explanation blue bibcodes open ADS page with paths to full text
Author name code: sterling
ADS astronomy entries on 2022-09-14
author:"Sterling, Alphonse"
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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: NuSTAR observations of a quiet Sun minifilament eruption
Authors: Hannah, Iain; Sterling, Alphonse; Grefenstette, Brian;
Glesener, Lindsay; White, Stephen; Smith, David; Cooper, Kristopher;
Krucker, Sam; Paterson, Sarah; Hudson, Hugh
2022cosp...44.2538H Altcode:
We present a unique set of observations of a confined minifilament
eruption from the quiet-Sun during solar minimum. The Nuclear
Spectroscopic Telescope Array (NuSTAR) spotted a tiny, compact hard
X-ray (HXR) flare on 2019 April 26, peaking about 02:06UT for a few
minutes, finding brief emission >5MK. Observations with SDO/AIA
and Hinode/XRT show this HXR emission was due to a tiny flare arcade
underneath a confined minifilament eruption - behaviour similar to those
seen in both major active-region filament eruptions and minifilament
eruptions that lead to coronal jets. Line-of-sight magnetograms from
SDO/HMI show that this eruption is due to opposite polarity flux
moving together and cancelling and not due to flux emergence. This
eruption occurred near disk-centre, so the Earth orbiting observatories
provide a top-down view of the event, but fortuitously a side-on view
is obtained from STEREO-A/SECCHI, giving a clearer sense of eruption
geometry. We also explore the possibility of non-thermal emission
due to accelerated electrons in the NuSTAR HXR observations of this
small-scale phenomena in the quiet Sun.
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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: Homologous Compact Major Blowout-eruption Solar Flares and
their Production of Broad CMEs
Authors: Sahu, Suraj; Joshi, Bhuwan; Sterling, Alphonse C.; Mitra,
Prabir K.; Moore, Ronald L.
2022ApJ...930...41S Altcode: 2022arXiv220303954S
We analyze the formation mechanism of three homologous broad coronal
mass ejections (CMEs) resulting from a series of solar blowout-eruption
flares with successively increasing intensities (M2.0, M2.6, and
X1.0). The flares originated from NOAA Active Region 12017 during
2014 March 28-29 within an interval of ≍24 hr. Coronal magnetic
field modeling based on nonlinear force-free field extrapolation
helps to identify low-lying closed bipolar loops within the flaring
region enclosing magnetic flux ropes. We obtain a double flux rope
system under closed bipolar fields for all the events. The sequential
eruption of the flux ropes led to homologous flares, each followed by a
CME. Each of the three CMEs formed from the eruptions gradually attained
a large angular width, after expanding from the compact eruption-source
site. We find these eruptions and CMEs to be consistent with the
"magnetic-arch-blowout" scenario: each compact-flare blowout eruption
was seated in one foot of a far-reaching magnetic arch, exploded up
the encasing leg of the arch, and blew out the arch to make a broad CME.
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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: Further Evidence for the Minifilament-eruption Scenario for
Solar Polar Coronal Jets
Authors: Baikie, Tomi K.; Sterling, Alphonse C.; Moore, Ronald L.;
Alexander, Amanda M.; Falconer, David A.; Savcheva, Antonia; Savage,
Sabrina L.
2022ApJ...927...79B Altcode: 2022arXiv220108882B
We examine a sampling of 23 polar-coronal-hole jets. We first identified
the jets in soft X-ray (SXR) images from the X-ray telescope (XRT) on
the Hinode spacecraft, over 2014-2016. During this period, frequently
the polar holes were small or largely obscured by foreground coronal
haze, often making jets difficult to see. We selected 23 jets among
those adequately visible during this period, and examined them further
using Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly
(AIA) 171, 193, 211, and 304 Å images. In SXRs, we track the lateral
drift of the jet spire relative to the jet base's jet bright point
(JBP). In 22 of 23 jets, the spire either moves away from (18 cases)
or is stationary relative to (4 cases) the JBP. The one exception
where the spire moved toward the JBP may be a consequence of
line-of-sight projection effects at the limb. From the AIA images,
we clearly identify an erupting minifilament in 20 of the 23 jets,
while the remainder are consistent with such an eruption having taken
place. We also confirm that some jets can trigger the onset of nearby
"sympathetic" jets, likely because eruption of the minifilament field of
the first jet removes magnetic constraints on the base-field region of
the second jet. The propensity for spire drift away from the JBP, the
identification of the erupting minifilament in the majority of jets,
and the magnetic-field topological changes that lead to sympathetic
jets, all support or are consistent with the minifilament-eruption
model for jets.
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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: Studying Solar Active-Region Magnetic Evolution Leading to
a Confined Eruption
Authors: Zigament, Benjamin; Sterling, Alphonse; Moore, Ronald;
Falconer, David
2021AGUFMSH35B2037Z Altcode:
Current research suggests that there exists a continuum of solar
eruptions ranging from the comparatively small, such as coronal jets,
to extremely large eruptions that produce coronal mass ejections (CMEs)
and solar flares, with all sharing a common triggering mechanism: a
filament/flux rope eruption triggered by magnetic flux cancellation. For
coronal jets the erupting "minifilaments" are of length ~10,000 km
(Sterling et al. 2015, Panesar et al. 2016), while the larger eruptions
are accompanied by eruptions of typical filaments of size ~several x
10^4 --- ~3x10^5 km. Sterling et al. (2018) examined this idea for
two small ARs (flux ~ 2x10^21 Mx) that erupted to make CMEs. They
tracked the evolution of the ARs from emergence to eruption and found
eruption to occur when some of the emerged flux drifted together and
underwent cancellation along the main magnetic neutral line on the
interior of the AR, with eruption occurring after about 30---50% of
the total flux of the respective regions canceled. Here we perform a
similar study, using Solar Dynamics Observatory (SDO) AIA EUV images and
SDO/HMI magnetograms, of a smaller AR (total flux <~10^21 Mx) that
emerged in isolation near the neutral line in a large overarching old
weak-field magnetic arcade on 2014 September 8. It produced a confined
eruption (i.e., one that did not make a CME) about three days later,
on September 10 near 18:45 UT. The ARs flux reached maximum about 12
hr after emergence start, and then decreased continuously, with the
decrease being partly from cancellation of small flux clumps in the
interior of the AR. The eruption occurred when the flux had decreased
by about 20%, and was centered on the neutral line of the emerged AR,
but also involved filament-holding field along some of the old arcades
neutral line. That filament underwent a confined eruption as part of
the overall confined eruption. The emerged ARs being inside the larger
arcade, its smaller size, and its smaller amount of cancellation may
be reasons why the eruption was confined, instead of being ejective
and producing a CME as in the two cases of Sterling et al (2018). This
work was supported by funding from NASA's HGI Program.
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Title: Probing Upflowing Regions in the Quiet Sun and Coronal Holes
Authors: Schwanitz, Conrad; Harra, Louise; Raouafi, Nour E.; Sterling,
Alphonse C.; Moreno Vacas, Alejandro; del Toro Iniesta, Jose Carlos;
Orozco Suárez, David; Hara, Hirohisa
2021SoPh..296..175S Altcode: 2021arXiv211012753S
Recent observations from Parker Solar Probe have revealed that the
solar wind has a highly variable structure. How this complex behaviour
is formed in the solar corona is not yet known, since it requires
omnipresent fluctuations, which constantly emit material to feed
the wind. In this article we analyse 14 upflow regions in the solar
corona to find potential sources for plasma flow. The upflow regions
are derived from spectroscopic data from the EUV Imaging Spectrometer
(EIS) on board Hinode determining their Doppler velocity and defining
regions which have blueshifts stronger than −6 kms−<SUP>1</SUP>. To
identify the sources of these blueshift data from the Atmospheric
Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI),
on board the Solar Dynamics Observatory (SDO), and the X-ray Telescope
(XRT), on board Hinode, are used. The analysis reveals that only 5 out
of 14 upflows are associated with frequent transients, like obvious
jets or bright points. In contrast to that, seven events are associated
with small-scale features, which show a large variety of dynamics. Some
resemble small bright points, while others show an eruptive nature, all
of which are faint and only live for a few minutes; we cannot rule out
that several of these sources may be fainter and, hence, less obvious
jets. Since the complex structure of the solar wind is known, this
suggests that new sources have to be considered or better methods used
to analyse the known sources. This work shows that small and frequent
features, which were previously neglected, can cause strong upflows in
the solar corona. These results emphasise the importance of the first
observations from the Extreme-Ultraviolet Imager (EUI) on board Solar
Orbiter, which revealed complex small-scale coronal structures.
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Title: Relation of Microstreams in the Polar Solar Wind to Switchbacks
and Coronal X-Ray Jets
Authors: Neugebauer, Marcia; Sterling, Alphonse C.
2021ApJ...920L..31N Altcode: 2021arXiv211000079N
Ulysses data obtained at high solar latitudes during periods of
minimum solar activity in 1994 and 2007 are examined to determine the
relation between velocity structures called microstreams and folds in
the magnetic field called switchbacks. A high correlation is found. The
possibility of velocity peaks in microstreams originating from coronal
X-ray jets is reexamined; we now suggest that microstreams are the
consequence of the alternation of patches of switchbacks and quiet
periods, where the switchbacks could be generated by minifilament/flux
rope eruptions that cause coronal jets.
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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.
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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.
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Title: The Missing Cool Corona In The Flat Magnetic Field Around
Solar Active Regions
Authors: Singh, T.; Sterling, A.; Moore, R.
2021AAS...23831321S Altcode:
SDO/AIA images the full solar disk in several EUV bands that are
each sensitive to coronal plasma emissions of one or more specific
temperatures. We observe that when isolated active regions (ARs) are on
the disk, full-disk images in some of the coronal EUV channels show the
outskirts of the AR as a dark moat surrounding the AR. Here we present
several specific examples, selected from time periods when there was
only a single AR present on the disk. Visually, moats are observed to
be most prominent in the AIA 171 Angstrom band, which has the most
sensitivity to emission from plasma at log10 T = 5.8. By using the
emission measure distribution with temperature, we find the intensity
of the moat to be most depressed over the temperature range log10 T ~
5.7-6.2 for all the cases. We argue that the dark moat exists because
the pressure from the strong magnetic field that splays out from the
AR presses down on underlying magnetic loops, flattening those loops
— along with the lowest of the AR's own loops over the moat — to a
low altitude. Those loops, which would normally emit the bulk of the
171 Angstrom emission, are restricted to heights above the surface
that are too low to have 171 Angstrom emitting plasmas sustained in
them, while hotter EUV-emitting plasmas are sustained in the overlying
higher-altitude long AR-rooted coronal loops. This potentially explains
the low-coronal-temperature dark moats surrounding the ARs.
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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.
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Title: Coronal-jet-producing Minifilament Eruptions As A Possible
Source Of Parker Solar Probe (PSP) Switchbacks
Authors: Sterling, A.; Moore, R.
2021AAS...23812306S Altcode:
The Parker Solar Probe (PSP) has observed copious rapid magnetic field
direction changes in the near-Sun solar wind. These features have
been called "switchbacks," and their origin is a mystery. But their
widespread nature suggests that they may be generated by a frequently
occurring process in the Sun's atmosphere. We examine the possibility
that the switchbacks originate from coronal jets. Recent work suggests
that many coronal jets result when photospheric magnetic flux cancels,
and forms a small-scale "minifilament" flux rope that erupts and
reconnects with coronal field. We argue that the reconnected erupting
minifilament flux rope can manifest as an outward propagating Alfvenic
fluctuation that steepens into an increasingly compact disturbance as
it moves through the solar wind. Using previous observed properties
of coronal jets that connect to coronagraph-observed white-light
jets (a.k.a. "narrow CMEs"), along with typical solar wind speed
values, we expect the coronal-jet-produced disturbances to traverse
near-perihelion PSP in less than or about 25 min, with a velocity of
about 400 km/s. To consider further the plausibility of this idea, we
show that a previously studied series of equatorial latitude coronal
jets, originating from the periphery of an active region, generate
white-light jets in the outer corona (seen in STEREO/COR2 coronagraph
images; 2.5 — 15 solar radii), and into the inner heliosphere (seen
in STEREO/Hi1 heliospheric imager images; 15 — 84 solar radii). Thus
it is tenable that disturbances put onto open coronal magnetic field
lines by coronal-jet-producing erupting minifilament flux ropes can
propagate out to PSP space and appear as switchbacks. This work was
supported by the NASA Heliophysics Division, and by the NASA/MSFC
Hinode Project. For further details see Sterling & Moore (2020,
ApJ, 896, L18).
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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.
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Title: Fine-Scale Features of the Sun's Atmosphere: Spicules and Jets
Authors: Sterling, Alphonse C.
2021GMS...258..221S Altcode:
No abstract at ADS
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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: The Missing Cool Corona in the Flat Magnetic Field around
Solar Active Regions
Authors: Singh, Talwinder; Sterling, Alphonse C.; Moore, Ronald L.
2021ApJ...909...57S Altcode: 2020arXiv201215406S
Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA) images the full solar disk in several extreme-ultraviolet
(EUV) bands that are each sensitive to coronal plasma emissions of
one or more specific temperatures. We observe that when isolated
active regions (ARs) are on the disk, full-disk images in some of
the coronal EUV channels show the outskirts of the AR as a dark
moat surrounding the AR. Here we present seven specific examples,
selected from time periods when there was only a single AR present
on the disk. Visually, we observe the moat to be most prominent in
the AIA 171 Å band, which has the most sensitivity to emission from
plasma at log<SUB>10</SUB> T = 5.8. By examining the 1D line-of-sight
emission measure temperature distribution found from six AIA EUV
channels, we find the intensity of the moat to be most depressed over
the temperature range log<SUB>10</SUB> T ≍ 5.7-6.2 for most of the
cases. We argue that the dark moat exists because the pressure from
the strong magnetic field that splays out from the AR presses down
on underlying magnetic loops, flattening those loops—along with the
lowest of the AR's own loops over the moat—to a low altitude. Those
loops, which would normally emit the bulk of the 171 Å emission, are
restricted to heights above the surface that are too low to have 171
Å emitting plasmas sustained in them, according to Antiochos &
Noci, while hotter EUV-emitting plasmas are sustained in the overlying
higher-altitude long AR-rooted coronal loops. This potentially explains
the low-coronal-temperature dark moats surrounding the ARs.
---------------------------------------------------------
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: 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: Sequential Lid Removal in a Triple-decker Chain of
CME-producing Solar Eruptions
Authors: Joshi, Navin Chandra; Sterling, Alphonse C.; Moore, Ronald
L.; Joshi, Bhuwan
2020ApJ...901...38J Altcode: 2020arXiv200804525J
We investigate the onsets of three consecutive coronal mass ejection
(CME) eruptions in 12 hr from a large bipolar active region (AR)
observed by the Solar Dynamics Observatory (SDO), the Solar Terrestrial
Relations Observatory (STEREO), the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI), and the Geostationary Operational
Environmental Satellite (GOES). Evidently, the AR initially had a
"triple-decker" configuration: three flux ropes in a vertical stack
above the polarity inversion line (PIL). Upon being bumped by a confined
eruption of the middle flux rope, the top flux rope erupts to make the
first CME and its accompanying AR-spanning flare arcade rooted in a far
apart pair of flare ribbons. The second CME is made by eruption of the
previously arrested middle flux rope, which blows open the flare arcade
of the first CME and produces a flare arcade rooted in a pair of flare
ribbons closer to the PIL than those of the first CME. The third CME
is made by blowout eruption of the bottom flux rope, which blows open
the second flare arcade and makes its own flare arcade and pair of
flare ribbons. Flux cancellation observed at the PIL likely triggers
the initial confined eruption of the middle flux rope. That confined
eruption evidently triggers the first CME eruption. The lid-removal
mechanism instigated by the first CME eruption plausibly triggers the
second CME eruption. Further lid removal by the second CME eruption
plausibly triggers the final CME eruption.
---------------------------------------------------------
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: Coronal-jet-producing Minifilament Eruptions as a Possible
Source of Parker Solar Probe Switchbacks
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2020ApJ...896L..18S Altcode: 2020arXiv200604990S
The Parker Solar Probe (PSP) has observed copious rapid magnetic
field direction changes in the near-Sun solar wind. These features
have been called "switchbacks," and their origin is a mystery. But
their widespread nature suggests that they may be generated by a
frequently occurring process in the Sun's atmosphere. We examine the
possibility that the switchbacks originate from coronal jets. Recent
work suggests that many coronal jets result when photospheric
magnetic flux cancels, and forms a small-scale "minifilament" flux
rope that erupts and reconnects with coronal field. We argue that the
reconnected erupting-minifilament flux rope can manifest as an outward
propagating Alfvénic fluctuation that steepens into an increasingly
compact disturbance as it moves through the solar wind. Using previous
observed properties of coronal jets that connect to coronagraph-observed
white-light jets (a.k.a. "narrow CMEs"), along with typical solar
wind speed values, we expect the coronal-jet-produced disturbances to
traverse near-perihelion PSP in ≲25 minutes, with a velocity of ∼400
km s<SUP>-1</SUP>. To consider further the plausibility of this idea,
we show that a previously studied series of equatorial latitude coronal
jets, originating from the periphery of an active region, generate
white-light jets in the outer corona (seen in STEREO/COR2 coronagraph
images; 2.5-15 R<SUB>⊙</SUB>), and into the inner heliosphere (seen in
Solar-Terrestrial Relations Observatory (STEREO)/Hi1 heliospheric imager
images; 15-84 R<SUB>⊙</SUB>). Thus it is tenable that disturbances
put onto open coronal magnetic field lines by coronal-jet-producing
erupting-minifilament flux ropes can propagate out to PSP space and
appear as switchbacks.
---------------------------------------------------------
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: Possible Production of Solar Spicules by Microfilament
Eruptions
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Samanta, Tanmoy;
Yurchyshyn, Vasyl
2020ApJ...893L..45S Altcode: 2020arXiv200404187S
We examine Big Bear Solar Observatory (BBSO) Goode Solar Telescope
(GST) high spatial resolution (0"06), high-cadence (3.45 s), Hα-0.8
Å images of central-disk solar spicules, using data of Samanta et
al. We compare with coronal-jet chromospheric-component observations
of Sterling et al. Morphologically, bursts of spicules, referred to as
"enhanced spicular activities" by Samanta et al., appear as scaled-down
versions of the jet's chromospheric component. Both the jet and the
enhanced spicular activities appear as chromospheric-material strands,
undergoing twisting-type motions of ∼20-50 km s<SUP>-1</SUP>
in the jet and ∼20-30 km s<SUP>-1</SUP> in the enhanced spicular
activities. Presumably, the jet resulted from a minifilament-carrying
magnetic eruption. For two enhanced spicular activities that we
examine in detail, we find tentative candidates for corresponding
erupting microfilaments, but not the expected corresponding base
brightenings. Nonetheless, the enhanced-spicular-activities'
interacting mixed-polarity base fields, frequent-apparent-twisting
motions, and morphological similarities to the coronal jet's
chromospheric-temperature component, suggest that erupting
microfilaments might drive the enhanced spicular activities but be hard
to detect, perhaps due to Hα opacity. Degrading the BBSO/GST-image
resolution with a 1"0-FWHM smoothing function yields enhanced spicular
activities resembling the "classical spicules" described by, e.g.,
Beckers. Thus, a microfilament eruption might be the fundamental driver
of many spicules, just as a minifilament eruption is the fundamental
driver of many coronal jets. Similarly, a 0"5-FWHM smoothing renders
some enhanced spicular activities to resemble previously reported
"twinned" spicules, while the full-resolution features might account
for spicules sometimes appearing as 2D-sheet-like structures.
---------------------------------------------------------
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: Early Results from the Solar-Minimum 2019 Total Solar Eclipse
Authors: Pasachoff, J. M.; Lockwood, C. A.; Inoue, J. L.; Meadors,
E. N.; Voulgaris, A.; Sliski, D.; Sliski, A.; Reardon, K. P.; Seaton,
D. B.; Caplan, R. M.; Downs, C.; Linker, J. A.; Sterling, A. C.
2020AAS...23535903P Altcode:
We report on first results from our observations in Chile on July
2, 2019, that revealed the extreme-solar-minimum corona, with only
equatorial streamers and with visible polar plumes. We have observations
in clear skies from our three observing sites: (1) The Cerro Tololo
Inter-American Observatory, 7,240-foot altitude, 2 min 6 sec; (2)
La Higuera, centerline, 2,500-foot altitude, 2 min 35 sec totality;
(3) La Serena, sea level, 2 min 15 sec totality. Prominences on the
limb provided orientation and coordination with spacecraft observations
from NOAA's GOES-R Solar Ultraviolet Imager (SUVI) and the Atmospheric
Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory (SDO). The
double-diamond ring at second contact will extend our determination of
a new IAU-recommended value of the solar diameter through comparison
with models taking into account the precise lunar profile. Our coronal
spectra from slitless spectrographs, from CTIO, showed the Fe XIV 530.3
nm green line substantially weaker than the Fe X 637.4 nm red line,
corresponding to the relatively low coronal temperature at this phase
of the solar-activity cycle. On the spectra we also detected the weak
coronal emission line of Ar X at 553.3 nm, as we also detected at
the previous total solar eclipse of August 21, 2017, in the USA. We
show a comparison of the eclipse observation with a prediction of the
structure of the corona from an MHD model, carried out by Predictive
Science Inc. (PSI). We consider the lines of sight to NASA's Parker
Solar Probe at the times of total eclipses, when we can examine the
coronal imaging in terms of electron density to compare with the in
situ measurements. <P />We received major support from grant AGS-903500
from the Solar Terrestrial Program, Atmospheric and Geospace Sciences
Division, U.S. National Science Foundation. The CTIO site was courtesy
of Associated Universities for Research in Astronomy (AURA). We had
additional student support from the Massachusetts NASA Space Grant
Consortium; Sigma Xi; the Global Initiatives Fund at Williams College;
and the University of Pennsylvania. PSI was supported by AFOSR, NASA,
and NSF. ACS received support from the NASA/HGI program, and from
the MSFC Hinode project. AV thanks the mathematician Christophoros
Mouratidis for his help with the data reduction of the spectra.
---------------------------------------------------------
Title: Early results from the solar-minimum 2019 total solar eclipse
Authors: Pasachoff, Jay M.; Lockwood, Christian A.; Inoue, John L.;
Meadors, Erin N.; Voulgaris, Aristeidis; Sliski, David; Sliski, Alan;
Reardon, Kevin P.; Seaton, Daniel B.; Caplan, Ronald M.; Downs, Cooper;
Linker, Jon A.; Schneider, Glenn; Rojo, Patricio; Sterling, Alphonse C.
2020IAUS..354....3P Altcode:
We observed the 2 July 2019 total solar eclipse with a variety of
imaging and spectroscopic instruments recording from three sites
in mainland Chile: on the centerline at La Higuera, from the Cerro
Tololo Inter-American Observatory, and from La Serena, as well
as from a chartered flight at peak totality in mid-Pacific. Our
spectroscopy monitored Fe X, Fe XIV, and Ar X lines, and we imaged Ar
X with a Lyot filter adjusted from its original H-alpha bandpass. Our
composite imaging has been compared with predictions based on modeling
using magnetic-field measurements from the pre-eclipse month. Our
time-differenced sites will be used to measure motions in coronal
streamers.
---------------------------------------------------------
Title: A Two-Sided-Loop X-Ray Solar Coronal Jet and a Sudden
Photospheric Magnetic-field Change, Both Driven by a Minifilament
Eruption
Authors: Sterling, A. C.; Harra, L. K.; Moore, R. L.; Falconer, D. A.
2019AGUFMSH11D3382S Altcode:
Most of the commonly discussed solar coronal jets are of the
type consisting of a <P />single spire extending approximately
vertically from near the solar surface into the <P />corona. Recent
research shows that eruption of a miniature filament (minifilament)
<P />drives at least many such single-spire jets, and concurrently
generates a miniflare at the <P />eruption site. A different type of
coronal jet, identified in X-ray images during the <P />Yohkoh era, are
two-sided-loop jets, which extend from a central excitation location <P
/>in opposite directions, along two opposite low-lying coronal loops
that are more-or-less <P />horizontal to the surface. We observe such
a two-sided-loop jet from the edge of active <P />region (AR) 12473,
using data from Hinode XRT and EIS, and SDO AIA and HMI. Similar <P />to
single-spire jets, this two-sided-loop jet results from eruption of a
minifilament, which <P />accelerates to over 140 km/s before abruptly
stopping upon striking overlying <P />nearly-horizontal magnetic field
at ∼ 30,000 km altitude and producing the two-sided-loop <P />jet
via interchange reconnection. Analysis of EIS raster scans show that
a hot <P />brightening, consistent with a small flare, develops in the
aftermath of the eruption, <P />and that Doppler motions (∼ 40 km/s)
occur near the jet-formation region. As with <P />many single-spire
jets, the trigger of the eruption here is apparently magnetic <P />flux
cancelation, which occurs at a rate of ∼ 4×10^18 Mx/hr, comparable
to the rate <P />observed in some single-spire AR jets. An apparent
increase in the (line-of-sight) <P />flux occurs within minutes of
onset of the minifilament eruption, consistent with the <P />apparent
increase being due to a rapid reconfiguration of low-lying magnetic
field <P />during the minifilament eruption. Details appear in Sterling
et al. (2019, ApJ, 871, 220).
---------------------------------------------------------
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: 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: Further Evidence for Magnetic Flux Cancelation as the Build-up
and Trigger Mechanism for Eruptions in Isolated Solar Active Regions
Authors: Sterling, A. C.; Buell, A.; Moore, R. L.; Falconer, D. A.
2019AGUFMSH11D3388S Altcode:
We examine the magnetic evolution of three eruption-producing solar
active regions (ARs), one each from 2013, 2014, and 2017, using data
from SDO HMI and AIA. Each of the ARs is relatively small, so that
we can follow its entire development during a single disk passage,
from birth by emergence through the time of the respective eruptions;
the first-, second-, and third-born respectively lived 3, 6.5, and 3
days before eruption. Each AR was relatively isolated, with minimal
interaction with surrounding ARs, allowing us to study each AR as an
approximately isolated system. CMEs resulted from eruptions in the
first two ARs, while the third AR's eruption was smaller and appeared
confined. In each AR, the eruption was seated on an interval of the AR's
magnetic polarity inversion line (neutral line) where opposite-polarity
flux was merging together and undergoing apparent cancelation. Our
results, together with an earlier pilot study of two ARs by Sterling
et al. (2018), and along with recent studies of solar coronal jets,
support the view that the magnetic field that explodes to produce
solar eruptions of size scales ranging from jets to CMEs are usually
built and triggered by flux cancelation along a sharp neutral line.
---------------------------------------------------------
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi;
Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu;
Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie
2019Sci...366..890S Altcode: 2020arXiv200602571S
Spicules are rapidly evolving fine-scale jets of magnetized plasma in
the solar chromosphere. It remains unclear how these prevalent jets
originate from the solar surface and what role they play in heating
the solar atmosphere. Using the Goode Solar Telescope at the Big Bear
Solar Observatory, we observed spicules emerging within minutes of the
appearance of opposite-polarity magnetic flux around dominant-polarity
magnetic field concentrations. Data from the Solar Dynamics Observatory
showed subsequent heating of the adjacent corona. The dynamic
interaction of magnetic fields (likely due to magnetic reconnection)
in the partially ionized lower solar atmosphere appears to generate
these spicules and heat the upper solar atmosphere.
---------------------------------------------------------
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
2019PASJ...71R...1H Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
---------------------------------------------------------
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: 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: A Two-Sided-Loop X-Ray Solar Coronal Jet and a Sudden
Photospheric Magnetic-field Change, Both Driven by a Minifilament
Eruption
Authors: Sterling, Alphonse C.; Harra, Louise; Moore, Ronald L.;
Falconer, David
2019AAS...23431701S Altcode:
Most of the commonly discussed solar coronal jets are of the type
consisting of a single spire extending approximately vertically from
near the solar surface into the corona. Recent research shows that
eruption of a miniature filament (minifilament) drives at least many
such single-spire jets, and concurrently generates a miniflare at the
eruption site. A different type of coronal jet, identified in X-ray
images during the Yohkoh era, are two-sided-loop jets, which extend
from a central excitation location in opposite directions, along two
opposite low-lying coronal loops that are more-or-less horizontal
to the surface. We observe such a two-sided-loop jet from the edge
of active region (AR) 12473, using data from Hinode XRT and EIS, and
SDO AIA and HMI. Similar to single-spire jets, this two-sided-loop jet
results from eruption of a minifilament, which accelerates to over 140
km/s before abruptly stopping upon striking overlying nearly-horizontal
magnetic field at ∼30,000 km altitude and producing the two-sided-loop
jet via interchange reconnection. Analysis of EIS raster scans show
that a hot brightening, consistent with a small flare, develops in
the aftermath of the eruption, and that Doppler motions (∼40 km/s)
occur near the jet-formation region. As with many single-spire jets, the
trigger of the eruption here is apparently magnetic flux cancelation,
which occurs at a rate of ∼4×10<SUP>18</SUP> Mx/hr, comparable to the
rate observed in some single-spire AR jets. An apparent increase in the
(line-of-sight) flux occurs within minutes of onset of the minifilament
eruption, consistent with the apparent increase being due to a rapid
reconfiguration of low-lying magnetic field during the minifilament
eruption. Details appear in Sterling et al. (2019, ApJ, 871, 220).
---------------------------------------------------------
Title: A Two-sided Loop X-Ray Solar Coronal Jet Driven by a
Minifilament Eruption
Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L.;
Falconer, David A.
2019ApJ...871..220S Altcode: 2018arXiv181105557S
Most of the commonly discussed solar coronal jets are the type that
consist of a single spire extending approximately vertically from
near the solar surface into the corona. Recent research supports
that eruption of a miniature filament (minifilament) drives many such
single-spire jets and concurrently generates a miniflare at the eruption
site. A different type of coronal jet, identified in X-ray images during
the Yohkoh era, are two-sided loop jets, which extend from a central
excitation location in opposite directions, along low-lying coronal
loops that are more-or-less horizontal to the surface. We observe
such a two-sided loop jet from the edge of active region (AR) 12473,
using data from Hinode X-Ray Telescope (XRT) and Extreme Ultraviolet
Imaging Spectrometer (EIS), and from Solar Dynamics Observatory’s
(SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic
Imager (HMI). Similar to single-spire jets, this two-sided loop jet
results from eruption of a minifilament, which accelerates to over 140
km s<SUP>-1</SUP> before abruptly stopping after striking an overlying
nearly horizontal-loop field at ∼30,000 km in altitude and producing
the two-sided loop jet. An analysis of EIS raster scans shows that a hot
brightening, consistent with a small flare, develops in the aftermath
of the eruption, and that Doppler motions (∼40 km s<SUP>-1</SUP>)
occur near the jet formation region. As with many single-spire jets, the
magnetic trigger here is apparently flux cancelation, which occurs at
a rate of ∼4 × 10<SUP>18</SUP> Mx hr<SUP>-1</SUP>, broadly similar
to the rates observed in some single-spire quiet-Sun and AR jets. An
apparent increase in the (line-of-sight) flux occurs within minutes of
the onset of the minifilament eruption, consistent with the apparent
increase being due to a rapid reconfiguration of low-lying fields
during and soon after the minifilament-eruption onset.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Coronal Jets, and the Jet-CME Connection
Authors: Sterling, Alphonse C.
2018JPhCS1100a2024S Altcode: 2019arXiv191202808S
Solar coronal jets have been observed in detail since the early
1990s. While it is clear that these jets are magnetically driven, the
details of the driving process has recently been updated. Previously
it was suspected that the jets were a consequence of magnetic flux
emergence interacting with ambient coronal field. New evidence however
indicates that often the direct driver of the jets is erupting field,
often carrying cool material (a “minifilament”), that undergoes
interchange magnetic reconnection with preexisting field ([1]). More
recent work indicates that the trigger for eruption of the minifilament
is frequently cancelation of photospheric magnetic fields at the base
of the minifilament. These erupting minifilaments are analogous to the
better-known larger-scale filament eruptions that produce solar flares
and, frequently, coronal mass ejections (CMEs). A subset of coronal
jets drive narrow “white-light jets,” which are very narrow CME-like
features, and apparently a few jets can drive wider, although relatively
weak, “streamer-puff” CMEs. Here we summarize these recent findings.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Solar Explosions Imager (SEIM): A Next-Generation
High-Resolution and High-Cadence EUV Telescope for Unraveling Eruptive
Solar Features
Authors: Sterling, Alphonse C.; Moore, Ronald Lee; Winebarger, Amy R.
2018tess.conf11002S Altcode:
We present a skeletal proposal for a space-based EUV telescope to
fly on the Next Generation Solar Physics Mission (NGSPM). A primary
motivation is to unravel physical processes leading to small-scale
solar features, such as solar coronal jets, and the processes leading
to larger eruptions as well. Recent evidence suggests that jets
result from eruptions of small-scale filaments (size scale: ~1—a
few arcsec), analogous to larger filament eruptions that drive CMEs,
and it is plausible that the even-smaller-scale spicules (∼0′′.1)
operate in a similar fashion. Therefore an instrument planned around
the concept of observing jet features, but with the highest practical
resolution and cadence, would be valuable for observing various erupting
solar features on many size and time scales. Resolution and cadence
should be comparable to or better than that of Hi-C, i.e. ≤0”.1
pixels and ≤10 s cadence. While no single instrument could span the
entire needed data-set space needed to address fully these questions,
the proposed instrument would complement first-rate instrumentation
(namely, DKIST) expected to be in operation around the time of expected
deployment. If resources permit, the proposed EUV instrument could
be supplemented with additional instrumentation, or such additional
instrumentation could be proposed as (a) separate effort(s). Especially
complementary would be a photospheric magnetograph having ≤0”.1
pixels, ≤1-minute cadence, line-of-sight-field sensitivity of ≤10
G, and few-arc-minute FOV. (The SEIM concept has been presented as a
WhitePaper with the same title to the NGSPM planning committee.)
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: A Microfilament-Eruption Mechanism for Solar Spicules
Authors: Sterling, A. C.; Moore, R. L.
2017AGUFMSH43A2791S Altcode:
Recent studies indicate that solar coronal jets result from eruption
of small-scale filaments, or "minifilaments" (Sterling et al. 2015,
Nature, 523, 437; Panesar et al. ApJL, 832L, 7). In many aspects,
these coronal jets appear to be small-scale versions of long-recognized
large-scale solar eruptions that are often accompanied by eruption of
a large-scale filament and that produce solar flares and coronal mass
ejections (CMEs). In coronal jets, a jet-base bright point (JBP) that
is often observed to accompany the jet and that sits on the magnetic
neutral line from which the minifilament erupts, corresponds to the
solar flare of larger-scale eruptions that occurs at the neutral line
from which the large-scale filament erupts. Large-scale eruptions are
relatively uncommon ( 1/day) and occur with relatively large-scale
erupting filaments ( 10^5 km long). Coronal jets are more common (>
100s/day), but occur from erupting minifilaments of smaller size ( 10^4
km long). It is known that solar spicules are much more frequent (many
millions/day) than coronal jets. Just as coronal jets are small-scale
versions of large-scale eruptions, here we suggest that solar spicules
might in turn be small-scale versions of coronal jets; we postulate that
the spicules are produced by eruptions of “microfilaments” of length
comparable to the width of observed spicules ( 300 km). A plot of the
estimated number of the three respective phenomena (flares/CMEs, coronal
jets, and spicules) occurring on the Sun at a given time, against the
average sizes of erupting filaments, minifilaments, and the putative
microfilaments, results in a size distribution that can be fit with a
power-law within the estimated uncertainties. The counterparts of the
flares of large-scale eruptions and the JBPs of jets might be weak,
pervasive, transient brightenings observed in Hinode/CaII images, and
the production of spicules by microfilament eruptions might explain why
spicules spin, as do coronal jets. The expected small-scale neutral
lines from which the microfilaments would be expected to erupt would
be difficult to detect reliably with current instrumentation, but
might be apparent with instrumentation of the near future. A summary
of this work appears in Sterling and Moore 2016, ApJL, 829, L9.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Onset of a Large Ejective Solar Eruption from a Typical
Coronal-jet-base Field Configuration
Authors: Joshi, Navin Chandra; Sterling, Alphonse C.; Moore, Ronald
L.; Magara, Tetsuya; Moon, Yong-Jae
2017ApJ...845...26J Altcode: 2017arXiv170609176J
Utilizing multiwavelength observations and magnetic field data from
the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA), SDO/Helioseismic and Magnetic Imager (HMI), the Geostationary
Operational Environmental Satellite (GOES), and RHESSI, we investigate
a large-scale ejective solar eruption of 2014 December 18 from active
region NOAA 12241. This event produced a distinctive “three-ribbon”
flare, having two parallel ribbons corresponding to the ribbons of a
standard two-ribbon flare, and a larger-scale third quasi-circular
ribbon offset from the other two. There are two components to this
eruptive event. First, a flux rope forms above a strong-field polarity
inversion line and erupts and grows as the parallel ribbons turn on,
grow, and spread apart from that polarity inversion line; this evolution
is consistent with the mechanism of tether-cutting reconnection for
eruptions. Second, the eruption of the arcade that has the erupting
flux rope in its core undergoes magnetic reconnection at the null
point of a fan dome that envelops the erupting arcade, resulting
in formation of the quasi-circular ribbon; this is consistent with
the breakout reconnection mechanism for eruptions. We find that
the parallel ribbons begin well before (∼12 minutes) the onset
of the circular ribbon, indicating that tether-cutting reconnection
(or a non-ideal MHD instability) initiated this event, rather than
breakout reconnection. The overall setup for this large-scale eruption
(diameter of the circular ribbon ∼10<SUP>5</SUP> km) is analogous to
that of coronal jets (base size ∼10<SUP>4</SUP> km), many of which,
according to recent findings, result from eruptions of small-scale
“minifilaments.” Thus these findings confirm that eruptions of
sheared-core magnetic arcades seated in fan-spine null-point magnetic
topology happen on a wide range of size scales on the Sun.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
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: Babcock Redux: An Amendment of Babcock's Schematic of the
Sun's Magnetic Cycle
Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.
2017SPD....4811103M Altcode:
We amend Babcock's original scenario for the global dynamo process
that sustains the Sun's 22-year magnetic cycle. The amended scenario
fits post-Babcock observed features of the magnetic activity cycle and
convection zone, and is based on ideas of Spruit & Roberts (1983,
Nature, 304, 401) about magnetic flux tubes in the convection zone. A
sequence of four schematic cartoons lays out the proposed evolution
of the global configuration of the magnetic field above, in, and at
the bottom of the convection zone through sunspot Cycle 23 and into
Cycle 24. Three key elements of the amended scenario are: (1) as the
net following-polarity magnetic field from the sunspot-region Ω-loop
fields of an ongoing sunspot cycle is swept poleward to cancel and
replace the opposite-polarity polar-cap field from the previous sunspot
cycle, it remains connected to the ongoing sunspot cycle's toroidal
source-field band at the bottom of the convection zone; (2) topological
pumping by the convection zone's free convection keeps the horizontal
extent of the poleward-migrating following-polarity field pushed to
the bottom, forcing it to gradually cancel and replace old horizontal
field below it that connects the ongoing-cycle source-field band to
the previous-cycle polar-cap field; (3) in each polar hemisphere,
by continually shearing the poloidal component of the settling new
horizontal field, the latitudinal differential rotation low in the
convection zone generates the next-cycle source-field band poleward
of the ongoing-cycle band. The amended scenario is a more-plausible
version of Babcock's scenario, and its viability can be explored
by appropriate kinematic flux-transport solar-dynamo simulations. A
paper giving a full description of our dynamo scenario is posted on
arXiv (http://arxiv.org/abs/1606.05371).This work was funded by the
Heliophysics Division of NASA's Science Mission Directorate through
the Living With a Star Targeted Research and Technology Program and
the Hinode Project.
---------------------------------------------------------
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: 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: Evaluation of the Minifilament-Eruption Scenario for Solar
Coronal Jets in Polar Coronal Holes
Authors: Sterling, A. C.; Baikie, T. K.; Falconer, D. A.; Moore,
R. L.; Savage, S. L.
2016AGUFMSH31B2574S Altcode:
Solar coronal jets are suspected to result from magnetic reconnection
low in the Sun's atmosphere. Sterling et al. (2015) looked at 20 jets
in polar coronal holes, using X-ray images from the Hinode/X-Ray
Telescope (XRT) and EUV images from the Solar Dynamics Observatory
(SDO) Atmospheric Imaging Assembly (AIA). They suggested that each jet
was driven by the eruption of twisted closed magnetic field carrying
a small-scale filament, which they call a "minifilament", and that
the jet was produced by reconnection of the erupting field with
surrounding open field. In this study, we carry out a more extensive
examination of polar coronal jets. From 280 hours of XRT polar coronal
hole observations spread over two years (2014-2016), we identified 117
clearly-identifiable X-ray jet events. From the broader set, we selected
25 of the largest and brightest events for further study in AIA 171,
193, 211, and 304 Angstrom images. We find that at least the majority
of the jets follow the minifilament-eruption scenario, although for some
cases the evolution of the minifilament in the onset of its eruption is
more complex then presented in the simplified schematic of Sterling et
al. (2015). For all cases in which we could make a clear determination,
the spire of the X-ray jet drifted laterally away from the jet-base-edge
bright point; this spire drift away from the bright point is consistent
with expectations of the minifilament-eruption scenario for coronal-jet
production. This work was supported with funding from the NASA/MSFC
Hinode Project Office, and from the NASA HGI program.
---------------------------------------------------------
Title: Solar Coronal Jets in Active Regions
Authors: Sterling, A. C.; Moore, R. L.; Martinez, F.; Falconer, D. A.
2016AGUFMSH43E..06S Altcode:
Solar coronal jets are common in both coronal holes and in active
regions. Recently, Sterling et al. (2015, Nature 523, 437), 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 process, such
as emerging flux. Here we present observations of NOAA active region
12259, over 13-20 Jan 2015, using observations from Hinode/XRT, and
from SDO/AIA and HMI. We focused on 13 standout jets that we identified
from an initial survey of the XRT X-ray images, and we found many more
jets in the AIA data set, which have higher cadence and more continuous
coverage than our XRT data. All 13 jets originated from identifiable
magnetic neutral lines; we further found magnetic flux cancelation to
be occurring at essentially all of these neutral lines. At least 6 of
those 13 jets were homologous, developing with similar morphology from
nearly the same location, and in fact there were many more jets in the
homologous sequence apparent in the higher-fidelity AIA data. Each of
these homologous jets was consistent with minifilament-like ejections at
the start of the jets. Other jets displayed a variety of morphologies,
at least some of which were consistent with minifilament eruptions. For
other jets however we have not yet clearly deciphered the driving
mechanism. Our overall conclusions are similar to those of our earlier
study of active region jets (Sterling et al. 2016, ApJ, 821, 100), where
we found: some jets clearly to result from mini-filament eruptions;
it was difficult to disentangle the mechanism of some other jets;
and all of the jets originated from magnetic neutral lines, most of
which were undergoing flux cancelation. This work was supported by
funding from NASA/HGI, from the Hinode project, and (for FM) from the
NASA/MSFC Research Experience for Undergraduates (REU) program.
---------------------------------------------------------
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: Coronal Jets from Minifilament Eruptions in Active Regions
Authors: Sterling, A. C.; Martinez, F.; Falconer, D. A.; Moore, R. L.
2016AGUFMSH31B2567S Altcode:
Solar coronal jets are transient (frequently of lifetime 10 min)
features that shoot out from near the solar surface, become much
longer than their width, and occur in all solar regions, including
coronal holes, quiet Sun, and active regions (e.g., Shimojo et
al. 1996, Certain et al. 2007). Sterling et al. (2015) and other
studies found that in coronal holes and in quiet Sun the jets
result when small-scale filaments, called “minifilaments,” erupt
onto nearby open or high-reaching field lines. Additional studies
found that coronal-jet-onset locations (and hence presumably the
minifilament-eruption-onset locations) coincided with locations of
magnetic-flux cancellation. For active region (AR) jets however the
situation is less clear. Sterling et al. (2016) studied jets in one
active region over a 24-hour period; they found that some AR jets
indeed resulted from minifilament eruptions, usually originating
from locations of episodes of magnetic-flux cancelation. In some
cases however they could not determine whether flux was emerging or
canceling at the polarity inversion line from which the minifilament
erupted; and for other jets of that region minifilaments were not
conclusively apparent prior to jet occurrence. Here we further study
AR jets, by observing them in a single AR over a one-week period,
using X-ray images from Hinode/XRT and EUV/UV images from SDO/AIA,
and line-of-sight magnetograms and white-light intensity-grams from
SDO/HMI. We initially identified 13 prominent jets in the XRT data,
and examined corresponding AIA and HMI data. For at least several of
the jets, our findings are consistent with the jets resulting from
minifilament eruptions, and originating from sights of magnetic-field
cancelation. Thus our findings support that, at least in many cases,
AR coronal jets result from the same physical processes that produce
coronal jets in quiet-Sun and coronal-hole regions. FM was supportedby
the Research Experience for Undergraduates (REU) program at NASA/MSFC
and the University of Alabama, Huntsville. Additional support was from
the NASA HGI program and the Hinode project.
---------------------------------------------------------
Title: Solar Coronal Jets: Observations, Theory, and Modeling
Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.;
Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.;
DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.;
Meyer, K.; Dalmasse, K.; Matsui, Y.
2016SSRv..201....1R Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R
Coronal jets represent important manifestations of ubiquitous solar
transients, which may be the source of significant mass and energy
input to the upper solar atmosphere and the solar wind. While
the energy involved in a jet-like event is smaller than that of
"nominal" solar flares and coronal mass ejections (CMEs), jets
share many common properties with these phenomena, in particular,
the explosive magnetically driven dynamics. Studies of jets could,
therefore, provide critical insight for understanding the larger,
more complex drivers of the solar activity. On the other side of the
size-spectrum, the study of jets could also supply important clues on
the physics of transients close or at the limit of the current spatial
resolution such as spicules. Furthermore, jet phenomena may hint to
basic process for heating the corona and accelerating the solar wind;
consequently their study gives us the opportunity to attack a broad
range of solar-heliospheric problems.
---------------------------------------------------------
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: The 2016 Transit of Mercury Observed from Major Solar
Telescopes and Satellites
Authors: Pasachoff, Jay M.; Schneider, Glenn; Gary, Dale; Chen, Bin;
Sterling, Alphonse C.; Reardon, Kevin P.; Dantowitz, Ronald; Kopp,
Greg A.
2016DPS....4811705P Altcode:
We report observations from the ground and space of the 9 May 2016
transit of Mercury. We build on our explanation of the black-drop
effect in transits of Venus based on spacecraft observations of the 1999
transit of Mercury (Schneider, Pasachoff, and Golub, Icarus 168, 249,
2004). In 2016, we used the 1.6-m New Solar Telescope at the Big Bear
Solar Observatory with active optics to observe Mercury's transit at
high spatial resolution. We again saw a small black-drop effect as 3rd
contact neared, confirming the data that led to our earlier explanation
as a confluence of the point-spread function and the extreme solar
limb darkening (Pasachoff, Schneider, and Golub, in IAU Colloq. 196,
2004). We again used IBIS on the Dunn Solar Telescope of the Sacramento
Peak Observatory, as A. Potter continued his observations, previously
made at the 2006 transit of Mercury, at both telescopes of the sodium
exosphere of Mercury (Potter, Killen, Reardon, and Bida, Icarus 226,
172, 2013). We imaged the transit with IBIS as well as with two RED
Epic IMAX-quality cameras alongside it, one with a narrow passband. We
show animations of our high-resolution ground-based observations along
with observations from XRT on JAXA's Hinode and from NASA's Solar
Dynamics Observatory. Further, we report on the limit of the transit
change in the Total Solar Irradiance, continuing our interest from
the transit of Venus TSI (Schneider, Pasachoff, and Willson, ApJ 641,
565, 2006; Pasachoff, Schneider, and Willson, AAS 2005), using NASA's
SORCE/TIM and the Air Force's TCTE/TIM. See http://transitofvenus.info
and http://nicmosis.as.arizona.edu.Acknowledgments: We were glad for
the collaboration at Big Bear of Claude Plymate and his colleagues of
the staff of the Big Bear Solar Observatory. We also appreciate the
collaboration on the transit studies of Robert Lucas (Sydney, Australia)
and Evan Zucker (San Diego, California). JMP appreciates the sabbatical
hospitality of the Division of Geosciences and Planetary Sciences of
the California Institute of Technology, and of Prof. Andrew Ingersoll
there. The solar observations lead into the 2017 eclipse studies,
for which JMP is supported by grants from the NSF AGS and National
Geographic CRE.
---------------------------------------------------------
Title: Babcock Redux: An Amendment of Babcock's Schematic of the
Sun's Magnetic Cycle
Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.
2016usc..confE...5M Altcode: 2016arXiv160605371M
We amend Babcock's original scenario for the global dynamo process
that sustains the Sun's 22-year magnetic cycle. The amended scenario
fits post-Babcock observed features of the magnetic activity cycle
and convection zone, and is based on ideas of Spruit & Roberts
(1983) about magnetic flux tubes in the convection zone. A sequence of
four schematic cartoons lays out the proposed evolution of the global
configuration of the magnetic field above, in, and at the bottom of the
convection zone through sunspot Cycle 23 and into Cycle 24. Three key
elements of the amended scenario are: (1) as the net following-polarity
magnetic field from the sunspot-region -loop fields of an
ongoing sunspot cycle is swept poleward to cancel and replace the
opposite-polarity polar-cap field from the previous sunspot cycle, it
remains connected to the ongoing sunspot cycle's toroidal source-field
band at the bottom of the convection zone; (2) topological pumping by
the convection zone's free convection keeps the horizontal extent of
the poleward-migrating following-polarity field pushed to the bottom,
forcing it to gradually cancel and replace old horizontal field below it
that connects the ongoing-cycle source-field band to the previous-cycle
polar-cap field; (3) in each polar hemisphere, by continually shearing
the poloidal component of the settling new horizontal field, the
latitudinal differential rotation low in the convection zone generates
the next-cycle source-field band poleward of the ongoing-cycle band. The
amended scenario is a more-plausible version of Babcock's scenario, and
its viability can be explored by appropriate kinematic flux-transport
solar-dynamo simulations. A paper of the above title and authors, giving
a full description of the solar dynamo scenario of this abstract, is
available at http://arxiv.org/abs/1606.05371. This work was funded by
the Heliophysics Division of NASA's Science Mission Directorate through
the Living With a Star Targeted Research and Technology Program and
the Hinode Project.
---------------------------------------------------------
Title: A Microfilament-eruption Mechanism for Solar Spicules
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2016ApJ...828L...9S Altcode: 2016arXiv161200430S
Recent investigations indicate that solar coronal jets result from
eruptions of small-scale chromospheric filaments, called minifilaments;
that is, the jets are produced by scaled-down versions of typical-sized
filament eruptions. We consider whether solar spicules might in turn
be scaled-down versions of coronal jets, being driven by eruptions
of microfilaments. Assuming a microfilament's size is about a
spicule's width (∼300 km), the estimated occurrence number plotted
against the estimated size of erupting filaments, minifilaments, and
microfilaments approximately follows a power-law distribution (based
on counts of coronal mass ejections, coronal jets, and spicules),
suggesting that many or most spicules could result from microfilament
eruptions. Observed spicule-base Ca II brightenings plausibly result
from such microfilament eruptions. By analogy with coronal jets,
microfilament eruptions might produce spicules with many of their
observed characteristics, including smooth rise profiles, twisting
motions, and EUV counterparts. The postulated microfilament eruptions
are presumably eruptions of twisted-core micro-magnetic bipoles
that are ∼1.″0 wide. These explosive bipoles might be built and
destabilized by merging and cancelation of approximately a few to 100
G magnetic-flux elements of size ≲ 0\buildrel{\prime\prime}\over{.}
5{--}1\buildrel{\prime\prime}\over{.} 0. If, however, spicules
are relatively more numerous than indicated by our extrapolated
distribution, then only a fraction of spicules might result from this
proposed mechanism.
---------------------------------------------------------
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: Analysis of an Anemone-Type Eruption in an On-Disk Coronal Hole
Authors: Adams, Mitzi; Tennant, Allyn F.; Alexander, Caroline E.;
Sterling, Alphonse C.; Moore, Ronald L.; Woolley, Robert
2016SPD....4740701A Altcode:
We report on an eruption seen in a very small coronal hole (about
120” across), beginning at approximately 19:00 UT on March 3,
2016. The event was initially observed by an amateur astronomer (RW)
in an H-alpha movie from the Global Oscillation Network Group (GONG);
the eruption attracted the attention of the observer because there was
no nearby active region. To examine the region in detail, we use data
from the Solar Dynamics Observatory (SDO), provided by the Atmospheric
Imaging Assembly (AIA) in wavelengths 193 Å, 304 Å, and 94 Å, and the
Helioseismic and Magnetic Imager (HMI). Data analysis and calibration
activities such as scaling, rotation so that north is up, and removal of
solar rotation are accomplished with SunPy. The eruption in low-cadence
HMI data begins with the appearance of a bipole in the location of
the coronal hole, followed by (apparent) expansion outwards when the
intensity of the AIA wavelengths brighten; as the event proceeds,
the coronal hole disappears. From high-cadence data, we will present
results on the magnetic evolution of this structure, how it is related
to intensity brightenings seen in the various SDO/AIA wavelengths,
and how this event compares with the standard-anemone picture.
---------------------------------------------------------
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: Early Evaluation of the Corona at the 2016 March 9 Total
Solar Eclipse
Authors: Pasachoff, Jay M.; Seaton, Daniel B.; Sterling, Alphonse C.
2016SPD....47.0326P Altcode:
We observed the corona on 2016 March 9 with a variety of assets on
the ground and in space. The umbra of the total eclipse swept across
Indonesia and into the Pacific, with totality at our Indonesian
observation sites lasting 2 min 45 s at Ternate in the Spice Islands
(Malukus) and 2 min 10 at Belitung. We compare our ground-based
results with the coronal configurations observed with PROBA2/SWAP
and Hinode XRT. One of our scientific goals is to follow the coronal
configuration over the solar-activity cycle, with the sunspot number
now half its maximum of either its 2012 or 2014 peak. We are evaluating
temporal changes by comparing eclipse observations made at several
ground-based sites along the path, with the longest span being 75 min
from Belitung to the Woleia atoll in mid-Pacific, 1:25 UTC to 2:40 UTC;
we are evaluating whether the airborne observations made at 3:35 UTC
on March 8 (across the International Dateline) are of suitable quality
to provide further comparison at high spatial resolution. We also
compare our images with the near-simultaneous coronal observations
made with SOHO/LASCO, SDO/AIA, STEREO-A/SECCHI, and the Mauna Loa
Solar Observatory's K-cor coronagraph. ACS received support for image
analysis from the Hinode project.
---------------------------------------------------------
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: Probing Solar Eruption by Tracking Magnetic Cavities and
Filaments
Authors: Sterling, A. C.; Johnson, J. R.; Moore, R. L.; Gibson, S. E.
2015AGUFMSH53B2489S Altcode:
A solar eruption is a tremendous explosion on the Sun that happens when
energy stored in twisted (or distorted) magnetic fields is suddenly
released. When this field is viewed along the axis of the twist in
projection at the limb, e.g. in EUV or white-light coronal images,
the outer portions of the pre-eruption magnetic structure sometimes
appears as a region of weaker emission, called a "coronal cavity,"
surrounded by a brighter envelope. Often a chromospheric filament
resides near the base of the cavity and parallel to the cavity's central
axis. Typically, both the cavity and filament move outward from the Sun
at the start of an eruption of the magnetic field in which the cavity
and filament reside. Studying properties the cavities and filaments
just prior to and during eruption can help constrain models that
attempt to explain why and how the eruptions occur. In this study,
we examined six different at-limb solar eruptions using images from
the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and
Heliospheric Observatory (SOHO). For four of these eruptions we observed
both cavities and filaments, while for the remaining two eruptions,
one had only a cavity and the other only a filament visible in EIT
images. All six eruptions were in comparatively-quiet solar regions,
with one in the neighborhood of the polar crown. We measured the height
and velocities of the cavities and filaments just prior to and during
the start of their fast-eruption onsets. Our results support that the
filament and cavity are integral parts of a single large-scale erupting
magnetic-field system. We examined whether the eruption-onset heights
were correlated with the expected magnetic field strengths of the
eruption-source regions, but no clear correlation was found. We discuss
possible reasons for this lack of correlation, and we also discuss
future research directions. The research performed was supported
by the National Science Foundation under Grant No. AGS-1460767;
J.J. participated in the Research Experience for Undergraduates (REU)
program, at NASA/MSFC. Additional support was from a grant from the
NASA LWS program.
---------------------------------------------------------
Title: Revised View of Solar X-Ray Jets
Authors: Sterling, A. C.; Moore, R. L.; Falconer, D. A.; Adams, M.
2015AGUFMSH23D..04S Altcode:
We investigate the onset of ~20 random X-ray jets observed by
Hinode/XRT. Each jetwas near the limb in a polar coronal hole,
and showed a ”bright point” in anedge of the base of the jet, as
is typical for previously-observed X-ray jets. Weexamined SDO/AIA
EUV images of each of the jets over multiple AIA channels,including
304 Ang, which detects chromospheric emissions, and 171, 193, and
211 Ang,which detect cooler-coronal emissions. We find the jets to
result from eruptionsof miniature (size <~10 arcsec) filaments from
the bases of the jets. In manycases, much of the erupting-filament
material forms a chromospheric-temperaturejet. In the cool-coronal
channels, often the filament appears in absorption andthe hotter
EUV component of the jet appears in emission. The jet bright point
formsat the location from which the miniature filament erupts,
analogous to theformation of a standard solar flare arcade via flare
(“internal”) reconnection in the wake of the eruption of a typical
larger-scale chromospheric filament. Thespire of the jet forms on open
field lines that presumably have undergoneinterchange (”external”)
reconnection with the erupting field that envelops andcarries the
miniature filament. This is consistent with what we found for theonset
of an on-disk coronal jet we examined in Adams et al. (2014), and
theobservations of other workers. It is however not consistent with
the basicversion of the ”emerging-flux model” for X-ray jets. This
work was supported byfunding from NASA/LWS, Hinode, and ISSI.
---------------------------------------------------------
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: Visibility of Hinode/XRT X-Ray Jets at AIA/EUV Wavelengths,
a Temperature Indicator
Authors: Sterling, A. C.; Bakucz Canario, D.; Moore, R. L.; Falconer,
D. A.
2015AGUFMSH31B2415S Altcode:
X-ray jets have been observed for years using data from the X-Ray
Telescope (XRT) on the Hinode Satellite. Recently with the launch of the
Solar Dynamics Observatory (SDO) it has been possible to observe solar
jets over a range of EUV of wavelengths using the Atmospheric Imaging
Assembly (AIA). In this study, we investigated the appearance of X-ray
jets in AIA images at wavelengths of 304, 171, 193, 211, 131, 94, and
335 Å. We selected 20 random X-ray jets from XRT movies of the polar
coronal holes and then examined AIA EUV images from the same locations
and times to determine the visibility of the jets at the different EUV
wavelengths. We found that the jets were almost always visible in the
193 and 211 Å channel images. In the "hottest" EUV channels (94 Å, 335
Å), usually the spire of the jet was not visible, although sometimes
a base brightening could be discerned. At other wavelengths (171, 131,
and 335), the results were mixed. Based on the response characteristics
of AIA (Lemen et al, 2011) to the temperature of the observed radiating
solar plasma, our finding that most jets are visible in the 193 and 211
Å channels is consistent with other recent studies that measured jet
temperatures of 1.5~2.0 MK (Pucci et al, 2012 & Paraschiv et al,
2015). This work was supported by the NASA LWS and HGI programs.
---------------------------------------------------------
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: Small-scale filament eruptions as the driver of X-ray jets
in solar coronal holes
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.;
Adams, Mitzi
2015Natur.523..437S Altcode: 2017arXiv170503373S
Solar X-ray jets are thought to be made by a burst of reconnection
of closed magnetic field at the base of a jet with ambient open
field. In the accepted version of the `emerging-flux' model, such
a reconnection occurs at a plasma current sheet between the open
field and the emerging closed field, and also forms a localized X-ray
brightening that is usually observed at the edge of the jet's base. Here
we report high-resolution X-ray and extreme-ultraviolet observations
of 20 randomly selected X-ray jets that form in coronal holes at
the Sun's poles. In each jet, contrary to the emerging-flux model,
a miniature version of the filament eruptions that initiate coronal
mass ejections drives the jet-producing reconnection. The X-ray bright
point occurs by reconnection of the `legs' of the minifilament-carrying
erupting closed field, analogous to the formation of solar flares in
larger-scale eruptions. Previous observations have found that some
jets are driven by base-field eruptions, but only one such study, of
only one jet, provisionally questioned the emerging-flux model. Our
observations support the view that solar filament eruptions are formed
by a fundamental explosive magnetic process that occurs on a vast range
of scales, from the biggest mass ejections and flare eruptions down
to X-ray jets, and perhaps even down to smaller jets that may power
coronal heating. A similar scenario has previously been suggested,
but was inferred from different observations and based on a different
origin of the erupting minifilament.
---------------------------------------------------------
Title: Physical properties of solar polar jets. A statistical study
with Hinode XRT data
Authors: Paraschiv, A. R.; Bemporad, A.; Sterling, A. C.
2015A&A...579A..96P Altcode: 2015arXiv150507191P
<BR /> Aims: The target of this work is to investigate the physical
nature of polar jets in the solar corona and their possible contribution
to coronal heating and solar wind flow based on the analysis of
X-ray images acquired by the Hinode XRT telescope. We estimate the
different forms of energy associated with many of these small-scale
eruptions, in particular the kinetic energy and enthalpy. <BR />
Methods: Two Hinode XRT campaign datasets focusing on the two polar
coronal holes were selected to analyze the physical properties of
coronal jets; the analyzed data were acquired using a series of
three XRT filters. Typical kinematical properties (e.g., length,
thickness, lifetime, ejection rate, and velocity) of 18 jets are
evaluated from the observed sequences, thus providing information
on their possible contribution to the fast solar wind flux escaping
from coronal holes. Electron temperatures and densities of polar-jet
plasmas are also estimated using ratios of the intensities observed
in different filters. <BR /> Results: We find that the largest amount
of energy eventually provided to the corona is thermal. The energy
due to waves may also be significant, but its value is comparatively
uncertain. The kinetic energy is lower than thermal energy, while other
forms of energy are comparatively low. Lesser and fainter events seem
to be hotter, thus the total contribution by polar jets to the coronal
heating could have been underestimated so far. The kinetic energy flux
is usually around three times smaller than the enthalpy counterpart,
implying that this energy is converted into plasma heating more than in
plasma acceleration. This result suggests that the majority of polar
jets are most likely not escaping from the Sun and that only cooler
ejections could possibly have enough kinetic energy to contribute to
the total solar wind flow.
---------------------------------------------------------
Title: Magnetic Untwisting in Solar Jets that Go into the Outer
Corona in Polar Coronal Holes
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A.
2015ApJ...806...11M Altcode: 2015arXiv150403700M
We study 14 large solar jets observed in polar coronal holes. In
EUV movies from the Solar Dynamics Observatory/Atmospheric Imaging
Assembly (AIA), each jet appears similar to most X-ray jets and
EUV jets that erupt in coronal holes; but each is exceptional in
that it goes higher than most, so high that it is observed in the
outer corona beyond 2.2 R <SUB>Sun</SUB> in images from the Solar
and Heliospheric Observatory/Large Angle Spectroscopic Coronagraph
(LASCO)/C2 coronagraph. From AIA He ii 304 Å movies and LASCO/C2
running-difference images of these high-reaching jets, we find: (1)
the front of the jet transits the corona below 2.2 R <SUB>Sun</SUB> at
a speed typically several times the sound speed; (2) each jet displays
an exceptionally large amount of spin as it erupts; (3) in the outer
corona, most of the jets display measureable swaying and bending of
a few degrees in amplitude; in three jets the swaying is discernibly
oscillatory with a period of order 1 hr. These characteristics suggest
that the driver in these jets is a magnetic-untwisting wave that is
basically a large-amplitude (i.e., nonlinear) torsional Alfvén wave
that is put into the reconnected open field in the jet by interchange
reconnection as the jet erupts. From the measured spinning and swaying,
we estimate that the magnetic-untwisting wave loses most of its energy
in the inner corona below 2.2 R <SUB>Sun</SUB>. We point out that the
torsional waves observed in Type-II spicules might dissipate in the
corona in the same way as the magnetic-untwisting waves in our big jets,
and thereby power much of the coronal heating in coronal holes.
---------------------------------------------------------
Title: Small-Scale Filament Eruptions Leading to Solar X-Ray Jets
Authors: Sterling, Alphonse; Moore, Ronald; Falconer, David
2015TESS....140701S Altcode:
We investigate the onset of ~10 random X-ray jets observed by
Hinode/XRT. Each jet was near the limb in a polar coronal hole, and
showed a “bright point” in an edge of the base of the jet, as is
typical for previously-observed X-ray jets. We examined SDO/AIA EUV
images of each of the jets over multiple AIA channels, including
304 Å, which detects chromospheric emissions, and 171, 193, and
211 Å, which detect cooler-coronal emissions. We find the jets to
result from eruptions of miniature (size <~10 arcsec) filaments
from the bases of the jets. Much of the erupting-filament material
forms a chromospheric-temperature jet. In the cool-coronal channels,
often the filament appears in absorption and the hotter EUV component
of the jet appears in emission. The jet bright point forms at the
location from which the miniature filament erupts, analogous to the
formation of a standard solar flare arcade in the wake of the eruption
of a typical larger-scalechromospheric filament. The spire of the jet
forms on open field lines that presumably have undergone interchange
reconnection with the erupting field that envelops and carries the
miniature filament. Thus these X-ray jets and their bright points are
made by miniature filament eruptions via “internal” and “external”
reconnection of the erupting field. This is consistent with what we
found for the onset of an on-disk coronal jet we examined in Adams et
al. (2014). This work was supported by funding from NASA/LWS, Hinode,
and ISSI.
---------------------------------------------------------
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: More Macrospicule Jets in On-Disk Coronal Holes
Authors: Adams, Mitzi; Sterling, Alphonse; Moore, Ronald
2015TESS....120301A Altcode:
We examine the magnetic structure and dynamics of multiple jets found
in coronal holes close to or at disk center. All data are from the
Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic
Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on
observations of about ten jets in an equatorial coronal hole spanning
2011 February 27 and 28. We show the evolution of these jets in AIA 193
Å, examine the magnetic field configuration and flux changes in the
jet area, and discuss the probable trigger mechanism of these events. We
reported on another jet in this same coronal hole on 2011 February 27,
~13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously
unrecognized variety of blowout jet, in which the base-edge bright
point is a miniature filament-eruption flare arcade made by internal
reconnection of the legs of the erupting field. In contrast, in the
presently-accepted "standard" picture for blowout jets, the base-edge
bright point is made by interchange reconnection of initially-closed
erupting jet-base field with ambient open field. This poster presents
further evidence of the production of the base-edge bright point in
blowout jets by internal reconnection. Our observations suggest that
most of the bigger and brighter EUV jets in coronal holes are blowout
jets of the new-found variety.
---------------------------------------------------------
Title: Reconnection and Spire Drift in Coronal Jets
Authors: Moore, Ronald; Sterling, Alphonse; Falconer, David
2015TESS....140702M Altcode:
It is observed that there are two morphologically-different kinds of
X-ray/EUV jets in coronal holes: standard jets and blowout jets. In
both kinds: (1) in the base of the jet there is closed magnetic
field that has one foot in flux of polarity opposite that of the
ambient open field of the coronal hole, and (2) in coronal X-ray/EUV
images of the jet there is typically a bright nodule at the edge
of the base. In the conventional scenario for jets of either kind,
the bright nodule is a compact flare arcade, the downward product of
interchange reconnection of closed field in the base with impacted
ambient open field, and the upper product of this reconnection is the
jet-outflow spire. It is also observed that in most jets of either
kind the spire drifts sideways away from the bright nodule. We present
the observed bright nodule and spire drift in an example standard
jet and in two example blowout jets. With cartoons of the magnetic
field and its reconnection in jets, we point out: (1) if the bright
nodule is a compact flare arcade made by interchange reconnection,
then the spire should drift toward the bright nodule, and (2) if
the bright nodule is instead a compact flare arcade made, as in a
filament-eruption flare, by internal reconnection of the legs of the
erupting sheared-field core of a lobe of the closed field in the base,
then the spire, made by the interchange reconnection that is driven on
the outside of that lobe by the lobe’s internal convulsion, should
drift away from the bright nodule. Therefore, from the observation
that the spire usually drifts away from the bright nodule, we infer:
(1) in X-ray/EUV jets of either kind in coronal holes the interchange
reconnection that generates the jet-outflow spire usually does not make
the bright nodule; instead, the bright nodule is made by reconnection
inside erupting closed field in the base, as in a filament eruption,
the eruption being either a confined eruption for a standard jet or
a blowout eruption (as in a CME) for a blowout jet, and (2) in this
respect, the conventional reconnection picture for the bright nodule in
coronal jets is usually wrong for observed coronal jets of either kind.
---------------------------------------------------------
Title: Exploring Euv Spicules Using 304 Ang He II Data from SDO/AIA
Authors: Snyder, I. R.; Sterling, A. C.; Falconer, D. A.; Moore, R. L.
2014AGUFMSH51C4179S Altcode:
We present results from an exploratory study of He II 304 ŠEUV
spicules at the limb of the Sun. We also measured properties of
one macrospicule; macrospicules are longer than most spicules, and
much broader in width than spicules. We use high-cadence (12 sec)
and high-resolution (0.6 arcsec pixels) data from the Atmospheric
Imaging Array (AIA) instrument on the Solar Dynamic Observatory
(SDO). All of the observed events occurred near the solar north pole,
in quiet-Sun or coronal-hole environments. We examined the maximum
lengths, maximum rise velocities, and lifetimes of about 30 EUV spicules
and the macrospicule. For the bulk of the EUV spicules the ranges of
these quantities are respectively ~10,000----40,000 km, 20---100 km/s,
and ~100--- ~600 sec. For the macrospicule the corresponding quantities
are respectively ~60,000 km, ~130 km/s, and ~1800 sec, which is typical
of macrospicules measured by other workers. Therefore macrospicules
are taller, longer-lived, and faster than most EUV spicules. The
rise profiles of both the spicules and the macrospicules fit well to
a second-order ("parabolic”) trajectory, although the acceleration
was often weaker than that of solar gravity in the profiles fitted to
the trajectories. Our macrospicule also had an obvious brightening at
its base at birth, whereas such brightenings were not apparent for
the EUV spicules. Most of the EUV spicules remained visible during
their decent back to the solar surface, although a small percentage
of the spicules and the macrospicule faded out before falling back
to the surface. Our sample of macrospicules is not yet large enough
to address whether they are scaled-up versions of EUV spicules, or
independent phenomena. A.C.S. and R.L.M. were supported by funding from
the Heliophysics Division of NASA's Science Mission Directorate through
the Living With a Star Targeted Research and Technology Program, and
the Hinode Project. I.R.S. was supported by NSF's Research Experience
for Undergraduates Program.
---------------------------------------------------------
Title: Macrospicule Jets in On-Disk Coronal Holes
Authors: Adams, M.; Sterling, A. C.; Moore, R. L.
2014AGUFMSH51C4178A Altcode:
We examine the magnetic structure and dynamics of multiple jets found
in coronal holes close to or on disk center. All data are from the
Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic
Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on
observations of ten jets in an equatorial coronal hole from 2011
February 27 and multiple jets found in equatorial coronal holes
on these dates: 2010-June-4, 2012-March-13, 2013-May 29-2013, and
2014-February-24. We will show in detail the evolution of the jets
and will compare the magnetic field arrangement and probable trigger
mechanism of these events to those of a specific macrospicule jet
observed on 2011 February 27. We recently discovered that this jet is
a previously-unrecognized variety of blowout jet (Adams et al 2014,
ApJ, 783: 11). In this variety, the reconnection bright point is not
made by interchange reconnection of initially-closed erupting field
in the base of the jet with ambient open field but is a miniature
filament-eruption flare arcade made by internal reconnection of the
legs of the erupting field.
---------------------------------------------------------
Title: Exploring He II 304 Å Spicules and Macrospicules at the
Solar Limb
Authors: Sterling, A. C.; Snyder, I. R.; Falconer, D. A.; Moore, R. L.
2014AGUFMSH53D..04S Altcode:
We present results from a study of He II 304 Ang spicules and
macrospiculesobserved at the limb of the Sun in 304 Ang channel image
sequences from theAtmospheric Imaging Assembly (AIA) on the Solar
Dynamics Observatory (SDO). Thesedata have both high spatial (0.6 arcsec
pixels) and temporal (12 s) resolution. All of the observed events
occurred in quiet or coronal hole regions near the solarpole. He II 304
Ang spicules and macrospicules are both transient jet-likefeatures,
with the macrospicules being wider and having taller maximum heights
thanthe spicules. We looked for characteristics of the populations
of these twophenomena that might indicate whether they have the same
initiation mechanisms. Weexamine the maximum heights, time-averaged
rise velocities, and lifetimes of about30 spicules and about five
macrospicules. For the spicules, these quantities are,respectively,
~10,000----40,000 km, 20---100 km/s, and a few 100--- ~600 sec. Forthe
macrospicules the corresponding properties are >~60,000 km, >~55
km/s, andlifetimes of >~1800 sec. Therefore the macrospicules have
velocities comparable tothose of the fastest spicules and live longer
than the spicules. The leading-edgetrajectories of both the spicules
and the macrospicules match well a second-order(“parabolic”)
profile, although the acceleration in the fitted profiles is
generally weaker than that of solar gravity. The macrospicules also
have obviousbrightenings at their bases at their birth, while such
brightenings are notapparent for most of the spicules. Our findings are
suggestive of the twophenomena possibly having different initiation
mechanisms, but this is not yetconclusive. A.C.S. and R.L.M. were
supported by funding from the HeliophysicsDivision of NASA's Science
Mission Directorate through the Living With a StarTargeted Research
and Technology Program, and the Hinode Project. I.R.S. wassupported
by NSF's Research Experience for Undergraduates Program.
---------------------------------------------------------
Title: Birth, Life, and Death of a Solar Coronal Plume
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2014ApJ...793...86P Altcode:
We analyze a solar polar-coronal-hole (CH) plume over its entire
≈40 hr lifetime, using high-resolution Solar Dynamic Observatory
Atmospheric Imaging Assembly (AIA) data. We examine (1) the plume's
relationship to a bright point (BP) that persists at its base, (2)
plume outflows and their possible contribution to the solar wind
mass supply, and (3) the physical properties of the plume. We find
that the plume started ≈2 hr after the BP first appeared and became
undetectable ≈1 hr after the BP disappeared. We detected radially
moving radiance variations from both the plume and from interplume
regions, corresponding to apparent outflow speeds ranging over
≈(30-300) km s<SUP>-1</SUP> with outflow velocities being higher
in the "cooler" AIA 171 Å channel than in the "hotter" 193 Å and
211 Å channels, which is inconsistent with wave motions; therefore,
we conclude that the observed radiance variations represent material
outflows. If they persist into the heliosphere and plumes cover ≈10%
of a typical CH area, these flows could account for ≈50% of the
solar wind mass. From a differential emission measure analysis of the
AIA images, we find that the average electron temperature of the plume
remained approximately constant over its lifetime, at T <SUB>e</SUB>
≈ 8.5 × 10<SUP>5</SUP> K. Its density, however, decreased with the
age of the plume, being about a factor of three lower when the plume
faded compared to when it was born. We conclude that the plume died
due to a density reduction rather than to a temperature decrease.
---------------------------------------------------------
Title: New Aspects of a Lid-removal Mechanism in the Onset of an
Eruption Sequence that Produced a Large Solar Energetic Particle
(SEP) Event
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.;
Knox, Javon M.
2014ApJ...788L..20S Altcode:
We examine a sequence of two ejective eruptions from a single active
region on 2012 January 23, using magnetograms and EUV images from the
Solar Dynamics Observatory's (SDO) Helioseismic and Magnetic Imager
(HMI) and Atmospheric and Imaging Assembly (AIA), and EUV images from
STEREO/EUVI. This sequence produced two coronal mass ejections (CMEs)
and a strong solar energetic particle event (SEP); here we focus on
the magnetic onset of this important space weather episode. Cheng
et al. showed that the first eruption's ("Eruption 1") flux rope was
apparent only in "hotter" AIA channels, and that it removed overlying
field that allowed the second eruption ("Eruption 2") to begin via
ideal MHD instability; here we say that Eruption 2 began via a "lid
removal" mechanism. We show that during Eruption 1's onset, its flux
rope underwent a "tether weakening" (TW) reconnection with field that
arched from the eruption-source active region to an adjacent active
region. Standard flare loops from Eruption 1 developed over Eruption
2's flux rope and enclosed filament, but these overarching new loops
were unable to confine that flux rope/filament. Eruption 1's flare
loops, from both TW reconnection and standard-flare-model internal
reconnection, were much cooler than Eruption 2's flare loops (GOES
thermal temperatures of ~7.5 MK and 9 MK, compared to ~14 MK). The
corresponding three sequential GOES flares were, respectively, due to TW
reconnection plus earlier phase Eruption 1 tether-cutting reconnection,
Eruption 1 later-phase tether-cutting reconnection, and Eruption 2
tether-cutting reconnection.
---------------------------------------------------------
Title: New Aspects of a Lid-Removal Mechanism in the Onset of a
SEP-Producing Eruption Sequence
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David;
Knox, Javon M
2014AAS...22421202S Altcode:
We examine a sequence of two ejective eruptions from a single active
region on 2012 January 23, using magnetograms and EUV images from
SDO/HMI and SDO/AIA, and EUV images from STEREO. Cheng et al. (2013)
showed that the first eruption's (“Eruption 1”) flux rope was apparent
only in “hotter” AIA channels, and that it removed overlying field
that allowed the second eruption (“Eruption 2”) to begin via ideal
MHD instability; here we say Eruption 2 began via a “lid removal”
mechanism. We show that during Eruption-1's onset, its flux rope
underwent “tether weakening” (TW) reconnection with the field of an
adjacent active region. Standard flare loops from Eruption 1 developed
over Eruption-2's flux rope and enclosed filament, but these overarching
new loops were unable to confine that flux rope/filament. Eruption-1's
flare loops, from both TW reconnection and standard-flare-model internal
reconnection, were much cooler than Eruption-2's flare loops (GOES
thermal temperatures of ~9 MK compared to ~14 MK). This eruption
sequence produced a strong solar energetic particle (SEP) event
(10 MeV protons, >10^3 pfu for 43 hrs), apparently starting when
Eruption-2's CME blasted through Eruption-1's CME at 5---10 R_s. This
occurred because the two CMEs originated in close proximity and in
close time sequence: Eruption-1's fast rise started soon after the TW
reconnection; the lid removal by Eruption-1's ejection triggered the
slow onset of Eruption 2; and Eruption-2's CME, which started ~1 hr
later, was three times faster than Eruption-1's CME.
---------------------------------------------------------
Title: Magnetic Untwisting in Jets that Go into the Outer Solar
Corona in Polar Coronal Holes
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David
2014AAS...22440803M Altcode:
We present results from a study of 14 jets that were observed in SDO/AIA
EUV movies to erupt in the Sun’s polar coronal holes. These jets
were similar to the many other jets that erupt in coronal holes, but
reached higher than the vast majority, high enough to be observed in the
outer corona beyond 2 solar radii from Sun center by the SOHO/LASCO/C2
coronagraph. We illustrate the characteristic structure and motion of
these high-reaching jets by showing observations of two representative
jets. We find that (1) the speed of the jet front from the base of the
corona out to 2-3 solar radii is typically several times the sound speed
in jets in coronal holes, (2) each high-reaching jet displays unusually
large rotation about its axis (spin) as it erupts, and (3) in the outer
corona, many jets display lateral swaying and bending of the jet axis
with an amplitude of a few degrees and a period of order 1 hour. From
these observations we infer that these jets are magnetically driven,
propose that the driver is a magnetic-untwisting wave that is basically
a large-amplitude (non-linear) torsional Alfven wave that is put into
the open magnetic field in the jet by interchange reconnection as the
jet erupts, and estimate that the magnetic-untwisting wave loses most
of its energy before reaching the outer corona. These observations of
high-reaching coronal jets suggest that the torsional magnetic waves
observed in Type-II spicules can similarly dissipate in the corona and
thereby power much of the coronal heating in coronal holes and quiet
regions. This work is funded by the NASA/SMD Heliophysics Division’s
Living With a Star Targeted Research & Technology Program.
---------------------------------------------------------
Title: A Small-scale Eruption Leading to a Blowout Macrospicule Jet
in an On-disk Coronal Hole
Authors: Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.; Gary,
G. Allen
2014ApJ...783...11A Altcode:
We examine the three-dimensional magnetic structure and dynamics
of a solar EUV-macrospicule jet that occurred on 2011 February 27
in an on-disk coronal hole. The observations are from the Solar
Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and
the SDO Helioseismic and Magnetic Imager (HMI). The observations
reveal that in this event, closed-field-carrying cool absorbing
plasma, as in an erupting mini-filament, erupted and opened,
forming a blowout jet. Contrary to some jet models, there was no
substantial recently emerged, closed, bipolar-magnetic field in the
base of the jet. Instead, over several hours, flux convergence and
cancellation at the polarity inversion line inside an evolved arcade
in the base apparently destabilized the entire arcade, including its
cool-plasma-carrying core field, to undergo a blowout eruption in the
manner of many standard-sized, arcade-blowout eruptions that produce
a flare and coronal mass ejection. Internal reconnection made bright
"flare" loops over the polarity inversion line inside the blowing-out
arcade field, and external reconnection of the blowing-out arcade field
with an ambient open field made longer and dimmer EUV loops on the
outside of the blowing-out arcade. That the loops made by the external
reconnection were much larger than the loops made by the internal
reconnection makes this event a new variety of blowout jet, a variety
not recognized in previous observations and models of blowout jets.
---------------------------------------------------------
Title: The contribution of X-ray polar blowout jets to the solar
wind mass and energy
Authors: Poletto, Giannina; Sterling, Alphonse C.; Pucci, Stefano;
Romoli, Marco
2014IAUS..300..239P Altcode:
Blowout jets constitute about 50% of the total number of X-ray jets
observed in polar coronal holes. In these events, the base magnetic
loop is supposed to blow open in what is a scaled-down representation
of two-ribbon flares that accompany major coronal mass ejections
(CMEs): indeed, miniature CMEs resulting from blowout jets have been
observed. This raises the question of the possible contribution of
this class of events to the solar wind mass and energy flux. Here we
make a first crude evaluation of the mass contributed to the wind and
of the energy budget of the jets and related miniature CMEs, under
the assumption that small-scale events behave as their large-scale
analogs. This hypothesis allows us to adopt the same relationship
between jets and miniature-CME parameters that have been shown to hold
in the larger-scale events, thus inferring the values of the mass and
kinetic energy of the miniature CMEs, currently not available from
observations. We conclude our work estimating the mass flux and the
energy budget of a blowout jet, and giving a crude evaluation of the
role possibly played by these events in supplying the mass and energy
that feeds the solar wind.
---------------------------------------------------------
Title: Physical Parameters of Standard and Blowout Jets
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2013ApJ...776...16P Altcode:
The X-ray Telescope on board the Hinode mission revealed the
occurrence, in polar coronal holes, of much more numerous jets than
previously indicated by the Yohkoh/Soft X-ray Telescope. These plasma
ejections can be of two types, depending on whether they fit the
standard reconnection scenario for coronal jets or if they include a
blowout-like eruption. In this work, we analyze two jets, one standard
and one blowout, that have been observed by the Hinode and STEREO
experiments. We aim to infer differences in the physical parameters
that correspond to the different morphologies of the events. To this
end, we adopt spectroscopic techniques and determine the profiles of
the plasma temperature, density, and outflow speed versus time and
position along the jets. The blowout jet has a higher outflow speed,
a marginally higher temperature, and is rooted in a stronger magnetic
field region than the standard event. Our data provide evidence for
recursively occurring reconnection episodes within both the standard
and the blowout jet, pointing either to bursty reconnection or to
reconnection occurring at different locations over the jet lifetimes. We
make a crude estimate of the energy budget of the two jets and show
how energy is partitioned among different forms. Also, we show that
the magnetic energy that feeds the blowout jet is a factor of 10 higher
than the magnetic energy that fuels the standard event.
---------------------------------------------------------
Title: Magnetic Untwisting in Most Solar X-Ray Jets
Authors: Moore, Ronald L.; Sterling, A. C.; Falconer, D.; Robe, D. M.
2013SPD....4410304M Altcode:
From 54 X-ray jets observed in the polar coronal holes by Hinode’s
X-Ray Telescope (XRT) during coverage in movies from Solar Dynamic
Observatory’s Atmospheric Imaging Assembly (AIA) taken in its
He II 304 Å band at a cadence of 12 s, we have established a basic
characteristic of solar X-ray jets: untwisting motion in the spire. In
this presentation, we show the progression of few of these X-ray jets
in XRT images and track their untwisting in AIA He II images. From
their structure displayed in their XRT movies, 19 jets were evidently
standard jets made by interchange reconnection of the magnetic-arcade
base with ambient open field, 32 were evidently blowout jets made by
blowout eruption of the base arcade, and 3 were of ambiguous form. As
was anticipated from the >10,000 km span of the base arcade in
most polar X-ray jets and from the disparity of standard jets and
blowout jets in their magnetic production, few of the standard X-ray
jets (3 of 19) but nearly all of the blowout X-ray jets (29 of 32)
carried enough cool (T ~ 10^5 K) plasma to be seen in their He II
movies. In the 32 X-ray jets that showed a cool component, the He II
movies show 10-100 km/s untwisting motions about the axis of the spire
in all 3 standard jets and in 26 of the 29 blowout jets. Evidently,
the open magnetic field in nearly all blowout X-ray jets and probably
in most standard X-ray jets carries transient twist. This twist
apparently relaxes by propagating out along the open field as a
torsional wave. High-resolution spectrograms and Dopplergrams have
shown that most Type-II spicules have torsional motions of 10-30
km/s. Our observation of similar torsional motion in X-ray jets (1)
strengthens the case for Type-II spicules being made in the same way
as X-ray jets, by blowout eruption of a twisted magnetic arcade in the
spicule base and/or by interchange reconnection of the twisted base
arcade with the ambient open field, and hence (2) strengthens the case
made by Moore et al (2011, ApJ, 731: L18) that the Sun's granule-size
emerging magnetic bipoles, by making Type-II spicules, power the global
corona and solar wind. This work was funded by NASA’s LWS TRT Program,
NASA's Hinode Project, and NSF's REU Program.
---------------------------------------------------------
Title: An Automatic Detection Technique for Prominence Eruptions
and Surges using SDO/AIA Images
Authors: Yashiro, Seiji; Gopalswamy, N.; Makela, P.; Akiyama, S.;
Sterling, A. C.
2013SPD....44...99Y Altcode:
We present an automatic technique to detect and characterize eruptive
events (EEs), e.g. prominence eruptions and surges, using SDO/AIA
304 Å images. The technique works as follows. 1) The SDO 304 Å
images are polar-transformed for easy handling of the outward motion
of EEs and for saving computer resources. 2) The transformed images
are divided by a background map, which is determined as the minimum
intensity of each pixel during 24 hours. 3) The EEs are defined as a
region in the ratio maps with pixels having a ratio >2. Because a
stationary prominence has relatively high background, the prominence
is detected only when it moves. 4) Pattern recognition is performed to
separate different EEs at different locations. 5) In successive images,
two EEs with more than 50% of pixels overlapping are considered to
be the same EE. 6) If the height of an EE increases monotonically
in 5 successive images, we consider it as a reliable eruption. The
technique detects 1428 prominence eruptions and 1921 surges from 2010
May to 2012 December. The locations of PEs identified by this technique
clearly indicated decayed onset of the maximum phase in the south with
respect to the north. This work was supported by NASA Living with a
Star TR&T programAbstract (2,250 Maximum Characters): We present
an automatic technique to detect and characterize eruptive events
(EEs), e.g. prominence eruptions and surges, using SDO/AIA 304 Å
images. The technique works as follows. 1) The SDO 304 Å images are
polar-transformed for easy handling of the outward motion of EEs and
for saving computer resources. 2) The transformed images are divided by
a background map, which is determined as the minimum intensity of each
pixel during 24 hours. 3) The EEs are defined as a region in the ratio
maps with pixels having a ratio >2. Because a stationary prominence
has relatively high background, the prominence is detected only when it
moves. 4) Pattern recognition is performed to separate different EEs at
different locations. 5) In successive images, two EEs with more than 50%
of pixels overlapping are considered to be the same EE. 6) If the height
of an EE increases monotonically in 5 successive images, we consider it
as a reliable eruption. The technique detects 1428 prominence eruptions
and 1921 surges from 2010 May to 2012 December. The locations of PEs
identified by this technique clearly indicated decayed onset of the
maximum phase in the south with respect to the north. This work was
supported by NASA Living with a Star TR&T program
---------------------------------------------------------
Title: A Small-Scale Filament Eruption Leading to a Blowout
Macrospicule Jet in an On-Disk Coronal Hole
Authors: Sterling, Alphonse C.; Adams, M.; Moore, R. L.; Tennant,
A. F.; Gary, G. A.
2013SPD....44...17S Altcode:
We observe an eruptive jet that occurred in an on-disk solar coronal
hole, using EUV images from the Solar Dynamics Observatory (SDO)
Atmospheric Imaging Assembly (AIA), supplemented by magnetic data from
the SDO Helioseismic and Magnetic Imager (HMI). This jet is similar to
features variously called macrospicules or erupting minifilaments. After
an initial pre-eruptive phase, a concentration of absorbing, cool
material in the AIA images moves with a substantially-horizontal motion
toward a region of open magnetic field, and subsequently jets out along
that vertical field. Prior to and during the jet's ~20 min lifetime,
the magnetic flux integrated over the local region shows flux changes
of &lt 20% of the background flux levels, with a time-averaged
emergence rate of no more than <3 × 10^15 Mx/s in the neighborhood
of the jet. Contrary to some jet models, there was no substantial
recently-emerged bipolar field in the base of the jet. Instead, there
was an established evolving magnetic arcade that held mini-filament-like
cool plasma in its core field. We propose that subtle evolution of the
magnetic flux in and around this arcade destabilized its core field,
as in some standard-sized arcade blowout eruptions that produce a flare
and CME following the slow rise of a standard-sized filament in the
core of the arcade. Closed field carrying the cool plasma erupted into
the open field and formed the blowout jet, evidently at least partly
by interchange reconnection with the open field. Internal reconnection
made compact bright "flare" loops inside the blowing-out arcade, while,
on the outside, interchange reconnection made longer and dimmer EUV
"crinkle" loops. That the loops made by the external reconnection were
considerably larger than the loops made by the internal reconnection
makes this event a new variety of blowout jet, a variety not recognized
in previous observations and models of blowout jets.
---------------------------------------------------------
Title: The 2012 Total Eclipse Expeditions in Queensland
Authors: Pasachoff, Jay M.; Babcock, B. A.; Lu, M.; Dantowitz, R.;
Lucas, R.; Seiradakis, J. H.; Voulgaris, A.; Gaintatzis, P.; Steele,
A.; Sterling, A. C.; Rusin, V.; Saniga, M.
2013SPD....44...51P Altcode:
A total eclipse swept across Queensland and other sites in northeastern
Australia on the early morning of 14 November 2012, local time. We
mounted equipment to observe coronal images and spectra during the
approximately 2 minutes of totality, the former for comparison with
spacecraft images and to fill in the doughnut of imaging not well
covered with space coronagraphs. Matching weather statistics, viewing
was spotty, and our best observations were from a last-minute inland
site on the Tablelands, with some observations from a helicopter at 9000
feet altitude over our original viewing site at Miallo. Only glimpses of
the corona were visible at our Port Douglas and Trinity Beach, Cairns,
locations, with totality obscured from our sites at Newell and Miallo,
though some holes in the clouds provided coronal views from Palm Cove
and elsewhere along the coast. Preliminary analysis of the spectra
again shows Fe XIV stronger than Fe X, as in 2010 but not earlier,
a sign of solar maximum, as was the coronal shape. An intriguing CME
is discernible in the SE. Acknowledgments: We thank Terry Cuttle, Aram
Friedman, Michael Kentrianakis, and Nicholas Weber for assistance and
collaboration in Australia and Wendy Carlos for image processing. Our
expedition was supported in part by NSF grant AGS-1047726 from Solar
Terrestrial Research of the Atmospheric and Geospace Sciences Division,
and by the Rob Spring Fund and Science Center funds at Williams
College. ML was also supported in part by a Grant-In-Aid of Research
from the National Academy of Sciences, administered by Sigma Xi, The
Scientific Research Society (Grant ID: G20120315159311). VR and MS
acknowledge support from projects VEGA 2/0003/13 and NGS-3139-12 of
the National Geographic Society. We are grateful to K. Shiota (Japan)
for kindly providing us with some of his 2012 eclipse coronal images.
---------------------------------------------------------
Title: The Cool Component and the Dichotomy, Lateral Expansion,
and Axial Rotation of Solar X-Ray Jets
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A.;
Robe, Dominic
2013ApJ...769..134M Altcode:
We present results from a study of 54 polar X-ray jets that were
observed in coronal X-ray movies from the X-ray Telescope on Hinode and
had simultaneous coverage in movies of the cooler transition region (T
~ 10<SUP>5</SUP> K) taken in the He II 304 Å band of the Atmospheric
Imaging Assembly (AIA) on Solar Dynamics Observatory. These dual
observations verify the standard-jet/blowout-jet dichotomy of polar
X-ray jets previously found primarily from XRT movies alone. In accord
with models of blowout jets and standard jets, the AIA 304 Å movies
show a cool (T ~ 10<SUP>5</SUP> K) component in nearly all blowout X-ray
jets and in a small minority of standard X-ray jets, obvious lateral
expansion in blowout X-ray jets but none in standard X-ray jets, and
obvious axial rotation in both blowout X-ray jets and standard X-ray
jets. In our sample, the number of turns of axial rotation in the
cool-component standard X-ray jets is typical of that in the blowout
X-ray jets, suggesting that the closed bipolar magnetic field in the
jet base has substantial twist not only in all blowout X-ray jets but
also in many standard X-ray jets. We point out that our results for
the dichotomy, lateral expansion, and axial rotation of X-ray jets add
credence to published speculation that type-II spicules are miniature
analogs of X-ray jets, are generated by granule-size emerging bipoles,
and thereby carry enough energy to power the corona and solar wind.
---------------------------------------------------------
Title: An upper limit to the solar wind mass loading by X-ray
polar jets
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2013AIPC.1539...62P Altcode:
Hinode observations of polar coronal holes revealed a larger population
of X-ray jets than previously reported. Some of these comply with
the standard reconnection model suggested by Shibata et al. (1992),
others, likely analogous to CME eruptions and referred to as blow-out
jets (e.g. Moore et al., 2010), show a more structured morphology. We
present here two events, representative of the two jet categories, that
have been observed by HINODE and STEREO in polar coronal holes. Their
outward speed has been evaluated from high resolution images; also,
because the jets have been observed in multiple filters, we have been
able to derive, via spectroscopic techniques, their temperature and
density evolution, both along the jets and in time. Knowledge of these
parameters allows us to estimate the mass flux that jets of the two
types transport to the solar wind and, assuming a given frequency of
events, to infer a value for the wind mass loading contributed by polar
jets. Because there are insufficient data to establish the percentage
of ejections which eventually fall back to the Sun and because the
jets we analyzed are probably among the more energetic within their
respective class of events, the estimate we give is an upper limit to
the jet wind mass loading.
---------------------------------------------------------
Title: Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
Edelman, E.; Reardon, K.; Widemann, T.; Tanga, P.; Dantowitz, R.;
Silverstone, M. D.; Ehrenreich, D.; Vidal-Madjar, A.; Nicholson,
P. D.; Willson, R. C.; Kopp, G. A.; Yurchyshyn, V. B.; Sterling,
A. C.; Scherrer, P. H.; Schou, J.; Golub, L.; McCauley, P.; Reeves, K.
2013AAS...22131506P Altcode:
We observed the 2012 June 6/5 transit seen from Earth (E/ToV),
simultaneously with Venus Express and several other spacecraft
not only to study the Cytherean atmosphere but also to provide an
exoplanet-transit analog. From Haleakala, the whole transit was visible
in coronal skies; among our instruments was one of the world-wide Venus
Twilight Experiment's nine coronagraphs. Venus's atmosphere became
visible before first contact. SacPeak/IBIS provided high-resolution
images at Hα/carbon-dioxide. Big Bear's NST also provided
high-resolution observations of the Cytherean atmosphere and black-drop
evolution. Our liaison with UH's Mees Solar Observatory scientists
provided magneto-optical imaging at calcium and potassium. Solar
Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope
(SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
measurements with ACRIMSAT and SORCE/TIM, were used to observe the
event as an exoplanet-transit analog. On September 20, we imaged
Jupiter for 14 Hubble Space Telescope orbits, centered on a 10-hour
ToV visible from Jupiter (J/ToV), as an exoplanet-transit analog in
our own solar system, using Jupiter as an integrating sphere. Imaging
was good, although much work remains to determine if we can detect
the expected 0.01% solar irradiance decrease at Jupiter and the even
slighter differential effect between our violet and near-infrared
filters caused by Venus's atmosphere. We also give a first report on our
currently planned December 21 Cassini UVIS observations of a transit of
Venus from Saturn (S/ToV). Our E/ToV expedition was sponsored by the
Committee for Research and Exploration/National Geographic Society;
supplemented: NASA/AAS's Small Research Grant Program. We thank Rob
Ratkowski, Stan Truitt, Rob Lucas, Aram Friedman, and Eric Pilger
'82 at Haleakala, and Joseph Gangestad '06 at Big Bear for assistance,
and Lockheed Martin Solar and Astrophysics Lab and Hinode science and
operations teams for support for coordinated observations with NASA
satellites. Our J/ToV observations were based on observations made
with HST, operated by AURA, Inc., under NASA contract NAS 5-26555;
these observations are associated with program #13067.
---------------------------------------------------------
Title: Observations from SDO, Hinode, and STEREO of a Twisting and
Writhing Start to a Solar-filament-eruption Cascade
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Hara, Hirohisa
2012ApJ...761...69S Altcode:
We analyze data from SDO (AIA, HMI), Hinode (SOT, XRT, EIS), and STEREO
(EUVI) of a solar eruption sequence of 2011 June 1 near 16:00 UT,
with an emphasis on the early evolution toward eruption. Ultimately,
the sequence consisted of three emission bursts and two filament
ejections. SDO/AIA 304 Å images show absorbing-material strands
initially in close proximity which over ~20 minutes form a
twisted structure, presumably a flux rope with ~10<SUP>29</SUP>
erg of free energy that triggers the resulting evolution. A jump
in the filament/flux rope's displacement (average velocity ~20 km
s<SUP>-1</SUP>) and the first burst of emission accompanies the
flux-rope formation. After ~20 more minutes, the flux rope/filament
kinks and writhes, followed by a semi-steady state where the flux
rope/filament rises at (~5 km s<SUP>-1</SUP>) for ~10 minutes. Then
the writhed flux rope/filament again becomes MHD unstable and violently
erupts, along with rapid (50 km s<SUP>-1</SUP>) ejection of the filament
and the second burst of emission. That ejection removed a field that
had been restraining a second filament, which subsequently erupts as
the second filament ejection accompanied by the third (final) burst of
emission. Magnetograms from SDO/HMI and Hinode/SOT, and other data,
reveal several possible causes for initiating the flux-rope-building
reconnection, but we are not able to say which is dominant. Our
observations are consistent with magnetic reconnection initiating the
first burst and the flux-rope formation, with MHD processes initiating
the further dynamics. Both filament ejections are consistent with the
standard model for solar eruptions.
---------------------------------------------------------
Title: Production of High-Temperature Plasmas During the Early Phases
of a C9.7 Flare. II. Bi-directional Flows Suggestive of Reconnection
in a Pre-flare Brightening Region
Authors: Watanabe, T.; Hara, H.; Sterling, A. C.; Harra, L. K.
2012SoPh..281...87W Altcode: 2012SoPh..tmp..185W
The 6 June 2007 16:55 UT flare was well observed with high time-cadence
sparse raster scans by the EUV Imaging Spectrometer (EIS) on board
the Hinode spacecraft. The observation covers an active region area
of 240 arcsec × 240 arcsec with the 1 arcsec slit in about 160 seconds.
---------------------------------------------------------
Title: The 2012 Transit of Venus for Cytherean Atmospheric Studies
and as an Exoplanet Analog
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
Reardon, K. P.; Widemann, T.; Tanga, P.; Dantowitz, R.; Willson,
R.; Kopp, G.; Yurchyshyn, V.; Sterling, A.; Scherrer, P.; Schou, J.;
Golub, L.; Reeves, K.
2012DPS....4450806P Altcode:
We worked to assemble as complete a dataset as possible for the
Cytherean atmosphere in collaboration with Venus Express in situ
and to provide an analog of spectral and total irradiance exoplanet
measurements. From Haleakala, the whole transit was visible in
coronal skies; our B images showed the evolution of the visibility
of Venus's atmosphere and of the black-drop effect, as part of the
Venus Twilight Experiment's 9 coronagraphs distributed worldwide
with BVRI. We imaged the Cytherean atmosphere over two minutes before
first contact, with subarcsecond resolution, with the coronagraph and
a separate refractor. The IBIS imaging spectrometer at Sacramento
Peak Observatory at H-alpha and carbon-dioxide also provided us
high-resolution imaging. The NST of Big Bear Solar Observatory
also provided high-resolution vacuum observations of the Cytherean
atmosphere and black drop evolution. Our liaison with UH's Mees Solar
Observatory scientists provided magneto-optical imaging at calcium
and potassium. Spaceborne observations included the Solar Dynamics
Observatory's AIA and HMI, and the Solar Optical Telescope (SOT)
and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
measurements with ACRIMSAT and SORCE/TIM, to characterize the
event as an exoplanet-transit analog. Our expedition was sponsored
by the Committee for Research and Exploration/National Geographic
Society. Some of the funds for the carbon-dioxide filter for IBIS were
provided by NASA through AAS's Small Research Grant Program. We thank
Rob Lucas, Aram Friedman, and Eric Pilger '82 for assistance with
Haleakala observing, Rob Ratkowski of Haleakala Amateur Astronomers
for assistance with equipment and with the site, Stan Truitt for the
loan of his Paramount ME, and Steve Bisque/Software Bisque for TheSky
X controller. We thank Joseph Gangestad '06 of Aerospace Corp., a
veteran of our 2004 expedition, for assistance at Big Bear. We thank
the Lockheed Martin Solar and Astrophysics Laboratory and Hinode
science and operations teams for planning and support.
---------------------------------------------------------
Title: Solar Spicules near and at the Limb, Observed from Hinode
Authors: Sterling, A. C.; Moore, R. L.
2012ASPC..454...87S Altcode:
Solar spicules appear as narrow jets emanating from the chromosphere and
extending into the corona. They have been observed for over a hundred
years, mainly in chromospheric spectral lines such as H-alpha. Because
they are at the limit of visibility of ground-based instruments,
their nature has long been a puzzle. In recent years however, vast
progress has been made in understanding them both theoretically
and observationally, as spicule studies have undergone a revolution
because of the superior resolution and time cadence of ground-based
and space-based instruments. Even more rapid progress is currently
underway, due to the Solar Optical Telescope (SOT) instrument on the
Hinode spacecraft. Here we give a synopsis of our recent findings from
a movie of sharpened images from the Hinode SOT Ca II filtergraph of
spicules at and near the limb in a polar coronal hole.
---------------------------------------------------------
Title: Observational Evidence for Interaction Between X-ray Jets
and Multiple Bright Points
Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M.
2012ASPC..456..217P Altcode:
The Hinode X-ray telescope (XRT) observed in November 2007 the Northen
polar Coronal Hole (CH) over extended time periods. Among these we
selected two 20 hours long time intervals and carried out a photometric
analysis of several X-ray Bright Points (BPs), within a selected area,
aiming at ascertaining whether there is any correlation between the
BPs intensity fluctuations and the occurrence of jets originating
within this area. Our results indicate that jets result from magnetic
connectivity changes that also produced BP variability: the interaction
between BPs and jets may be interpreted as the small scale version of
the Active Regions phenomena where flares and eruptions are initiated
by interacting bipoles.
---------------------------------------------------------
Title: Physical Parameters of a Blowout Jet Observed by HINODE
and STEREO/EUVI
Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M.
2012ASPC..456..219P Altcode:
The present work aims at identifying a typical blowout jet and
inferring its physical parameters. To this end, we present a preliminary
multi-instrument analysis of the bright X-ray jet that occurred in the
north polar coronal hole on Nov. 3, 2007, at 11:50 UT. The jet shows
the typical characteristics of “blowout jets” (Moore et al. 2010),
and was observed by Hinode/X-Ray Telescope (XRT) and by Stereo/Extreme
UltraViolett Imager (EUVI) and COR1. Temperatures and Emission Measures
(EMs) of the jet have been derived from the EUVI A data via the filter
ratio technique in the pre-event, near maximum and in the post-maximum
phases. Temperatures and EMs inferred from EUVI data are then used to
calculate the predicted XRT Al-poly intensity: predicted values are
compared with observed values and found to be consistent.
---------------------------------------------------------
Title: The Limit of Magnetic-Shear Energy in Solar Active Regions
Authors: Moore, Ronald L.; Falconer, D. A.; Sterling, A. C.
2012AAS...22020438M Altcode:
It has been found previously, by measuring from active-region
magnetograms a proxy of the free energy in the active region’s
magnetic field, (1) that there is a sharp upper limit to the free energy
the field can hold that increases with the amount of magnetic field
in the active region, the active region’s magnetic flux content,
and (2) that most active regions are near this limit when their field
explodes in a CME/flare eruption. That is, explosive active regions are
concentrated in a main-sequence path bordering the free-energy-limit
line in (flux content, free-energy proxy) phase space. Here we present
evidence that specifies the underlying magnetic condition that gives
rise to the free-energy limit and the accompanying main sequence of
explosive active regions. Using a suitable free energy proxy measured
from vector magnetograms of 44 active regions, we find evidence that
(1) in active regions at and near their free-energy limit, the ratio of
magnetic-shear free energy to the non-free magnetic energy the potential
field would have is of order 1 in the core field, the field rooted along
the neutral line, and (2) this ratio is progressively less in active
regions progressively farther below their free-energy limit. Evidently,
most active regions in which this core-field energy ratio is much less
than 1 cannot be triggered to explode; as this ratio approaches 1,
most active regions become capable of exploding; and when this ratio
is 1, most active regions are compelled to explode. <P />This work was
funded by NASA’s Science Mission Directorate through the Heliophysics
Guest Investigators Program, the Hinode Project, and the Living With
a Star Targeted Research & Technology Program.
---------------------------------------------------------
Title: Observations from SDO and Hinode of a Twisting and Writhing
Start to a Solar-filament-eruption Cascade
Authors: Sterling, Alphonse C.; Moore, R. L.
2012AAS...22050802S Altcode:
We analyze data from SDO and hinode of a solar eruption sequence of
1 June 2011 near 16:00 UT, with emphasis on the early evolution
toward eruption. Ultimately, the sequence consisted of three
emission bursts and two filament ejections. SDO/AIA 304 Ang images
show absorbing-material strands initially in close proximity that
over 20 min form a twisted structure, presumably a flux rope with
10<SUP>29 </SUP>ergs of free energy that triggers the resulting
evolution. A jump in the filament/flux rope's height (average velocity
20 km s<SUP>-1</SUP>) and the first burst of emission accompanies
the flux-rope formation. After 20 min more, the flux rope/filament
kinks and writhes, followed by a semi-steady state where the flux
rope/filament rises at ( 5 km s<SUP>-1</SUP>) for 10 min. Then the
writhed flux rope/filament again becomes MHD unstable and violently
erupts, along with rapid (> 50 km s<SUP>-1</SUP>) ejection of the
filament and the second burst of emission. That ejection removed field
that had been restraining a second filament, which subsequently erupts
as the second filament ejection accompanied by the third (final) burst
of emission. Magnetograms from SDO/HMI and hinode/SOT, and other data,
reveal several possible causes for initiating the flux-rope-building
reconnection, but we are not able to say which is dominant. Our
observations are consistent with tether-cutting reconnection initiating
the first burst and the flux-rope formation, with MHD processes
initiating the further dynamics. Both filament ejections are consistent
with the standard model for solar eruptions. NASA supported this work
through its Heliophysics program.
---------------------------------------------------------
Title: The Limit of Magnetic-shear Energy in Solar Active Regions
Authors: Moore, Ronald L.; Falconer, David A.; Sterling, Alphonse C.
2012ApJ...750...24M Altcode:
It has been found previously, by measuring from active-region
magnetograms a proxy of the free energy in the active region's magnetic
field, (1) that there is a sharp upper limit to the free energy the
field can hold that increases with the amount of magnetic field
in the active region, the active region's magnetic flux content,
and (2) that most active regions are near this limit when their
field explodes in a coronal mass ejection/flare eruption. That is,
explosive active regions are concentrated in a main-sequence path
bordering the free-energy-limit line in (flux content, free-energy
proxy) phase space. Here, we present evidence that specifies the
underlying magnetic condition that gives rise to the free-energy limit
and the accompanying main sequence of explosive active regions. Using
a suitable free-energy proxy measured from vector magnetograms of 44
active regions, we find evidence that (1) in active regions at and near
their free-energy limit, the ratio of magnetic-shear free energy to the
non-free magnetic energy the potential field would have is of the order
of one in the core field, the field rooted along the neutral line, and
(2) this ratio is progressively less in active regions progressively
farther below their free-energy limit. Evidently, most active regions
in which this core-field energy ratio is much less than one cannot
be triggered to explode; as this ratio approaches one, most active
regions become capable of exploding; and when this ratio is one,
most active regions are compelled to explode.
---------------------------------------------------------
Title: Solar Polar X-Ray Jets and Multiple Bright Points: Evidence
for Sympathetic Activity
Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.;
Romoli, Marco
2012ApJ...745L..31P Altcode:
We present an analysis of X-ray bright points (BPs) and X-ray jets
observed by Hinode/X-Ray Telescope on 2007 November 2-4, within the
solar northern polar coronal hole. After selecting small subregions
that include several BPs, we followed their brightness evolution over
a time interval of a few hours, when several jets were observed. We
find that most of the jets occurred in close temporal association
with brightness maxima in multiple BPs: more precisely, most jets
are closely correlated with the brightening of at least two BPs. We
suggest that the jets result from magnetic connectivity changes that
also induce the BP variability. We surmise that the jets and implied
magnetic connectivity we describe are small-scale versions of the
active-region-scale phenomenon, whereby flares and eruptions are
triggered by interacting bipoles.
---------------------------------------------------------
Title: The Global Context of Solar Activity During the Whole
Heliosphere Interval Campaign
Authors: Webb, D. F.; Cremades, H.; Sterling, A. C.; Mandrini, C. H.;
Dasso, S.; Gibson, S. E.; Haber, D. A.; Komm, R. W.; Petrie, G. J. D.;
McIntosh, P. S.; Welsch, B. T.; Plunkett, S. P.
2011SoPh..274...57W Altcode:
The Whole Heliosphere Interval (WHI) was an international observing and
modeling effort to characterize the 3-D interconnected "heliophysical"
system during this solar minimum, centered on Carrington Rotation
2068, March 20 - April 16, 2008. During the latter half of the WHI
period, the Sun presented a sunspot-free, deep solar minimum type
face. But during the first half of CR 2068 three solar active regions
flanked by two opposite-polarity, low-latitude coronal holes were
present. These departures from the quiet Sun led to both eruptive
activity and solar wind structure. Most of the eruptive activity,
i.e., flares, filament eruptions and coronal mass ejections (CMEs),
occurred during this first, active half of the interval. We determined
the source locations of the CMEs and the type of associated region,
such as active region, or quiet sun or active region prominence. To
analyze the evolution of the events in the context of the global solar
magnetic field and its evolution during the three rotations centered
on CR 2068, we plotted the CME source locations onto synoptic maps of
the photospheric magnetic field, of the magnetic and chromospheric
structure, of the white light corona, and of helioseismological
subsurface flows. Most of the CME sources were associated with the
three dominant active regions on CR 2068, particularly AR 10989. Most
of the other sources on all three CRs appear to have been associated
with either isolated filaments or filaments in the north polar crown
filament channel. Although calculations of the flux balance and
helicity of the surface magnetic features did not clearly identify a
dominance of one region over the others, helioseismological subsurface
flows beneath these active regions did reveal a pronounced difference
among them. These preliminary results suggest that the "twistedness"
(i.e., vorticity and helicity) of subsurface flows and its temporal
variation might be related to the CME productivity of active regions,
similar to the relationship between flares and subsurface flows.
---------------------------------------------------------
Title: Lateral Offset of the Coronal Mass Ejections from the X-flare
of 2006 December 13 and Its Two Precursor Eruptions
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Harra, Louise K.
2011ApJ...743...63S Altcode:
Two GOES sub-C-class precursor eruptions occurred within ~10 hr prior
to and from the same active region as the 2006 December 13 X4.3-class
flare. Each eruption generated a coronal mass ejection (CME) with
center laterally far offset (gsim 45°) from the co-produced bright
flare. Explaining such CME-to-flare lateral offsets in terms of the
standard model for solar eruptions has been controversial. Using
Hinode/X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS)
data, and Solar and Heliospheric Observatory (SOHO)/Large Angle and
Spectrometric Coronagraph (LASCO) and Michelson Doppler Imager (MDI)
data, we find or infer the following. (1) The first precursor was a
"magnetic-arch-blowout" event, where an initial standard-model eruption
of the active region's core field blew out a lobe on one side of the
active region's field. (2) The second precursor began similarly, but the
core-field eruption stalled in the side-lobe field, with the side-lobe
field erupting ~1 hr later to make the CME either by finally being blown
out or by destabilizing and undergoing a standard-model eruption. (3)
The third eruption, the X-flare event, blew out side lobes on both
sides of the active region and clearly displayed characteristics of the
standard model. (4) The two precursors were offset due in part to the
CME originating from a side-lobe coronal arcade that was offset from
the active region's core. The main eruption (and to some extent probably
the precursor eruptions) was offset primarily because it pushed against
the field of the large sunspot as it escaped outward. (5) All three CMEs
were plausibly produced by a suitable version of the standard model.
---------------------------------------------------------
Title: Observed Aspects of Reconnection in Solar Eruptions
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Gary, G. Allen;
Cirtain, Jonathan W.; Falconer, David A.
2011SSRv..160...73M Altcode: 2011SSRv..tmp..113M; 2011SSRv..tmp..189M; 2011SSRv..tmp...30M
The observed magnetic field configuration and signatures of reconnection
in the large solar magnetic eruptions that make major flares and coronal
mass ejections and in the much smaller magnetic eruptions that make
X-ray jets are illustrated with cartoons and representative observed
eruptions. The main reconnection signatures considered are the imaged
bright emission from the heated plasma on reconnected field lines. In
any of these eruptions, large or small, the magnetic field that drives
the eruption and/or that drives the buildup to the eruption is initially
a closed bipolar arcade. From the form and configuration of the magnetic
field in and around the driving arcade and from the development of the
reconnection signatures in coordination with the eruption, we infer
that (1) at the onset of reconnection the reconnection current sheet
is small compared to the driving arcade, and (2) the current sheet can
grow to the size of the driving arcade only after reconnection starts
and the unleashed erupting field dynamically forces the current sheet to
grow much larger, building it up faster than the reconnection can tear
it down. We conjecture that the fundamental reason the quasi-static
pre-eruption field is prohibited from having a large current sheet is
that the magnetic pressure is much greater than the plasma pressure
in the chromosphere and low corona in eruptive solar magnetic fields.
---------------------------------------------------------
Title: Spectroscopic Observations of a Coronal Moreton Wave
Authors: Harra, Louise K.; Sterling, Alphonse C.; Gömöry, Peter;
Veronig, Astrid
2011ApJ...737L...4H Altcode:
We observed a coronal wave (EIT wave) on 2011 February 16, using
EUV imaging data from the Solar Dynamics Observatory/Atmospheric
Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV
Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that
produced a surge and a coronal mass ejection (CME). EIS data of the
wave show a prominent redshifted signature indicating line-of-sight
velocities of ~20 km s<SUP>-1</SUP> or greater. Following the main
redshifted wave front, there is a low-velocity period (and perhaps
slightly blueshifted), followed by a second redshift somewhat weaker
than the first; this progression may be due to oscillations of the EUV
atmosphere set in motion by the initial wave front, although alternative
explanations may be possible. Along the direction of the EIS slit the
wave front's velocity was ~500 km s<SUP>-1</SUP>, consistent with
its apparent propagation velocity projected against the solar disk
as measured in the AIA images, and the second redshifted feature had
propagation velocities between ~200 and 500 km s<SUP>-1</SUP>. These
findings are consistent with the observed wave being generated by the
outgoing CME, as in the scenario for the classic Moreton wave. This
type of detailed spectral study of coronal waves has hitherto been a
challenge, but is now possible due to the availability of concurrent
AIA and EIS data.
---------------------------------------------------------
Title: Insights into Filament Eruption Onset from Solar Dynamics
Observatory Observations
Authors: Sterling, Alphonse C.; Moore, R. L.; Freeland, S. L.
2011SPD....42.0904S Altcode: 2011BAAS..43S.0904S
We examine the buildup to and onset of an active region filament
confined eruption of 2010 May 12, using EUV imaging data from the Solar
Dynamics Observatory (SDO) Atmospheric Imaging Array and line-of-sight
magnetic data from the SDO Helioseismic and Magnetic Imager. Over the
hour preceding eruption the filament undergoes a slow rise averaging
3 km/s, with a step-like trajectory. Accompanying a final rise step 20
minutes prior to eruption is a transient preflare brightening, occurring
on loops rooted near the site where magnetic field had canceled over
the previous 20 hr. Flow-type motions of the filament are relatively
smooth with speeds 50 km/s prior to the preflare brightening and appear
more helical, with speeds 50-100 km/s, after that brightening. After
a final plateau in the filament's rise, its rapid eruption begins,
and concurrently an outer shell "cocoon" of the filament material
increases in emission in hot EUV lines, consistent with heating in
a newly formed magnetic flux rope. The main flare brightenings start
5 minutes after eruption onset. The main flare arcade begins between
the legs of an envelope-arcade loop that is nearly orthogonal to the
filament, suggesting that the flare results from reconnection among
the legs of that loop. This progress of events is broadly consistent
with flux cancellation leading to formation of a helical flux rope
that subsequently erupts due to onset of a magnetic instability and/or
runaway tether cutting. A full description of this work appears in
ApJ Letters 2011, 731, L3. NASA supported this work through its Solar
Physics Supporting Research and Technology, Sun-Earth Connection
Guest Investigator, and Living With a Star Targeted Research &
Technology programs.
---------------------------------------------------------
Title: Insights into Filament Eruption Onset from Solar Dynamics
Observatory Observations
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Freeland, Samuel L.
2011ApJ...731L...3S Altcode:
We examine the buildup to and onset of an active region filament
confined eruption of 2010 May 12, using EUV imaging data from the Solar
Dynamics Observatory (SDO) Atmospheric Imaging Array and line-of-sight
magnetic data from the SDO Helioseismic and Magnetic Imager. Over the
hour preceding eruption the filament undergoes a slow rise averaging
~3 km s<SUP>-1</SUP>, with a step-like trajectory. Accompanying a
final rise step ~20 minutes prior to eruption is a transient preflare
brightening, occurring on loops rooted near the site where magnetic
field had canceled over the previous 20 hr. Flow-type motions of the
filament are relatively smooth with speeds ~50 km s<SUP>-1</SUP>
prior to the preflare brightening and appear more helical, with
speeds ~50-100 km s<SUP>-1</SUP>, after that brightening. After a
final plateau in the filament's rise, its rapid eruption begins,
and concurrently an outer shell "cocoon" of the filament material
increases in emission in hot EUV lines, consistent with heating in
a newly formed magnetic flux rope. The main flare brightenings start
~5 minutes after eruption onset. The main flare arcade begins between
the legs of an envelope-arcade loop that is nearly orthogonal to the
filament, suggesting that the flare results from reconnection among
the legs of that loop. This progress of events is broadly consistent
with flux cancellation leading to formation of a helical flux rope
that subsequently erupts due to onset of a magnetic instability and/or
runaway tether cutting.
---------------------------------------------------------
Title: Solar X-ray Jets, Type-II Spicules, Granule-size Emerging
Bipoles, and the Genesis of the Heliosphere
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Cirtain, Jonathan
W.; Falconer, David A.
2011ApJ...731L..18M Altcode:
From Hinode observations of solar X-ray jets, Type-II spicules, and
granule-size emerging bipolar magnetic fields in quiet regions and
coronal holes, we advocate a scenario for powering coronal heating
and the solar wind. In this scenario, Type-II spicules and Alfvén
waves are generated by the granule-size emerging bipoles (EBs) in the
manner of the generation of X-ray jets by larger magnetic bipoles. From
observations and this scenario, we estimate that Type-II spicules and
their co-generated Alfvén waves carry into the corona an area-average
flux of mechanical energy of ~7 × 10<SUP>5</SUP> erg cm<SUP>-2</SUP>
s<SUP>-1</SUP>. This is enough to power the corona and solar wind
in quiet regions and coronal holes, and therefore indicates that the
granule-size EBs are the main engines that generate and sustain the
entire heliosphere.
---------------------------------------------------------
Title: Simultaneous Observations of the Chromosphere with TRACE
and SUMER
Authors: Pasachoff, Jay M.; Tingle, Evan D.; Dammasch, Ingolf E.;
Sterling, Alphonse C.
2011SoPh..268..151P Altcode: 2010SoPh..tmp..209P; 2010SoPh..tmp..233P; 2010arXiv1010.4814P
Using mainly the 1600 Å continuum channel and also the 1216 Å Lyman-α
channel (which includes some UV continuum and C IV emission) aboard
the TRACE satellite, we observed the complete lifetime of a transient,
bright chromospheric loop. Simultaneous observations with the SUMER
instrument aboard the SOHO spacecraft revealed interesting material
velocities through the Doppler effect existing above the chromospheric
loop imaged with TRACE, possibly corresponding to extended nonvisible
loops, or the base of an X-ray jet.
---------------------------------------------------------
Title: Hinode extreme-ultraviolet imaging spectrometer observations
of a limb active region
Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Sterling, A. C.;
Tripathi, D.; Young, P. R.
2011A&A...525A.137O Altcode:
<BR /> Aims: We investigate the electron density and temperature
structure of a limb active region. <BR /> Methods: We have carried out
a study of an active region close to the solar limb using observations
from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray
telescope (XRT) on board Hinode. The electron density and temperature
distributions of the coronal emission have been determined using
emission line intensity ratios. Differential emission measure (DEM)
analysis and the emission measure (EM) loci technique were used to
examine the thermal structure of the emitting plasma as a function
of distance from the limb. <BR /> Results: The highest temperature
and electron density values are found to be located in the core of
the active region, with a peak electron number density value of 1.9
× 10<SUP>10</SUP> cm<SUP>-3</SUP> measured using the Fe XII 186.887
Å to 192.394 Å line intensity ratio. The plasma along the line of
sight in the active region was found to be multi-thermal at different
distances from the limb. The EIS and XRT DEM analyses appear to be
in agreement in the temperature interval from log T = 6.5-6.7. <BR />
Conclusions: Our results provide new constraints for models of coronal
heating in active regions.
---------------------------------------------------------
Title: Three-dimensional morphology of a coronal prominence cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
Toma, G.; Hao, J.; Hill, S. M.; Hudson, H. S.; Marque, C.; McIntosh,
P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
Sterling, A.; Tripathi, D.; Williams, D. R.; Zhang, M.
2010AGUFMSH51A1667G Altcode:
We present a three-dimensional density model of coronal prominence
cavities, and a morphological fit that has been tightly constrained
by a uniquely well-observed cavity. Observations were obtained as part
of an International Heliophysical Year campaign by instruments from a
variety of space- and ground-based observatories, spanning wavelengths
from radio to soft-X-ray to integrated white light. From these data
it is clear that the prominence cavity is the limb manifestation of
a longitudinally-extended polar-crown filament channel, and that
the cavity is a region of low density relative to the surrounding
corona. As a first step towards quantifying density and temperature
from campaign spectroscopic data, we establish the three-dimensional
morphology of the cavity. This is critical for taking line-of-sight
projection effects into account, since cavities are not localized in the
plane of the sky and the corona is optically thin. We have augmented
a global coronal streamer model to include a tunnel-like cavity with
elliptical cross-section and a Gaussian variation of height along
the tunnel length. We have developed a semi-automated routine that
fits ellipses to cross-sections of the cavity as it rotates past the
solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI)
observations from the two Solar Terrestrial Relations Observatory
(STEREO) spacecraft. This defines the morphological parameters of our
model, from which we reproduce forward-modeled cavity observables. We
find that cavity morphology and orientation, in combination with the
viewpoints of the observing spacecraft, explains the observed variation
in cavity visibility for the east vs. west limbs.
---------------------------------------------------------
Title: Three-dimensional Morphology of a Coronal Prominence Cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
Toma, G.; Hao, J.; Hill, S.; Hudson, H. S.; Marqué, C.; McIntosh,
P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
Seaton, D. B.; Sterling, A. C.; Tripathi, D.; Williams, D. R.;
Zhang, M.
2010ApJ...724.1133G Altcode:
We present a three-dimensional density model of coronal prominence
cavities, and a morphological fit that has been tightly constrained
by a uniquely well-observed cavity. Observations were obtained as part
of an International Heliophysical Year campaign by instruments from a
variety of space- and ground-based observatories, spanning wavelengths
from radio to soft X-ray to integrated white light. From these data
it is clear that the prominence cavity is the limb manifestation of
a longitudinally extended polar-crown filament channel, and that the
cavity is a region of low density relative to the surrounding corona. As
a first step toward quantifying density and temperature from campaign
spectroscopic data, we establish the three-dimensional morphology
of the cavity. This is critical for taking line-of-sight projection
effects into account, since cavities are not localized in the plane of
the sky and the corona is optically thin. We have augmented a global
coronal streamer model to include a tunnel-like cavity with elliptical
cross-section and a Gaussian variation of height along the tunnel
length. We have developed a semi-automated routine that fits ellipses
to cross-sections of the cavity as it rotates past the solar limb, and
have applied it to Extreme Ultraviolet Imager observations from the
two Solar Terrestrial Relations Observatory spacecraft. This defines
the morphological parameters of our model, from which we reproduce
forward-modeled cavity observables. We find that cavity morphology
and orientation, in combination with the viewpoints of the observing
spacecraft, explain the observed variation in cavity visibility for
the east versus west limbs.
---------------------------------------------------------
Title: Eruptive Signatures in the Solar Atmosphere During the WHI
Campaign (20 March-16 April 2008)
Authors: Sterling, Alphonse C.
2010HiA....15..498S Altcode:
We examined EUV movies of the Sun during the period of the Whole
Heliospheric Interval (WHI) campaign of 20 March-16 April 2008,
searching for indications of eruptive events. Our data set was
obtained from EIT on SOHO, using its 195 Å filter, and from EUVI
on the two STEREO satellites, using their 171 Å, 195 Å, 284 Å,
and 304 Å filters. Here we present a table showing results from our
preliminary search.
---------------------------------------------------------
Title: Fibrillar Chromospheric Spicule-like Counterparts to an
Extreme-ultraviolet and Soft X-ray Blowout Coronal Jet
Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L.
2010ApJ...722.1644S Altcode:
We observe an erupting jet feature in a solar polar coronal hole, using
data from Hinode/Solar Optical Telescope (SOT), Extreme Ultraviolet
Imaging Spectrometer (EIS), and X-Ray Telescope (XRT), with supplemental
data from STEREO/EUVI. From extreme-ultraviolet (EUV) and soft X-ray
(SXR) images we identify the erupting feature as a blowout coronal
jet: in SXRs it is a jet with a bright base, and in EUV it appears
as an eruption of relatively cool (~50,000 K) material of horizontal
size scale ~30” originating from the base of the SXR jet. In SOT
Ca II H images, the most pronounced analog is a pair of thin (~1”)
ejections at the locations of either of the two legs of the erupting
EUV jet. These Ca II features eventually rise beyond 45”, leaving the
SOT field of view, and have an appearance similar to standard spicules
except that they are much taller. They have velocities similar to that
of "type II" spicules, ~100 km s<SUP>-1</SUP>, and they appear to have
spicule-like substructures splitting off from them with horizontal
velocity ~50 km s<SUP>-1</SUP>, similar to the velocities of splitting
spicules measured by Sterling et al. Motions of splitting features and
of other substructures suggest that the macroscopic EUV jet is spinning
or unwinding as it is ejected. This and earlier work suggest that a
subpopulation of Ca II type II spicules are the Ca II manifestation
of portions of larger scale erupting magnetic jets. A different
subpopulation of type II spicules could be blowout jets occurring on
a much smaller horizontal size scale than the event we observe here.
---------------------------------------------------------
Title: Evidence for magnetic flux cancelation leading to an ejective
solar eruption observed by Hinode, TRACE, STEREO, and SoHO/MDI
Authors: Sterling, A. C.; Chifor, C.; Mason, H. E.; Moore, R. L.;
Young, P. R.
2010A&A...521A..49S Altcode:
<BR /> Aims: We study the onset of a solar eruption involving a
filament ejection on 2007 May 20. <BR /> Methods: We observe the
filament in Hα images from Hinode/SOT and in EUV with TRACE and
STEREO/SECCHI/EUVI. Hinode/XRT images are used to study the eruption in
soft X-rays. From spectroscopic data taken with Hinode/EIS we obtain
bulk-flow velocities, line profiles, and plasma densities in the
onset region. The magnetic field evolution was observed in SoHO/MDI
magnetograms. <BR /> Results: We observed a converging motion between
two opposite polarity sunspots that form the primary magnetic polarity
inversion line (PIL), along which resides filament material before
eruption. Positive-flux magnetic elements, perhaps moving magnetic
features (MMFs) flowing from the spot region, appear north of the
spots, and the eruption onset occurs where these features cancel
repeatedly in a negative-polarity region north of the sunspots. An
ejection of material observed in Hα and EUV marks the start of the
filament eruption (its “fast-rise”). The start of the ejection is
accompanied by a sudden brightening across the PIL at the jet's base,
observed in both broad-band images and in EIS. Small-scale transient
brightenings covering a wide temperature range (Log T<SUB>e</SUB> =
4.8-6.3) are also observed in the onset region prior to eruption. The
preflare transient brightenings are characterized by sudden, localized
density enhancements (to above Log n<SUB>e</SUB> [ cm<SUP>-3</SUP>] =
9.75, in Fe XIII) that appear along the PIL during a time when pre-flare
brightenings were occurring. The measured densities in the eruption
onset region outside the times of those enhancements decrease with
temperature. Persistent downflows (red-shifts) and line-broadening
(Fe XII) are present along the PIL. <BR /> Conclusions: The array of
observations is consistent with the pre-eruption sheared-core magnetic
field being gradually destabilized by evolutionary tether-cutting flux
cancelation that was driven by converging photospheric flows, and the
main filament ejection being triggered by flux cancelation between the
positive flux elements and the surrounding negative field. A definitive
statement however on the eruption's ultimate cause would require
comparison with simulations, or additional detailed observations of
other eruptions occurring in similar magnetic circumstances. <P />The
video that accompanies Fig. 3 is only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets
Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse
C.; Falconer, David A.
2010ApJ...720..757M Altcode:
By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray
movies of the polar coronal holes, we found that there is a dichotomy
of polar X-ray jets. About two thirds fit the standard reconnection
picture for coronal jets, and about one third are another type. We
present observations indicating that the non-standard jets are
counterparts of erupting-loop Hα macrospicules, jets in which the
jet-base magnetic arch undergoes a miniature version of the blowout
eruptions that produce major coronal mass ejections. From the coronal
X-ray movies we present in detail two typical standard X-ray jets
and two typical blowout X-ray jets that were also caught in He II
304 Å snapshots from STEREO/EUVI. The distinguishing features of
blowout X-ray jets are (1) X-ray brightening inside the base arch
in addition to the outside bright point that standard jets have,
(2) blowout eruption of the base arch's core field, often carrying a
filament of cool (T ~ 10<SUP>4</SUP> - 10<SUP>5</SUP> K) plasma, and
(3) an extra jet-spire strand rooted close to the bright point. We
present cartoons showing how reconnection during blowout eruption of
the base arch could produce the observed features of blowout X-ray
jets. We infer that (1) the standard-jet/blowout-jet dichotomy of
coronal jets results from the dichotomy of base arches that do not
have and base arches that do have enough shear and twist to erupt open,
and (2) there is a large class of spicules that are standard jets and
a comparably large class of spicules that are blowout jets.
---------------------------------------------------------
Title: Production of High-temperature Plasmas During the Early Phases
of a C9.7 Flare
Authors: Watanabe, Tetsuya; Hara, Hirohisa; Sterling, Alphonse C.;
Harra, Louise K.
2010ApJ...719..213W Altcode:
Explosive chromospheric evaporation is predicted from some current
solar flare models. In this paper, we analyze a flare with high time
cadence raster scans with the EUV Imaging Spectrometer (EIS) on board
the Hinode spacecraft. This observation covers an area of 240” ×
240”, with the 1” slit in about 160 s. The early phases of a C9.7
flare that occurred on 2007 June 6 were well observed. The purpose of
our analysis is to study for the first time the spatially resolved
spectra of high-temperature plasma, especially from Fe XXIII and Fe
XXIV, allowing us to explore the explosive chromospheric evaporation
scenario further. Sections of raster images obtained between 17:20:09
and 17:20:29 (UT) show a few bright patches of emission from Fe
XXIII/Fe XXIV lines at the footpoints of the flaring loops; these
footpoints were not clearly seen in the images taken earlier, between
17:17:30 and 17:17:49 (UT). Fe XXIII spectra at these footpoints show
dominating blueshifted components of -(300 to 400) km s<SUP>-1</SUP>,
while Fe XV/XIV lines are nearly stationary; Fe XII lines and/or
lower temperature lines show slightly redshifted features, and Fe
VIII and Si VII to He II lines show ~+50 km s<SUP>-1</SUP> redshifted
components. The density of the 1.5-2 MK plasma at these footpoints is
estimated to be 3 × 10<SUP>10</SUP> cm<SUP>-3</SUP> by the Fe XIII/XIV
line pairs around the maximum of the flare. High-temperature loops
connecting the footpoints appear in the Fe XXIII/XXIV images taken over
17:22:49-17:23:08 (UT) which is near the flare peak. Line profiles of
these high-temperature lines at this flare peak time show only slowly
moving components. The concurrent cooler Fe XVII line at 254.8 Å is
relatively weak, indicating the predominance of high-temperature plasma
(>10<SUP>7</SUP> K) in these loops. The characteristics observed
during the early phases of this flare are consistent with the scenario
of explosive chromospheric evaporation.
---------------------------------------------------------
Title: Hinode Solar Optical Telescope Observations of the Source
Regions and Evolution of "Type II" Spicules at the Solar Polar Limb
Authors: Sterling, Alphonse C.; Moore, Ronald L.; DeForest, Craig E.
2010ApJ...714L...1S Altcode:
We examine solar spicules using high-cadence Ca II data of the north
pole coronal hole region, using the Solar Optical Telescope (SOT)
on the Hinode spacecraft. The features we observe are referred to as
"Type II" spicules by De Pontieu et al. in 2007. By convolving the
images with the inverse-point-spread function for the SOT Ca II filter,
we are able to investigate the roots of some spicules on the solar
disk, and the evolution of some spicules after they are ejected from
the solar surface. We find that the source regions of at least some of
the spicules correspond to locations of apparent-fast-moving (~few ×
10 km s<SUP>-1</SUP>), transient (few 100 s), Ca II brightenings on the
disk. Frequently the spicules occur when these brightenings appear to
collide and disappear. After ejection, when seen above the limb, many
of the spicules fade by expanding laterally (i.e., roughly transverse
to their motion away from the solar surface), splitting into two or
more spicule "strands," and the spicules then fade without showing
any downward motion. Photospheric/chromospheric acoustic shocks alone
likely cannot explain the high velocities (~100 km s<SUP>-1</SUP>) of
the spicules. If the Ca II brightenings represent magnetic elements,
then reconnection among those elements may be a candidate to explain
the spicules. Alternatively, many of the spicules could be small-scale
magnetic eruptions, analogous to coronal mass ejections, and the
apparent fast motions of the Ca II brightenings could be analogs of
flare loops heated by magnetic reconnection in these eruptions.
---------------------------------------------------------
Title: Blowout Jets: Hinode X-Ray Jets that Don't Fit the Standard
Model
Authors: Moore, Ronald L.; Cirtain, J. W.; Sterling, A. C.
2010AAS...21640620M Altcode: 2010BAAS...41..883M
Nearly half of all H-alpha macrospicules in polar coronal holes appear
to be miniature filament eruptions (Yamauchi et al 2004, ApJ, 605,
511). This suggests that there is a large class of X-ray jets in which
the jet-base magnetic arcade undergoes a blowout eruption as in a CME,
instead of remaining static as in most solar X-ray jets, the standard
jets that fit the model advocated by Shibata (e.g., Shibata et al 1992,
PASJ, 44, L173). Along with a cartoon depicting the standard model,
we present a cartoon depicting the signatures expected of blowout
jets in coronal X-ray images. From Hinode/XRT movies and STEREO/EUVI
snapshots in polar coronal holes, we present examples of (1) X-ray jets
that fit the standard model, and (2) X-ray jets that do not fit the
standard model but do have features appropriate for blowout jets. These
features are (1) a flare arcade inside the jet-base arcade in addition
to the small flare arcade (bright point) outside that standard jets
have, (2) a filament of cool (T 80,000 K) plasma that erupts from
the core of the jet-base arcade, and (3) an extra jet strand that
should not be made by the reconnection for standard jets but could
be made by reconnection between the ambient unipolar open field and
the opposite-polarity leg of the filament-carrying flux-rope core
field of the erupting jet-base arcade. We therefore infer that these
non-standard jets are blowout jets, jets made by miniature versions of
the sheared-core-arcade eruptions that make CMEs. <P />This work was
funded by NASA's Science Mission Directorate through the Heliophysics
Guest Investigators Program, the Hinode Project, and the Living With
a Star Targeted Research and Technology Program.
---------------------------------------------------------
Title: Solar Polar Spicules Observed with Hinode
Authors: Sterling, Alphonse C.; Moore, R. L.; DeForest, C. E.
2010AAS...21640303S Altcode: 2010BAAS...41Q.878S
We examine solar polar region spicules using high-cadence Ca II data
from the Solar Optical Telescope (SOT) on the Hinode spacecraft. We
sharpened the images by convolving them with the inverse-point-spread
function of the SOT Ca II filter, and we are able to see some of
the spicules originating on the disk just inside the limb. Bright
points are frequently at the root of the disk spicules. These “Ca
II brightenings” scuttle around at few x 10 km/s, live for 100 sec,
and may be what are variously known as “H<SUB>2V</SUB> grains,”
“K<SUB>2V</SUB> grains,” or "K<SUB>2V</SUB> bright points.” When
viewed extending over the limb, some of the spicules appear to expand
horizontally or spit into two or more components, with the horizontal
expansion or splitting velocities reaching 50 km/s. This work was
funded by NASA's Science Mission Directorate through the Living
With a Star Targeted Research and Technology Program, the Supporting
Research and Program, the Heliospheric Guest Investigator Program,
and the Hinode project.
---------------------------------------------------------
Title: Geometric Model of a Coronal Cavity
Authors: Kucera, Therese A.; Gibson, S. E.; Rastawicki, D.; Dove, J.;
de Toma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.;
Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.;
Williams, D. R.; Zhang, M.
2010AAS...21640510K Altcode: 2010BAAS...41..890K
We observed a coronal cavity from August 8-18 2007 during a
multi-instrument observing campaign organized under the auspices of
the International Heliophysical Year (IHY). Here we present initial
efforts to model the cavity with a geometrical streamer-cavity
model. The model is based the white-light streamer model of Gibson et
al. (2003), which has been enhanced by the addition of a cavity and
the capability to model EUV and X-ray emission. The cavity is modeled
with an elliptical cross-section and Gaussian fall-off in length and
width inside the streamer. Density and temperature can be varied in the
streamer and cavity and constrained via comparison with data. Although
this model is purely morphological, it allows for three-dimensional,
multi-temperature analysis and characterization of the data, which
can then provide constraints for future physical modeling. Initial
comparisons to STEREO/EUVI images of the cavity and streamer show that
the model can provide a good fit to the data. This work is part of the
effort of the International Space Science Institute International Team
on Prominence Cavities.
---------------------------------------------------------
Title: Triggering of solar magnetic eruptions on various size scales
Authors: Sterling, Alphonse
2010cosp...38.2839S Altcode: 2010cosp.meet.2839S
A solar eruption that produces a coronal mass ejection (CME) together
with a flare is driven by the eruption of a closed-loop magnetic
arcade that has a sheared-field core. Before eruption, the sheared
core envelops a polarity inversion line along which cool filament
material may reside. The sheared-core arcade erupts when there is
a breakdown in the balance between the confining downward-directed
magnetic tension of the overall arcade field and the upward-directed
force of the pent-up magnetic pressure of the sheared field in the
core of the arcade. What triggers the breakdown in this balance in
favor of the upward-directed force is still an unsettled question. We
consider several eruption examples, using imaging data from the SoHO,
TRACE and Hinode satellites, and other sources, along with information
about the magnetic field of the erupting regions. In several cases,
observations of large-scale eruptions, where the magnetic neutral line
spans ∼ few ×10,000 km, are consistent with magnetic flux cancelation
being the trigger to the eruption's onset, even though the amount of
flux canceled is only ∼ few percent of the total magnetic flux of
the erupting region. In several other cases, an initial compact (small
size-scale) eruption occurs embedded inside of a larger closed magnetic
loop system, so that the smaller eruption destabilizes and causes the
eruption of the much larger system. In this way, small-scale eruptive
events can result in eruption of much larger-scale systems. This work
was funded by NASA's Science Mission Directorate thought the Living
With a Star Targeted Research and Technology Program, the Supporting
Research and Program, and the Hinode project.
---------------------------------------------------------
Title: Two types of magnetic flux cancelation in the solar eruption
of 2007 May 20
Authors: Sterling, Alphonse; Moore, Ronald; Mason, Helen
2010cosp...38.1946S Altcode: 2010cosp.meet.1946S
We study a solar eruption on 2007 May 20, in an effort to understand the
cWe study a solar eruption of 2007 May 20, in an effort to understand
the cause of the eruption's onset. The event produced a GOES class
B6.7 flare peaking at 05:56 UT, while ejecting a surge/filament and
producing a coronal mass ejection (CME). We examine several data
sets, including Hα images from the Solar Optical Telescope (SOT) on
Hinode, EUV images from TRACE, and line-of-sight magnetograms from
SoHO/MDI. Flux cancelation occurs among two different sets of flux
elements inside of the erupting active region: First, for several days
prior to eruption, opposite-polarity sunspot groups inside the region
move toward each other, leading to the cancelation of ∼ 1021 Mx
of flux over three days. Second, within hours prior to the eruption,
positive-polarity moving magnetic features (MMFs) flowing out of the
positive-flux spots at ∼ 1 km/s repeatedly cancel with field inside
a patch of negative-polarity flux located north of the sunspots. The
filament erupts as a surge whose base is rooted in the location where
the MMF cancelation occurs, while during the eruption that filament
flows out along the polarity inversion line between the converging spot
groups. We conclude that a plausible scenario is that the converging
spot fields brought the magnetic region to the brink of instability,
and the MMF cancelation pushed the system "over the edge," triggering
the eruption. This work was funded by NASA's Science Mission Directorate
thought the Living With a Star Targeted Research and Technology Program,
the Supporting Research and Program, and the Hinode project.
---------------------------------------------------------
Title: Limb Spicules from the Ground and from Space
Authors: Pasachoff, Jay M.; Jacobson, William A.; Sterling, Alphonse C.
2009SoPh..260...59P Altcode: 2009arXiv0909.0027P
We amassed statistics for quiet-sun chromosphere spicules at the limb
using ground-based observations from the Swedish 1-m Solar Telescope on
La Palma and simultaneously from NASA's Transition Region and Coronal
Explorer (TRACE) spacecraft. The observations were obtained in July
2006. With the 0.2 arcsecond resolution obtained after maximizing
the ground-based resolution with the Multi-Object Multi-Frame Blind
Deconvolution (MOMFBD) program, we obtained specific statistics for
sizes and motions of over two dozen individual spicules, based on
movies compiled at 50-second cadence for the series of five wavelengths
observed in a very narrow band at Hα, on-band and at ± 0.035 nm
and ± 0.070 nm (10 s at each wavelength) using the SOUP filter,
and had simultaneous observations in the 160 nm EUV continuum from
TRACE. The MOMFBD restoration also automatically aligned the images,
facilitating the making of Dopplergrams at each off-band pair. We
studied 40 Hα spicules, and 14 EUV spicules that overlapped Hα
spicules; we found that their dynamical and morphological properties
fit into the framework of several previous studies. From a preliminary
comparison with spicule theories, our observations are consistent with
a reconnection mechanism for spicule generation, and with UV spicules
being a sheath region surrounding the Hα spicules.
---------------------------------------------------------
Title: Large-Scale Flows in Prominence Cavities
Authors: Schmit, D. J.; Gibson, S. E.; Tomczyk, S.; Reeves, K. K.;
Sterling, Alphonse C.; Brooks, D. H.; Williams, D. R.; Tripathi, D.
2009ApJ...700L..96S Altcode:
Regions of rarefied density often form cavities above quiescent
prominences. We observed two different cavities with the Coronal
Multichannel Polarimeter on 2005 April 21 and with Hinode/EIS on 2008
November 8. Inside both of these cavities, we find coherent velocity
structures based on spectral Doppler shifts. These flows have speeds of
5-10 km s<SUP>-1</SUP>, occur over length scales of tens of megameters,
and persist for at least 1 hr. Flows in cavities are an example of
the nonstatic nature of quiescent structures in the solar atmosphere.
---------------------------------------------------------
Title: Flows and Plasma Properties in Quiescent Cavities
Authors: Schmit, Donald; Gibson, S.; Reeves, K.; Sterling, A.;
Tomczyk, S.
2009SPD....40.1015S Altcode:
Regions of rarefied density often form cavities above quiescent
prominences. In an attempt to constrain the plasma properties of
"equilibrium" cavities we conduct several diagnostics using Hinode/EIS,
STEREO/EUVI, and CoMP. One novel observation is of large scale flows in
cavities. Using different instruments to observe two distinct cavities
off the solar limb in coronal emission lines, we find that spectral
doppler shifts imply LOS velocities within cavities on the order of
1-10 km/s. These flows occur over length scales of several hundred Mm
and persist for hours.
---------------------------------------------------------
Title: Solar Spicules Near and at the Limb, Observed from Hinode
Authors: Sterling, Alphonse C.
2009SPD....40.1006S Altcode:
Solar spicules appear as narrow jets emanating from the chromosphere and
extending into the corona. They have been observed for over a hundred
years, mainly in chromospheric spectral lines such as Hα. Because they
are at the limit of visibility of ground-based instruments, their nature
has long been a puzzle. In recent years however, vast progress has been
made in understanding them both theoretically and observationally. Most
recently, spicule studies have undergone a revolution because of the
superior resolution, time cadence, and atmosphere-free observations
from the Solar Optical Telescope (SOT) instrument on the Hinode
spacecraft. Here we present observations of spicules from Hinode SOT,
and consider how the observations from Hinode compare with historical
observations. We include data taken in the blue and red wings of Hα,
where the spicules have widths of a few 100 kms, and the longest ones
reach 10<SUP>4 </SUP>km in extent, similar to sizes long reported from
ground-based instruments. Their dynamics are not easy to generalize,
with many showing the upward movement followed by falling or fading,
as traditionally reported, but with others showing more dynamic or
even ejective aspects. There is a strong transverse component to their
motion, as extensively reported previously from the Hinode data as
evidence for Alfven waves. <P />NASA supported this work through its
Living with a Star program.
---------------------------------------------------------
Title: Coronal Nonthermal Velocity Following Helicity Injection
Before an X-Class Flare
Authors: Harra, L. K.; Williams, D. R.; Wallace, A. J.; Magara, T.;
Hara, H.; Tsuneta, S.; Sterling, A. C.; Doschek, G. A.
2009ApJ...691L..99H Altcode:
We explore the "pre-flare" behavior of the corona in a three-day
period building up to an X-class flare on 2006 December 13 by analyzing
EUV spectral profiles from the Hinode EUV Imaging Spectrometer (EIS)
instrument. We found an increase in the coronal spectral line widths,
beginning after the time of saturation of the injected helicity as
measured by Magara & Tsuneta. In addition, this increase in line
widths (indicating nonthermal motions) starts before any eruptive
activity occurs. The Hinode EIS has the sensitivity to measure changes
in the buildup to a flare many hours before the flare begins.
---------------------------------------------------------
Title: New Evidence that CMEs are Self-Propelled Magnetic Bubbles
Authors: Moore, R. L.; Sterling, A. C.; Suess, S. T.
2008ASPC..397...98M Altcode:
We briefly describe the “standard model” for the production of coronal
mass ejections (CMEs), and our view of how it works. We then summarize
pertinent recent results that we have found from SOHO observations of
CMEs and the flares at the sources of these magnetic explosions. These
results support our interpretation of the standard model: a CME is
basically a self-propelled magnetic bubble, a low-beta plasmoid,
that (1) is built and unleashed by the tether-cutting reconnection
that builds and heats the coronal flare arcade, (2) can explode from
a flare site that is far from centered under the full-blown CME in
the outer corona, and (3) drives itself out into the solar wind by
pushing on the surrounding coronal magnetic field.
---------------------------------------------------------
Title: Early Hinode Observations of a Solar Filament Eruption
Authors: Sterling, A. C.; Moore, R. L.
2008ASPC..397..115S Altcode:
We use Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT)
filtergraph (FG) Stokes-V magnetogram observations to study the early
onset of a solar eruption that includes an erupting filament that we
observe in TRACE EUV images; this is one of the first filament eruptions
seen with Hinode. The filament undergoes a slow rise for at least
30 min prior to its fast eruption and strong soft X-ray flaring, and
the new Hinode data elucidate the physical processes occurring during
the slow-rise period. During the slow-rise phase, a soft X-ray (SXR)
sigmoid forms from apparent reconnection low in the sheared core field
traced by the filament, and there is a low-level intensity peak in both
EUV and SXRs during the slow rise. The SOT data show that magnetic flux
cancelation occurs along the neutral line of the filament in the hours
before eruption, and this likely caused the low-lying reconnection that
produced the microflaring and the slow rise leading up to the eruption.
---------------------------------------------------------
Title: Magnetic Flux Cancelation Leading to the Eruption of a Coronal
Mass Ejection: Observations from Hinode, SOHO, TRACE, and STEREO
Authors: Sterling, A. C.; Chifor, C.; Mason, H.; Moore, R. L.
2008AGUSMSP23B..05S Altcode:
We study a solar eruption involving ejection of a filament on 2007 May
20, using instruments on Hinode, STEREO, TRACE, and SOHO. We observe
the filament in EUV from TRACE and STEREO, and in H-alpha from SOT on
Hinode. We also see the eruption in soft X-rays with XRT on Hinode,
and in several EUV lines from EIS on Hinode. SOHO/MDI magnetograms
show that converging motion between opposite-polarity sunspots in the
region result in expansion of large-scale loops overlying the region's
primary magnetic neutral line, along which sits filament material prior
to its eruption. The source location of an EUV filament's surge-like
ejection is a negative-polarity magnetic region that is north of the
interacting spots, and patches of magnetic field flow at ~ 0.5 km/s
from the positive converging spots into the negative region in the
north. Apparently, repeated episodes of flux cancelation occur where
the flowing positive flux collides with the northern negative flux,
and the source of the EUV filament's ejection is near this cancelation
site. Spectroscopic data from EIS are available for a portion of the
active region that includes the northern cancelation site, and from
these data we obtain bulk-flow velocities, line-broadening turbulent
velocities, and densities of plasma in the region. The array of
observations is consistent with the pre-eruption sheared-core magnetic
arcade being gradually destabilized by evolutionary tether-cutting
flux cancelation that was driven by converging photospheric flows.
---------------------------------------------------------
Title: Initiation of Solar Eruptions
Authors: Sterling, A. C.; Moore, R. L.
2008ASPC..383..163S Altcode:
We consider processes occurring just prior to and at the start of
the onset of flare- and CME-producing solar eruptions. Our recent
work uses observations of filament motions around the time of
eruption onset as a proxy for the evolution of the fields involved
in the eruption. Frequently the filaments show a slow rise prior to
fast eruption, indicative of a slow expansion of the field that is
about to explode. Work by us and others suggests that reconnection
involving emerging or canceling flux results in a lengthening of
fields restraining the filament-carrying field, and the consequent
upward expansion of the field in and around the filament produces the
filament's slow rise; that is, the reconnection weakens the magnetic
“tethers” (“tether-weakening” reconnection), and results in the slow
rise of the filament. It is still inconclusive, however, what mechanism
is responsible for the switch from the slow rise to the fast eruption.
---------------------------------------------------------
Title: Hinode Observations of the Onset Stage of a Solar Filament
Eruption
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Berger, Thomas
E.; Bobra, Monica; Davis, John M.; Jibben, Patricia; Kano, Ryohei;
Lundquist, Loraine L.; Myers, D.; Narukage, Noriyuki; Sakao, Taro;
Shibasaki, Kiyoto; Shine, Richard A.; Tarbell, Theodore D.; Weber, Mark
2007PASJ...59S.823S Altcode:
We used Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT)
filtergraph (FG) Stokes-V magnetogram observations, to study the
early onset of a solar eruption that includes an erupting filament
that we observe in TRACE EUV images. The filament undergoes a slow
rise for at least 20min prior to its fast eruption and strong soft
X-ray (SXR) flaring; such slow rises have been previously reported,
and the new Hinode data elucidate the physical processes occurring
during this period. XRT images show that during the slow-rise phase,
an SXR sigmoid forms from apparent reconnection low in the sheared core
field traced by the filament, and there is a low-level intensity peak
in both EUV and SXRs during the slow rise. MDI and SOT FG Stokes-V
magnetograms show that the pre-eruption filament is along a neutral
line between opposing-polarity enhanced network cells, and the SOT
magnetograms show that these opposing fields are flowing together
and canceling for at least six hours prior to eruption. From the MDI
data we measured the canceling network fields to be ∼ 40G, and we
estimated that ∼ 10<SUP>19</SUP> Mx of flux canceled during the
five hours prior to eruption; this is only ∼ 5% of the total flux
spanned by the eruption and flare, but apparently its tether-cutting
cancellation was enough to destabilize the sigmoid field holding the
filament and resulted in that field's eruption.
---------------------------------------------------------
Title: Coronal Dimming Observed with Hinode: Outflows Related to a
Coronal Mass Ejection
Authors: Harra, Louise K.; Hara, Hirohisa; Imada, Shinsuke; Young,
Peter R.; Williams, David R.; Sterling, Alphonse C.; Korendyke,
Clarence; Attrill, Gemma D. R.
2007PASJ...59S.801H Altcode:
Coronal dimming has been a signature used to determine the source
of plasma that forms part of a coronal mass ejection (CME) for many
years. Generally dimming is detected through imaging instruments such
as SOHO EIT by taking difference images. Hinode tracked active region
10930 from which there were a series of flares. We combined dimming
observations from EIT with Hinode data to show the impact of flares
and coronal mass ejections on the region surrounding the flaring
active region, and we discuss evidence that the eruption resulted in
a prolonged steady outflow of material from the corona. The dimming
region shows clear structure with extended loops whose footpoints are
the source of the strongest outflow (≈ 40 kms<SUP>-1</SUP>). This
confirms that the loops that are disrupted during the event do lose
plasma and hence are likely to form part of the CME. This is the
first time the velocity of the coronal plasma has been measured in an
extended dimming region away from the flare core. In addition there
was a weaker steady outflow from extended, faint loops outside the
active region before the eruption, which is also long lasting. These
were disturbed and the velocity increased following the flare. Such
outflows could be the source of the slow solar wind.
---------------------------------------------------------
Title: New Evidence for the Role of Emerging Flux in a Solar
Filament's Slow Rise Preceding Its CME-producing Fast Eruption
Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L.
2007ApJ...669.1359S Altcode:
We observe the eruption of a large-scale (~300,000 km) quiet-region
solar filament leading to an Earth-directed “halo” coronal mass
ejection (CME), using data from EIT, CDS, MDI, and LASCO on SOHO
and from SXT on Yohkoh. Initially the filament shows a slow (~1 km
s<SUP>-1</SUP> projected against the solar disk) and approximately
constant velocity rise for about 6 hr, before erupting rapidly, reaching
a velocity of ~8 km s<SUP>-1</SUP> over the next ~25 minutes. CDS
Doppler data show Earth-directed filament velocities ranging from
<20 km s<SUP>-1</SUP> (the noise limit) during the slow-rise phase,
to ~100 km s<SUP>-1</SUP> early in the eruption. Beginning within 10
hr prior to the start of the slow rise, localized new magnetic flux
emerged near one end of the filament. Near the start of and during the
slow-rise phase, soft X-ray (SXR) microflaring occurred repeatedly at
the flux-emergence site, and the magnetic arcade over the filament
progressively brightened in a fan of illumination in SXRs. These
observations are consistent with “tether-weakening” reconnection
occurring between the newly emerging flux and the overlying arcade
field containing the filament, and apparently this reconnection is the
cause of the filament's slow rise. We cannot, however, discern whether
the transition from slow rise to fast eruption was caused by a final
episode of tether-weakening reconnection, or by one or some combination
of other possible mechanisms allowed by the observations. Intensity
“dimmings” and “brightenings” occurring both near to and relatively
far from the location of the filament are possible signatures of the
expansion (“opening”) of the erupting field and its reconnection
with overarching field during the eruption.
---------------------------------------------------------
Title: Origin of the Sheared Magnetic Fields that Explode in Flares
and Coronal Mass Ejections
Authors: Moore, R. L.; Sterling, A. C.
2007ASPC..369..539M Altcode:
From observations of 37 flare-arcade events, their magnetic settings,
their sheared core fields, and the coronal mass ejections from these
events, we find evidence that the sheared core fields in mature
magnetic arcades are not formed by bodily emergence of a twisted flux
rope along the neutral line. This implies that these sigmoidal sheared
fields are instead formed by reconnection and flows above and in the
photosphere. A high priority of Solar-B should be to discover the
evolutionary processes that build the sigmoidal sheared fields along
mature neutral lines.
---------------------------------------------------------
Title: The Width of a Solar Coronal Mass Ejection and the Source of
the Driving Magnetic Explosion: A Test of the Standard Scenario for
CME Production
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Suess, Steven T.
2007ApJ...668.1221M Altcode:
We show that the strength (B<SUB>Flare</SUB>) of the magnetic
field in the area covered by the flare arcade following
a CME-producing ejective solar eruption can be estimated
from the final angular width (Final θ<SUB>CME</SUB>)
of the CME in the outer corona and the final angular width
(θ<SUB>Flare</SUB>) of the flare arcade: B<SUB>Flare</SUB>~1.4[(Final
θ<SUB>CME</SUB>)/θ<SUB>Flare</SUB><SUP>2</SUP> G. We assume (1) the
flux-rope plasmoid ejected from the flare site becomes the interior of
the CME plasmoid; (2) in the outer corona (R>2 R<SUB>solar</SUB>)
the CME is roughly a “spherical plasmoid with legs” shaped like a
lightbulb; and (3) beyond some height in or below the outer corona
the CME plasmoid is in lateral pressure balance with the surrounding
magnetic field. The strength of the nearly radial magnetic field
in the outer corona is estimated from the radial component of the
interplanetary magnetic field measured by Ulysses. We apply this
model to three well-observed CMEs that exploded from flare regions
of extremely different size and magnetic setting. One of these CMEs
was an over-and-out CME, that is, in the outer corona the CME was
laterally far offset from the flare-marked source of the driving
magnetic explosion. In each event, the estimated source-region field
strength is appropriate for the magnetic setting of the flare. This
agreement (1) indicates that CMEs are propelled by the magnetic field
of the CME plasmoid pushing against the surrounding magnetic field;
(2) supports the magnetic-arch-blowout scenario for over-and-out CMEs;
and (3) shows that a CME's final angular width in the outer corona
can be estimated from the amount of magnetic flux covered by the
source-region flare arcade.
---------------------------------------------------------
Title: Analysis of Erupting Solar Prominences in Terms of an
Underlying Flux-Rope Configuration
Authors: Krall, Jonathan; Sterling, Alphonse C.
2007ApJ...663.1354K Altcode:
Data from four solar prominence eruptions are analyzed so as to
examine the flux-rope configuration at the onset of eruption and
to test specific aspects of an analytic flux-rope model of solar
eruptions. The model encompasses both prominence eruptions and coronal
mass ejections (CMEs) as generic elements of a typical erupting
flux-rope structure. The hypothesized relationship between prominence
footpoint separation and prominence acceleration profile is examined, as
is the hypothesized geometrical relationship between the prominence and
the CME leading edge (LE). While the simple model does not account for
some observed features, the prominence and “loop” (LE) data are shown
to be consistent with both the geometrical model and the theoretical
acceleration profile. This analysis further suggests that the onset
of eruption is associated with a situation in which the underlying
flux-rope geometry maximizes the outward magnetic “hoop” force.
---------------------------------------------------------
Title: Coronal dimming observed with Hinode
Authors: Harra, Louise; Hara, H.; Young, P.; Williams, D.; Sterling,
A.; Attrill, G.
2007AAS...210.6305H Altcode: 2007BAAS...39..172H
Coronal dimming has been a technique used to determine the source
of plasma that forms part of a coronal mass ejection. Generally
dimming is detected through imaging instruments such as SOHO EIT by
taking difference images. In a few cases the SOHO-CDS has been used
to determine outflowing material, and a decrease in density. Hinode
tracked active region 10930 from which there were a series of flares. We
combine dimming observations from EIT with Hinode data to show the
impact of flares and coronal mass ejections on the region surrounding
the flaring active region, and we discuss evidence that the eruption
resulted in a prolonged steady outflow of material from the corona.
---------------------------------------------------------
Title: The Coronal-dimming Footprint of a Streamer-Puff Coronal Mass
Ejection: Confirmation of the Magnetic-Arch-Blowout Scenario
Authors: Moore, Ronald L.; Sterling, Alphonse C.
2007ApJ...661..543M Altcode:
A streamer puff is a recently identified variety of coronal mass
ejection (CME) of narrow to moderate width. It (1) travels out along
a streamer, transiently inflating the streamer but leaving it largely
intact, and (2) occurs in step with a compact ejective flare in an
outer flank of the base of the streamer. These aspects suggest the
following magnetic-arch-blowout scenario for the production of these
CMEs: the magnetic explosion that produces the flare also produces a
plasmoid that explodes up the leg of an outer loop of the arcade base
of the streamer, blows out the top of this loop, and becomes the core
of the CME. In this paper, we present a streamer-puff CME that produced
a coronal dimming footprint. The coronal dimming, its magnetic setting,
and the timing and magnetic setting of a strong compact ejective flare
within the dimming footprint nicely confirm the magnetic-arch-blowout
scenario. From these observations, together with several published
cases of a transequatorial CME produced in tandem with an ejective
flare or filament eruption that was far offset from directly under the
CME, we propose the following. Streamer-puff CMEs are a subclass (one
variety) of a broader class of “over-and-out” CMEs that are often
much larger than streamer puffs but are similar to them in that they
are produced by the blowout of a large quasi-potential magnetic arch
by a magnetic explosion that erupts from one foot of the large arch,
where it is marked by a filament eruption and/or an ejective flare.
---------------------------------------------------------
Title: Analysis of Polar Plumes Observed During March 29, 2006 Total
Solar Eclipse
Authors: Farid, Samaiyah; Winebarger, A.; Oluseyi, H.; Sterling, A.;
Tan, A.
2007AAS...210.9508F Altcode: 2007BAAS...39..224F
Polar plumes are long lived structures that occur in coronal holes
and are thought to be the source region of the slow solar wind. In
this poster, we present analysis of polar plumes observed during the
March 29, 2006 solar eclipse from Cape Coast, Ghana. We have analyzed
SOHO/EIT data of the same time and date of the eclipse to determine how
the EUV intensity varies as a function of height. We have developed a
steady-state one dimensional hydrodynamic model of plumes that includes
a stratified heating rate, area expansion, and a non-zero velocity
at the plume base. We have compared the intensity profiles from the
model calculated for different heating rates and base velocities with
the intensity profiles of the observed plumes. We present the results
of our model and the analysis and make a conjecture about the mass
contribution of plumes to the solar wind.
---------------------------------------------------------
Title: The Coronal-dimming Footprint Of A Streamer-puff Coronal Mass
Ejection: Confirmation Of The Magnetic-arch-blowout Scenario
Authors: Moore, Ronald L.; Sterling, A. C.
2007AAS...210.2907M Altcode: 2007BAAS...39..138M
A streamer puff is a recently identified variety of coronal mass
ejection (CME) of narrow to moderate width. It (1) travels out along
a streamer, transiently inflating the streamer but leaving it largely
intact, and (2) occurs in step with a compact ejective flare in an
outer flank of the base of the streamer. These aspects suggest the
following magnetic-arch-blowout scenario for the production of these
CMEs: the magnetic explosion that produces the flare also produces a
plasmoid that explodes up the leg of an outer loop of the arcade base
of the streamer, blows out the top of this loop, and becomes the core
of the CME. In this paper, we present a steamer-puff CME that produced
a coronal dimming footprint. The coronal dimming, its magnetic setting,
and the timing and magnetic setting of a strong compact ejective flare
within the dimming footprint nicely confirm the magnetic-arch-blowout
scenario. From these observations, together with several published
cases of a trans-equatorial CME produced in tandem with an ejective
flare or filament eruption that was far offset from directly under the
CME, we propose the following. Streamer-puff CMEs are a subclass (one
variety) of a broader class of “over-and-out” CMEs that are often
much larger than steamer puffs but are similar to them in that they
are produced by the blowout of a large quasi-potential magnetic arch
by a magnetic explosion that erupts from one foot of the large arch,
where it is marked by a filament eruption and/or an ejective flare. <P
/>This work was funded by the Heliophysics Division of NASA's Science
Mission Directorate.
---------------------------------------------------------
Title: Combined Hinode, STEREO, And TRACE Observations of a Solar
Filament Eruption: Evidence For Destabilization By Flux-Cancelation
Tether Cutting
Authors: Sterling, Alphonse C.; Moore, R. L.; Hinode Team
2007AAS...210.7207S Altcode: 2007BAAS...39R.179S
We present observations from Hinode, STEREO, and TRACE of a solar
filament eruption and flare that occurred on 2007 March 2. Data
from the two new satellites, combined with the TRACE observations,
give us fresh insights into the eruption onset process. HINODE/XRT
shows soft X-ray (SXR) activity beginning approximately 30 minutes
prior to ignition of bright flare loops. STEREO and TRACE images show
that the filament underwent relatively slow motions coinciding with
the pre-eruption SXR brightenings, and it underwent rapid eruptive
motions beginning near the time of flare onset. Concurrent HINODE/SOT
magnetograms showed substantial flux cancelation under the filament at
the site of the pre-eruption SXR activity. From these observations
we infer that progressive tether-cutting reconnection driven by
photospheric convection caused the slow rise of the filament and
led to its eruption. <P />NASA supported this work through a NASA
Heliosphysics GI grant.
---------------------------------------------------------
Title: Cool-Plasma Jets that Escape into the Outer Corona
Authors: Corti, Gianni; Poletto, Giannina; Suess, Steve T.; Moore,
Ronald L.; Sterling, Alphonse C.
2007ApJ...659.1702C Altcode:
We report on observations acquired in 2003 May during a SOHO-Ulysses
quadrature campaign. The UVCS slit was set normal to the radial of
the Sun along the direction to Ulysses at 1.7 R<SUB>solar</SUB>, at
a northern latitude of 14.5°. From May 25 to May 28, UVCS acquired
spectra of several short-lived ejections that represent the extension
at higher altitudes of recursive EIT jets, imaged in He II λ304. The
jets were visible also in LASCO images and seem to propagate along
the radial to Ulysses. UVCS spectra showed an unusually high emission
in cool lines, lasting for about 10-25 minutes, with no evidence of
hot plasma. Analysis of the cool line emission allowed us to infer
the physical parameters (temperature, density, and outward velocity)
of jet plasma and the evolution of these quantities as the jet crossed
the UVCS slit. From these quantities, we estimated the energy needed
to produce the jet. We also looked for any evidence of the events in
the in situ data. We conclude by comparing our results with those of
previous works on similar events and propose a scenario that accounts
for the observed magnetic setting of the source of the jets and allows
the jets to be magnetically driven.
---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections
Authors: Moore, Ronald L.; Sterling, Alphonse C.
2006GMS...165...43M Altcode:
This paper is a synopsis of the initiation of the strong-field magnetic
explosions that produce large, fast coronal mass ejections. The
presentation outlines our current view of the eruption onset, based on
results from our own observational work and from the observational and
modeling work of others. From these results and from physical reasoning,
we and others have inferred the basic processes that trigger and
drive the explosion. We describe and illustrate these processes using
cartoons. The magnetic field that explodes is a sheared-core bipole
that may or may not be embedded in surrounding strong magnetic field,
and may or may not contain a flux rope before it starts to explode. We
describe three different mechanisms that singly or in combination
can trigger the explosion: (1) runaway internal tether-cutting
reconnection, (2) runaway external tether-cutting reconnection, and
(3) ideal MHD instability or loss or equilibrium. For most eruptions,
high-resolution, high-cadence magnetograms and chromospheric and coronal
movies (such as from TRACE or Solar-B) of the pre-eruption region and
of the onset of the eruption and flare are needed to tell which one
or which combination of these mechanisms is the trigger. Whatever the
trigger, it leads to the production of an erupting flux rope. Using
a simple model flux rope, we demonstrate that the explosion can be
driven by the magnetic pressure of the expanding flux rope, provided
the shape of the expansion is "fat" enough.
---------------------------------------------------------
Title: Wide and Narrow CMEs and their Source Explosions Observed at
the Spring 2003 SOHO-Sun-Ulysses Quadrature
Authors: Suess, S. T.; Corti, G.; Poletto, G.; Sterling, A.; Moore, R.
2006ESASP.617E.147S Altcode: 2006soho...17E.147S
No abstract at ADS
---------------------------------------------------------
Title: Characteristics of EIT Dimmings in Solar Eruptions
Authors: Adams, Mitzi; Sterling, A. C.
2006SPD....37.0114A Altcode: 2006BAAS...38..217A
Intensity "dimmings" in coronal images are a key feature of solar
eruptions. Such dimmings are likely the source locations for much of
the material expelled in coronal mass ejections (CMEs). Characteristics
such as the timing of the dimmings with respect to the onset of other
eruption signatures, and the location of the dimmings in the context of
the magnetic field environment of the erupting region, are indicative
of the mechanism leading to the eruption. We examine dimmings of six
eruptions in images from the EUV Imaging Telescope (EIT) on SOHO,
along with supplementary soft X-ray (SXR) data from GOES and the SXR
Telescope (SXT) on Yohkoh. We examine the timing of the dimming onset
and compare with the time of EUV and SXR brightening and determine
the timescale for the recovery from dimming for each event. With
line-of-sight photospheric magnetograms from the MDI instrument on
SOHO, we determine the magnetic structure of the erupting regions
and the locations of the dimmings in those regions. >From our
analysis we consider which mechanism likely triggered each eruption:
internal tether cutting, external tether cutting ("breakout"), loss
of equilibrium, or some other mechanism.
---------------------------------------------------------
Title: Initiation of the Slow-Rise and Fast-Rise Phases of an Erupting
Solar Filamentby Localized Emerging Magnetic Field via Microflaring
Authors: Sterling, Alphonse C.; Moore, R. L.; Harra, L. K.
2006SPD....37.0823S Altcode: 2006BAAS...38..234S
EUV data from EIT show that a filament of 2001 February 28 underwent
aslow-rise phase lasting about 6 hrs, before rapidly erupting in a
fast-risephase. Concurrent images in soft X-rays (SXRs) from Yohkoh/SXT
show that aseries of three microflares, prominent in SXT images but weak
in EIT 195 AngEUV images, occurred near one end of the filament. The
first and lastmicroflares occurred respectively in conjunction with
the start of theslow-rise phase and the start of the fast-rise phase,
and the second microflarecorresponded to a kink in the filament
trajectory. Beginning within 10 hoursof the start of the slow rise,
new magnetic flux emerged at the location of themicroflaring. This
localized new flux emergence and the resulting microflares,consistent
with reconnection between the emerging field and the sheared sigmoidcore
magnetic field holding the filament, apparently caused the slow
rise ofthis field and the transition to explosive eruption. For the
first time insuch detail, the observations show this direct action of
localized emergingflux in the progressive destabilization of a sheared
core field in the onset ofa coronal mass ejection (CME). Similar
processes may have occurred in otherrecently-studied events.NASA
supported this work through NASA SR&T and SEC GI grants.
---------------------------------------------------------
Title: The Origin Of The Sheared Magnetic Fields That Erupt In Flares
And Coronal Mass Ejections
Authors: Moore, Ronald L.; Sterling, A. C.
2006SPD....37.2001M Altcode: 2006BAAS...38R.247M
From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and
2001, we found 37 flare-arcade events for which there were full-disk
magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and
before and after full-disk chromospheric images from SOHO/EIT and/or
from ground-based observatories. For each event, the observations show
or strongly imply that the flare arcade was produced in the usual way
by the eruption of sheared core field (as a flux rope) from along the
neutral line inside a mature bipolar magnetic arcade. Two-thirds (25)
of these arcades had the normal leading-trailing magnetic polarity
arrangement of the active regions in the hemisphere of the arcade, but
the other third (12) had reversed polarity, their leading flux being
the trailing-polarity remnant of one or more old active regions and
their trailing flux being the leading-polarity remnant of one or more
other old active regions. >From these observations, we conclude:
(1) The sheared core field in a reversed-polarity arcade must be formed
by processes in and above the photosphere, not by the emergence of a
twisted flux rope bodily from below the photosphere. (2) The sheared
core fields in the normal-polarity arcades were basically the same as
those in the reversed-polarity arcades: both showed similar sigmoidal
form and produced similar explosions (similar flares and CMEs). (3)
Hence, the sheared core fields in normal-polarity mature arcades are
likely formed mainly by the same processes as in reversed-polarity
arcades. (4) These processes should be discernible in high-resolution
magnetogram sequences and movies of the photosphere, chromosphere, and
corona such those to come from Solar-B.This work was supported by NASA's
Science Mission Directorate through its Solar and Heliospheric Physics
Supporting Research & Technology program and its Heliophysics
Guest Investigators program.
---------------------------------------------------------
Title: Recursive Narrowcmes Within a Coronal Streamer
Authors: Bemporad, A.; Sterling, A. C.; Moore, R. L.; Poletto, G.
2005ESASP.600E.153B Altcode: 2005ESPM...11..153B; 2005dysu.confE.153B
No abstract at ADS
---------------------------------------------------------
Title: A New Variety of Coronal Mass Ejection: Streamer Puffs from
Compact Ejective Flares
Authors: Bemporad, A.; Sterling, Alphonse C.; Moore, Ronald L.;
Poletto, G.
2005ApJ...635L.189B Altcode:
We report on SOHO UVCS, LASCO, EIT, and MDI observations of a
series of narrow ejections that occurred at the solar limb. These
ejections originated from homologous compact flares whose source
was an island of included polarity located just inside the base of
a coronal streamer. Some of these ejections result in narrow CMEs
(“streamer puffs”) that move out along the streamer. These streamer
puffs differ from “streamer blowout” CMEs in that (1) while the
streamer is transiently inflated by the puff, it is not disrupted, and
(2) each puff comes from a compact explosion in the outskirts of the
streamer arcade, not from an extensive eruption along the main neutral
line of the streamer arcade. From the observations, we infer that
each streamer puff is produced by means of the inflation or blowing
open of an outer loop of the arcade by ejecta from the compact-flare
explosion in the foot of the loop. So, in terms of their production,
our streamer puffs are a new variety of CME.
---------------------------------------------------------
Title: Slow-Rise and Fast-Rise Phases of an Erupting Solar Filament,
and Flare Emission Onset
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2005ApJ...630.1148S Altcode:
We observe the eruption of an active-region solar filament on
1998 July 11 using high time cadence and high spatial resolution
EUV observations from the TRACE satellite, along with soft X-ray
images from the soft X-ray telescope (SXT) on the Yohkoh satellite,
hard X-ray fluxes from the BATSE instrument on the CGRO satellite
and from the hard X-ray telescope (HXT) on Yohkoh, and ground-based
magnetograms. We concentrate on the initiation of the eruption in an
effort to understand the eruption mechanism. Prior to eruption the
filament undergoes a slow upward movement in a slow-rise phase with an
approximately constant velocity of ~15 km s<SUP>-1</SUP> that lasts
about 10 minutes. It then erupts in a fast-rise phase, accelerating
to a velocity of ~200 km s<SUP>-1</SUP> in about 5 minutes and then
decelerating to ~150 km s<SUP>-1</SUP> over the next 5 minutes. EUV
brightenings begin about concurrently with the start of the filament's
slow rise and remain immediately beneath the rising filament during
the slow rise; initial soft X-ray brightenings occur at about the same
time and location. Strong hard X-ray emission begins after the onset
of the fast rise and does not peak until the filament has traveled
to a substantial altitude (to a height about equal to the initial
length of the erupting filament) beyond its initial location. Our
observations are consistent with the slow-rise phase of the eruption
resulting from the onset of “tether cutting” reconnection between
magnetic fields beneath the filament, and the fast rise resulting from
an explosive increase in the reconnection rate or by catastrophic
destabilization of the overlying filament-carrying fields. About 2
days prior to the event, new flux emerged near the location of the
initial brightenings, and this recently emerged flux could have been
a catalyst for initiating the tether-cutting reconnection. With the
exception of the sudden transition from the slow-rise phase to the
fast-rise phase in our event, our filament's height-time profile is
qualitatively similar to the plot of the erupting flux rope height as
a function of time recently computed by Chen and Shibata for a model
in which the eruption is triggered by reconnection between an emerging
field and another field under the flux rope.
---------------------------------------------------------
Title: Shape and Reconnection of the Exploding Magnetic Field in
the Onset of CMEs
Authors: Moore, R. L.; Sterling, A. C.; Falconer, D. A.; Gary, G. A.
2005AGUSMSH54B..01M Altcode:
From chromospheric and coronal images and line-of-sight and vector
magnetograms of magnetic regions that produce CMEs, and from
chromospheric and coronal movies of the onsets of CME eruptions,
it appears that the magnetic field that explodes to drive the CME
is initially the strongly sheared core of a magnetic arcade encasing
a polarity dividing line in the magnetic flux. Before or during the
onset of the explosion, the sheared core field becomes a flux rope,
often carrying chromospheric material within it. For the erupting flux
rope to drive the explosion, that is, for its magnetic energy content
to decrease in the explosion, the flux rope's cross-sectional area
must increase faster than its length. For instance, for isotropic
expansion, the area increases as the square of the length, and the
magnetic energy content of the flux rope decreases as the inverse of
the length. The instability that initiates the eruption of the flux
rope might be an ideal MHD kink instability, or might involve runaway
tether-cutting reconnection. The reconnection begins below the flux
rope (internal to the arcade) when the overall field configuration
of the region is effectively that of a single bipole. When the flux
rope resides in a multi-bipolar configuration having a magnetic null
above the flux rope, the runaway tether-cutting reconnection might
begin either below the flux rope or at the null above (external to)
the arcade. We present examples of observed CME onsets that illustrate
the above alternatives. In each example, reconnection below the flux
rope begins early in the eruption. This indicates that internal
tether cutting reconnection (classic tether-cutting reconnection)
is important in unleashing the CME explosion in all cases, including
those in which the explosion may be triggered by MHD kinking or by
external reconnection (classic breakout reconnection).
---------------------------------------------------------
Title: Flare Emission Onset in the Slow-Rise and Fast-Rise Phases
of an Erupting Solar Filament Observed with TRACE
Authors: Sterling, A. C.; Moore, R. L.
2005AGUSMSP44A..02S Altcode:
We observe the eruption of an active-region solar filament of 1998
July~11 using high time cadence and high spatial resolution EUV
observations from the TRACE satellite, along with soft X-ray images
from the soft X-ray telescope (SXT) on the Yohkoh satellite, hard X-ray
fluxes from the BATSE instrument on the ( CGRO) satellite and from the
hard X-ray telescope (HXT) on Yohkoh, and ground-based magnetograms. We
concentrate on the initiation of the eruption in an effort to
understand the eruption mechanism. First the filament undergoes slow
upward movement in a "slow rise" phase with an approximately constant
velocity of ≍ 15~km~s-1 that lasts about 10~min, and then it erupts
in a "fast-rise" phase, reaching a velocity of ≍ 200~km~s-1 in about
5~min, followed by a period of deceleration. EUV brightenings begin just
before the start of the filament's slow rise, and remain immediately
beneath the rising filament during the slow rise; initial soft X-ray
brightenings occur at about the same time and location. Strong hard
X-ray emission begins after the onset of the fast rise, and does not
peak until the filament has traveled a substantial altitude (to a
height about equal to the initial length of the erupting filament)
beyond its initial location. Our observations are consistent with
the slow-rise phase of the eruption resulting from the onset of
"tether cutting" reconnection between magnetic fields beneath the
filament, and the fast rise resulting from an explosive increase
in the reconnection rate or by catastrophic destabilization of the
overlying filament-carrying fields. About two days prior to the event
new flux emerged near the location of the initial brightenings, and
this recently-emerged flux could have been a catalyst for initiating
the tether-cutting reconnection. With the exception of the initial
slow rise, our findings qualitatively agree with the prediction for
erupting-flux-rope height as a function of time in a model discussed
by Chen & Shibata~(2000) based on reconnection between emerging
flux and a flux rope. NASA supported this work through NASA SR&T
and SEC GI grants.
---------------------------------------------------------
Title: X-Ray and EUV Observations of CME Eruption Onset
Authors: Sterling, Alphonse C.
2005IAUS..226...27S Altcode:
Why CMEs erupt is a major outstanding puzzle of solar
physics. Signatures observable at the earliest stages of eruption
onset may hold precious clues about the onset mechanism. We summarize
and discuss observations from SOHO/EIT in EUV and from Yohkoh/SXT
in soft X-rays of the pre-eruption and eruption phases of three CME
expulsions, along with the eruptions' magnetic setting inferred from
SOHO/MDI magnetograms. Our events involve clearly-observable filament
eruptions and multiple neutral lines, and we use the magnetic settings
and motions of the filaments to help infer the geometry and behavior of
the associated erupting magnetic fields. Pre-eruption and early-eruption
signatures include a relatively slow filament rise prior to eruption,
and intensity dimmings and brightenings, both in the immediate
neighborhood of the "core" (location of greatest magnetic shear)
of the erupting fields and at locations remote from the core. These
signatures and their relative timings place observational constraints
on eruption mechanisms; our recent work has focused on implications
for the so-called "tether cutting" and "breakout" models, but the same
observational constraints are applicable to any model.
---------------------------------------------------------
Title: Tether-Cutting Energetics of a Solar Quiet Region Prominence
Eruption
Authors: Sterling, A. C.
2004ASPC..325..395S Altcode:
We study the morphology and energetics of a slowly-evolving quiet
region solar prominence eruption occurring on 1999 February 8-9 in the
solar north polar crown region, using ion{Fe{xv}} EUV 284 AA data from
the EUV Imaging Telescope (EIT) on SOHO and soft X-ray data from the
soft X-ray telescope (SXT) on Yohkoh. After rising at approximately 1
kmps for about six hours, the prominence accelerates to a velocity of
approximately 10 kmps leaving behind EUV and soft X-ray loop arcades
of a weak flare in its source region. These flare brightenings are
consistent with “tether-cutting” reconnection occurring beneath the
rising prominence, but they only become apparent about two hours after
the prominence's acceleration. Nonetheless, via energetic arguments
we show that tether cutting could have been occurring nearer the
time of the start of the fast rise, but not yet discernible in SXT
images. Therefore we are unable to assess whether tether cutting was
responsible for the the prominence's acceleration from these data alone.
---------------------------------------------------------
Title: The Relationship between Prominence Eruptions and Global
Coronal Waves
Authors: Attrill, G. D. R.; Harra, L. K.; Matthews, S. A.; Foley,
C. R.; Sterling, A. C.
2004ASPC..325..409A Altcode:
There has been much debate over the physical mechanism for producing
global coronal waves (`EIT waves'). In this work, we investigate
whether filament eruptions are directly associated with coronal
waves. We analyse 45 coronal waves and search for evidence of
filament eruptions. We used SOHO-EIT data, and EIT data along with
any available ground-based Hα data to search for filament eruptions,
and found that more than 50 % of coronal waves are clearly associated
with eruptions. The speeds of the coronal waves, and the filament
eruptions are similar. We discuss the implications of these results.
---------------------------------------------------------
Title: External and Internal Reconnection in Two Filament-Carrying
Magnetic Cavity Solar Eruptions
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2004ApJ...613.1221S Altcode:
We observe two near-limb solar filament eruptions, one of 2000 February
26 and the other of 2002 January 4. For both we use 195 Å Fe XII images
from the Extreme-Ultraviolet Imaging Telescope (EIT) and magnetograms
from the Michelson Doppler Imager (MDI), both of which are on the
Solar and Heliospheric Observatory (SOHO). For the earlier event
we also use soft X-ray telescope (SXT), hard X-ray telescope (HXT),
and Bragg Crystal Spectrometer (BCS) data from the Yohkoh satellite,
and hard X-ray data from the BATSE experiment on the Compton Gamma
Ray Observatory (CGRO). Both events occur in quadrupolar magnetic
regions, and both have coronal features that we infer belong to the
same magnetic cavity structures as the filaments. In both cases, the
cavity and filament first rise slowly at ~10 km s<SUP>-1</SUP> prior
to eruption and then accelerate to ~100 km s<SUP>-1</SUP> during the
eruption, although the slow-rise movement for the higher altitude cavity
elements is clearer in the later event. We estimate that both filaments
and both cavities contain masses of ~10<SUP>14</SUP>-10<SUP>15</SUP> and
~10<SUP>15</SUP>-10<SUP>16</SUP> g, respectively. We consider whether
two specific magnetic reconnection-based models for eruption onset,
the “tether cutting” and the “breakout” models, are consistent
with our observations. In the earlier event, soft X-rays from SXT
show an intensity increase during the 12 minute interval over which
fast eruption begins, which is consistent with tether-cutting-model
predictions. Substantial hard X-rays, however, do not occur until
after fast eruption is underway, and so this is a constraint the
tether-cutting model must satisfy. During the same 12 minute interval
over which fast eruption begins, there are brightenings and topological
changes in the corona indicative of high-altitude reconnection early
in the eruption, and this is consistent with breakout predictions. In
both eruptions, the state of the overlying loops at the time of onset
of the fast-rise phase of the corresponding filament can be compared
with expectations from the breakout model, thereby setting constraints
that the breakout model must meet. Our findings are consistent with
both runaway tether-cutting-type reconnection and fast breakout-type
reconnection, occurring early in the fast phase of the February eruption
and with both types of reconnection being important in unleashing
the explosion, but we are not able to say which, if either, type of
reconnection actually triggered the fast phase. In any case, we have
found specific constraints that either model, or any other model,
must satisfy if correct.
---------------------------------------------------------
Title: External and Internal Reconnection in Two Filament-Carrying
Magnetic-Cavity Solar Eruptions
Authors: Sterling, A. C.; Moore, R. L.
2004AAS...204.1804S Altcode: 2004BAAS...36..683S
We observe two near-limb solar filament eruptions, one of 2000 February
26 and the other of 2002 January 4, using 195 Å Fe xii\ images from
SOHO/EIT and magnetograms from SOHO/MDI\@. For the earlier event
we also use soft X-ray data from Yohkoh/SXT, and hard X-ray data
from Yohkoh/HXT and CGRO/BATSE\@. Both events occur in quadrupolar
magnetic regions, and both have coronal features belonging to the same
magnetic-cavity-structures as the filaments. In both cases the cavity
and filament have a slow-rise phase of ∼ 10 km s<SUP>-1</SUP> prior to
eruption, followed by a fast-rise phase of ∼ 100 km s<SUP>-1</SUP>
during eruption. We estimate both filaments and both cavities to
contain masses of ∼ 10<SUP>14-15</SUP> g and ∼ 10<SUP>15-16</SUP>
g, respectively. We consider two specific magnetic-reconnection-based
models for eruption onset, the “tether cutting” and the “breakout”
models. In the earlier event SXT images show an intensity increase
during the 12-minute interval over which the fast phase begins,
consistent with tether-cutting. Substantial hard X-rays, however,
do not occur until after fast eruption is underway, which provides
a constraint on the tether-cutting model. Also around the time fast
eruption begins there are brightenings and topological changes in
the corona indicative of high-altitude reconnection, consistent with
breakout. In both eruptions, however, fast rise onset occurs while
cavity-related coronal loops are still evolving from “closed” to
“open,” providing constraints on the breakout model. Therefore our
findings are consistent with aspects of both models, but we cannot
say which, if either, mechanism triggered the fast phase. We have
also found specific constraints that either model, or any other
eruption-onset model, must satisfy if correct. NASA supported this
work through SR&T and SEC GI grants.
---------------------------------------------------------
Title: Evidence for Gradual External Reconnection before Explosive
Eruption of a Solar Filament
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2004ApJ...602.1024S Altcode:
We observe a slowly evolving quiet-region solar eruption of 1999
April 18, using extreme-ultraviolet (EUV) images from the EUV
Imaging Telescope (EIT) on the Solar and Heliospheric Observatory
(SOHO) and soft X-ray images from the Soft X-ray Telescope (SXT) on
Yohkoh. Using difference images, in which an early image is subtracted
from later images, we examine dimmings and brightenings in the region
for evidence of the eruption mechanism. A filament rose slowly at
about 1 km s<SUP>-1</SUP> for 6 hours before being rapidly ejected at
about 16 km s<SUP>-1</SUP>, leaving flare brightenings and postflare
loops in its wake. Magnetograms from the Michelson Doppler Imager
(MDI) on SOHO show that the eruption occurred in a large quadrupolar
magnetic region with the filament located on the neutral line of the
quadrupole's central inner lobe between the inner two of the four
polarity domains. In step with the slow rise, subtle EIT dimmings
commence and gradually increase over the two polarity domains on one
side of the filament, i.e., in some of the loops of one of the two
sidelobes of the quadrupole. Concurrently, soft X-ray brightenings
gradually increase in both sidelobes. Both of these effects suggest
heating in the sidelobe magnetic arcades, which gradually increase
over several hours before the fast eruption. Also, during the slow
pre-eruption phase, SXT dimmings gradually increase in the feet and
legs of the central lobe, indicating expansion of the central-lobe
magnetic arcade enveloping the filament. During the rapid ejection,
these dimmings rapidly grow in darkness and in area, especially in
the ends of the sigmoid field that erupts with the filament, and flare
brightenings begin underneath the fast-moving but still low-altitude
filament. We consider two models for explaining the eruption:
“breakout,” which says that reconnection occurs high above the
filament prior to eruption, and “tether cutting,” which says that
the eruption is unleashed by reconnection beneath the filament. The
pre-eruption evolution is consistent with gradual breakout that led to
(and perhaps caused) the fast eruption. Tether-cutting reconnection
below the filament begins early in the rapid ejection, but our data are
not complete enough to determine whether this reconnection began early
enough to be the cause of the fast-phase onset. Thus, our observations
are consistent with gradual breakout reconnection causing the long slow
rise of the filament, but allow the cause of the sudden onset of the
explosive fast phase to be either a jump in the breakout reconnection
rate or the onset of runaway tether-cutting reconnection, or both.
---------------------------------------------------------
Title: Solar Spicules: Prospects for Breakthroughs in Understanding
with Solar-B
Authors: Sterling, A.
2004cosp...35.2435S Altcode: 2004cosp.meet.2435S
Spicules densely populate the lower solar atmosphere; any image or
movie of the chromosphere shows a plethora of them or their "cousins,"
such as mottles or fibrils. Yet despite several decades of effort we
still do not know the mechanism that generates them, or how important
their contribution is to the material and energy balance of the overall
solar atmosphere. Solar-B will provide exciting new chromospheric
observations at high time- and spatial-resolution, along with associated
quality magnetic field data, that promise to open doors to revolutionary
breakthroughs in spicule research. In this presentation we will review
the current observational and theoretical status of spicule studies,
and discuss prospects for advances in spicule understanding during
the Solar-B era.
---------------------------------------------------------
Title: Solar 'EIT Waves' - What are They?
Authors: Harra, L. K.; Sterling, A. C.
2004IAUS..219..498H Altcode: 2003IAUS..219E..65H
Using spectral data from the Coronal Diagnostic Spectrometer (CDS)
instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft
we observe a coronal wave feature which occurred in association with a
solar eruption and flare on 1998 June~13. EUV images from the Transition
Region and Coronal Explorer (TRACE) satellite show that the coronal
wave consists of two aspects: (1) a “bright wave” which shows up
prominently in the TRACE difference images moves with a velocity of
approximately 200km/s and is followed by a strong dimming region behind
it and (2) a “weak wave” which is faint in the TRACE images has a
velocity of about 500km/s and appears to disperse out of the bright
wave. A “high-velocity” CDS feature however occurs after the weak wave
passes which appears to correspond to ejection of cool filament-like
material in TRACE images. Our observations have similarities with a
numerical simulation model of coronal waves presented by Chen etal
(2002) who suggests that coronal waves consist of a faster-propagating
piston-driven portion and a more slowly-propagating portion due to
the opening of field lines associated with an erupting filament.
---------------------------------------------------------
Title: Tether-cutting Energetics of a Solar Quiet-Region Prominence
Eruption
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2003ApJ...599.1418S Altcode:
We study the morphology and energetics of a slowly evolving quiet-region
solar prominence eruption occurring on 1999 February 8-9 in the solar
north polar crown region, using soft X-ray data from the soft X-ray
telescope (SXT) on Yohkoh and Fe XV EUV 284 Å data from the EUV
Imaging Telescope (EIT) on the Solar and Heliospheric Observatory
(SOHO). After rising at ~1 km s<SUP>-1</SUP> for about six hours,
the prominence accelerates to a velocity of ~10 km s<SUP>-1</SUP>,
leaving behind EUV and soft X-ray loop arcades of a weak flare in
its source region. Intensity dimmings occur in the eruption region
cospatially in EUV and soft X-rays, indicating that the dimmings
result from a depletion of material. Over the first two hours of
the prominence's rapid rise, flarelike brightenings occur beneath
the rising prominence that might correspond to “tether-cutting”
magnetic reconnection. These brightenings have heating requirements of
up to ~10<SUP>28</SUP>-10<SUP>29</SUP> ergs, and this is comparable
to the mechanical energy required for the rising prominence over the
same time period. If the ratio of mechanical energy to heating energy
remains constant through the early phase of the eruption, then we infer
that coronal signatures for the tether cutting may not be apparent
at or shortly after the start of the fast phase in this or similar
low-energy eruptions, since the plasma-heating energy levels would
not exceed that of the background corona.
---------------------------------------------------------
Title: Tether-Cutting Energetics of a Solar Quiet Region Prominence
Eruption
Authors: Sterling, A. C.; Moore, R. L.
2003AGUFMSH22A0182S Altcode:
We study the morphology and energetics of a slowly-evolving quiet region
solar prominence eruption occurring on 1999 February 8---9 in the
solar north polar crown region, using Fe~xv EUV 284~Å data from the
EUV Imaging Telescope (EIT) on SOHO and soft X-ray data from the soft
X-ray telescope (SXT) on Yohkoh. After rising at ≈ 1~km~s<SUP>-1</SUP>
for about six hours, the prominence accelerates to a velocity of ≈
10~km~s<SUP>-1</SUP>, leaving behind EUV and soft X-ray loop arcades
of a weak flare in its source region. Intensity dimmings occur in the
eruption region cospatially in EUV and soft X-rays, indicating that
the dimmings result from a depletion of material. Over the first two
hours of the prominence's rapid rise, flare-like brightenings occur
beneath the rising prominence which may correspond to “tether cutting”
magnetic reconnection. These brightenings have heating requirements of
up to ∼ 10<SUP>28</SUP>---10<SUP>29</SUP>~ergs, and this is comparable
to the mechanical energy required for the rising prominence over the
same time period. If the ratio of mechanical energy to heating energy
remains constant through the early phase of the eruption, then we infer
that coronal signatures for the tether cutting may not be apparent at
or shortly after the start of the faster-rise phase of the prominence
in this or similar low-energy eruptions, since the plasma-heating
energy levels would not exceed that of the background corona. Our
findings have strong implications for the correct use of observations
in testing theoretical ideas for the onset of solar eruptions.
---------------------------------------------------------
Title: A near-solar-cycle's worth of CME studied with Yohkoh
Authors: Sterling, Alphonse C.
2003ESASP.535..415S Altcode: 2003iscs.symp..415S
Yohkoh observed the Sun virtually continuously between August 1991
and December 2001, covering nearly a complete solar cycle. Among the
instruments on board was the Soft X-ray Telescope (SXT), which gave
us fresh perspectives on the dynamic nature of the solar corona. Data
from Yohkoh, and from SXT in particular, are helping us undertstand
the nature of Coronal Mass Ejections (CMEs). Although CMEs were a
topic of interest from the start of the mission, major progress in
relating Yohkoh observations to CMEs began in late 1996, following the
start of observations of CMEs with the instruments on board the SOHO
satellite. Since then we have learned much by combining the direct and
indirect observations of CMEs from SOHO, with the coronal observations
from SXT. We now have both an improved understanding of, and new
questions about: the coronal source regions of CMEs, the nature of
the material ejected in CMEs, the relation between CMEs and soft X-ray
flares, and the underlying mechanism driving general solar eruptions.
---------------------------------------------------------
Title: Evidence for Gradual External Reconnection Leading to Explosive
Eruption of a Solar Filament
Authors: Sterling, A. C.; Moore, R. L.
2003SPD....34.2301S Altcode: 2003BAAS...35..851S
We observe a slowly-evolving quiet region solar eruption of 1999
April 18, using images in 195 Å Fe xii from EIT on SOHO, and in soft
X-rays from SXT on Yohkoh. We examine dimmings and brightenings in
difference images, where an early image is subtracted from later
images, for evidence of the eruption mechanism. A filament rose
slowly at about 1 km s<SUP>-1</SUP> for six hours before being
rapidly ejected at about 10 km s<SUP>-1</SUP>, leaving flare
brightenings and post-flare loops in its wake. SOHO MDI data show
that the eruption occurred in a quadrupolar region, with the filament
location splitting the four magnetic sources. During the slow rise,
subtle EIT dimmings occur between the filament and one of the remote
magnetic regions. Concurrently, soft X-ray brightenings occur between
the filament and either remote magnetic region. Both of these effects
suggest temperature enhancements in magnetic loop systems on either
side of the filament prior to eruption. Pre-eruption SXT dimmings
occur on either side of and very close to the slowly rising filament,
indicating expansion of enveloping magnetic loops. At the start of the
rapid ejection, intense dimmings occur at the locations evacuated by
the filament, and brightenings occur underneath the fast-moving but
still low-altitude filament. We consider two models for explaining
the eruption: “breakout,” which says that reconnection occurs high
above the filament prior to eruption, and “tether cutting,” which
says that the eruption is driven by reconnecting field lines beneath
the filament. We find that pre-eruption evolution is consistent with
breakout. Tether cutting-type reconnection occurs during the rapid
ejection, but our data are not complete enough to determine whether
that reconnection is the primary cause of the fast-phase onset.
---------------------------------------------------------
Title: Imaging and Spectroscopic Investigations of a Solar Coronal
Wave: Properties of the Wave Front and Associated Erupting Material
Authors: Harra, Louise K.; Sterling, Alphonse C.
2003ApJ...587..429H Altcode:
Using spectral data from the Coronal Diagnostic Spectrometer (CDS)
instrument on the Solar and Heliospheric Observatory spacecraft, we
observe a coronal wave feature (often referred to as an EIT wave) that
occurred in association with a solar eruption and flare on 1998 June
13. EUV images from the Transition Region and Coronal Explorer (TRACE)
satellite show that the coronal wave consists of two aspects: (1) a
“bright wave,” which shows up prominently in the TRACE difference
images, moves with a velocity of approximately 200 km s<SUP>-1</SUP>,
and is followed by a strong dimming region behind it and (2) a “weak
wave,” which is faint in the TRACE images, has a velocity of about 500
km s<SUP>-1</SUP>, and appears to disperse out of the bright wave. The
weak wave passes through the CDS field of view but shows little or
no line-of-sight motions in CDS spectra (velocities less than about
10 km s<SUP>-1</SUP>). Only a small portion of the bright wave passes
the CDS field of view, with the spectral lines showing insignificant
shifts. A high-velocity CDS feature, however, occurs after the weak wave
passes, which appears to correspond to ejection of cool, filament-like
material in TRACE images. Our observations have similarities with
a numerical simulation model of coronal waves presented by Chen et
al., who suggest that coronal waves consist of a faster propagating,
piston-driven portion and a more slowly propagating portion due to
the opening of field lines associated with an erupting filament.
---------------------------------------------------------
Title: Doppler Detection of Material Outflows from Coronal Intensity
“Dimming Regions” During Coronal Mass Ejection Onset
Authors: Sterling, A.; Harra, Louise
2002AAS...200.3709S Altcode: 2002BAAS...34..696S
“Coronal dimmings,” localized regions showing a precipitous drop in
EUV or X-ray emission, are a key coronal signature of the sources of
Coronal Mass Ejections (CMEs). Researchers often assume that dimmings
result from a depletion of coronal material (i.e., a decrease in density
along the line-of-sight), even when no obvious moving structure can be
detected in images. Yet, this explanation has not been unambiguously
established; in principle the dimmings could, for example, be due
to a dramatic change in the temperature of the emitting material
instead. Here we present the most direct evidence to-date that the
dimmings result from mass loss, by observing Doppler motions of material
leaving the regions as they dim. Using spectral data from the Coronal
Diagnostic Spectrometer (CDS) on SOHO, we observe Doppler shifts in
two different events. One of these, from 1998 March 31 near 9 UT,
was near the solar limb and was associated with a CME traveling in the
plane of the sky, while the other event, from 1999 July 19 near 1:50
UT, was on the solar disk and was associated with an Earth-directed
“halo” CME\@. The limb event shows Doppler signatures of ≈ 30 km
s<SUP>-1</SUP> in coronal (Fe xvi and Mg ix) emission lines, where the
enhanced velocities coincide with the locations of coronal dimming. An
“EIT wave” accompanies the disk event, and a dimming region behind
the wave shows strong blue-shifted Doppler signatures of ≈ 100 km
s<SUP>-1</SUP> in the O v transition region line. These results provide
strong evidence that material from the dimming regions feeds into
the CMEs. This work was supported by NASA's SR&T and GI Programs,
and by PPARC.
---------------------------------------------------------
Title: SXT and EIT Observations of A Quiet Region Large-Scale
Eruption: Implications for Eruption Theories
Authors: Sterling, A. C.; Moore, R. L.; Thompson, B. J.
2002mwoc.conf..165S Altcode:
We present Yohkoh/SXT and SOHO/EIT observations of a set of slow, large
scale, quiet-region solar eruptions. In SXT data, these events seem to
appear “out of nothing,” indicating that they are associated initially
with weak magnetic fields and corresponding low heating rates. These
events evolve relatively slowly, affording us an opportunity to
examine in detail their development. We look for signatures of the
start of the eruptions through intensity variations, physical motions,
and dimming signatures in the SXT and EIT data. In particular, we look
to see whether the earliest signatures are brightenings occurring in
the “core” region (i.e., the location where the magnetic shear is
strongest and the post-flare loops develop); such early brightenings in
the core could be indicative of a “tether-cutting” process, whereby
the eruption is instigated by magnetic reconnection among highly-sheared
core fields. In our best-observed case, we find motions of the core
fields beginning well before brightenings in the core. This is new
evidence that tether-cutting is not the primary mechanism operating
in solar eruptions. Rather, our observations are more consistent with
the eruption process known as the “breakout model” (Antiochos et
al. 1999), which holds that the eruption results from initial slow
magnetic reconnections occurring high above (far from) the core region.
---------------------------------------------------------
Title: Contagious Coronal Heating from Recurring Emergence of
Magnetic Flux
Authors: Moore, R. L.; Falconer, D. A.; Sterling, A. C.
2002mwoc.conf...39M Altcode:
For each of six old bipolar active regions, we present and interpret
Yohkoh/SXT and SOHO/MDI observations of the development, over several
days, of enhanced coronal heating in and around the old bipole in
response to new magnetic flux emergence within the old bipole. The
observations show: 1. In each active region, new flux emerges in the
equatorward side of the old bipole, around a lone remaining leading
sunspot and/or on the equatorward end of the neutral line of the old
bipole. 2. The emerging field is marked by intense internal coronal
heating, and enhanced coronal heating occurs in extended loops stemming
from the emergence site. 3. In five of the six cases, a "rooster tail"
of coronal loops in the poleward extent of the old bipole also brightens
in response to the flux emergence. 4. There are episodes of enhanced
coronal heating in surrounding magnetic fields that are contiguous
with the old bipole but are not directly connected to the emerging
field. From these observations, we suggest that the accommodation
of localized newly emerged flux within an old active region entails
far reaching adjustments in the 3D magnetic field throughout the
active region and in surrounding fields in which the active region is
embedded, and that these adjustments produce the extensive enhanced
coronal heating. We Also Note That The Reason For The recurrence
of flux emergence in old active regions may be that active-region
flux tends to emerge in giant-cell convection downflows. If so, the
poleward "rooster tail" is a coronal flag of a long-lasting downflow
in the convection zone. This work was funded by NASA's Office of Space
Science through the Solar Physics Supporting Research and Technology
Program and the Sun-Earth Connection Guest Investigator Program.
---------------------------------------------------------
Title: Hα Proxies for EIT Crinkles: Further Evidence for Preflare
“Breakout”-Type Activity in an Ejective Solar Eruption
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Qiu, Jiong; Wang,
Haimin
2001ApJ...561.1116S Altcode:
We present Hα observations from Big Bear Solar Observatory of an
eruptive flare in NOAA Active Region 8210, occurring near 22:30 UT
on 1998 May 1. Previously, using the EUV Imaging Telescope (EIT)
on the SOHO spacecraft, we found that a pattern of transient,
localized brightenings, which we call “EIT crinkles,” appears in
the neighborhood of the eruption near the time of flare onset. These
EIT crinkles occur at a location in the active region well separated
from the sheared core magnetic fields, which is where the most intense
features of the eruption are concentrated. We also previously found
that high-cadence images from the Soft X-ray Telescope (SXT) on
Yohkoh indicate that soft X-ray intensity enhancements in the core
begin after the start of the EIT crinkles. With the Hα data, we find
remote flare brightening counterparts to the EIT crinkles. Light curves
as functions of time of various areas of the active region show that
several of the remote flare brightenings undergo intensity increases
prior to the onset of principal brightenings in the core region,
consistent with our earlier findings from EIT and SXT data. These timing
relationships are consistent with the eruption onset mechanism known
as the breakout model, introduced by Antiochos and colleagues, which
proposes that eruptions begin with reconnection at a magnetic null high
above the core region. Our observations are also consistent with other
proposed mechanisms that do not involve early reconnection in the core
region. As a corollary, our observations are not consistent with the
so-called tether-cutting models, which say that the eruption begins with
reconnection in the core. The Hα data further show that a filament in
the core region becomes activated near the time of EIT crinkle onset,
but little if any of the filament actually erupts, despite the presence
of a halo coronal mass ejection (CME) associated with this event.
---------------------------------------------------------
Title: Material Outflows from Coronal Intensity “Dimming Regions”
during Coronal Mass Ejection Onset
Authors: Harra, Louise K.; Sterling, Alphonse C.
2001ApJ...561L.215H Altcode:
One signature of expulsion of coronal mass ejections (CMEs) from the
solar corona is the appearance of transient intensity dimmings in
coronal images. These dimmings have generally been assumed to be due
to discharge of CME material from the corona, and thus the “dimming
regions” are thought of as an important signature of the sources of
CMEs. We present spectral observations of two dimming regions at the
time of expulsion of CMEs, using the Coronal Diagnostic Spectrometer
(CDS) on the SOHO satellite. One of the dimming regions is at the
solar limb and associated with a CME traveling in the plane of the
sky, while the other region is on the solar disk and associated with
an Earth-directed “halo” CME. From the limb event, we see Doppler
signatures of ~30 km s<SUP>-1</SUP> in coronal (Fe XVI and Mg IX)
emission lines, where the enhanced velocities coincide with the
locations of coronal dimming. This provides direct evidence that the
dimmings are associated with outflowing material. We also see larger
(~100 km s<SUP>-1</SUP>) Doppler velocities in transition region (O V
and He I) emission lines, which are likely to be associated with motions
of a prominence and loops at transition region temperatures. An “EIT
wave” accompanies the disk event, and a dimming region behind the wave
shows strong blueshifted Doppler signatures of ~100 km s<SUP>-1</SUP>
in O V, suggesting that material from the dimming regions behind the
wave may be feeding the CME.
---------------------------------------------------------
Title: EIT and SXT Observations of a Quiet-Region Filament Ejection:
First Eruption, Then Reconnection
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Thompson, Barbara J.
2001ApJ...561L.219S Altcode:
We observe a slow-onset quiet-region filament eruption with the EUV
Imaging Telescope (EIT) on the Solar Heliospheric Observatory (SOHO)
and the soft X-ray telescope (SXT) on Yohkoh. This event occurred on
1999 April 18 and was likely the origin of a coronal mass ejection
detected by SOHO at 08:30 UT on that day. In the EIT observation,
one-half of the filament shows two stages of evolution: stage 1 is a
slow, roughly constant upward movement at ~1 km s<SUP>-1</SUP> lasting
~6.5 hr, and stage 2 is a rapid upward eruption at ~16 km s<SUP>-1</SUP>
occurring just before the filament disappears into interplanetary
space. The other half of the filament shows little motion along the
line of sight during the time of stage 1 but erupts along with the rest
of the filament during stage 2. There is no obvious emission from the
filament in the SXT observation until stage 2; at that time, an arcade
of EUV and soft X-ray loops forms first at the central location of the
filament and then expands outward along the length of the filament
channel. A plot of EUV intensity versus time of the central portion
of the filament (where the postflare loops initially form) shows a
flat profile during stage 1 and a rapid upturn after the start of
stage 2. This light curve is delayed from what would be expected if
“tether-cutting” reconnection in the core of the erupting region
were responsible for the initiation of the eruption. Rather, these
observations suggest that a loss of stability of the magnetic field
holding the filament initiates the eruption, with reconnection in the
core region occurring only as a by-product.
---------------------------------------------------------
Title: Internal and external reconnection in a series of homologous
solar flares
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2001JGR...10625227S Altcode:
Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO
and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of
morphologically homologous solar flares occurring in National Oceanic
and Atmospheric Administration (NOAA) active region 8210 over May 1-2,
1998. An emerging flux region (EFR) impacted against a sunspot to
the west and next to a coronal hole to the east is the source of the
repeated flaring. An SXT sigmoid parallels the EFR's neutral line at
the site of the initial flaring in soft X rays. In EIT each flaring
episode begins with the formation of a crinkle pattern external to
the EFR. These EIT crinkles move out from, and then in toward, the
EFR with velocities ~20 km s<SUP>-1</SUP>. A shrinking and expansion
of the width of the coronal hole coincides with the crinkle activity,
and generation and evolution of a postflare loop system begins near the
time of crinkle formation. Using a schematic based on magnetograms of
the region, we suggest that these observations are consistent with the
standard reconnection-based model for solar eruptions but are modified
by the presence of the additional magnetic fields of the sunspot
and coronal hole. In the schematic, internal reconnection begins
inside of the EFR-associated fields, unleashing a flare postflare
loops, and a coronal mass ejection (CME). External reconnection,
first occurring between the escaping CME and the coronal hole field
and second occurring between fields formed as a result of the first
external reconnection, results in the EIT crinkles and changes in the
coronal hole boundary. By the end of the second external reconnection,
the initial setup is reinstated; thus the sequence can repeat, resulting
in morphologically homologous eruptions. Our inferred magnetic topology
is similar to that suggested in the “breakout model” of eruptions
[Antiochos, 1998], although we cannot determine if our eruptions are
released primarily by the breakout mechanism (external reconnection)
or, alternatively, primarily by the internal reconnection.
---------------------------------------------------------
Title: EIT Crinkles as Evidence for the Breakout Model of Solar
Eruptions
Authors: Sterling, Alphonse C.; Moore, Ronald L.
2001ApJ...560.1045S Altcode:
We present observations of two homologous flares in NOAA Active Region
8210 occurring on 1998 May 1 and 2, using EUV data from the EUV Imaging
Telescope (EIT) on board the Solar and Heliospheric Observatory,
high-resolution and high-time cadence images from the soft X-ray
telescope on Yohkoh, images or fluxes from the hard X-ray telescope
on Yohkoh and the BATSE experiment on board the Compton Gamma Ray
Observatory, and Ca XIX soft X-ray spectra from the Bragg crystal
spectrometer (BCS) on Yohkoh. Magnetograms indicate that the flares
occurred in a complex magnetic topology, consisting of an emerging flux
region (EFR) sandwiched between a sunspot to the west and a coronal
hole to the east. In an earlier study we found that in EIT images,
both flaring episodes showed the formation of a crinkle-like pattern
of emission (“EIT crinkles”) occurring in the coronal hole vicinity,
well away from a central “core field” area near the EFR-sunspot
boundary. With our expanded data set, here we find that most of the
energetic activity occurs in the core region in both events, with some
portions of the core brightening shortly after the onset of the EIT
crinkles, and other regions of the core brightening several minutes
later, coincident with a burst of hard X-rays there are no obvious core
brightenings prior to the onset of the EIT crinkles. These timings are
consistent with the “breakout model” of solar eruptions, whereby the
emerging flux is initially constrained by a system of overlying magnetic
field lines, and is able to erupt only after an opening develops in
the overlying fields as a consequence of magnetic reconnection at a
magnetic null point. In our case, the EIT crinkles would be a signature
of this pre-impulsive phase magnetic reconnection, and brightening of
the core only occurs after the core fields begin to escape through the
newly created opening in the overlying fields. Morphology in soft X-ray
images and properties in hard X-rays differ between the two events,
with complexities that preclude a simple determination of the dynamics
in the core at the times of eruption. From the BCS spectra, we find
that the core region expends energy at a rate of ~10<SUP>26</SUP> ergs
s<SUP>-1</SUP> during the time of the growth of the EIT crinkles; this
rate is an upper limit to energy expended in the reconnections opening
the overlying fields. Energy losses occur at an order of magnitude
higher rate near the time of the peak of the events. There is little
evidence of asymmetry in the spectra, consistent with the majority of
the mass flows occurring normal to the line of sight. Both events have
similar electron temperature dependencies on time.
---------------------------------------------------------
Title: Velocity observations of an active region during the onset
phase of a coronal mass ejection
Authors: Harra, Louise K.; Sterling, Alphonse C.
2001ESASP.493..237H Altcode: 2001sefs.work..237H
No abstract at ADS
---------------------------------------------------------
Title: Energetics of an Active Region Observed from Helium-Like
Sulphur Lines
Authors: Watanabe, Tetsuya; Sterling, Alphonse C.; Hudson, Hugh S.;
Harra, Louise K.
2001SoPh..201...71W Altcode:
We report temperature diagnostics derived from helium-like ions of
sulphur for an active region NOAA 7978 obtained with Bragg Crystal
Spectrometer (BCS) on board the Yohkoh satellite. For the same
region we estimate conductive flux downward to the chromosphere by
the Coronal Diagnostic Spectrometer (CDS) on board the Solar and
Heliospheric Observatory (SOHO) satellite. This region appeared as a
region of soft X-ray enhancement in May 1996, underwent a period of
enhanced activity coinciding with flux emergence between 6 July and
12 July, and then continued to exist in a nearly flareless state for
several solar rotations until November 1996. Energy balance of the
non-flaring active region is basically consistent with a model of
an arcade of coronal loops having an average loop-top temperature of
4×10<SUP>6</SUP> K. Energy from flare activity during a period of flux
emergence is comparable to the energy requirements of the non-flaring
active region. However, the non-flaring energy is roughly constant
for the subsequent solar rotations following the birth of the active
region even after the flare activity essentially subsided. Energy
partition between flare activity and steady active-region heating
thus varies significantly over the lifetime of the active region,
and active-region emission cannot always be identified with flaring.
---------------------------------------------------------
Title: Onset of the Magnetic Explosion in Solar Flares and Coronal
Mass Ejections
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Hudson, Hugh S.;
Lemen, James R.
2001ApJ...552..833M Altcode:
We present observations of the magnetic field configuration and its
transformation in six solar eruptive events that show good agreement
with the standard bipolar model for eruptive flares. The observations
are X-ray images from the Yohkoh soft X-ray telescope (SXT) and
magnetograms from Kitt Peak National Solar Observatory, interpreted
together with the 1-8 Å X-ray flux observed by GOES. The observations
yield the following interpretation. (1) Each event is a magnetic
explosion that occurs in an initially closed single bipole in which the
core field is sheared and twisted in the shape of a sigmoid, having an
oppositely curved elbow on each end. The arms of the opposite elbows are
sheared past each other so that they overlap and are crossed low above
the neutral line in the middle of the bipole. The elbows and arms seen
in the SXT images are illuminated strands of the sigmoidal core field,
which is a continuum of sheared/twisted field that fills these strands
as well as the space between and around them. (2) Although four of
the explosions are ejective (appearing to blow open the bipole) and
two are confined (appearing to be arrested within the closed bipole),
all six begin the same way. In the SXT images, the explosion begins
with brightening and expansion of the two elbows together with the
appearance of short bright sheared loops low over the neutral line
under the crossed arms and, rising up from the crossed arms, long
strands connecting the far ends of the elbows. (3) All six events are
single-bipole events in that during the onset and early development
of the explosion they show no evidence for reconnection between the
exploding bipole and any surrounding magnetic fields. We conclude that
in each of our events the magnetic explosion was unleashed by runaway
tether-cutting via implosive/explosive reconnection in the middle of the
sigmoid, as in the standard model. The similarity of the onsets of the
two confined explosions to the onsets of the four ejective explosions
and their agreement with the model indicate that runaway reconnection
inside a sheared core field can begin whether or not a separate system
of overlying fields, or the structure of the bipole itself, allows the
explosion to be ejective. Because this internal reconnection apparently
begins at the very start of the sigmoid eruption and grows in step
with the explosion, we infer that this reconnection is essential for
the onset and growth of the magnetic explosion in eruptive flares and
coronal mass ejections.
---------------------------------------------------------
Title: EIT Crinkles as Evidence for the Breakout Model of Solar
Eruptions
Authors: Sterling, A. C.; Moore, R. L.
2001AGUSM..SH51B02S Altcode:
Ejective solar eruptions generally involve: (i) a strong magnetic
field “core” region, which envelops a magnetic inversion line and
is the site of the earliest post-flare loop footpoints, and (ii)
weaker magnetic fields surrounding the core. Determining whether the
eruption begins in the core or in the surrounding fields is vital
to understanding the eruption process. Here we discuss observational
tests of two different models with opposing views on where the eruption
begins. The “tether-cutting model” suggests that magnetic reconnection
among fields in the core is the primary cause of the eruption; in this
case, we expect the earliest signature of the start of the eruption to
be brightenings inside the core. In contrast, the “breakout model”
(Antiochos et al.~1999, ApJ, 510, 485) suggests that the eruption
begins when overlying coronal fields are eroded away by low-energy
reconnection far from the core; in this case, we would expect initial
brightenings at sites remote from the core. To test these ideas, we
examine relative timings of brightenings inside and outside the core
region of a series of homologous flares in NOAA AR~8210 over 1998
May 1-2. As we previously reported (Sterling and Moore 2001, JGR, in
press), these events displayed a crinkle-like pattern of emission in
EIT 195 images (“EIT crinkles”) near the time of the eruptions, at
locations remote from the core. We examine the onset of these remote
brightenings relative to the core brightenings, observing the core
using EIT data and high-cadence ( ~ 10~s), high resolution (2.5”
pixels) data from the Soft X-ray Telescope (SXT) on Yohkoh. We find
that the EIT crinkles precede the core brightenings by several minutes,
which is consistent with the breakout model, but inconsistent with
the tether-cutting model. ACS is an NRC---MSFC Research Associate.
---------------------------------------------------------
Title: Sigmoid CME source regions at the Sun: some recent results
Authors: Sterling, A. C.
2000JASTP..62.1427S Altcode: 2000JATP...62.1427S
Identifying coronal mass ejection (CME) precursors in the solar corona
would be an important step in space weather forecasting, as well as
a vital key to understanding the physics of CMEs. Twisted magnetic
field structures are suspected of being the source of at least some
CMEs. These features can appear sigmoid (S or inverse-S) shaped
in soft X-ray (SXR) images. We review recent observations of these
structures and their relation to CMEs, using SXR data from the Soft
X-ray Telescope (SXT) on the Yohkoh satellite, and EUV data from the
EUV Imaging Telescope (EIT) on the SOHOsatellite. These observations
indicate that the pre-eruption sigmoid patterns are more prominent
in SXRs than in EUV, and that sigmoid precursors are present in over
50% of CMEs. These findings are important for CME research, and may
potentially be a major component to space weather forecasting. So far,
however, the studies have been subject to restrictions that will have
to be relaxed before sigmoid morphology can be used as a reliable
predictive tool. Moreover, some CMEs do not display a SXR sigmoid
structure prior to eruption, and some others show no prominent SXR
signature of any kind before or during eruption.
---------------------------------------------------------
Title: Solar Spicules: A Review of Recent Models and Targets for
Future Observations - (Invited Review)
Authors: Sterling, Alphonse C.
2000SoPh..196...79S Altcode:
Since their discovery over 100 years ago, there have been many
suggestions for the origin and development of solar spicules. Because
the velocities of spicules are comparable to the sound and Alfvén
speeds of the low chromosphere, linear theory cannot fully describe
them. Consequently, detailed tests of theoretical ideas had to await
the development of computing power that only became available during
the 1970s. This work reviews theories for spicules and spicule-like
features over approximately the past 25 years, with an emphasis on
the models based on nonlinear numerical simulations. These models have
given us physical insight into wave propagation in the solar atmosphere,
and have helped elucidate how such waves, and associated shock waves,
may be capable of creating motions and structures on magnetic flux tubes
in the lower solar atmosphere. So far, however, it has been difficult to
reproduce the most-commonly-quoted parameters for spicules with these
models, using what appears to be the most suitable input parameters. A
key impediment to developing satisfactory models has been the lack of
reliable observational information, which is a consequence of the small
angular size and transient lifetime of spicules. I close with a list of
key observational questions to be addressed with space-based satellites,
such as the currently operating TRACE satellite, and especially the
upcoming Solar-B mission. Answers to these questions will help determine
which, if any, of the current models correctly explains spicules.
---------------------------------------------------------
Title: Internal and External Reconnection in a Series of Homologous
Solar Flares
Authors: Sterling, A. C.; Moore, R. L.
2000SPD....31.1405S Altcode: 2000BAAS...32..847S
Using data from the Extreme Ultraviolet Telescope (EIT) on SOHO and
the Soft X-ray Telescope (SXT) on Yohkoh, we examine a series of
morphologically homologous solar flares occurring in NOAA AR 8210
over May 1---2, 1998. An emerging flux region (EFR) impacted against
a sunspot to the west and next to a coronal hole to the east is the
source of the repeated flaring. An SXT sigmoid traces the EFR's neutral
line at the site of the initial flaring in soft X-rays. In EIT, each
flaring episode begins with the formation of a crinkle pattern external
to the EFR\@. These EIT crinkles move out from, and then in toward, the
EFR with velocities ~ 20 km s<SUP>-1</SUP>. A shrinking and expansion
of the width of the coronal hole coincides with the crinkle activity,
and generation and evolution of a postflare loop system begins near the
time of crinkle formation. Using a schematic based on magnetograms of
the region, we suggest that these observations are consistent with the
standard reconnection-based model for solar eruptions, but modified
by the presence of the additional magnetic fields of the sunspot and
coronal hole. In the schematic, internal reconnection begins inside of
the EFR-associated fields, unleashing a flare, postflare loops, and a
CME\@. External reconnection, occurring between the escaping CME and
the surrounding fields, results in the EIT crinkles and changes in the
coronal hole boundary. Our inferred magnetic topology is similar to that
suggested in the ` ` breakout model" of eruptions [Antiochos, 1998],
although we cannot determine if the ultimate source of the eruptions
in this case is due to the breakout mechanism or, alternatively, is
primarily released by the internal reconnection. ACS is an NRC---MSFC
Research Associate
---------------------------------------------------------
Title: Yohkoh SXT and SOHO EIT Observations of Sigmoid-to-Arcade
Evolution of Structures Associated with Halo Coronal Mass Ejections
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Thompson, Barbara J.;
Zarro, Dominic M.
2000ApJ...532..628S Altcode:
A subset of the solar-disk counterparts to halo coronal mass ejections
(CMEs) displays an evolution in soft X-rays (SXR) that is characterized
by a preflare S-shaped structure, dubbed a “sigmoid,” which evolves
into a postflare cusp or arcade. We examine the morphological properties
of the evolution of sigmoids into cusps and arcades for four such
regions associated with SXR flares, using the Soft X-Ray Telescope
(SXT) on the Yohkoh satellite and the EUV Imaging Telescope (EIT) on
the Solar and Heliospheric Observatory (SOHO) satellite. Most of our
EIT observations are with the 1.5 MK 195 Å Fe XII channel. At most,
there is only a weak counterpart to the SXR sigmoid in the preflare 195
Å EUV images, indicating that the preflare sigmoid has a temperature
greater than 1.5 MK. While more identifiable than in the 195 Å channel,
a clear preflare sigmoid is also not observed in the 2.0 MK EIT 284 Å
Fe XV channel. During the time of the flare, however, an EUV sigmoid
brightens near the location of the SXR preflare sigmoid. Initially
the SXR sigmoid lies along a magnetic neutral line. As the SXR flare
progresses, new field lines appear with orientation normal to the
neutral line and with footpoints rooted in regions of opposite polarity;
these footpoints are different from those of the preflare sigmoid. The
cusp structures in SXRs develop from these newly ignited field lines. In
EIT images, the EUV sigmoid broadens as the flare progresses, forming
an arcade beneath the SXR cusp. Our findings are consistent with a
standard picture in which the origin of the flare and CME is caused by
the eruption of a filament-like feature, with the stretching of field
lines producing a cusp. We infer that the cusp-producing fields may
be overlying the sigmoid fields in the preflare phase, but we do not
directly observe such preflare overlying fields.
---------------------------------------------------------
Title: Variation of Thermal Structure with Height of a Solar Active
Region Derived from SOHO CDS and YOHKOH BCS Observations
Authors: Sterling, Alphonse C.; Pike, C. D.; Mason, Helen E.; Watanabe,
Tetsuya; Antiochos, Spiro K.
1999ApJ...524.1096S Altcode:
We present observations of NOAA solar Active Region 7999 when it was
near the west solar limb on 1996 December 2 and 3, using data from
the Coronal Diagnostic Spectrometer (CDS) experiment on the SOHO
satellite. Ratios of intensities of 2 MK material (as observed in
CDS Fe XVI images) to 1 MK material (from CDS Mg IX images) indicate
that there is a drop in the ratio of the hotter to the cooler material
with height in the region, up to an altitude of about 10<SUP>5</SUP>
km. At low altitudes the relative amount of 2 MK emission measure to
1 MK emission measure ranges from 8 to 10, while the ratio is minimum
near 10<SUP>5</SUP> km, ranging from 1.3 to 3.5. The decrease with
height of the CDS ratio qualitatively resembles the decrease in S
XV election temperature with height (measurable up to ~85,000 km) in
the same active region obtained from the Bragg crystal spectrometer
instrument on Yohkoh. The CDS images indicate that the highest S
XV temperatures and largest CDS ratios correspond to regions of
microflares, and somewhat lower S XV temperatures and CDS ratios
correspond to diffuse regions. Above 10<SUP>5</SUP> km, the trend of
the CDS ratios changes, either increasing or remaining approximately
constant with height. At these altitudes the CDS images show faint,
large-scale diffuse structures.
---------------------------------------------------------
Title: SOHO EIT Observations of Extreme-Ultraviolet “Dimming”
Associated with a Halo Coronal Mass Ejection
Authors: Zarro, Dominic M.; Sterling, Alphonse C.; Thompson, Barbara
J.; Hudson, Hugh S.; Nitta, Nariaki
1999ApJ...520L.139Z Altcode:
A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope
(SXT) on Yohkoh. The flare was associated with a “halo” coronal
mass ejection (CME). The flaring region showed areas of reduced soft
X-ray (SXR) brightness--“dimmings”--that developed prior to the CME
observed in white light and persisted for several hours following the
CME. The most prominent dimming regions were located near the ends of
a preflare SXR S-shaped (sigmoid) feature that disappeared during the
event, leaving behind a postflare SXR arcade and cusp structure. Based
upon these and similar soft X-ray observations, it has been postulated
that SXR dimming regions are the coronal signatures (i.e., remnants)
of magnetic flux ropes ejected during CMEs. This Letter reports
new observations of coronal dimming at extreme-ultraviolet (EUV)
wavelengths obtained with the Extreme-ultraviolet Imaging Telescope
(EIT) on the Solar and Heliospheric Observatory (SOHO). A series of
EIT observations in the 195 Å Fe XII wavelength band were obtained
simultaneously with SXT during the 1997 April 7 flare/CME. The EIT
observations show that regions of reduced EUV intensity developed at
the same locations and at the same time as SXR dimming features. The
decrease in EUV intensity (averaged over each dimming region) occurred
simultaneously with an increase in EUV emission from flaring loops in
the active region. We interpret these joint observations within the
framework of flux-rope eruption as the cause of EUV and SXR coronal
dimmings, and as the source of at least part of the CME.
---------------------------------------------------------
Title: Electron temperatures of a late-phase solar active region
from it YOHKOH BCS and SXT observations
Authors: Sterling, Alphonse C.
1999A&A...346..995S Altcode:
We deduce electron temperatures in a 2-3 month old active region from
1996 September and October, using soft X-ray S Xv spectra from the Bragg
Crystal Spectrometer (BCS) and images from the Soft X-ray Telescope
(SXT), both on board the Yohkoh satellite. Our observations cover a
full transit of the region, from before its appearance around the east
limb until after it disappeared around the west limb. Over most of this
transit the region is diffuse and extremely quiescent, with few strong
X-ray intensity enhancements (microflares) seen in plots of the GOES
flux. During the passage the region's temperature is roughly constant
at 2.5+/-0.2 MK in S Xv and at 1.9+/-0.1 MK from SXT, with emission
measures of about 10(48) cm(-3) for both instruments. Temperatures
obtained from SXT are consistently lower then the S Xv values,
indicating a multithermal plasma. A high-temperature (>~ 5 MK)
component, seen in younger active regions, is virtually absent in this
mature active region. Our findings, combined with earlier work, provide
a method for estimating S Xv temperatures of structures based on their
intensity in SXT, even when these structures are not isolated on the Sun
and hence not directly resolvable with the full-Sun BCS instrument. Our
work also suggests that old active regions form a fundamental component
of the quiet-Sun corona during periods of high solar activity.
---------------------------------------------------------
Title: YOHKOH SXT and SOHO EIT Observations of “Sigmoid-to-Arcade”
Evolution of Structures Associated with Halo CMEs
Authors: Sterling, A. C.; Hudson, H. S.; Thompson, B. J.; Zarro, D. M.
1999AAS...19410107S Altcode: 1999BAAS...31..999S
A subset of the solar-disk counterparts to halo coronal mass ejections
(CMEs) display an evolution in soft X-rays (SXR) characterized by a
preflare “S”-shaped structure, dubbed a “sigmoid,” evolving into
a postflare cusp or arcade. We examine the morphological properties
of the evolution of sigmoids into cusps and arcades for four such
regions associated with SXR flares, using the Soft X-ray Telescope
(SXT) on Yohkoh and the 195 Angstroms Fe xii\ channel of the EUV Imaging
Telescope (EIT) on SOHO. There is, at most, only a weak counterpart to
the SXR sigmoid in the preflare EUV images, indicating that the preflare
sigmoid has a temperature >1.5 MK\@. During the time of the flare
itself, however, an EUV sigmoid brightens near the location of the
SXR preflare sigmoid. Initially the SXR sigmoid lies along a magnetic
neutral line. As the SXR flare progresses new field lines appear with
orientation normal to the neutral line and with footpoints rooted in
opposite polarity regions; these footpoints are different from those of
the preflare sigmoid. The cusp structures in SXRs develop from these
newly-ignited field lines. In EIT images the EUV sigmoid broadens out
as the flare progresses, forming an arcade which resides beneath the
SXR cusp. In many respects, our findings are consistent with a standard
picture where the origin of the flare and CME is due to the eruption
of a filament-like feature, and the stretching of overlying preflare
fields produces the cusp. We do not, however, observe these preflare
overlying fields prior to flare onset. This work was supported by the
NRL Naval basic research program and NASA.
---------------------------------------------------------
Title: Alfvénic Resonances on Ultraviolet Spicules
Authors: Sterling, Alphonse C.
1998ApJ...508..916S Altcode:
We consider the propagation of small-amplitude torsional Alfvén waves
on spicule-like structures seen at UV and EUV wavelengths. We assume
that such UV spicules have densities an order of magnitude lower than
chromospheric spicules. Extending the earlier analysis of Sterling &
Hollweg, we find that UV spicules can act as resonance cavities, whereby
Alfvén waves of preferred frequencies have strong transmission into the
structures. The resonance cavity forms because of the sharp changes in
Alfvén velocity between the photosphere/chromosphere and the UV spicule
at the UV spicule's base and between the UV spicule and the corona at
the top of the UV spicule. For a canonical UV spicule residing on a
magnetic flux tube of strength B<SUB>0</SUB> = 40 G with length L =
10,000 km and density ρ = 1.0 × 10<SUP>-14</SUP> g cm<SUP>-3</SUP>,
we predict a fundamental resonance period of about 35 s, some 3 times
shorter than for a corresponding chromospheric spicule. Velocities
along the length of the UV spicule vary from about 30 to 150 km
s<SUP>-1</SUP>, increasing with height along the structure. Longer UV
spicules have longer resonance periods and lower rotational velocities,
and stronger magnetic fields result in shorter resonance periods and
higher velocities. The same qualitative parameter dependencies also
hold for chromospheric spicules. Damping flattens out the velocity
amplitude's profile along the structure and reduces the maximum velocity
but does not appreciably change the periods of the resonances.
---------------------------------------------------------
Title: X-ray coronal changes during Halo CMEs
Authors: Hudson, H. S.; Lemen, J. R.; St. Cyr, O. C.; Sterling, A. C.;
Webb, D. F.
1998GeoRL..25.2481H Altcode:
Using the Yohkoh soft X-ray images, we examine the coronal structures
associated with “halo” coronal mass ejections (CMEs). These may
correspond to events near solar disk center. Starting with a list
of eleven confirmed halo CMEs over the time range from December 1996
through May 1997, we find seven with surface features identifiable in
soft X-rays, with GOES classifications ranging from A1 to M1.3. These
have a characteristic pattern of sigmoid → arcade development. In each
of these events, the pre-flare structure disrupted during the flare,
leaving the appearance of compact transient coronal holes. The four
remaining events had weak or indistinguishable signatures in the X-ray
images. For the events for which we could see well-defined coronal
changes, we confirm our previous result that the estimated mass loss
inferred from the soft X-ray dimming is a small fraction of typical
CME masses [Sterling & Hudson 1997].
---------------------------------------------------------
Title: S XV Spectral Properties of an Active Region from the YOHKOH
Bragg Crystal Spectrometer
Authors: Sterling, A. C.
1998ASSL..229..245S Altcode: 1998opaf.conf..245S
No abstract at ADS
---------------------------------------------------------
Title: Numerical simulations of solar spicules
Authors: Sterling, A.
1998ESASP.421...35S Altcode: 1998sjcp.conf...35S
No abstract at ADS
---------------------------------------------------------
Title: NOAA 7978: the Last best Old-Cycle Region
Authors: Hudson, H. S.; Labonte, B. J.; Sterling, A. C.; Watanabe, Te.
1998ASSL..229..237H Altcode: 1998opaf.conf..237H
No abstract at ADS
---------------------------------------------------------
Title: Yohkoh SXT Observations of X-Ray “Dimming” Associated with
a Halo Coronal Mass Ejection
Authors: Sterling, Alphonse C.; Hudson, Hugh S.
1997ApJ...491L..55S Altcode:
A sudden depletion or intensity “dimming” of the X-ray corona
sometimes accompanies a solar eruptive flare or coronal mass ejection
(CME). We have identified a dimming that occurred just prior to a
“halo” CME, observed on 1997 April 7 using the Soft X-ray Telescope
(SXT) on Yohkoh. Halo CMEs are prime candidates for “space weather”
effects. The dimming occurred in compact regions near a flare of
14 UT on April 7, over a projected area of about 10<SUP>20</SUP>
cm<SUP>-2</SUP>, and indicate that a mass of a few times 10<SUP>14</SUP>
g was ejected. This is a lower limit imposed by the obscuration
of the dimming volume by the brightness of the accompanying flare
and other factors. Most of the mass deficit comes from two regions
close to the ends of a preflare S-shaped active-region structure,
and the resulting dimmings in these regions persisted for more than
three days following the flare. A cusp-shaped loop--not apparent
prior to the flare--dominates the emission in the flare decay phase,
and has a mass comparable to that lost in the dimming regions. Our
findings are consistent with the source of the CME being a flux rope
that erupted, leaving behind the dimming regions. The cusp-shaped loop
probably represents magnetic fields reconfigured or reconnected by the
eruption. We do not see an X-ray analog of the wavelike disturbance
evident in SOHO EUV images.
---------------------------------------------------------
Title: X-ray spectral observations of a solar active region corona
Authors: Sterling, Alphonse C.
1997GeoRL..24.2263S Altcode:
We study the X-ray flux and electron temperature variation of the corona
above a solar active region. Electron temperatures are determined using
data from the S xv channel of the Bragg crystal spectrometer (BCS)
instrument on board the Yohkoh satellite. The active region, designated
NOAA AR 7999, rotated from just inside the west solar limb to beyond
the limb over the period December 2-4, 1996, allowing us to map the
electron temperature as a function of height in the active region's
corona. Consistent with previous findings, we find two components to
the active region coronal temperature, with a hotter (T<SUB>e</SUB>
≳5.0 MK) component due to transient flares and microflares, and a
cooler component present in between the times of the microflares. There
is a steady decrease in the frequency of occurrence of flares and
microflares as the occultation progresses, implying that the flaring
structures are low lying. For the cool component, the average electron
temperature is about 4.5 MK when the region is just inside the limb,
and gradually decreases to under 3.0 MK as the region rotates around
the limb, indicating that temperature decreases with height.
---------------------------------------------------------
Title: Electron Temperatures of the Corona Above a Solar Active
Region Determined from S XV Spectra
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Watanabe, Tetsuya
1997SPD....28.0136S Altcode: 1997BAAS...29..885S
We present high resolution soft X-ray spectral observations of the
corona above an active region, using data from the Bragg crystal
spectrometer (BCS) on board the Yohkoh satellite. We observed NOAA AR
7978 as it rotated beyond the solar limb so that the lower portions of
the region were occulted. Long integrations from times after the region
had totally disappeared some days later show a substantial background
in S xv. Since the background spectrum is featureless, spectral lines
obtained from the time of occultation must originate from the upper
corona of the active region. Our results support previous findings that
the corona consists of two components: a cooler, steady component with
T_e ~ 3 MK, and a hotter, transient component in excess of 5 MK. This
hotter component is due to microflares; outside the time of microflares
there is relatively little or no active region upper coronal plasma
with T_e gtrsim 3.5 MK. There is evidence for a decrease in T_e with
height for the cool component.
---------------------------------------------------------
Title: Temporal Variations of Solar Flare Spectral Properties: Hard
X-Ray Fluxes and Fe XXV, Ca XIX, and Wide-Band Soft X-Ray Fluxes,
Temperatures, and Emission Measures
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R.;
Zarro, Dominic A.
1997ApJS..110..115S Altcode:
We present fluxes, temperatures, and emission measures for nine
solar flares, using data from both the Fe XXV and Ca XIX channels
of the Bragg Crystal Spectrometer (BCS) experiment on the Yohkoh
satellite and from the wide-band soft X-ray spectrometers on the GOES
spacecraft. We also present hard X-ray fluxes from the Hard X-ray
Telescope (HXT) on Yohkoh and the BATSE spectrometer on the Compton
Gamma-Ray Observatory (CGRO). All events occurred during 1992 and
ranged in size from GOES class C5 to M2. Three of the events occurred
near the solar limb. For each flare we give two sets of plots. The
first set shows flux, electron temperature, and emission measures
for Fe XXV, Ca XIX, and GOES as functions of time. The second set of
plots gives log electron temperature as functions of log (emission
measure)<SUP>1/2</SUP> for these three wavelength ranges; we refer to
these plots as E<SUP>1/2</SUP>-T diagrams. Hard X-ray flux information
is included in both sets of plots. Our observations indicate that (1)
cooler plasmas are located along the legs of, or are evenly distributed
along, the flaring loops, while hotter plasmas are concentrated near
the loop tops, (2) peaks in temperature in each of the wavelength
bands are closely associated with hard X-ray enhancements, and (3)
the emission from both relatively hot and relatively cool flaring
plasmas emanates from the same loop or from closely related loops.
---------------------------------------------------------
Title: Electron Temperatures of the Corona Above a Solar Active
Region Determined from S XV Spectra
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Watanabe, Tetsuya
1997ApJ...479L.149S Altcode:
We present the first high-resolution soft X-ray spectral observations of
the corona above an active region, using the Bragg crystal spectrometer
(BCS) on board the Yohkoh satellite. We observed NOAA AR 7978 as it
rotated beyond the solar limb so that the lower portions of the region
were occulted. Long integrations from times after the region had totally
disappeared some days later show a substantial, variable background
in S XV. Since the background spectrum is featureless, spectral lines
obtained from the time of occultation must originate from the upper
corona of the active region. Our results support previous findings that
the active region corona consists of two components: a cooler, steady
component with T<SUB>e</SUB> ~ 3 MK and a hotter, transient component
in excess of 5 MK. This hotter component is due to microflares; outside
the time of microflares there is relatively little or no active region
upper coronal plasma with T<SUB>e</SUB> >~ 3.5 MK. There is evidence
for a decrease in T<SUB>e</SUB> with height for the cool component.
---------------------------------------------------------
Title: S XV Spectral Properties of an Active Region from the Yohkoh
Bragg Crystal Spectrometer
Authors: Sterling, Alphonse C.
1997ApJ...478..807S Altcode:
Using the Bragg crystal spectrometer (BCS) on board the Yohkoh
satellite, we examine the spectral properties of a solar active region
from 1996 March 22-24. Because the region, NOAA AR 7953, was the
only one on the Sun over the 3-day period, it was possible to obtain
quality spectra for that region alone despite the BCS being a full-Sun
instrument. We analyzed about 150 S XV spectra with integration times
ranging from about 15 to 3000 s. At least one sub-C-class flare and one
C-class flare were observed during the period. Lower level transient
brightenings occur nearly continuously in the region. We find average
electron temperatures for the nonflaring active region ranging from
5.5 to 6.2 MK, and an average nonthermal velocity of 43.5 +/- 11.8 km
s<SUP>-1</SUP> over the 3 days. Temporal variations of S XV values for
flux and electron temperature, for electron temperature and emission
measure, and for flux and emission measure are all strongly correlated
both when the region is nonflaring and when it is flaring. Correlations
between nonthermal velocity and flux and between nonthermal velocity
and electron temperature are strong when flares are included in the
analysis, but the correlation is weak when spectra from times of flares
are excluded. It is, however, difficult to deconvolve the contribution
of the source distribution to the nonthermal velocity estimate when
flux from the region is low.
---------------------------------------------------------
Title: Isolating the Footpoint Characteristics of a Solar Flare Loop
Authors: Harra-Murnion, L. K.; Culhane, J. L.; Hudson, H. S.; Fujiwara,
T.; Kato, T.; Sterling*, A. C.
1997SoPh..171..103H Altcode:
We analyse the physical characteristics of a C5.7 class flare which
was observed on 27 September, 1993 using data from the soft X-ray
telescope (SXT), the Bragg crystal spectrometer (BCS), and the hard
X-ray telescope (HXT) on Yohkoh. The flare takes the form of a simple
loop which is much brighter at one of its footpoints than anywhere
else for a period of 2 min. During this time there is an increase in
the soft X-ray fluxes, and a corresponding peak in hard X-rays. The
parameters derived from the hard X-ray and soft X-ray spectra and images
are assumed to be from the footpoint. This flare showed two peaks in
the non-thermal velocity, the first one simultaneous with the footpoint
brightening. The non-thermal velocity corresponding to these first few
minutes is unusually large - by a factor of 80%, 68%, and 26% relative
to the second peak in the Fexxv, Caxix, and Sxv channels respectively.
---------------------------------------------------------
Title: Active Region Coronal Temperatures from YOHKOH BCS Sxv Spectra
Authors: Sterling, A. C.; Hudson, H. S.; Watanabe, T.
1997IAUJD..19E...9S Altcode:
Using the Bragg crystal spectrometer (BCS) on board the Yohkoh
satellite, we present high resolution soft X-ray spectral observations
of the corona above an active region. We observed NOAA AR 7978 as
it rotated beyond the solar limb so that the lower portions of the
region were occulted. Long integrations from times after the region
had totally disappeared some days later show a substantial background
in Sxv. Since the background spectrum is featureless, spectral lines
obtained from the time of occultation must originate from the upper
corona of the active region. Our results support previous findings
that the active region corona consists of two components: a cooler,
steady component with electron temperature T_e ~3 MK, and a hotter,
transient component in excess of 5 MK @. This hotter component is due
to micro-flares; outside the time of micro-flares there is relatively
little or no active region upper coronal plasma with T_e higher than
about 3.5 MK @. There is evidence for a decrease in T_e with height
for the cool component.
---------------------------------------------------------
Title: Active Region Energetics via Yohkoh/BCS and SOHO/CDS
Authors: Watanabe, T.; Sterling, Alphonse C.; Hudson, Hugh S.;
Harra-Murnion, Louise K.
1997ESASP.404..723W Altcode: 1997cswn.conf..723W
No abstract at ADS
---------------------------------------------------------
Title: YOHKOH Observations of Fe XXVI X-Ray Line Emission from
Solar Flares
Authors: Pike, C. D.; Phillips, K. J. H.; Lang, J.; Sterling, A.;
Watanabe, T.; Hiei, E.; Culhane, J. L.; Cornille, M.; Dubau, J.
1996ApJ...464..487P Altcode:
We report on observations from the Bragg Crystal Spectrometer (B CS)
on board the Japanese solar flare spacecraft Yohkoh showing Fe XXVI
Lyα X-ray line emission at 1.78 Å. Some 75 events over a 2 yr period
between 1991 December 6 and 1993 December 31 have been analyzed. The
greater sensitivity of the BCS compared with previous instruments has
enabled such emission to be detected from a wider group of flares than
has previously been possible. The likelihood of detecting Fe XXVI lines
in a flare is found to increase sharply with the electron temperature
obtained from the Fe XXV line spectrum, also observed by the BCS,
and with GOES X-ray class. The width of the Lyα<SUB>1</SUB>, line,
measured after the impulsive stage, is greater than that determined by
thermal Doppler broadening, but this is explained by the nonzero spatial
extent of flares. Electron temperatures from the intensity ratio of a
nearby feature due to Fe XXV dielectronic satellites and the Fe XXVI
Lyα<SUB>1</SUB> line are obtained from new atomic parameters from
the superstructure code, details of which are described. This revises
earlier calculations that have been extensively used. Comparison
of these temperatures with those from the Fe XXV spectra provides
evidence for a single loose grouping of flares, with the difference
between the two temperatures ranging from nearly zero to about 20 MK. A
"superhot" component would seem to be more or less developed according
to whether the temperature difference is large or nearly zero. Flares
at both extremes are examined in detail. The gradually varying part
of the 14-33 keV X-ray emission for these events, as observed by the
Hard X-ray Telescope on Yohkoh, has a hardness ratio corresponding
to temperatures and emission measures similar to those from Fe XXVI
line ratios, pointing to a common origin for their emission. Many of
the flares studied occurred in particular active regions with great
magnetic complexity, although Fe XXVI flares do not seem to be a
distinct class within large X-ray flares.
---------------------------------------------------------
Title: Solar coronal abundances: Some recent X-ray flare observations
Authors: Sterling, Alphonse C.
1996AIPC..374..343S Altcode: 1996hesp.conf..343S
I review recent elemental abundance studies from X-ray flare spectra
obtained with Bragg crystal spectrometer experiments on board the SMM,
P78-1, and Yohkoh spacecraft. Using the line-to-continuum method, data
from all three satellites indicate an enhancement of the abundance of
low-FIP Ca relative to H. But the average magnitude of the enhancement
is somewhat uncertain. Flare-to-flare variations in the enhancement are
also seen. Fe flare abundances seem to be close to photospheric values,
with differing methods giving somewhat differing values. These findings,
in conjunction with results for S, leave open the possibility that
H may behave as an intermediate-FIP element or that a more complex
characterization may apply. Further studies of the Yohkoh data, and
studies comparing different analysis methods are needed to clarify
these issues.
---------------------------------------------------------
Title: YOHKOH Observations of an Over-the-Limb Solar Flare with
Large Spectral Line Shifts
Authors: Sterling, Alphonse C.; Harra-Murnion, Louise K.; Hudson,
Hugh S.; Lemen, James R.
1996ApJ...464..498S Altcode:
We present observations of a solar flare of 1993 April 15 near 9 UT,
using data from the Yohkoh Bragg crystal spectrometer (BC S) and soft
X-ray telescope (SXT). Observations from SXT indicate that the flare
occurred well beyond the solar limb, meaning that our observations
are restricted to the uppermost portions of the flaring structure. BCS
spectra show strong bulk blueshifts of the spectral line profiles for a
short period near the start of the event, followed by an extended period
of strong bulk redshifts of the line profiles. Concurrent with these
bulk line shifts, the spectra show "blue wing" asymmetries. Both bulk
line shifts and blue wings are infrequent characteristics of flares
observed near the solar limb. Our observations are consistent with
strong upward mass motions occurring on a high-altitude flaring loop
oriented edge-on with the Earth. We find nonthermal line broadenings
in the spectra which are qualitatively and quantitatively similar to
line broadenings in spectra of disk flares. Near peak intensity of the
flare, ≤10% of the residual nonthermal broadening can be explained
by the spatial distribution of the soft X-ray flaring structure.
---------------------------------------------------------
Title: Temporal Variations of Solar Flare Spectral Properties in CA
XIX and GOES
Authors: Sterling, A. C.; Hudson, H. S.; Lemen, J. R.; Zarro, D. A.
1996AAS...188.1905S Altcode: 1996BAAS...28..850S
Since the advent of space borne X-ray observations, there has been
a strong interest in the nature of the X-ray solar flare. Examining
the relationships between radiations produced in different portions
of the X-ray spectrum gives us information on the properties of the
constituent flaring plasmas. We have studied the joint variation of
electron temperatures and emission measures for a number of flares in
two different wavelength ranges, using data from the narrow band Ca xix
channel (near 3.18 Angstroms) of the Bragg crystal spectrometer (BCS)
experiment on board the Yohkoh spacecraft, and data from the wide band
X-ray monitors on the Geostationary Operational Environmental Satellites
(GOES, covering 0.5---8 Angstroms). A power law relationship often
describes the relationship between temperature and emission measure
during the decay phase in both wavelength ranges. According to work of
Sylwester et al. (1993, A&A 267, 586), energy input parameters and
physical properties of the flaring loop(s) determine the slope of this
power law. We find that ratios of Ca xix to GOES slopes generally fall
between .6 and 1.0, when slopes in both channels are measured during the
flare decay in each respective wavelength range. This relatively good
agreement between slopes in the two channels suggests that emissions
in both wavelength ranges originate from either the same flaring loop,
or differing loops with similar global properties.
---------------------------------------------------------
Title: Fe XXVI line emission observed by YOHKOH
Authors: Pike, C. D.; Pillips, K. J. H.; Lang, J.; Sterling, A.;
Watanabe, T.; Hiei, E.; Culhane, J. L.
1996AdSpR..17d..51P Altcode: 1996AdSpR..17...51P
Observations from the Bragg Crystal Spectrometer (BCS) on board
the Japanese solar flare space-craftYohkoh showing Fe xxvi Ly-alpha
X-ray line emission at about 1.78 Angstroms are reported. Some 75
events over a two-year-long period between December 1991 and December
1993 have been analyzed. The greater sensitivity of the BCS compared
with previous instruments has enabled such emission to be detected
from a wider group of flares than has previously been possible. The
likelihood of detecting Fe xxvi lines in a flare is found to increase
sharply with the electron temperature obtained from the Fe xxv line
spectrum, also observed by the BCS, and with GOES X-ray class. The
width of the Lyalpha_1 line, measured after the impulsive stage, is
rather greater than that determined by thermal Doppler broadening,
and if the excess broadening is attributed to turbulence, velocities
of up to 70 km s^-1 are indicated. Comparison of electron temperatures
obtained from the Fe xxvi spectrum with Fe xxv temperatures provides
evidence for a single loose grouping of flares, with the difference
between the two temperatures ranging from nearly zero to about 20 x
10^6K. A “superhot” component would seem to be more or less developed
according as the temperature difference is large or nearly zero.
---------------------------------------------------------
Title: YOHKOH SXT and BCS Observations of the "Reconnection Region"
of a Solar Flare
Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R.
1996ASPC..111..177S Altcode: 1997ASPC..111..177S
The authors find strong line shifts in Bragg crystal spectrometer
(BCS) spectra of a flare which occurred well beyond the solar limb on
1993 April 15. Since the flare is beyond the limb, only the uppermost
regions of the flare are visible. If reconnection is acting in flares,
than one may expect that the line shifts from this event are due to
reconnection jets emanating from above the region of the main flaring
loops. The authors show, however, that details of the line shifts
are not consistent with this picture. Rather than being a result of
reconnection jets, it is more likely that the line shifts are due
to plasma motions on a flaring loop oriented edge on with respect to
the Earth.
---------------------------------------------------------
Title: Isolating the Footpoint Characteristics of a Solar Flare Loop
Authors: Harra-Murnion, L. K.; Culhane, J. L.; Fujiwara, T.; Hudson,
H. S.; Kato, T.; Sterling, A. C.
1996mpsa.conf..527H Altcode: 1996IAUCo.153..527H
No abstract at ADS
---------------------------------------------------------
Title: X-ray Observations of an Over-the-Limb Solar Flare with Large
Spectral Line Shifts
Authors: Sterling, A. C.; Harra-Murnion, L. K.; Hudson, H. S.; Lemen,
J. R.; Strong, K. T.
1996mpsa.conf..557S Altcode: 1996IAUCo.153..557S
No abstract at ADS
---------------------------------------------------------
Title: A Loop Flare Observed by YOHKOH on 1992 July 11
Authors: Khan, Josef I.; Hudson, Hugh S.; Sterling, Alphonse C.;
Lemen, James R.
1996ASPC..111..162K Altcode: 1997ASPC..111..162K
The authors present Yohkoh soft and hard X-ray observations of a
flare. Soft X-ray morphology shows the structure of this flare to
be a relatively simple loop. Nonetheless several interesting points
were found including: (i) bright soft X-ray footpoints persist long
after completion of the impulsive hard X-ray bursts; (ii) both legs
and footpoints of the flare loop appear to move together rather than
apart during the course of the flare; (iii) initially the flare loop
appears to have a fairly uniform thickness but as the flare progresses
the loop-top region becomes broader; (iv) 'low energy' hard X-rays
appear to originate from high in the loop near the loop apex; and (v)
soft X-ray spectra show strong line asymmetries suggesting the presence
of upflowing plasma oriented nearly directly towards the Earth.
---------------------------------------------------------
Title: Yohkho Soft X-Ray Spectroscopic Observations of the Bright
Loop-Top Kernels of Solar Flares
Authors: Khan, Josef I.; Harra-Murnion, Louise K.; Hudson, Hugh S.;
Lemen, James R.; Sterling, Alphonse C.
1995ApJ...452L.153K Altcode:
Observations of solar flares by the Soft X-ray Telescope (SXT) on
board Yohkoh frequently show strongly enhanced brightenings near the
tops of the magnetic loops containing hot plasma. The Yohkoh Bragg
Crystal Spectrometer (BCS) cannot normally make observations of these
loop-top sources in the absence of contamination by the legs and the
feet of the loops since it has no spatial resolution. We have overcome
this limitation by using the solar limb as an occulting edge in a
sequence of similar flares that occurred over an interval of ~10 hr
near the west limb on 1992 November 24. The progressive occultation by
the limb restricts the line of sight to higher and higher altitudes
during this sequence, with the final event showing only a compact
source of the type often found at loop tops. BCS observations in Fe
XXV, Ca XIX, and S XV show that electron temperatures and nonthermal
velocities in these compact sources are similar to those quantities
determined for disk flares in previous studies. As with disk flares,
the nonthermal line broadening persists late into the decay phase
of the flaring isolated loop tops. Our results favor mechanisms for
nonthermal-velocity generation that are either independent of height
or place the source near the apex of the flaring loop. In addition,
there may be a temporal relationship between the hard X-ray emission
and the nonthermal velocity, which suggests a possible association
between the primary energy release of the flare, the nonthermal-velocity
generation mechanism, and the loop top.
---------------------------------------------------------
Title: Yohkoh Multi-Wavelength Observations of the Bright Loop-Top
Kernels in Solar Flares
Authors: Sterling, A.; Khan, J.; Harra-Murnion, L.; Hudson, H.;
Lemen, J.
1995SPD....26.1211S Altcode: 1995BAAS...27..985S
No abstract at ADS
---------------------------------------------------------
Title: Fe XXV Temperatures in Flares from the YOHKOH Bragg Crystal
Spectrometer
Authors: Sterling, Alphonse C.; Doschek, George A.; Pike, C. David
1994ApJ...435..898S Altcode:
Studies by Doschek et al. using P78-1 and Solar Maximum Misson
(SMM) data have shown that the ratio of intensities of the Fe XXV
and Ca XIX resonance lines can be expressed as a function of Fe XXV
temperature. Using a more recent data set consisting of 13 flares
observed by the Bragg crystal spectrometer (BCS) experiment on board
Yohkoh, we find a nearly identical functional relationship between
the same resonance line ratios and Fe XXV temperatures. We use this
functional relationship to obtain resonance line ratio temperatures
(T<SUB>RLR</SUB>) for each flare in our data set, and compare them
with temperatures resulting from application of a simple spectral
fitting method. (T<SUB>SSF</SUB>) to individal Fe XXV spectra. We also
use a more involved free-parameter spectral fitting method to deduce
temperatures (T<SUB>FSF</SUB>) from some of these spectra. On average,
agreement between T<SUB>RLR</SUB> and T<SUB>SSF</SUB> improves as a
flare progresses in time, with average agreements of 10.0% +/- 5.2%,
6.4% +/- 5.4%, and 5.0% +/- 3.9% over the rise, peak, and decay phases,
respectively. Deviations between T<SUB>RLR</SUB> and T<SUB>FSF</SUB>
are about the same or smaller. Thus, for most analysis purposes, all
three methods yield virtually identical temperatures in flares. The
somewhat poorer agreement between T<SUB>SSF</SUB> and T<SUB>RLR</SUB>
during the earlier phases may be partially a result of difficulties
in obtaining precise values for temperatures from spectral fits
when blueshifts and large nonthermal broadenings are present in the
spectra. Because of the high sensitivity of the Yohkoh BCS compared
to that of BCS experiments on earlier spacecraft, we can for the first
time consistently observe the heating phase of flares in Fe XXV.
---------------------------------------------------------
Title: Jets and brightenings generated by energy deposition in the
middle and upper solar chromosphere
Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T.
1994SSRv...70...77S Altcode:
Numerical simulations of energy depositions in the middle and upper
solar chromosphere result in ejection of chromospheric material into
the corona and heating of the chromospheric gas. These simulations may
be capable of describing some of the features seen by the soft X-ray
telescope on board theYohkoh satellite.
---------------------------------------------------------
Title: The 1991 November 9 Flare at 03.2 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Mariska, J. T.; Strong, K. T.; Bentley, R. D.;
Brown, C. M.; Culhane, J. L.; Lang, J.; Sterling, A. C.; Watanabe, T.
1994ApJ...431..888D Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1991 November 9 near 03.2 UT. These data were obtained with
instrumentation on the Japanese Yohkoh spacecraft. They cover the entire
rise phase and peak flare emission, and the beginning of the decay
phase. We determine the dynamics, temperature, and emission measure
of the flare as inferred from the X-ray line profiles of resonance
lines of Fe XXV, Ca XIX, and S XV. We discuss the morphology of the
flare as inferred from the soft X-ray images. The November 9 flare is
atypical in that a stronger than usual blueshifted emission component
(relative to the stationary component) is observed for the resonance
lines at flare onset. We discuss several methods for deconvolving the
blueshifted component from the stationary component. The X-ray line
profiles are consistent with predictions of numerical simulations
of chromospheric evaporation. The X-ray images reveal a flare with a
complicated loop geometry that is not fully understood. Many of the
features in the images are moving upwards at speeds ranging from a
few km/s to about 800 km/s. The blueshifted emission begins near the
onset of hard X-ray emission, implying that particle acceleration and
upflowing plasma have a common energy source.
---------------------------------------------------------
Title: YOHKOH Bragg Crystal Spectrometer(BCS) Observations of the
6-Feb-1992 Limb Flare
Authors: Sterling, A. C.
1994kofu.symp..131S Altcode:
We present Yohkoh BCS observations of a near-limb solar flare of 6
Feb 1992. SXT images show that the event was composed of at least
two flaring loops. The first of these to flare had a maximum Fe XXV
temperature of about 19 MK and no substantial Fe XXVI component, while
the second flaring loop achieved a Fe XXV temperature in excess of 21
MK and had a superhot (30--40 MK) Fe XXVI component.
---------------------------------------------------------
Title: YOHKOH Observations of Weak Events Within AR7218
Authors: Linford, G. A.; Hudson, H.; Sterling, A.
1994xspy.conf...49L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Resonance Line Rations Method for Determining Flare
Temperatures Using YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G.; Mariska, J. T.; Hiei, E.;
Watanabe, T.
1994xspy.conf..127S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-Thermal Effects in Slow Solar Flares
Authors: Hudson, H. S.; Acton, L. W.; Sterling, A. C.; Tsuneta, S.;
Fishman, J.; Meegan, C.; Paciesas, W.; Wilson, R.
1994xspy.conf..143H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The 1992 January 5 Flare at 13.3 UT: Observations from YOHKOH
Authors: Doschek, G. A.; Strong, K. T.; Bentley, R. D.; Brown, C. M.;
Culhane, J. L.; Fludra, A.; Hiei, E.; Lang, J.; Mariska, J. T.;
Phillips, K. J. H.; Pike, C. D.; Sterling, A. C.; Watanabe, T.; Acton,
L. W.; Bruner, M. E.; Hirayama, T.; Tsuneta, S.; Rolli, E.; Kosugi,
T.; Yoshimori, M.; Hudson, H. S.; Metcalf, T. R.; Wuelser, J. -P.;
Uchida, Y.; Ogawara, Y.
1993ApJ...416..845D Altcode:
We discuss X-ray spectra and soft X-ray images of an M1.9 flare that
occurred on 1992 January 5 near 13.3 UT. These data were obtained
with instrumentation on the Japanese Yohkoh spacecraft. They cover
the entire rise phase of the flare. To supplement these data we have
ground-based magnetograms and Hα spectroheliograms. We calculate
the electron temperature and emission measure of the flare as a
function of time during the early rise phase using X-ray spectral
line intensities and line ratios. Using spectral line widths, line
profile asymmetries, and wavelength shifts due to the Doppler effect,
we calculate the dynamical properties of the flare. The time development
of the morphology of the flare, as revealed by the soft X-ray images
and the Hα spectroheliograms, and the physical quantities inferred
from the X-ray spectra, are compared with chromospheric evaporation
models. There is an enhancement of blueshifted emission that is closely
correlated with the hard X-ray bursts. Heating of one loop in the flare
is consistent with a conduction-evaporation model, but heating is found
in several structures that do not appear to be physically associated
with each other. No standard evaporation model can adequately explain
all of the observations.
---------------------------------------------------------
Title: Yohkoh observations of plasma upflows during solar flares
Authors: Culhane, J. L.; Phillips, A. T.; Pike, C. D.; Fludra, A.;
Bentley, R. D.; Bromage, B.; Doschek, G. A.; Hiei, E.; Inda, M.;
Mariska, J. T.; Phillips, K. J. H.; Sterling, A. C.; Watanabe, T.
1993AdSpR..13i.303C Altcode: 1993AdSpR..13..303C
Observations of two flares, an M 2.2 event on 16 December, 1991 and the
precursor to an X1 flare on 15 November, 1991 are presented. Spectra
obtained with the Bragg Crystal Spectrometer (BCS) are compared with
data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide
Band Spectrometer (WBS) on the satellite. For both events the creation
of upflowing plasma is detected. While the first event seems to conform
well to the chromospheric evaporation model for high temperature plasma
production, the behaviour for the second event is more complex.
---------------------------------------------------------
Title: Determination of coronal abundances of sulphur, calcium and
iron using the yohkoh bragg crystal spectrometer
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
1993AdSpR..13i.395F Altcode: 1993AdSpR..13..395F
Using spectra from the Bragg Crystal Spectrometer on Yohkoh we have
derived coronal abundances of sulphur, calcium and iron during several
flares from the ratio of the flux in the resonance line to the nearby
continuum. Multi-thermal effects have been taken into account using
differential emission measure analysis. We have also determined the
abundance of S in cool active regions during a period of very low solar
activity. We compare the coronal abundances of S, Ca and Fe with their
photospheric values.
---------------------------------------------------------
Title: Temperatures in Flares Determined from Fe XXV Spectra,
Resonance Line Ratios, and GOES X-ray Flux
Authors: Sterling, A. C.; Doschek, G. A.; Pike, C. D.; Hudson, H. S.;
Lemen, J. R.; Zarro, D. M.
1993BAAS...25.1178S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Chromospheric and Transition Region Response to Energy
Deposition in the Middle and Upper Chromosphere
Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T.
1993ApJ...407..778S Altcode:
A series of numerical simulations modeling the chromosphere and
transition region response to deposition of thermal energy ranging
from about 5 x 10 exp 24 to 5 x 10 exp 28 ergs in the middle or upper
chromosphere is reported. The dissipative effects of heat conduction,
optically thin radiation losses in the corona, and an approximate
expression for the radiation losses of lower temperature plasma are
calculated. In response to the energy deposition, chromospheric material
is ejected into the corona in the form of pressure gradient generated
jets, jets with pressure-gradient, and shock-generated components,
or high-speed gas plugs. Category of ejection depends on the spatial
and temporal distribution and the magnitude of the input energy source.
---------------------------------------------------------
Title: On the Absolute Abundance of Calcium in Solar Flares
Authors: Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri
1993ApJ...404..394S Altcode:
The abundance of calcium relative to hydrogen in soft X-ray-emitting
solar flare plasmas is determined. Results were obtained for 25
flares. An average calcium-to-hydrogen abundance of about 5 x 10
exp -6, which is about a factor of 2 greater than measured for the
photosphere, is found. This result is consistent with an enhancement
of low first ionization elements in soft X-ray flare plasmas. For
one flare, the calcium abundance was higher, at about 1.6 times the
average results. It is inferred that the calcium abundance can vary
among flares. Significant variations of the calcium abundance during
the course of a flare were not detected.
---------------------------------------------------------
Title: Determination of element abundances using the Yohkoh Bragg
Crystal Spectrometer.
Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.;
Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T.
1993uxrs.conf..542F Altcode: 1993uxsa.conf..542F
No abstract at ADS
---------------------------------------------------------
Title: Observations of Several Small Flares with the Bragg Crystal
Spectrometer on YOHKOH
Authors: Culhane, J. Leonard; Fludra, Andrzej; Bentley, Robert D.;
Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James;
Carter, Martin K.; Mariska, John T.; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Pike, C. David; Sterling, Alphonse C.
1992PASJ...44L.101C Altcode:
We have analysed data from two flares of GOES class C7.1 and C8.5
observed by the Yohkoh Bragg Crystal Spectrometer. The high sensitivity
of the Yohkoh instrument allows us to observe the very early stages of
flare development and to study small events with a high signal-to-noise
ratio. Spectral fitting programs have been used to derive plasma
temperatures, emission measures and velocities from spectra of S XV,
Ca XIX and Fe XXV. Large plasma motions indicative of chromospheric
evaporation have been found. A more detailed analysis of a flare which
occurred on 1991 October 30 is presented.
---------------------------------------------------------
Title: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics
and Temperature Behavior of a Soft X-Ray Flare
Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya;
Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.;
Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips,
Kenneth J. H.; Sterling, Alphonse C.
1992PASJ...44L..95D Altcode:
We describe X-ray spectra of an M1.5 flare that occurred on 1991
November 9, starting at about 0313 UT. This flare is unusual in that
very intense blueshifted components are observed in the resonance
lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare,
the resonance lines of Ca XIX and Fe XXV are primarily due to
this blueshifted component, which from the Doppler effect indicates
line-of-sight speeds and turbulent motions that in combination extend
up to 800 km s(-1) .
---------------------------------------------------------
Title: Yohkoh BCS Observations of Doppler Shifts Early in Solar Flares
Authors: Mariska, J. T.; Doschek, G. A.; Sterling, A. C.; Culhane,
J. L.; Hiei, E.; Watanabe, T.; Lang, J.
1992AAS...180.2308M Altcode: 1992BAAS...24..761M
No abstract at ADS
---------------------------------------------------------
Title: Time Variation of Solar Flare Temperatures Determined from
YOHKOH BCS Spectra
Authors: Sterling, A. C.; Doschek, G. A.; Mariska, J. T.; Pike, C. D.;
Culhane, J. L.; Hiei, E.; Watanabe, T.; YOHKOH BCS Team
1992AAS...180.3001S Altcode: 1992BAAS...24..775S
Bragg Crystal Spectrometer (BCS) X-ray spectra analysis from past
satellite missions indicate that it is possible to estimate temperatures
in highly ionized flare plasmas to within about 12\ resonance lines
in different He-like ions. This procedure is particularly valuable
in cases where other temperature measuring methods are insufficient,
such as during the rise phase of flares with strong X-ray spectra
blue shifts. Here we examine this ratio variation in several flares
using data from the Fe XXV, Ca XIX, and S XV channels of the BCS
experiment onboard the Yohkoh satellite. We select flares for
which we have good rise phase data, and calibrate the ratios using
dielectronic-to-resonance line ratios in selected Fe XXV spectra
assuming constant elemental abundances in each event. The Yohkoh BCS is
about an order of magnitude more sensitive than previous X-ray flare
spectrometers, and is therefore able to examine the early stages of
flare development in greater detail than previously possible. For this
study we select events for which we have good rise phase data, but data
well into the decay phase is available for a number of the selected
events. This allows us, for the first time, to follow the evolution
of flare spectra from relatively cool temperatures (~ 12 MK in Fe XXV)
to previously quoted “typical" flare temperatures (~ 17 MK in Fe XXV).
---------------------------------------------------------
Title: Emergence of Magnetic Flux from the Convection Zone into the
Solar Atmosphere. I. Linear and Nonlinear Adiabatic Evolution of
the Convective-Parker Instability
Authors: Nozawa, S.; Shibata, K.; Matsumoto, R.; Sterling, A. C.;
Tajima, T.; Uchida, Y.; Ferrari, A.; Rosner, R.
1992ApJS...78..267N Altcode:
The linear and nonlinear properties of the evolution of emerging
magnetic flux from the solar convection zone into the photosphere,
chromosphere, and corona are studied. A linear stability analysis
of the partially magnetized convection zone is presented. The growth
rate of this combined convective-Parker instability is found to differ
significantly from that of the Parker instability in the absence of
convection. When beta(=pg/pm) is greater than 10 in the initial flux
sheet, the growth rate increases with horizontal wavenumber, and there
is no maximum growth rate. A local maximum can occur when the flux
is initially located near the top of the convection zone. When beta
is less than 10, the convective-Parker instability behaves like the
Parker instability for long-wavelength modes, and like the convective
instability for short-wavelength modes. A 2D MHD code is used to study
the nonlinear evolution of the system. When the initial flux sheet has
beta less than 10, the long-wavelength mode dominates the nonlinear
evolution of the system, independently of the initial perturbation
wavelength.
---------------------------------------------------------
Title: Numerical Simulations of Microflare Evolution in the Solar
Transition Region and Corona
Authors: Sterling, Alphonse C.; Mariska, John T.; Shibata, Kazunari;
Suematsu, Yoshinori
1991ApJ...381..313S Altcode:
Several observers report transient ultraviolet brightenings, often
referred to as microflares, in the solar atmosphere. In this paper,
the results are presented of a series of one-dimensional numerical
simulations examining possible relationships between microflares
and the generation of dynamical chromospheric and transition region
features. Low-energy and medium-energy microflares eject long-lived
cool, dense gas plugs into the corona, with the gas plug traversing
the loop apex in the medium energy case. In the case of high-energy
microflares, the gas plug is rapidly heated to the temperature of the
surrounding corona, and the results resemble the dynamics occurring
in standard solar flare thick-target electron beam models.
---------------------------------------------------------
Title: On the Absolute Abundance of Ca in Solar Flares
Authors: Sterling, A. C.; Doschek, G. A.
1991BAAS...23.1467S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical Studies of Atmospheric Dynamics Driven by Energy
Deposition in the Chromosphere
Authors: Sterling, A. C.; Mariska, J. T.; Shibata, K.
1991BAAS...23.1029S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical Simulations of Ultraviolet and X-ray Microflares
Authors: Sterling, A. C.; Shibata, K.; Mariska, J. T.
1991LNP...387...71S Altcode: 1991fpsa.conf...71S
A series of numerical simulations indicates that thermal energy
releases of 1025 - 1027 ergs in the middle chromosphere can produce
ejections into the corona in the form of pressure gradient generated
jets, jets with pressure gradient and shock generated components, or
high speed gas plugs. Heating of the chromosphere to X-ray emitting
temperatures occurs in association with gas plugs, perhaps generating
X-ray microflares observable by Solar-A. Chromospheric UV-microflares
can occur in association with some jets, but do not generally occur
with spicules.
---------------------------------------------------------
Title: Atmospheric Heating in Emerging Flux Regions (With 2 Figures)
Authors: Shibata, K.; Nozawa, S.; Matsumoto, R.; Tajima, T.; Sterling,
A. C.
1991mcch.conf..609S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical Simulation of Microflare Evolution in the Solar
Transition Region and Corona (With 4 Figures)
Authors: Sterling, A. C.; Mariska, J. T.
1991mcch.conf..630S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emergence of Solar Magnetic Flux from the Convection Zone
into the Photosphere and Chromosphere
Authors: Shibata, K.; Nozawa, S.; Matsumoto, R.; Sterling, A. C.;
Tajima, T.
1990ApJ...351L..25S Altcode:
A two-dimensional MHD code is used to study the nonlinear dynamics
of solar magnetic flux emerging from the convection zone into the
photosphere and chromosphere. An isolated horizontal magnetic flux with
beta of about 4 is initially located in a convectively unstable layer
(solar convection zone) beneath a two-temperature layered atmosphere
(solar corona-chromosphere/photosphere). The combined effects of
convection and magnetic buoyancy carry the magnetic flux from the
convection zone into the photosphere, where it then expands through
the photosphere and chromosphere. Gas slides down the expanding loop,
resulting in its evacuation and subsequent rise due to enhanced
magnetic buoyancy. Initially, weak convection zone magnetic flux (B
of about 600 G) is amplified up to 1000 G or more after emerging into
the photosphere. The resulting velocity fields are similar to those
observed in arch filament systems.
---------------------------------------------------------
Title: Numerical Simulations of the Rebound Shock Model for Solar
Spicules
Authors: Sterling, Alphonse C.; Mariska, John T.
1990ApJ...349..647S Altcode:
Using time-dependent numerical simulations, the proposed rebound shock
mechanism for spicules has been examined. At temperatures above a
critical value, T(c), the radiation is characteristic of the conditions
in the optically thin corona and near optically thin transition
region. When T less than T(c), the atmosphere has a radiative cooling
time, tau(rad) characteristic of chromosphere. The spicule is initiated
with a quasi-impulsive force in the low chromosphere, which drives a
train of upward propagating rebound shocks along the rigid magnetic flux
tube. These shocks then move the transition region upward. The material
below the displaced transition region has temperatures and densities
similar to those of spicules when T(c) = 20,000 K or more and tau(rad)
= 500 s or more, but not when T(c) = 10,000 K, and probably not when
tau(rad) = 100 s. For all the cases where the cross sectional area
diverges rapidly with height, the upward velocity of the transition
region is less than that of spicules. Moreover, the maximum height is
less than that of average spicules. Taller, higher velocity spicules
result when the magnetic field cross sectional area is constant. In
all cases, the rebound shock mechanism produces substantial motions
and temperature and density variations in chromospheric and transition
region material. It is suggested that this may be a partial explanation
for the continuous dynamic state of the lower solar atmosphere.
---------------------------------------------------------
Title: Emergence of Solar Magnetic Flux from the Convection Zone
into the Photosphere aand Chromosphere
Authors: Sterling, A. C.; Shibata, K.; Nozawa, S.; Matsumoto, R.;
Tajima, T.
1989BAAS...21.1179S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Rebound Shock Mechanism for Solar Fibrils
Authors: Sterling, Alphonse C.; Hollweg, Joseph V.
1989ApJ...343..985S Altcode:
Flows along a rigid solar magnetic flux tube which is horizontal over
a substantial portion of its length are numerically investigated. A
single, quasi-impulsive force near the base of the first vertical
segment drives a series of upward propagating rebound shocks on the
flux tube. When the horizontal segment is in the corona, the shocks
raise the transition region onto the horizontal segment and eventually
onto the coronal vertical segment. The material behind the displaced
transition region resembles a fibril on the horizontal segment, and a
short spicule on the second vertical segment. A full-sized spicule does
not develop. The resulting density of the material on the horizontal
segment is 10 to the -14th g/cu cm, which is consistent with the
observed densities in fibrils. When the horizontal segment is in the
chromosphere, the motions and densities induced on the horizontal
segment do not resemble those of observed fibrils, and a full-sized
spicule again does not develop.
---------------------------------------------------------
Title: Numerical Simulations of the Rebound Shock Model for Spicules
Authors: Sterling, A. C.; Mariska, J. T.
1988BAAS...20Q.989S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Rebound Shock Model for Solar Spicules: Dynamics at
Long Times
Authors: Sterling, Alphonse C.; Hollweg, Joseph V.
1988ApJ...327..950S Altcode:
The spicule model due to Hollweg is extended and developed. The
dynamics is emphasized here; radiative and ionization losses, heat
conduction, and nonshock heat input, are not included. In the model,
a series of rebound shocks results in chromospheric material with
spicule-like properties below a raised transition region. The shocks
result from a single quasi-impulsive source in the photosphere. It
is found that at long times, the model approaches a new hydrostatic
equilibrium with the transition region remaining raised, and with a
region of shock-heated chromosphere below it. Attention is given to
the variation of the properties of the model in response to different
values for the magnitude and location of the source, and to different
initial transition region heights. It is concluded that the model
is capable of generating structures with properties consistent with
observations of spicules (with the exception of temperature) when only
the dynamics is considered.
---------------------------------------------------------
Title: A Rebound Shock Model for Solar Fibrils
Authors: Sterling, A. C.; Hollweg, J. V.
1988BAAS...20..690S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the Solar Atmosphere: Spicules and Fibrils.
Authors: Sterling, Alphonse Christopher
1988PhDT.........2S Altcode:
Numerical and analytical studies of MHD waves on magnetic flux tubes are
applied to problems of the solar atmosphere. In particular, theoretical
analysis of the chromospheric features known as spicules and fibrils
are undertaken. The thesis consists of three principal segments:. i. A
preexisting spicule model is extended and developed. In the model, a
series of rebound shocks propagating on a vertical magnetic flux tube
results in chromospheric material with spicule-like properties below a
raised transition region. The model emphasizes dynamic motions and shock
heating, but excludes radiative and ionization losses. At long times,
the model approaches a new hydrostatic equilibrium with the transition
region remaining raised, and with a region of shock-heated chromosphere
below it. The variation of the model properties in response to different
initial parameters is investigated. One conclusion is that the model
is capable of generating structures with properties consistent with
observations of spicules (with the exception of temperature) when
only the dynamics is considered. ii. An analytical study is performed
using linearized MHD equations to demonstrate that spicules may act as
resonance cavities for MHD Alfven waves propagating along a vertical
magnetic flux tube. When the resonances are excited, large amounts of
wave energy from the photosphere and lower chromosphere can propagate
into the spicule. This may result in the observed heating, fading,
and twisting motions of spicules. It is assumed that the wave energy
can be dissipated as heat via a turbulent cascade which follows
a Kolmogorov. iii. The spicule model used in the first segment of
the thesis is applied to a magnetic field geometry which is vertical
through the photosphere and chromosphere, turns horizontal in the low
corona, and eventually turns vertical again and extends into the outer
corona. Radiative and ionization losses are again omitted. A structure
develops on the horizontal segment which may be identifiable with a
fibril, but a full spicule does not develop. At long times, the fibril
and short spicule remain extended, and a standing wave develops on
the flux tube.
---------------------------------------------------------
Title: Spicule Dynamics: Long Time Behavior
Authors: Sterling, A. C.; Hollweg, J. V.
1985BAAS...17Q.631S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Alfvenic resonances on solar spicules
Authors: Sterling, A. C.; Hollweg, J. V.
1984ApJ...285..843S Altcode:
It is suggested that twisting and heating of solar spicules can
be produced by Alfven waves which enter the spicule from below. The
spicule is treated as a region of constant Alfven speed which is bounded
above by a region of much higher Alfven speed (the corona) and below
by a region of exponentially increasing Alfven speed (the photosphere
and chromosphere). It is shown how the spicule can act as a resonant
cavity. The transmission of the waves into the cavity is analytically
determined to be enhanced at certain resonant frequencies. With
reasonable spicule parameters, and assuming the spicule damping to be
moderately large, it is found that twisting velocities of approximately
20-30 km/s can be induced on the spicule. It is suggested that the
Alfven waves are dissipated via a turbulent cascade of their energy to
higher wavenumbers. It is shown that the waves can thereby heat the
spicules to the observed temperatures. It is further suggested that
the continued input of energy can explain why H-alpha spicules fade,
since the predicted heating rate is sufficient to heat the spicules
to temperatures at which the hydrogen is fully ionized; thus H-alpha
spicules may evolve into EUV spicules.
---------------------------------------------------------
Title: Resonant heating - an interpretation of coronal loop data
Authors: Hollweg, J. V.; Sterling, A. C.
1984ApJ...282L..31H Altcode:
The authors show that the resonant heating theory of Hollweg can be
used to organize the coronal loop data of Golub et al. When combined
with a reasonable form for the input power spectrum, the resonant
heating theory is fully compatible with the loop data.
---------------------------------------------------------
Title: Coronal Loop Heating: Theory and Data
Authors: Hollweg, J. V.; Sterling, A. C.
1984BAAS...16..527H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Alfvenic Heating: An Interpretation of Coronal Loop Data
Authors: Sterling, A. C.; Hollweg, J. V.
1984BAAS...16Q.527S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Resonances of Solar Spicules
Authors: Hollweg, J. V.; Sterling, A. C.
1983BAAS...15R.994H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Study of Earth Tides, Earthquakes and Terrestrial Spectroscopy
by Analysis of the Level Fluctuations in a Borehole at Heibaart
(Belgium)
Authors: Sterling, A.; Smets, E.
1971GeoJ...23..225S Altcode: 1971GeoJI..23..225S
No abstract at ADS
---------------------------------------------------------
Title: Etude des marées terrestres et des séismes par l'analyse
des variations du niveau d'eau dans un puits à Heibaart
Authors: Sterling, A.; Smets, E.
1970C&T....86...23S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Effets de dilatations cubiques dues aux marées terrestres
observés sous forme de variations de niveau dans un puits à
Basècles (Hainaut)
Authors: Melchior, P.; Sterling, A.; Wery, A.
1963C&T....79..353M Altcode:
No abstract at ADS