugget Badge
|title = SOL2017-09-04 (M5.5) 2017 as a Source of Relativistic Electrons and Protons
|number = 373
|first_author = Alexei STRUMINSKII
| (see text)
|publish_date = 16 March 2020
|description = Flare-accelerated particles, rather than SEPs, energize sustained gamma-ray emission
|image=Icon373.png}}

{{Nugget Badge
|title = Heating of the solar photosphere during a white-light flare‎
|number = 372
|first_author = Jan JURČÁK
| (see text)
|publish_date = 2 March 2020
|description = The best-ever spectrum of the flare photosphere
|image=Icon372.png}}

{{Nugget Badge
|title = A Hot Cusp-Shaped Confined Solar Flare
|number = 371
|first_author = Aaron HERNANDEZ-PEREZ
|publish_date = 24 February 2020
|description = A flare may have a prominent hot cusp with the help of any eruption
|image=Icon371.png}}

{{Nugget Badge
|title = The Temporal and Spatial Extension of Gamma-ray Emission from the Sun
|number = 370
|first_author = Nat GOPALSWAMY
|publish_date = 17 February 2020
|description = Sustained solar γ-rays and solar cosmic rays
|image=Icon370.ng.png}}

{{Nugget Badge
|title = A PSP Perihelion
|number = 369
|first_author = Jessie DUNCAN
|second_author = and Hugh Hudson
|publish_date = 20 January 2020
|description = The Parker Solar Probe enters its fourth perihelion already. Now
|image=Icon369.png}}

{{Nugget Badge
|title = Remembering John Brown
|number = 368
|first_author = Alec MacKINNON
|second_author =
|publish_date = 13 January 2020
|description = John passed away unexpectedly on 16 November 2019
|image=Icon368.png}}

{{Nugget Badge
|title = A Global Survey of EUV Coronal Power Spectra
|number = 367
|first_author = Karl Battams
|second_author =
|publish_date = 30 December 2019
|description = Time-series parameter maps of imaged power spectra from an AIA pipeline
|image=Icon367.png}}

{{Nugget Badge
|title = Cosmic Rays over the Rainbow Bridge
|number = 366
|first_author = Hugh Hudson
|second_author = Alec MacKinnon
|publish_date = 16 December 2019
|description = Cosmic rays approach the Sun
|image=Icon366.png}}

{{Nugget Badge
|title = Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare
|number = 365
|first_author = Ryan French
|second_author =
|publish_date = 9 December 2019
|description = CoMP polarization patterns in SOL2017-09-10 are amazing
|image=Icon365.png}}

{{Nugget Badge
|title = Lorentz Force Evolution Reveals the Energy Build-up Processes during Recurrent Eruptive Solar Flares‎
|number = 364
|first_author = Ranadeep Sarkar,
|second_author = Nandita Srivastava and Astrid Veronig
|publish_date = 18 November 2019
|description = The net Lorentz force clearly exhibits a build-up and release pattern
|image=Icon364.png}}

{{Nugget Badge
|title = Flare waiting times depend on their magnitudes
|number = 363
|first_author = Hugh Hudson
|second_author =
|publish_date = 11 November 2019
|description = Surprising new evidence for the flare build-up and release process
|image=Icon363.png}}

{{Nugget Badge
|title = Can magnetic reconnection cause solar rainstorms?‎
|number = 362
|first_author = Petra Kohutova
|second_author =
|publish_date = 4 November 2019
|description = Impulsive coronal heating resulting from reconnection can trigger coronal rain
|image=Icon362.png}}

{{Nugget Badge
|title = Non-radial jets on the edges of active regions
|number = 361
|first_author = Peter Wyper
|second_author =
|publish_date = 14 October 2019
|description = The very common jet structures we see can naturally combine twist and breakout
|image=Icon361.png}}

{{Nugget Badge
|title = Searching SOLfully within the Nuggets
|number = 360
|first_author = Hugh Hudson
|second_author =
|publish_date = 7 October 2019
|description = The IAU target identifier works well for finding items about a particular event
|image=Icon360.png}}

{{Nugget Badge
|title = Submillimeter Radiation as the Thermal Component of the Neupert Effect
|number = 359
|first_author = Guillermo Giménez de Castro
|second_author =
|publish_date = 31 September 2019
|description = Flare radiation at the highest frequencies can be bremsstrahlung
|image=Icon359.png}}

{{Nugget Badge
|title = The "Last Best" Flares
|number = 358
|first_author = Hugh Hudson,
|second_author = Ed Cliver, and Brian Dennis
|publish_date = 24 September 2019
|description = Major flares tend to happen at the very ends of sunspot cycles
|image=Icon358.png}}

{{Nugget Badge
|title = Dynamic Processes of the Moreton Wave on 2014 March 29‎
|number = 357
|first_author = Denis Cabezas
|second_author = and the FMT team
|publish_date = 16 September 2019
|description = A beautiful Moreton wave excited by the best-observed flare ever
|image=Icon357.png}}

{{Nugget Badge
|title = EVE-RHESSI DEM Models and the Low-energy Cutoff for Nonthermal Electrons
|number = 356
|first_author = Jim McTiernan
|second_author =
|publish_date = 9 September 2019
|description = Characterizing flare temperature distributions helps to define the non-thermal energy release
|image=Icon356.png}}

{{Nugget Badge
|title = Stealth Coronal Mass Ejections from Active Regions
|number = 355
|first_author = Jennifer O'Kane
|second_author =
|publish_date = 26 August 2019
|description = Perhaps just feeble versions of the same magnetic disease...
|image=Icon355.png}}

{{Nugget Badge
|title = Do Kepler Superflare Stars Really Include Slowly Rotating Sun-like Stars?‎
|number = 354
|first_author = Yuta NOTSU
|second_author =
|publish_date = 15 July 2019
|description = Kepler superflares hint at solar superflares
|image=Icon354.png}}

{{Nugget Badge
|title = Localized Microwave and EUV Bright Structures in an Eruptive Prominence
|number = 353
|first_author = Jing HUANG
|second_author =
|publish_date = 22 June 2019
|description = Detailed correlations between EUV and microwaves in prominence fine structures
|image=Icon353.png}}

{{Nugget Badge
|title = Broken-up hard X-ray spectra found for a loop-top source during a solar limb flare
|number = 352
|first_author = Hao NING,
|second_author = Yao CHEN and Jeongwoo LEE
|publish_date = 16 June 2019
|description = SOL2017-09-10 coronal hard X-ray sources
|image=Icon352.png}}

{{Nugget Badge
|title = The Cosmic-Ray Shadow and Coronal Magnetism
|number = 351
|first_author = Frederik Tenholt
|second_author =
|publish_date = 27 May 2019
|description = The coronal magnetic field measured in Antarctica
|image=Icon351.png}}

{{Nugget Badge
|title = Kristian Birkeland
|number = 350
|first_author = Hugh HUDSON
|second_author = and Lyndsay FLETCHER
|publish_date = 6 May 2019
|description = Space weather a century ago: Kristian Birkeland
|image=Icon350.png}}

{{Nugget Badge
|title = Warm UV loops heated by small-scale cancellation events
|number = 349
|first_author = Seray ŞAHIN
|second_author = and Vasyl YURCHYSHYN
|publish_date = 22 April 2019
|description = Precisely locating the footpoints of warm coronal loops helps identify their source(s) of excitation
|image=Icon349.png}}

{{Nugget Badge
|title = Multiple Regions of Shock-accelerated Particles during a Solar Coronal Mass Ejection
|number = 348
|first_author = Diana MOROSAN
|second_author =
|publish_date = 1 April 2019
|description = LOFAR identifies herringbone sources within the flank of the SOL2017-09-10 shock - no joke
|image=Icon348.png}}

{{Nugget Badge
|title = Persistent Quasi-Periodic Pulsations Detected During the Large X8.2 Solar Flare
|number = 347
|first_author = Laura HAYES
|second_author = and Peter GALLAGHER
|publish_date = 25 March 2019
|description = The most beautiful flare has the most beautiful pulsations
|image=Icon347.png}}

{{Nugget Badge
|title = Is the coronal magnetic field braiding?
|number = 346
|first_author = Markus ASCHWANDEN
|second_author =
|publish_date = 11 March 2019
|description = This iconic cartoon does not relate well to the observations
|image=Icon346.png}}

{{Nugget Badge
|title = An energetic pre-flare: electron distributions in magnetic reconnection outflows
|number = 345
|first_author = Marina BATTAGLIA,
|second_author = Eduard KONTAR and Galina MOTORINA
|publish_date = 18 February 2019
|description = Assessing energy partition in a pre-impulsive flare development
|image=Icon345.png}}

{{Nugget Badge
|title = Linear Polarization in H-alpha Flares
|number = 344
|first_author = Tomoko KAWATE
|second_author = and Yoichiro HANAOKA
|publish_date = 4 February 2019
|description = H-alpha polarization is rarely observable but, in once case, very suggestive
|image=Icon344.png}}

{{Nugget Badge
|title = Short-Period Waves
|number = 343
|first_author = Sijie YU
|second_author = and Bin CHEN
|publish_date = 21 January 2019
|description = New decimetric imaging spectroscopy suggests Alfvénic energy transport in flares
|image=Icon343.png}}

{{Nugget Badge
|title = The Interesting RHESSI/SAS Archive
|number = 342
|first_author = Hugh HUDSON
|second_author = and Martin FIVIAN
|publish_date = 8 January 2019
|description = The full mission database shows RHESSI to have been very stable geometrically
|image=Icon342.png}}

{{Nugget Badge
|title = Homologous White Light Solar Flares‎
|number = 341
|first_author = Paolo ROMANO
|second_author = and Abouazza ELMHAMDI
|publish_date = 31 December 2018
|description = Homologous white-light flares, in rapid succession, and coronal null points
|image=Icon341.png}}

{{Nugget Badge
|title = The flight of FOXSI-3
|number = 340
|first_author = Lindsay GLESENER
|second_author = and Noriyuki NARUKAGE
|publish_date = 10 December 2018
|description = Single-photon counting and direct focusing across hard and soft energies
|image=Icon340.png}}

{{Nugget Badge
|title = Stellar Flares and Starspots
|number = 339
|first_author = Lauren DOYLE
|second_author =
|publish_date = 3 December 2018
|description = Stellar flares don't spatially match their starspots
|image=Icon339.png}}

{{Nugget Badge
|title = Neutron Production in Solar Flares
|number = 338
|first_author = Ron MURPHY
|second_author = and Gerry SHARE
|publish_date = 26 November 2018
|description = Neutron astronomy helps us understand solar flares
|image=Icon338.png}}

{{Nugget Badge
|title = Cycle 25 Strikes Again
|number = 337
|first_author = Kamil BICZ
|second_author =
|publish_date = 20 November 2018
|description = A second, larger Cycle 25 sunspot
|image=Icon337.png}}

{{Nugget Badge
|title = Remembering Marcos Machado via his research
|number = 336
|first_author = Hugh HUDSON
|second_author =
|publish_date = 13 November 2018
|description = Recalling a friend and colleague, and admiring his final paper
|image=Icon336.png}}

{{Nugget Badge
|title = CORONAS/SPIRIT Mg XII and Nanoflares‎
|number = 335
|first_author = Anton REVA
|second_author =
|publish_date = 22 October 2018
|description = Monochromatic Mg XII spectroheliography sets severe limits on nanoflare heating models
|image=Icon335.png}}

{{Nugget Badge
|title = White-light Emission and Non-thermal Electrons‎
|number = 334
|first_author = Kyoung-Sun LEE
|second_author =
|publish_date = 8 October 2018
|description = An intimate relationship between accelerated electrons and visible flare continuum
|image=Icon334.png}}

{{Nugget Badge
|title = Coronal Hard X-ray Sources Revisited
|number = 333
|first_author = Brian DENNIS
|second_author =
|publish_date = 24 September 2018
|description = Reporting some over-interpretation of the evidence for "coronal thick targets"
|image=Icon333.png}}

{{Nugget Badge
|title = Photospheric response to a flare
|number = 332
|first_author = Mike WHEATLAND
|second_author =
|publish_date = 17 September 2018
|description = Sudden changes in the magnetic field in the low atmosphere associated with particle acceleration
|image=Icon332.png}}

{{Nugget Badge
|title = New Views of Global Solar Magnetic Field Evolution Over Four Solar Cycles
|number = 331
|first_author = David WEBB
|second_author =
|publish_date = 27 August 2018
|description = A digital archive of Pat McIntosh's 44 years of solar synoptic observations
|image=Icon331.png}}

{{Nugget Badge
|title = Understanding the co-spatial return current in solar flares
|number = 330
|first_author = Meriem ALAOUI
|second_author = and Gordon HOLMAN
|publish_date = 6 August 2018
|description = Completing the circuit in a thick-target model
|image=Icon330.png}}

{{Nugget Badge
|title = 3D Magnetic Reconnection at a Coronal Null Point
|number = 329
|first_author = Shane MALONEY,
|second_author = Aidan O'Flannagain and Peter Gallagher
|publish_date = 30 July 2018
|description = Large-scale reconnection involved in Type I radio noise storm
|image=Icon329.png}}

{{Nugget Badge
|title = The true dawn of multimessenger astronomy
|number = 328
|first_author = Hugh Hudson
|second_author =
|publish_date = 23 July 2018
|description = Ever since the Carrington flare
|image=Icon328.png}}

{{Nugget Badge
|title = Microwave Imaging Spectroscopy of Flares is Here‎
|number = 327
|first_author = Dale E. Gary,
|second_author = EOVSA and RHESSI Teams
|publish_date = 16 July 2018
|description = Microwave imaging spectroscopy takes a giant leap forward with SOL2017-09-10
|image=Icon327.png}}

{{Nugget Badge
|title = Coronal nanoflares powered by footpoint reconnection
|number = 326
|first_author = Pradeep Chitta,
|second_author = Hardi Peter, and Sami Solanki
|publish_date = 9 July 2018
|description = Coronal nanoflares in active region cores can be powered by the magnetic reconnection in the lower solar atmosphere
|image=Icon326.png}}

{{Nugget Badge
|title = A remarkable, but confused, coronal hard X-ray source
|number = 325
|first_author = Alexandra Lysenko,
|second_author = Larisa Kashapova and Hugh Hudson
|publish_date = 25 June 2018
|description = A remarkable flare in 1999 adds to our short list of extended coronal hard X-ray/microwave sources
|image=Icon325.png}}

{{Nugget Badge
|title = Understanding HMI pseudocontinuum in white-light flares‎
|number = 324
|first_author = Michal &Scaron;vanda
|second_author = et al.
|publish_date = 28 May 2018
|description = The HMI pseudocontinuum (Ic) is ill-calibrated in regions with strong fields, i.e. for white-light flares
|image=Icon324.png}}

{{Nugget Badge
|title = To beam or not to beam - that is (still) the question
|number = 323
|first_author = Paulo Simões
|second_author = and Hugh Hudson
|publish_date = 14 May 2018
|description = Descriptions of the lower solar atmosphere of flares ca. Cycle 21 sound surprisingly current
|image=Icon323.png}}

{{Nugget Badge
|title = Observation of Cosmic Ray Spallation Events from SoHO‎
|number = 322
|first_author = Serge Koutchmy
|second_author = and Ehsan Tavabi
|publish_date = 7 May 2018
|description = LASCO's images capture high-energy nuclear interactions from cosmic-ray hits
|image=Icon322.png}}

{{Nugget Badge
|title = A Sunspot from Cycle 25 for sure
|number = 321
|first_author = Tomek Mrozek
|second_author = and Hugh Hudson
|publish_date = 10 April 2018
|description = YES! Cycle 25 is here!
|image=Icon321.png}}

{{Nugget Badge
|title = Blue-wing enhancement of the Mg II h and k lines in a flare
|number = 320
|first_author = Akiko TEI
|second_author =
|publish_date = 9 April 2018
|description = Flare loops involve a cool upflow preceding the hot evaporation flow
|image=Icon320.png}}

{{Nugget Badge
|title = NuSTAR detects X-ray flares in the quiet Sun
|number = 319
|first_author = Matej Kuhar
|second_author = and Säm Krucker
|publish_date = 26 March 2018
|description = Quiet-Sun flares may not be powerful, but they look a lot like ordinary flares
|image=Icon319.png}}

{{Nugget Badge
|title = Homologous CME/flares from AR 12371
|number = 318
|first_author = Panditi Vemareddy
|second_author = and Pascal Demoulín
|publish_date = 19 March 2018
|description = An excellent set of homologous flare/CMEs analyzed and explained
|image=Icon318.png}}

{{Nugget Badge
|title = Non-Maxwellian Diagnostics from SDO/EVE Spectra of an X-class Flare
|number = 317
|first_author = Elena Dzifčáková
|second_author = and Jaroslav Dudík
|publish_date = 16 February 2018
|description = Ratios of high-excitation ions can readily detect κ-distributions in flare plasmas
|image=Icon317.png}}

{{Nugget Badge
|title = Joint MinXSS and RHESSI Flare X-ray Spectra between 1 and 15 keV
|number = 316
|first_author = Chris Moore, Brian Dennis and the MinXSS Science Team
|publish_date = 5 February 2018
|description = MinXSS adds systematic views of flare soft X-ray spectra to RHESSI imagery
|image=Icon316.png}}

{{Nugget Badge
|title = Parameterized Flare Models with Chromospheric Compressions
|number = 315
|first_author = Adam Kowalski & Joel Allred
|publish_date = 17 January 2018
|description = A new approach to modeling the lower flare atmosphere
|image=FlareModelsKowalskiAllred.png}}

{{Nugget Badge
|title = A Curious Sunspot Group in 2018
|number = 314
|first_author = Hugh Hudson
|publish_date = 14 January 2018
|description = The first new sunspot group of 2018 emerged at the wrong latitude
|image = Icon314.png}}

{{Nugget Badge
|title = Tecumseh's Eclipse and Astrophysics
|number = 313
|first_author = Hugh Hudson
|publish_date = 25 December 2017
|description = The solar corona was first recognized as such, and named, in an eclipse of 1806
|image = Icon313.png}}

{{Nugget Badge
|title = Hunting for Hidden Tiny Flares
|number = 312
|first_author = Shin-nosuke ISHIKAWA
|publish_date = 27 November 2017
|description = FOXSI-2 says that episodic energy releases are still viable as a part of the coronal heating problem.
|image = Icon312.png}}

{{Nugget Badge
|title = Unusual Type III Burst Dynamics Produced by Diverging Magnetic Fields
|number = 311
|first_author = Patrick McCauley
|publish_date = 20 November 2017
|description = Unusual type III bursts follow coronal separatrix structures.
|image = Icon311.png}}

{{Nugget Badge
|title = Valderrama in the 21st Century
|number = 310
|first_author = Hugh Hudson
|publish_date = 31 October 2017
|description = A newly-described white-light flare from the 19th century!..
|image = Icon310.png}}

{{Nugget Badge
|title = Electron Scattering in the Flaring Corona
|number = 309
|first_author = Sophie Musset
|publish_date = 24 October 2017
|description = Diffusive transport may contribute to the trapping of electrons in coronal X-ray sources
|image = Icon309.png}}

{{Nugget Badge
|title = The Power of Turbulence
|number = 308
|first_author = Nic Bian
|publish_date = 25 September 2017
|description = Turbulent energy content may underlie flare energy transfer, magnetic reconnection, and particle acceleration
|image = Icon308.png}}

{{Nugget Badge
|title = The Kelvin Force and Loop-Top Concentration
|number = 307
|first_author = Kiyoto SHIBASAKI
|publish_date = 18 September 2017
|description = New physics can explain the perplexing overpressure at the flare looptop regions
|image = Icon307.png}}

{{Nugget Badge
|title = The Last Best Flare of Cycle 24?
|number = 306
|first_author = Säm Krucker
|second_author = and Hugh Hudson
|publish_date = 11 September 2017
|description = Right on schedule, Cycle 24 has produced a great flare (with a GLE)
|image = Icon306.png}}

{{Nugget Badge
|title = Electric Current Neutralization and Solar Eruption in Active Regions
|number = 305
|first_author = Yang LIU
|second_author =
|publish_date = 28 August 2017
|description = Active current systems in the solar corona don't have return currents
|image = Icon305.png}}

{{Nugget Badge
|title = RHESSI and the Megamovie
|number = 304
|first_author = Hugh Hudson, Laura Peticolas,
|second_author = and Juan Carlos Martínez Oliveros
|publish_date = 31 July 2017
|description = A wholly new way to view a solar eclipse, and to do solar astrometry
|image = Icon304.png}}

{{Nugget Badge
|title = Bastille Day 2017
|number = 303
|first_author = Hugh Hudson
|second_author = and Säm Krucker
|publish_date = 24 July 2017
|description = Interesting flares really do happen on Bastille Day...
|image = Icon303.png}}

{{Nugget Badge
|title = The Solar X-ray Limb III
|number = 302
|first_author = Marina Battaglia
|second_author = and Gordon Hurford
|publish_date = 12 June 2017
|description = RHESSI succeeds with a wholly new way to measure the solar diameter
|image = Icon302.png}}

{{Nugget Badge
|title = Double Coronal X-ray and Microwave Sources Associated With A Magnetic Breakout Solar Eruption
|number = 301
|first_author = Yao CHEN
|second_author =
|publish_date = 29 May 2017
|description = A different explanation of the double coronal hard X-ray sources
|image = Icon301.png}}

{{Nugget Badge
|title = A Lasso Model for Solar Gamma-ray Events
|number = 300
|first_author = Hugh Hudson
|second_author =
|publish_date = 15 May 2017
|description = A toy model hoping to explain the SEP/LAT relationship
|image = Icon300.png}}

[[RHESSI Science Nuggets 200 to 299|Next Nuggets]]

Spatially resolved plasma composition evolution in a solar flare

2024-11-21T09:24:37Z

Dbarrous: Created page with "{{Infobox Nugget |name = Nugget |title = Spatially resolved plasma composition evolution in a solar flare: the effect of reconnection outflow |number = 476 |first_author = Andy S. H. TO et al. |next_nugget = Return currents |previous_nugget = {{#ask: Category:Nugget RHESSI Nugget Index::475}} }} == Introduction == Solar flares can significantly affect the elemental composition in the corona. The observed variations of elemental abundances reflect the..."

{{Infobox Nugget
|name = Nugget
|title = Spatially resolved plasma composition evolution in a solar flare: the effect of reconnection outflow
|number = 476
|first_author = Andy S. H. TO et al.
|next_nugget = Return currents
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::475]]}}
}}

== Introduction ==

Solar flares can significantly affect the elemental composition in
the corona.
The observed variations of elemental abundances reflect
the First Ionization Potential (FIP) effect, where easily
ionized elements (low FIP, < 10 eV) such as Ca and Fe show abundances
that are relative to high-FIP elements (≥ 10 eV) like Ar and S.
The ratio between coronal and photospheric abundances of these elements,
known as the "FIP bias," helps us understand the physical processes
occurring during flares.
Previous studies using Sun-as-a-star
measurements often show photospheric abundances during flares,
suggesting that chromospheric ablation pulls up low and high-FIP
element indiscriminantly.
The spatial variation of composition within flare structures
has thus remained poorly understood (e.g., Ref. [1]).

== Observations ==

We have analyzed the famous flare SOL2017-09-10 (X11.9)
using the Hinode/EIS instrument, which provided 12 spectroscopic
observations spanning 3.5 hours (Ref. [2]).
Using both Ca XIV/Ar XIV and Fe XVI/S XIII composition diagnostics,
we found consistently that:

* The flare loop tops maintained high FIP bias values (> 2-6) throughout the observation period for both Ca/Ar and Fe/S;

* FIP bias gradually decreased from loop tops toward footpoints, reaching photospheric values (FIP bias ~ 1);

* The temporal evolution showed higher FIP bias during the peak phase, gradually decreasing in later stages.

[[File: 476f1.png|thumb|center|600px|Figure 1:

Flare images and time sequences for SOL2017-09-10.
Upper panel, abundance-ratio maps (left) and EUV intensities (right)
in each image pair.
See Ref. [2] for fuller details.
Middle, [https://www.swpc.noaa.gov/products/goes-x-ray-flux GOES]
soft X-ray time seriess; lower,
[https://hesperia.gsfc.nasa.gov/rhessi3/ RHESSI] hard X-rays.
]]

These maps show FIP enhancements at the loop tops, closely matching
the images themselves; the footpoints of these loops instead
have normal photospheric abundances.

== Discussion and Conclusions ==

to explain this striking discovery, we propose a scenario similar to that
for the loop plasma itself.
The persistent high FIP bias at loop tops results from plasma downflow from the
plasma sheet, where pre-existing coronal loops with high FIP bias
undergo reconnection; see Ref. [1] for a description of
composition in this current sheet.
This highly fractionated plasma (FIP bias > 2) becomes
confined at loop tops, while chromospheric evaporation fills the
lower parts of loops with unfractionated plasma (FIP bias = 1).

[[File: 476f2.png|thumb|center|600px|Figure 2:

Illustration of how plasma downflow following magnetic reconnection
can create high-FIP looptops, with lower FIP at the footpoints
resulting from evaporation.
Note that in Sun-as-a-star measurements, the looptop
high FIP bias is likely diluted due to the bright low FIP bias loop
footpoints, which dominate.
]]

Our observations provide new insights into flare heating mechanisms
and the formation of bright loop-top "EUV knots" - dense plasma
concentrations commonly observed at flare loop tops. While the
standard flare model suggests heating through chromospheric
evaporation, our composition measurements reveal that flare heating
is more complex, involving both directly heated coronal plasma and
evaporated chromospheric material.

The high FIP bias we observe at loop tops contradicts models where
EUV knots form solely through colliding evaporation flows, as such
flows would carry photospheric composition plasma. Instead, our
results support scenarios where reconnection outflows contribute
to the formation of these bright loop-top features.

This scenario helps explain several key observational features:

* The spatial gradient in composition along flare loops - from
highly fractionated plasma at loop tops to photospheric values at
footpoints

* The remarkable persistence of high FIP bias at loop tops over 3.5
hours - maintained by continuous downflows from the current sheet

* Why Sun-as-a-star measurements typically show photospheric
abundances - the localized high FIP bias at loop tops is diluted
by bright footpoint emission in spatially-averaged observations

* The formation mechanism of bright loop-top "EUV knots" - these
features arise from confined, highly

Our findings demonstrate that flare plasma heating is more complex
than previously thought, involving both directly heated coronal
plasma and evaporated chromospheric material. This dual heating
mechanism provides new insights into how energy is transported and
dissipated during these powerful solar events, and highlights the
importance of spatially-resolved observations in understanding flare
processes.

For more details, see Ref. [2].

== Acknowledegement ==

This Nugget and Ref. [2] are the work of the author and colleagues
David H. Brooks, Shinsuke Imada, Ryan J. French, Lidia van Driel-
Gesztelyi, Deborah Baker, David M. Long, William Ashfield IV, and
Laura A. Hayes

== References ==

[1] [https://ui.adsabs.harvard.edu/abs/2018ApJ...853..178D/abstract "Photospheric and Coronal Abundances in an X8.3 Class Limb Flare"]

[2] [https://ui.adsabs.harvard.edu/abs/2024A%26A...691A..95T/abstract "Spatially resolved plasma composition evolution in a solar flare - The effect of reconnection outflow"]

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2024-11-19T17:20:59Z

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2024-11-06T09:43:50Z

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Main Page

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Dbarrous:

This is the official [[RHESSI]] Wiki. This wiki contains the following
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