explanation blue bibcodes open ADS page with paths to full text
Author name code: panesar
ADS astronomy entries on 2022-09-14
author:"Panesar, Navdeep Kaur"
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Title: Genesis and Coronal-jet-generating Eruption of a Solar
Minifilament Captured by IRIS Slit-raster Spectra
Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Moore, Ronald L.;
Sterling, Alphonse C.; De Pontieu, Bart
2022arXiv220900059P Altcode:
We present the first IRIS Mg II slit-raster spectra that fully capture
the genesis and coronal-jet-generating eruption of a central-disk solar
minifilament. The minifilament arose in a negative-magnetic-polarity
coronal hole. The Mg II spectroheliograms verify that the minifilament
plasma temperature is chromospheric. The Mg II spectra show that
the erupting minifilament's plasma has blueshifted upflow in the
jet spire's onset and simultaneous redshifted downflow at the
location of the compact jet bright point (JBP). From the Mg II
spectra together with AIA EUV images and HMI magnetograms, we find:
(i) the minifilament forms above a flux cancelation neutral line
at an edge of a negative-polarity network flux clump; (ii) during
the minifilament's fast-eruption onset and jet-spire onset, the
JBP begins brightening over the flux-cancelation neutral line. From
IRIS2 inversion of the Mg II spectra, the JBP's Mg II bright plasma
has electron density, temperature, and downward (red-shift) Doppler
speed of 1012 cm^-3, 6000 K, and 10 kms, respectively, and the growing
spire shows clockwise spin. We speculate: (i) during the slow rise
of the erupting minifilament-carrying twisted flux rope, the top of
the erupting flux-rope loop, by writhing, makes its field direction
opposite that of encountered ambient far-reaching field; (ii) the
erupting kink then can reconnect with the far-reaching field to make
the spire and reconnect internally to make the JBP. We conclude that
this coronal jet is normal in that magnetic flux cancelation builds a
minifilament-carrying twisted flux rope and triggers the JBP-generating
and jet-spire-generating eruption of the flux rope.
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Title: The Magnetic Origin of Solar Campfires: Observations by Solar
Orbiter and SDO
Authors: Panesar, Navdeep Kaur; Zhukov, Andrei; Berghmans, David;
Auchere, Frederic; Müller, Daniel; Tiwari, Sanjiv Kumar; Cheung, Mark
2022cosp...44.2564P Altcode:
Solar campfires are small-scale, short-lived coronal brightenings,
recently observed in 174 Å images by Extreme Ultraviolet Imager (EUI)
on board Solar Orbiter (SolO). Here we investigate the magnetic origin
of 52 campfires, in quiet-Sun, using line-of-sight magnetograms from
Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager
(HMI) together with extreme ultraviolet images from SolO /EUI and
SDO/Atmospheric Imaging Assembly (AIA). We find that the campfires
are rooted at the edges of photospheric magnetic network lanes; (ii)
most of the campfires reside above neutral lines and 77% of them appear
at sites of magnetic flux cancelation between the majority-polarity
magnetic flux patch and a merging minority-polarity flux patch, with
a flux cancelation rate of ∼1018 Mx hr‑1; some of the smallest
campfires come from the sites where magnetic flux elements were barely
discernible in HMI; (iii) some of the campfires occur repeatedly
from the same neutral line; (iv) in the large majority of instances
(79%), campfires are preceded by a cool-plasma structure, analogous to
minifilaments in coronal jets; and (v) although many campfires have
"complex" structure, most campfires resemble small-scale jets, dots,
or loops. Thus, "campfire" is a general term that includes different
types of small-scale solar dynamic features. They contain sufficient
magnetic energy (∼1026-1027 erg) to heat the solar atmosphere
locally to 0.5-2.5 MK. Their lifetimes range from about 1 minute to
over 1 hour, with most of the campfires having a lifetime of <10
minutes. The average lengths and widths of the campfires are 5400 ±
2500 km and 1600 ± 640 km, respectively. Our observations suggest that
(a) the presence of magnetic flux ropes may be ubiquitous in the solar
atmosphere and not limited to coronal jets and larger-scale eruptions
that make CMEs, and (b) magnetic flux cancelation, most likely driven
by magnetic reconnection in the lower atmosphere, is the fundamental
process for the formation and triggering of most campfires.
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Title: Fine-scale, Dot-like, Brightenings in an Emerging Flux Region:
SolO/EUI Observations, and Bifrost MHD Simulations
Authors: Tiwari, Sanjiv Kumar; Berghmans, David; De Pontieu, Bart;
Hansteen, Viggo; Panesar, Navdeep Kaur
2022cosp...44.2529T Altcode:
Numerous tiny bright dots are observed in SolO's EUI/\hri\ data
of an emerging flux region (a coronal bright point) in 174 \AA,
emitted by the coronal plasma at $\sim$1 MK. These dots are roundish,
with a diameter of 675$\pm$300 km, a lifetime of 50$\pm$35 seconds,
and an intensity enhancement of 30% $\pm$10% from their immediate
surroundings. About half of the dots remain isolated during their
evolution and move randomly and slowly ($<$10 \kms). The other half
show extensions, appearing as a small loop or surge/jet, with intensity
propagations below 30\,\kms. Some dots form at the end of a fine-scale
explosion. Many of the bigger and brighter EUI/HRI dots are discernible
in SDO/AIA 171 \AA\ channel, have significant EM in the temperature
range of 1--2 MK, and are often located at polarity inversion lines
observed in HMI LOS magnetograms. Bifrost MHD simulations of an emerging
flux region do show dots in synthetic Fe IX/X images, although dots
in simulations are not as pervasive as in observations. The dots
in simulations show distinct Doppler signatures -- blueshifts and
redshifts coexist, or a redshift of the order of 10 \kms\ is followed
by a blueshift of similar or higher magnitude. The synthetic images of
O V/VI and Si IV lines, which form in the transition region, also show
the dots that are observed in Fe IX/X images, often expanded in size,
or extended as a loop, and always with stronger Doppler velocities (up
to 100 \kms) than that in Fe IX/X lines. Our results, together with the
field geometry of dots in the simulations, suggest that most dots in
emerging flux regions form in the lower solar atmosphere (at $\approx$1
Mm) by magnetic reconnection between emerging and pre-existing/emerged
magnetic field. The dots are smaller in Fe IX/X images (than in O V/VI
& Si IV lines) most likely because only the hottest counterpart of
the magnetic reconnection events is visible in the hotter emission. Some
dots might be manifestations of magneto-acoustic shocks (from the
lower atmosphere) through the line formation region of Fe IX/X. A
small number of dots could also be a response of supersonic downflows
impacting transition-region/chromospheric density.
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Title: Observations of magnetic reconnection and particle acceleration
locations in solar coronal jets
Authors: Zhang, Yixian; Musset, Sophie; Glesener, Lindsay; Panesar,
Navdeep; Fleishman, Gregory
2022arXiv220705668Z Altcode:
We present a multi-wavelength analysis of two flare-related jets
on November 13, 2014, using data from SDO/AIA, RHESSI, Hinode/XRT,
and IRIS. Unlike most coronal jets where hard X-ray (HXR) emissions
are usually observed near the jet base, in these events HXR emissions
are found at several locations, including in the corona. We carry out
the first differential emission measure (DEM) analysis that combines
both AIA (and XRT when available) bandpass filter data and RHESSI HXR
measurements for coronal jets, and obtain self-consistent results
across a wide temperature range and into non-thermal energies. In
both events, hot plasma first appeared at the jet base, but as the
base plasma gradually cooled, hot plasma also appeared near the jet
top. Moreover, non-thermal electrons, while only mildly energetic,
are found in multiple HXR locations and contain a large amount of
total energy. Particularly, the energetic electrons that produced the
HXR sources at the jet top were accelerated near the top location,
rather than traveling from a reconnection site at the jet base. This
means that there was more than one particle acceleration site in
each event. Jet velocities are consistent with previous studies,
including upward and downward velocities around ~200 km/s and ~100
km/s respectively, and fast outflows of 400-700 km/s. We also examine
the energy partition in the later event, and find that the non-thermal
energy in accelerated electrons is most significant compared to other
energy forms considered. We discuss the interpretations and provide
constraints on mechanisms for coronal jet formation.
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Title: Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation,
and Solar Magnetic Explosions
Authors: Moore, Ronald L.; Panesar, Navdeep K.; Sterling, Alphonse C.;
Tiwari, Sanjiv K.
2022ApJ...933...12M Altcode: 2022arXiv220313287M
We examine the cradle-to-grave magnetic evolution of 10 bipolar
ephemeral active regions (BEARs) in solar coronal holes, especially
aspects of the magnetic evolution leading to each of 43 obvious
microflare events. The data are from the Solar Dynamics Observatory: 211
Å coronal EUV images and line-of-sight photospheric magnetograms. We
find evidence that (1) each microflare event is a magnetic explosion
that results in a miniature flare arcade astride the polarity
inversion line (PIL) of the explosive lobe of the BEAR's anemone
magnetic field; (2) relative to the BEAR's emerged flux-rope Ω loop,
the anemone's explosive lobe can be an inside lobe, an outside lobe,
or an inside-and-outside lobe; (3) 5 events are confined explosions,
20 events are mostly confined explosions, and 18 events are blowout
explosions, which are miniatures of the magnetic explosions that
make coronal mass ejections (CMEs); (4) contrary to the expectation
of Moore et al., none of the 18 blowout events explode from inside
the BEAR's Ω loop during the Ω loop's emergence; and (5) before
and during each of the 43 microflare events, there is magnetic flux
cancellation at the PIL of the anemone's explosive lobe. From finding
evident flux cancellation at the underlying PIL before and during all
43 microflare events-together with BEARs evidently being miniatures of
all larger solar bipolar active regions-we expect that in essentially
the same way, flux cancellation in sunspot active regions prepares
and triggers the magnetic explosions for many major flares and CMEs.
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Title: SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots
in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation
Authors: Tiwari, Sanjiv K.; Hansteen, Viggo H.; De Pontieu, Bart;
Panesar, Navdeep K.; Berghmans, David
2022ApJ...929..103T Altcode: 2022arXiv220306161T
We report on the presence of numerous tiny bright dots in and around
an emerging flux region (an X-ray/coronal bright point) observed with
SolO's EUI/HRI<SUB>EUV</SUB> in 174 Å. These dots are roundish and have
a diameter of 675 ± 300 km, a lifetime of 50 ± 35 s, and an intensity
enhancement of 30% ± 10% above their immediate surroundings. About
half of the dots remain isolated during their evolution and move
randomly and slowly (<10 km s<SUP>-1</SUP>). The other half show
extensions, appearing as a small loop or surge/jet, with intensity
propagations below 30 km s<SUP>-1</SUP>. Many of the bigger and brighter
HRI<SUB>EUV</SUB> dots are discernible in the SDO/AIA 171 Å channel,
have significant emissivity in the temperature range of 1-2 MK, and
are often located at polarity inversion lines observed in SDO/HMI LOS
magnetograms. Although not as pervasive as in observations, a Bifrost
MHD simulation of an emerging flux region does show dots in synthetic
Fe IX/X images. These dots in the simulation show distinct Doppler
signatures-blueshifts and redshifts coexist, or a redshift of the
order of 10 km s<SUP>-1</SUP> is followed by a blueshift of similar
or higher magnitude. The synthetic images of O V/VI and Si IV lines,
which represent transition region radiation, also show the dots that
are observed in Fe IX/X images, often expanded in size, or extended
as a loop, and always with stronger Doppler velocities (up to 100
km s<SUP>-1</SUP>) than that in Fe IX/X lines. Our observation and
simulation results, together with the field geometry of dots in the
simulation, suggest that most dots in emerging flux regions form in the
lower solar atmosphere (at ≍ 1 Mm) by magnetic reconnection between
emerging and preexisting/emerged magnetic field. Some dots might be
manifestations of magnetoacoustic shocks through the line formation
region of Fe IX/X emission.
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Title: Another Look at Erupting Minifilaments at the Base of Solar
X-Ray Polar Coronal "Standard" and "Blowout" Jets
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K.
2022ApJ...927..127S Altcode: 2022arXiv220112314S
We examine 21 solar polar coronal jets that we identify in soft X-ray
images obtained from the Hinode/X-ray telescope (XRT). We identify 11 of
these as blowout jets and four as standard jets (with six uncertain),
based on their X-ray-spire widths being respectively wide or narrow
(compared to the jet's base) in the XRT images. From corresponding
extreme ultraviolet (EUV) images from the Solar Dynamics Observatory's
(SDO) Atmospheric Imaging Assembly (AIA), essentially all (at least
20 of 21) of the jets are made by minifilament eruptions, consistent
with other recent studies. Here, we examine the detailed nature of the
erupting minifilaments (EMFs) in the jet bases. Wide-spire ("blowout")
jets often have ejective EMFs, but sometimes they instead have an
EMF that is mostly confined to the jet's base rather than ejected. We
also demonstrate that narrow-spire ("standard") jets can have either
a confined EMF, or a partially confined EMF where some of the cool
minifilament leaks into the jet's spire. Regarding EMF visibility:
we find that in some cases the minifilament is apparent in as few as
one of the four EUV channels we examined, being essentially invisible
in the other channels; thus, it is necessary to examine images from
multiple EUV channels before concluding that a jet does not have an
EMF at its base. The sizes of the EMFs, measured projected against the
sky and early in their eruption, is 14″ ± 7″, which is within a
factor of 2 of other measured sizes of coronal-jet EMFs.
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Title: Multi-wavelength Analysis of Two Flare-related RHESSI
Coronal Jets
Authors: Zhang, Yixian; Musset, Sophie; Glesener, Lindsay; Panesar,
Navdeep K.; Fleishman, Gregory
2021AGUFMSH25E2142Z Altcode:
Current models for solar coronal jets generally suggest that they are
formed by magnetic reconnection between open and closed magnetic field
lines, but details of triggering process for such magnetic reconnection
are still not fully clear. Here we present multi-wavelength analysis
of two flare-rated jets on November 13, 2014, using data from the
Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory
(SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI). Usually, hot plasma in a coronal jet is located near
the reconnection site or the base of the jet, as suggested by most
models. However, for these two events, both the differential emission
measure (DEM) analysis and RHESSI observations suggested that hot
plasma appeared not only at the base of the jet at the beginning of
each event, but also near the top of the jet a few minutes after the
starting time. We performed the first comparison of the DEM in extreme
ultraviolet (EUV) and the hard X-ray (HXR) spectrum for coronal jets,
which qualitatively validated the hot component of the DEM. In one of
the events, HXR emissions were observed at three different locations
and different times: first at the base of the jet, then near the top
of the jet, and finally at a location to the north of the jet. These
HXR sources showed evidence of accelerated electrons which extended
to fairly low energies. Jet velocities were consistent with previous
studies, including major upward and downward velocities of 200km/s
and 100km/s respectively, and fast outflows of 680km/s or 390km/s
only visible in the 131A filter. Combining the temperature profile,
the velocity profile, and the accelerated electron population for these
two events, this work will provide new constraints on mechanisms for
coronal jet formation.
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Title: Birth and Evolution of a Jet-Base-Topology Solar Magnetic
Field with Four Consecutive Major Flare Explosions
Authors: Doran, Ilana; Panesar, Navdeep K.; Tiwari, Sanjiv; Moore,
Ron; Bobra, Monica; Sterling, Alphonse
2021AGUFMSH35B2039D Altcode:
During 2011 September 6-8, NOAA solar active region (AR) 11283
produced four consecutive major coronal mass ejections (CMEs) each
with a co-produced major flare (GOES class M5.3, X2.1, X1.8, and
M6.7). We examined the ARs magnetic field evolution leading to and
following each of these major solar magnetic explosions. We follow
flux emergence, flux cancellation and magnetic shear buildup leading
to each explosion, and look for sudden flux changes and shear changes
wrought by each explosion. We use AIA 193 A images and line-of-sight
HMI vector magnetograms from Solar Dynamics Observatory (SDO), and
SunPy, SHARPkeys, and IDL Solarsoft to prepare and analyze these
data. The observed evolution of the vector field informs how magnetic
field emergence and cancellation lead to and trigger the magnetic
explosions, and thus informs how major CMEs and their flares are
produced. We find that (1) all four flares are triggered by flux
cancellation, (2) the third and fourth explosions (X1.8 and M6.7)
begin with a filament eruption from the cancellation neutral line,
(3) in the first and second explosions a filament erupts in the core
of a secondary explosion that lags the main explosion and is probably
triggered by Hudson-effect field implosion under the adjacent main
exploding field, and (4) the transverse field suddenly strengthens along
each main explosions underlying neutral line during the explosion,
also likely due to Hudson-effect field implosion. Our observations
are consistent with flux cancellation at the explosions underlying
neutral line being essential in the buildup and triggering of each
of the four explosions in the same way as in smaller-scale magnetic
explosions that drive coronal jets.
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Title: Characterizing Steady and Bursty Coronal Heating of a Solar
Active Region
Authors: Wilkerson, Lucy; Tiwari, Sanjiv; Panesar, Navdeep K.;
Moore, Ronald
2021AGUFMSH15E2060W Altcode:
One of the biggest problems in solar physics today is our inability
to explain why the solar corona is so hot. In this project, we
aimed to quantify transient and background coronal heating for a
given active region in order to better understand coronal heating. We
used SDO/AIA data of the active region NOAA 12712 observed on May 29,
2018 over a period of 24 hours with a 3-minute cadence. We calculated
FeXVIII emission (hot component of AIA 94 Å channel) by removing
warm components using AIA 171 and 193 Å channels. From the maximum,
minimum, and mean brightness values of each pixel over the full 24 hour
period, we made maximum, minimum, and mean brightness maps. We repeated
this process in moving time windows of 16 hours, 8 hours, 5 hours, 3
hours, 1 hour, and 30 minutes. We used the total luminosity for each
of these maps over time to make lightcurves that show the evolution
of maximum, minimum, and mean brightness over time for each running
window. Finally, we took the ratio of the total maximum and total
minimum luminosity to total mean luminosity, and plotted these ratios
over time. The average maximum to mean ratio was 8.40±0.00, 6.36±0.46,
5.29±0.34, 4.73±0.24, 4.19±0.19, 3.21±0.17, and 2.64±0.15 and the
average minimum to mean ratio was 0.053±0.00, 0.08±0.00, 0.12±0.01,
0.14±0.02, 0.17±0.02, 0.26±0.02, and 0.33±0.03 for 24h, 16h, 8h,
5h, 3h, 1h, and 30m windows, respectively. As expected, the ratio of
background to mean luminosity increased as the time window decreased,
and the ratio of transient to mean luminosity decreased as the time
window decreased. As such, the ratio of background to mean luminosity
is a new and effective technique to quantify the background intensity
of the active region. Our 24h window result suggests that at most 5%
of the luminosity of the AR at a given time comes from the steady
background heating. This upper limit increases to 33% of the luminosity
of the AR for the 30 min running window.
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Title: Solar Jet Hunter: a citizen science investigation of coronal
solar jets
Authors: Musset, Sophie; Glesener, Lindsay; Fortson, Lucy; Kapsiak,
Charles; Ostlund, Erik; Alnahari, Suhail; Jeunon, Mariana; Zhang,
Yixian; Panesar, Navdeep; Fleishman, Gregory; Hurlburt, Neal
2021AGUFMSA32A..07M Altcode:
The Sun is the source of energetic particles that fill the heliosphere,
interact with planets magnetospheres, and impact human activities. The
origins of those energetic particles are still under investigation,
as well as the mechanisms responsible for their escape from the solar
atmosphere where they are energized. Solar jets, collimated ejections of
solar plasma along magnetic field lines extending to the interplanetary
medium, offer a possible route for particle escape. Coronal solar
jets are commonly observed in soft X-rays and extreme ultraviolet
(EUV) and are ubiquitous in the solar atmosphere, assuming various
shapes, sizes and velocities. To date, autonomous algorithms are not
detecting solar jets reliably, and they are usually reported manually
by human observers, resulting in an incomplete and inhomogeneous
database of jets. In order to produce a reliable, extensive, and
consistent database of jets, that will be used to statistically study
the jet phenomenon and its relationship to solar energetic particles,
we initiated a citizen science project called Solar Jet Hunter whose
goal is to explore the huge amount of EUV observations of the Sun in
order to identify and characterize the solar jets in the dataset. The
resulting database will also be used to train algorithms to identify
solar jets in the EUV data. We will present here the preliminary
results of this Zooniverse project.
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Title: Campfires observed by EUI: What have we learned so far?
Authors: Berghmans, David; Auchere, F.; Zhukov, Andrei; Mierla,
Marilena; Chen, Yajie; Peter, Hardi; Panesar, Navdeep; Chitta, Lakshmi
Pradeep; Antolin, Patrick; Aznar Cuadrado, Regina; Tian, Hui; Hou,
Zhenyong; Podladchikova, Olena
2021AGUFMSH21A..02B Altcode:
Since its very first light images of the corona, the EUI/HRIEUV
telescope onboard Solar Orbiter has observed small localised
brightenings in the Quiet Sun. These small localised brightenings,
have become known as campfires, and are observed with length scales
between 400 km and 4000 km and durations between 10 sec and 200
sec. The smallest and weakest of these HRIEUV brightenings have
not been previously observed. Simultaneous observations from the
EUI High-resolution Lyman- telescope (HRILYA) do not show localised
brightening events, but the locations of the HRIEUV events clearly
correspond to the chromospheric network. Comparisons with simultaneous
AIA images shows that most events can also be identified in the
17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although
they appear weaker and blurred. Some of the larger campfires have
the appearance of small interacting loops with the brightening
expanding from the contact point of the loops. Our differential
emission measure (DEM) analysis indicated coronal temperatures. We
determined the height for a few of these campfires to be between 1
and 5 Mm above the photosphere. We interpret these events as a new
extension to the flare-microflare-nanoflare family. Given their low
height, the EUI campfires could stand as a new element of the fine
structure of the transition region-low corona, that is, as apexes
of small-scale loops that undergo internal heating all the way up to
coronal temperatures. 3D MHD simulations with the MURaM code revealed
brightenings that are in many ways similar to the campfires by EUI. The
brightenings in the simulations suggest that campfires are triggered by
component reconnection inside flux bundles rather than flux emergence
or cancellation. Nevertheless, some of the observed campfires can
be clearly linked to flux cancellation events and, intriguingly,
are preceded by an erupting cool plasma structure. Analysis of the
dynamics of campfires revealed that some have the appearance of coronal
microjets, the smallest coronal jets observed in the quiet Sun. The
HRIEUV images also reveal transient jets on a somewhat bigger scale
with repeated outflows on the order of 100 km s1. In this paper we
will provide an overview of the campfire related phenomena that EUI
has observed and discuss the possible relevance for coronal heating.
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Title: The Magnetic Origin of Solar Campfires
Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Berghmans, David;
Cheung, Mark C. M.; Müller, Daniel; Auchere, Frederic; Zhukov, Andrei
2021ApJ...921L..20P Altcode: 2021arXiv211006846P
Solar campfires are fine-scale heating events, recently observed by
Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Here we use EUI
174 Å images, together with EUV images from Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly (AIA), and line-of-sight magnetograms
from SDO/Helioseismic and Magnetic Imager (HMI) to investigate the
magnetic origin of 52 randomly selected campfires in the quiet solar
corona. We find that (i) the campfires are rooted at the edges of
photospheric magnetic network lanes; (ii) most of the campfires reside
above the neutral line between majority-polarity magnetic flux patch and
a merging minority-polarity flux patch, with a flux cancelation rate of
~10<SUP>18</SUP> Mx hr<SUP>-1</SUP>; (iii) some of the campfires occur
repeatedly from the same neutral line; (iv) in the large majority of
instances, campfires are preceded by a cool-plasma structure, analogous
to minifilaments in coronal jets; and (v) although many campfires have
"complex" structure, most campfires resemble small-scale jets, dots,
or loops. Thus, "campfire" is a general term that includes different
types of small-scale solar dynamic features. They contain sufficient
magnetic energy (~10<SUP>26</SUP>-10<SUP>27</SUP> erg) to heat the solar
atmosphere locally to 0.5-2.5 MK. Their lifetimes range from about 1
minute to over 1 hr, with most of the campfires having a lifetime of
<10 minutes. The average lengths and widths of the campfires are 5400
± 2500 km and 1600 ± 640 km, respectively. Our observations suggest
that (a) the presence of magnetic flux ropes may be ubiquitous in the
solar atmosphere and not limited to coronal jets and larger-scale
eruptions that make CMEs, and (b) magnetic flux cancelation is the
fundamental process for the formation and triggering of most campfires.
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Title: Multi-wavelength analysis of flare-related RHESSI coronal jets
Authors: Zhang, Y.; Musset, S.; Glesener, L.; Panesar, N.; Fleishman,
G.
2021AAS...23821315Z Altcode:
Current models for solar coronal jets generally suggest that they
are formed by magnetic reconnection between open and closed magnetic
field lines, but details of the triggering process for such magnetic
reconnection are still not fully clear. Here we report observations
of a set of coronal jets on November 13 2014 using data from the
Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the
Atmospheric Imaging Assembly (AIA). Usually, hot plasma in a coronal
jet is located near the reconnection site or the base of the jet, as
suggested by most models. However, for the first and one of the later
jets in this series, RHESSI found strong hard x-ray (HXR) emissions at
the top of the jet, well-modeled by an isothermal distribution, which
indicates the existence of hot material at the top. The differential
emission measure (DEM) analysis with AIA data shows qualitatively
consistent results with RHESSI observations, and we present a comparison
between HXR flux deduced from AIA DEMs and HXR flux directly measured by
RHESSI. To identify possible drivers for those jets, we calculate the
jet speeds in multiple AIA filters and compare them with, for example,
the upper limit of chromospheric evaporation. This work will provide
new constraints on mechanisms for coronal jet formation.
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Title: What Causes Faint Solar Coronal Jets From Emerging Flux
Regions In Coronal Holes?
Authors: Harden, A.; Panesar, N.; Moore, R.; Sterling, A.; Adams, M.
2021AAS...23821314H Altcode:
Using EUV images and line-of-sight magnetograms from Solar Dynamics
Observatory, we examine eight emerging bipolar magnetic regions (BMRs)
in central-disk coronal holes for whether the emerging magnetic arch
made any noticeable coronal jets directly, via reconnection with
ambient open field as modeled by Yokoyama & Shibata (1995). During
emergence, each BMR produced no obvious EUV coronal jet of normal
brightness, but each produced one or more faint EUV coronal jets that
are discernible in AIA 193 Å images. The spires of these jets are much
fainter and usually narrower than for typical EUV jets that have been
observed to be produced by minifilament eruptions in quiet regions and
coronal holes. For each of 26 faint jets from the eight emerging BMRs,
we examine whether the faint spire was evidently made a la Yokoyama
& Shibata (1995). We find: (1) 16 of these faint spires evidently
originate from sites of converging opposite-polarity magnetic flux
and show base brightenings like those in minifilament-eruption-driven
coronal jets, (2) the 10 other faint spires maybe were made by a burst
of the external-magnetic-arcade-building reconnection of the emerging
magnetic arch with the ambient open field, reconnection directly driven
by the arch's emergence, but (3) none were unambiguously made by such
emergence-driven reconnection. Thus, for these eight emerging BMRs,
the observations indicate that emergence-driven external reconnection
of the emerging magnetic arch with ambient open field at most produces
a jet spire that is much fainter than in previously-reported, much
more obvious coronal jets driven by minifilament eruptions.
---------------------------------------------------------
Title: Network Jets As The Driver Of Counter-streaming Flows In A
Solar Filament
Authors: Panesar, N. K.; Tiwari, S.; Moore, R.; Sterling, A.
2021AAS...23820506P Altcode:
We investigate the driving mechanism of counter-streaming flows
in a solar filament, using EUV images from SDO/AIA, line of sight
magnetograms from SDO/HMI, IRIS SJ images, and H-alpha data from
GONG. We find that: (i) persistent counter-streaming flows along
adjacent threads of a small (100" long) solar filament is present;
(ii) both ends of the solar filament are rooted at the edges of
magnetic network flux lanes; (iii) recurrent small-scale jets (also
known as network jets) occur at both ends of the filament; (iv) some
of the network jets occur at the sites of flux cancelation between the
majority-polarity flux and merging minority-polarity flux patches;
(v) these multiple network jets clearly drive the counter-streaming
flows along the adjacent threads of the solar filament for ~2 hours
with an average speed of 70 km s<SUP>-1</SUP>; (vi) some the network
jets show base brightenings, analogous to the base brightenings of
coronal jets; and (vii) the filament appears wider (4") in EUV images
than in H-alpha images (2.5"), consistent with previous studies. Thus,
our observations show that counter-streaming flows in the filament
are driven by network jets and possibly these driving network jet
eruptions are prepared and triggered by flux cancelation.
---------------------------------------------------------
Title: On Making Magnetic-flux-rope Omega Loops For Solar Bipolar
Magnetic Regions Of All Sizes By Convection Cells
Authors: Moore, R.; Tiwari, S.; Panesar, N.; Sterling, A.
2021AAS...23831318M Altcode:
This poster gives an overview of Moore, R. L., Tiwari, S. K., Panesar,
N. K., & Sterling, A. C. 2020, ApJ Letters, 902:L35. We propose that
the magnetic-flux-rope omega loop that emerges to become any bipolar
magnetic region (BMR) is made by a convection cell of the omega-loop's
size from initially horizontal magnetic field ingested through the
cell's bottom. This idea is based on (1) observed characteristics of
BMRs of all spans (~1000 to ~200,000 km), (2) a well-known simulation
of the production of a BMR by a supergranule-sized convection cell
from horizontal field placed at cell bottom, and (3) a well-known
convection-zone simulation. From the observations and simulations,
we (1) infer that the strength of the field ingested by the biggest
convection cells (giant cells) to make the biggest BMR omega loops
is ~10<SUP>3</SUP> G, (2) plausibly explain why the span and flux of
the biggest observed BMRs are ~200,000 km and ~10<SUP>22</SUP> Mx,
(3) suggest how giant cells might also make "failed BMR" omega loops
that populate the upper convection zone with horizontal field, from
which smaller convection cells make BMR omega loops of their size,
(4) suggest why sunspots observed in a sunspot cycle's declining
phase tend to violate the hemispheric helicity rule, and (5) support a
previously proposed amended Babcock scenario (Moore, R. L., Cirtain,
J. W., & Sterling, A. C. 2016, arXiv:1606.05371) for the sunspot
cycle's dynamo process. Because the proposed convection-based heuristic
model for making a sunspot-BMR omega loop avoids having ~10<SUP>5</SUP>
G field in the initial flux rope at the bottom of the convection zone,
it is an appealing alternative to the present magnetic-buoyancy-based
standard scenario and warrants testing by high-enough-resolution
giant-cell magnetoconvection simulations.
---------------------------------------------------------
Title: What Percentage Of The Brightest Coronal Loops Are Rooted In
Mixed-polarity Magnetic Flux?
Authors: Tiwari, S. K.; Evans, C. L.; Panesar, N.; Prasad, A.;
Moore, R.
2021AAS...23820502T Altcode:
We have previously shown (Tiwari et al. 2017, ApJ Letters, 843,
L20) that the heating in active region (AR) coronal loops depends
systematically on their photospheric magnetic setting. There, we found
that the brightest and hottest loops of ARs are the ones connecting
sunspot umbra/penumbra at one end to (a) penumbra, (b) unipolar plage,
or (c) mixed-polarity plage on the other end. The coolest loops are
the ones that connect sunspot umbra at both ends. In this work we
study the brightest loops during 24 hours in the core of the active
region that was observed by Hi-C 2.1. These loops have neither foot in
sunspot umbra or penumbra, but in plage. We investigate what percentage
of the brightest coronal loops (in SDO/AIA Fe XVIII emission) have
mixed-polarity magnetic flux at least at one of their feet, and so the
heating could be driven by magnetic flux cancellation. We confirm the
footpoint locations of loops via non-force-free field extrapolations
(using SDO/HMI magnetograms) and find that ∼40% of the loops have
both feet in unipolar flux, and ∼60% of the loops have at least one
foot in mixed-polarity flux. The loops having mixed-polarity foot-point
flux are ∼15% longer lived on average than the ones with both feet
unipolar, but their peak-intensity averages do not show any significant
difference. While the presence of mixed-polarity magnetic flux at least
at one foot in majority of loops strongly supports the cancellation
idea, the absence of mixed-polarity magnetic flux (to the detection
limit of HMI) in about 40% of the loops suggests cancellation may not be
necessary for heating coronal loops, but rather might enhance heating by
some factor. We will further discuss some points that support, and some
points that challenge, the flux cancellation idea of coronal heating.
---------------------------------------------------------
Title: What Causes Faint Solar Coronal Jets from Emerging Flux
Regions in Coronal Holes?
Authors: Harden, Abigail R.; Panesar, Navdeep K.; Moore, Ronald L.;
Sterling, Alphonse C.; Adams, Mitzi L.
2021ApJ...912...97H Altcode: 2021arXiv210307813H
Using EUV images and line-of-sight magnetograms from Solar Dynamics
Observatory, we examine eight emerging bipolar magnetic regions (BMRs)
in central-disk coronal holes for whether the emerging magnetic arch
made any noticeable coronal jets directly, via reconnection with ambient
open field as modeled by Yokoyama & Shibata. During emergence,
each BMR produced no obvious EUV coronal jet of normal brightness, but
each produced one or more faint EUV coronal jets that are discernible
in AIA 193 &angst; images. The spires of these jets are much
fainter and usually narrower than for typical EUV jets that have been
observed to be produced by minifilament eruptions in quiet regions and
coronal holes. For each of 26 faint jets from the eight emerging BMRs,
we examine whether the faint spire was evidently made a la Yokoyama
& Shibata. We find that (1) 16 of these faint spires evidently
originate from sites of converging opposite-polarity magnetic flux
and show base brightenings like those in minifilament-eruption-driven
coronal jets, (2) the 10 other faint spires maybe were made by a burst
of the external-magnetic-arcade-building reconnection of the emerging
magnetic arch with the ambient open field, with reconnection directly
driven by the arch's emergence, but (3) none were unambiguously made by
such emergence-driven reconnection. Thus, for these eight emerging BMRs,
the observations indicate that emergence-driven external reconnection
of the emerging magnetic arch with ambient open field at most produces
a jet spire that is much fainter than in previously reported, much
more obvious coronal jets driven by minifilament eruptions.
---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
---------------------------------------------------------
Title: Are the Brightest Coronal Loops Always Rooted in Mixed-polarity
Magnetic Flux?
Authors: Tiwari, Sanjiv K.; Evans, Caroline L.; Panesar, Navdeep K.;
Prasad, Avijeet; Moore, Ronald L.
2021ApJ...908..151T Altcode: 2021arXiv210210146T
A recent study demonstrated that freedom of convection and strength of
magnetic field in the photospheric feet of active-region (AR) coronal
loops, together, can engender or quench heating in them. Other studies
stress that magnetic flux cancellation at the loop-feet potentially
drives heating in loops. We follow 24 hr movies of a bipolar AR, using
extreme ultraviolet images from the Atmospheric Imaging Assembly/Solar
Dynamics Observatory (SDO) and line-of-sight (LOS) magnetograms from
the Helioseismic and Magnetic Imager (HMI)/SDO, to examine magnetic
polarities at the feet of 23 of the brightest coronal loops. We derived
Fe XVIII emission (hot-94) images (using the Warren et al. method)
to select the hottest/brightest loops, and confirm their footpoint
locations via non-force-free field extrapolations. From 6″ × 6″
boxes centered at each loop foot in LOS magnetograms we find that ∼40%
of the loops have both feet in unipolar flux, and ∼60% of the loops
have at least one foot in mixed-polarity flux. The loops with both feet
unipolar are ∼15% shorter lived on average than the loops having
mixed-polarity foot-point flux, but their peak-intensity averages
are equal. The presence of mixed-polarity magnetic flux in at least
one foot in the majority of the loops suggests that flux cancellation
at the footpoints may drive most of the heating. But the absence of
mixed-polarity magnetic flux (to the detection limit of HMI) in ∼40%
of the loops suggests that flux cancellation may not be necessary to
drive heating in coronal loops—magnetoconvection and field strength
at both loop feet possibly drive much of the heating, even in the
cases where a loop foot presents mixed-polarity magnetic flux.
---------------------------------------------------------
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of a solar active region: Hi-C 2.1,
IRIS and SDO observations
Authors: Tiwari, Sanjiv Kumar; Moore, Ronald; De Pontieu, Bart;
Winebarger, Amy; Panesar, Navdeep Kaur
2021cosp...43E1779T Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
(~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 A, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is resemble IRIS bombs (in size,
and brightness with respect to surroundings), our dot-like events are
apparently much hotter, and shorter in span (70 s). Because Dot-like
brightenings are not as clearly discernible in AIA 171 A as in Hi-C 172
A, they were not reported before. We complement the 5-minute-duration
Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images,
and IRIS UV spectra and slit-jaw images to examine, at the sites of
these events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the microflare's polarity inversion line. In the
IRIS spectra and images, we find confirming evidence of field-aligned
outflow from brightenings at the ends of loops of the arch filament
system. In types I and II the explosion is confined, while in type
III the explosion is ejective and drives jet-like outflow. The light
curves from Hi-C, AIA and IRIS peak nearly simultaneously for many
of these events and none of the events display a systematic cooling
sequence as seen in typical coronal flares, suggesting that these tiny
brightening events have chromospheric/transition-region origin.
---------------------------------------------------------
Title: Coronal Jets Observed at Sites of Magnetic Flux Cancelation
Authors: Panesar, Navdeep Kaur; Sterling, Alphonse; Moore, Ronald;
Tiwari, Sanjiv Kumar
2021cosp...43E1783P Altcode:
Solar jets of all sizes are magnetically channeled narrow eruptive
events; the larger ones are often observed in the solar corona in EUV
and coronal X-ray images. Recent observations show that the buildup and
triggering of the minifilament eruptions that drive coronal jets result
from magnetic flux cancelation under the minifilament, at the neutral
line between merging majority-polarity and minority-polarity magnetic
flux patches. Here we investigate the magnetic setting of on-disk
small-scale jets (also known as jetlets) by using high resolution 172A
images from the High-resolution Coronal Imager (Hi-C2.1) and EUV images
from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA), and UV images from the Interface Region Imaging Spectrograph
(IRIS), and line-of-sight magnetograms from the SDO/Helioseismic
and Magnetic Imager (HMI). We observe jetlets at edges of magnetic
network lanes. From magnetograms co-aligned with the Hi-C, IRIS,
and AIA images, we find that the jetlets stem from sites of flux
cancelation between merging majority-polarity and minority-polarity
flux patches, and some of the jetlets show faint brightenings at their
bases reminiscent of the base brightenings in coronal jets. Based on
these observations of jetlets and our previous observations of ∼90
coronal jets in quiet regions and coronal holes, we infer that flux
cancelation is the essential process in the buildup and triggering of
jetlets. Our observations suggest that network jetlet eruptions are
small-scale analogs of both larger-scale coronal jet eruptions and
the still-larger-scale eruptions that make major CMEs.
---------------------------------------------------------
Title: Citizen science to identify and analyze coronal jets in
SDO/AIA data
Authors: Musset, S.; Glesener, L.; Fortson, L.; Wright, D.; Kapsiak,
C.; Hurlburt, N. E.; Panesar, N. K.; Fleishman, G. D.
2020AGUFMSH0240006M Altcode:
Coronal jets are collimated ejections of plasma that are found to
be ubiquitous in the solar atmosphere, at different scales and in
different regions of the Sun. They are interpreted as the result of
energy release in the solar atmosphere when magnetic reconnection
involves both closed and open magnetic field lines. Jets are therefore
suspected to be associated with the escape of energetic particles
from the solar atmosphere and possibly with perturbations of the solar
wind. The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
Observatory (SDO) provides high-cadence and high-resolution images
of the solar atmosphere in which coronal jets can be identified and
studied. However, the detection of such events via automatic algorithms
has been limited and is better achieved by human annotation of the
data. In order to detect and catalog coronal jets in the AIA data set,
we designed a citizen science project on the Zooniverse platform, where
participants can report the precise position and timing of solar jets,
along with an indication of their extent. The use of citizen science
provides the opportunity to perform this kind of analysis on a large
amount of data, and to derive the average values of the jet properties
reported by multiple volunteers, removing some of the bias inherent in
a single expert observer reporting such properties. This catalog of jet
events will provide a useful database for future jet studies, including
statistical studies, and a training set for a machine learning approach
to the problem of the detection of coronal jets in EUV data sets.
---------------------------------------------------------
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of a solar active region: Hi-C 2.1,
IRIS and SDO observations
Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu,
B.; Winebarger, A. R.
2020AGUFMSH0010007T Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
(~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is resemble IRIS bombs (in size,
and brightness with respect to surroundings), our dot-like events are
apparently much hotter, and shorter in span (70 s). Because Dot-like
brightenings are not as clearly discernible in AIA 171 Å as in Hi-C 172
Å, they were not reported before. We complement the 5-minute-duration
Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images,
and IRIS UV spectra and slit-jaw images to examine, at the sites of
these events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the microflare's polarity inversion line. In the
IRIS spectra and images, we find confirming evidence of field-aligned
outflow from brightenings at the ends of loops of the arch filament
system. In types I and II the explosion is confined, while in type
III the explosion is ejective and drives jet-like outflow. The light
curves from Hi-C, AIA and IRIS peak nearly simultaneously for many
of these events and none of the events display a systematic cooling
sequence as seen in typical coronal flares, suggesting that these tiny
brightening events have chromospheric/transition-region origin.
---------------------------------------------------------
Title: Network Jets as the Driver of Counter-streaming Flows in a
Solar Filament
Authors: Panesar, N. K.; Tiwari, S. K.; Moore, R. L.; Sterling, A. C.
2020AGUFMSH0240004P Altcode:
We investigate the driving mechanism of counter-streaming flows
in a solar filament, using EUV images from SDO/AIA, line of sight
magnetograms from SDO/HMI, IRIS SJ images, and H-alpha data from
GONG. We find that: (i) persistent counter-streaming flows along
adjacent threads of a small (100" long) solar filament is present;
(ii) both ends of the solar filament are rooted at the edges of
magnetic network flux lanes; (iii) recurrent small-scale jets (also
known as network jets) occur at both ends of the filament; (iv) some
of the network jets occur at the sites of flux cancelation between the
majority-polarity flux and merging minority-polarity flux patches;
(v) these multiple network jets clearly drive the counter-streaming
flows along the adjacent threads of the solar filament for ~2 hours
with an average speed of 70 km s<SUP>-1</SUP>; (vi) some the network
jets show base brightenings, analogous to the base brightenings of
coronal jets; and (vii) the filament appears wider (4") in EUV images
than in H-alpha images (2.5"), consistent with previous studies. Thus,
our observations show that counter-streaming flows in the filament
are driven by network jets and possibly these driving network jet
eruptions are prepared and triggered by flux cancelation.
---------------------------------------------------------
Title: On Making Magnetic-flux-rope Ω Loops for Solar Bipolar
Magnetic Regions of All Sizes by Convection Cells
Authors: Moore, Ronald L.; Tiwari, Sanjiv K.; Panesar, Navdeep K.;
Sterling, Alphonse C.
2020ApJ...902L..35M Altcode: 2020arXiv200913694M
We propose that the flux-rope Ω loop that emerges to become any bipolar
magnetic region (BMR) is made by a convection cell of the Ω-loop's size
from initially horizontal magnetic field ingested through the cell's
bottom. This idea is based on (1) observed characteristics of BMRs
of all spans (∼1000 to ∼200,000 km), (2) a well-known simulation
of the production of a BMR by a supergranule-sized convection cell
from horizontal field placed at cell bottom, and (3) a well-known
convection-zone simulation. From the observations and simulations,
we (1) infer that the strength of the field ingested by the biggest
convection cells (giant cells) to make the biggest BMR Ω loops is
∼10<SUP>3</SUP> G, (2) plausibly explain why the span and flux of
the biggest observed BMRs are ∼200,000 km and ∼10<SUP>22</SUP>
Mx, (3) suggest how giant cells might also make "failed-BMR" Ω loops
that populate the upper convection zone with horizontal field, from
which smaller convection cells make BMR Ω loops of their size, (4)
suggest why sunspots observed in a sunspot cycle's declining phase
tend to violate the hemispheric helicity rule, and (5) support a
previously proposed amended Babcock scenario for the sunspot cycle's
dynamo process. Because the proposed convection-based heuristic model
for making a sunspot-BMR Ω loop avoids having ∼10<SUP>5</SUP> G
field in the initial flux rope at the bottom of the convection zone,
it is an appealing alternative to the present magnetic-buoyancy-based
standard scenario and warrants testing by high-enough-resolution
giant-cell magnetoconvection simulations.
---------------------------------------------------------
Title: Possible Evolution of Minifilament-Eruption-Produced Solar
Coronal Jets, Jetlets, and Spicules, into Magnetic-Twist-Wave
“Switchbacks” Observed by the Parker Solar Probe (PSP)
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K.;
Samanta, Tanmoy
2020JPhCS1620a2020S Altcode: 2020arXiv201012991S
Many solar coronal jets result from erupting miniature-filament
(“minifilament”) magnetic flux ropes that reconnect with encountered
surrounding far-reaching field. Many of those minifilament flux
ropes are apparently built and triggered to erupt by magnetic flux
cancelation. If that cancelation (or some other process) results in
the flux rope’s field having twist, then the reconnection with the
far-reaching field transfers much of that twist to that reconnected
far-reaching field. In cases where that surrounding field is open, the
twist can propagate to far distances from the Sun as a magnetic-twist
Alfvénic pulse. We argue that such pulses from jets could be the
kinked-magnetic-field structures known as “switchbacks,” detected
in the solar wind during perihelion passages of the Parker Solar Probe
(PSP). For typical coronal-jet-generated Alfvénic pulses, we expect
that the switchbacks would flow past PSP with a duration of several
tens of minutes; larger coronal jets might produce switchbacks with
passage durations ∼1hr. Smaller-scale jet-like features on the Sun
known as “jetlets” may be small-scale versions of coronal jets,
produced in a similar manner as the coronal jets. We estimate that
switchbacks from jetlets would flow past PSP with a duration of a few
minutes. Chromospheric spicules are jet-like features that are even
smaller than jetlets. If some portion of their population are indeed
very-small-scale versions of coronal jets, then we speculate that the
same processes could result in switchbacks that pass PSP with durations
ranging from about ∼2 min down to tens of seconds.
---------------------------------------------------------
Title: Network Jets as the Driver of Counter-streaming Flows in a
Solar Filament/Filament Channel
Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Moore, Ronald L.;
Sterling, Alphonse C.
2020ApJ...897L...2P Altcode: 2020arXiv200604249P
Counter-streaming flows in a small (100″ long) solar filament/filament
channel are directly observed in high-resolution Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) extreme-ultraviolet
(EUV) images of a region of enhanced magnetic network. We combine
images from SDO/AIA, SDO/Helioseismic and Magnetic Imager (HMI), and the
Interface Region Imaging Spectrograph (IRIS) to investigate the driving
mechanism of these flows. We find that: (I) counter-streaming flows are
present along adjacent filament/filament channel threads for ∼2 hr,
(II) both ends of the filament/filament channel are rooted at the
edges of magnetic network flux lanes along which there are impinging
fine-scale opposite-polarity flux patches, (III) recurrent small-scale
jets (known as network jets) occur at the edges of the magnetic network
flux lanes at the ends of the filament/filament channel, (IV) the
recurrent network jet eruptions clearly drive the counter-streaming
flows along threads of the filament/filament channel, (V) some
of the network jets appear to stem from sites of flux cancelation,
between network flux and merging opposite-polarity flux, and (VI) some
show brightening at their bases, analogous to the base brightening in
coronal jets. The average speed of the counter-streaming flows along the
filament/filament channel threads is 70 km s<SUP>-1</SUP>. The average
widths of the AIA filament/filament channel and the Hα filament are
4″ and 2"5, respectively, consistent with the earlier findings
that filaments in EUV images are wider than in Hα images. Thus,
our observations show that the continually repeated counter-streaming
flows come from network jets, and these driving network jet eruptions
are possibly prepared and triggered by magnetic flux cancelation.
---------------------------------------------------------
Title: Onset of Magnetic Explosion in Solar Coronal Jets in Quiet
Regions on the Central Disk
Authors: Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C.
2020ApJ...894..104P Altcode: 2020arXiv200604253P
We examine the initiation of 10 coronal jet eruptions in quiet
regions on the central disk, thereby avoiding near-limb spicule-forest
obscuration of the slow-rise onset of the minifilament eruption. From
the Solar Dynamics Observatory/Atmospheric Imaging Assembly 171 Å 12
s cadence movie of each eruption, we (1) find and compare the start
times of the minifilament's slow rise, the jet-base bright point,
the jet-base-interior brightening, and the jet spire, and (2) measure
the minifilament's speed at the start and end of its slow rise. From
(a) these data, (b) prior observations showing that each eruption was
triggered by magnetic flux cancelation under the minifilament, and
(c) the breakout-reconnection current sheet observed in one eruption,
we confirm that quiet-region jet-making minifilament eruptions are
miniature versions of CME-making filament eruptions, and surmise that
in most quiet-region jets: (1) the eruption starts before runaway
reconnection starts, (2) runaway reconnection does not start until
the slow-rise speed is at least ∼1 km s<SUP>-1</SUP>, and (3) at
and before eruption onset, there is no current sheet of appreciable
extent. We therefore expect that (I) many CME-making filament eruptions
are triggered by flux cancelation under the filament, (II) emerging
bipoles seldom, if ever, directly drive jet production because the
emergence is seldom, if ever, fast enough, and (III) at a separatrix
or quasi-separatrix in any astrophysical setting of a magnetic field
in low-beta plasma, a current sheet of appreciable extent can be built
only dynamically by a magnetohydrodynamic convulsion of the field,
not by quasi-static gradual converging of the field.
---------------------------------------------------------
Title: A Solar Magnetic-fan Flaring Arch Heated by Nonthermal
Particles and Hot Plasma from an X-Ray Jet Eruption
Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi,
Anand D.; Brooks, David H.; Imada, Shinsuke; Prasad, Avijeet; Dang,
Phillip; Shimizu, Toshifumi; Savage, Sabrina L.; Moore, Ronald;
Panesar, Navdeep K.; Reep, Jeffrey W.
2020ApJ...895...42L Altcode: 2020arXiv200509875L
We have investigated an M1.3 limb flare, which develops as a magnetic
loop/arch that fans out from an X-ray jet. Using Hinode/EIS, we
found that the temperature increases with height to a value of over
10<SUP>7</SUP> K at the loop top during the flare. The measured Doppler
velocity (redshifts of 100-500 km s<SUP>-1</SUP>) and the nonthermal
velocity (≥100 km s<SUP>-1</SUP>) from Fe XXIV also increase with
loop height. The electron density increases from 0.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> early in the flare rise to 1.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> after the flare peak. The 3D structure of the loop
derived with Solar TErrestrial RElations Observatory/EUV Imager
indicates that the strong redshift in the loop-top region is due to
upflowing plasma originating from the jet. Both hard X-ray and soft
X-ray emission from the Reuven Ramaty High Energy Solar Spectroscopic
Imager were only seen as footpoint brightenings during the impulsive
phase of the flare, then, soft X-ray emission moved to the loop top in
the decay phase. Based on the temperature and density measurements and
theoretical cooling models, the temperature evolution of the flare arch
is consistent with impulsive heating during the jet eruption followed
by conductive cooling via evaporation and minor prolonged heating in
the top of the fan loop. Investigating the magnetic field topology and
squashing factor map from Solar Dynamics Observatory/HMI, we conclude
that the observed magnetic-fan flaring arch is mostly heated from low
atmospheric reconnection accompanying the jet ejection, instead of from
reconnection above the arch as expected in the standard flare model.
---------------------------------------------------------
Title: Hi-C 2.1 Observations of Small-scale
Miniature-filament-eruption-like Cool Ejections in an Active Region
Plage
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep
K.; Reardon, Kevin P.; Molnar, Momchil; Rachmeler, Laurel A.; Savage,
Sabrina L.; Winebarger, Amy R.
2020ApJ...889..187S Altcode: 2019arXiv191202319S
We examine 172 Å ultra-high-resolution images of a solar plage region
from the High-Resolution Coronal Imager, version 2.1 (Hi-C 2.1, or Hi-C)
rocket flight of 2018 May 29. Over its five minute flight, Hi-C resolved
a plethora of small-scale dynamic features that appear near noise level
in concurrent Solar Dynamics Observatory (SDO) Atmospheric Imaging
Assembly (AIA) 171 Å images. For 10 selected events, comparisons with
AIA images at other wavelengths and with Interface Region Imaging
Spectrograph (IRIS) images indicate that these features are cool
(compared to the corona) ejections. Combining Hi-C 172 Å, AIA 171 Å,
IRIS 1400 Å, and Hα, we see that these 10 cool ejections are similar
to the Hα "dynamic fibrils" and Ca II "anemone jets" found in earlier
studies. The front of some of our cool ejections are likely heated,
showing emission in IRIS 1400 Å. On average, these cool ejections
have approximate widths 3"2 ± 2"1, (projected) maximum heights and
velocities 4"3 ± 2"5 and 23 ± 6 km s<SUP>-1</SUP>, and lifetimes 6.5
± 2.4 min. We consider whether these Hi-C features might result from
eruptions of sub-minifilaments (smaller than the minifilaments that
erupt to produce coronal jets). Comparisons with SDO's Helioseismic and
Magnetic Imager (HMI) magnetograms do not show magnetic mixed-polarity
neutral lines at these events' bases, as would be expected for true
scaled-down versions of solar filaments/minifilaments. But the features'
bases are all close to single-polarity strong-flux-edge locations,
suggesting possible local opposite-polarity flux unresolved by HMI. Or
it may be that our Hi-C ejections instead operate via the shock-wave
mechanism that is suggested to drive dynamic fibrils and the so-called
type I spicules.
---------------------------------------------------------
Title: A CME-Producing Solar Eruption from the Interior of a Twisted
Emerging Bipole
Authors: Moore, R. L.; Adams, M.; Panesar, N. K.; Falconer, D. A.;
Tiwari, S. K.
2019AGUFMSH43D3355M Altcode:
In a negative-polarity coronal hole, magnetic flux emergence, seen by
the Solar Dynamics Observatory's (SDO) Helioseismic Magnetic Imager
(HMI), begins at approximately 19:00 UT on March 3, 2016. The emerged
magnetic field produced sunspots with penumbrae by 3:00 UT on March
4, which NOAA numbered 12514. The emerging magnetic field is largely
bipolar with the opposite-polarity fluxes spreading apart overall,
but there is simultaneously some convergence and cancellation of
opposite-polarity flux at the polarity inversion line (PIL) inside the
emerging bipole. The emerging bipole shows obvious overall left-handed
shear and/or twist in its magnetic field and corresponding clockwise
rotation of the two poles of the bipole about each other as the bipole
emerges. The eruption comes from inside the emerging bipole and blows
it open to produce a CME observed by SOHO/LASCO. That eruption is
preceded by flux cancellation at the emerging bipole's interior PIL,
cancellation that plausibly builds a sheared and twisted flux rope
above the interior PIL and finally triggers the blow-out eruption of
the flux rope via photospheric-convection-driven slow tether-cutting
reconnection of the legs of the sheared core field, low above the
interior PIL, as proposed by van Ballegooijen and Martens (1989, ApJ,
343, 971) and Moore and Roumeliotis (1992, in Eruptive Solar Flares,
ed. Z. Svestka, B.V. Jackson, and M.E. Machado [Berlin:Springer],
69). The production of this eruption is a (perhaps rare) counterexample
to solar eruptions that result from external collisional shearing
between opposite polarities from two distinct emerging and/or emerged
bipoles (Chintzoglou et al., 2019, ApJ, 871:67).
---------------------------------------------------------
Title: Are the brightest coronal loops always rooted in mixed-polarity
magnetic flux?
Authors: Evans, C.; Tiwari, S. K.; Panesar, N. K.; Prasad, A.; Moore,
R. L.
2019AGUFMSH41F3324E Altcode:
Magnetic energy dissipated in coronal loops heats the Sun's corona
to millions of Kelvin. Some recent investigations indicate that in
addition to the required magnetoconvection and field strength, heating
in the brightest coronal loops are driven by flux cancellation at
the loop-feet. To find coronal loop footpoints , we selected extreme
ultraviolet (EUV) data from the Atmospheric Imaging Assembly (AIA)
and line- of-sight (LOS) magnetograms from the Helioseismic and
Magnetic Imager (HMI), both on-board the Solar Dynamics Observatory
(SDO). We located the footpoints of 28 brightest coronal loops of
the bipolar active region NOAA 12712 on 28 May 2018 in hot 94 images
(calculated using the Warren et al. method) and confirm the location
of these footpoints via non-force free field extrapolations. We examine
the photospheric magnetic field in 6" boxes centered at each footpoint
and find that ~20% of loops have both feet in unipolar magnetic flux,
~10% loops have both feet in mixed-polarity flux, and ~70% of loops
have one foot in unipolar and one in mixed-polarity flux. The presence
of mixed-polarity magnetic flux in at least one foot of majority
of the brightest coronal loops suggests that flux cancellation at
the footpoints may drive heating in them. However, the absence of
mixed-polarity magnetic flux (to the detection limit of HMI) in a
significant number of the brightest coronal loops suggests that flux
cancellation may not be necessary to drive heating in the loops - the
combination of magnetoconvection and the magnetic field strength at the
footpoints could be responsible for much of the coronal loop heating
even in cases where a footpoint presents mixed-polarity magnetic flux.
---------------------------------------------------------
Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar
Magnetic Network Lanes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon
E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P.
2019ApJ...887L...8P Altcode: 2019arXiv191102331P
We present high-resolution, high-cadence observations of six,
fine-scale, on-disk jet-like events observed by the High-resolution
Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We
combine the Hi-C 2.1 images with images from the Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface
Region Imaging Spectrograph (IRIS), and investigate each event’s
magnetic setting with co-aligned line-of-sight magnetograms from the
SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six
events are jetlet-like (having apparent properties of jetlets), (ii)
all six are rooted at edges of magnetic network lanes, (iii) four of
the jetlet-like events stem from sites of flux cancelation between
majority-polarity network flux and merging minority-polarity flux, and
(iv) four of the jetlet-like events show brightenings at their bases
reminiscent of the base brightenings in coronal jets. The average
spire length of the six jetlet-like events (9000 ± 3000 km) is three
times shorter than that for IRIS jetlets (27,000 ± 8000 km). While
not ruling out other generation mechanisms, the observations suggest
that at least four of these events may be miniature versions of both
larger-scale coronal jets that are driven by minifilament eruptions
and still-larger-scale solar eruptions that are driven by filament
eruptions. Therefore, we propose that our Hi-C events are driven by
the eruption of a tiny sheared-field flux rope, and that the flux rope
field is built and triggered to erupt by flux cancelation.
---------------------------------------------------------
Title: Fine-scale explosive energy release at sites of magnetic flux
cancellation in the core of the solar active region observed by Hi-C
2.1, IRIS and SDO
Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu,
B.; Winebarger, A. R.
2019AGUFMSH31C3323T Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
---------------------------------------------------------
Title: Cradle-to-Grave Evolution and Explosiveness of the Magnetic
Field from Bipolar Ephemeral Active Regions (BEARs) in Solar
Coronal Holes
Authors: Panesar, N. K.; Nagib, C.; Moore, R. L.; Sterling, A. C.
2019AGUFMSH11D3386P Altcode:
We report on the entire magnetic evolution and history of
magnetic-explosion eruption production of each of 7 bipolar
ephemeral active regions (BEARs) observed in on-disk coronal holes
in line-of-sight magnetograms and in coronal EUV images. One of
these BEARs made no eruptions. The other 6 BEARs together display
three kinds of magnetic-explosion eruptions: (1) blowout eruptions
(eruptions that make a wide-spire blowout jet), (2) partially-confined
eruptions (eruptions that make a narrow-spire standard jet), (3)
confined eruptions (eruptions that make no jet, i.e., make only a
spireless EUV microflare). The 7 BEARs are a subset of a set of 60
random coronal-hole BEARs that were observed from the advent to the
final dissolution of the BEAR's minority-polarity magnetic flux. The
emergence phase (time interval from advent to maximum minority flux)
for the 60 BEARs had been previously visually estimated using the
magnetograms, to find if magnetic-explosion eruption events commonly
occur inside a BEAR's emerging magnetic field (as had been assumed by
Moore et al 2010, ApJ 720:757). That inspection found no inside eruption
during the estimated emergence phase of any of the 60 BEARs. In this new
work, for each of the 7 BEARs, we obtain a more reliable determination
of when the emergence phase ended by finding the time of the BEAR's
maximum minority flux from a time plot of the BEAR's minority flux
measured from the magnetograms. These plots show: (1) none of the 7
BEARs had an inside eruption while the BEAR was emerging, and (2)
for these 7 BEARs, the visually-estimated emergence end time was
never more than 6 hours before the measured time of maximum minority
flux. Of the 60 BEARs, in only 6 was there an inside eruption within
6 hours after the visually-estimated end of emergence. The above two
results for the 7 BEARs, together with the previous visual inspection
of the 60 BEARs, support that a great majority (at least 90%) of the
explosive magnetic fields from BEARs in coronal holes are prepared
and triggered to explode by magnetic flux cancellation, and that
such flux cancellation seldom occurs inside an emerging BEAR. The
visual inspection of the magnetograms of the 60 BEARs showed that the
pre-eruption flux cancellation was either on the outside of the BEAR
during or after the BEAR's emergence or on the inside of the BEAR
after the BEAR's emergence.
---------------------------------------------------------
Title: Onset of the Magnetic Explosion in On-disk Solar Coronal Jets
Authors: Panesar, N. K.; Moore, R. L.; Sterling, A. C.
2019AGUFMSH11D3384P Altcode:
In our recent studies of ~10 quiet region and ~13 coronal hole coronal,
we found that flux cancelation is the fundamental process in the
buildup and triggering of the minifilament eruption that drives the
production of the jet. Here, we investigate the onset and growth of
the ten on-disk quiet region jets, using EUV images from SDO/AIA and
magnetograms from SDO/HMI. We find that: (i) in all ten events the
minifilament starts to rise at or before the onset of the signature
of internal or external reconnection; (ii) in two out of ten jets
brightening from the external reconnection starts at the same time as
the slow rise of the minifilament and (iii) in six out of ten jets
brightening from the internal reconnection starts before the start
of the brightening from external reconnection. These observations
show that the magnetic explosion in coronal jets begins in the same
way as the magnetic explosion in filament eruptions that make solar
flares and coronal mass ejections (CMEs). Our results indicate (1) that
coronal jets are miniature versions of CME-producing eruptions and flux
cancelation is the fundamental process that builds and triggers both
the small-scale and the large-scale eruptions, and (2) that, contrary to
the view of Moore et al (2018), the current sheet at which the external
reconnection occurs in coronal jets usually starts to form at or after
the onset of (and as a result of) the slow rise of the minifilament
flux-rope eruption, and so is seldom of appreciable size before the
onset of the slow rise of the minifilament flux-rope eruption.
---------------------------------------------------------
Title: Fine-scale Explosive Energy Release at Sites of Prospective
Magnetic Flux Cancellation in the Core of the Solar Active Region
Observed by Hi-C 2.1, IRIS, and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.;
De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.;
Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Walsh, Robert W.
2019ApJ...887...56T Altcode: 2019arXiv191101424T
The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial
and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X
emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56
UT. Three morphologically different types (I: dot-like; II: loop-like;
III: surge/jet-like) of fine-scale sudden-brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is (not reported before) resemble
IRIS bombs (in size, and brightness with respect to surroundings),
our dot-like events are apparently much hotter and shorter in span
(70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI
magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
images to examine, at the sites of these events, brightenings and
flows in the transition region and corona and evolution of magnetic
flux in the photosphere. Most, if not all, of the events are seated
at sites of opposite-polarity magnetic flux convergence (sometimes
driven by adjacent flux emergence), implying likely flux cancellation
at the microflare’s polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. In types
I and II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow. The light curves from Hi-C,
AIA, and IRIS peak nearly simultaneously for many of these events,
and none of the events display a systematic cooling sequence as seen in
typical coronal flares, suggesting that these tiny brightening events
have chromospheric/transition region origin.
---------------------------------------------------------
Title: Magnetic Flux Cancellation as the Trigger Mechanism of Solar
Coronal Jets
Authors: McGlasson, Riley A.; Panesar, Navdeep K.; Sterling, Alphonse
C.; Moore, Ronald L.
2019ApJ...882...16M Altcode: 2019arXiv190606452M
Coronal jets are transient narrow features in the solar corona that
originate from all regions of the solar disk: active regions, quiet Sun,
and coronal holes. Recent studies indicate that at least some coronal
jets in quiet regions and coronal holes are driven by the eruption of a
minifilament following flux cancellation at a magnetic neutral line. We
have tested the veracity of that view by examining 60 random jets in
quiet regions and coronal holes using multithermal (304, 171, 193, and
211 Å) extreme ultraviolet images from the Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly and line-of-sight magnetograms from
the SDO/Helioseismic and Magnetic Imager. By examining the structure
and changes in the magnetic field before, during, and after jet onset,
we found that 85% of these jets resulted from a minifilament eruption
triggered by flux cancellation at the neutral line. The 60 jets have
a mean base diameter of 8800 ± 3100 km and a mean duration of 9 ±
3.6 minutes. These observations confirm that minifilament eruption
is the driver and magnetic flux cancellation is the primary trigger
mechanism for most coronal hole and quiet region coronal jets.
---------------------------------------------------------
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of the solar active region observed
by HiC2.1, IRIS and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep; Moore, Ronald L.;
De Pontieu, Bart; Testa, Paola; Winebarger, Amy R.
2019AAS...23411702T Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(HiC2.1) provided unprecedentedly-high spatial and temporal resolution
(150 km, 4.5 s) coronal EUV images of Fe IX/X emission at 172 Å, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament
system in the core of the AR. We complement the 5-minute-duration
HiC2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and
IRIS UV spectra and slit-jaw images to examine, at the sites of these
events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. These
outflows from both ends of the arch filament system are seen as
bi-directional flows in the arch filament system, suggesting that the
well-known counter-streaming flows in large classical filaments could be
driven in the same way as in this arch filament system: by fine-scale
jet-like explosions from fine-scale sites of mixed-polarity field in
the feet of the sheared field that threads the filament. Plausibly,
the flux cancellation at these sites prepares and triggers a fine scale
core-magnetic-field structure (a small sheared/twisted core field or
flux rope along and above the cancellation line) to explode. In types
I & II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow in the manner of larger jets
in coronal holes, quiet regions, and active regions.
---------------------------------------------------------
Title: Hi-C2.1 Observations of Solar Jetlets at Sites of Flux
Cancelation
Authors: Panesar, Navdeep; Sterling, Alphonse C.; Moore, Ronald L.
2019AAS...23411701P Altcode:
Solar jets of all sizes are magnetically channeled narrow eruptive
events; the larger ones are often observed in the solar corona in EUV
and coronal X-ray images. Recent observations show that the buildup
and triggering of the minifilament eruptions that drive coronal jets
result from magnetic flux cancelation under the minifilament, at the
neutral line between merging majority-polarity and minority-polarity
magnetic flux patches. Here we investigate the magnetic setting
of six on-disk small-scale jet-like/spicule-like eruptions (also
known as jetlets) by using high resolution 172A images from the
High-resolution Coronal Imager (Hi-C2.1) and EUV images from Solar
Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and
line-of-sight magnetograms from SDO/Helioseismic and Magnetic Imager
(HMI). From magnetograms co-aligned with the Hi-C and AIA images, we
find that (i) these jetlets are rooted at edges of magnetic network
lanes (ii) some jetlets stem from sites of flux cancelation between
merging majority-polarity and minority-polarity flux patches (iii)
some jetlets show faint brightenings at their bases reminiscent of
the base brightenings in coronal jets. Based on the 6 Hi-C jetlets
that we have examined in detail and our previous observations of 30
coronal jets in quiet regions and coronal holes, we infer that flux
cancelation is the essential process in the buildup and triggering of
jetlets. Our observations suggest that network jetlets result from
small-scale eruptions that are analogs of both larger-scale coronal
jet minifilament eruptions and the still-larger-scale eruptions that
make major CMEs. This work was supported by the NASA/MSFC NPP program
and the NASA HGI Program.
---------------------------------------------------------
Title: Invisibility of Solar Active Region Umbra-to-Umbra Coronal
Loops: New Evidence that Magnetoconvection Drives Solar-Stellar
Coronal Heating
Authors: Moore, Ronald L.; Tiwari, Sanjiv; Thalmann, Julia; Panesar,
Navdeep; Winebarger, Amy
2019AAS...23410603M Altcode:
How magnetic energy is injected and released in the solar corona,
keeping it heated to several million degrees, remains elusive. The
corona is shaped by the magnetic field that fills it and the heating
of the corona generally increases with increasing strength of the
field. For each of two bipolar solar active regions having one or
more sunspots in each of the two main opposite-polarity domains of
magnetic flux, from comparison of a nonlinear force-free model of the
active region's three-dimensional coronal magnetic field to observed
extreme-ultraviolet coronal loops, we find that (1) umbra-to-umbra
loops, despite being rooted in the strongest magnetic flux at both ends,
are invisible, and (2) the brightest loops have one foot in a sunspot
umbra or penumbra and the other foot in another sunspot's penumbra or
in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra
loops is new evidence that magnetoconvetion drives solar-stellar coronal
heating: evidently, the strong umbral field at both ends quenches the
magnetoconvection and hence the heating. Broadly, our results indicate
that depending on the field strength in both feet, the photospheric feet
of a coronal loop on any convective star can either engender or quench
coronal heating in the body of the loop. <P />This work was supported
by funding from the Heliophysics Division of NASA's Science Mission
Directorate, from NASA's Postdoctoral Program, and from the Austrian
Science Fund. The results have been published in The Astrophysical
Journal Letters (Tiwari, S. K., Thalmann, J. K., Panesar, N. K., Moore,
R. L., & Winebarger, A. R. 2017, ApJ Letters, 843:L20).
---------------------------------------------------------
Title: A CME-Producing Solar Eruption from the Interior of an Emerging
Bipolar Active Region
Authors: Adams, Mitzi L.; Moore, Ronald L.; Panesar, Navdeep;
Falconer, David
2019AAS...23430501A Altcode:
In a negative-polarity coronal hole, magnetic flux emergence, seen
by the Solar Dynamics Observatory's (SDO) Helioseismic Magnetic
Imager (HMI), begins at approximately 19:00 UT on March 3, 2016. The
emerged magnetic field produced sunspots, which NOAA numbered 12514
two days later. The emerging magnetic field is largely bipolar with
the opposite-polarity fluxes spreading apart overall, but there is
simultaneously some convergence and cancellation of opposite-polarity
flux at the polarity inversion line (PIL) inside the emerging bipole. In
the first fifteen hours after emergence onset, three obvious eruptions
occur, observed in the coronal EUV images from SDO's Atmospheric
Imaging Assembly (AIA). The first two erupt from separate segments
of the external PIL between the emerging positve-polarity flux and
the extant surrounding negative-polarity flux, with the exploding
magnetic field being prepared and triggered by flux cancellation at the
external PIL. The emerging bipole shows obvious overall left-handed
shear and/or twist in its magnetic field. The third and largest
eruption comes from inside the emerging bipole and blows it open to
produce a CME observed by SOHO/LASCO. That eruption is preceded by flux
cancellation at the emerging bipole's interior PIL, cancellation that
plausibly builds a sheared and twisted flux rope above the interior
PIL and finally triggers the blow-out eruption of the flux rope via
photospheric-convection-driven slow tether-cutting reconnection of
the legs of the sheared core field, low above the interior PIL, as
proposed by van Ballegooijen and Martens (1989, ApJ, 343, 971) and
Moore and Roumeliotis (1992, in Eruptive Solar Flares, ed. Z. Svestka,
B.V. Jackson, and M.E. Machado [Berlin:Springer], 69). The production of
this eruption is a (perhaps rare) counterexample to solar eruptions that
result from external collisional shearing between opposite polarities
from two distinct emerging and/or emerged bipoles (Chintzoglou et al.,
2019, ApJ, 871:67). <P />This work was supported by NASA, the NASA
Postdoctoral Program (NPP), and NSF.
---------------------------------------------------------
Title: Evidence of Twisting and Mixed-polarity Solar Photospheric
Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations
Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy R.;
Sterling, Alphonse C.
2018ApJ...869..147T Altcode: 2018arXiv181109554T
A recent study using Hinode (Solar Optical Telescope/Filtergraph
[SOT/FG]) data of a sunspot revealed some unusually large penumbral
jets that often repeatedly occurred at the same locations in the
penumbra, namely, at the tail of a penumbral filament or where the
tails of multiple penumbral filaments converged. These locations had
obvious photospheric mixed-polarity magnetic flux in Na I 5896 Stokes-V
images obtained with SOT/FG. Several other recent investigations have
found that extreme-ultraviolet (EUV)/X-ray coronal jets in quiet-Sun
regions (QRs), in coronal holes (CHs), and near active regions (ARs)
have obvious mixed-polarity fluxes at their base, and that magnetic
flux cancellation prepares and triggers a minifilament flux-rope
eruption that drives the jet. Typical QR, CH, and AR coronal jets are
up to 100 times bigger than large penumbral jets, and in EUV/X-ray
images they show a clear twisting motion in their spires. Here,
using Interface Region Imaging Spectrograph (IRIS) Mg II k λ2796 SJ
images and spectra in the penumbrae of two sunspots, we characterize
large penumbral jets. We find redshift and blueshift next to each
other across several large penumbral jets, and we interpret these as
untwisting of the magnetic field in the jet spire. Using Hinode/SOT
(FG and SP) data, we also find mixed-polarity magnetic flux at the
base of these jets. Because large penumbral jets have a mixed-polarity
field at their base and have a twisting motion in their spires, they
might be driven the same way as QR, CH, and AR coronal jets.
---------------------------------------------------------
Title: IRIS and SDO Observations of Solar Jetlets Resulting from
Network-edge Flux Cancelation
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Tiwari, Sanjiv K.; De Pontieu, Bart; Norton, Aimee A.
2018ApJ...868L..27P Altcode: 2018arXiv181104314P
Recent observations show that the buildup and triggering of minifilament
eruptions that drive coronal jets result from magnetic flux cancelation
at the neutral line between merging majority- and minority-polarity
magnetic flux patches. We investigate the magnetic setting of 10
on-disk small-scale UV/EUV jets (jetlets, smaller than coronal X-ray
jets but larger than chromospheric spicules) in a coronal hole by using
IRIS UV images and SDO/AIA EUV images and line-of-sight magnetograms
from SDO/HMI. We observe recurring jetlets at the edges of magnetic
network flux lanes in the coronal hole. From magnetograms coaligned
with the IRIS and AIA images, we find, clearly visible in nine cases,
that the jetlets stem from sites of flux cancelation proceeding at
an average rate of ∼1.5 × 10<SUP>18</SUP> Mx hr<SUP>-1</SUP>, and
show brightenings at their bases reminiscent of the base brightenings
in larger-scale coronal jets. We find that jetlets happen at many
locations along the edges of network lanes (not limited to the base
of plumes) with average lifetimes of 3 minutes and speeds of 70 km
s<SUP>-1</SUP>. The average jetlet-base width (4000 km) is three
to four times smaller than for coronal jets (∼18,000 km). Based on
these observations of 10 obvious jetlets, and our previous observations
of larger-scale coronal jets in quiet regions and coronal holes, we
infer that flux cancelation is an essential process in the buildup and
triggering of jetlets. Our observations suggest that network jetlet
eruptions might be small-scale analogs of both larger-scale coronal
jets and the still-larger-scale eruptions producing CMEs.
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Title: Magnetic Flux Cancelation as the Buildup and Trigger Mechanism
for CME-producing Eruptions in Two Small Active Regions
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K.
2018ApJ...864...68S Altcode: 2018arXiv180703237S
We follow two small, magnetically isolated coronal mass ejection
(CME)-producing solar active regions (ARs) from the time of their
emergence until several days later, when their core regions erupt to
produce the CMEs. In both cases, magnetograms show: (a) following
an initial period where the poles of the emerging regions separate
from each other, the poles then reverse direction and start to retract
inward; (b) during the retraction period, flux cancelation occurs along
the main neutral line of the regions; (c) this cancelation builds
the sheared core field/flux rope that eventually erupts to make the
CME. In the two cases, respectively 30% and 50% of the maximum flux
of the region cancels prior to the eruption. Recent studies indicate
that solar coronal jets frequently result from small-scale filament
eruptions, with those “minifilament” eruptions also being built up
and triggered by cancelation of magnetic flux. Together, the small-AR
eruptions here and the coronal jet results suggest that isolated bipolar
regions tend to erupt when some threshold fraction, perhaps in the
range of 50%, of the region's maximum flux has canceled. Our observed
erupting filaments/flux ropes form at sites of flux cancelation, in
agreement with previous observations. Thus, the recent finding that
minifilaments that erupt to form jets also form via flux cancelation
is further evidence that minifilaments are small-scale versions of
the long-studied full-sized filaments.
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Title: Critical Magnetic Field Strengths for Solar Coronal Plumes
in Quiet Regions and Coronal Holes?
Authors: Avallone, Ellis A.; Tiwari, Sanjiv K.; Panesar, Navdeep K.;
Moore, Ronald L.; Winebarger, Amy
2018ApJ...861..111A Altcode: 2018arXiv180511188A
Coronal plumes are bright magnetic funnels found in quiet regions (QRs)
and coronal holes (CHs). They extend high into the solar corona and last
from hours to days. The heating processes of plumes involve dynamics
of the magnetic field at their base, but the processes themselves
remain mysterious. Recent observations suggest that plume heating is
a consequence of magnetic flux cancellation and/or convergence at
the plume base. These studies suggest that the base flux in plumes
is of mixed polarity, either obvious or hidden in Solar Dynamics
Observatory (SDO)/HMI data, but do not quantify it. To investigate the
magnetic origins of plume heating, we select 10 unipolar network flux
concentrations, four in CHs, four in QRs, and two that do not form a
plume, and track plume luminosity in SDO/AIA 171 Å images along with
the base flux in SDO/HMI magnetograms, over each flux concentration’s
lifetime. We find that plume heating is triggered when convergence of
the base flux surpasses a field strength of ∼200-600 G. The luminosity
of both QR and CH plumes respond similarly to the field in the plume
base, suggesting that the two have a common formation mechanism. Our
examples of non-plume-forming flux concentrations, reaching field
strengths of 200 G for a similar number of pixels as for a couple of our
plumes, suggest that a critical field might be necessary to form a plume
but is not sufficient for it, thus advocating for other mechanisms,
e.g., flux cancellation due to hidden opposite-polarity field, at play.
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Title: Flux Cancelation as the Trigger of Coronal Hole Jet Eruptions
Authors: Panesar, Navdeep Kaur; Sterling, Alphonse C.; Moore,
Ronald Lee
2018tess.conf40806P Altcode:
Coronal jets are magnetically channeled narrow eruptions often observed
in the solar corona. Recent observations show that coronal jets are
driven by the eruption of a small-scale filament (minifilament). Here
we investigate the triggering mechanism of jet-driving minifilament
eruptions in coronal holes, by using X-ray images from Hinode, EUV
images from SDO/AIA, and line of sight magnetograms from SDO/HMI. We
study 13 on-disk randomly selected coronal hole jets, and track
the evolution of the jet-base. In each case we find that there is a
minifilament present in the jet-base region prior to jet eruption. The
minifilaments reside above a neutral line between majority-polarity
and minority-polarity magnetic flux patches. HMI magnetograms
show continuous flux cancelation at the neutral line between the
opposite polarity flux patches. Persistent flux cancelation eventually
destabilizes the field that holds the minifilament plasma. The erupting
field reconnects with the neighboring far-reaching field and produces
the jet spire. From our study, we conclude that flux cancelation is
the fundamental process for triggering coronal hole jets. Other recent
studies show that jets in quiet regions and active regions also are
accompanied by flux cancelation at minifilament neutral lines (Panesar
et al. 2016b, Sterling et al. 2017); therefore the same fundamental
process - namely, magnetic flux cancelation - triggers at least many
coronal jets in all regions of the Sun.
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Title: Onset of the Magnetic Explosion in Solar Polar X-Ray Jets
Authors: Moore, Ronald Lee; Sterling, Alphonse C.; Panesar, Navdeep
Kaur
2018tess.conf30598M Altcode:
We follow up on the Sterling et al (2015, Nature, 523, 437) discovery
that nearly all solar polar X-ray jets are made by an explosive
eruption of closed magnetic field carrying a miniature cool-plasma
filament in its core. In the same X-ray and EUV movies used by Sterling
et al (2015), we examine the onset and growth of the driving magnetic
explosion in 15 of the 20 jets that they studied. We find evidence that:
(1) in a large majority of polar X-ray jets, the runaway internal
tether-cutting reconnection under the erupting minifilament flux rope
starts after both the minifilament's rise and the spire-producing
breakout reconnection have started; and (2) in a large minority,
(a) before the eruption starts there is a current sheet between the
explosive closed field and the ambient open field, and (b) the eruption
starts with breakout reconnection at that current sheet. The observed
sequence of events as the eruptions start and grow support the idea
that the magnetic explosions that make polar X-ray jets work the same
way as the much larger magnetic explosions that make a flare and coronal
mass ejection (CME). That idea, and recent observations indicating that
magnetic flux cancelation is the fundamental process that builds the
field in and around the pre-jet minifilament and triggers that field's
jet-driving explosion, together suggest that flux cancelation inside
the magnetic arcade that explodes in a flare/CME eruption is usually
the fundamental process that builds the explosive field in the core
of the arcade and triggers that field's explosion. <P />This work
was funded by the Heliophysics Division of NASA's Science Mission
Directorate through the Living With a Star Science Program and the
Heliophysics Guest Investigators Program.
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Title: Birth of a Bipolar Active Region in a Small Solar Coronal Hole
Authors: Adams, Mitzi; Panesar, Navdeep Kaur; Moore, Ronald L.
2018tess.conf20235A Altcode:
We report on an the emergence of an anemone active region in a very
small
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Title: Observations of Large Penumbral Jets from IRIS and Hinode
Authors: Tiwari, Sanjiv K.; Moore, Ronald Lee; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep Kaur; Winebarger, Amy R.;
Sterling, Alphonse C.
2018tess.conf40807T Altcode:
Recent observations from Hinode (SOT/FG) revealed the presence of
large penumbral jets (widths ≥ 500 km, larger than normal penumbral
microjets, which have widths < 400 km) repeatedly occurring at
the same locations in a sunspot penumbra, at the tail of a penumbral
filament or where the tails of several penumbral filaments apparently
converge (Tiwari et al. 2016, ApJ). These locations were observed
to have mixed-polarity flux in Stokes-V images from SOT/FG. Large
penumbral jets displayed direct signatures in AIA 1600, 304, 171,
and 193 channels; thus they were heated to at least transition region
temperatures. Because large jets could not be detected in AIA 94 Å,
whether they had any coronal-temperature plasma remains unclear. In
the present work, for another sunspot, we use IRIS Mg II k 2796
slit jaw images and spectra and magnetograms from Hinode SOT/FG and
SOT/SP to examine: whether penumbral jets spin, similar to spicules
and coronal jets in the quiet Sun and coronal holes; whether they stem
from mixed-polarity flux; and whether they produce discernible coronal
emission, especially in AIA 94 Å images.
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Title: Onset of the Magnetic Explosion in Solar Polar Coronal
X-Ray Jets
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Panesar, Navdeep K.
2018ApJ...859....3M Altcode: 2018arXiv180512182M
We follow up on the Sterling et al. discovery that nearly all polar
coronal X-ray jets are made by an explosive eruption of a closed
magnetic field carrying a miniature filament in its core. In the same
X-ray and EUV movies used by Sterling et al., we examine the onset
and growth of the driving magnetic explosion in 15 of the 20 jets
that they studied. We find evidence that (1) in a large majority of
polar X-ray jets, the runaway internal/tether-cutting reconnection
under the erupting minifilament flux rope starts after both the
minifilament’s rise and the spire-producing external/breakout
reconnection have started; and (2) in a large minority, (a) before
the eruption starts, there is a current sheet between the explosive
closed field and the ambient open field, and (b) the eruption starts
with breakout reconnection at that current sheet. The variety of
event sequences in the eruptions supports the idea that the magnetic
explosions that make polar X-ray jets work the same way as the much
larger magnetic explosions that make a flare and coronal mass ejection
(CME). That idea and recent observations indicating that magnetic
flux cancellation is the fundamental process that builds the field
in and around the pre-jet minifilament and triggers that field’s
jet-driving explosion together suggest that flux cancellation inside
the magnetic arcade that explodes in a flare/CME eruption is usually
the fundamental process that builds the explosive field in the core
of the arcade and triggers that field’s explosion.
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Title: Magnetic Flux Cancelation as the Trigger of Solar Coronal
Jets in Coronal Holes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.
2018ApJ...853..189P Altcode: 2018arXiv180105344P
We investigate in detail the magnetic cause of minifilament eruptions
that drive coronal-hole jets. We study 13 random on-disk coronal-hole
jet eruptions, using high-resolution X-ray images from the Hinode/X-ray
telescope(XRT), EUV images from the Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly (AIA), and magnetograms from the
SDO/Helioseismic and Magnetic Imager (HMI). For all 13 events, we track
the evolution of the jet-base region and find that a minifilament of
cool (transition-region-temperature) plasma is present prior to each jet
eruption. HMI magnetograms show that the minifilaments reside along a
magnetic neutral line between majority-polarity and minority-polarity
magnetic flux patches. These patches converge and cancel with each
other, with an average cancelation rate of ∼0.6 × 10<SUP>18</SUP>
Mx hr<SUP>-1</SUP> for all 13 jets. Persistent flux cancelation at
the neutral line eventually destabilizes the minifilament field, which
erupts outward and produces the jet spire. Thus, we find that all 13
coronal-hole-jet-driving minifilament eruptions are triggered by flux
cancelation at the neutral line. These results are in agreement with
our recent findings for quiet-region jets, where flux cancelation at
the underlying neutral line triggers the minifilament eruption that
drives each jet. Thus, from that study of quiet-Sun jets and this
study of coronal-hole jets, we conclude that flux cancelation is the
main candidate for triggering quiet-region and coronal-hole jets.
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Title: Critical Magnetic Field Strengths for Unipolar Solar Coronal
Plumes in Quiet Regions and Coronal Holes?
Authors: Avallone, E. A.; Tiwari, S. K.; Panesar, N. K.; Moore, R. L.
2017AGUFMSH43A2797A Altcode:
Coronal plumes are sporadic fountain-like structures that are bright
in coronal emission. Each is a magnetic funnel rooted in a strong
patch of dominant-polarity photospheric magnetic flux surrounded by
a predominantly-unipolar magnetic network, either in a quiet region
or a coronal hole. The heating processes that make plumes bright
evidently involve the magnetic field in the base of the plume, but
remain mysterious. Raouafi et al. (2014) inferred from observations
that plume heating is a consequence of magnetic reconnection in the
base, whereas Wang et al. (2016) showed that plume heating turns
on/off from convection-driven convergence/divergence of the base
flux. While both papers suggest that the base magnetic flux in their
plumes is of mixed polarity, these papers provide no measurements
of the abundance and strength of the evolving base flux or consider
whether a critical magnetic field strength is required for a plume to
become noticeably bright. To address plume production and evolution,
we track the plume luminosity and the abundance and strength of the
base magnetic flux over the lifetimes of six coronal plumes, using
Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 171
Å images and SDO/Helioseismic and Magnetic Imager (HMI) line-of-sight
magnetograms. Three of these plumes are in coronal holes, three are in
quiet regions, and each plume exhibits a unipolar base flux. We track
the base magnetic flux over each plume's lifetime to affirm that its
convergence and divergence respectively coincide with the appearance
and disappearance of the plume in 171 Å images. We tentatively find
that plume formation requires enough convergence of the base flux to
surpass a field strength of ∼300-500 Gauss, and that quiet Sun and
coronal-hole plumes both exhibit the same behavior in the response of
their luminosity in 171 Å to the strength of the magnetic field in
the base.
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Title: Dynamic Solar Coronal Jets occurring in a Near-Limb Active
Region
Authors: Velasquez, J.; Sterling, A. C.; Falconer, D. A.; Moore,
R. L.; Panesar, N. K.
2017AGUFMSH43A2792V Altcode:
Coronal Jets are long, narrow columns of plasma ejected from the lower
solar atmosphere into the corona and observed at coronal wavelengths. In
this study, we observe a series of coronal jets occurring in NOAA
active region (AR) 12473 on 2015 December 30. At that time the AR was
approaching the Sun's west limb, allowing for observation of the jets in
profile, contrasting with our recent studies of on-disk active region
jets (Sterling et al. 2016, ApJ, 821, 100; and 2017, ApJ, 844, 28). We
observe the jets using X-ray images from Hinode's X-Ray Telescope
(XRT) and EUV images from the Solar Dynamic Observatory's (SDO)
Atmospheric Imaging Assembly (AIA). Here, we investigate the dynamic
trajectories of about 9 jets, by measuring the distance between the jet
base and the leading edge of the erupting jet (i.e., the jet length)
as a function of time, when observed in 304 Angstrom AIA images. All
of the selected jets are concurrently visible in X-rays, and thus we
are measuring properties of the chromospheric-transition region "cool
component" of X-ray jets; in most cases, the appearance of the jets,
such as the length of their spire, differs substantially between the
X-ray and EUV 304 Angstrom images. For our selection of jets, we find
that in the 304 Angstrom images many of them spin as they extend. Most
of those in our selection do not make coronal mass ejections (CMEs);
on average our jets have outward velocities of about 126 km/s, average
maximum lengths of 84,000 km, and average lifetimes of 38 min. These
values fall in the range of outward velocities and lifetimes found by
Panesar et al. (2016, ApJ, 822, L23) for active-region 304 Angstrom jets
that did not make CMEs. These values are also comparable to those found
by Moschou et al. (2013, Solar Phys, 284, 427) for a selection of quiet
Sun and coronal hole 304 Angstrom jets. One of our selected jets did
make a CME, and it has outward velocity of about 240 km/s, consistent
with the Panesar et al. (2016) results for CME-producing jets.
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Title: Magnetic Flux Cancellation as the Trigger of Solar Coronal Jets
Authors: McGlasson, R.; Panesar, N. K.; Sterling, A. C.; Moore, R. L.
2017AGUFMSH43A2796M Altcode:
Coronal jets are narrow eruptions in the solar corona, and are often
observed in extreme ultraviolet (EUV) and X-ray images. They occur
everywhere on the solar disk: in active regions, quiet regions,
and coronal holes (Raouafi et al. 2016). Recent studies indicate
that most coronal jets in quiet regions and coronal holes are driven
by the eruption of a minifilament (Sterling et al. 2015), and that
this eruption follows flux cancellation at the magnetic neutral line
under the pre-eruption minifilament (Panesar et al. 2016). We confirm
this picture for a large sample of jets in quiet regions and coronal
holes using multithermal (304 Å 171 Å, 193 Å, and 211 Å) extreme
ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO)
/Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from
the SDO /Helioseismic and Magnetic Imager (HMI). We report observations
of 60 randomly selected jet eruptions. We have analyzed the magnetic
cause of these eruptions and measured the base size and the duration of
each jet using routines in SolarSoft IDL. By examining the evolutionary
changes in the magnetic field before, during, and after jet eruption,
we found that each of these jets resulted from minifilament eruption
triggered by flux cancellation at the neutral line. In agreement
with the above studies, we found our jets to have an average base
diameter of 7600 ± 2700 km and an average duration of 9.0 ± 3.6
minutes. These observations confirm that minifilament eruption is the
driver and magnetic flux cancellation is the primary trigger mechanism
for nearly all coronal hole and quiet region coronal jet eruptions.
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Title: Invisibility of Solar Active Region Umbra-to-Umbra Coronal
Loops: New Evidence that Magnetoconvection Drives Solar-Stellar
Coronal Heating
Authors: Tiwari, S. K.; Thalmann, J. K.; Panesar, N. K.; Moore, R. L.;
Winebarger, A. R.
2017AGUFMSH43A2789T Altcode:
Coronal heating generally increases with increasing magnetic field
strength: the EUV/X-ray corona in active regions is 10-100 times more
luminous and 2-4 times hotter than that in quiet regions and coronal
holes, which are heated to only about 1.5 MK, and have fields that are
10-100 times weaker than that in active regions. From a comparison of
a nonlinear force-free model of the three-dimensional active region
coronal field to observed extreme-ultraviolet loops, we find that (1)
umbra-to-umbra coronal loops, despite being rooted in the strongest
magnetic flux, are invisible, and (2) the brightest loops have one
foot in an umbra or penumbra and the other foot in another sunspot's
penumbra or in unipolar or mixed-polarity plage. The invisibility of
umbra-to-umbra loops is new evidence that magnetoconvection drives
solar-stellar coronal heating: evidently, the strong umbral field at
both ends quenches the magnetoconvection and hence the heating. Our
results from EUV observations and nonlinear force-free modeling of
coronal magnetic field imply that, for any coronal loop on the Sun or
on any other convective star, as long as the field can be braided by
convection in at least one loop foot, the stronger the field in the
loop, the stronger the coronal heating.
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Title: Origin of Pre-Coronal-Jet Minifilaments: Flux Cancellation
Authors: Panesar, N. K.; Sterling, A. C.; Moore, R. L.
2017AGUFMSH41C..03P Altcode:
We recently investigated the triggering mechanism of ten quiet-region
coronal jet eruptions and found that magnetic flux cancellation at the
neutral line of minifilaments is the main cause of quiet-region jet
eruptions (Panesar et al 2016). However, what leads to the formation
of the pre-jet minifilaments remained unknown. In the present work,
we study the longer-term evolution of the magnetic field that leads
to the formation of pre-jet minifilaments by using SDO/AIA intensity
images and concurrent line of sight SDO/HMI magnetograms. We find
that each of the ten pre-jet minifilaments formed due to progressive
flux cancellation between the minority-polarity and majority-polarity
flux patches (with a minority-polarity flux loss of 10% - 40% prior
to minifilament birth). Apparently, the flux cancellation between the
opposite polarity flux patches builds a highly-sheared field at the
magnetic neutral line, and that field holds the cool transition region
minifilament plasma. Even after the formation of minifilaments, the
flux continues to cancel, making the minifilament body more thick and
prominent. Further flux cancellation between the opposite-flux patches
leads to the minifilament eruption and a resulting jet. From these
observations, we infer that flux cancellation is usually the process
that builds up the sheared and twisted field in pre-jet minifilaments,
and that triggers it to erupt and drive a jet.
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Title: Onset of the Magnetic Explosion in Solar Polar Coronal
X-Ray Jets
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Panesar, Navdeep
2017SPD....4820006M Altcode:
We examine the onset of the driving magnetic explosion in 15 random
polar coronal X-ray jets. Each eruption is observed in a coronal
X-ray movie from Hinode and in a coronal EUV movie from Solar Dynamics
Observatory. Contrary to the Sterling et al (2015, Nature, 523, 437)
scenario for minifilament eruptions that drive polar coronal jets,
these observations indicate: (1) in most polar coronal jets (a)
the runaway internal tether-cutting reconnection under the erupting
minifilament flux rope starts after the spire-producing breakout
reconnection starts, not before it, and (b) aleady at eruption onset,
there is a current sheet between the explosive closed magnetic field
and ambient open field; and (2) the minifilament-eruption magnetic
explosion often starts with the breakout reconnection of the outside
of the magnetic arcade that carries the minifilament in its core. On
the other hand, the diversity of the observed sequences of occurrence
of events in the jet eruptions gives further credence to the Sterlling
et al (2015, Nature, 523, 437) idea that the magnetic explosions that
make a polar X-ray jet work the same way as the much larger magnetic
explosions that make and flare and CME. We point out that this idea,
and recent observations indicating that magnetic flux cancelation is
the fundamental process that builds the field in and around pre-jet
minifilaments and triggers the jet-driving magnetic explosion, together
imply that usually flux cancelation inside the arcade that explodes
in a flare/CME eruption is the fundamental process that builds the
explosive field and triggers the explosion.This work was funded by the
Heliophysics Division of NASA's Science Mission Directorate through
its Living With a Star Targeted Research and Technology Program,
its Heliophsyics Guest Investigators Program, and the Hinode Project.
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Title: Active Region Jets II: Triggering and Evolution of Violent Jets
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David;
Panesar, Navdeep K.; Martinez, Francisco
2017SPD....4830403S Altcode:
We study a series of X-ray-bright, rapidly evolving active-region
coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT,
SDO/AIA and HMI, and IRIS/SJ data. The detailed evolution of such
rapidly evolving “violent” jets remained a mystery after our
previous investigation of active region jets (Sterling et al. 2016,
ApJ, 821, 100). The jets we investigate here erupt from three
localized subregions, each containing a rapidly evolving (positive)
minority-polarity magnetic-flux patch bathed in a (majority)
negative-polarity magnetic-flux background. At least several of
the jets begin with eruptions of what appear to be thin (thickness
∼<2‧‧) miniature-filament (minifilament) “strands” from
a magnetic neutral line where magnetic flux cancelation is ongoing,
consistent with the magnetic configuration presented for coronal-hole
jets in Sterling et al. (2015, Nature, 523, 437). For some jets strands
are difficult/ impossible to detect, perhaps due to their thinness,
obscuration by surrounding bright or dark features, or the absence
of erupting cool-material minifilaments in those jets. Tracing
in detail the flux evolution in one of the subregions, we find
bursts of strong jetting occurring only during times of strong flux
cancelation. Averaged over seven jetting episodes, the cancelation
rate was ~1.5×10^19 Mx/hr. An average flux of ~5×10^18 Mx canceled
prior to each episode, arguably building up ~10^28—10^29 ergs of
free magnetic energy per jet. From these and previous observations,
we infer that flux cancelation is the fundamental process responsible
for the pre-eruption buildup and triggering of at least many jets in
active regions, quiet regions, and coronal holes.
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Title: Flux Cancelation as the trigger of quiet-region coronal
jet eruptions
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.
2017SPD....4830402P Altcode:
Coronal jets are frequent transient features on the Sun, observed
in EUV and X-ray emissions. They occur in active regions, quiet
Sun and coronal holes, and appear as a bright spire with base
brightenings. Recent studies show that many coronal jets are driven by
the eruption of a minifilament. Here we investigate the magnetic cause
of jet-driving minifilament eruptions. We study ten randomly-found
on-disk quiet-region coronal jets using SDO/AIA intensity images
and SDO/HMI magnetograms. For all ten events, we track the evolution
of the jet-base region and find that (a) a cool (transition-region
temperature) minifilament is present prior to each jet eruption; (b)
the pre-eruption minifilament resides above the polarity-inversion line
between majority-polarity and minority-polarity magnetic flux patches;
(c) the opposite-polarity flux patches converge and cancel with each
other; (d) the ongoing cancelation between the majority-polarity and
minority-polarity flux patches eventually destabilizes the field holding
the minifilament to erupt outwards; (e) the envelope of the erupting
field barges into ambient oppositely-directed far-reaching field and
undergoes external reconnection (interchange reconnection); (f) the
external reconnection opens the envelope field and the minifilament
field inside, allowing reconnection-heated hot material and cool
minifilament material to escape along the reconnected far-reaching
field, producing the jet spire. In summary, we found that each of our
ten jets resulted from a minifilament eruption during flux cancelation
at the magnetic neutral line under the pre-eruption minifilament. These
observations show that flux cancelation is usually the trigger of
quiet-region coronal jet eruptions.
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Title: Magnetic Flux Cancellation as the Origin of Solar Quiet-region
Pre-jet Minifilaments
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.
2017ApJ...844..131P Altcode: 2017arXiv170609079P
We investigate the origin of 10 solar quiet-region pre-jet
minifilaments, using EUV images from the Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly (AIA) and magnetograms from the
SDO Helioseismic and Magnetic Imager (HMI). We recently found that
quiet-region coronal jets are driven by minifilament eruptions, where
those eruptions result from flux cancellation at the magnetic neutral
line under the minifilament. Here, we study the longer-term origin of
the pre-jet minifilaments themselves. We find that they result from
flux cancellation between minority-polarity and majority-polarity flux
patches. In each of 10 pre-jet regions, we find that opposite-polarity
patches of magnetic flux converge and cancel, with a flux reduction
of 10%-40% from before to after the minifilament appears. For our 10
events, the minifilaments exist for periods ranging from 1.5 hr to 2
days before erupting to make a jet. Apparently, the flux cancellation
builds a highly sheared field that runs above and traces the neutral
line, and the cool transition region plasma minifilament forms in this
field and is suspended in it. We infer that the convergence of the
opposite-polarity patches results in reconnection in the low corona
that builds a magnetic arcade enveloping the minifilament in its core,
and that the continuing flux cancellation at the neutral line finally
destabilizes the minifilament field so that it erupts and drives the
production of a coronal jet. Thus, our observations strongly support
that quiet-region magnetic flux cancellation results in both the
formation of the pre-jet minifilament and its jet-driving eruption.
---------------------------------------------------------
Title: Evidence from IRIS that Sunspot Large Penumbral Jets Spin
Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy; Sterling,
Alphonse C.
2017SPD....4810506T Altcode:
Recent observations from {\it Hinode} (SOT/FG) revealed the presence of
large penumbral jets (widths $\ge$500 km, larger than normal penumbral
microjets, which have widths $<$ 400 km) repeatedly occurring at the
same locations in a sunspot penumbra, at the tail of a filament or where
the tails of several penumbral filaments apparently converge (Tiwari et
al. 2016, ApJ). These locations were observed to have mixed-polarity
flux in Stokes-V images from SOT/FG. Large penumbral jets displayed
direct signatures in AIA 1600, 304, 171, and 193 channels; thus they
were heated to at least transition region temperatures. Because
large jets could not be detected in AIA 94 \AA, whether they had
any coronal-temperature plasma remains unclear. In the present work,
for another sunspot, we use IRIS Mg II k 2796 Å slit jaw images and
spectra and magnetograms from Hinode SOT/FG and SOT/SP to examine:
whether penumbral jets spin, similar to spicules and coronal jets in the
quiet Sun and coronal holes; whether they stem from mixed-polarity flux;
and whether they produce discernible coronal emission, especially in
AIA 94 Å images. The few large penumbral jets for which we have IRIS
spectra show evidence of spin. If these have mixed-polarity at their
base, then they might be driven the same way as coronal jets and CMEs.
---------------------------------------------------------
Title: Solar Active Region Coronal Jets. II. Triggering and Evolution
of Violent Jets
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.;
Panesar, Navdeep K.; Martinez, Francisco
2017ApJ...844...28S Altcode: 2017arXiv170503040S
We study a series of X-ray-bright, rapidly evolving active region
coronal jets outside the leading sunspot of AR 12259, using Hinode/X-ray
telescope, Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA) and Helioseismic and Magnetic Imager (HMI), and Interface
Region Imaging Spectrograph (IRIS) data. The detailed evolution of
such rapidly evolving “violent” jets remained a mystery after our
previous investigation of active region jets. The jets we investigate
here erupt from three localized subregions, each containing a rapidly
evolving (positive) minority-polarity magnetic-flux patch bathed in a
(majority) negative-polarity magnetic-flux background. At least several
of the jets begin with eruptions of what appear to be thin (thickness
≲ 2<SUP>\prime\prime</SUP> ) miniature-filament (minifilament)
“strands” from a magnetic neutral line where magnetic flux
cancelation is ongoing, consistent with the magnetic configuration
presented for coronal-hole jets in Sterling et al. (2016). Some jets
strands are difficult/impossible to detect, perhaps due to, e.g.,
their thinness, obscuration by surrounding bright or dark features,
or the absence of erupting cool-material minifilaments in those
jets. Tracing in detail the flux evolution in one of the subregions,
we find bursts of strong jetting occurring only during times of strong
flux cancelation. Averaged over seven jetting episodes, the cancelation
rate was ∼ 1.5× {10}<SUP>19</SUP> Mx hr<SUP>-1</SUP>. An average
flux of ∼ 5× {10}<SUP>18</SUP> Mx canceled prior to each episode,
arguably building up ∼10<SUP>28</SUP>-10<SUP>29</SUP> erg of free
magnetic energy per jet. From these and previous observations, we infer
that flux cancelation is the fundamental process responsible for the
pre-eruption build up and triggering of at least many jets in active
regions, quiet regions, and coronal holes.
---------------------------------------------------------
Title: New Evidence that Magnetoconvection Drives Solar-Stellar
Coronal Heating
Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Panesar, Navdeep K.;
Moore, Ronald L.; Winebarger, Amy R.
2017ApJ...843L..20T Altcode: 2017arXiv170608035T
How magnetic energy is injected and released in the solar
corona, keeping it heated to several million degrees, remains
elusive. Coronal heating generally increases with increasing magnetic
field strength. From a comparison of a nonlinear force-free model
of the three-dimensional active region coronal field to observed
extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal
loops, despite being rooted in the strongest magnetic flux, are
invisible, and (2) the brightest loops have one foot in an umbra or
penumbra and the other foot in another sunspot’s penumbra or in
unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra
loops is new evidence that magnetoconvection drives solar-stellar
coronal heating: evidently, the strong umbral field at both ends
quenches the magnetoconvection and hence the heating. Broadly, our
results indicate that depending on the field strength in both feet,
the photospheric feet of a coronal loop on any convective star can
either engender or quench coronal heating in the loop’s body.
---------------------------------------------------------
Title: The Triggering Mechanism of Coronal Jets and CMEs: Flux
Cancelation
Authors: Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald
2017shin.confE..27P Altcode:
Recent investigations (e.g. Sterling et al 2015, Panesar et al 2016)
show that coronal jets are driven by the eruption of a small-scale
filament (10,000 - 20,000 km long, called a minifilament) following
magnetic flux cancelation at the neutral line underneath the
minifilament. Minifilament eruptions appear to be analogous to
larger-scale solar filament eruptions: they both reside, before
the eruption, in the highly sheared field between the adjacent
opposite-polarity magnetic flux patches (neutral line); jet-producing
minifilament and larger-scale solar filament first show a slow-rise,
followed by a fast-rise as they erupt; during the jet-producing
minifilament eruption a jet bright point (JBP) appears at the
location where the minifilament was rooted before the eruption,
analogous to the situation with CME-producing larger-scale filament
eruptions where a solar flare arcade forms during the filament eruption
along the neutral line along which the filament resided prior to its
eruption. In the present study we investigate the triggering mechanism
of CME-producing large solar filament eruptions, and find that enduring
flux cancelation at the neutral line of the filaments often triggers
their eruptions. This corresponds to the finding that persistent flux
cancelation at the neutral is the cause of jet-producing minifilament
eruptions. Thus our observations support coronal jets being miniature
version of CMEs.
---------------------------------------------------------
Title: Flux Cancellation Leading to Solar Filament Eruptions
Authors: Popescu, R. M.; Panesar, N. K.; Sterling, A. C.; Moore, R. L.
2016AGUFMSH31B2572P Altcode:
Solar filaments are strands of relatively cool, dense plasma
magnetically suspended in the lower density hotter solar corona. They
trace magnetic polarity inversion lines (PILs) in the photosphere
below, and are supported against gravity at heights of up to 100 Mm
above the chromosphere by the magnetic field in and around them. This
field erupts when it is rendered unstable by either magnetic flux
cancellation or emergence at or near the PIL. We have studied the
evolution of photospheric magnetic flux leading to ten observed filament
eruptions. Specifically, we look for gradual magnetic changes in the
neighborhood of the PIL prior to and during eruption. We use Extreme
Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA),
and magnetograms from the Helioseismic and Magnetic Imager (HMI),
both onboard the Solar Dynamics Observatory (SDO), to study filament
eruptions and their photospheric magnetic fields. We examine whether
flux cancellation or/and emergence leads to filament eruptions and
find that continuous flux cancellation was present at the PIL for many
hours prior to each eruption. We present two events in detail and find
the following: (a) the pre-eruption filament-holding core field is
highly sheared and appears in the shape of a sigmoid above the PIL;
(b) at the start of the eruption the opposite arms of the sigmoid
reconnect in the middle above the site of (tether-cutting) flux
cancellation at the PIL; (c) the filaments first show a slow-rise,
followed by a fast-rise as they erupt. We conclude that these two
filament eruptions result from flux cancellation in the middle of
the sheared field and are in agreement with the standard model for
a CME/flare filament eruption from a closed bipolar magnetic field
[flux cancellation (van Ballegooijen and Martens 1989 and Moore and
Roumelrotis 1992) and runaway tether-cutting (Moore et. al 2001)].
---------------------------------------------------------
Title: Magnetic Flux Cancelation as the Trigger of Solar Quiet-region
Coronal Jets
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Chakrapani, Prithi
2016ApJ...832L...7P Altcode: 2016arXiv161008540P
We report observations of 10 random on-disk solar quiet-region coronal
jets found in high-resolution extreme ultraviolet (EUV) images from the
Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly and having
good coverage in magnetograms from the SDO/Helioseismic and Magnetic
Imager (HMI). Recent studies show that coronal jets are driven by the
eruption of a small-scale filament (called a minifilament). However,
the trigger of these eruptions is still unknown. In the present
study, we address the question: what leads to the jet-driving
minifilament eruptions? The EUV observations show that there is a
cool-transition-region-plasma minifilament present prior to each jet
event and the minifilament eruption drives the jet. By examining pre-jet
evolutionary changes in the line of sight photospheric magnetic field,
we observe that each pre-jet minifilament resides over the neutral line
between majority-polarity and minority-polarity patches of magnetic
flux. In each of the 10 cases, the opposite-polarity patches approach
and merge with each other (flux reduction between 21% and 57%). After
several hours, continuous flux cancelation at the neutral line
apparently destabilizes the field holding the cool-plasma minifilament
to erupt and undergo internal reconnection, and external reconnection
with the surrounding coronal field. The external reconnection opens the
minifilament field allowing the minifilament material to escape outward,
forming part of the jet spire. Thus, we found that each of the 10 jets
resulted from eruption of a minifilament following flux cancelation at
the neutral line under the minifilament. These observations establish
that magnetic flux cancelation is usually the trigger of quiet-region
coronal jet eruptions.
---------------------------------------------------------
Title: Suppression of heating of coronal loops rooted in opposite
polarity sunspot umbrae
Authors: Tiwari, Sanjiv K.; Thalmann, Julia; Moore, Ronald; Panesar,
Navdeep; Winebarger, Amy
2016shin.confE..61T Altcode:
EUV observations of active region (AR) coronae reveal the presence
of loops at different temperatures. To understand the mechanisms that
result in hotter or cooler loops, we study a typical bipolar AR, near
solar disk center, which has moderate overall magnetic twist and at
least one fully developed sunspot of each polarity. From AIA 193 and
94 Å images we identify many clearly discernible coronal loops that
connect plage or a sunspot of one polarity to an opposite-polarity
plage region. The AIA 94 Å images show dim regions in the umbrae of
the sunspots. To see which coronal loops are rooted in a dim umbral
area, we performed a non-linear force-free field (NLFFF) modeling
using photospheric vector magnetic field measurements obtained with
the Heliosesmic Magnetic Imager (HMI) onboard SDO. The NLFFF model,
validated by comparison of calculated model field lines with observed
loops in AIA 193 and 94 Å, specifies the photospheric roots of the
model field lines. Some model coronal magnetic field lines arch from
the dim umbral area of the positive-polarity sunspot to the dim umbral
area of a negative-polarity sunspot. Because these coronal loops are
not visible in any of the coronal EUV and X-ray images of the AR, we
conclude they are the coolest loops in the AR. This result suggests
that the loops connecting opposite polarity umbrae are the least heated
because the field in umbrae is so strong that the convective braiding
of the field is strongly suppressed.
---------------------------------------------------------
Title: Homologous Jet-driven Coronal Mass Ejections from Solar Active
Region 12192
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.
2016ApJ...822L..23P Altcode: 2016arXiv160405770P
We report observations of homologous coronal jets and their coronal mass
ejections (CMEs) observed by instruments onboard the Solar Dynamics
Observatory (SDO) and the Solar and Heliospheric Observatory (SOHO)
spacecraft. The homologous jets originated from a location with emerging
and canceling magnetic field at the southeastern edge of the giant
active region (AR) of 2014 October, NOAA 12192. This AR produced in
its interior many non-jet major flare eruptions (X- and M- class) that
made no CME. During October 20 to 27, in contrast to the major flare
eruptions in the interior, six of the homologous jets from the edge
resulted in CMEs. Each jet-driven CME (∼200-300 km s<SUP>-1</SUP>)
was slower-moving than most CMEs, with angular widths (20°-50°)
comparable to that of the base of a coronal streamer straddling the AR
and were of the “streamer-puff” variety, whereby the preexisting
streamer was transiently inflated but not destroyed by the passage
of the CME. Much of the transition-region-temperature plasma in the
CME-producing jets escaped from the Sun, whereas relatively more of
the transition-region plasma in non-CME-producing jets fell back to
the solar surface. Also, the CME-producing jets tended to be faster and
longer-lasting than the non-CME-producing jets. Our observations imply
that each jet and CME resulted from reconnection opening of twisted
field that erupted from the jet base and that the erupting field did
not become a plasmoid as previously envisioned for streamer-puff CMEs,
but instead the jet-guiding streamer-base loop was blown out by the
loop’s twist from the reconnection.
---------------------------------------------------------
Title: A Series of Streamer-Puff CMEs Driven by Solar Homologous
Jets from Active Region 12192
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.
2016SPD....47.0622P Altcode:
We investigate characteristics of solar coronal jets that originated
from active region NOAA 12192 and produced coronal mass ejections
(CMEs). This active region produced many non-jet major flare eruptions
(X and M class) that made no CME. A multitude of jets occurred from the
southeast edge of the active region, and in contrast to the major-flare
eruptions in the core, six of these jets resulted in CMEs. Our jet
observations are from multiple SDO/AIA EUV channels, including 304,
171 and 193Å, and CME observations are taken from SOHO/LASCO C2
coronograph. Each jet-driven CME was relatively slow-moving (~200
- 300 km s<SUP>-1</SUP>) compared to most CMEs; had angular width
(20° - 50°) comparable to that of the streamer base; and was of
the “streamer-puff” variety, whereby a preexisting streamer was
transiently inflated but not removed (blown out) by the passage of
the CME. Much of the chromospheric-temperature plasma of the jets
producing the CMEs escaped from the Sun, whereas relatively more of
the chromospheric plasma in the non-CME-producing jets fell back to
the solar surface. We also found that the CME-producing jets tended to
be faster in speed and longer in duration than the non-CME-producing
jets. We expect that the jets result from eruptions of minifilaments
(Sterling et al. 2015). We further propose that the CMEs are driven
by magnetic twist injected into streamer-base coronal loops when
erupting-twisted-minifilament field reconnects with the ambient field
at the foot of those loops. This research was supported by funding
from NASA's LWS program.
---------------------------------------------------------
Title: Minifilament Eruptions that Drive Coronal Jets in a Solar
Active Region
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David;
Panesar, Navdeep; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat
2016SPD....47.0334S Altcode:
Solar coronal jets are common in both coronal holes and in active
regions. Recently, Sterling et al. (2015), using data from Hinode/XRT
and SDO/AIA, found that coronal jets originating in polar coronal holes
result from the eruption of small-scale filaments (minifilaments). The
jet bright point (JBP) seen in X-rays and hotter EUV channels off to one
side of the base of the jet's spire develops at the location where the
minifilament erupts, consistent with the JBPs being miniature versions
of typical solar flares that occur in the wake of large-scale filament
eruptions. Here we consider whether active region coronal jets also
result from the same minifilament-eruption mechanism, or whether they
instead result from a different mechanism, such as the hitherto popular
“emerging flux” model for jets. We present observations of an on-disk
active region that produced numerous jets on 2012 June 30, using data
from SDO/AIA and HMI, and from GOES/SXI. We find that several of these
active region jets also originate with eruptions of miniature filaments
(size scale ~20”) emanating from small-scale magnetic neutral lines
of the region. This demonstrates that active region coronal jets are
indeed frequently driven by minifilament eruptions. Other jets from the
active region were also consistent with their drivers being minifilament
eruptions, but we could not confirm this because the onsets of those
jets were hidden from our view. This work was supported by funding
from NASA/LWS, NASA/HGI, and Hinode.
---------------------------------------------------------
Title: Suppression of heating of coronal loops rooted in opposite
polarity sunspot umbrae
Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.;
Panesar, Navdeep; Winebarger, Amy R.
2016SPD....47.0336T Altcode:
EUV observations of active region (AR) coronae reveal the presence
of loops at different temperatures. To understand the mechanisms that
result in hotter or cooler loops, we study a typical bipolar AR, near
solar disk center, which has moderate overall magnetic twist and at
least one fully developed sunspot of each polarity. From AIA 193 and
94 A images we identify many clearly discernible coronal loops that
connect plage or a sunspot of one polarity to an opposite-polarity
plage region. The AIA 94 A images show dim regions in the umbrae of
the spots. To see which coronal loops are rooted in a dim umbral area,
we performed a non-linear force-free field (NLFFF) modeling using
photospheric vector magnetic field measurements obtained with the
HMI onboard SDO. After validation of the NLFFF model by comparison of
calculated model field lines and observed loops in AIA 193 and 94, we
specify the photospheric roots of the model field lines. The model field
then shows the coronal magnetic loops that arch from the dim umbral
areas of the opposite polarity sunspots. Because these coronal loops
are not visible in any of the coronal EUV and X-ray images of the AR,
we conclude they are the coolest loops in the AR. This result suggests
that the loops connecting opposite polarity umbrae are the least
heated because the field in umbrae is so strong that the convective
braiding of the field is strongly suppressed.We hypothesize that the
convective freedom at the feet of a coronal loop, together with the
strength of the field in the body of the loop, determines the strength
of the heating. In particular, we expect the hottest coronal loops
to have one foot in an umbra and the other foot in opposite-polarity
penumbra or plage (coronal moss), the areas of strong field in which
convection is not as strongly suppressed as in umbra. Many transient,
outstandingly bright, loops in the AIA 94 movie of the AR do have this
expected rooting pattern. We will also present another example of AR
in which we find a similar rooting pattern of coronal loops.
---------------------------------------------------------
Title: Minifilament Eruptions that Drive Coronal Jets in a Solar
Active Region
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.;
Panesar, Navdeep K.; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat
2016ApJ...821..100S Altcode:
We present observations of eruptive events in an active region adjacent
to an on-disk coronal hole on 2012 June 30, primarily using data from
the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA),
SDO/Helioseismic and Magnetic Imager (HMI), and STEREO-B. One eruption
is of a large-scale (∼100″) filament that is typical of other
eruptions, showing slow-rise onset followed by a faster-rise motion
starting as flare emissions begin. It also shows an “EUV crinkle”
emission pattern, resulting from magnetic reconnections between
the exploding filament-carrying field and surrounding field. Many
EUV jets, some of which are surges, sprays and/or X-ray jets, also
occur in localized areas of the active region. We examine in detail
two relatively energetic ones, accompanied by GOES M1 and C1 flares,
and a weaker one without a GOES signature. All three jets resulted
from small-scale (∼20″) filament eruptions consistent with a slow
rise followed by a fast rise occurring with flare-like jet-bright-point
brightenings. The two more-energetic jets showed crinkle patters, but
the third jet did not, perhaps due to its weakness. Thus all three jets
were consistent with formation via erupting minifilaments, analogous
to large-scale filament eruptions and to X-ray jets in polar coronal
holes. Several other energetic jets occurred in a nearby portion of
the active region; while their behavior was also consistent with their
source being minifilament eruptions, we could not confirm this because
their onsets were hidden from our view. Magnetic flux cancelation
and emergence are candidates for having triggered the minifilament
eruptions.
---------------------------------------------------------
Title: Exploring the properties of Solar Prominence Tornados
Authors: Ahmad, E.; Panesar, N. K.; Sterling, A. C.; Moore, R. L.
2015AGUFMSH53B2485A Altcode:
Solar prominences consist of relatively cool and dense plasma
embedded in the hotter solar corona above the solar limb. They
form along magnetic polarity inversion lines, and are magnetically
supported against gravity at heights of up to ~100 Mm above the
chromosphere. Often, parts of prominences visually resemble Earth-based
tornados, with inverted-cone-shaped structures and internal motions
suggestive of rotation. These "prominence tornados" clearly possess
complex magnetic structure, but it is still not certain whether
they actually rotate around a ”rotation” axis, or instead just
appear to do so because of composite internal material motions such
as counter-streaming flows or lateral (i.e. transverse to the field)
oscillations. Here we study the structure and dynamics of five randomly
selected prominences, using extreme ultraviolet (EUV) 171 Å images
obtained with high spatial and temporal resolution by the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
spacecraft. All of the prominences resided in non-active-region
locations, and displayed what appeared to be tornado-like rotational
motions. Our set includes examples oriented both broadside and end-on to
our line-of-sight. We created time-distance plots of horizontal slices
at several different heights of each prominence, to study the horizontal
plasma motions. We observed patterns of oscillations at various heights
in each prominence, and we measured parameters of these oscillations. We
find the oscillation time periods to range over ~50 - 90 min, with
average amplitudes of ~6,000 km, and with average velocities of ~7
kms-1. We found similar values for prominences viewed either broadside
or end-on; this observed isotropy of the lateral oscillatory motion
suggests that the apparent oscillations result from actual rotational
plasma motions and/or lateral oscillations of the magnetic field,
rather than to counter-streaming flows. This research was supported
by the National Science Foundation under Grant No. AGS-1460767;
EA participated in the Research Experience for Undergraduates (REU)
program, at NASA/MSFC. Additional support was from a grant from the
NASA LWS program.
---------------------------------------------------------
Title: A Series of Streamer-Puff CMEs Driven by Solar Homologous Jets
Authors: Panesar, N. K.; Sterling, A. C.; Moore, R. L.
2015AGUFMSH54B..07P Altcode:
Solar coronal jets are magnetically channeled narrow eruptions
often observed in the solar atmosphere, typically in EUV and X-ray
emission, and occurring in various solar environments including
active regions and coronal holes. Their driving mechanism is still
under discussion, but facts that we know about jets include: (a)
they are ejected from or near sites of compact magnetic explosions
(compact ejective solar flares), (b) they sometimes carry chromospheric
material high into the corona along with coronal-temperature plasma,
(c) the cool-material jet velocities can reach 100 km s-1 or more, and
(d) some active-region jets produce coronal mass ejections (CMEs). Here
we investigate characteristics of EUV jets that originated from active
region NOAA 12192 and produced CMEs. This active region produced many
non-jet major flare eruptions (X and M class) that made no CME. A
multitude of jets also occurred in the region, and in contrast to the
major-flare eruptions, seven of these jets resulted in CMEs. Our jet
observations are from multiple SDO/AIA EUV channels, including 304,
171, 193 and 94 Å, and our CME observations are from SOHO/LASCO C2
images. Each jet-driven CME was relatively slow-moving; had angular
width (30° - 70°) comparable to that of the streamer base; and was
of the "streamer-puff" variety, whereby a preexisting streamer was
transiently inflated but not removed (blown out) by the passage of
the CME. Much of the chromospheric-temperature plasma of the jets
producing the CMEs escaped from the Sun, whereas relatively more of
the chromospheric plasma in the non-CME-producing jets fell back to
the solar surface. We also found that the CME-producing jets tended to
be faster in speed and longer in duration than the non-CME-producing
jets. This research was supported by funding from NASA's LWS program.
---------------------------------------------------------
Title: Destabilization of a Solar Prominence/Filament Field System
by a Series of Eight Homologous Eruptive Flares Leading to a CME
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Innes, Davina E.;
Moore, Ronald L.
2015ApJ...811....5P Altcode: 2015arXiv150801952P
Homologous flares are flares that occur repetitively in the same
active region, with similar structure and morphology. A series of at
least eight homologous flares occurred in active region NOAA 11237 over
2011 June 16-17. A nearby prominence/filament was rooted in the active
region, and situated near the bottom of a coronal cavity. The active
region was on the southeast solar limb as seen from the Solar Dynamics
Observatory/Atmospheric Imaging Assembly, and on the disk as viewed from
the Solar TErrestrial RElations Observatory/EUVI-B. The dual perspective
allows us to study in detail behavior of the prominence/filament
material entrained in the magnetic field of the repeatedly erupting
system. Each of the eruptions were mainly confined, but expelled hot
material into the prominence/filament cavity system (PFCS). The field
carrying and containing the ejected hot material interacted with the
PFCS and caused it to inflate, resulting in a step-wise rise of the
PFCS approximately in step with the homologous eruptions. The eighth
eruption triggered the PFCS to move outward slowly, accompanied by
a weak coronal dimming. As this slow PFCS eruption was underway, a
final “ejective” flare occurred in the core of the active region,
resulting in strong dimming in the EUVI-B images and expulsion of a
coronal mass ejection (CME). A plausible scenario is that the repeated
homologous flares could have gradually destabilized the PFCS, and its
subsequent eruption removed field above the acitive region and in turn
led to the ejective flare, strong dimming, and CME.
---------------------------------------------------------
Title: A Prominence/filament eruption triggered by eight homologous
flares
Authors: Panesar, Navdeep K.; Sterling, Alphonse; Innes, Davina;
Moore, Ronald
2015TESS....140805P Altcode:
Eight homologous flares occurred in active region NOAA 11237 over 16 -
17 June 2011. A prominence system with a surrounding coronal cavity
was adjacent to, but still magnetically connected to the active
region. The eight eruptions expelled hot material from the active
region into the prominence/filament cavity system (PFCS) where the
ejecta became confined. We mainly aim to diagnose the 3D dynamics of
the PFCS during the series of eight homologous eruptions by using data
from two instruments: SDO/AIA and STEREO/EUVI-B, covering the Sun from
two directions. The field containing the ejected hot material interacts
with the PFCS and causes it to inflate, resulting in a discontinuous
rise of the prominence/filament approximately in steps with the
homologous eruptions. The eighth eruption triggers the PFCS to move
outward slowly, accompanied by a weak coronal dimming. Subsequently the
prominence/filament material drains to the solar surface. This PFCS
eruption evidently slowly opens field overlying the active region,
which results in a final ‘ejective’ eruption from the core of
the active region. A strong dimming appears adjacent to the final
eruption’s flare loops in the EUVI-B images, followed by a CME. We
propose that the eight homologous flares gradually disrupted the PFCS
and removed the overlying field above the active region, leading to
the CME via the ‘lid removal’ mechanism.
---------------------------------------------------------
Title: Evidence of suppressed heating of coronal loops rooted in
opposite polarity sunspot umbrae
Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Winebarger, Amy R.;
Panesar, Navdeep K.; Moore, Ronald
2015TESS....120404T Altcode:
Observations of active region (AR) coronae in different EUV wavelengths
reveal the presence of various loops at different temperatures. To
understand the mechanisms that result in hotter or cooler loops, we
study a typical bipolar AR, near solar disk center, which has moderate
overall magnetic twist and at least one fully developed sunspot of
each polarity. From AIA 193 and 94 A images we identify many clearly
discernible coronal loops that connect opposite-polarity plage or
a sunspot to a opposite-polarity plage region. The AIA 94 A images
show dim regions in the umbrae of the spots. To see which coronal
loops are rooted in a dim umbral area, we performed a non-linear
force-free field (NLFFF) modeling using photospheric vector magnetic
field measurements obtained with the Heliosesmic Magnetic Imager (HMI)
onboard SDO. After validation of the NLFFF model by comparison of
calculated model field lines and observed loops in AIA 193 and 94 A,
we specify the photospheric roots of the model field lines. The model
field then shows the coronal magnetic loops that arch from the dim
umbral area of the positive-polarity sunspot to the dim umbral area of a
negative-polarity sunspot. Because these coronal loops are not visible
in any of the coronal EUV and X-ray images of the AR, we conclude they
are the coolest loops in the AR. This result suggests that the loops
connecting opposite polarity umbrae are the least heated because the
field in umbrae is so strong that the convective braiding of the field
is strongly suppressed.From this result, we further hypothesize that
the convective freedom at the feet of a coronal loop, together with the
strength of the field in the body of the loop, determines the strength
of the heating. In particular, we expect the hottest coronal loops
to have one foot in an umbra and the other foot in opposite-polarity
penumbra or plage (coronal moss), the areas of strong field in which
convection is not as strongly suppressed as in umbrae. Many transient,
outstandingly bright, loops in the AIA 94 A movie of the AR do have
this expected rooting pattern.
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Title: On the Structure and Evolution of a Polar Crown
Prominence/Filament System
Authors: Panesar, N. K.; Innes, D. E.; Schmit, D. J.; Tiwari, S. K.
2014SoPh..289.2971P Altcode: 2014arXiv1402.4989P; 2014SoPh..tmp...50P
Polar crown prominences, that partially circle the Sun's poles between
60° and 70° latitude, are made of chromospheric plasma. We aim to
diagnose the 3D dynamics of a polar crown prominence using high-cadence
EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304,
171, and 193 Å and the Ahead spacecraft of the Solar Terrestrial
Relations Observatory (STEREO-A)/EUVI at 195 Å. Using time series
across specific structures, we compare flows across the disk in
195 Å with the prominence dynamics seen on the limb. The densest
prominence material forms vertical columns that are separated by many
tens of Mm and connected by dynamic bridges of plasma that are clearly
visible in 304/171 Å two-colour images. We also observe intermittent
but repetitious flows with velocity 15 km s<SUP>−1</SUP> in the
prominence that appear to be associated with EUV bright points on
the solar disk. The boundary between the prominence and the overlying
cavity appears as a sharp edge. We discuss the structure of the coronal
cavity seen both above and around the prominence. SDO/HMI and GONG
magnetograms are used to infer the underlying magnetic topology. The
evolution and structure of the prominence with respect to the magnetic
field seems to agree with the filament-linkage model.
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Title: A Study of quiescent prominences using SDO and STEREO data
Authors: Panesar, Navdeep Kaur
2014PhDT........78P Altcode:
In this dissertation, we have studied the structure, dynamics and
evolution of two quiescent prominences. Quiescent prominences are large
structures and mainly associated with the quiet Sun region. For the
analysis, we have used the high spatial and temporal cadence data from
the Solar Dynamic Observatory (SDO), and the Solar Terrestrial Relations
Observatory (STEREO). We combined the observations from two different
directions and studied the prominence in 3D. In the study of polar crown
prominence, we mainly investigated the prominence flows on limb and
found its association with on-disk brightenings. The merging of diffused
active region flux in the already formed chain of prominence caused
the several brightenings in the filament channel and also injected the
plasma upward with an average velocity of 15 km/s. In another study,
we investigated the triggering mechanism of a quiescent tornado-like
prominence. Flares from the neighboring active region triggered the
tornado-like motions of the top of the prominence. Active region field
contracts after the flare which results in the expansion of prominence
cavity. The prominence helical magnetic field expands and plasma moves
along the field lines which appear as a tornado-like activity. In
addition, the thermal structure of the tornado-like prominence and
neighbouring active region was investigated by analysing emission
in six of the seven EUV channels from the SDO. These observational
investigations led to our understanding of structure and dynamics
of quiescent prominences, which could be useful for theoretical
prominence models.
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Title: A solar tornado caused by flares
Authors: Panesar, N. K.; Innes, D. E.; Tiwari, S. K.; Low, B. C.
2014IAUS..300..235P Altcode:
An enormous solar tornado was observed by SDO/AIA on 25 September
2011. It was mainly associated with a quiescent prominence with an
overlying coronal cavity. We investigate the triggering mechanism
of the solar tornado by using the data from two instruments: SDO/AIA
and STEREO-A/EUVI, covering the Sun from two directions. The tornado
appeared near to the active region NOAA 11303 that produced three
flares. The flares directly influenced the prominence-cavity system. The
release of free magnetic energy from the active region by flares
resulted in the contraction of the active region field. The cavity,
owing to its superior magnetic pressure, expanded to fill this vacated
space in the corona. We propose that the tornado developed on the top
of the prominence due to the expansion of the prominence-cavity system.
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Title: A solar tornado triggered by flares?
Authors: Panesar, N. K.; Innes, D. E.; Tiwari, S. K.; Low, B. C.
2013A&A...549A.105P Altcode: 2012arXiv1211.6569P
Context. Solar tornados are dynamical, conspicuously helical magnetic
structures that are mainly observed as a prominence activity. <BR />
Aims: We investigate and propose a triggering mechanism for the solar
tornado observed in a prominence cavity by SDO/AIA on September 25,
2011. <BR /> Methods: High-cadence EUV images from the SDO/AIA and
the Ahead spacecraft of STEREO/EUVI are used to correlate three
flares in the neighbouring active-region (NOAA 11303) and their EUV
waves with the dynamical developments of the tornado. The timings
of the flares and EUV waves observed on-disk in 195 Å are analysed
in relation to the tornado activities observed at the limb in 171
Å. <BR /> Results: Each of the three flares and its related EUV wave
occurred within ten hours of the onset of the tornado. They have an
observed causal relationship with the commencement of activity in
the prominence where the tornado develops. Tornado-like rotations
along the side of the prominence start after the second flare. The
prominence cavity expands with the accelerating tornado motion after
the third flare. <BR /> Conclusions: Flares in the neighbouring active
region may have affected the cavity prominence system and triggered
the solar tornado. A plausible mechanism is that the active-region
coronal field contracted by the "Hudson effect" through the loss of
magnetic energy as flares. Subsequently, the cavity expanded by its
magnetic pressure to fill the surrounding low corona. We suggest that
the tornado is the dynamical response of the helical prominence field
to the cavity expansion. <P />Movies are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: A study of quiescent prominences using SDO and STEREO data
Authors: Panesar, Navdeep Kaur
2013PhDT.......414P Altcode:
No abstract at ADS