Author name code: yurchyshyn
ADS astronomy entries on 2022-09-14
author:Yurchyshyn, V. B.
------------------------------------------------------------------------
Title: Solar Chromospheric Network as a Source for Solar Wind
Switchbacks
Authors: Lee, Jeongwoo; Yurchyshyn, Vasyl; Wang, Haimin; Yang, Xu;
Cao, Wenda; Carlos Martínez Oliveros, Juan
Bibcode: 2022ApJ...935L..27L
Altcode:
Recent studies suggest that the magnetic switchbacks (SBs) detected
by the Parker Solar Probe carry information on the scales of solar
supergranulation (large scale) and granulation (medium scale). We test
this claim using high-resolution Hα images obtained with the visible
spectropolarimeters of the Goode Solar Telescope in Big Bear Solar
Observatory. As possible solar sources, we count all the spicule-like
features standing along the chromospheric networks near the coronal
hole boundary visible in the Hα blue-wing but absent in the red-wing
images and measure the geometric parameters of dense sections of
individual flux tubes. Intervals between adjacent spicules located
along the chromospheric networks are found in the range of 0.4-1.5
Mm (0.°03-0.°12) tending to be smaller than the medium scale of
SBs. Interdistances between all pairs of the flux tubes are also counted
and they appear in a single peak distribution around 0.7 Mm (0.°06)
unlike the waiting-time distribution of SBs in a scale-free single
power-law form. The length-to-diameter ratio of the dense section
of flux tubes is as high as 6-40, similar to the aspect ratio of
SBs. The number of spicules along a network can be as high as 40-100,
consistent with numerous SBs within a patch. With these numbers, it is
argued that the medium scale of SBs can be understood as an equilibrium
distance resulting from a random walk within each diverging magnetic
field funnel connected to the chromospheric networks.
Title: Erratum: "A Study of Sunspot 3 Minute Oscillations Using ALMA
and GST" (2022, ApJ, 924, 100)
Authors: Chai, Yi; Gary, Dale E.; Reardon, Kevin P.; Yurchyshyn, Vasyl
Bibcode: 2022ApJ...933..247C
Altcode:
No abstract at ADS
Title: Triggering Mechanism for Eruption of Two Filaments Observed by
the Solar Dynamics Observatory, Nobeyama Radioheliograph, and RHESSI
Authors: Kim, Sujin; Yurchyshyn, Vasyl
Bibcode: 2022ApJ...932L..18K
Altcode:
We investigate the eruptive process of two filaments, which is
associated with an M-class flare that occurred in 2011 August 4. The
filaments are partly overlapped, one in the active region and the
other just beside it, and erupt together as a halo coronal mass
ejection. For this study, we used the Atmospheric Imaging Assembly
and the Heliospheric Magnetic Imager on board the Solar Dynamics
Observatory, the Nobeyama Radioheliograph 17 GHz, and the RHESSI Hard
X-ray satellite. We found three distinct phases in the microwave flux
profile and in the rising pattern of the filaments during the event. In
the first phase, there was weak nonthermal emission at 17 GHz and hard
X-rays. Those nonthermal sources appeared on one edge of the western
filament (F2) in the active region. The F2 began to be bright and rose
upward rapidly, while the eastern filament (F1), which was extended to
the quiet region, started to brighten from the peak time of the 17 GHz
flux. In the second phase, the nonthermal emission weakened and the
F2 rose up slowly, while the F1 began to rise up. In the third phase,
two filaments erupted together. Since the F1 was stable for a long time
in the quiet region, breaking the equilibrium state of the F1 would be
decisive for the successful eruption of two filaments and it seems clear
that the evolution of the F2 provoked the unstable F1. We suggest that
tether-cutting reconnection between two overlapped filaments triggers
the eruption of the two filaments as a tangled identity.
Title: Magnetic Field Re-configuration Associated With a Slow Rise
Eruptive X1.2 Flare in NOAA Active Region 11944
Authors: Yurchyshyn, Vasyl; Yang, Xu; Nita, Gelu; Fleishman, Gregory;
Abramenko, Valentina; Inoue, Satoshi; Lim, Eun-Kyung; Cao, Wenda
Bibcode: 2022FrASS...916523Y
Altcode:
Using multi-wavelength observations, we analysed magnetic field
variations associated with a gradual X1.2 flare that erupted on
January 7, 2014 in active region (AR) NOAA 11944 located near the disk
center. A fast coronal mass ejection (CME) was observed following the
flare, which was noticeably deflected in the south-west direction. A
chromospheric filament was observed at the eruption site prior to and
after the flare. We used SDO/HMI data to perform non-linear force-free
field extrapolation of coronal magnetic fields above the AR and to
study the evolution of AR magnetic fields prior to the eruption. The
extrapolated data allowed us to detect signatures of several magnetic
flux ropes present at the eruption site several hours before the
event. The eruption site was located under slanted sunspot fields
with a varying decay index of 1.0-1.5. That might have caused the
erupting fields to slide along this slanted magnetic boundary rather
than vertically erupt, thus explaining the slow rise of the flare
as well as the observed direction of the resulting CME. We employed
sign-singularity tools to quantify the evolutionary changes in the
model twist and observed current helicity data, and found rapid and
coordinated variations of current systems in both data sets prior to
the event as well as their rapid exhaustion after the event onset.
Title: Observations of Extremely Strong Magnetic Fields in Active
Region NOAA 12673 Using GST Magnetic Field Measurement
Authors: Lozitsky, Vsevolod; Yurchyshyn, Vasyl; Ahn, Kwangsu; Wang,
Haimin
Bibcode: 2022ApJ...928...41L
Altcode:
We present a detailed study of very strong magnetic fields in the
NOAA Active Region (AR) 12673, which was the most flare productive
AR in solar cycle 24. It produced four X-class flares including the
X9.3 flare on 2017 September 6 and the X8.2 limb event on September
10. Our analysis is based on direct measurements of full Zeeman
splitting of the Fe I 1564.85 nm line using all Stokes I, Q, U, and
V profiles. This approach allowed us to obtain reliable estimates
of the magnitude of magnetic fields independent of the filling
factor and atmosphere models. Thus, the strongest fields up to 5.5
kG were found in a light bridge (LB) of a spot, while in the dark
umbra magnetic fields did not exceed 4 kG. In the case of the LB,
the magnitude of the magnetic field is not related to the underlying
continuum intensity, while in the case of umbral fields we observed
a well-known anticorrelation between the continuum intensity and the
field magnitude. In this study, the LB was cospatial with a polarity
inversion line of δ-sunspot, and we speculate that the 5.5 kG strong
horizontal fields may be associated with a compact twisted flux rope
at or near the photosphere. A comparison of the depth of the Zeeman
π and σ components showed that in the LB magnetic fields are, on
average, more horizontal than those in the dark umbra.
Title: A Study of Sunspot 3 Minute Oscillations Using ALMA and GST
Authors: Chai, Yi; Gary, Dale E.; Reardon, Kevin P.; Yurchyshyn, Vasyl
Bibcode: 2022ApJ...924..100C
Altcode: 2021arXiv211105812C
Waves and oscillations are important solar phenomena, not only because
they can propagate and dissipate energy in the chromosphere, but also
because they carry information about the structure of the atmosphere
in which they propagate. The nature of the 3 minute oscillations
observed in the umbral region of sunspots is considered to be an
effect of propagation of magnetohydrodynamic waves upward from below
the photosphere. We present a study of sunspot oscillations and wave
propagation in NOAA Active Region 12470 using an approximately 1
hr long data set acquired on 2015 December 17 by the Atacama Large
Millimeter/submillimeter Array (ALMA), the Goode Solar Telescope
(GST) operating at the Big Bear Solar Observatory, the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory, and the
Interface Region Imaging Spectrograph. The ALMA data are unique in
providing a time series of direct temperature measurements in the
sunspot chromosphere. The 2 s cadence of ALMA images allows us to well
resolve the 3 minute periods typical of sunspot oscillations in the
chromosphere. Fourier analysis is applied to ALMA Band 3 (~100 GHz, ~3
mm) and GST Hα data sets to obtain power spectra as well as oscillation
phase information. We analyzed properties of the wave propagation by
combining multiple wavelengths that probe physical parameters of solar
atmosphere at different heights. We find that the ALMA temperature
fluctuations are consistent with that expected for a propagating
acoustic wave, with a slight asymmetry indicating nonlinear steepening.
Title: Solar Chromospheric Ejections and Solar Wind Switchbacks
Authors: Lee, Jeongwoo; Yang, Xu; Yurchyshyn, Vasyl; Wang, Haimin
Bibcode: 2021AGUFMSH33B..01L
Altcode:
Small-scale jet-like ejections in the solar atmosphere are of renewed
interest to NASA's Parker Solar Probe (PSP) mission, because they may
develop into the mysterious solar wind structure of plasma and magnetic
field called switchbacks detected by the PSP. We investigate high
resolution H-alpha images and magnetograms obtained with the visible
(VIS) and near-infrared (NIRIS) spectro-polarimeters of the Goode
Solar Telescope (GST) in Big Bear Solar Observatory (BBSO) to explore
solar origin for the switchbacks. In this effort, we measure spatial
dimensions, orientation, eruption speed of tiny magnetic arcades,
mini-filaments, and plumelets for comparison with the properties of
the switchbacks established from the PSP observations. The spatial
dimensions of these objects range from tens of arcsecond down to sub
arcsecond (200 km), small enough to produce short duration switchbacks
in the PSP locations. However, the orientation combined with the
speed can be tested against the surprisingly high aspect ratio of
the switchbacks, thus providing a strong constraint on the possible
candidates. Other properties of the switchbacks such as clustering and
one-sidedness make this search a narrower choice. We argue that the most
ideal solar candidate should be the tiny upright flux tubes that can
develop into an S-shape after ejection, and that the KelvinHelmholtz
instability arising from the density inhomogeneity along the flux
tube could be a plausible mechanism for transforming the chromospheric
structure into the solar wind switchbacks.
Title: Exploring Nature Of Type II Spicules With GST Data
Authors: Yurchyshyn, V.
Bibcode: 2021AAS...23820504Y
Altcode:
Large- and small-scale jets and upflows observed in the lower
atmosphere of the quiet Sun (QS) are thought to play an important
role in the transfer of mass and energy from the dense chromosphere
into the corona. However, their origin and connection to dynamic
magnetic fields are not yet well understood and explored. Type II
spicules are a subset of these small-scale phenomena discovered in
off-limb Hinode data. Although their formation may affect the corona
by generating shocks, flows, waves, and electric currents, their
detailed physical cause and role in providing mass and energy to the
corona remain largely unknown. Here we will present recent progress
in studying type II spicules facilitated by data from the Goode Solar
Telescope. Various data sets and approaches to analysis all seem to
indicate that these events result from magnetic reconnection driven by
rapidly varying small-scale magnetic fields present in highly turbulent
solar photosphere. In particular, we observe very rapid morphological
changes on timescales of the order of 1 s. They very frequently appear
in situ without any clear evidence of H-alpha material being injected
from below. Their evolution includes various splitting patterns as well
as sudden formation of a diffuse region followed by branching. These
observations suggest that faint and numerous type II spicules may
be formed as a result of component reconnection within a bundle of
unipolar large scale fields.
Title: Magnetic Field Configuration Associated With A Slow Rise
Eruptive X1.2 Flare In Active Region 11944
Authors: Yang, X.; Yurchyshyn, V.; Nita, G.; Abramenko, V.; Lim, E.;
Cao, W.
Bibcode: 2021AAS...23812707Y
Altcode:
Using multi-wavelength observations, we studied a gradual X1.2 flare
that erupted on January 7, 2014, in active region (AR) NOAA 11944
located near the disk center. A fast coronal mass ejection (CME) was
observed following the flare; however, it was strongly deflected in the
south-west direction. We used SDO/HMI data to perform extrapolation of
coronal magnetic fields and to study the evolution of AR magnetic fields
before the eruption. Extrapolated data allowed us to detect a flux rope
(FR) present at the eruption site several hours before the event. That
was the only well-defined FR present in the AR. Although the strapping
and core fields in the model have significantly changed after the flare,
the model FR did not erupt. We note that a chromospheric filament
was observed at the eruption site prior to and after the flare. The
eruption site was located under sunspot canopy fields with a decay
index of about 0.5, which is not favorable for torus instability to
develop. That might have caused the erupting fields to slide along the
canopy rather than vertically erupt, thus explaining the slow rise of
the flare as well as the observed direction of the resulting CME. We
employed sign-singularity tools to quantify the evolutionary changes
in a model twist and observed current helicity data, and found rapid
enhancements in the current systems in both data sets prior to the
event as well as their rapid exhaustion after the event onset.
Title: Detection of Opposite Magnetic Polarity in a Light Bridge:
Its Emergence and Cancellation in Association with LB Fan-shaped Jets
Authors: Lim, Eun-Kyung; Yang, Heesu; Yurchyshyn, Vasyl; Chae,
Jongchul; Song, Donguk; Madjarska, Maria S.
Bibcode: 2020ApJ...904...84L
Altcode: 2020arXiv201010713L
Light bridges (LBs) are relatively bright structures that divide
sunspot umbrae into two or more parts. Chromospheric LBs are known to
be associated with various activities including fan-shaped jet-like
ejections and brightenings. Although magnetic reconnection is
frequently suggested to be responsible for such activities, not many
studies present firm evidence to support the scenario. We carry out
magnetic field measurements and imaging spectroscopy of an LB where
fan-shaped jet-like ejections occur with co-spatial brightenings
at their footpoints. We study LB fine structure and magnetic field
changes using TiO images, Near-InfraRed Imaging Spectropolarimeter,
and Hα data taken by the 1.6 m Goode Solar Telescope. We detect
magnetic flux emergence in the LB that is of opposite polarity to that
of the sunspot. The new magnetic flux cancels with the pre-existing
flux at a rate of 5.6 × 1018 Mx hr-1. Both
the recurrent jet-like ejections and their base brightenings are
initiated at the vicinity of the magnetic flux cancellation, and show
apparent horizontal extension along the LB at a projected speed of up
to $18.4$ km s-1 to form a fan-shaped appearance. Based on
these observations, we suggest that the fan-shaped ejections may have
resulted from slipping reconnection between the new flux emerging in
the LB and the ambient sunspot field.
Title: Accelerating and Supersonic Density Disturbances in Solar
Polar Plumes
Authors: Cho, I. H.; Moon, Y. J.; Nakariakov, V. M.; Lee, J. Y.; Yu,
D. J.; Cho, K. S. F.; Yurchyshyn, V.; Lee, H.
Bibcode: 2020AGUFMSH0290003C
Altcode:
Propagating intensity disturbances in solar coronal holes are often
considered as wave propagations or mass flows. By applying the
differential emission measure technique for the extreme ultraviolet
images taken by the Atmospheric Imaging Assembly on board the Solar
Dynamics Observatory, we analyze the propagation speed of density
disturbances of plume structure in an off-limb coronal hole for a
given temperature. We construct the map of cross-correlation between
density profile for a given height and the profile at the height
of 50 Mm. The evolution of density disturbances is well fitted by
the second-order polynomial. The acceleration is calculated to be
36 m s-2. The initial speed is 134 km s-1
which is comparable with the sound speed given by the DEM-weighted
temperature. Hence, density disturbances are accelerating and supersonic
at around the base of the solar corona. The excess speed relative
to the sound speed is ∼ 30 km s-1 at the height of 1.23
solar radii, which is consistent with the Doppler speeds and Doppler
dimming speeds observed by different instruments. The extrapolated
sonic distance of the excess speed is ∼ 2.16 solar radii which is
consistent with those of solar winds. The lower limit of the mass
flux corresponds to 7% of the global solar wind. Hence, we interpret
that the observed density disturbances are slow magnetoacoustic waves
propagating in subsonic and accelerating solar winds.
Title: Temporal and Periodic Variation of the MCMESI for the Last
Two Solar Cycles; Comparison with the Number of Different Class
X-ray Solar Flares
Authors: Kilcik, Ali; Chowdhury, Partha; Sarp, Volkan; Yurchyshyn,
Vasyl; Donmez, Burcin; Rozelot, Jean-Pierre; Ozguc, Atila
Bibcode: 2020SoPh..295..159K
Altcode: 2020arXiv200811506K
In this study we compared the temporal and periodic variations of
the Maximum CME Speed Index (MCMESI) and the the number of different
class (C, M, and X) solar X-ray flares for the last two solar cycles
(Solar Cycles 23 and 24). To obtain the correlation between the MCMESI
and solar flare numbers the cross-correlation analysis was applied to
monthly data sets. Also to investigate the periodic behavior of all
data sets the Multi Taper Method (MTM) and the Morlet wavelet analysis
method were performed with daily data from 2009 to 2018. To evaluate our
wavelet analysis Cross Wavelet Transform (XWT) and Wavelet Transform
Coherence (WTC) methods were performed. Causal relationship between
data sets were further examined by Convergence Cross Mapping (CCM)
method. As results of our analysis we found the following: i) The C
class X-ray flare numbers increased about 16% during the Solar Cycle 24
compared to Cycle 23, while all other data sets decreased; the MCMESI
decreased about 16% and the number of M and X class flares decreased
about 32%. ii) All the X-ray solar flare classes show remarkable
positive correlation with the MCMESI. While the correlation between the
MCMESI and C class flares comes from the general solar cycle trend,
it mainly results from the fluctuations in the data in case of the X
class flares. iii) In general, all class flare numbers and the MCMESI
show similar periodic behavior. iv) The 546-day periodicity detected
in the MCMESI may not be of solar origin or at least the solar flares
are not the source of this periodicity. v) C and M class solar flares
have a stronger causative effect on the MCMESI compared to X class
solar flares. However, the only bidirectional causal relationship is
obtained between the MCMESI and C class flare numbers.
Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
Bibcode: 2020SSRv..216..131P
Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.
Title: Analysis of quiet-sun turbulence on the basis of SDO/HMI and
goode solar telescope data
Authors: Abramenko, Valentina I.; Yurchyshyn, Vasyl B.
Bibcode: 2020MNRAS.497.5405A
Altcode: 2020arXiv200806264A; 2020MNRAS.tmp.2438A
We analysed line-of-sight magnetic fields and magnetic power
spectra of an undisturbed photosphere using magnetograms acquired
by the Helioseismic and Magnetic Imager (HMI) on-board the Solar
Dynamic Observatory and the Near InfraRed Imaging Spectrapolarimeter
(NIRIS) operating at the Goode Solar Telescope of the Big Bear Solar
Observatory. In the NIRIS data, we revealed thin flux tubes of 200-400
km in diameter and of 1000-2000 G field strength. The HMI power spectra
determined for a coronal hole, a quiet sun, and a plage areas exhibit
the same spectral index of -1 on a broad range of spatial scales from
10-20 Mm down to 2.4 Mm. This implies that the same mechanism(s)
of magnetic field generation operate everywhere in the undisturbed
photosphere. The most plausible one is the local turbulent dynamo. When
compared to the HMI spectra, the -1.2 slope of the NIRIS spectrum
appears to be more extended into the short spatial range until the
cut-off at 0.8-0.9 Mm, after which it continues with a steeper slope of
-2.2. Comparison of the observed and Kolmogorov-type spectra allowed
us to infer that the Kolmogorov turbulent cascade cannot account for
more than 35 per cent of the total magnetic energy observed in the
scale range of 3.5-0.3 Mm. The energy excess can be attributed to other
mechanisms of field generation such as the local turbulent dynamo and
magnetic superdiffusivity observed in an undisturbed photosphere that
can slow down the rate of the Kolmogorov cascade leading to a shallower
resulting spectrum.
Title: Accelerating and Supersonic Density Fluctuations in Coronal
Hole Plumes: Signature of Nascent Solar Winds
Authors: Cho, Il-Hyun; Nakariakov, Valery M.; Moon, Yong-Jae; Lee,
Jin-Yi; Yu, Dae Jung; Cho, Kyung-Suk; Yurchyshyn, Vasyl; Lee, Harim
Bibcode: 2020ApJ...900L..19C
Altcode: 2020arXiv200807848C
Slow magnetoacoustic waves in a static background provide a
seismological tool to probe the solar atmosphere in the analytic
frame. By analyzing the spatiotemporal variation of the electron
number density of plume structure in coronal holes above the limb for
a given temperature, we find that the density perturbations accelerate
with supersonic speeds in the distance range from 1.02 to 1.23 solar
radii. We interpret them as slow magnetoacoustic waves propagating at
about the sound speed with accelerating subsonic flows. The average
sonic height of the subsonic flows is calculated to be 1.27 solar
radii. The mass flux of the subsonic flows is estimated to be 44.1%
relative to the global solar wind. Hence, the subsonic flow is likely
to be the nascent solar wind. In other words, the evolution of the
nascent solar wind in plumes at the low corona is quantified for the
first time from imaging observations. Based on the interpretation,
propagating density perturbations present in plumes could be used as
a seismological probe of the gradually accelerating solar wind.
Title: Date Co-alignment for Ground-Based High-Resolution Solar
Imaging
Authors: Yang, X.; Ji, K.; Cao, W.; Yurchyshyn, V.; Xu, Z.
Bibcode: 2020SPD....5120501Y
Altcode:
The multi-wavelength analysis is a well-spread method in solar
physics studies, and the community increasingly relies on coordinated
observations involving multiple instruments. The calibration of
heliographic coordinates is therefore vital for the co-alignment
of such multi-instrument, multi-wavelength data. However, this is
particularly difficult for ground-based high-resolution observations
because of the limited field of view. Manually co-aligning data with
low-contrast features (e.g., photospheric observations of quiet Sun
regions) between different telescopes requires exceptional efforts
and patience. Here, we developed a technique to accurately determine
coordinates of high-resolution images acquired by the Goode Solar
Telescope (GST) at the Big Bear Solar Observatory. The technique employs
a scale-invariant feature transform (SIFT) method, which performs
without human interference. With this new approach, we co-aligned
multi-wavelength GST data sets to the continuum intensity data from
the Helioseismic and Magnetic Imager (HMI) precisely. The inferred
heliographic coordinates are saved in each FITS file header, which
is compatible with the common mapping methods available in the Solar
SoftWare (SSW) package. GST data are fully open to the scientific
community, and a substantial portion of observing time on the GST
opens to the community as well.
Title: Hard X-Ray Emission from an Activated Flux Rope and Subsequent
Evolution of an Eruptive Long-duration Solar Flare
Authors: Sahu, Suraj; Joshi, Bhuwan; Mitra, Prabir K.; Veronig,
Astrid M.; Yurchyshyn, V.
Bibcode: 2020ApJ...897..157S
Altcode: 2020arXiv200506221S
In this paper, we present a comprehensive study of the evolutionary
phases of a major M6.6 long duration event with special emphasize on
its pre-flare phase. The event occurred in NOAA 12371 on 2015 June
22. A remarkable aspect of the event was an active pre-flare phase
lasting for about an hour during which a hot EUV coronal channel
was in the build-up stage and displayed cospatial hard X-ray (HXR)
emission up to energies of 25 keV. This is the first evidence of the
HXR coronal channel. The coronal magnetic field configuration based
on nonlinear-force-free-field modeling clearly exhibited a magnetic
flux rope (MFR) oriented along the polarity inversion line (PIL) and
cospatial with the coronal channel. We observed significant changes
in the AR's photospheric magnetic field during an extended period of
≍42 hr in the form of rotation of sunspots, moving magnetic features,
and flux cancellation along the PIL. Prior to the flare onset, the MFR
underwent a slow rise phase (≍14 km s-1) for ≍12 minutes,
which we attribute to the faster build-up and activation of the MFR
by tether-cutting reconnection occurring at multiple locations along
the MFR itself. The sudden transition in the kinematic evolution of
the MFR from the phase of slow to fast rise (≍109 km s-1
with acceleration ≍110 m s-2) precisely divides the
pre-flare and impulsive phase of the flare, which points toward the
feedback process between the early dynamics of the eruption and the
strength of the flare magnetic reconnection.
Title: Spatial Distribution of the Origin of Umbral Waves in a
Sunspot Umbra
Authors: Yurchyshyn, Vasyl; Kilcik, Ali; Şahin, Seray; Abramenko,
Valentina; Lim, Eun-Kyung
Bibcode: 2020ApJ...896..150Y
Altcode: 2020arXiv200504202Y
Umbral flashes (UFs) are emissions in the core of chromospheric lines
caused by upward propagating waves steepening into shocks. UFs are
followed by an expanding blueshifted umbral wave and redshifted plasma
returning to the initial state. Here we use 5 s cadence images acquired
at ±0.04 nm off the H ${}_{\alpha }$ line center by the Visible Imaging
Spectrometer installed on the Goode Solar Telescope (GST) to detect
the origin of UFs and umbral waves (UWs) in a sunspot with a uniform
umbra free of light bridges and clusters of umbral dots. The data
showed that UFs do not randomly originate over the umbra. Instead, they
appear to be repeatedly triggered at locations with the lowest umbral
intensity and the most powerful oscillations of H ${}_{\alpha }$ -0.04
nm intensity. GST magnetic field measurements using the Near-Infrared
Imaging Spectropolarimeter also showed that the dominant location of
prevalent UF origin is cospatial associated with the strongest fields
in the umbra. Interface Region Imaging Spectrograph 149.0 nm images
showed that no bright UV loops were anchored in the umbra in general,
and near the UF patches in particular, suggesting that UFs and UWs
alone cannot be responsible for the origin of warm coronal loops. We
thus conclude that the existence of locations with prevalent origin of
UFs confirms the idea that they may be driven by a subsurface source
located near the axis of a flux rope, while the presence of several UFs
trigger centers may indicate the complex structure of a sunspot umbra.
Title: Possible Production of Solar Spicules by Microfilament
Eruptions
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Samanta, Tanmoy;
Yurchyshyn, Vasyl
Bibcode: 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-1
in the jet and ∼20-30 km s-1 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: Physical Characteristics of Umbral Dots Derived from a
High-Resolution Observations
Authors: Kilcik, Ali; Sarp, Volkan; Yurchyshyn, Vasyl; Rozelot,
Jean-Pierre; Ozguc, Atila
Bibcode: 2020SoPh..295...58K
Altcode: 2020arXiv200407687K
The aim of this study is to revisit the physical parameters of
umbral dots (UDs) with the latest high-resolution observations and
contribute to the scientific understanding of their formation and
evolution. In this study, we applied a particle tracking algorithm for
detecting UDs in NOAA AR 12384 observed on June 14, 2015 by the Goode
Solar Telescope (GST). We analyzed average position distributions,
location dependencies, and general properties of the detected total
2892 UDs separately during their life time and the periodic behavior
of ten selected long-lived UDs. We found: i) the brightest, largest,
fastest and most elliptic UDs tend to be located at the umbra-penumbra
boundary while their lifetime does not display any meaningful location
dependency, ii) average dynamic velocity of all detected UDs is about
twice (0.76 km s−1) of the previously reported average
values, iii) obtained trajectories from the longest-lived 354 UDs show
that they have generally inward motion, iv) chosen 10 long-lived UDs
generally have similar periodic behavior showing 8.5 - 32, 3.5 - 4.1,
1.5 - 1.9, and 1.1 - 1.3 minutes periodicities, v) generally, detected
UDs have an elliptical shape with the averaged eccentricity of 0.29,
with a 0.11 standard deviation, vi) larger UDs tend to be more elliptic
and more dynamic.
Title: Rapid Evolution of Type II Spicules Observed in Goode Solar
Telescope On-disk Hα Images
Authors: Yurchyshyn, Vasyl; Cao, Wenda; Abramenko, Valentina; Yang,
Xu; Cho, Kyung-Suk
Bibcode: 2020ApJ...891L..21Y
Altcode: 2020arXiv200504253Y
We analyze ground-based chromospheric data acquired at a high temporal
cadence of 2 s in wings of the Hα spectral line using the
Goode Solar Telescope operating at the Big Bear Solar Observatory. We
inspected a 30 minute long Hα-0.08 nm data set to find
that rapid blueshifted Hα excursions (RBEs), which are a
cool component of type II spicules, experience very rapid morphological
changes on timescales of the order of 1 s. Unlike typical reconnection
jets, RBEs very frequently appear in situ without any clear evidence
of Hα material being injected from below. Their evolution
includes inverted "Y," "V," "N," and parallel splitting (doubling)
patterns as well as sudden formation of a diffuse region followed
by branching. We also find that the same feature may undergo several
splitting episodes within about a 1 minute time interval.
Title: Magnetic Field Dynamics and Varying Plasma Emission in Large
Scale Coronal Loops
Authors: Yurchyshyn, V.; Sahin, S.; Goode, P. R.; Kumar, P.; Kilcik,
A.; Ahn, K.; Yang, X.
Bibcode: 2019AGUFMSH11C3399Y
Altcode:
We studied the evolution of magnetic fields at footpoints of two warm
coronal loops observed on 5 May 2016 in NOAA AR 12542 (Loop I) and
17 Dec 2015 in NOAA AR 12470 (Loop II). These loops were connecting
a plage region with sunspot periphery (Loop I) and a sunspot umbra
(Loop II). We used Solar Dynamics Observatory (SDO) and Goode Solar
Telescope (GST) data to describe the phenomenon and understand its
causes. The study indicates loop brightening episodes were associated
with magnetic flux emergence and cancellation processes observed in
SDO's Helioseismic and Magnetic Imager (HMI) and GST's Near InfraRed
Imaging Spectrapolarimeter (NIRIS) data. The observed activity was
driven by magnetic reconnection between small-scale emerging dipoles
and large-scale pre-existing fields, suggesting that the reconnection
occurred in the lower chromosphere at the edge of an extended plage
region, where the loops were rooted. We suggest that plasma, evaporated
during these reconnection events, gradually filled the loops and as it
cooled the visible density front propagated from one footpoint of the
loop to another at a rate of 90-110 km/s. This study also indicates
that at least some of the bright loops seen in SDO Atmospheric Imaging
Assembly images rooted in sunspot umbra may be heated due to magnetic
activity taking place at the remote (non-sunspot) footpoint.
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
Bibcode: 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: Light Bridge Brightening and Plasma Ejection Driven by a
Magnetic Flux Emergence Event
Authors: Yang, Xu; Yurchyshyn, Vasyl; Ahn, Kwangsu; Penn, Matt;
Cao, Wenda
Bibcode: 2019ApJ...886...64Y
Altcode:
Observations with the Goode Solar Telescope (GST) are presented
here showing that the emergence of 1.91 × 1018 Mx of
new magnetic flux occurred at the edge of a filamentary light bridge
(LB). This emergence was accompanied by brightness enhancement of a
photospheric overturning convection cell (OCC) at the endpoints of the
emerging magnetic structure. We present an analysis of the origin and
the dynamics of this event using high-resolution GST Fe I 1564.85 nm
vector magnetic field data, TiO photospheric, and Hα chromospheric
images. The emerged structure was 1.5 × 0.3 Mm in size at the peak
of development and lasted for 17 minutes. Doppler observations showed
presence of systematic upflows before the appearance of the magnetic
field signal and downflows during the decay phase. Changes in the
orientation of the associated transverse fields, determined from
the differential angle, suggest the emergence of a twisted magnetic
structure. A fan-shaped jet was observed to be spatially and temporally
correlated with the endpoint of the OCC intruding into the LB. Our data
suggest that the emerging fields may have reconnected with the magnetic
fields in the vicinity of the LB, which could lead to the formation of
the jet. Our observation is the first report of flux emergence within
a granular LB with evidence in the evolution of vector magnetic field,
as well as photosphere convection motions, and supports the idea that
the impulsive jets above the LB are caused by magnetic reconnection.
Title: Analysis of the Hemispheric Sunspot Number Time Series for
the Solar Cycles 18 to 24
Authors: Chowdhury, P.; Kilcik, A.; Yurchyshyn, V.; Obridko, V. N.;
Rozelot, J. P.
Bibcode: 2019SoPh..294..142C
Altcode:
In this article, we investigate temporal and periodic variations of the
hemispheric sunspot number using sunspot data from Kanzelhöhe Solar
Observatory (KSO) for the time period of 1944 - 2017, which covers Solar
Cycles 18 to 23 and almost the entire Solar Cycle 24 (2009 - 2017). The
KSO data set was verified against the International Sunspot Number
(ISSN) data. Temporal and periodic variations in the KSO data were
analyzed using cross-correlation analysis, Morlet wavelet and multitaper
(MTM) period analysis methods. We find that: i) sunspot numbers, as
derived from both KSO and ISSN time series, are highly correlated with
one another; ii) the temporal evolution of the sunspot number differs
from one hemisphere to another with the solar cycle peaking at different
times in each hemisphere; iii) the northern hemisphere showed two-
and seven-month lead in Solar Cycles 18 and 19, respectively, while
the southern hemisphere was leading in the rest of the cycles with
the varying lead time ranging from 2 to 14 months; iv) apart from the
fundamental mode of ≈ 11 years, Solar Cycle, the KSO data also show
several midterm variations in the opposite hemispheres, specifically,
Rieger-type and quasi-biennial periodicities - the detected midterm
periodicities also differ in the northern and southern hemispheres;
v) our results confirm the Waldmeier effect, which correlates the rise
time with the cycle amplitude using the new sunspot data set from KSO.
Title: Vortex Formations and Its Associated Surges in a Sunspot
Light Bridge
Authors: Yang, Heesu; Lim, Eun-Kyung; Iijima, Haruhisa; Yurchyshyn,
Vasyl; Cho, Kyung-Suk; Lee, Jeongwoo; Schmieder, Brigitte; Kim,
Yeon-Han; Kim, Sujin; Bong, Su-Chan
Bibcode: 2019ApJ...882..175Y
Altcode:
We report on the successive occurrence of 0.″5 wide photospheric
vortices with strong transverse shear flows at the edge of a sunspot
light bridge (LB), and the subsequent ejection of chromospheric surges
observed using a Visible Inteferometry Spectrograph, a broadband
TiO filter, and a Near InfRared Imaging Spectrograph of the Goode
Solar Telescope operating at Big Bear Solar Observatory. The Hα
surges ejected at the location of the vortices often appeared in
a hollow cylindrical structure. We also observed quasi-periodic
vortex-associated bright Hα plasma blobs moving upward with a speed
of up to 4 km s-1. In view of the strong shear flow at
the edge of the LB, it is likely that the vortices form under the
Kelvin-Helmholtz instability. The surges may result from either the
magnetic tension generated after magnetic reconnection or an acoustic
impulse of a fast photospheric transverse flow. Otherwise, the surges
could also be associated with Alfvénic waves, in which case their
origin could be torsional magnetic fields generated in the process of
the vortex formation.
Title: Cosmic Ray Modulation with the Maximum CME Speed Index During
Solar Cycles 23 and 24
Authors: Sarp, Volkan; Kilcik, Ali; Yurchyshyn, Vasyl; Ozguc, Atila;
Rozelot, Jean-Pierre
Bibcode: 2019SoPh..294...86S
Altcode:
We analyzed modulation of cosmic-ray intensities (CRIs) during
Solar Cycles 23 and 24 by using the international sunspot numbers
(ISSN) and the maximum CME speed index (MCMESI) as proxies for solar
activity. Temporal variations, cross-correlations, and hysteresis
patterns of CRI, MCMESI, and ISSN data were investigated. As a result,
we concluded that the MCMESI better describes solar modulation of the
CRI as compared to the ISSN. This is mainly because the correlation
between CRI and ISSN is caused by the general cyclic trend of solar
activity, while the correlation between the CRI and the MCMESI is
mainly due to short-term fluctuations related to Forbush decreases. In
contrast to the ISSN, there is no time lag between the CRI and the
MCMESI variations.
Title: Magnetic Field Dynamics and Varying Plasma Emission in Large
Scale Coronal Loops
Authors: Yurchyshyn, Vasyl B.; Sahin, Seray; Kumar, Pankaj; Kilcik,
Ali; Ahn, Kwangsu; Yang, Xu
Bibcode: 2019AAS...23431104Y
Altcode:
We report detailed observations of magnetic environment at four
footpoints of two warm coronal loops observed on 5 May 2016 in NOAA
AR 12542 (Loop I) and 17 Dec 2015 in NOAA AR 12470 (Loop II). These
loops were connecting a plage region with sunspot periphery (Loop I)
and a sunspot umbra (Loop II). We used Solar Dynamics Observatory (SDO)
and Goode Solar Telescope (GST) data to describe the phenomenon and
understand its causes. The study indicates loop brightening episodes
were associated with magnetic flux emergence and cancellation processes
observed in SDO's Helioseismic and Magnetic Imager (HMI) and GST's Near
InfraRed Imaging Spectrapolarimeter (NIRIS) data. The observed activity
was driven by magnetic reconnection between small-scale emerging dipoles
and large-scale pre-existing fields, suggesting that the reconnection
occurred in the lower chromosphere at the edge of an extended plage
region, where the loops were rooted. We suggest that plasma, evaporated
during these reconnection events, gradually filled the loops and as it
cooled the visible density front propagated from one footpoint of the
loop to another at a rate of 90-110 km/s. This study also indicates
that at least some of the bright loops seen in SDO Atmospheric Imaging
Assembly images rooted in sunspot umbra may be heated due to magnetic
activity taking place at the remote (non-sunspot) footpoint.
Title: Multi-wavelength Multi-height Study of Super Strong Surface
and Coronal Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Chen, Bin; Jing, Ju; Yu, Sijie; Liu, Chang;
Yurchyshyn, Vasyl B.; Ahn, Kwangsu; Okamoto, Takenori; Toriumi, Shin;
Cao, Wenda; Gary, Dale E.
Bibcode: 2019AAS...23440205W
Altcode:
Using the joint observations of Goode Solar telescope (GST), Expanded
Owens Valley Solar Array (EOVSA), Solar Dynamics Observatory (SDO)
and Hinode, we study the Solar Active Region (AR) 12673 in September
2017, which is the most flare productive AR in the solar cycle 24. GST
observations show the strong photospheric magnetic fields (nearly
6000 G) in polarity inversion line (PIL) and apparent photospheric
twist. Consistent upward flows are also observed in Dopplergrams
of Hinode, HMI and GST at the center part of that section of PIL,
while the down flows are observed in two ends, indicating that the
structure was rising from subsurface. Combining Non-Linear Force Free
Extrapolation and EOVSA microwave imaging spectroscopy, we also look
into the coronal structure of magnetic fields in this unusual AR,
including the evolution before and after the X9.3 flare on September
6, 2017. Coronal fields between 1000 and 2000 gauss are found above
the flaring PIL at the height range between 8 and 4Mm, outlining the
structure of a fluxrope or sheared arcade.
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
Bibcode: 2019shin.confE.194P
Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.
Title: Oscillation of a Small Hα Surge in a Solar Polar Coronal Hole
Authors: Cho, Kyung-Suk; Cho, Il-Hyun; Nakariakov, V. M.; Yurchyshyn,
Vasyl B.; Yang, Heesu; Kim, Yeon-Han; Kumar, Pankaj; Magara, Tetsuya
Bibcode: 2019ApJ...877L...1C
Altcode:
Hα surges (i.e., cool/dense collimated plasma ejections) may act as
a guide for a propagation of magnetohydrodynamic waves. We report
a high-resolution observation of a surge observed with 1.6 m Goode
Solar Telescope (GST) on 2009 August 26, from 18:20 UT to 18:45
UT. Characteristics of plasma motions in the surge are determined
with the normalizing radial gradient filter and the Fourier motion
filter. The shape of the surge is found to change from a “C”
shape to an inverse “C” shape after a formation of a cusp, a
signature of reconnection. There are apparent upflows seen above
the cusp top and downflows below it. The upflows show rising and
rotational motions in the right-hand direction, with the rotational
speed decreasing with height. Near the cusp top, we find a transverse
oscillation of the surge, with the period of ∼2 minutes. There is no
change of the oscillation phase below the cusp top, but above the top
a phase change is identified, giving a vertical phase speed about 86
km s-1. As the height increases, the initial amplitude of
the oscillation increases, and the oscillation damping time decreases
from 5.13 to 1.18 minutes. We conclude that the oscillation is a
propagating kink wave that is possibly excited by the repetitive
spontaneous magnetic reconnection.
Title: Flame-like Ellerman Bombs and Their Connection to Solar
Ultraviolet Bursts
Authors: Chen, Yajie; Tian, Hui; Peter, Hardi; Samanta, Tanmoy;
Yurchyshyn, Vasyl; Wang, Haimin; Cao, Wenda; Wang, Linghua; He, Jiansen
Bibcode: 2019ApJ...875L..30C
Altcode: 2019arXiv190301981C
Ellerman bombs (EBs) are small-scale intense brightenings in Hα
wing images, which are generally believed to be signatures of
magnetic reconnection around the temperature minimum region of the
solar atmosphere. They have a flame-like morphology when observed
near the solar limb. Recent observations from the Interface Region
Imaging Spectrograph (IRIS) reveal another type of small-scale
reconnection event called an ultraviolet (UV) burst, in the lower solar
atmosphere. Though previous observations have shown a clear coincidence
between the occurrence of some UV bursts and EBs, the exact relationship
between these two phenomena is still debated. We investigate the spatial
and temporal relationship between flame-like EBs and UV bursts using
joint near-limb observations between the 1.6 m Goode Solar Telescope
(GST) and IRIS. In total, 161 EBs have been identified from the GST
observations, and ∼20 of them reveal signatures of UV bursts in
the IRIS images. Interestingly, we find that these UV bursts have a
tendency to appear at the upper parts of their associated flame-like
EBs. The intensity variations of most EB-related UV bursts and their
corresponding EBs match well. Our results suggest that some of these
UV bursts and EBs likely form at different heights during a common
reconnection process.
Title: Magnetic Field Dynamics and Varying Plasma Emission in
Large-scale Coronal Loops
Authors: Şahin, S.; Yurchyshyn, V.; Kumar, P.; Kilcik, A.; Ahn, K.;
Yang, X.
Bibcode: 2019ApJ...873...75S
Altcode: 2019arXiv190312148S
In this study we report detailed observations of magnetic environment at
four footpoints of two warm coronal loops observed on 2016 May 5 in NOAA
AR 12542 (Loop I) and 2015 December 17 in NOAA AR 12470 (Loop II). These
loops were connecting a plage region with sunspot periphery (Loop I)
and a sunspot umbra (Loop II). We used Solar Dynamics Observatory (SDO)
and Goode Solar Telescope (GST) data to describe the phenomenon and
understand its causes. The study indicates loop brightening episodes
were associated with magnetic flux emergence and cancellation processes
observed in SDO’s Helioseismic and Magnetic Imager and GST’s Near
InfraRed Imaging Spectrapolarimeter data. The observed activity was
driven by magnetic reconnection between small-scale emerging dipoles
and large-scale pre-existing fields, suggesting that the reconnection
occurred in the lower chromosphere at the edge of an extended plage
region, where the loops were rooted. We suggest that plasma, evaporated
during these reconnection events, gradually filled the loops and as it
cooled the visible density front propagated from one footpoint of the
loop to another at a rate of 90-110 km s-1. This study also
indicates that at least some of the bright loops seen in SDO Atmospheric
Imaging Assembly images rooted in sunspot umbra may be heated due to
magnetic activity taking place at the remote (nonsunspot) footpoint.
Title: Prediction of solar cycle 25: a non-linear approach
Authors: Sarp, V.; Kilcik, A.; Yurchyshyn, V.; Rozelot, J. P.;
Ozguc, A.
Bibcode: 2018MNRAS.481.2981S
Altcode: 2018MNRAS.tmp.2359S
Predicting the solar activity is an important task for space weather
and solar physics. There are various approaches to predict the
solar activity and these predictions are used in various areas such
as planning space missions, approximating the mechanism of solar
dynamo, etc. In this paper, a non-linear prediction algorithm based
on delay-time and phase space reconstruction is used to forecast the
maximum of Solar Cycle 25. Apart from embedding dimension and delay-time
which are the key parameters of such methods, we further found a new
parameter (starting point) that should be taken into account to get
better solar cycle predictions. This method was tested on last five
solar cycles and the results are quite acceptable. We predicted that
the maximum of Solar Cycle 25 will be at the year 2023.2 ± 1.1 with a
peak sunspot number of 154 ± 12. Our results are compared with other
available predictions.
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
Bibcode: 2018A&A...619L...6N
Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.
Title: Magnetic Flux Emergence Triggered Light Bridge Brightening
and Reconnection Jets
Authors: Yang, Xu; Cao, Wenda; Yurchyshyn, Vasyl; Ahn, Kwangsu
Bibcode: 2018cosp...42E3744Y
Altcode:
Light bridges (LBs) are elongated, bright, granular structures that
divide the umbra of a large and complex sunspot into two or more umbral
regions with the same magnetic polarity. Surge-like activities are
common phenomenon appear above the LBs which always accompanied by the
magnetic flux emergence process. Former works tried to interpret the
triggering mechanism for them, however they often lacked the support of
high spatial and temporal resolution vector magnetic measurement. Our
recent Observation shows a strong magnetic flux emergence happened
at the edge of a filamentary Light Bridge (LB) and accompanied by
brightness enhancement of photospheric granulations at the endpoints
of the emerged magnetic structure. We study the origin and dynamics of
this magnetic flux emergence event with high resolution Fe I 1.56 μm
polarimetry magnetogram, TiO photosphere image and Hα chromosphere
image from the Goode Solar Telescope. The emerged magnetic structure
was 1.5 Mm × 0.3 Mm in size at its peak time and lasted for 17
minutes. Doppler map detected upflows before its formation and downflows
during the destruction. The magnetic orientation change was obtained by
calculating the shear angle and plotting the magnetic field vectors. The
result indicates that the new emerged more transverse magnetic field
reconnected with the pre-existing more vertical field, which triggered
the fan-shaped jets. The expanding fields at the endpoints due to the
flux emergence pushed and compressed the existing granulations and
led to their enhanced brightness.
Title: Erupting Solar Magnetic Flux Ropes and the Bz Challenge:
Understanding details of CME propagation in the Interplanetary Media
Authors: Yurchyshyn, Vasyl
Bibcode: 2018cosp...42E3786Y
Altcode:
Understanding the connection between magnetic topologies of a
coronal mass ejection (CME) as observed closer to the Sun and in
the interplanetary medium close to the Earth is vital for successful
predictions of geomagnetic storms. Recent solar and magnetospheric
data convincingly demonstrate that fast CME originating from near
the solar disk center are the major cause of extreme space weather
events. Moreover, topology and helicity of the ejected fields tends
to be mainly preserved as the ejecta propagates and evolves in the
interplanetary space. The interplanetary CME that is often observed near
the Earth as a well organized helical structure called _ a magnetic
cloud (MC) is the result of expansion of the original ejecta and its
interaction with the heliospheric plasma and magnetic fields that
may cause the ejecta to alter its shape, rotate and shed its magnetic
flux. Therefore the probability of a strong geomagnetic storm to occur
as well as its intensity depend on both initial properties of the
erupted structure and the further interactions that the ejecta may be
subjected to as it expands into the heliosphere. Detailed understanding
of this interaction may shed light on the problems related to connecting
solar surface phenomena to their interplanetary counterparts. In this
talk I will briefly review current progress on the CME evolution in
the heliosphere.
Title: The evolution of flaring and non-flaring active regions
Authors: Kilcik, A.; Yurchyshyn, V.; Sahin, S.; Sarp, V.; Obridko,
V.; Ozguc, A.; Rozelot, J. P.
Bibcode: 2018MNRAS.477..293K
Altcode:
According to the modified Zurich classification, sunspot groups are
classified into seven different classes (A, B, C, D, E, F and H) based
on their morphology and evolution. In this classification, classes
A and B, which are small groups, describe the beginning of sunspot
evolution, while classes D, E and F describe the large and evolved
groups. Class C describes the middle phase of sunspot evolution and
the class H describes the end of sunspot evolution. Here, we compare
the lifetime and temporal evolution of flaring and non-flaring active
regions (ARs), and the flaring effect on ARs in these groups in detail
for the last two solar cycles (1996 through 2016). Our main findings
are as follows: (i) Flaring sunspot groups have longer lifetimes
than non-flaring ones. (ii) Most of the class A, B and C flaring
ARs rapidly evolve to higher classes, while this is not applicable
for non-flaring ARs. More than 50 per cent of the flaring A, B and
C groups changed morphologically, while the remaining D, E, F and
H groups did not change remarkably after the flare activity. (iii)
75 per cent of all flaring sunspot groups are large and complex. (iv)
There is a significant increase in the sunspot group area in classes A,
B, C, D and H after flaring activity. In contrast, the sunspot group
area of classes E and F decreased. The sunspot counts of classes D, E
and F decreased as well, while classes A, B, C and H showed an increase.
Title: Signature of a possible relationship between the maximum CME
speed index and the critical frequencies of the F1 and F2 ionospheric
layers: Data analysis for a mid-latitude ionospheric station during
the solar cycles 23 and 24
Authors: Kilcik, Ali; Ozguc, Atila; Yiğit, Erdal; Yurchyshyn, Vasyl;
Donmez, Burcin
Bibcode: 2018JASTP.171..131K
Altcode:
We analyze temporal variations of two solar indices, the monthly
mean Maximum CME Speed Index (MCMESI) and the International Sunspot
Number (ISSN) as well as the monthly median ionospheric critical
frequencies (foF1, and foF2) for the time period of 1996-2013,
which covers the entire solar cycle 23 and the ascending branch of
the cycle 24. We found that the maximum of foF1 and foF2 occurred
respectively during the first and second maximum of the ISSN solar
activity index in the solar cycle 23. We compared these data sets by
using the cross-correlation and hysteresis analysis and found that
both foF1 and foF2 show higher correlation with ISSN than the MCMESI
during the investigated time period, but when significance levels are
considered correlation coefficients between the same indices become
comparable. Cross-correlation analysis showed that the agreement between
these data sets (solar indices and ionospheric critical frequencies)
is better pronounced during the ascending phases of solar cycles, while
they display significant deviations during the descending phase. We
conclude that there exists a signature of a possible relationship
between MCMESI and foF1 and foF2, which means that MCMESI could be
used as a possible indicator of solar and geomagnetic activity, even
though other investigations are needed.
Title: High-resolution Observations of a White-light Flare with
Goode Solar Telescope
Authors: Yurchyshyn, Vasyl; Kumar, Pankaj; Abramenko, Valentyna; Xu,
Yan; Goode, Philip R.; Cho, Kyung-Suk F.
Bibcode: 2018tess.conf21702Y
Altcode:
Using high resolution data from the Goode Solar Telescope (GST)
we studied the fine spatial and temporal structure of an M1.3 white
light (WL) flare, which was one of the three homologous solar flares
(C6.8, M1.3, and M2.3) observed in a close proximity to the west solar
limb. The RHESSI photon spectra for the M1.3 flare showed strongly
accelerated electrons with energies above 100 keV. Comparison of
HXR photon spectra for the three flares suggests that either thermal
energy of order of 1030 ergs and/or high energy electrons
(>50 keV) are necessary to produce a WL flare. The strong and
compact WL cores were ≈0.15 Mm across with an area of about
1014 cm2 . The observed TiO enhancements are
not normally distributed and are structured by the magnetic field of
the penumbra. Several of the TiO cores were not co-spatial with the Hα
emission, which suggests that the TiO and chromospheric emission did not
originate in the same chromospheric volume as some models suggest. We
thus conclude that fine temporal and spatial structure of the WL flare
was largely defined by the associated magnetic fields, which favors
the direct heating models, where the flare energy is directly deposited
in the temperature minimum region by the accelerated electrons.
Title: Observation of Light Bridge Brightening and Plasma Ejection
Triggered by a Magnetic Flux Emergence Event
Authors: Yang, Xu; Yurchyshyn, Vasyl; Ahn, Kwangsu; Cao, Wenda
Bibcode: 2018tess.conf10906Y
Altcode:
Light bridges (LBs) are elongated, bright, granular structures that
divide the umbra of a large and complex sunspot into two or more umbral
regions with the same magnetic polarity. Surge-like activities are
common phenomenon appear above the LBs which always accompanied by the
magnetic flux emergence process. Former works tried to interpret the
triggering mechanism for them, however they often lacked the support of
high spatial and temporal resolution vector magnetic measurement. Our
recent Observation shows a strong magnetic flux emergence happened
at the edge of a filamentary Light Bridge (LB) and accompanied by
brightness enhancement of photospheric granulations at the endpoints
of the emerged magnetic structure. We study the origin and dynamics of
this magnetic flux emergence event with high resolution Fe I 1.56 μm
polarimetry magnetogram, TiO photosphere image and Hα chromosphere
image from the Goode Solar Telescope. The emerged magnetic structure
was 1.5 Mm × 0.3 Mm in size at its peak time and lasted for 17
minutes. Doppler map detected upflows before its formation and downflows
during the destruction. The magnetic orientation change was obtained by
calculating the shear angle and plotting the magnetic field vectors. The
result indicates that the new emerged more transverse magnetic field
reconnected with the pre-existing more vertical field, which triggered
the fan-shaped jets. The expanding fields at the endpoints due to the
flux emergence pushed and compressed the existing granulations and
led to their enhanced brightness.
Title: Study of 3D magnetic Structure Corresponding to Extremely
Strong Photospheric Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Chen, Bin;
Jing, Ju; Ahn, Kwangsu; Toriumi, Shin; Cao, Wenda
Bibcode: 2018tess.conf31902W
Altcode:
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emission. Yang et al. (2017)
described the detailed morphological evolution of this AR. In this work,
we first study the unusual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and the apparent photospheric twist as seen in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
Goode Solar Telescope (GST) at the Big Bear Solar Observatory. Using the
newly commissioned Expanded Owens Valley Solar Array (EOVSA), we carried
out diagnoses of magnetic fields in this AR with microwave imaging
spectroscopy from 2.5 to 18 GHz. Finally, we utilized Non-Linear Force
Free Field (NLFFF) extrapolation to reveal 3-D magnetic structure to
gain a physical understanding of GST and EOVSA observations of this AR.
Title: The evolution of a small complex active region AR 12550
observed by the GST
Authors: Kim, Yeon-Han; Xu, Yan; Yurchyshyn, Vasyl; Lim, Eun-Kyung
Bibcode: 2018EGUGA..2013133K
Altcode:
The 1.6m Goode Solar Telescope (GST: formerly NST) at Big Bear Solar
Observatory (BBSO) provides us with unprecedented high-resolution
data of the Sun since 2009. On 2016 May 30, we observed a small
complex active region AR 12550 using the GST equipped with the He I D3
filter, the photospheric broadband filter (G-band), and Near IR imaging
spectrograph (NIRIS). This active region showed a small loop eruption
in He I D3 images associated with several B class brightenings from
17:00 UT to 18:00 UT and dynamic variations of photospheric features
in G-band and NIRIS images. Additionally, we examined the SDO data
and found several brightenings and loop activities in the higher
temperature plasmas. Interestingly, the loop activities appeared as
dark features in D3 images and did as bright ones in SDO data. In
order to interpret both data, we performed DEM analysis using SDO AIA
data. In this presentation, we will describe the whole evolution of
the AR 12550 and give the observation results.
Title: Temporal and Periodic Variations of Sunspot Counts in Flaring
and Non-Flaring Active Regions
Authors: Kilcik, A.; Yurchyshyn, V.; Donmez, B.; Obridko, V. N.;
Ozguc, A.; Rozelot, J. P.
Bibcode: 2018SoPh..293...63K
Altcode: 2017arXiv170509065K
We analyzed temporal and periodic variations of sunspot counts (SSCs)
in flaring (C-, M-, or X-class flares), and non-flaring active regions
(ARs) for nearly three solar cycles (1986 through 2016). Our main
findings are as follows: i) temporal variations of monthly means of
the daily total SSCs in flaring and non-flaring ARs behave differently
during a solar cycle and the behavior varies from one cycle to another;
during Solar Cycle 23 temporal SSC profiles of non-flaring ARs are wider
than those of flaring ARs, while they are almost the same during Solar
Cycle 22 and the current Cycle 24. The SSC profiles show a multi-peak
structure and the second peak of flaring ARs dominates the current
Cycle 24, while the difference between peaks is less pronounced during
Solar Cycles 22 and 23. The first and second SSC peaks of non-flaring
ARs have comparable magnitude in the current solar cycle, while the
first peak is nearly absent in the case of the flaring ARs of the same
cycle. ii) Periodic variations observed in the SSCs profiles of flaring
and non-flaring ARs derived from the multi-taper method (MTM) spectrum
and wavelet scalograms are quite different as well, and they vary from
one solar cycle to another. The largest detected period in flaring
ARs is 113 ±1.6 days while we detected much longer periodicities (327
±13 , 312 ±11 , and 256 ±8 days) in the non-flaring AR profiles. No
meaningful periodicities were detected in the MTM spectrum of flaring
ARs exceeding 55 ±0.7 days during Solar Cycles 22 and 24, while a 113
±1.3 days period was detected in flaring ARs of Solar Cycle 23. For
the non-flaring ARs the largest detected period was only 31 ±0.2
days for Cycle 22 and 72 ±1.3 days for the current Cycle 24, while
the largest measured period was 327 ±13 days during Solar Cycle 23.
Title: Frequently Occurring Reconnection Jets from Sunspot Light
Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
Linghua; Chen, Yajie
Bibcode: 2018ApJ...854...92T
Altcode: 2018arXiv180106802T
Solid evidence of magnetic reconnection is rarely reported within
sunspots, the darkest regions with the strongest magnetic fields
and lowest temperatures in the solar atmosphere. Using the world’s
largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
prevalent reconnection through frequently occurring fine-scale jets
in the Hα line wings at light bridges, the bright lanes that may
divide the dark sunspot core into multiple parts. Many jets have an
inverted Y-shape, shown by models to be typical of reconnection in a
unipolar field environment. Simultaneous spectral imaging data from
the Interface Region Imaging Spectrograph show that the reconnection
drives bidirectional flows up to 200 km s-1, and that the
weakly ionized plasma is heated by at least an order of magnitude up
to ∼80,000 K. Such highly dynamic reconnection jets and efficient
heating should be properly accounted for in future modeling efforts
of sunspots. Our observations also reveal that the surge-like activity
previously reported above light bridges in some chromospheric passbands
such as the Hα core has two components: the ever-present short surges
likely to be related to the upward leakage of magnetoacoustic waves
from the photosphere, and the occasionally occurring long and fast
surges that are obviously caused by the intermittent reconnection jets.
Title: Strong Transverse Photosphere Magnetic Fields and Twist in
Light Bridge Dividing Delta Sunspot of Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Ahn, Kwangsu;
Toriumi, Shin; Cao, Wenda
Bibcode: 2018RNAAS...2....8W
Altcode: 2018RNAAS...2a...8W; 2018arXiv180102928W
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emissions. Yang at al. (2017)
described the detailed morphological evolution of this AR. In this
report, we focus on usual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and apparent photospheric twist as shown in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
telescope at Big Bear Solar Observatory.
Title: Problem of Super-Strong Magnetic Fields on the Sun: Brief
Chronology and New Observational Data
Authors: Lozitsky, V. G.; Yurchyshyn, V. B.; Ahn, K.; Wang, H.;
Lozitska, N. I.
Bibcode: 2018OAP....31..152L
Altcode:
In this study we present the old and new observational data
concerning the problem of extreme magnetic fields (≥ 5 kG)
in the Sun's atmosphere. We emphasize that the upper limit of the
intensity of the magnetic field in the solar atmosphere is unknown to
date. Severny (1957) heuristically suggested that the magnetic fields
in the sunspots could reach 50 kG. As for the observational data, at
least three arguments in favor of the magnetic fields of the order
of ≤104 G can be specified: (1) the dependence of the
measured magnetic field on the factor geffλ2
of magnetosensitive lines (Gopasyuk et al., 1973; Lozitsky, 1980),
(2) local extremums in splitting of bisectors in the profiles I
± V for lines with different Lande factors (Lozitsky, 1980; 2015)
and (3) the reliable splitting of emission peaks in Fe I lines with
very low Lande factors, about 0.01, in the spectra of powerful solar
flares (Lozitsky, 1993; 1998). Theoretically, superstrong fields
should have gigantic magnetic pressure and can exist only with a
specific topology of field lines, apparently of a force-free type
(Soloviev and Lozitsky, 1986). To further develop this problem,
we are analyzing new observational data obtained with the NIRIS
spectropolarimeter of the largest GST solar telescope of the Big Bear
Solar Observatory (BBSO). Our observations relate to the active region
NOAA 12673, which was the most flare-productive in the 24th
cycle. Stokes-metric measurements are made in the FeI 15648.5 Å line
with a signal-to-noise ratio of about 10-4. In this active
region, superstrong magnetic field of 5.57 kG was discovered recently by
Wang et al. (2018). An additional study of about 70 different places in
this active region suggested that there were two types of places that
can be conventionally called "typical" and "peculiar". In "typical"
areas, the magnitude of the magnetic field in general is the greater,
the less the intensity in the spectral continuum, and the maximum field
here does not exceed 4 kG. All "peculiar" places correspond to positions
with the highest intensity in the spectral continuum, and the magnetic
field strength is here in the range of 3.0-5.7 kG. Notice, such strong
magnetic fields were firstly discovered outside the sunspot umbra. The
orientation of the magnetic field vector in "peculiar" places is close
to the transversal, which is also atypical for "typical" regions and
can reflect strong twisting of field lines.
Title: Multi-wavelength Observation of Filament Eruption associated
with M-class Flare
Authors: Kim, S.; Yurchyshyn, V.; Jiang, C.
Bibcode: 2017AGUFMSH41A2748K
Altcode:
We have investigated a M-class flare associated with filament eruption
which developed into a Halo CME. The M-class flare occurred in 2011
August 4. For this study, we used the Nobryama Radioheliograph (NoRH)
17 and 34 GHz, RHESSI Hard X-ray satellite, and Atmo- spheric Imaging
Assembly (AIA) and the Heliospheric Magentic Imager(HMI) onboard the
Solar Dynamic Observatory (SDO). During the pre-eruption phase, clear
nonthermal emission was detected in microwaves of NoRH and hard-X-ray
of RHESSI. At the moment that the nonthermal emission start, the
nonthermal sources appeared at the one edge of the filament structure on
a polarity inversion line, and the slowing rising filament structure in
AIA 94A underwent a sudden acceleration on its ascendance. Magnetograms
showed converging motion of magnetic elements at the source position
of HXR and MW. Based on the results, we conjecture that the plausible
trigger of the filament eruption is magnetic reconnections at the HXR
source position by converging motion of magnetic elements. In addition,
we will discuss on the magnetic flux variation before and after the
eruption based on the result of Nonlinear force-free field model.
Title: Observation of a Large-scale Quasi-circular Secondary Ribbon
Associated with Successive Flares and a Halo CME
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Kumar, Pankaj; Cho,
Kyuhyoun; Jiang, Chaowei; Kim, Sujin; Yang, Heesu; Chae, Jongchul;
Cho, Kyung-Suk; Lee, Jeongwoo
Bibcode: 2017ApJ...850..167L
Altcode: 2017arXiv171100622L
Solar flare ribbons provide an important clue to the magnetic
reconnection process and associated magnetic field topology in the
solar corona. We detected a large-scale secondary flare ribbon of
a circular shape that developed in association with two successive
M-class flares and one coronal mass ejection. The ribbon revealed
interesting properties such as (1) a quasi-circular shape and enclosing
the central active region (AR); (2) the size as large as 500″ by
650″ (3) successive brightenings in the clockwise direction at a
speed of 160 km s-1 starting from the nearest position to
the flaring sunspots; (4) radial contraction and expansion in the
northern and the southern part, respectively, at speeds of ≤10
km s-1. Using multi-wavelength data from Solar Dynamics
Observatory, RHESSI, XRT, and Nobeyama, along with magnetic field
extrapolations, we found that: (1) the secondary ribbon location is
consistent with those of the field line footpoints of a fan-shaped
magnetic structure that connects the flaring region and the ambient
decaying field; (2) the second M2.6 flare occurred when the expanding
coronal loops driven by the first M2.0 flare encountered the background
decayed field; (3) immediately after the second flare, the secondary
ribbon developed along with dimming regions. Based on our findings,
we suggest that interaction between the expanding sigmoid field and
the overlying fan-shaped field triggered the secondary reconnection
that resulted in the field opening and formation of the quasi-circular
secondary ribbon. We thus conclude that interaction between the AR and
the ambient large-scale fields should be taken into account to fully
understand the entire eruption process.
Title: Three-minute Sunspot Oscillations Driven by Magnetic
Reconnection in a Light Bridge
Authors: Song, Donguk; Chae, Jongchul; Kwak, Hannah; Kano, Ryouhei;
Yurchyshyn, Vasyl; Moon, Yong-Jae; Lim, Eun-Kyung; Lee, Jeongwoo
Bibcode: 2017ApJ...850L..33S
Altcode: 2017arXiv171106489S
We report a different type of three-minute chromospheric oscillation
above a sunspot in association with a small-scale impulsive event
in a light bridge (LB). During our observations, we found a transient
brightening in the LB. The brightening was composed of elementary bursts
that may be a manifestation of fast repetitive magnetic reconnections
in the LB. Interestingly, the oscillations in the nearby sunspot umbra
were impulsively excited when the intensity of the brightening reached
its peak. The initial period of the oscillations was about 2.3 minutes
and then gradually increased to 3.0 minutes with time. In addition,
we found that the amplitude of the excited oscillations was twice the
amplitude of oscillations before the brightening. Based on our results,
we propose that magnetic reconnection occurring in an LB can excite
oscillations in the nearby sunspot umbra.
Title: Contribution to the Solar Mean Magnetic Field from Different
Solar Regions
Authors: Kutsenko, A. S.; Abramenko, V. I.; Yurchyshyn, V. B.
Bibcode: 2017SoPh..292..121K
Altcode: 2017arXiv170705971K
Seven-year-long seeing-free observations of solar magnetic fields
with the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) were used to study the sources of the solar
mean magnetic field, SMMF, defined as the net line-of-sight magnetic
flux divided over the solar disk area. To evaluate the contribution
of different regions to the SMMF, we separated all the pixels of
each SDO/HMI magnetogram into three subsets: weak (BW),
intermediate (BI), and strong (BS) fields. The
BW component represents areas with magnetic flux densities
below the chosen threshold; the BI component is mainly
represented by network fields, remains of decayed active regions (ARs),
and ephemeral regions. The BS component consists of magnetic
elements in ARs. To derive the contribution of a subset to the total
SMMF, the linear regression coefficients between the corresponding
component and the SMMF were calculated. We found that i) when the
threshold level of 30 Mx cm−2 is applied, the BI
and BS components together contribute from 65% to 95% of the
SMMF, while the fraction of the occupied area varies in a range of 2 -
6% of the disk area; ii) as the threshold magnitude is lowered to 6 Mx
cm−2, the contribution from BI+BS
grows to 98%, and the fraction of the occupied area reaches a value
of about 40% of the solar disk. In summary, we found that regardless
of the threshold level, only a small part of the solar disk area
contributes to the SMMF. This means that the photospheric magnetic
structure is an intermittent inherently porous medium, resembling a
percolation cluster. These findings suggest that the long-standing
concept that continuous vast unipolar areas on the solar surface are
the source of the SMMF may need to be reconsidered.
Title: Multi-wavelength Observation of M-class Flare associated with
Filament eruption
Authors: Kim, Sujin; Yurchyshyn, Vasyl B.; Jiang, Chaowei; Cho,
Kyung-Suk
Bibcode: 2017SPD....4810822K
Altcode:
We have investigated a M-class flare associated with filament eruption
which developed into a Halo CME. The M-class flare occurred in 2011
August 4. For this study, we used the Nobryama Radioheliograph (NoRH)
17 and 34 GHz, RHESSI Hard X-ray satellite, and Atmo- spheric Imaging
Assembly (AIA) and the Heliospheric Magentic Imager(HMI) onboard the
Solar Dynamic Observatory (SDO). During the pre-eruption phase, clear
nonthermal emission was detected in microwaves of NoRH and hard-X-ray
of RHESSI. At the moment that the nonthermal emission start, the
nonthermal sources appeared at the one edge of the filament structure on
a polarity inversion line, and the slowing rising filament structure in
AIA 94A underwent a sudden acceleration on its ascendance. Magnetograms
showed converging motion of magnetic elements at the source position
of HXR and MW. Based on the results, we conjecture that the plausible
trigger of the filament eruption is magnetic reconnections at the HXR
source position by converging motion of magnetic elements. In addition,
we will discuss on the magnetic flux variation before and after the
eruption based on the result of Nonlinear force-free field model.
Title: The NST observation of a small loop eruption in He I D3 line
on 2016 May 30
Authors: Kim, Yeon-Han; Xu, Yan; Bong, Su-Chan; Lim, Eunkyung; Yang,
Heesu; Park, Young-Deuk; Yurchyshyn, Vasyl B.; Ahn, Kwangsu; Goode,
Philip R.
Bibcode: 2017SPD....4810505K
Altcode:
Since the He I D3 line has a unique response to a flare impact on the
low solar atmosphere, it can be a powerful diagnostic tool for energy
transport processes. In order to obtain comprehensive data sets for
studying solar flare activities in D3 spectral line, we performed
observations for several days using the 1.6m New Solar Telescope of
Big Bear Solar Observatory (BBSO) in 2015 and 2016, equipped with
the He I D3 filter, the photospheric broadband filter, and Near IR
imaging spectrograph (NIRIS). On 2016 May 30, we observed a small
loop eruption in He I D3 images associated with a B class brightening,
which is occurred around 17:10 UT in a small active region, and dynamic
variations of photospheric features in G-band images. Accordingly,
the cause of the loop eruption can be magnetic reconnection driven by
photospheric plasma motions. In this presentation, we will give the
observation results and the interpretation.
Title: Multiwavelength observations of a flux rope formation by
series of magnetic reconnection in the chromosphere
Authors: Kumar, Pankaj; Yurchyshyn, Vasyl; Cho, Kyung-Suk; Wang, Haimin
Bibcode: 2017A&A...603A..36K
Altcode: 2017arXiv170309871K
Using high-resolution observations from the 1.6 m New Solar Telescope
(NST) operating at the Big Bear Solar Observatory (BBSO), we report
direct evidence of merging and reconnection of cool Hα loops in the
chromosphere during two homologous flares (B and C class) caused by a
shear motion at the footpoints of two loops. The reconnection between
these loops caused the formation of an unstable flux rope that showed
counterclockwise rotation. The flux rope could not reach the height of
torus instability and failed to form a coronal mass ejection. The HMI
magnetograms revealed rotation of the negative and positive (N1/P2)
polarity sunspots in the opposite directions, which increased the
right- and left-handed twist in the magnetic structures rooted at
N1/P2. Rapid photospheric flux cancellation (duration 20-30 min,
rate ≈3.44 × 1020 Mx h-1) was observed
during and even after the first B6.0 flare and continued until
the end of the second C2.3 flare. The RHESSI X-ray sources were
located at the site of the loop coalescence. To the best of our
knowledge, such a clear interaction of chromospheric loops along
with rapid flux cancellation has not been reported before. These
high-resolution observations suggest the formation of a small flux
rope by a series of magnetic reconnections within chromospheric
loops that are associated with very rapid flux cancellation. Movies attached to Figs. 2, 7, 8, and 10 are available at http://www.aanda.org
Title: Analysis of the Flux Growth Rate in Emerging Active Regions
on the Sun
Authors: Abramenko, V. I.; Kutsenko, A. S.; Tikhonova, O. I.;
Yurchyshyn, V. B.
Bibcode: 2017SoPh..292...48A
Altcode: 2017arXiv170300739A
We studied the emergence process of 42 active regions (ARs) by analyzing
the time derivative, R (t ), of the total unsigned flux. Line-of-sight
magnetograms acquired by the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) were used. A continuous
piecewise linear fitting to the R (t )-profile was applied to detect
an interval, Δ t2, of nearly constant R (t ) covering
one or several local maxima. The magnitude of R (t ) averaged over Δ
t2 was accepted as an estimate of the maximum value of the
flux growth rate, RMAX, which varies in a range of (0.5 -5
)×1020Mxhour−1 for ARs with a maximum total
unsigned flux of (0.5 -3 )×1022Mx. The normalized flux
growth rate, RN, was defined under the assumption that the
saturated total unsigned flux, FMAX, equals unity. Out of 42
ARs in our initial list, 36 events were successfully fitted, and they
form two subsets (with a small overlap of eight events): the ARs with
a short (<13 hours) interval Δ t2 and a high (>0.024
hour−1) normalized flux emergence rate, RN,
form the "rapid" emergence event subset. The second subset consists of
"gradual" emergence events, and it is characterized by a long (>13
hours) interval Δ t2 and a low RN (<0.024
hour−1). In diagrams of RMAX plotted versus
FMAX, the events from different subsets do not overlap,
and each subset displays an individual power law. The power-law index
derived from the entire ensemble of 36 events is 0.69 ±0.10 . The
rapid emergence is consistent with a two-step emergence process of a
single twisted flux tube. The gradual emergence is possibly related
to a consecutive rising of several flux tubes emerging at nearly the
same location in the photosphere.
Title: Impact of the Icme-Earth Geometry on the Strength of the
Associated Geomagnetic Storm: The September 2014 and March 2015 Events
Authors: Cho, K. S.; Marubashi, K.; Kim, R. S.; Park, S. H.; Lim,
E. K.; Kim, S. J.; Kumar, P.; Yurchyshyn, V.; Moon, Y. J.; Lee, J. O.
Bibcode: 2017JKAS...50...29C
Altcode:
No abstract at ADS
Title: High-resolution Observations of a White-light Flare with NST
Authors: Yurchyshyn, V.; Kumar, P.; Abramenko, V.; Xu, Y.; Goode,
P. R.; Cho, K. -S.; Lim, E. -K.
Bibcode: 2017ApJ...838...32Y
Altcode:
Using high-resolution data from the New Solar Telescope, we studied
fine spatial and temporal details of an M1.3 white-light (WL) flare,
which was one of three homologous solar flares (C6.8, M1.3, and M2.3)
observed in close proximity to the west solar limb on 2014 October 29
in NOAA active region 12192. We report that the TiO WL flare consists of
compact and intense cores surrounded by less intense spatial halos. The
strong and compact WL cores were measured to be ≈ 0.2 Mm across,
with an area of about 1014 cm2. Several TiO
features were not cospatial with Hα flare ribbons and were displaced
toward the disk center by about 500 km, which suggests that the TiO
and Hα radiation probably did not originate in the same chromospheric
volume. The observed TiO intensity enhancements are not normally
distributed and are structured by the magnetic field of the penumbra.
Title: Photospheric Origin of Three-minute Oscillations in a Sunspot
Authors: Chae, Jongchul; Lee, Jeongwoo; Cho, Kyuhyoun; Song, Donguk;
Cho, Kyungsuk; Yurchyshyn, Vasyl
Bibcode: 2017ApJ...836...18C
Altcode:
The origin of the three-minute oscillations of intensity and velocity
observed in the chromosphere of sunspot umbrae is still unclear. We
investigated the spatio-spectral properties of the 3 minute oscillations
of velocity in the photosphere of a sunspot umbra as well as those
in the low chromosphere using the spectral data of the Ni I λ5436,
Fe I λ5435, and Na I D2 λ5890 lines taken by the Fast
Imaging Solar Spectrograph of the 1.6 m New Solar Telescope at the Big
Bear Solar Observatory. As a result, we found a local enhancement of
the 3 minute oscillation power in the vicinities of a light bridge
(LB) and numerous umbral dots (UDs) in the photosphere. These
3 minute oscillations occurred independently of the 5 minute
oscillations. Through wavelet analysis, we determined the amplitudes
and phases of the 3 minute oscillations at the formation heights of the
spectral lines, and they were found to be consistent with the upwardly
propagating slow magnetoacoustic waves in the photosphere with energy
flux large enough to explain the chromospheric oscillations. Our results
suggest that the 3 minute chromospheric oscillations in this sunspot may
have been generated by magnetoconvection occurring in the LB and UDs.
Title: Flare-production potential associated with different sunspot
groups
Authors: Eren, S.; Kilcik, A.; Atay, T.; Miteva, R.; Yurchyshyn, V.;
Rozelot, J. P.; Ozguc, A.
Bibcode: 2017MNRAS.465...68E
Altcode:
In this study, we analysed different types (C, M, and X classes)
of X-ray solar flares occurring in sunspot groups. The data cover
1996-2014 time interval, and a total of 4262 active regions (ARs)
were included in the data set. We defined the solar-flare-production
potential as the ratio of the total number of flares observed in a
sunspot group to the total number of the same-class sunspot groups. Our
main findings are as follows: (1) large and complex sunspot groups
(D+E+F) have the flare-production potential about eight times higher
than the small and simple (A+B+C+H) ARs; (2) 79 per cent of all flares
were produced by the large and complex sunspot groups, while only 21 per
cent of flares were produced by the small groups; (3) the largest and
the most complex F-class (very large and very complex) sunspot groups
exhibit the highest flare-production potential (2.16 flare per sunspot
group), while the smallest and the least complex A class sunspot groups
show the lowest (0.05 flare per group) flare-production potential;
(4) temporal variation of sunspot counts, sunspot group areas, and the
total number of flares (including C flares) showed similar time profiles
during both cycles with multiple peaks; (5) the mean area of ARs very
well describes the flare-production potential of each group with the
regression coefficient of <italic>R2</italic>
= 0.99. Most of these sunspot groups (>70 per cent) are, according
to the Zurich Classification, complex ARs.
Title: Chromospheric Plasma Ejections in a Light Bridge of a Sunspot
Authors: Song, Donguk; Chae, Jongchul; Yurchyshyn, Vasyl; Lim,
Eun-Kyung; Cho, Kyung-Suk; Yang, Heesu; Cho, Kyuhyoun; Kwak, Hannah
Bibcode: 2017ApJ...835..240S
Altcode: 2017arXiv170106808S
It is well-known that light bridges (LBs) inside a sunspot produce
small-scale plasma ejections and transient brightenings in the
chromosphere, but the nature and origin of such phenomena are still
unclear. Utilizing the high-spatial and high-temporal resolution
spectral data taken with the Fast Imaging Solar Spectrograph
and the TiO 7057 Å broadband filter images installed at the 1.6
m New Solar Telescope of Big Bear Solar Observatory, we report
arcsecond-scale chromospheric plasma ejections (1.″7) inside a
LB. Interestingly, the ejections are found to be a manifestation of
upwardly propagating shock waves as evidenced by the sawtooth patterns
seen in the temporal-spectral plots of the Ca II 8542 Å and Hα
intensities. We also found a fine-scale photospheric pattern (1″)
diverging with a speed of about 2 km s-1 two minutes before
the plasma ejections, which seems to be a manifestation of magnetic
flux emergence. As a response to the plasma ejections, the corona
displayed small-scale transient brightenings. Based on our findings,
we suggest that the shock waves can be excited by the local disturbance
caused by magnetic reconnection between the emerging flux inside the
LB and the adjacent umbral magnetic field. The disturbance generates
slow-mode waves, which soon develop into shock waves, and manifest
themselves as the arcsecond-scale plasma ejections. It also appears
that the dissipation of mechanical energy in the shock waves can heat
the local corona.
Title: Solar and Geomagnetic Activity Relation for the Last two
Solar Cycles
Authors: Kilcik, A.; Yiǧit, E.; Yurchyshyn, V.; Ozguc, A.; Rozelot,
J. P.
Bibcode: 2017SunGe..12...31K
Altcode:
The long-term relationship between solar (sunspot counts in different
Zurich sunspot groups, International Sunspot Number (ISSN), solar wind,
and X-Ray solar flare index and geomagnetic indices (Ap and Dst)
is investigated. Data sets used in this study cover a time period
from January 1996 to March 2014. Our main findings are as follows: 1)
The best correlation between the sunspot counts and the Ap index are
obtained for the large group time series, while the other categories
exhibited lower (final and medium) or no correlation at all (small). It
is interesting to note that Ap index is delayed by about 13 months
relatively to all sunspot count series and ISSN data. 2) The best
correlation between the sunspot counts and the Dst index was as well
obtained for the large AR time series. The Dst index delays with respect
to the large group by about 2 months. 3) The highest correlation between
the solar and geomagnetic indices were obtained between the solar wind
speed and Ap and Dst indices with zero time delays (r = 0.76, r = 0.52,
respectively). 4) The correlation coefficients between the geomagnetic
indices (Ap, Dst) and X-Ray solar flare index (r = 0.59, r = -0.48,
respectively) are a little higher than the correlation coefficients
between these geomagnetic indices and ISSN (r = 0.57, r = -0.43,
respectively). 5) The magnitude of all solar and geomagnetic indices
(except the solar wind speed) has significantly decreased during the
current solar cycle as compared to the same phase of the previous cycle.
Title: Pre-eruption Oscillations in Thin and Long Features in a
Quiescent Filament
Authors: Joshi, Anand D.; Hanaoka, Yoichiro; Suematsu, Yoshinori;
Morita, Satoshi; Yurchyshyn, Vasyl; Cho, Kyung-Suk
Bibcode: 2016ApJ...833..243J
Altcode: 2016arXiv161204917J
We investigate the eruption of a quiescent filament located close to
an active region. Large-scale activation was observed in only half of
the filament in the form of pre-eruption oscillations. Consequently
only this half erupted nearly 30 hr after the oscillations
commenced. Time-slice diagrams of 171 Å images from the Atmospheric
Imaging Assembly were used to study the oscillations. These were
observed in several thin and long features connecting the filament
spine to the chromosphere below. This study traces the origin of
such features and proposes their possible interpretation. Small-scale
magnetic flux cancellation accompanied by a brightening was observed
at the footpoint of the features shortly before their appearance, in
images recorded by the Helioseismic and Magnetic Imager. A slow rise of
the filament was detected in addition to the oscillations, indicating
a gradual loss of equilibrium. Our analysis indicates that a change in
magnetic field connectivity between two neighbouring active regions
and the quiescent filament resulted in a weakening of the overlying
arcade of the filament, leading to its eruption. It is also suggested
that the oscillating features are filament barbs, and the oscillations
are a manifestation during the pre-eruption phase of the filaments.
Title: Sub-Pixel Magnetic Field Dynamics Derived from Photospheric
Spectral Line Profiles
Authors: Rasca, A.; Chen, J.; Pevtsov, A. A.; Yurchyshyn, V.;
Bertello, L.
Bibcode: 2016AGUFMSH13C2308R
Altcode:
Current high-resolution observations of the photosphere show
small dynamic features at the resolving limit during emerging flux
events. However, line-of-sight (LOS) magnetogram pixels only contain
the net uncanceled magnetic flux, which is expected to increase
for fixed regions as resolution limits improve. Using a new method
with spectrographic images, we quantify distortions in photospheric
absorption (or emission) lines caused by sub-pixel magnetic field and
plasma dynamics in the vicinity of active regions and emerging flux
events. Absorption lines—quantified by their displacement, width,
asymmetry, and peakedness—have previously been used with Stokes
I images from SOLIS/VSM to relate line distortions with sub-pixel
plasma dynamics driven by solar flares or small-scale flux ropes. The
method is extended to include the full Stokes parameters and relate
inferred sub-pixel dynamics with small-scale magnetic fields. Our
analysis is performed on several sets of spectrographic images taken
by SOLIS/VSM and NST/NIRIS while observing eruptive and non-eruptive
active regions. We discuss the results of this application and their
relevance for understanding magnetic fields signatures and coupled
plasma properties on sub-pixel scales.
Title: How did a Major Confined Flare Occur in Super Solar Active
Region 12192?
Authors: Jiang, C.; Wu, S. T.; Yurchyshyn, V.; Wang, H.; Feng, X. S.;
Hu, Q.
Bibcode: 2016AGUFMSH12B..04J
Altcode:
We study the physical mechanism of a major X-class solar flare
that occurred in the super NOAA active region (AR) 12192 using a
data-driven numerical magnetohydrodynamic (MHD) modeling complemented
with observations. With the evolving magnetic fields observed at the
solar surface as bottom boundary input, we drive an MHD system to
evolve self-consistently in correspondence with the realistic coronal
evolution. During a two-day time interval, the modeled coronal field
has been slowly stressed by the photospheric field evolution,which
gradually created a large-scale coronal current sheet, i.e., a narrow
layer with intense current, in the core of the AR. The current layer
was successively enhanced until it became so thin that a tether-cutting
reconnection between the sheared magnetic arcades was set in, which led
to a flare. The modeled reconnecting field lines and their footpoints
match well the observed hot flaring loops and the flare ribbons,
respectively, suggesting that the model has successfully "reproduced"
the macroscopic magnetic process of the flare. In particular, with
simulation, we explained why this event is a confined eruption-the
consequent of the reconnection is the shared arcade instead of a newly
formed flux rope. We also found much weaker magnetic implosion effect
comparing to many other X-class flares.
Title: Pre-Eruption Oscillations in Quiescent Filament Observed in
AIA 171 Å
Authors: Joshi, Anand D.; Yurchyshyn, Vasyl; Cho, Kyung-Suk
Bibcode: 2016usc..confE..62J
Altcode:
A large quiescent filament located near the south-west limb of the
Sun underwent an eruption on 14 August 2013. Shortly before the
eruption two flares occur in NOAA Active Region (AR) 11817, located
near the filament. The temporal and spatial proximity suggests that
the flares caused the filament to erupt. However, there is no extreme
ultraviolet (EUV) wave or ejection which seemed to cause this. We use
171 Å images for over two days before the eruption from Atmospheric
Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) to
investigate this event. We observe oscillations in the western portion
of the quiescent filament almost 40 hours prior to eruption, but not
so much in the eastern portion. For several hours prior to eruption,
the western portion is seen to undergo a slow rise. Subsequently, it
is this western portion which erupts, while the eastern portion does
not. We also use Helioseismic and Magnetic Imager (HMI) to study changes
in the active region, and find that along with a continuous emergence
of magnetic flux in the region, there was also a migration of polarity
producing a large shear. We make use of the hmi.sharp to determine shear
in the active region. We suggest that the oscillations are a result of
natural perturbation, and the flares acted as a destabilising factor
which resulted in the eruption.
Title: Multi-wavelength Study of Transition Region Penumbral
Subarcsecond Bright Dots Using IRIS and NST
Authors: Deng, Na; Yurchyshyn, Vasyl; Tian, Hui; Kleint, Lucia; Liu,
Chang; Xu, Yan; Wang, Haimin
Bibcode: 2016ApJ...829..103D
Altcode: 2016arXiv160700306D
Using high-resolution transition region (TR) observations taken by
the Interface Region Imaging Spectrograph (IRIS) mission, Tian et
al. revealed numerous short-lived subarcsecond bright dots (BDs)
above sunspots (mostly located in the penumbrae), which indicate yet
unexplained small-scale energy releases. Moreover, whether or not
these subarcsecond TR brightenings have any signature in the lower
atmosphere and how they are formed are still not fully resolved. This
paper presents a multi-wavelength study of the TR penumbral BDs using a
coordinated observation of a near disk center sunspot with IRIS and the
1.6 m New Solar Telescope (NST) at the Big Bear Solar Observatory. NST
provides high-resolution chromospheric and photospheric observations
with narrowband Hα imaging spectroscopy and broadband TiO images,
respectively, complementary to IRIS TR observations. A total of 2692
TR penumbral BDs are identified from a 37 minute time series of IRIS
1400 Å slit-jaw images. Their locations tend to be associated more
with downflowing and darker fibrils in the chromosphere, and weakly
associated with bright penumbral features in the photosphere. However,
temporal evolution analyses of the BDs show that there is no consistent
and convincing brightening response in the chromosphere. These results
are compatible with a formation mechanism of the TR penumbral BDs
by falling plasma from coronal heights along more vertical and dense
magnetic loops. The BDs may also be produced by small-scale impulsive
magnetic reconnection taking place sufficiently high in the atmosphere
that has no energy release in the chromosphere.
Title: Fine-scale Photospheric Connections of Ellerman Bombs
Authors: Yang, Heesu; Chae, Jongchul; Lim, Eun-Kyung; Song, Donguk;
Cho, Kyuhyoun; Kwak, Hannah; Yurchyshyn, Vasyl B.; Kim, Yeon-Han
Bibcode: 2016ApJ...829..100Y
Altcode:
We investigate the photospheric and magnetic field structures
associated with Ellerman bombs (EBs) using the 1.6 m New Solar
Telescope at Big Bear Solar Observatory. The nine observed EBs were
accompanied by elongated granule-like features (EGFs) that showed
transverse motions prior to the EBs with an average speed of about
3.8 km s-1. Each EGF consisted of a sub-arcsecond bright
core encircled by a dark lane around its moving front. The bright
core appeared in the TiO broadband filter images and in the far wings
of the Hα and Ca II 8542 Å lines. In four EBs, the bi-directional
expanding motion of the EGFs was identified in the TiO images. In
those cases, the EGFs were found to be accompanied by an emerging flux
(EF). In four other EBs, the EGF developed at the edge of a penumbra and
traveled in the sunspot’s radial direction. The EGFs in these cases
were identified as a moving magnetic feature (MMF). Our results show a
clear connection among the magnetic elements, photospheric features, and
EBs. This result suggests that the EBs result from magnetic reconnection
forced by EFs or MMFs that are frequently manifested by EGFs.
Title: How Did a Major Confined Flare Occur in Super Solar Active
Region 12192?
Authors: Jiang, Chaowei; Wu, S. T.; Yurchyshyn, Vasyl; Wang, Haiming;
Feng, Xueshang; Hu, Qiang
Bibcode: 2016ApJ...828...62J
Altcode: 2016arXiv160609334J
We study the physical mechanism of a major X-class solar flare
that occurred in the super NOAA active region (AR) 12192 using
data-driven numerical magnetohydrodynamic (MHD) modeling complemented
with observations. With the evolving magnetic fields observed at
the solar surface as bottom boundary input, we drive an MHD system
to evolve self-consistently in correspondence with the realistic
coronal evolution. During a two-day time interval, the modeled coronal
field has been slowly stressed by the photospheric field evolution,
which gradually created a large-scale coronal current sheet, I.e.,
a narrow layer with intense current, in the core of the AR. The
current layer was successively enhanced until it became so thin that
a tether-cutting reconnection between the sheared magnetic arcades
was set in, which led to a flare. The modeled reconnecting field
lines and their footpoints match well the observed hot flaring loops
and the flare ribbons, respectively, suggesting that the model has
successfully “reproduced” the macroscopic magnetic process of the
flare. In particular, with simulation, we explained why this event is
a confined eruption—the consequence of the reconnection is a shared
arcade instead of a newly formed flux rope. We also found a much weaker
magnetic implosion effect compared to many other X-class flares.
Title: Ionospheric criticial frequencies and solar cycle effects
Authors: Kilcik, Ali; Ozguc, Atila; Rozelot, Jean Pierre; Yiǧit,
Erdal; Elias, Ana; Donmez, Burcin; Yurchyshyn, Vasyl
Bibcode: 2016cosp...41E.996K
Altcode:
The long term solar activity dependencies of ionospheric F1 and
F2 regions critical frequencies (foF1 and foF2) are investigated
observationally for the last four solar cycles (1976-2015). We here
show that the ionospheric F1 and F2 regions have different solar
activity dependencies in terms of the sunspot group (SG) numbers:
F1 region critical frequency (foF1) peaks at the same time with small
SG numbers, while the foF2 reaches its maximum at the same time with
the large SG numbers especially during the solar cycle 23. Thus, we
may conclude that the sensitivities of ionospheric F1 and F2 region
critical frequencies to sunspot group (SG) numbers are associated
with different physical processes that are yet to be investigated
in detail. Such new results provide further evidence that the two
ionospheric regions have different responses to the solar activity. We
also analyzed short term oscillatory behavior of ionospheric critical
frequencies and found some solar signatures.
Title: Temporal Variation of Different Categories Sunspot Groups
since 1996: Their Relation with Geomagnetic Ap and Dst Indices
Authors: Kilcik, Ali; Ozguc, Atila; Rozelot, Jean Pierre; Donmez,
Burcin; Yurchyshyn, Vasyl
Bibcode: 2016cosp...41E.995K
Altcode:
We studied the temporal variation of the number of sunspot groups and
sunspot counts in these groups in four categories as small (A, B),
medium (C), large (D, E, F) and final (H modified Zurich classes)
since 1996. Then we compared these data sets with geomagnetic Ap
and Dst indices. In results of our analysis we found followings: 1)
different categories sunspot groups and sunspot counts in these groups
behave differently during a solar cycle. ii) Response of geomagnetic
indices to these data sets are also different.
Title: Multi-wavelength Study of Transition Region Penumbral
Bright Dots Using Interface Region Imaging Spectrograph and New
Solar Telescope
Authors: Deng, Na; Yurchyshyn, Vasyl B.; Tian, Hui; Kleint, Lucia;
Liu, Chang; Xu, Yan; Wang, Haimin
Bibcode: 2016SPD....47.0101D
Altcode:
Using high-resolution transition region (TR) observations taken by
the Interface Region Imaging Spectrograph (IRIS) mission, Tian et
al. (2014b) revealed numerous short-lived sub-arcsecond bright dots
above sunspots (mostly located in the penumbrae), which indicate yet
unexplained small-scale energy releases. Moreover, whether these TR
brightenings have any signature in the lower atmosphere and how they
are formed are still not fully resolved. This paper presents a study of
these bright dots using a coordinated observation of a near disk-center
sunspot with IRIS and the 1.6 m New Solar Telescope (NST) at the Big
Bear Solar Observatory. NST provides high-resolution chromospheric
and photospheric observations with narrow-band H-alpha imaging
spectroscopy and broad-band TiO images, respectively, complementary
to IRIS TR observations. A total of 2692 TR penumbral bright dots
are identified from a 37-minute time series of IRIS 1400 A slitjaw
images. Their locations tend to be associated more with downflowing and
darker fibrils in the chromosphere, and weakly associated with bright
penumbral features in the photosphere. However, temporal evolution
analyses of the dots show that there is no consistent and convincing
brightening response in the chromosphere. These results are compatible
with a formation mechanism of the TR penumbral bright dots by falling
plasma from coronal heights along more vertical and dense magnetic
loops. The dots may also be produced by small-scale impulsive magnetic
reconnection taking place sufficiently high in the atmosphere that
has no energy release in the chromosphere.Acknowledgement: This work
is mainly supported by NASA grants NNX14AC12G, NNX13AF76G and by NSF
grant AGS 1408703.
Title: Active Latitude Oscillations Observed on the Sun
Authors: Kilcik, A.; Yurchyshyn, V.; Clette, F.; Ozguc, A.; Rozelot,
J. -P.
Bibcode: 2016SoPh..291.1077K
Altcode: 2016SoPh..tmp...62K; 2016arXiv160400831K
We investigate periodicities in the mean heliographic latitudes of
sunspot groups, called active latitudes, for the past six complete
solar cycles (1945 - 2008). For this purpose, the multitaper method
and Morlet wavelet analysis were used. We found that solar rotation
periodicities (26 - 38 days) are present in active latitudes of both
hemispheres for all the investigated cycles (18 to 23). Both in the
northern and southern hemispheres, active latitudes drifted toward the
equator from the beginning to the end of each cycle and followed an
oscillating path. These motions are well described by a second-order
polynomial. There are no meaningful periods of between 55 and about
300 days in either hemisphere for all cycles. A periodicity of 300
to 370 days appears in both hemispheres for Cycle 23, in the northern
hemisphere for Cycle 20, and in the southern hemisphere for Cycle 18.
Title: Observations of a Series of Flares and Associated Jet-like
Eruptions Driven by the Emergence of Twisted Magnetic Fields
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Park, Sung-Hong; Kim,
Sujin; Cho, Kyung-Suk; Kumar, Pankaj; Chae, Jongchul; Yang, Heesu;
Cho, Kyuhyoun; Song, Donguk; Kim, Yeon-Han
Bibcode: 2016ApJ...817...39L
Altcode: 2015arXiv151201330L
We studied temporal changes of morphological and magnetic properties
of a succession of four confined flares followed by an eruptive flare
using the high-resolution New Solar Telescope (NST) operating at the Big
Bear Solar Observatory (BBSO) and Helioseismic and Magnetic Imager (HMI)
magnetograms and Atmospheric Image Assembly (AIA) EUV images provided by
the Solar Dynamics Observatory (SDO). From the NST/Hα and the SDO/AIA
304 Å observations we found that each flare developed a jet structure
that evolved in a manner similar to evolution of the blowout jet: (1)
an inverted-Y-shaped jet appeared and drifted away from its initial
position; (2) jets formed a curtain-like structure that consisted
of many fine threads accompanied by subsequent brightenings near
the footpoints of the fine threads; and finally, (3) the jet showed
a twisted structure visible near the flare maximum. Analysis of the
HMI data showed that both the negative magnetic flux and the magnetic
helicity have been gradually increasing in the positive-polarity region,
indicating the continuous injection of magnetic twist before and during
the series of flares. Based on these results, we suggest that the
continuous emergence of twisted magnetic flux played an important role
in producing successive flares and developing a series of blowout jets.
Title: Multiwavelength Observations of a Slow Raise, Multi-Step X1.6
Flare and the Associated Eruption
Authors: Yurchyshyn, V.
Bibcode: 2015AGUFMSH21C..04Y
Altcode:
Using multi-wavelength observations we studied a slow rise, multi-step
X1.6 flare that began on November 7, 2014 as a localized eruption of
core fields inside a δ-sunspot and later engulfed the entire active
region. This flare event was associated with formation of two systems
of post eruption arcades (PEAs) and several J-shaped flare ribbons
showing extremely fine details, irreversible changes in the photospheric
magnetic fields, and it was accompanied by a fast and wide coronal mass
ejection. Data from the Solar Dynamics Observatory, IRIS spacecraft
along with the ground based data from the New Solar Telescope (NST)
present evidence that i) the flare and the eruption were directly
triggered by a flux emergence that occurred inside a δ--sunspot at
the boundary between two umbrae; ii) this event represented an example
of an in-situ formation of an unstable flux rope observed only in hot
AIA channels (131 and 94Å) and LASCO C2 coronagraph images; iii)
the global PEA system spanned the entire AR and was due to global
scale reconnection occurring at heights of about one solar radii,
indicating on the global spatial and temporal scale of the eruption.
Title: Simultaneous observations of Ellerman bombs by NST and IRIS
Authors: Kim, Y. H.; Yurchyshyn, V.; Cho, I. H.; Lee, J.; Park, Y. D.;
Yang, H.; Ahn, K.; Goode, P.
Bibcode: 2015AGUFMSH31B2413K
Altcode:
In this study, we present the simultaneous observations of Ellerman
bombs made by New Solar Telescope (NST) of Big Bear Solar Observatory
(BBSO) and Interface Region Imaging Spectrograph (IRIS) in space. The
data obtained during joint NST-IRIS observations on 30 and 31 in July
2014. We observed two representative events on both days. The first
one was a relatively weak Ellerman bomb occurred around 19:20 UT on
30 July 2014. IRIS observed this event by sit-and-stare mode thus we
analyzed high cadence spectral data and slit-jaw data simultaneously. We
found that this event was a hot explosion that occurred by magnetic
reconnection in the lower atmosphere of the Sun. The second event
was quite strong Ellerman bomb (20:20 UT on 31 July 2014) that is
well observed by NST FISS (Fast Imaging Solar Spectrograph), while
there was no IRIS spectral data. We had IRIS slit-jaw data only. The
Ellerman bomb was clearly coincident with the IRIS brightening at the
same location. Since the Ellerman bombs are usually believed to occur
in the photosphere with no coronal emission, it should be explained its
higher atmospheric emission in IRIS data. We will present the result
of simultaneous observations by IRIS and NST instruments and discuss
physical connection between Ellerman bombs and IRIS brightenings.
Title: Multiwavelength Observations of a Slow-rise, Multistep X1.6
Flare and the Associated Eruption
Authors: Yurchyshyn, V.; Kumar, P.; Cho, K. -S.; Lim, E. -K.;
Abramenko, V. I.
Bibcode: 2015ApJ...812..172Y
Altcode:
Using multiwavelength observations, we studied a slow-rise, multistep
X1.6 flare that began on 2014 November 7 as a localized eruption of core
fields inside a δ-sunspot and later engulfed the entire active region
(AR). This flare event was associated with formation of two systems
of post-eruption arcades (PEAs) and several J-shaped flare ribbons
showing extremely fine details, irreversible changes in the photospheric
magnetic fields, and it was accompanied by a fast and wide coronal mass
ejection. Data from the Solar Dynamics Observatory and IRIS spacecraft,
along with the ground-based data from the New Solar Telescope, present
evidence that (i) the flare and the eruption were directly triggered
by a flux emergence that occurred inside a δ-sunspot at the boundary
between two umbrae; (ii) this event represented an example of the
formation of an unstable flux rope observed only in hot AIA channels
(131 and 94 Å) and LASCO C2 coronagraph images; (iii) the global
PEA spanned the entire AR and was due to global-scale reconnection
occurring at heights of about one solar radius, indicating the global
spatial and temporal scale of the eruption.
Title: Simultaneous observation of a hot explosion by NST and IRIS
Authors: Kim, Yeon-Han; Yurchyshyn, Vasyl; Bong, Su-Chan; Cho, Il-Hyun;
Cho, Kyung-Suk; Lee, Jaejin; Lim, Eun-Kyung; Park, Young-Deuk; Yang,
Heesu; Ahn, Kwangsu; Goode, Philip R.; Jang, Bi-Ho
Bibcode: 2015ApJ...810...38K
Altcode:
We present the first simultaneous observations of so-called “hot
explosions” in the cool atmosphere of the Sun made by the New Solar
Telescope (NST) of Big Bear Solar Observatory and the Interface Region
Imaging Spectrograph (IRIS) in space. The data were obtained during
the joint IRIS-NST observations on 2014 July 30. The explosion of
interest started around 19:20 UT and lasted for about 10 minutes. Our
findings are as follows: (1) the IRIS brightening was observed in
three channels of slit-jaw images, which cover the temperature range
from 4000 to 80,000 K; (2) during the brightening, the Si iv emission
profile showed a double-peaked shape with highly blue and redshifted
components (-40 and 80 km s-1) (3) wing brightening occurred
in Hα and Ca ii 8542 Å bands and related surges were observed in both
bands of the NST Fast Imaging Solar Spectrograph (FISS) instrument;
(4) the elongated granule, seen in NST TiO data, is clear evidence of
the emergence of positive flux to trigger the hot explosion; (5) the
brightening in Solar Dynamics Observatory/Atmospheric Imaging Assembly
1600 Å images is quite consistent with the IRIS brightening. These
observations suggest that our event is a hot explosion that occurred
in the cool atmosphere of the Sun. In addition, our event appeared as
an Ellerman bomb (EB) in the wing of Hα, although its intensity is
weak and the vertical extent of the brightening seems to be relatively
high compared with the typical EBs.
Title: Statistical Comparison Between Pores and Sunspots by Using
SDO/HMI
Authors: Cho, I. -H.; Cho, K. -S.; Bong, S. -C.; Lim, E. -K.; Kim,
R. -S.; Choi, S.; Kim, Y. -H.; Yurchyshyn, V.
Bibcode: 2015ApJ...811...49C
Altcode:
We carried out an extensive statistical study of the properties of
pores and sunspots, and investigated the relationship among their
physical parameters such as size, intensity, magnetic field, and the
line-of-sight (LOS) velocity in the umbrae. For this, we classified
9881 samples into three groups of pores, transitional sunspots, and
mature sunspots. As a result, (1) we find that the total magnetic
flux inside the umbra of pores, transitional sunspots, and mature
sunspots increases proportionally to the powers of the area and
the power indices in the three groups significantly differ from each
other. (2) The umbral area distribution of each group shows a Gaussian
distribution and they are clearly separated, displaying three distinct
peak values. All of the quantities significantly overlap among the three
groups. (3) The umbral intensity shows a rapid decrease with increasing
area, and their magnetic field strength shows a rapid increase with
decreasing intensity. (4) The LOS velocity in pores is predominantly
redshifted and its magnitude decreases with increasing magnetic field
strength. The decreasing trend becomes nearly constant with marginal
blueshift in the case of mature sunspots. The dispersion of LOS
velocities in mature sunspots is significantly suppressed compared
to pores. From our results, we conclude that the three groups have
different characteristics in their area, intensity, magnetic field,
and LOS velocity as well in their relationships.
Title: Formation and Eruption of a Small Flux Rope in the Chromosphere
Observed by NST, IRIS, and SDO
Authors: Kumar, Pankaj; Yurchyshyn, Vasyl; Wang, Haimin; Cho, Kyung-Suk
Bibcode: 2015ApJ...809...83K
Altcode: 2015arXiv150701761K
Using high-resolution images from the 1.6 m New Solar Telescope
at Big Bear Solar Observatory, we report the direct evidence of
chromospheric reconnection at the polarity inversion line between
two small opposite polarity sunspots. Small jetlike structures
(with velocities of ∼20-55 km s-1) were observed at the
reconnection site before the onset of the first M1.0 flare. The slow
rise of untwisting jets was followed by the onset of cool plasma inflow
(∼10 km s-1) at the reconnection site, causing the onset
of a two-ribbon flare. The reconnection between two sheared J-shaped
cool Hα loops causes the formation of a small twisted (S-shaped) flux
rope in the chromosphere. In addition, Helioseismic and Magnetic Imager
magnetograms show the flux cancellation (both positive and negative)
during the first M1.0 flare. The emergence of negative flux and the
cancellation of positive flux (with shear flows) continue until the
successful eruption of the flux rope. The newly formed chromospheric
flux rope becomes unstable and rises slowly with a speed of ∼108 km
s-1 during a second C8.5 flare that occurred after ∼3
hr of the first M1.0 flare. The flux rope was destroyed by repeated
magnetic reconnection induced by its interaction with the ambient field
(fan-spine topology) and looks like an untwisting surge (∼170 km
s-1) in the coronal images recorded by the Solar Dynamics
Observatory/Atmospheric Imaging Assembly. These observations suggest
the formation of a chromospheric flux rope (by magnetic reconnection
associated with flux cancellation) during the first M1.0 flare and
its subsequent eruption/disruption during the second C8.5 flare.
Title: An Ellerman bomb observed by NST and IRIS
Authors: Kim, Yeon-Han; Yurchyshyn, Vasyl; Ahn, Kwangsu; Cho, Il-Hyun;
Lee, Jaejin; Park, Young-Deuk; Goode, Phillip
Bibcode: 2015IAUGA..2257560K
Altcode:
Recent observations by Interface Region Imaging Spectrograph (IRIS)
instrument have shown a variety of brightenings around the large-scale
active region in the solar atmosphere from the photosphere to the
corona. Interestingly while some brightenings are clearly related to
Ellerman bombs, some seem to have nothing to do with them. On 2014
July 31, New Solar Telescope (NST) in Big Bear Solar Observatory (BBSO)
performed a joint observation with IRIS instrument for the NOAA AR 12127
from 20:00 UT to 22:00 UT. Around the sunspot several IRIS brightenings
were observed in 3-channels of slit-jaw images (SJI_2796, SJI_1400,
and SJI_1330), which can monitor the upper chromosphere and transition
region. The NST’s Fast Imaging Solar Spectrograph (FISS) observed a
well-developed Ellerman bomb in the upper right side of the sunspot. The
Ellerman bomb is clearly coincident with the IRIS brightening at the
same location. Since the Ellerman bombs are usually believed to occur
in the photosphere with no coronal emission, it should be explained
its higher atmospheric emission in IRIS data. We will present the
result of simultaneous observations by IRIS and NST instruments.
Title: Detection of Shock Merging in the Chromosphere of a Solar Pore
Authors: Chae, Jongchul; Song, Donguk; Seo, Minju; Cho, Kyung-Suk;
Park, Young-Deuk; Yurchyshyn, Vasyl
Bibcode: 2015ApJ...805L..21C
Altcode:
It was theoretically demonstrated that a shock propagating in the solar
atmosphere can overtake another and merge with it. We provide clear
observational evidence that shock merging does occur quite often in
the chromosphere of sunspots. Using Hα imaging spectral data taken by
the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope
at the Big Bear Soar Observatory, we construct time-distance maps
of line-of-sight velocities along two appropriately chosen cuts in
a pore. The maps show a number of alternating redshift and blueshift
ridges, and we identify each interface between a preceding redshift
ridge and the following blueshift ridge as a shock ridge. The important
finding of ours is that two successive shock ridges often merge with
each other. This finding can be theoretically explained by the merging
of magneto-acoustic shock waves propagating with lower speeds of about
10 km s-1 and those propagating at higher speeds of about
16-22 km s-1. The shock merging is an important nonlinear
dynamical process of the solar chromosphere that can bridge the gap
between higher-frequency chromospheric oscillations and lower-frequency
dynamic phenomena such as fibrils.
Title: The Chromosphere above the sunspot umbra as seen in the New
Solar Telescope and Interface Region Imaging Spectrograph
Authors: Yurchyshyn, Vasyl; Goode, Phil; Abramenko, Valentyna;
Kilcik, Ali
Bibcode: 2015TESS....131202Y
Altcode:
Recent observations of sunspot's umbra suggested that it may be finely
structured at a sub-arcsecond scale representing a mix of hot and cool
plasma elements. In this study we report observations from the New Solar
Telescope (NST) of the umbral spikes, which are cool jet-like structures
seen in the chromosphere of an umbra. Our analysis indicates that
the spikes are not associated with photospheric umbral dots and they
tend to occur above darkest parts of the umbra, where magnetic fields
are strongest. The spikes exhibit up and down oscillatory motions and
their spectral evolution suggests that they might be driven by upward
propagating shocks generated by photospheric oscillations.We analyze
sunspot oscillations using Interface Region Imaging Spectrograph
(IRIS) data and narrow-band NST images and found long term variations
in the intensity of chromospheric shocks. Also, sunspot umbral flashes
(UFs) appear as narrow bright lanes running along the light bridges
(LBs) and clusters of umbral dots (UDs). Time series suggested that
UFs preferred to appear on the sunspot-center side of LBs, which may
indicate the existence of a compact sub-photospheric driver of sunspot
oscillations. We find that the sunspot's umbra appears bright in IRIS
images above LBs and UDs. Co-spatial and co-temporal SDO/AIA data showed
that these locations were associated with bright footpoints of umbral
loops suggesting that LBs may play an important role in heating these
loops. The power spectra analysis showed that the intensity of umbral
oscillations significantly varies across the umbra and with height,
suggesting that umbral non-uniformities and the structure of sunspot
magnetic fields may play a role in wave propagation and heating of
umbral loops.
Title: Intensity and Doppler Velocity Oscillations in Pore Atmospheres
Authors: Cho, K. -S.; Bong, S. -C.; Nakariakov, V. M.; Lim, E. -K.;
Park, Y. -D.; Chae, J. C.; Yang, H. -S.; Park, H. -M.; Yurchyshyn, V.
Bibcode: 2015ApJ...802...45C
Altcode:
We have investigated chromospheric traveling features running across two
merged pores from their centers at speeds of about 55 km s-1,
in the active region AR 11828. The pores were observed on 2013 August
24 by using high-time, spatial, and spectral resolution data from the
Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope. We
infer a line-of-sight (LOS) velocity by applying the lambdameter method
to the Ca ii 8542 Å band and Hα band, and investigate intensity and
LOS velocity changes at different wavelengths and different positions
at the pores. We find that they have three-minute oscillations, and
the intensity oscillation from the line center (0.0 \overset{\circ}A
) is preceded by that from the core (-0.3 \overset{\circ}A ) of the
bands. There is no phase difference between the intensity and the
LOS velocity oscillations at a given wavelength. The amplitude of LOS
velocity from the near core spectra ({Δ }λ =0.10-0.21 \overset{\circ}A
) is greater than that from the far core spectra ({Δ }λ =0.24-0.36
\overset{\circ}A ). These results support the interpretation of the
observed wave as a slow magnetoacoustic wave propagating along the
magnetic field lines in the pores. The apparent horizontal motion and
a sudden decrease of its speed beyond the pores can be explained by
the projection effect caused by inclination of the magnetic field with
a canopy structure. We conclude that the observed wave properties of
the pores are quite similar to those from the sunspot observations.
Title: Dynamics in Sunspot Umbra as Seen in New Solar Telescope and
Interface Region Imaging Spectrograph Data
Authors: Yurchyshyn, V.; Abramenko, V.; Kilcik, A.
Bibcode: 2015ApJ...798..136Y
Altcode: 2014arXiv1411.0192Y
We analyze sunspot oscillations using Interface Region Imaging
Spectrograph (IRIS) slit-jaw and spectral data and narrow-band
chromospheric images from the New Solar Telescope (NST) for the main
sunspot in NOAA AR 11836. We report that the difference between the
shock arrival times as measured by the Mg II k 2796.35 Å and Si IV
1393.76 Å line formation levels changes during the observed period,
and peak-to-peak delays may range from 40 s to zero. The intensity
of chromospheric shocks also displays long-term (about 20 min)
variations. NST's high spatial resolution Hα data allowed us to
conclude that, in this sunspot, umbral flashes (UFs) appeared in the
form of narrow bright lanes stretched along the light bridges and around
clusters of umbral bright points. The time series also suggested that
UFs preferred to appear on the sunspot-center side of light bridges,
which may indicate the existence of a compact sub-photospheric
driver of sunspot oscillations. The sunspot's umbra as seen in the
IRIS chromospheric and transition region data appears bright above
the locations of light bridges and the areas where the dark umbra
is dotted with clusters of umbral dots. Co-spatial and co-temporal
data from the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory showed that the same locations were associated with bright
footpoints of coronal loops suggesting that the light bridges may play
an important role in heating the coronal sunspot loops. Finally, the
power spectra analysis showed that the intensity of chromospheric and
transition region oscillations significantly vary across the umbra and
with height, suggesting that umbral non-uniformities and the structure
of sunspot magnetic fields may play a role in wave propagation and
heating of umbral loops.
Title: Kinematics of Solar Chromospheric Surges of AR 10930
Authors: Bong, Su-Chan; Cho, Kyung-Suk; Yurchyshyn, Vasyl
Bibcode: 2014JKAS...47..311B
Altcode:
No abstract at ADS
Title: Sunspot Count Periodicities in Different Zurich Sunspot Group
Classes Since 1986
Authors: Kilcik, A.; Ozguc, A.; Yurchyshyn, V.; Rozelot, J. P.
Bibcode: 2014SoPh..289.4365K
Altcode: 2014arXiv1407.5895K; 2014SoPh..tmp..119K
We used two methods to investigate the periodic behavior of sunspot
counts in four categories for the time period January 1986 - October
2013. These categories include the counts from simple (A and B),
medium (C), large (D, E, and F), and final (final-stage; H) sunspot
groups. We used i) the multitaper method with red noise approximation,
and ii) the Morlet wavelet transform for periodicity analysis. Our
main findings are that 1) the solar rotation periodicity of about 25
to 37 days, which is of obvious significance, is found in all groups
with at least a 95 % significance level; 2) the periodic behavior of
a cycle is strongly related to its amplitude and group distribution
during the cycle; 3) the appearance of periods follows the amplitude
of the investigated solar cycles; and that 4) meaningful periods do
not appear during the minimum phases of the investigated cycles.
Title: Multi-wavelength High-resolution Observations of a Small-scale
Emerging Magnetic Flux Event and the Chromospheric and Coronal
Response
Authors: Vargas Domínguez, Santiago; Kosovichev, Alexander;
Yurchyshyn, Vasyl
Bibcode: 2014ApJ...794..140V
Altcode: 2014arXiv1405.3550V
State-of-the-art solar instrumentation is now revealing magnetic
activity of the Sun with unprecedented temporal and spatial
resolutions. Observations with the 1.6 m aperture New Solar Telescope
(NST) of the Big Bear Solar Observatory are making next steps in our
understanding of the solar surface structure. Granular-scale magnetic
flux emergence and the response of the solar atmosphere are among the
key research topics of high-resolution solar physics. As part of a joint
observing program with NASA's Interface Region Imaging Spectrograph
(IRIS) mission on 2013 August 7, the NST observed active region
NOAA 11,810 in the photospheric TiO 7057 Å band with a resolution
of pixel size of 0.''034 and chromospheric He I 10830 Å and Hα
6563 Å wavelengths. Complementary data are provided by the Solar
Dynamics Observatory (SDO) and Hinode space-based telescopes. The
region displayed a group of solar pores, in the vicinity of which we
detect a small-scale buoyant horizontal magnetic flux tube causing
granular alignments and interacting with the preexisting ambient field
in the upper atmospheric layers. Following the expansion of distorted
granules at the emergence site, we observed a sudden appearance of an
extended surge in the He I 10830 Å data (bandpass of 0.05 Å). The
IRIS transition region imaging caught ejection of a hot plasma jet
associated with the He I surge. The SDO/HMI data used to study the
evolution of the magnetic and Doppler velocity fields reveal emerging
magnetic loop-like structures. Hinode/Ca II H and IRIS filtergrams
detail the connectivities of the newly emerged magnetic field in the
lower solar chromosphere. From these data, we find that the orientation
of the emerging magnetic field lines from a twisted flux tube formed
an angle of ~45° with the overlying ambient field. Nevertheless,
the interaction of emerging magnetic field lines with the pre-existing
overlying field generates high-temperature emission regions and boosts
the surge/jet production. The localized heating is detected before
and after the first signs of the surge/jet ejection. We compare the
results with previous observations and theoretical models and propose a
scenario for the activation of plasma jet/surges and confined heating
triggered by buoyant magnetic flux tubes rising up into a magnetized
upper environment. Such process may play a significant role in the
mass and energy flow from the interior to the corona.
Title: Solar Cycle 24: Curious Changes in the Relative Numbers of
Sunspot Group Types
Authors: Kilcik, A.; Yurchyshyn, V. B.; Ozguc, A.; Rozelot, J. P.
Bibcode: 2014ApJ...794L...2K
Altcode:
Here, we analyze different sunspot group (SG) behaviors from the points
of view of both the sunspot counts (SSCs) and the number of SGs, in
four categories, for the time period of 1982 January-2014 May. These
categories include data from simple (A and B), medium (C), large (D,
E, and F), and decaying (H) SGs. We investigate temporal variations of
all data sets used in this study and find the following results. (1)
There is a very significant decrease in the large groups' SSCs and
the number of SGs in solar cycle 24 (cycle 24) compared to cycles
21-23. (2) There is no strong variation in the decaying groups' data
sets for the entire investigated time interval. (3) Medium group data
show a gradual decrease for the last three cycles. (4) A significant
decrease occurred in the small groups during solar cycle 23, while no
strong changes show in the current cycle (cycle 24) compared to the
previous ones. We confirm that the temporal behavior of all categories
is quite different from cycle to cycle and it is especially flagrant
in solar cycle 24. Thus, we argue that the reduced absolute number
of the large SGs is largely, if not solely, responsible for the weak
cycle 24. These results might be important for long-term space weather
predictions to understand the rate of formation of different groups
of sunspots during a solar cycle and the possible consequences for
the long-term geomagnetic activity.
Title: Sunspot activity for last cycles
Authors: Kilcik, A.; Ozguc, A.; Yurchyshyn, V.; Rozelot, J. P.
Bibcode: 2014simi.conf....3K
Altcode:
Here we analyzed the behavior of different class sunspot groups by
separating them in different categories for last cycles. In result of
our analysis, we found that observed sunspot groups behave differently
for different solar cycles, and each class sunspots have different
relation with geomagnetic indices. Our main findings are as follows:
1) All groups behave similarly during the solar cycle 22, while the
situation is quite different for other cycles (cycle 23 and 24). 2)
Complex sunspot groups describe the geomagnetic activity better than
simple groups. 3) The periodic behavior of different group sunspot
counts show remarkable differences that it may explain the unusual
behavior of solar cycle 23, and may be the behavior of current cycle.
Title: High Resolution Observations of Chromospheric Jets in
Sunspot Umbra
Authors: Yurchyshyn, Vasyl B.; Abramenko, Valentyna; Kosovichev,
Alexander G.; Goode, Philip R.
Bibcode: 2014AAS...22432301Y
Altcode:
Recent observations of sunspot's umbra suggested that it may be finely
structured at a sub-arcsecond scale representing a mix of hot and cool
plasma elements. In this study we report the first detailed observations
of the umbral spikes, which are cool jet-like structures seen in the
chromosphere of an umbra. The spikes are cone-shaped features with
a typical height of 0.5-1. Mm and a width of about 0. Mm. Their life
time ranges from 2 to 3 ~min and they tend to re-appear at the same
location. The preliminary analysis indicates that the spikes are not
associated with photospheric umbral dots and they rather tend to
occur above darkest parts of the umbra, where magnetic fields are
strongest. The spikes exhibit up and down oscillatory motions and
their spectral evolution suggests that they might be driven by upward
propagating shocks generated by photospheric oscillations. It is worth
noting that triggering of the running penumbral waves seems to occur
during the interval when the spikes reach their maximum height.
Title: Photospheric and Chromospheric Dynamics of Sunspots Observed
with New Solar Telescope
Authors: Kosovichev, Alexander G.; Yurchyshyn, Vasyl B.
Bibcode: 2014AAS...22421811K
Altcode:
The 1.6m New Solar Telescope (NST) of Big Bear Solar Observatory
allows us to investigate the structure and dynamics of sunspots with
unprecedented spatial and temporal resolutions. We present results
of simultaneous observations of a sunspot in the photosphere with a
broad-band TiO-line filter and in the chromospheric H-alpha line with
Visible Imaging Spectrometer, and compare the observational results with
MHD models of sunspots. The observations reveal previously unresolved
features of the sunspot umbra and penumbra. In particular, the TiO data
clearly demonstrate highly twisted dynamics of penumbral filaments and
umbral dots and reveal strong shearing plasma flows in sunspot bridges,
not explained by the MHD simulations. The high-resolution H-alpha
spectroscopic data provide new views of the sunspot chromospheric
dynamics, including the fine structure of oscillations and waves,
penumbral jets, ubiquitous small-scale eruptions, and accretion
flows in a form of dense plasma sheets. The diffraction-limited NST
observations show that the sunspot dynamics is more complicated and
much richer than it is described by the current sunspot models.
Title: High Resolution Observations of Chromospheric Jets in
Sunspot Umbra
Authors: Yurchyshyn, V.; Abramenko, V.; Kosovichev, A.; Goode, P.
Bibcode: 2014ApJ...787...58Y
Altcode: 2014arXiv1404.7444Y
Recent observations of a sunspot's umbra have suggested that it may
be finely structured on a subarcsecond scale representing a mix of hot
and cool plasma elements. In this study, we report the first detailed
observations of umbral spikes, which are cool jet-like structures seen
in the chromosphere of an umbra. The spikes are cone-shaped features
with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their
lifetime ranges from 2 to 3 minutes and they tend to re-appear at
the same location. The spikes are not associated with photospheric
umbral dots and they instead tend to occur above the darkest parts of
the umbra where magnetic fields are strongest. The spikes exhibit up
and down oscillatory motions and their spectral evolution suggests
that they might be driven by upward propagating shocks generated by
photospheric oscillations. It is worth noting that triggering of the
running penumbral waves seems to occur during the interval when the
spikes reach their maximum height.
Title: Emergence of a small-scale magnetic flux tube and the response
of the solar atmosphere
Authors: Vargas Dominguez, S.; Kosovichev, A. G.; Yurchyshyn, V.
Bibcode: 2014CEAB...38...25V
Altcode:
Cutting-edge observations with the 1.6-meter telescope at Big Bear
Solar Observatory (BBSO) in California have taken research into the
activity of the Sun to new levels of understanding of the structure
and evolution of the solar atmosphere at high-resolution spatial and
temporal scales. On August 7, 2013 the NST observed active region NOAA
11810 in photospheric and chromospheric wavelengths. The observations
were performed as part of a program conducted jointly with NASA's
Interface Region Imaging Spectrograph (IRIS) mission, Solar Dynamics
Observatory (SDO) and Hinode satellite. These observations provided a
unique view on the emergence of a buoyant small-scale magnetic-flux
rope in the solar photosphere. The event is accompanied by response
of the solar atmosphere once the newly emerged field interacts with
the pre-existing overlying one. The reconnection process that takes
place in the region produces jet emission and high-temperature points
in the chromosphere and corona.
Title: Characteristic Length of Energy-containing Structures at the
Base of a Coronal Hole
Authors: Abramenko, V. I.; Zank, G. P.; Dosch, A.; Yurchyshyn, V. B.;
Goode, P. R.; Ahn, K.; Cao, W.
Bibcode: 2013ApJ...773..167A
Altcode: 2013arXiv1307.4421A
An essential parameter for models of coronal heating and fast solar
wind acceleration that rely on the dissipation of MHD turbulence is
the characteristic energy-containing length λ of the
squared velocity and magnetic field fluctuations (u 2
and b 2) transverse to the mean magnetic field inside a
coronal hole (CH) at the base of the corona. The characteristic length
scale directly defines the heating rate. We use a time series analysis
of solar granulation and magnetic field measurements inside two CHs
obtained with the New Solar Telescope at Big Bear Solar Observatory. A
data set for transverse magnetic fields obtained with the Solar Optical
Telescope/Spectro-Polarimeter on board the Hinode spacecraft was
utilized to analyze the squared transverse magnetic field fluctuations
b_t^2. Local correlation tracking was applied to derive the squared
transverse velocity fluctuations u 2. We find that for u
2 structures, the Batchelor integral scale λ varies in
a range of 1800-2100 km, whereas the correlation length sigmav and
the e-folding length L vary between 660 and 1460 km. Structures for
b_t^2 yield λ ≈ 1600 km, sigmav ≈ 640 km, and L ≈ 620 km. An
averaged (over λ, sigmav, and L) value of the characteristic length
of u 2 fluctuations is 1260 ± 500 km, and that of b_t^2
is 950 ± 560 km. The characteristic length scale in the photosphere
is approximately 1.5-50 times smaller than that adopted in previous
models (3-30 × 103 km). Our results provide a critical
input parameter for current models of coronal heating and should yield
an improved understanding of fast solar wind acceleration.
Title: Observation of a Non-radial Penumbra in a Flux Emerging Region
under Chromospheric Canopy Fields
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Goode, Philip; Cho,
Kyung-Suk
Bibcode: 2013ApJ...769L..18L
Altcode:
The presence of a penumbra is one of the main properties of a mature
sunspot, but its formation mechanism has been elusive due to a lack
of observations that fully cover the formation process. Utilizing the
New Solar Telescope at the Big Bear Solar Observatory, we observed
the formation of a partial penumbra for about 7 hr simultaneously at
the photospheric (TiO; 7057 Å) and the chromospheric (Hα - 1 Å)
spectral lines with high spatial and temporal resolution. From this
uninterrupted, long observing sequence, we found that the formation of
the observed penumbra was closely associated with flux emergence under
the pre-existing chromospheric canopy fields. Based on this finding,
we suggest a possible scenario for penumbra formation in which a
penumbra forms when the emerging flux is constrained from continuing
to emerge, but rather is trapped at the photospheric level by the
overlying chromospheric canopy fields.
Title: Dynamics of Chromospheric Upflows and Underlying Magnetic
Fields
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P.
Bibcode: 2013ApJ...767...17Y
Altcode: 2013arXiv1303.4766Y
We used Hα-0.1 nm and magnetic field (at 1.56μ) data obtained with
the New Solar Telescope to study the origin of the disk counterparts to
type II spicules, so-called rapid blueshifted excursions (RBEs). The
high time cadence of our chromospheric (10 s) and magnetic field
(45 s) data allowed us to generate x-t plots using slits parallel
to the spines of the RBEs. These plots, along with potential field
extrapolation, led us to suggest that the occurrence of RBEs is
generally correlated with the appearance of new, mixed, or unipolar
fields in close proximity to network fields. RBEs show a tendency
to occur at the interface between large-scale fields and small-scale
dynamic magnetic loops and thus are likely to be associated with the
existence of a magnetic canopy. Detection of kinked and/or inverse
"Y"-shaped RBEs further confirm this conclusion.
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.
Bibcode: 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: Investigation of Small-Scale Turbulent MHD Phenomena Using
Numerical Simulations and NST Observations
Authors: Kitiashvili, I.; Abramenko, V.; Goode, P. R.; Kosovichev,
A.; Mansour, N.; Wray, A.; Yurchyshyn, V.
Bibcode: 2012IAUSS...6E.104K
Altcode:
Recent progress in observational capabilities and numerical modeling
have provided unique high-resolution information demonstrating
complicated dynamics and structures of turbulent flows and magnetic
field on the Sun. The realistic approach to numerical simulations is
based on physical first principles and takes into account compressible
fluid flow in a highly stratified magnetized medium, 3D multi-bin
radiative energy transfer between fluid elements, a real-gas equation
of state, ionization, and excitation of all abundant species, magnetic
effects and sub-grid turbulence. We present new results of 3D radiative
MHD simulations of the upper solar convection zone and chromosphere
that reveal a fundamental role of small-scale vortex dynamics, and
compare the numerical results and predictions with observational
results from the 1.6 m clear aperture New Solar Telescope (NST) at
Big Bear Observatory. In particular, we investigate formation and
dynamics of ubiquitous small-scale vortex tubes mostly concentrated
in the intergranular lanes and their role in magnetic structuring
and acoustic emission of the Sun. These whirlpool-like flows are
characterized by very strong horizontal shear velocities (7 - 11 km/s)
and downflows (~7 km/s), and are accompanied by sharp decreases in
temperature, density and pressure at the surface. High-speed whirlpool
flows can attract and capture other vortices, penetrate into the low
chromosphere, and form stable magnetic flux tubes. The simulations also
reveal a strong connection between acoustic wave excitation events and
the dynamics of vortex tubes. In this talk, we will discuss different
aspects of small-scale turbulent dynamics of the low atmosphere from the
high-resolution simulations in comparison with recent NST observations,
and the strategy for future synergies of numerical simulations and
observations with large aperture solar telescopes.
Title: Energy-Containing Length Scale at the Base of a Coronal Hole:
New Observational Findings
Authors: Abramenko, V.; Dosch, A.; Zank, G. P.; Yurchyshyn, V.; Goode,
P. R.
Bibcode: 2012AGUFMSH33D2253A
Altcode:
Dynamics of the photospheric flux tubes is thought to be a key
factor for generation and propagation of MHD waves and magnetic
stress into the corona. Recently, New Solar Telescope (NST, Big
Bear Solar Observatory) imaging observations in helium I 10830 Å
revealed ultrafine, hot magnetic loops reaching from the photosphere
to the corona and originating from intense, compact magnetic field
elements. One of the essential input parameters to run the models of
the fast solar wind is a characteristic energy-containing length scale,
lambda, of the dynamical structures transverse to the mean magnetic
field in a coronal hole (CH) in the base of the corona. We used NST
time series of solar granulation motions to estimate the velocity
fluctuations, as well as NST near-infrared magnetograms to derive
the magnetic field fluctuations. The NST adaptive optics corrected
speckle-reconstructed images of 10 seconds cadence were an input for the
local correlation tracking (LCT) code to derive the squared transverse
velocity patterns. We found that the characteristic length scale for
the energy-carrying structures in the photosphere is about 300 km,
which is two orders of magnitude lower than it was adopted in previous
models. The influence of the result on the coronal heating and fast
solar wind modeling will be discussed.; Correlation functions calculated
from the squared velocities for the three data sets: a coronal hole,
quiet sun and active region plage area.
Title: The relationship between the occurrence of type II spicules
and the dynamics of underlying magnetic fields
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
Bibcode: 2012AGUFMSH32A..05Y
Altcode:
Type II spicules are thought to be small-scale chromospheric
up-flows. When observed against the solar disk they can be identified
as rapid blue shifted events (or excursions, RBE, Rouppe van der
Voort et al.). While their nature is being questioned and their
associated driving mechanism remains elusive, these up-flows may be
instrumental in the processes of coronal heating and solar wind. We use
high resolution photospheric, chromospheric and magnetic field data
from the New Solar Telescope operating at Big Bear Solar Observatory
to further determine the properties of these events and refine the
role that they may play. We find that the majority of RBEs, occurring
around network clusters of bright points, can be linked to episodes
of small flux emergence, in particular appearance of opposite polarity
fields. Case studies further indicate that some of the RBEs appear to
have kink and inverted "Y" shaped roots. The data thus suggest that
magnetic reconnection may be responsible for at least some fraction
of observed RBEs. We will present these observations in details and
discuss possible implications.Sequence of H-alpha-0.075nm images
spanning 7 min showing evolution of RBE activity near a cluster
of network fields. The two yellow circles enclose the area where
multipolar fields rapidly appeared. Comparing panels 19:05:11 UT and
19:05:55 UT one may notice that a new magnetic dipole and a dark jet
appeared in the encircled area. The same is true about the encircled
area in 19:07:26UT panel. The RBE activity ceased as soon as the the
field of view was cleared from small-scale magnetic elements.
Title: Coronal Mass Ejections and the Index of Effective Solar
Multipole
Authors: Obridko, V. N.; Ivanov, E. V.; Özgüç, A.; Kilcik, A.;
Yurchyshyn, V. B.
Bibcode: 2012SoPh..281..779O
Altcode: 2012SoPh..tmp..199O
The paper considers the relationship between the cyclic variations
in the velocity of coronal mass ejections (CME) and the large-scale
magnetic field structure (LSMF) in cycles 21 - 23. To characterize
a typical size of the LSMF structure, we have used the index of
the effective solar multipole (ESMI). The cyclic behavior of the CME
occurrence rate and velocity proved to be similar to that of ESMI. The
hysteresis observed in variations of the CME maximum velocity is
interpreted as a manifestation of different contributions from the
two field structures (local and global magnetic fields) in different
phases of the 11-year activity cycle. It is suggested that cyclic
variations in the maximum velocity of coronal mass ejections are due
to different conditions for the formation of the complexes of active
regions connected by coronal arch systems, which are the main source
of high-velocity CMEs.
Title: Turbulent Pair Dispersion of Photospheric Bright Points
Authors: Lepreti, F.; Carbone, V.; Abramenko, V. I.; Yurchyshyn, V.;
Goode, P. R.; Capparelli, V.; Vecchio, A.
Bibcode: 2012ApJ...759L..17L
Altcode:
Observations of solar granulation obtained with the New Solar Telescope
of Big Bear Solar Observatory are used to study the turbulent pair
dispersion of photospheric bright points in a quiet-Sun area, a
coronal hole, and an active region plage. In all the three magnetic
environments, it is found that the pair mean-squared separation
Δ2(t) follows a power-law timescaling Δ2(t) ~ t
η in the range 10 s <~ t <~ 400 s. The power-law index
is found to be η ~= 1.5 for all the three investigated regions. It
is shown that these results can be explained in the same framework as
the classical Batchelor theory, under the hypothesis that the observed
range of timescales corresponds to a non-asymptotic regime in which the
photospheric bright points keep the memory of their initial separations.
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.
Bibcode: 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: Detection of Small-scale Granular Structures in the Quiet
Sun with the New Solar Telescope
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.;
Kitiashvili, I. N.; Kosovichev, A. G.
Bibcode: 2012ApJ...756L..27A
Altcode: 2012arXiv1208.4337A
Results of a statistical analysis of solar granulation are presented. A
data set of 36 images of a quiet-Sun area on the solar disk center was
used. The data were obtained with the 1.6 m clear aperture New Solar
Telescope at Big Bear Solar Observatory and with a broadband filter
centered at the TiO (705.7 nm) spectral line. The very high spatial
resolution of the data (diffraction limit of 77 km and pixel scale of
0farcs0375) augmented by the very high image contrast (15.5% ± 0.6%)
allowed us to detect for the first time a distinct subpopulation of
mini-granular structures. These structures are dominant on spatial
scales below 600 km. Their size is distributed as a power law with an
index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no
predominant scale. The regular granules display a Gaussian (normal)
size distribution with a mean diameter of 1050 km. Mini-granular
structures contribute significantly to the total granular area. They are
predominantly confined to the wide dark lanes between regular granules
and often form chains and clusters, but different from magnetic bright
points. A multi-fractality test reveals that the structures smaller
than 600 km represent a multi-fractal, whereas on larger scales the
granulation pattern shows no multi-fractality and can be considered
as a Gaussian random field. The origin, properties, and role of the
population of mini-granular structures in the solar magnetoconvection
are yet to be explored.
Title: Variations of Current Helicity in Active Region 10930 as
Inferred from Hinode Spectropolarimeter Data and Cancellation Exponent
Authors: Yurchyshyn, V.; Abramenko, V.; Watanabe, H.
Bibcode: 2012ASPC..454..311Y
Altcode:
Current helicity derived from vector magnetograms possesses a
well-pronounced scaling behavior, which can be studied by introducing
a signed measure and calculating the power-law exponent (cancellation
exponent). The time variations of this exponent seem to be related
to flare activity of an active region. Here we focus on changes
of current helicity in active region NOAA 10930 as derived from
a set of Hinode spectropolarimeter data. Our findings are that the
cancellation exponent first strongly increased on Dec 11 then rapidly
decreased after a small sunspot-satellite developed. Afterward, the
cancellation exponent began its gradual increase without significant
new magnetic flux emergence. These two different modes of behavior
may indicate different processes that ultimately led to an eruption:
the first process is rapid injection of current helicity, while the
second process is gradual redistribution of injected helicity over
all spatial scales in the active region.
Title: First Simultaneous Detection of Moving Magnetic Features in
Photospheric Intensity and Magnetic Field Data
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Goode, Philip
Bibcode: 2012ApJ...753...89L
Altcode: 2012arXiv1205.0574L
The formation and the temporal evolution of a bipolar moving magnetic
feature (MMF) was studied with high-spatial and temporal resolution. The
photometric properties were observed with the New Solar Telescope at
Big Bear Solar Observatory using a broadband TiO filter (705.7 nm),
while the magnetic field was analyzed using the spectropolarimetric
data obtained by Hinode. For the first time, we observed a bipolar
MMF simultaneously in intensity images and magnetic field data, and
studied the details of its structure. The vector magnetic field and the
Doppler velocity of the MMF were also studied. A bipolar MMF with its
positive polarity closer to the negative penumbra formed, accompanied by
a bright, filamentary structure in the TiO data connecting the MMF and
a dark penumbral filament. A fast downflow (<=2 km s-1)
was detected at the positive polarity. The vector magnetic field
obtained from the full Stokes inversion revealed that a bipolar MMF
has a U-shaped magnetic field configuration. Our observations provide
a clear intensity counterpart of the observed MMF in the photosphere,
and strong evidence of the connection between the MMF and the penumbral
filament as a serpentine field.
Title: Transverse Motions of Chromospheric Type II Spicules Observed
by the New Solar Telescope
Authors: Yurchyshyn, V.; Kilcik, A.; Abramenko, V.
Bibcode: 2012arXiv1207.6417Y
Altcode:
Using high resolution off-band \ha\ data from the New Solar Telescope
and Morlet wavelet analysis technique, we analyzed transverse motions
of type II spicules observed near the North Pole of the Sun. Our new
findings are that i) some of the observed type II spicules display
kink or an inverse "Y" features, suggesting that their origin may be
due to magnetic reconnection, and ii) type II spicules tend to display
coherent transverse motions/oscillations. Also, the wavelet analysis
detected significant presence of high frequency oscillations in type
II spicules, ranging from 30 to 180 s with the the average period of 90
s. We conclude that at least some of type II spicules and their coherent
transverse motions may be caused by reconnection between large scale
fields rooted in the intergranular lanes and and small-scale emerging
dipoles, a process that is know to generate high frequency kink mode
MHD waves propagating along the magnetic field lines.
Title: Small Scale Field Emergence and Its Impact on Photospheric
Granulation
Authors: Yurchyshyn, V.; Ahn, K.; Abramenko, V.; Goode, P.; Cao, W.
Bibcode: 2012arXiv1207.6418Y
Altcode:
We used photospheric intensity images and magnetic field measurements
from the New Solar Telescope in Big Bear and Helioseismic Magnetic
Imager on board Solar Dynamics Observatory (SDO) to study the the effect
that the new small-scale emerging flux induces on solar granulation. We
report that emerging flux appears to leave different types of footprint
on solar granulation: i) diffuse irregular patches of increased
brightness, ii) well defined filament-like structures and accompanied
bright points, and iii) bright point-like features that appear inside
granules. We suggest that the type of the footprint depends on the
intensity of emerging fields. Stronger fields, emerging as a part of
large magnetic structure, create on the solar surface a well defined
filamentary pattern with bright points at the ends of the filaments,
while weak turbulent fields are associated with bright patches inside
the host granule.
Title: New solar telescope in Big Bear: evidence for super-diffusivity
and small-scale solar dynamos?
Authors: Goode, Philip R.; Abramenko, Valentyna; Yurchyshyn, Vasyl
Bibcode: 2012PhyS...86a8402G
Altcode:
The 1.6 m clear aperture New Solar Telescope (NST) in Big Bear Solar
Observatory (BBSO) is now providing the highest resolution solar data
ever. These data have revealed surprises about the Sun on small-scales
including the observation that bright points (BPs), which can be
used as proxies for the intense, compact magnetic elements that are
apparent in photospheric intergranular lanes. The BPs are ever more
numerous on ever smaller spatial scales as though there were no limit
to how small the BPs can be. Here we discuss high resolution NST data
on BPs that provide support for the ideas that a turbulent regime
of super-diffusivity dominates in the quiet Sun, and there are local
dynamos operating near the solar surface.
Title: Turbulent Kinetic Energy Spectra of Solar Convection from
NST Observations and Realistic MHD Simulations
Authors: Kitiashvili, I. N.; Abramenko, V. I.; Goode, P. R.;
Kosovichev, A. G.; Lele, S. K.; Mansour, N. N.; Wray, A. A.;
Yurchyshyn, V. B.
Bibcode: 2012arXiv1206.5300K
Altcode:
Turbulent properties of the quiet Sun represent the basic state of
surface conditions, and a background for various processes of solar
activity. Therefore understanding of properties and dynamics of this
`basic' state is important for investigation of more complex phenomena,
formation and development of observed phenomena in the photosphere and
atmosphere. For characterization of the turbulent properties we compare
kinetic energy spectra on granular and sub-granular scales obtained
from infrared TiO observations with the New Solar Telescope (Big Bear
Solar Observatory) and from 3D radiative MHD numerical simulations
('SolarBox' code). We find that the numerical simulations require a high
spatial resolution with 10 - 25 km grid-step in order to reproduce the
inertial (Kolmogorov) turbulence range. The observational data require
an averaging procedure to remove noise and potential instrumental
artifacts. The resulting kinetic energy spectra show a good agreement
between the simulations and observations, opening new perspectives for
detailed joint analysis of more complex turbulent phenomena on the Sun,
and possibly on other stars. In addition, using the simulations and
observations we investigate effects of background magnetic field,
which is concentrated in self-organized complicated structures in
intergranular lanes, and find an increase of the small-scale turbulence
energy and its decrease at larger scales due to magnetic field effects.
Title: High spatial resolution VAULT H-Lyα observations and
multiwavelength analysis of an active region filament
Authors: Vial, J. -C.; Olivier, K.; Philippon, A. A.; Vourlidas, A.;
Yurchyshyn, V.
Bibcode: 2012A&A...541A.108V
Altcode:
Context. The search for the fine structure of prominences has
received considerable new attention thanks to the Swedish Solar
Telescope (SST) Hα pictures that provide an unsurpassed spatial
resolution. Recently, it has been shown that the filaments' coronal
environment, at least for quiescent filaments, is perturbed by either
cool absorbing material (in the EUV) or an "emissivity blocking"
(actually a lack of transition region and coronal material).
Aims: The aim is to assess the fine structure in an active region
filament and to determine the nature of the EUV absorption or lack
of emission phenomena, using the very optically thick line H-Lyα,
formed at a temperature higher than Hα.
Methods: We performed
a multiwavelength study where high-resolution imaging in the H-Lyα
line (VAULT) was analysed and compared with observations of an active
region filament in Hα (BBSO) and EUV lines (EIT and TRACE).
Results: As for the SST data, small-scale structures were detected at
a typical scale of about one to two arcseconds with, for some cuts,
an indication of fine scales down to 0.4 arcsec in the optically thick
H-Lyα line. The filament intensity relative to the intensity of the
(active) region it is embedded in is about 0.2 in H-Lyα. This ratio
(Lymanα ratio intensity or "LRI") is the lowest value compared to
other lines, e.g. Hα. The filament environment was also investigated
and evidence of an UV extension was found. The comparison of spatial
cuts in different lines across the filament shows evidence of strong
absorption, and consequently of cool plasma on one side of the filament,
but not on the other (that side is obscured by the filament itself).
Conclusions: The absence of very fine structure in H-Lyα compared
to Hα is explained by the formation temperature of the H-Lyα line
(~20 000 K), where the transition regions of the thin threads begin to
merge. From the detection of H-Lyα absorption on the observable side of
the filament side, we derive the presence of absorbing (cool) material
and possibly also of emissivity blocking (or coronal void). This poses
the question whether these absorption effects are typical of active
region filaments. Appendix A is available in electronic form at
http://www.aanda.org
Title: Direct Observation of the Intensity Counterpart of Moving
Magnetic Features on the Photosphere and the Corresponding Vector
Magnetic Fields
Authors: Lim, Eunkyung; Yurchyshyn, V.; Goode, P.
Bibcode: 2012AAS...22020622L
Altcode:
The formation and the temporal evolution of a bipolar moving magnetic
feature (MMF) was studied with high spatio-temporal resolution. The
photometric properties were observed with the New Solar Telescope at
Big Bear Solar Observatory using a broadband TiO filter at 705.7nm,
while the magnetic field was analyzed using the Spectropolarimetric
data obtained by Hinode/SOT. From our high resolution, multi-wavelength
observation, we studied 1) the detailed structure of the intensity
counterpart in the photosphere of a bipolar MMF, 2) the vector magnetic
field and the Doppler velocity of the MMF in time. A bipolar MMF
having its positive polarity closer to the negative penumbra formed
being accompanied by a bright, filamentary structure in the TiO line
connecting the MMF and a dark penumbral filament. A fast downflow
was detected in the positive polarity region, where the filamentary
structure is seen to be brighter than its surroundings. The vector
magnetic field obtained from the full Stokes inversion reveals a
developing U-shaped magnetic dip between the poles of the bipolar
MMF. Our observations provide the most clear intensity counterpart
in the photosphere to the observed MMF, and strong evidence of the
connection between the MMF and the local penumbral filament as a
serpentine field.
Title: Observational Signatures of the Small-Scale Dynamo in the
Quiet Sun
Authors: Abramenko, V.; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2012ASPC..455...17A
Altcode:
The generation and diffusion of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales—from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifest in two
types: as a global dynamo responsible for the solar cycle periodicity,
and as a small-scale turbulent dynamo responsible for the formation
of the magnetic carpet in the quiet Sun. Numerous MHD simulations of
solar turbulence did not yet reach a consensus as to the existence
of a turbulent dynamo on the Sun. At the same time, high-resolution
observations of the quiet Sun from Hinode instruments suggest
possibilities for the turbulent dynamo. Analysis of characteristics of
turbulence derived from observations would be beneficial in tackling
the problem. We analyze magnetic and velocity energy spectra as derived
from Hinode/SOT, SOHO/MDI, SDO/HMI and the New Solar Telescope (NST)
of Big Bear Solar Observatory (BBSO) to explore the possibilities for
the small-scale turbulent dynamo in the quiet Sun.
Title: Oscillations of Rapid Blueshifted Events as Derived from
NST Data
Authors: Yurchyshyn, Vasyl B.; Kilcik, A.; Abramenko, V.
Bibcode: 2012AAS...22020304Y
Altcode:
We studied oscillations of type II spicules observed near the north
pole of the sun. The study is based on high-resolution data recorded by
the New Solar Telescope at the Big Bear Solar Observatory. The spicule
oscillations were probed by applying the global wavelet method to a 34
min continuous time series of off-band Halpha images. The main findings
are: i) Type II spicules are oscillating with about 1 min period,
while the outside quiet regions show dominance of 3 min periods. ii)
Spicules belonging to a cluster, tend to oscillate as a group. We will
present details of these findings and discuss possible implications.
Title: Origin of Rapid Blueshifted Events in Coronal Holes
Authors: Yurchyshyn, Vasyl B.; Ahn, K.; Abramenko, V.; Goode, P.;
Cao, W.
Bibcode: 2012AAS...22042304Y
Altcode:
Clusters of photospheric bright points are surrounded by chromospheric
rosette-like structures. These rosettes, when observed in the far
off-band (-0.1nm) Halpha images often appear to consist of short living,
narrow rapid blueshifted events (RBEs). RBEs, in turn, are thought to
be disk counterparts of type II spicules (spicules II), detected in
Hinode data, which may be playing play an important role in coronal
heating since they are thought to supply mass to the solar corona. The
search for the origin of type II spicules was one of the main focus of
solar physics research in the recent years. Here we present our
findings on the possible driving mechanism of spicules II, which are
based on high resolution photospheric, chromospheric and magnetic field
data from the New Solar Telescope (NST) collected in a coronal hole. We
report that the majority of RBEs, occurring around a network cluster,
are associated with appearance of opposite polarity features within
the unipolar cluster fields, suggesting that magnetic reconnection
may be the driving mechanism. We will present these observations in
details and discuss possible implications.
Title: Observational Criteria For Small-scale Turbulent Dynamo In
The Solar Photosphere
Authors: Abramenko, Valentyna; Goode, P.; Yurchyshyn, V.
Bibcode: 2012AAS...22011002A
Altcode:
Generation and dispersal of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales - from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifested
in two types: as a global dynamo responsible for the solar cycle
periodicity, and as a small-scale turbulent dynamo (SSTD) responsible
for the formation of magnetic carpet in the quiet Sun. Numerous MHD
simulations of the solar turbulence did not yet reach a consensus
as to the existence and role of SSTD on the Sun. At the same time,
high-resolution observations of the quiet Sun are capable to provide
certain criteria to prove or rule out SSTD. We suggest to probe four
possible criteria: i) mutual behaviour of the kinetic and magnetic power
spectra; ii) intermittency/multifractality of the magnetic field; iii)
smallest observed scale of magnetic flux tubes; iv) regime of magnetic
diffusivity on smallest observable scales. We analyse magnetic, velocity
and solar granulation data as derived from Hinode/SOT, SOHO/MDI, SDO/HMI
and the New Solar Telescope (NST) of Big Bear Solar Observatory (BBSO)
to explore the possibilities for SSTD in the quiet Sun.
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Kilcik, A.; Yurchyshyn, V. B.; Rempel, M.; Abramenko, V.;
Kitai, R.; Goode, P. R.; Cao, W.; Watanabe, H.
Bibcode: 2012ApJ...745..163K
Altcode: 2011arXiv1111.3997K
We studied bright umbral dots (UDs) detected in a moderate size sunspot
and compared their statistical properties to recent MHD models. The
study is based on high-resolution data recorded by the New Solar
Telescope at the Big Bear Solar Observatory and three-dimensional (3D)
MHD simulations of sunspots. Observed UDs, living longer than 150 s,
were detected and tracked in a 46 minute long data set, using an
automatic detection code. A total of 1553 (620) UDs were detected
in the photospheric (low chromospheric) data. Our main findings
are (1) none of the analyzed UDs is precisely circular, (2) the
diameter-intensity relationship only holds in bright umbral areas, and
(3) UD velocities are inversely related to their lifetime. While nearly
all photospheric UDs can be identified in the low chromospheric images,
some small closely spaced UDs appear in the low chromosphere as a single
cluster. Slow-moving and long-living UDs seem to exist in both the low
chromosphere and photosphere, while fast-moving and short-living UDs
are mainly detected in the photospheric images. Comparison to the 3D
MHD simulations showed that both types of UDs display, on average, very
similar statistical characteristics. However, (1) the average number
of observed UDs per unit area is smaller than that of the model UDs,
and (2) on average, the diameter of model UDs is slightly larger than
that of observed ones.
Title: Magnetic and Kinetic Power Spectra as a Tool to Probe the
Turbulent Dynamo
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.
Bibcode: 2011arXiv1112.2750A
Altcode:
Generation and diffusion of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales - from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifest in two
types: as a global dynamo responsible for the solar cycle periodicity,
and as a small-scale turbulent dynamo responsible for the formation
of magnetic carpet in the quiet Sun. Numerous MHD simulations of the
solar turbulence did not yet reach a consensus as to the existence
of a turbulent dynamo on the Sun. At the same time, high-resolution
observations of the quiet Sun from Hinode instruments suggest
possibilities for the turbulent dynamo. Analysis of characteristics of
turbulence derived from observations would be beneficial in tackling
the problem. We analyse magnetic and velocity energy spectra as derived
from Hinode/SOT, SOHO/MDI, SDO/HMI and the New Solar Telescope (NST)
of Big Bear Solar Observatory (BBSO) to explore the possibilities for
the small-scale turbulent dynamo in the quiet Sun.
Title: Signatures of Small-Scale Magnetic Field Emergence as Seen
from the New Solar Telescope in Big Bear
Authors: Yurchyshyn, V.
Bibcode: 2011AGUFMSH33C..06Y
Altcode:
Increased resolution of solar telescopes allow us to study emerging
small-scale magnetic fields in unprecedented detail. First light Hinode
magnetograms showed evidence of both horizontal and line-of-sight field
being constantly brought to the solar surface by solar convection
motion. What are the signatures of these fields in the photosphere,
if any? The largest aperture ground-based solar telescope, the New
Solar Telescope (NST) of Big Bear Solar Observatory now allows us to
address many important issues of coupling between the photosphere and
chromosphere by means of simultaneous observations of photospheric
granulation with well-resolved bright points (BPs) and associated
dynamics in the low chromosphere, as seen in the H-alpha spectral
line. Excellent seeing conditions, augmented with an adaptive optics
system and speckle-reconstruction applications produce diffraction
limited images. We examine NST granulation and Halpha images co-temporal
with SDO, Hinode and BBSO/IRIM vector magnetograms. Our main finding
is that emerging magnetic flux leaves clear footprint in solar
granulation. Moreover, the granulation responds to the emerging flux
much earlier that it appears in magnetograms. NST granulation images
also reveal that various bright points as well as bright granular lanes
may form and evolve within a granule. These newly detected features
are believed to be associated with small-scale magnetic fields.
Title: Turbulent Diffusion in the Photosphere as Derived from
Photospheric Bright Point Motion
Authors: Abramenko, V. I.; Carbone, V.; Yurchyshyn, V.; Goode, P. R.;
Stein, R. F.; Lepreti, F.; Capparelli, V.; Vecchio, A.
Bibcode: 2011ApJ...743..133A
Altcode: 2011arXiv1111.4456A
On the basis of observations of solar granulation obtained with the
New Solar Telescope of Big Bear Solar Observatory, we explored proper
motion of bright points (BPs) in a quiet-sun area, a coronal hole, and
an active region plage. We automatically detected and traced BPs and
derived their mean-squared displacements as a function of time (starting
from the appearance of each BP) for all available time intervals. In all
three magnetic environments, we found the presence of a super-diffusion
regime, which is the most pronounced inside the time interval of 10-300
s. Super-diffusion, measured via the spectral index, γ, which is the
slope of the mean-squared displacement spectrum, increases from the
plage area (γ = 1.48) to the quiet-sun area (γ = 1.53) to the coronal
hole (γ = 1.67). We also found that the coefficient of turbulent
diffusion changes in direct proportion to both temporal and spatial
scales. For the minimum spatial scale (22 km) and minimum time scale
(10 s), it is 22 and 19 km2 s-1 for the coronal
hole and the quiet-sun area, respectively, whereas for the plage area
it is about 12 km2 s-1 for the minimum time
scale of 15 s. We applied our BP tracking code to three-dimensional
MHD model data of solar convection and found the super-diffusion with
γ = 1.45. An expression for the turbulent diffusion coefficient as
a function of scales and γ is obtained.
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Yurchyshyn, V.; Kilcik, A.; Rempel, M.; Abramenko, V.; Kitai,
R.; Goode, P. R.; Cao, W.; Watanabe, H.
Bibcode: 2011sdmi.confE..86Y
Altcode:
We studied bright umbral dots (UDs) detected in the main sunspot
of AR NOAA 11108 and compare their statistical properties to a
state-of-the-art MHD model of a sunspot. The study is based on
high resolution data recorded on September 20, 2010 by the New Solar
Telescope (NST) at Big Bear Solar Observatory and 3D MHD simulations of
sunspots. The 46 min data set included photospheric (0.3nm TiO filter
centered at 705.7 nm) and chromospheric (0.025nm Hα Lyot filter)
adaptive optics corrected and speckle reconstructed images. Bright
UDs, living longer than 150 s, were detected and tracked using an
automatic UD detection code. Total 1553 (620) UDs were detected
in the photospheric (chromospheric) data. Our main findings are:
i) none of the analyzed UDs is of an exact circular shape, ii) the
diameter-intensity relationship only works for bright umbral areas, and
iii) UD velocities inversely related to their life time. Comparison of
photospheric and chromospheric data showed that nearly all photospheric
UDs can be identified in the chromospheric images. However, it appears
that some small closely spaced UDs appear in the chromospheric images
as a single cluster, which may lead to the underestimation of the total
number of detected chromospheric UDs. Also, while slow moving and long
living UDs seem to exist in both chromosphere and photosphere, fast
moving and short living ones are detected mainly in the photospheric
images. Comparison of model and observed data shows that both types
of UDs display very similar statistical characteristics. The main
difference between parameters of model and observed UDs is that i)
the average number of observed UDs per unit area is smaller than that
of the model UDs, and ii) on average, the diameter of model UDs is
slightly larger than that of observed ones.
Title: High-resolution observations of the solar dynamics and
magnetism
Authors: Goode, Phil; Cao, Wenda; Yurchyshyn, Vasyl
Bibcode: 2011sdmi.confE..28G
Altcode:
The NST is the first facility-class solar telescope built in the US
in a generation. Images and movies illustrating the high resolution
capabilities of the NST will be shown. In particular, high resolution
NST observations reveal vortices in the granular field that are
associated with newly discovered, but ubiquitous small-scale jets,
which are much smaller-scale than Hinode type-II jets. NST observations
have been used to probe the nature of the diffusion of magnetic bright
points, which seems consistent with the operation of small-scale
dynamos, while seeming to be sufficient on large-scales to support the
Wang-Sheeley dynamo picture. Other recent NST results correlated with
satellite observations will be shown and discussed.
Title: Photospheric Signatures of Granular-scale Flux Emergence and
Cancellation at the Penumbral Boundary
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Abramenko, Valentyna;
Ahn, Kwangsu; Cao, Wenda; Goode, Philip
Bibcode: 2011ApJ...740...82L
Altcode: 2011arXiv1107.5254L
We studied flux emergence events of sub-granular scale in a solar
active region. The New Solar Telescope (NST) of the Big Bear Solar
Observatory made it possible to clearly observe the photospheric
signature of flux emergence with very high spatial (0farcs11 at 7057
Å) and temporal (15 s) resolution. From TiO observations with the
pixel scale of 0farcs0375, we found several elongated granule-like
features (GLFs) stretching from the penumbral filaments of a sunspot
at a relatively high speed of over 4 km s-1. After a
slender arched darkening appeared at the tip of a penumbral filament,
a bright point (BP) developed and quickly moved away from the filament,
forming and stretching a GLF. The size of a GLF was approximately
0farcs5 wide and 3'' long. The moving BP encountered nearby structures
after several minutes of stretching, and the well-defined elongated
shape of the GLF faded away. Magnetograms from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging
Magnetograph revealed that those GLFs are photospheric indicators of
small-scale flux emergence, and their disappearance is related to
magnetic cancellation. From two well-observed events, we describe
detailed development of the sub-structures of GLFs and different
cancellation processes that each of the two GLFs underwent.
Title: On the Origin of Intergranular Jets
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Steiner, O.
Bibcode: 2011ApJ...736L..35Y
Altcode: 2011arXiv1106.5535Y
We observe that intergranular jets, originating in the intergranular
space surrounding individual granules, tend to be associated with
granular fragmentation, in particular, with the formation and evolution
of a bright granular lane (BGL) within individual granules. The BGLs
have recently been identified as vortex tubes by Steiner et al. We
further discover the development of a well-defined bright grain
located between the BGL and the dark intergranular lane to which it
is connected. Signatures of a BGL may reach the lower chromosphere
and can be detected in off-band Hα images. Simulations also indicate
that vortex tubes are frequently associated with small-scale magnetic
fields. We speculate that the intergranular jets detected in the New
Solar Telescope (NST) data may result from the interaction between
the turbulent small-scale fields associated with the vortex tube
and the larger-scale fields existing in the intergranular lanes. The
intergranular jets are much smaller and weaker than all previously known
jet-like events. At the same time, they appear much more numerous than
the larger events, leading us to the speculation that the total energy
release and mass transport by these tiny events may not be negligible in
the energy and mass-flux balance near the temperature minimum atop the
photosphere. The study is based on the photospheric TiO broadband (1.0
nm) filter data acquired with the 1.6 m NST operating at the Big Bear
Solar Observatory. The data set also includes NST off-band Hα images
collected through a Zeiss Lyot filter with a passband of 0.025 nm.
Title: Dynamics of Photospheric Bright Points in a Transient
Coronal Hole
Authors: Yurchyshyn, Vasyl; BBSO Team
Bibcode: 2011shin.confE.165Y
Altcode:
We use data from the New Solar Telescope (NST) in Big Bear to search
for connection between typical dynamics of bright points (collision,
clustering and rapid motions) and chromospheric activity, such as
jets that are visible on all scales down to the smallest resolved
features. In this presentation we will highlight the most important
findings, which include the following. 1) In mostly unipolar coronal
holes, the majority of colliding/interacting BPs are not associated with
any detectable chromospheric activity. This means that the component
reconnection, presumably occurring when the same polarity BPs interact,
may not be very effective in producing chromospheric flows. 2) NST/TiO
images further reveal the hidden structure of plasma vortex tubes
abundant in coronal holes. Some vortex-tube events are co-spatial
with small-scale chromospheric jets, which suggests that the tubes
may be associated with new magnetic flux emerging within a granule. 3)
On large spatial scales of a CH we observe that displacements of BPs
display a well pronounced dominant direction of motion that corresponds
to the direction of migration of the CH.
Title: Effects of Hysteresis Between Maximum CME Speed Index and
Some Solar Activity Indicators during Cycle 23
Authors: Kilcik, A.; Ozguc, A.; Yurchyshyn, V. B.; Rozelot, J. P.
Bibcode: 2011simi.conf....6K
Altcode:
Using the smoothed time series of maximum CME speed index data set
for solar cycle 23 we find that maximum CME speed index and some solar
activity indicators show a hysteresis phenomenon. It is observed that
total sunspot number, total sunspot area, solar radio flux (10.7 cm)
and flare index follow different paths for the ascending and descending
phases of solar cycle 23 while saturation effect exists at the maximum
phase of the cycle. However we notice that the separations between
the paths are not the same for the solar activity indicators we used.
Title: Sunspot Umbral Dots Detected with the New Solar Telescope
Authors: Kilcik, Ali; Yurchyshyn, V.; Abramenko, V.; Goode, P.; Cao, W.
Bibcode: 2011SPD....42.1901K
Altcode: 2011BAAS..43S.1901K
We present a study of bright umbral dots detected inside a large sunspot
of NOAA AR 11108. This study is based on high resolution data recorded
on September 20, 2010 with the New Solar Telescope (NST) at Big Bear
Solar Observatory. The data set, spanning 46 min, consists of a total
of 184 adaptive optics corrected and speckle reconstructed images
obtained with a 0.3 nm passband TiO filter centered on the 705.7 nm
spectral line. The image cadence is 15 s and the pixel size of 0.0375
arcsec. Bright umbral dots (UDs) were detected and tracked using
an automatic routine. Here we only focus on long living UDs (>150
s in life time) and a total of 513 such features were detected during
the observed period. We found that the average lifetime of a UD is 7.4
min and an average size is 0.34 arcsec. There is a tendency for larger
UDs to be brighter (and more circular). Many UDs are not of circular
shape. We will also present probability distribution of various physical
parameters and compare the results to similar earlier studies.
Title: NST and Photospheric Fine -scale Structures Indicating the
Small Scale Flux Emergence in an Active Region
Authors: Lim, Eunkyung; Yurchyshyn, V.; Abramenko, V.; Goode, P.;
Ahn, K.
Bibcode: 2011SPD....42.0604L
Altcode: 2011BAAS..43S.0604L
We have studied very small-scale flux emergence events on granular
scales in a solar active region. The New Solar Telescope of Big Bear
Solar Observatory made it possible to clearly observe the photospheric
signature of flux emergence with a very high spatial (0".034/pixel) and
temporal (15s) resolution. From the TiO observations, we found several
elongated thread-like granules protruding from the penumbral filaments
of a sunspot at a relatively high speed of over 4km s-1. A slender
arched darkening protrudes from the tip of the penumbral filament, then
quickly stretches its length along the intergranular lane with a slight
bright point developing at the previously shaded leading edge. The size
of such granules is approximately 0".5 wide and 3” long, and their
stretching lasts for several minutes before contacting other magnetic
structures nearby. Magnetograms from HMI/SDO and IRIM/BBSO show that
such elongated granules are photospheric indicators of small-scale
flux emergence. The cancellation process is also described in detail
for two events that show different chromospheric signatures, such
as brightenings and jets during the cancellation. We speculate that
subsurface connectivity and the depth of the roots of magnetic field
are the main keys to determining different cancellation phenomena.
Title: Utilizing Nst Data To Look For Connection Between Photospheric
Dynamics And Small-scale Chromospheric Activity
Authors: Yurchyshyn, Vasyl B.
Bibcode: 2011SPD....42.0602Y
Altcode: 2011BAAS..43S.0602Y
The largest ground-based solar telescope, the new solar telescope (NST)
of Big Bear Solar Observatory now allows us to address many important
issues of coupling between the photosphere and chromosphere by means of
simultaneous observations of photospheric granulation with well resolved
bright points (BPs) and associated dynamics in the low chromosphere,
as seen in H-alpha spectral line. Excellent seeing conditions,
augmented with an adaptive optics system and speckle-reconstruction
applications produce diffraction limited images. We use these data to
search for any possible connection between typical dynamics of bright
points (collision, clustering and rapid motions) and chromospheric
activity, such as jets that are visible on all scales down to the
smallest resolved features. In this presentation we will highlight the
most important findings, which include the following. 1) In mostly
unipolar coronal holes, the majority of colliding/interacting BPs
are not associated with any detectable chromospheric activity. This
means that the component reconnection, presumably occurring when the
same polarity BPs interact, may not be very effective in producing
chromospheric flows. We speculate that interaction of opposite polarity
BPs may be more effective in generating up-flows. 2) NST/TiO images
further reveal the hidden structure of plasma vortex tubes, previously
predicted by Steiner et al. Besides the bright granular lane, a vortex
tube structure also includes rapidly developing bright grain co-spatial
with the tube's axis. Finally, some vortex tube events, detected in
a CH data set, are co-spatial with small-scale chromospheric jets,
which suggests that they may be associated with new magnetic flux
emerging within a granule.
Title: New View on Quiet-Sun Photospheric Dynamics Offered by NST Data
Authors: Abramenko, Valentyna; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2011SPD....42.0603A
Altcode: 2011BAAS..43S.0603A
Recent observations of the quiet sun photosphere obtained with the
1.6 meter New Solar telescope (NST) of Big Bear Solar observatory
(BBSO) delivered new information about photospheric fine structures
and their dynamics, as well as posing new questions. The 2-hour
uninterrupted data set of solar granulation obtained under excellent
seeing conditions on August 3, 2010 (with cadence of 10 sec) was the
basis for the study. Statistical analysis of automatically detected and
tracked magnetic bright points (MBPs) showed that the MBPs population
monotonically increases as their size decreases, down to 60-70 km. Our
analysis shows that if the smallest magnetic flux tubes exist, their
size is still smaller that 60-70 km, which impose strong restrictions on
the modeling of these structures. We also found that the distributions
of the MBP's size and lifetime do not follow a traditional Gaussian
distribution, typical for random processes. Instead, it follows a
log-normal distribution, typical for avalanches, catastrophes, stock
market data, etc. Our data set also demonstrated that a majority (98.6
%) of MBPs are short live (<2 min). This remarkable fact was not
obvious from previous studies because an extremely high time cadence
was required. The fact indicates that the majority of MBPs appear for a
very short time (tens of seconds), similar to other transient features,
for example, chromospheric jets. The most important point here is that
these small and short living MBPs significantly increase dynamics
(flux emergence, collapse into MBPs, and magnetic flux recycling)
of the solar surface magnetic fields.
Title: Response of Granulation to Small-scale Bright Features in
the Quiet Sun
Authors: Anđić, A.; Chae, J.; Goode, P. R.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
Bibcode: 2011ApJ...731...29A
Altcode: 2011arXiv1102.3404A
We detected 2.8 bright points (BPs) per Mm2 in the quiet
Sun with the New Solar Telescope at Big Bear Solar Observatory, using
the TiO 705.68 nm spectral line at an angular resolution ~0farcs1 to
obtain a 30 minute data sequence. Some BPs formed knots that were
stable in time and influenced the properties of the granulation
pattern around them. The observed granulation pattern within ~3''
of knots presents smaller granules than those observed in a normal
granulation pattern, i.e., around the knots a suppressed convection
is detected. Observed BPs covered ~5% of the solar surface and were
not homogeneously distributed. BPs had an average size of 0farcs22,
they were detectable for 4.28 minutes on average, and had an averaged
contrast of 0.1% in the deep red TiO spectral line.
Title: Time Distributions of Large and Small Sunspot Groups Over
Four Solar Cycles
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Ozguc, A.; Rozelot, J. P.; Cao, W.
Bibcode: 2011ApJ...731...30K
Altcode: 2011arXiv1111.3999K
Here we analyze solar activity by focusing on time variations of
the number of sunspot groups (SGs) as a function of their modified
Zurich class. We analyzed data for solar cycles 20-23 by using Rome
(cycles 20 and 21) and Learmonth Solar Observatory (cycles 22 and 23)
SG numbers. All SGs recorded during these time intervals were separated
into two groups. The first group includes small SGs (A, B, C, H, and
J classes by Zurich classification), and the second group consists
of large SGs (D, E, F, and G classes). We then calculated small and
large SG numbers from their daily mean numbers as observed on the
solar disk during a given month. We report that the time variations
of small and large SG numbers are asymmetric except for solar cycle
22. In general, large SG numbers appear to reach their maximum in the
middle of the solar cycle (phases 0.45-0.5), while the international
sunspot numbers and the small SG numbers generally peak much earlier
(solar cycle phases 0.29-0.35). Moreover, the 10.7 cm solar radio
flux, the facular area, and the maximum coronal mass ejection speed
show better agreement with the large SG numbers than they do with
the small SG numbers. Our results suggest that the large SG numbers
are more likely to shed light on solar activity and its geophysical
implications. Our findings may also influence our understanding of
long-term variations of the total solar irradiance, which is thought
to be an important factor in the Sun-Earth climate relationship.
Title: Maximum Coronal Mass Ejection Speed as an Indicator of Solar
and Geomagnetic Activities
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Gopalswamy, N.; Ozguc, A.; Rozelot, J. P.
Bibcode: 2011ApJ...727...44K
Altcode: 2011arXiv1111.4000K
We investigate the relationship between the monthly averaged maximal
speeds of coronal mass ejections (CMEs), international sunspot number
(ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008
time interval (solar cycle 23). Our new findings are as follows. (1)
There is a noteworthy relationship between monthly averaged maximum CME
speeds and sunspot numbers, Ap and Dst indices. Various peculiarities
in the monthly Dst index are correlated better with the fine structures
in the CME speed profile than that in the ISSN data. (2) Unlike the
sunspot numbers, the CME speed index does not exhibit a double peak
maximum. Instead, the CME speed profile peaks during the declining
phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3)
The CME number shows a double peak similar to that seen in the sunspot
numbers. The CME occurrence rate remained very high even near the
minimum of the solar cycle 23, when both the sunspot number and the
CME average maximum speed were reaching their minimum values. (4) A
well-defined peak of the Ap index between 2002 May and 2004 August was
co-temporal with the excess of the mid-latitude coronal holes during
solar cycle 23. The above findings suggest that the CME speed index may
be a useful indicator of both solar and geomagnetic activities. It may
have advantages over the sunspot numbers, because it better reflects
the intensity of Earth-directed solar eruptions.
Title: Relationship Between Earth Directed Solar Eruptions and
Magnetic Clouds at 1AU (Invited)
Authors: Yurchyshyn, V.
Bibcode: 2010AGUFMSH43C..03Y
Altcode:
Understanding the connection between the magnetic configurations of a
coronal mass ejection (CME) and their counterpart in the interplanetary
medium is very important in terms of space weather predictions. Recent
data convincingly demonstrate that fast CME originating from near
the solar disk center are the major cause of extreme space weather
events. There also appears to be a link between the CME orientation and
the direction of the magnetic fields in the underlying flux rope. Many
CMEs rotate as they propagate in the interplanetary medium so that the
probability of a strong geomagnetic storm depends on both the initial
properties of the erupted structure and the interaction between the
ejecta and heliospheric magnetic fields. Detailed understanding of
this interaction may shed light on the problems related to connecting
solar surface phenomena to their interplanetary counterparts. In
this presentation I will briefly review current progress on the CME
evolution in the heliosphere.
Title: Photosphere-Chromosphere Connection as Derived from Nst
Observations
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
Bibcode: 2010AGUFMSH31C1807Y
Altcode:
Largest ground-based new solar telescope (NST) of Big Bear Solar
Observatory allows us to simultaneously observe photospheric
granulation with luxurious filigree of bright points (BPs) and
low/middle chromosphere in H- alpha spectral line. Excellent climate
conditions of Big Bear Valley, augmented with an adaptive optics system
and speckle-reconstruction applications produce diffraction limited
images. Recent observations (July- August 2010) showed that BPs visible
in the photosphere with the TiO filter (centered at a wavelength of
705.7 nm) are co-spatial with the BPs visible in the blue wind of
H-alpha line. As evidenced from these data, the H-alpha BPs, in turn,
are frequently at origin of small-scale chromospheric jets. These jets
are visible at all scales down to the smallest resolved features. As
long as photospheric BPs are co-spatial with the magnetic elements,
one might conclude that photospheric magnetic fields are relevant
to the chromospheric jet formation. NST Ha-0.13nm image acquired on
June 28, 2010. The dark features are upward directed flows that have
velocities up to 60km/sec seen against the background of photospheric
granulation with inclusions of BPs. The corresponding movie shows
reveals significant dynamics associated with these rosette like
structures stemming from clusters of BPs.
Title: Relationship between orientations of halo CMEs and the
underlying filament / active regions
Authors: Kilcik, A.; Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
Bibcode: 2010AGUFMSH51C1684K
Altcode:
Coronal mass ejections (CMEs) are the most important objects of space
weather studies. Although they have been at focus of many studies for
a long time now, there are still many unanswered questions. Here we
focus on the possible relationship between the direction of CME rotation
and the prevailing magnetic twist of the CME's source region. We could
determine the predominant helicity for 45 filaments and active regions
that appeared on both hemispheres of the Sun. We thus further confirm
that 76% of all source regions in the southern hemisphere were “S”
shaped, while 79% of northern hemisphere events were reverse “S”
(“Z”) shaped. These ratios agree with the well known hemispheric
segregation rule. According to theoretical considerations, (Green,
et al. 2007; Lynch, et al. 2009) CMEs, associated with eruption of
“S” (“Z') shaped structures are expected to rotate clockwise
(counterclockwise). Here we report that 67% of all source regions in
the southern hemisphere showed a predominant twist that agreed with
the direction of rotation of the corresponding CMEs. In the northern
hemisphere this ration was 63%. These findings may significantly
improve our understanding of CME evolution and their connection to
magnetic clouds. They may are affect our ability to predict severity
of geomagnetic storms.
Title: Size and Life Time Distributions of Bright Points in the
Quiet Sun Photosphere
Authors: Abramenko, V.; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2010AGUFMSH31C1806A
Altcode:
We present results of two-hour uninterrupted observations of solar
granulation obtained at excellent seeing conditions on August 3, 2010
with the largest ground-based new solar telescope (NST) operating
at Big Bear Solar observatory. Adaptive optics corrected data were
acquired with a broad-band TiO filter (centered at a wavelength of
705.7 nm). The time cadence was 10s and the pixel size was 0.0375
arcsec. Photospheric bright points (BPs) were automatically detected
and traced. We find that NST TiO BPs are co-spatial with those visible
in Hinode/SOT G-band images. In cases where Hinode/SOT detects one
large BP, NST shows several fully resolved BPs. Extended filigree
features running along intergranular lanes appear in NST images clearly
fragmented into separate BPs. The distribution function of the NST
BPs size is exponential and extends to the diffraction limit of NST
(77 km) without any saturation. The life time distribution function
follows a power law with an index of -1.9. About 98.6% of all detected
BPs live shorter than 120 s, and the most persistent BP lasted for
44 minutes. The size and the maximum intensity of BPs were found to
be proportional to the life time. Results are discussed in framework
of coronal heating and turbulent dynamo. Left - Hinode G-band image
obtained on 2010 August 3 at 12:22:11 UT (pixel size 0.109"). Right -
NST TiO image obtained on 2010 August 3 at 12:22:10 UT. Both images
cover the same area of 18.8" x 18.8" on the Sun. PDFs of the BPs
diameter calculated from NST TiO images (black) and from Hinode/SOT
G-band images (by Utz et al. 2009, blue).
Title: Statistical Distribution of Size and Lifetime of Bright Points
Observed with the New Solar Telescope
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Goode, Philip;
Kilcik, Ali
Bibcode: 2010ApJ...725L.101A
Altcode: 2010arXiv1012.1584A
We present results of 2 hr non-interrupted observations of solar
granulation obtained under excellent seeing conditions with the largest
aperture ground-based solar telescope—the New Solar Telescope
(NST)—of Big Bear Solar Observatory. Observations were performed
with adaptive optics correction using a broadband TiO filter in the
705.7 nm spectral line with a time cadence of 10 s and a pixel size
of 0farcs0375. Photospheric bright points (BPs) were detected and
tracked. We find that the BPs detected in NST images are cospatial with
those visible in Hinode/SOT G-band images. In cases where Hinode/SOT
detects one large BP, NST detects several separated BPs. Extended
filigree features are clearly fragmented into separate BPs in NST
images. The distribution function of BP sizes extends to the diffraction
limit of NST (77 km) without saturation and corresponds to a log-normal
distribution. The lifetime distribution function follows a log-normal
approximation for all BPs with lifetime exceeding 100 s. A majority
of BPs are transient events reflecting the strong dynamics of the
quiet Sun: 98.6% of BPs live less than 120 s. The longest registered
lifetime was 44 minutes. The size and maximum intensity of BPs were
found to be proportional to their lifetimes.
Title: Chromospheric Signatures of Small-scale Flux Emergence as
Observed with New Solar Telescope and Hinode Instruments
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Chae,
J.; Cao, W.; Andic, A.; Ahn, K.
Bibcode: 2010ApJ...722.1970Y
Altcode: 2011arXiv1102.1034Y
With the ever-increasing influx of high-resolution images of the solar
surface obtained at a multitude of wavelengths, various processes
occurring at small spatial scales have become a greater focus of our
attention. Complex small-scale magnetic fields have been reported that
appear to have enough stored energy to heat the chromosphere. While
significant progress has been made in understanding small-scale
phenomena, many specifics remain elusive. We present here a detailed
study of a single event of disappearance of a magnetic dipole and
associated chromospheric activity. Based on New Solar Telescope Hα
data and Hinode photospheric line-of-sight magnetograms and Ca II
H images, we report the following. (1) Our analysis indicates that
even very small dipoles (elements separated by about 0farcs5 or less)
may reach the chromosphere and trigger non-negligible chromospheric
activity. (2) Careful consideration of the magnetic environment where
the new flux is deposited may shed light on the details of magnetic
flux removal from the solar surface. We argue that the apparent
collision and disappearance of two opposite polarity elements may
not necessarily indicate their cancellation (i.e., reconnection,
emergence of a "U" tube, or submergence of Ω loops). In our case, the
magnetic dipole disappeared by reconnecting with overlying large-scale
inclined plage fields. (3) Bright points (BPs) seen in off-band Hα
images are very well correlated with the Ca II H BPs, which in turn
are cospatial with G-band BPs. We further speculate that, in general,
Hα BPs are expected to be cospatial with photospheric BPs; however,
a direct comparison is needed to refine their relationship.
Title: Intermittency and Multifractality Spectra of the Magnetic
Field in Solar Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
Bibcode: 2010ApJ...722..122A
Altcode: 2010arXiv1012.1586A
We present the results of a study of intermittency and multifractality
of magnetic structures in solar active regions (ARs). Line-of-sight
magnetograms for 214 ARs of different flare productivity observed at
the center of the solar disk from 1997 January until 2006 December
are utilized. Data from the Michelson Doppler Imager (MDI) instrument
on board the Solar and Heliospheric Observatory operating in the high
resolution mode, the Big Bear Solar Observatory digital magnetograph,
and the Hinode SOT/SP instrument were used. Intermittency spectra
were derived from high-order structure functions and flatness
functions. The flatness function exponent is a measure of the degree
of intermittency. We found that the flatness function exponent at
scales below approximately 10 Mm is correlated with flare productivity
(the correlation coefficient is -0.63). The Hinode data show that the
intermittency regime is extended toward small scales (below 2 Mm) as
compared to the MDI data. The spectra of multifractality, derived from
the structure functions and flatness functions, are found to be broader
for ARs of higher flare productivity as compared to those of low flare
productivity. The magnetic structure of high-flaring ARs consists of
a voluminous set of monofractals, and this set is much richer than
that for low-flaring ARs. The results indicate the relevance of the
multifractal organization of the photospheric magnetic fields to the
flaring activity. The strong intermittency observed in complex and
high-flaring ARs is a hint that we observe a photospheric imprint of
enhanced sub-photospheric dynamics.
Title: Magnetic Energy Spectra in Solar Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
Bibcode: 2010ApJ...720..717A
Altcode: 2010arXiv1007.3702A
Line-of-sight magnetograms for 217 active regions (ARs) with different
flare rates observed at the solar disk center from 1997 January until
2006 December are utilized to study the turbulence regime and its
relationship to flare productivity. Data from the SOHO/MDI instrument
recorded in the high-resolution mode and data from the BBSO magnetograph
were used. The turbulence regime was probed via magnetic energy spectra
and magnetic dissipation spectra. We found steeper energy spectra for
ARs with higher flare productivity. We also report that both the power
index, α, of the energy spectrum, E(k) ~ k -α, and the
total spectral energy, W = ∫E(k)dk, are comparably correlated with the
flare index, A, of an AR. The correlations are found to be stronger than
those found between the flare index and the total unsigned flux. The
flare index for an AR can be estimated based on measurements of α and
W as A = 10 b (αW) c , with b = -7.92 ± 0.58
and c = 1.85 ± 0.13. We found that the regime of the fully developed
turbulence occurs in decaying ARs and in emerging ARs (at the very
early stage of emergence). Well-developed ARs display underdeveloped
turbulence with strong magnetic dissipation at all scales.
Title: Evidence of Filament Upflows Originating from Intensity
Oscillations on the Solar Surface
Authors: Cao, Wenda; Ning, Zongjun; Goode, Philip R.; Yurchyshyn,
Vasyl; Ji, Haisheng
Bibcode: 2010ApJ...719L..95C
Altcode:
A filament footpoint rooted in an active region (NOAA 11032) was well
observed for about 78 minutes with the 1.6 m New Solar Telescope at the
Big Bear Solar Observatory on 2009 November 18 in Hα ±0.75 Å. This
data set had high cadence (~15 s) and high spatial resolution (~0farcs1)
and offered a unique opportunity to study filament dynamics. As in
previous findings from space observations, several dark intermittent
upflows were identified, and they behave in groups at isolated locations
along the filament. However, we have two new findings. First, we
find that the dark upflows propagating along the filament channel are
strongly associated with the intensity oscillations on the solar surface
around the filament footpoints. The upflows start at the same time as
the peak in the oscillations, illustrating that the upflow velocities
are well correlated with the oscillations. Second, the intensity of
one of the seven upflows detected in our data set exhibits a clear
periodicity when the upflow propagates along the filament. The periods
gradually vary from ~10 to ~5 minutes. Our results give observational
clues on the driving mechanism of the upflows in the filament.
Title: Oscillatory Behavior in the Quiet Sun Observed with the New
Solar Telescope
Authors: Anđić, A.; Goode, P. R.; Chae, J.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
Bibcode: 2010ApJ...717L..79A
Altcode: 2010arXiv1007.0272A
Surface photometry of the quiet Sun has achieved an angular resolution
of 0farcs1 with the New Solar Telescope at Big Bear Solar Observatory,
revealing that a disproportionate fraction of the oscillatory events
appear above observed bright point-like structures. During the tracking
of these structures, we noted that the more powerful oscillatory events
are cospatial with them, indicating that observed flux tubes may be
the source of many observed oscillatory events.
Title: Flare Productivity Forecast Based on the Magnetic Energy
Spectrum of Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
Bibcode: 2010shin.confE.104A
Altcode:
Line-of-sight magnetograms for 217 active regions (ARs) of different
flare rate observed at the solar disk center from January 1997 until
December 2006 are utilized to study the turbulence regime and its
relationship to the flare productivity. Data from SOHO/MDI instrument
recorded in the high resolution mode were used. The turbulence regime
was probed via magnetic energy spectra and magnetic dissipation
spectra. We found steeper energy spectra for ARs of higher flare
productivity. We also report that both the power index, α, of the
energy spectrum, E(k)= const k^{-α}, and the total spectral energy,
W=\int E(k)dk, are comparably correlated with the flare index, A,
of an active region. The flare index for an AR can be forecasted
based on measurements of α and W as A=10^b (α W)^c, with b=-7.92
± 0.58 and c=1.85 ± 0.13. We find that regime of the classical
fully-developed turbulence occurs in decaying ARs and in emerging
ARs only at the very early stage of emergence. Well-developed ARs
display under-developed turbulence with strong magnetic dissipation
at all scales. The signature of under-developed turbulence indicates
that free cascading of energy from large to small scales is no longer
possible in mature active regions, and active region can no longer
evolve through series of quasi-stable states. Fraction of energy now
dissipates "along the way" via burst like energy release, a process
know as flaring in an active region.
Title: The NST: First results and some lessons for ATST and EST
Authors: Goode, P. R.; Coulter, R.; Gorceix, N.; Yurchyshyn, V.;
Cao, W.
Bibcode: 2010AN....331..620G
Altcode:
In January 2009, first light observations with the NST (New Solar
Telescope) in Big Bear Solar Observatory (BBSO) were made. NST has a
1.7 m primary with a 1.6 m clear aperture. First observational results
in TiO and Hα are shown and discussed. The NST primary mirror is the
most aspheric telescope mirror deployed to date. The NST is early in its
commissioning, and the plans for this phase will be sketched. Lessons
learned in building and implementing the NST are germane for the ATST
and EST telescopes and will be discussed. The NST has an off-axis
Gregorian configuration consisting of a parabolic primary, heat-stop,
elliptical secondary and diagonal flats. The focal ratio of the
primary mirror is f/2.4. The working wavelength range covers from 0.4
to 1.7 μm in the Coudé Lab beneath the telescope and all wavelengths
including the far infrared at the Nasmyth focus on the dome floor.
Title: Small Scale Chromospheric Dynamics Detected With The New
Solar Telescope In Big Bear
Authors: Yurchyshyn, Vasyl B.
Bibcode: 2010AAS...21630504Y
Altcode:
High resolution observations of quiet Sun areas obtained with the
New Solar Telescope (NST) in Big Bear Solar Observatory revealed
surprisingly storming small-scale chromospheric dynamics. We thus
discovered tiny chromospheric jets originating in the ubiquitous
lanes that surround individual granules characterizing the solar
surface. These jets do not appear to be exclusively associated with
photospheric bright points and/or vertices of the intergranular
lanes. They seem to have sufficient energy to resolve the mystery
of why the overlying chromosphere is hotter than the photosphere. We
will further address the nature of these chromospheric jets and their
relationship to ambient magnetic fields by combining high resolution
data from NST instruments and Hinode observatory.
Title: Relationship Between Earth-Directed Solar Eruptions and
Magnetic Clouds at 1 AU: A Brief Review
Authors: Yurchyshyn, Vasyl; Tripathi, Durgesh
Bibcode: 2010aogs...21...51Y
Altcode: 2009arXiv0904.2366Y
We review relationships between coronal mass ejections (CMEs), EIT
post eruption arcades, and the coronal neutral line associated with
global magnetic field and magnetic clouds near the Earth. Our previous
findings indicate that the orientation of a halo CME elongation may
correspond to the orientation of the underlying flux rope. Here we
revisit these preliminary reports by comparing orientation angles
of elongated LASCO CMEs, both full and partial halos, to the post
eruption arcades. Based on 100 analysed events, it was found that the
overwhelming majority of halo CMEs are elongated in the direction of
the axial field of the post eruption arcades. Moreover, this conclusion
also holds for partial halo CMEs as well as for events that originate
further from the disk center. This suggests that the projection effect
does not drastically change the appearance of full and partial halos
and their images still bear reliable information about the underlying
magnetic fields. We also compared orientations of the erupted fields
near the Sun and in the interplanetary space and found that the local
tilt of the coronal neutral line at 2.5 solar radii is well correlated
with the magnetic cloud axis measured near the Earth. We suggest that
the heliospheric magnetic fields significantly affect the propagating
ejecta. Sometimes, the ejecta may even rotate so that its axis locally
aligns itself with the heliospheric current sheet.
Title: Highest Resolution Observations of the Quietest Sun
Authors: Goode, Philip R.; Yurchyshyn, Vasyl; Cao, Wenda; Abramenko,
Valentyna; Andic, Aleksandra; Ahn, Kwangsu; Chae, Jongchul
Bibcode: 2010ApJ...714L..31G
Altcode:
Highest resolution observations made with the new 1.6 m aperture solar
telescope in Big Bear Solar Observatory during this time of historic
inactivity on the Sun reveal new insights into the small-scale dynamics
of the Sun's photosphere. The telescope's unprecedented resolution
enabled us to observe that the smallest scale photospheric magnetic
field seems to come in isolated points in the dark intergranular lanes,
rather than the predicted continuous sheets confined to the lanes, and
the unexpected longevity of the bright points implies a deeper anchoring
than predicted. Further, we demonstrated for the first time that the
photospheric plasma motion and magnetic fields are in equipartition
over a wide dynamic range, and both cascade energy to ever-smaller
scales according to classical Kolmogorov turbulence theory. Finally,
we discovered tiny jet-like features originating in the dark lanes that
surround the ubiquitous granules that characterize the solar surface.
Title: Low-Latitude Coronal Holes at the Minimum of the 23rd Solar
Cycle
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Linker, Jon; Mikić,
Zoran; Luhmann, Janet; Lee, Christina O.
Bibcode: 2010ApJ...712..813A
Altcode: 2010arXiv1002.1685A
Low- and mid-latitude coronal holes (CHs) observed on the Sun during
the current solar activity minimum (from 2006 September 21, Carrington
rotation (CR) 2048, to 2009 June 26, CR 2084) were analyzed using Solar
and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope and
STEREO-A SECCHI EUVI data. From both the observations and Potential
Field Source Surface modeling, we find that the area occupied by
CHs inside a belt of ±40° around the solar equator is larger in
the current 2007 solar minimum relative to the similar phase of the
previous 1996 solar minimum. The enhanced CH area is related to a
recurrent appearance of five persistent CHs, which survived during 7-27
solar rotations. Three of the CHs are of positive magnetic polarity
and two are negative. The most long-lived CH was being formed during
2 days and existed for 27 rotations. This CH was associated with fast
solar wind at 1 AU of approximately 620 ± 40 km s-1. The
three-dimensional magnetohydrodynamic modeling for this time period
shows an open field structure above this CH. We conclude that the global
magnetic field of the Sun possessed a multi-pole structure during
this time period. Calculation of the harmonic power spectrum of the
solar magnetic field demonstrates a greater prevalence of multi-pole
components over the dipole component in the 2007 solar minimum compared
to the 1996 solar minimum. The unusual large separation between the
dipole and multi-pole components is due to the very low magnitude
of the dipole component, which is three times lower than that in the
previous 1996 solar minimum.
Title: Vorticity of Granular Flows from NST Observations
Authors: Pevtsov, A. A.; Abramenko, V.; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2009AGUFMSH53B..04P
Altcode:
We use observations taken with the New Solar Telescope (NST) at Big
Bear Solar Observatory, the world largest solar optical telescope with
diffraction limited spatial resolution of 0.06 arc seconds, to study
vorticity of granular flows in quiet Sun areas. We employ sequence
of images observed with TiO (705.7 nm) filter with time cadence
of 30 seconds. The atmospheric seeing effects were removed using
speckle-reconstruction technique. We compare vorticity of granular
flows and intergranular vortices, and discuss our findings in the
framework of surface (turbulent) dynamo.
Title: SMALL SCALE DYNAMICS IN THE QUIESCENT CHROMOSPHERE AS SEEN
IN NST DATA
Authors: Yurchyshyn, V.
Bibcode: 2009AGUFMSH53B..03Y
Altcode:
High resolution NST data obtained in the blue wing (-0.75Å) of the
H-alpha spectral line show the presence of surprisingly numerous
small-scale bright emission features nearly evenly distributed over
the field of view. While larger features often exhibit association
with H-alpha jets, smaller events (size < 0.5 arcsec) are not
accompanied by any detectable plasma flows. We will present results
from a statistical study of these emission features and discuss life
time of these events, size, their distribution relative to the magnetic
field and the association with the plasma jets.
Title: Parameters of the Magnetic Flux inside Coronal Holes
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Watanabe, Hiroko
Bibcode: 2009SoPh..260...43A
Altcode: 2009arXiv0908.2460A
The parameters of the magnetic flux distribution inside low-latitude
coronal holes (CHs) were analyzed. A statistical study of 44 CHs
based on Solar and Heliospheric Observatory (SOHO)/MDI full disk
magnetograms and SOHO/EIT 284 Å images showed that the density of
the net magnetic flux, Bnet, does not correlate with the
associated solar wind speeds, Vx. Both the area and net flux
of CHs correlate with the solar wind speed and the corresponding spatial
Pearson correlation coefficients are 0.75 and 0.71, respectively. A
possible explanation for the low correlation between Bnet
and Vx is proposed. The observed non-correlation might
be rooted in the structural complexity of the magnetic field. As a
measure of the complexity of the magnetic field, the filling factor,
f(r), was calculated as a function of spatial scales. In CHs, f(r)
was found to be nearly constant at scales above 2 Mm, which indicates a
monofractal structural organization and smooth temporal evolution. The
magnitude of the filling factor is 0.04 from the Hinode SOT/SP data
and 0.07 from the MDI/HR data. The Hinode data show that at scales
smaller than 2 Mm, the filling factor decreases rapidly, which means
a multifractal structure and highly intermittent, burst-like energy
release regime. The absence of the necessary complexity in CH magnetic
fields at scales above 2 Mm seems to be the most plausible reason
why the net magnetic flux density does not seem to be related to the
solar wind speed: the energy release dynamics, needed for solar wind
acceleration, appears to occur at small scales below 1 Mm.
Title: Rotation of White-light Coronal Mass Ejection Structures as
Inferred from LASCO Coronagraph
Authors: Yurchyshyn, Vasyl; Abramenko, Valentyna; Tripathi, Durgesh
Bibcode: 2009ApJ...705..426Y
Altcode:
Understanding the connection between the magnetic configurations of a
coronal mass ejection (CME) and their counterpart in the interplanetary
medium is very important in terms of space weather predictions. Our
previous findings indicate that the orientation of a halo CME elongation
may correspond to the orientation of the underlying flux rope. Here
we further explore these preliminary results by comparing orientation
angles of elongated LASCO CMEs, both full and partial halos, to the
EUV Imaging Telescope post-eruption arcades (PEAs). By analyzing a
sample of 100 events, we found that the overwhelming majority of CMEs
are elongated in the direction of the axial field of PEAs. During their
evolution, CMEs appear to rotate by about 10° for most of the events
(70%) with about 30°-50° for some events, and the corresponding time
profiles display regular and gradual changes. It seems that there is
a slight preference for the CMEs to rotate toward the solar equator
and heliospheric current sheet (59% of the cases). We suggest that the
rotation of the ejecta may be due to the presence of a heliospheric
magnetic field, and it could shed light on the problems related to
connecting solar surface phenomena to their interplanetary counterparts.
Title: Analyses of magnetic field structures for active region 10720
using a data-driven 3D MHD model
Authors: Wu, S. T.; Wang, A. H.; Gary, G. Allen; Kucera, Ales; Rybak,
Jan; Liu, Yang; Vrśnak, Bojan; Yurchyshyn, Vasyl
Bibcode: 2009AdSpR..44...46W
Altcode:
In order to understand solar eruptive events (flares and CMEs) we
need to investigate the changes at the solar surface. Thus, we use
a data-driven, three-dimensional magnetohydrodynamic (MHD) model to
analyze a flare and coronal mass ejection productive active region,
AR 10720 on January 15, 2005. The measured magnetic field from Big
Bear Solar Observatory (BBSO) digital vector magnetograph (DGVM) was
used to model the non-potential coronal magnetic field changes and the
evolution of electric current before and after the event occurred. The
numerical results include the change of magnetic flux ( Φ), the net
electric current ( IN), the length of magnetic shear of the
main neutral line ( Lss), the flux normalized measure of
the field twist (α={μIN}/{Φ}) with μ being the magnetic
permeability. The current helicity ( Hc) injected into the
corona and the photospheric surface velocity are also computed. The
characteristic parameters of the buildup process before the event and
the decay process after the event are investigated and the amount of
magnetic energy converted to drive the event is estimated.
Title: Properties of Solar Active Regions and Their Relationship
with Solar Eruption: a Statistical Study
Authors: Liu, Yang; Akiyama, S.; Gopalswamy, N.; Mason, J.; Nitta,
N.; Tylka, A.; Yashiro, S.; Yurchyshyn, V.
Bibcode: 2009SPD....40.0920L
Altcode:
Using magnetograms taken by SOHO/MDI, we have calculated some parameters
for solar active regions, and explored possible relationships between
them and solar eruptions. The parameters of active regions we studied
are magnetic flux, net flux, potential field energy, orientation
and separation. We also estimated decay index of magnetic field
overlying the neutral line, and the configuration of ambient field
under which the active region sits. The data used were taken from
1996 to 2005. With these results as a reference, we studied the active
regions that produced the large solar energetic particle (SEP) events,
or produced ground level enhancement (GLE) events. Comparison is also
made between the active regions that produced full eruption and confine
eruption (based on an event list published by Yashiro et al 2005, JGR,
11012S05Y). We present our results here, together with a discussion.
Title: Statistical Assessment of Photospheric Magnetic Features in
Imminent Solar Flare Predictions
Authors: Song, Hui; Tan, Changyi; Jing, Ju; Wang, Haimin; Yurchyshyn,
Vasyl; Abramenko, Valentyna
Bibcode: 2009SoPh..254..101S
Altcode:
In this study we use the ordinal logistic regression method to establish
a prediction model, which estimates the probability for each solar
active region to produce X-, M-, or C-class flares during the next
1-day time period. The three predictive parameters are (1) the total
unsigned magnetic flux Tflux, which is a measure of an
active region's size, (2) the length of the strong-gradient neutral
line Lgnl, which describes the global nonpotentiality of an
active region, and (3) the total magnetic dissipation Ediss,
which is another proxy of an active region's nonpotentiality. These
parameters are all derived from SOHO MDI magnetograms. The ordinal
response variable is the different level of solar flare magnitude. By
analyzing 174 active regions, Lgnl is proven to be the
most powerful predictor, if only one predictor is chosen. Compared
with the current prediction methods used by the Solar Monitor at the
Solar Data Analysis Center (SDAC) and NOAA's Space Weather Prediction
Center (SWPC), the ordinal logistic model using Lgnl,
Tflux, and Ediss as predictors demonstrated
its automatic functionality, simplicity, and fairly high prediction
accuracy. To our knowledge, this is the first time the ordinal logistic
regression model has been used in solar physics to predict solar flares.
Title: Relationship betwwen of Coronal Mass Ejections and EIT Post
Flare Arcades
Authors: Yurchyshyn, V.
Bibcode: 2008AGUFMSH13B1551Y
Altcode:
Our recent study indicates the orientation of a halo CME elongation
may correspond to the orientation of the underlying flux rope. This is
a continuation of the research and here we compare orientation angles
of elongated LASCO CMEs, both halo and partial to the EIT post eruption
arcades (PEA). Data for 100 events had been analyzed and er report the
following: i) it is further supported that majority of halo CMEs are
elongated in the direction of the axial field of PEA arcades; ii) this
relationship holds true for partial CME and those events that originate
further from the disk center. There is also an indication that events
in the northern hemisphere generally exhibit better correlation that
those in the southern hemisphere.
Title: Intermittency in the Photosphere and Corona above an Active
Region
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Wang, Haimin
Bibcode: 2008ApJ...681.1669A
Altcode: 2009arXiv0903.2882A
Recent studies have demonstrated without doubt that the magnetic field
in the photosphere and corona is an intermittent structure, opening
new views of the underlying physics. In particular, such problems
as the existence in the corona of localized areas with extremely
strong resistivity (required to explain magnetic reconnection at all
scales) and the interchange between small and large scales (required
in the study of photospheric-coronal coupling), to name a few, can be
easily captured by the concept of intermittency. This study focuses
on simultaneous time variations of intermittency properties derived
in the photosphere, chromosphere, and corona. We analyze data for
NOAA Active Region 10930 acquired between 2006 December 8, 12:00 UT,
and December 13, 18:45 UT. Photospheric intermittency is inferred
from Hinode magnetic field measurements, while intermittency in the
transition region and corona is derived from Nobeyama 9 GHz radio
polarization measurements and high-cadence Hinode XRT (thin-Be) data,
as well as GOES 1-8 Å flux. The photospheric dynamics and its possible
relationship with the intermittency variations are also analyzed
by calculating the kinetic vorticity. In this case study, we find
the following chain of events: The intermittency of the photospheric
magnetic field peaked after the specific kinetic vorticity of plasma
flows in the active region reached its maximum (4 hr time delay). In
turn, a gradual increase of coronal intermittency occurred after the
peak of the photospheric intermittency. The time delay between the peak
of photospheric intermittency and the occurrence of the first strong
(X3.4) flare was approximately 1.3 days. Our analysis seems to suggest
that the enhancement of intermittency/complexity first occurs in the
photosphere and is later transported toward the corona.
Title: Statistical Study of Orientations of Coronal Mass Ejections
and EIT Flare Arcades
Authors: Yurchyshyn, V.; Tripathi, D.
Bibcode: 2008AGUSMSH43A..01Y
Altcode:
Coronal mass ejections (CMEs) and their interplanetary counterparts,
interplanetary CMEs (ICMEs) usually exhibit a complex structure that
very often includes a magnetic cloud (MC), which is thought to be
a magnetic fluxrope. Our recent study indicates the orientation of a
halo CME elongation may correspond to the orientation of the underlying
flux rope. This is a continuation of the research and here we compare
orientation angles of elongated LASCO CMEs, both halo and partial to the
EIT post eruption arcades (PEA). Data for 100 events had been analyzed
and er report the following: i) it is further supported that majority
of halo CMEs are elongated in the direction of the aixial field of
PEA arcades. This relationship is found to be weeker for partial CME
and those events that originate further from the disk center. There
also is an indication that events in the northern hemisphere generally
exhibit better correlation that those in the southern hemisphere.
Title: Intermittency in the photosphere and corona as derived from
the Hinode data
Authors: Abramenko, V.; Yurchyshyn, V.; Wang, H.
Bibcode: 2008AGUSMSP21B..01A
Altcode:
Recent studies undoubtedly demonstrate that the magnetic fields in the
photosphere and corona are strongly non-Gaussian and can be represented
as intermittent structures, which offers new views on the underlying
physics. In particular, such problems as the existence in the corona of
localized areas with extremely strong resistivity (required to explain
magnetic reconnection of all scales) and the interchange between
small and large scales (required in study of the photosphere/corona
coupling), to name a few, can be easily captured by the concept of
intermittency. This study is focused on simultaneous time variations
of intermittency properties derived in the photosphere, chromosphere
and corona. We analyzed data for NOAA AR 10930 acquired between Dec 08,
2006 12:00 UT and Dec 13, 2006 18:45 UT. Photospheric intermittency was
inferred from Hinode magnetic field measurements, while intermittency
in the transition region and corona was derived from Nobeyama 9 GHz
radio polarization measurements, high cadence Hinode/XRT/Be-thin data
as well as GOES 1-8Å~ flux. Photospheric dynamics and its possible
relationship with the intermittency variations were also analyzed by
calculating the kinetic vorticity. For this case study we found the
following chain of events. Intermittency of the photospheric magnetic
field peaked after the specific kinetic vorticity of plasma flows
in the AR reached its maximum level (4 hour time delay). In turn,
gradual increase of coronal intermittency occurred after the peak
of the photospheric intermittency. The time delay between the peak
of photospheric intermittency and the occurrence of the first strong
(X3.4) flare was approximately 1.3 days. Our analysis seems to suggest
that the enhancement of intermittency/complexity first occurs in the
photosphere and is later transported toward the corona.
Title: Global High Resolution Halpha Network Observations During
the Whole Heliosphere Interval Campaign.
Authors: Yurchyshyn, V.
Bibcode: 2008AGUSMSH51A..03Y
Altcode:
We will present the full disk Halpha data acquired by the Global
High Resolution Halpha Network during the Whole Heliosphere Interval
Campaign. The network includes seven stations located in China (2),
Europe (4) and USA (1). We will also briefly describe the layout and
data from the new BBSO full disk halpha telescope.
Title: The evolution of vector magnetic field associated with major
flares in NOAA AR10656
Authors: Wang, Shuo; Deng, Yuanyong; Jain, Rajmal; Yurchyshyn, Vasyl;
Wang, Haimin; Liu, Yuanyuan; Yang, Zhiliang
Bibcode: 2008JApA...29...57W
Altcode:
No abstract at ADS
Title: Relationship between EIT Posteruption Arcades, Coronal Mass
Ejections, the Coronal Neutral Line, and Magnetic Clouds
Authors: Yurchyshyn, Vasyl
Bibcode: 2008ApJ...675L..49Y
Altcode: 2007arXiv0710.1292Y
There is observational evidence that the elongation of an Earth-directed
coronal mass ejection (CME) may indicate the orientation of the
underlying erupting flux rope. In this study, we compare orientations of
CMEs, magnetic clouds (MCs), EIT (EUV Imaging Telescope) posteruption
arcades, and the coronal neutral line (CNL). We report on good
correlations between (1) the directions of the axial field in the
EIT arcades and the elongations of halo CMEs, and (2) the tilt of the
CNL and MC axis orientations. We found that majority of the eruptions
that had EIT arcades, CMEs, and MCs similarly oriented also had the
CNL co-aligned with them. On the other hand, those events that showed
no agreement between orientations of the EIT arcades, CMEs, and MCs
had their MCs aligned with the CNL. We speculate that the axis of the
ejecta may be rotated in such a way that it is locally aligns itself
with the heliospheric current sheet.
Title: Successive Flaring during the 2005 September 13 Eruption
Authors: Wang, Haimin; Liu, Chang; Jing, Ju; Yurchyshyn, Vasyl
Bibcode: 2007ApJ...671..973W
Altcode:
We report a detailed analysis of successive flaring during the
X1.5 event in the NOAA AR 0808 on 2005 September 13. We identify a
filament lying at the southeast boundary of the active region as the
physical linkage between the two flares in close succession. It is
noticeable that the filament erupted ~13 minutes after the initial
flare onset at ~19:22 UT near the central magnetic polarity inversion
line (PIL). During this time period, the filament only showed a slow
rising; meanwhile, a spatially associated large magnetic loop with one
leg connecting to the initial flaring site began to brighten in the
TRACE 195 Å channel. After ~19:35 UT, the filament abruptly erupted
together with the bright TRACE loop. Besides the moving ribbons at
the first flaring site, the filament eruption caused a secondary flare
identified with another set of moving ribbons. This event thus provides
a clear evidence for the successive flaring where the initial flare
destabilizes the nearby flux loop system, leading to the filament
eruption with the second flare. We also identify the initial flare
core by finding rapid, irreversible enhancements of the photospheric
transverse magnetic fields at a section of the PIL.
Title: Calculation of Intermittency in the Photosphere and Corona
From Hinode Data
Authors: Abramenko, V.; Yurchyshyn, V.
Bibcode: 2007AGUFMSH34A..05A
Altcode:
High spatial and temporal resolution observations of the photospheric
magnetic field and solar corona, offered recently by Hinode instrument,
provide us a unique opportunity to simultaneously estimate degree of
intermittency in the photosphere and the corona and to track their
variations in time. To do this, we adopted a flatness-function
technique, where the slope of the function defines degree of
intermittency. The function itself is calculated as the ratio of
the sixth-order structure function to the cube of the second-order
structure function. Three independent data sets, that were utilized
to calculate the intermittency in the corona (XRT/Hinode, GOES, and
Nobeyama 9.4 Hz polarization flux), showed a synchronous increase of
intermittency during a 5-day time interval that ends with the occurrence
of the X3.4 flare in the NOAA 10930. Photospheric intermittency,
calculated from SOT-FG/Hinode magnetograms, peaked approximately 1.5
days before the flare onset. The result allows to suggest a preceding
gain of intermittency in the photosphere with a following transport
of intermittency into the corona.
Title: Relationship between Halo Coronal Mass Ejections, EIT Flare
Arcades, Coronal Neutral Line and Magnetic Clouds
Authors: Yurchyshyn, V.
Bibcode: 2007AGUFMSH23B..04Y
Altcode:
Coronal mass ejections (CMEs) are the most important solar drivers of
geomagnetic storms. Their interplanetary counterparts, interplanetary
CMEs (ICMEs), can be detected in-situ, for example, by ACE and
Wind spacecraft. An ICME usually exhibits a complex structure that
very often includes a magnetic cloud (MC), which is thought to be a
magnetic flux rope, capable of providing prolonged periods of southward
interplanetary magnetic field at 1 AU. The magnitude of the storm
depends, in general, on the orientation and intensity of the magnetic
field in the ejecta. In this presentation we will discuss how the size
of the geomagnetic storm can be predicted from coronagraph images. There
is observational evidence that the orientation of a halo CME elongation
corresponds to the orientation of the underlying flux rope, while the
intensity of the magnetic field in an ejecta seems to be related to
the CME speed. Here we compare orientation angles of elongated LASCO
halo CMEs, EIT flare arcades (post flare loop system), the local tilt
of the heliospheric current sheet and the corresponding MCs. We report
that i) for about 64% of CME-ICME events, a good correspondence was
found between the orientation angles of CMEs and MC; ii) 20 out of 25
CMEs (80%) were oriented along the axis of the corresponding EIT flare
arcade; and iii) 19 out of 25 (76%) of CMEs are co- aligned with the
heliospheric current sheet at 2.5 solar radii. In the final part of
the presentation we will discuss the applications of our findings to
CME modeling, space weather forecast and possible future studies.
Title: The Eruption from a Sigmoidal Solar Active Region on 2005
May 13
Authors: Liu, Chang; Lee, Jeongwoo; Yurchyshyn, Vasyl; Deng, Na; Cho,
Kyung-suk; Karlický, Marian; Wang, Haimin
Bibcode: 2007ApJ...669.1372L
Altcode: 2007arXiv0707.2240L
This paper presents a multiwavelength study of the M8.0 flare and
its associated fast halo CME that originated from a bipolar NOAA
AR 10759 on 2005 May 13. The source active region has a conspicuous
sigmoid structure at the TRACE 171 Å channel as well as in the SXI
soft X-ray images, and we mainly concern ourselves with the detailed
process of the sigmoid eruption, as evidenced by the multiwavelength
data ranging from Hα, WL, EUV/UV, radio, and hard X-rays (HXRs). The
most important finding is that the flare brightening starts in the
core of the active region earlier than that of the rising motion of
the flux rope. This timing clearly addresses one of the main issues in
the magnetic eruption onset of sigmoid, namely, whether the eruption
is initiated by an internal tether cutting to allow the flux rope
to rise upward, or a flux rope rises due to a loss of equilibrium to
later induce tether cutting below it. Our high time cadence SXI and Hα
data show that the first scenario is relevant to this eruption. As in
other major findings, we have the RHESSI HXR images showing a change
of the HXR source from a confined footpoint structure to an elongated
ribbon-like structure after the flare maximum, which we relate to the
sigmoid-to-arcade evolution. The radio dynamic spectrum shows a type II
precursor that occurred at the time of expansion of the sigmoid and a
drifting pulsating structure in the flare rising phase in HXRs. Finally,
type II and III bursts are seen at the time of maximum HXR emission,
simultaneous with the maximum reconnection rate derived from the flare
ribbon motion in UV. We interpret these various observed properties
with the runaway tether-cutting model proposed by Moore et al. in 2001.
Title: Two-Dimensional Spectroscopy of Photospheric Shear Flows in
a Small δ Spot
Authors: Denker, C.; Deng, N.; Tritschler, A.; Yurchyshyn, V.
Bibcode: 2007SoPh..245..219D
Altcode: 2007arXiv0708.3490D
In recent high-resolution observations of complex active regions,
long-lasting and well-defined regions of strong flows were identified
in major flares and associated with bright kernels of visible,
near-infrared, and X-ray radiation. These flows, which occurred in the
proximity of the magnetic neutral line, significantly contributed to
the generation of magnetic shear. Signatures of these shear flows are
strongly curved penumbral filaments, which are almost tangential to
sunspot umbrae rather than exhibiting the typical radial filamentary
structure. Solar active region NOAA 10756 was a moderately complex
βδ sunspot group, which provided an opportunity to extend previous
studies of such shear flows to quieter settings. We conclude that
shear flows are a common phenomenon in complex active regions and δ
spots. However, they are not necessarily a prerequisite condition for
flaring. Indeed, in the present observations, the photospheric shear
flows along the magnetic neutral line are not related to any change of
the local magnetic shear. We present high-resolution observations of
NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar
Observatory (BBSO). Time series of speckle-reconstructed white-light
images and two-dimensional spectroscopic data were combined to study
the temporal evolution of the three-dimensional vector flow field
in the βδ sunspot group. An hour-long data set of consistent high
quality was obtained, which had a cadence of better than 30 seconds
and subarcsecond spatial resolution.
Title: Relationship Between Orientations of Halo Coronal Mass
Ejections, EIT Flare Arcades, Heliospheric Current Sheet and
Magnetic Clouds
Authors: Yurchyshyn, Vasyl B.
Bibcode: 2007AAS...210.2928Y
Altcode: 2007BAAS...39..325Y
Coronal mass ejections (CMEs) are the most important solar drivers of
geomagnetic storms. Their interplanetary counterparts, interplanetary
CMEs (ICMEs), can be detected in-situ, for example, by ACE and
Wind spacecraft. An ICME usually exhibits a complex structure that
very often includes a magnetic cloud (MC), which is thought to be a
magnetic flux rope, capable of providing prolonged periods of southward
interplanetary magnetic field at 1 AU. In our recent study we found that
the orientation of a halo CME elongation corresponds to the orientation
of the underlying flux rope. This is a continuation of this recent
research and here we compare orientation angles of elongated LASCO
halo CMEs, EIT flare arcades (post flare loop system), the local tilt
of the heliospheric current sheet and the corresponding MCs. We report
that i) for about 64% of CME-ICME events, a good correspondence was
found between the orientation angles of CMEs and MC; ii) 20 out of
25 CMEs (80%) were oriented along the axis of the corresponding EIT
flare arcade; and iii) 17 out of 25 (68%) of MCs are co-aligned with
the heliospheric current sheet at 2.5 solar radii. In the final part
of the presentation we will discuss the applications of our findings
to CME modeling, space weather forecast and possible future studies.
Title: Automatic Prediction of Super Geomagnetic Storms and Solar
Flares
Authors: Song, Hui; Yurchyshyn, V.; Tan, C.; Jing, J.; Wang, H.
Bibcode: 2007AAS...21010501S
Altcode: 2007BAAS...39..230S
In this study we first investigated the relationship between magnetic
structures of coronal mass ejection (CME) source regions and geomagnetic
storms, in particular, the super storms when the Dst index
decreases below -200 nT. By examining all full halo CMEs that erupted
between 1996 and 2004, we selected 73 events associated with M-class
and X-class solar flares, which have a clearly identifiable source
region. By analyzing daily full-disk MDI magnetograms, we found that
the horizontal gradient of the line-of-sight magnetic field is a viable
parameter to identify a flaring magnetic neutral line and thus can be
used to predict the possible source region of CMEs. We report that
for about 92% of super storms the orientation angle of the magnetic
structures of source regions was found to be southward. Our findings
demonstrate that this approach can be used to perform an automatic
prediction of the occurrence of large X-class flares and super
geomagnetic storms. In order to further extend our prediction
of flares, we next used the ordinal logistic regression method to
establish a prediction model, which estimates the probability for each
active region to produce X-, M- or C-class flares during the next 1-day
time period. Three predictive parameters are: total unsigned magnetic
flux Tflux, the length of strong gradient neutral line
Lgnl, and total magnetic dissipation Ediss. The
ordinal response variable is the different level of solar flares
magnitude. Compared the results with the current predictions methods
used by NASA SDAC and NOAA SEC, the ordinal logistic model using
Lgnl and Tflux as predictors demonstrated its
automaticity, simpleness and fairly high prediction accuracy. To our
knowledge, this is the first time the ordinal logistic regression
model was used in solar physics to predict solar flares.
Title: Filament Eruption after the Onset of the X1.5 Flare on 2005
September 13
Authors: Wang, Haimin; Liu, C.; Jing, J.; Yurchyshyn, V.
Bibcode: 2007AAS...210.9321W
Altcode: 2007BAAS...39..214W
Erupting filaments usually play the role as the initial driver of
flaring process preceding the subsequent flare emissions. In this
Letter, we report a rare case that during the X1.5 flare on 2005
September 13, a filament at the boundary of the NOAA AR 0808 erupted
about 13 minutes after the flare onset at 19:22 UT near the central AR
neutral line. During this time period, the filament only showed a slow
rising; meanwhile, a spatially associated large magnetic loop with
one leg connecting to the initial flaring site began to brighten in
the TRACE 195A channel. After 19:35 UT, the filament abruptly erupted
together with the bright TRACE loop. Besides the moving ribbons at the
first flaring site, the filament eruption caused a secondary flare
identified with another set of moving ribbons. We suggest possible
triggering mechanisms for the initial flare and the eruption of the
peripheral flux loop system, which leads to the sympathetic flaring.
Title: On The Magnetic Flux Budget In Low-corona Magnetic Reconnection
And Interplanetary Magnetic Flux Ropes
Authors: Qiu, Jiong; Hu, Q.; Howard, T. A.; Yurchyshyn, V. B.
Bibcode: 2007AAS...210.2927Q
Altcode: 2007BAAS...39..142Q
We present the first quantitative comparison between the total
magnetic reconnection flux in the low-corona in the wake of coronal
mass ejections (CMEs) and the magnetic flux in magnetic clouds
(MCs) that reach 1AU 2 - 3 days after the CME onset. The total
reconnection flux is measured from flare ribbons, and the MC flux
is computed using in-situ observations at 1 AU, all ranging from
1020 to 1022 Mx. It is found that for the
nine studied events in which the association between flares, CMEs,
and MCs is identified, the MC flux is correlated with the total
reconnection flux Φr. Further, the poloidal (azimuthal)
MC flux Φp is comparable with the reconnection flux
Φr and the toroidal (axial) MC flux Φt is a
fraction of Φr. Events associated with filament eruption
do not exhibit a different Φr - Φp relation
from events not accompanied by erupting filaments. The relations
revealed between these independently measured physical quantities
suggest that, for the studied samples, the magnetic flux and twist
of interplanetary magnetic flux ropes, reflected by MCs, are highly
relevant to low-corona magnetic reconnection during the eruption. We
discuss the implications of this result for the formation mechanism
of twisted magnetic flux ropes, namely, whether the helical structure
of the magnetic flux rope is largely pre-existing or formed in-situ
by low-corona magnetic reconnection. We also measure magnetic flux
encompassed in coronal dimming regions (Φd) and discuss its
relation to the reconnection flux inferred from flare ribbons and MC
flux. This work is supported by NSF grant ATM-0603789 and NASA grants
NNG04GF47G, NNG06GA37G, and NNG06GD41G.
Title: On the Magnetic Flux Budget in Low-Corona Magnetic Reconnection
and Interplanetary Coronal Mass Ejections
Authors: Qiu, Jiong; Hu, Qiang; Howard, Timothy A.; Yurchyshyn,
Vasyl B.
Bibcode: 2007ApJ...659..758Q
Altcode:
We present the first quantitative comparison between the total
magnetic reconnection flux in the low corona in the wake of
coronal mass ejections (CMEs) and the magnetic flux in magnetic
clouds (MCs) that reach 1 AU 2-3 days after CME onset. The total
reconnection flux is measured from flare ribbons, and the MC flux
is computed using in situ observations at 1 AU, all ranging from
1020 to 1022 Mx. It is found that for the
nine studied events in which the association between flares, CMEs,
and MCs is identified, the MC flux is correlated with the total
reconnection flux Φr. Further, the poloidal (azimuthal)
MC flux Φp is comparable with the reconnection flux
Φr, and the toroidal (axial) MC flux Φt is a
fraction of Φr. Events associated with filament eruption do
not exhibit a different Φt,p-Φr relation from
events not accompanied by erupting filaments. The relations revealed
between these independently measured physical quantities suggest that
for the studied samples, the magnetic flux and twist of interplanetary
magnetic flux ropes, reflected by MCs, are highly relevant to low-corona
magnetic reconnection during the eruption. We discuss the implications
of this result for the formation mechanism of twisted magnetic flux
ropes, namely, whether the helical structure of the magnetic flux
rope is largely pre-existing or formed in situ by low-corona magnetic
reconnection. We also measure magnetic flux encompassed in coronal
dimming regions (Φd) and discuss its relation to the
reconnection flux inferred from flare ribbons and MC flux.
Title: Orientations of LASCO Halo CMEs and their connection to the
flux rope structure of interplanetary CMEs
Authors: Yurchyshyn, V.; Hu, Q.; Lepping, R. P.; Lynch, B. J.;
Krall, J.
Bibcode: 2007AdSpR..40.1821Y
Altcode: 2007astro.ph..3627Y
Coronal mass ejections (CMEs) observed near the Sun via LASCO
coronographic imaging are the most important solar drivers
of geomagnetic storms. ICMEs, their interplanetary, near-Earth
counterparts, can be detected in situ, for example, by the Wind and
ACE spacecraft. An ICME usually exhibits a complex structure that very
often includes a magnetic cloud (MC). They can be commonly modelled
as magnetic flux ropes and there is observational evidence to expect
that the orientation of a halo CME elongation corresponds to the
orientation of the flux rope. In this study, we compare orientations
of elongated CME halos and the corresponding MCs, measured by Wind
and ACE spacecraft. We characterize the MC structures by using the
Grad-Shafranov reconstruction technique and three MC fitting methods
to obtain their axis directions. The CME tilt angles and MC fitted
axis angles were compared without taking into account handedness
of the underlying flux rope field and the polarity of its axial
field. We report that for about 64% of CME-MC events, we found a good
correspondence between the orientation angles implying that for the
majority of interplanetary ejecta their orientations do not change
significantly (less than 45 deg rotation) while travelling from the
Sun to the near-Earth environment.
Title: The May 13, 2005 Eruption: Observations, Data Analysis and
Interpretation
Authors: Yurchyshyn, V.; Liu, C.; Abramenko, V.; Krall, J.
Bibcode: 2006SoPh..239..317Y
Altcode: 2006SoPh..tmp...72Y
In this study, we present detailed description and analysis of the May
13, 2005 eruption, the corresponding coronal mass ejection (CME) and
intense geomagnetic storm observed near the Earth on May 15, 2005. This
isolated two-ribbon M8.0 flare and the very fast CME occurred in a
relatively simple magnetic configuration during a quiet period of solar
activity, which enabled us to reliably associate the solar surface event
with its counterpart observed in the Earth magnetosphere. In our study,
we utilized (i) various tools to analyze a multi-wavelength data set
that includes ground (BBSO vector magnetograms, Hα) and space (SOHO,
TRACE, RHESSI and ACE) based data; (ii) linear force-free modeling
to reconstruct the coronal field above the active region and (iii)
erupting flux rope (EFR) model to simulate a near-Sun halo CME and
a near-Earth interplanetary CME (ICME). Our findings indicate that
persisting converging and shearing motions near the main neutral line
could lead to the formation of twisted core fields and eventually
their eruption via reconnection. In the discussed scenario, the in
situ formed erupting loop can be observed as a magnetic cloud (MC)
when it reaches the Earth. The EFR model was able to produce both a
model halo CME and ICME providing a good global match to the overall
timing and components of the magnetic field in the observed MC. The
orientation of the model ICME and the sense of the twist, inferred
from the EFR model, agree well with the orientation and the magnetic
helicity found in the source active region.
Title: On Magnetic Flux Budget in Low-corona Magnetic Reconnection
and Interplanetary Coronal Mass Ejections
Authors: Qiu, J.; Hu, Q.; Howard, T.; Yurchyshyn, V.
Bibcode: 2006AGUFMSH33B0406Q
Altcode:
We present the first quantitative comparison between the total
magnetic reconnection flux in low-corona at the wake of coronal mass
ejections (CMEs) and the magnetic flux in magnetic clouds (MCs) that
reach 1~AU 2 - 3 days after CME onset. The total reconnection flux
is measured from flare ribbons, and the MC flux is computed using
in-situ observations at 1~AU, all ranging from 10^{20-22} Mx. It is
found that for the studied 9 events, in which the association between
flares, CMEs, and MCs is identified, the MC flux is correlated with
the total reconnection flux Φ_r. Further, the poloidal (azimuthal) MC
flux Φ_p is comparable with reconnection flux Φr, and the toroidal
(axial) MC flux Φ_t is a fraction of Φr. Events associated with
filament eruption do not exhibit a different Φt, p - Φ_r relation
from events not accompanied by erupting filaments. The revealed
relations between these independently measured physical quantities
suggest that, for the studied samples, the magnetic flux and twist of
the interplanetary magnetic flux rope, reflected by MCs, are highly
relevant to low-corona magnetic reconnection during the eruption. %which
contributes significantly to the formation of the helical structure of
the flux ropes. We discuss the implication on the formation mechanism
of twisted magnetic flux ropes, namely, whether the helical structure
of the magnetic flux rope is largely pre-existing or formed in-situ
by low-corona magnetic reconnection. We also measure magnetic flux
encompassed in coronal dimming regions (Φ_d) and discuss its relation
with reconnection flux inferred from flare ribbons and MC flux.
Title: The Automatic Predictability of Super Geomagnetic Storms from
halo CMEs associated with Large Solar Flares
Authors: Song, Hui; Yurchyshyn, Vasyl; Yang, Guo; Tan, Changyi; Chen,
Weizhong; Wang, Haimin
Bibcode: 2006SoPh..238..141S
Altcode: 2006SoPh..tmp...30S
We investigate the relationship between magnetic structures of
coronal mass ejection (CME) source regions and geomagnetic storms, in
particular, the super storms when the Dst index decreases
below −200 nT. By examining all full halo CMEs that erupted
between 1996 and 2004, we selected 73 events associated with M-class
and X-class solar flares, which have a clearly identifiable source
region. By analyzing daily full-disk MDI magnetograms, we found that
the horizontal gradient of the line-of-sight magnetic field is a viable
parameter to identify a flaring magnetic neutral line and thus can be
used to predict the possible source region of CMEs. The accuracy of
this prediction is about 75%, especially for those associated with
X-class flares (up to 89%). The mean orientation of the magnetic
structures of source regions was derived and characterized by the
orientation angle θ, which is defined to be ≤ 90∘
in the case of the southward orientation and ≥ 90∘,
when the magnetic structure is northwardly oriented. The orientation
angle was calculated as the median orientation angle of extrapolated
field lines relative to the flaring neutral line. We report that for
about 92% of super storms (12 out of 13 events) the orientation angle
was found to be southward. In the case of intense and moderate storms
(Dst≥ −200 nT), the relationship is less pronounced
(70%, 21 out of 30 events). Our findings demonstrate that the approach
presented in this paper can be used to perform an automatic prediction
of the occurrence of large X-class flares and super geomagnetic storms.
Title: An Overview of Existing Algorithms for Resolving the
180° Ambiguity in Vector Magnetic Fields: Quantitative
Tests with Synthetic Data
Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites,
Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam,
K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.;
Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J.
Bibcode: 2006SoPh..237..267M
Altcode: 2006SoPh..tmp...14M
We report here on the present state-of-the-art in algorithms used
for resolving the 180° ambiguity in solar vector magnetic field
measurements. With present observations and techniques, some assumption
must be made about the solar magnetic field in order to resolve
this ambiguity. Our focus is the application of numerous existing
algorithms to test data for which the correct answer is known. In
this context, we compare the algorithms quantitatively and seek to
understand where each succeeds, where it fails, and why. We have
considered five basic approaches: comparing the observed field to a
reference field or direction, minimizing the vertical gradient of the
magnetic pressure, minimizing the vertical current density, minimizing
some approximation to the total current density, and minimizing some
approximation to the field's divergence. Of the automated methods
requiring no human intervention, those which minimize the square of
the vertical current density in conjunction with an approximation for
the vanishing divergence of the magnetic field show the most promise.
Title: The Relationship between Magnetic Gradient and Magnetic Shear
in Five Super Active Regions Producing Great Flares
Authors: Wang, Hai-Min; Song, Hui; Jing, Ju; Yurchyshyn, Vasyl; Deng,
Yuan-Yong; Zhang, Hong-Qi; Falconer, David; Li, Jing
Bibcode: 2006ChJAA...6..477W
Altcode:
We study the magnetic structure of five well-known active regions that
produced great flares (X5 or larger). The six flares under investigation
are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July
14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare
on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the
X10 flare on 2003 October 29, both in AR 10486. The last five events
had corresponding LASCO observations and were all associated with Halo
CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory,
Huairou Solar Observing Station, Marshall Space Flight Center and Mees
Solar Observatory. In particular, we studied the magnetic gradient
derived from line-of-sight magnetograms and magnetic shear derived from
vector magnetograms, and found an apparent correlation between these
two parameters at a level of about 90%. We found that the magnetic
gradient could be a better proxy than the shear for predicting where a
major flare might occur: all six flares occurred in neutral lines with
maximum gradient. The mean gradient of the flaring neutral lines ranges
from 0.14 to 0.50 G km-1, 2.3 to 8 times the average value
for all the neutral lines in the active regions. If we use magnetic
shear as the proxy, the flaring neutral line in at least one, possibly
two, of the six events would be mis-identified.
Title: Orientations Of Lasco Halo Cmes And Their Connection To The
Flux Rope Structure Of Icmes
Authors: Yurchyshyn, Vasyl B.; Hu, Q.; Lepping, R. P.; Lynch, B. J.;
Krall, J.
Bibcode: 2006SPD....37.2402Y
Altcode: 2006BAAS...38..250Y
Coronal mass ejections (CMEs) are the most important solar drivers of
geomagnetic storms. They are observed by remote sensing, such as LASCO
coronographic imaging on board SOHO spacecraft. Their interplanetary
counterparts, ICMEs, can be detected in-situ, for example, by ACE
and Wind spacecraft. An ICME usually exhibits a complex structure
that very often includes a magnetic cloud (MC). MCs are distinctive
magnetic features that can be commonly modeled as magnetic flux
ropes which are capable of providing prolonged periods of southward
interplanetary magnetic field at 1 AU, due to the poloidal and/or
toroidal component of their internal magnetic field. It is thought that
the orientation of a halo CME elongation corresponds to the orientation
of the flux rope. Therefore, in this study we compare orientation
angles of elongated halo CMEs observed by the LASCO instrument and the
corresponding MCs, measured by Wind and ACE spacecraft. We characterize
the ICME structures by using the Grad-Shafranov reconstruction
technique and several ICME/MC fitting methods to obtain their axis
orientations. The CME and MC angles are compared without taking into
account handedness of the underlying flux rope field and the polarity
of its axial field. We report that for about 64\% of CME-ICME events,
we found a good correspondence between the orientation angles implying
that for two thirds of interplanetary ejecta their orientations do not
change more significantly (less than 45 deg rotation) while traveling
from the sun to the near earth environment. We also briefly discuss
the applications of our results to space weather forecast and possible
future studies.
Title: Sigmoid, Type II Precursor, and Coronal Mass Ejection
Authors: Lee, Jeongwoo; Liu, C.; Cho, K.; Gary, D. E.; Yurchyshyn,
V.; Deng, N.; Wang, H.
Bibcode: 2006SPD....37.0907L
Altcode: 2006BAAS...38..236L
The 2005 May 13 flare occurred in the sigmoidal active region, NOAA
10759, and its time dependent change on the TRACE, EIT, and SXI images
suggests an eruption process as envisioned by the runaway tether-cutting
model. However, the onset of the eruption in the low corona and the
final explosion of the magnetic field in the high corona are not
directly observable at these wavelengths and we infer them indirectly
from the radio data obtained with the Owens Valley Solar Array (OVSA),
Green Bank Solar Radio Burst Spectrometer (GBSRBS), PHOENIX-spectrograph
of ETH Zurich, and the Potsdam-Tremsdorf Spectrograph. The Potsdam
spectrograph shows a so-called Type II Precursor in the early phase
of loop expansion, indicating a coronal shock formed near the flare
site. The GBSRBS spectra show a type III burst followed by type II
bursts in the maximum phase, which implies opening of field lines
and strong shock formation in the high corona. Finally, the radio
pulsations are detected on the OVSA and PHOENIX spectrographs, which
we interpret as due to the magnetic loop oscillation as a dynamic
response to the mass ejection. These radio data along with the EUV
and X-ray images are used to infer the runaway tether-cutting process
during this event in all coronal heights.This work is supported by
NSF/SHINE grant ATM-0548952 and NSF grant AST-0307670 to NJIT.
Title: Flux Emergence Rate In Coronal Holes And In Adjacent Quiet-sun
Regions
Authors: Abramenko, Valentyna; Fisk, L.; Yurchyshyn, V.
Bibcode: 2006SPD....37.1403A
Altcode: 2006BAAS...38..243A
The rate of emergence of new magnetic flux in coronal holes, and in
surroundingregions on the quiet Sun was analyzed from observations
from the MichelsonDoppler Imager and the EUV Imager Telescope on the
Solar and HeliosphericObservatory (SOHO). Coronal holes are regions
where the open magnetic flux ofthe Sun, the component that forms the
heliospheric magnetic field, isconcentrated. It is determined that
the rate of emergence of new magnetic fluxis systematically lower,
by a factor of 2, in coronal holes relative to thesurrounding quiet
Sun. This result is consistent with a prediction in a recentmodel for
the transport of open magnetic flux on the Sun, which demonstratedthat
open flux tends to accumulate and concentrate in regions where the
rate ofemergence of new magnetic flux is a local minimum.
Title: The Eruption from a Sigmoid Active Region on 2005 May 13
Authors: Liu, Chang; Lee, J.; Yurchyshyn, V.; Cho, K.; Deng, N.;
Gary, D. E.; Wang, H.
Bibcode: 2006SPD....37.0821L
Altcode: 2006BAAS...38..234L
A sigmoidal structure of active regions has been of interest as is
believed to lead to magnetic eruption. We found from TRACE EUV images
that NOAA AR 10759 exhibited a typical sigmoid shape just before the
M8.0 flare and a fast halo CME on 2005 May 13, and reduced to a more
confined arcade after the eruption. We have thus examined these time
dependent changes during the flare by utilizing a multiwavelength
data set: EUV (TRACE, EIT), soft X-rays (SXI), H-alpha (BBSO,ISOON),
radio spectra (OVSA, Potsdam-Tremsdorf, GBSRBS, Phoenix, RSTN),
and CME (LASCO). Several similarities of this event with the runaway
tether-cutting scenario elaborated by Moore et al. (2001) has been
found. Before the maximum phase, the flare brightening first occurred in
the core of the active region, and then two elbows in the outer region
gradually expanded, which we compare to the tether-cutting in the
sigmoid center and the ejective eruption, respectively. At the flare
maximum, the large-scale disturbances such as Moreton waves, type II,
and III radio bursts were observed, which we suggest as evidence for
the blow-out of the envelope field and particle acceleration. Finally
the flare arcade formed along the neutral line as the opened legs of
the envelop field reconnect with each other. This dataset therefore
supports the idea that the eruption may start in the sheared core
field and proceeds outward with the rising plasmoid via the runaway
tether-cutting reconnection and finally becomes a CME.This work is
supported by NSF/SHINE grant ATM-0548952, NSF grant ATM-0536921,
and NASA grant NNG0-4GJ51G.
Title: Evidence for Tether-Cutting Reconnection in a Quadrupole
Magnetic Configuration in the April 9, 2001, M7.9 Flare
Authors: Yurchyshyn, V.; Karlický, M.; Hu, Q.; Wang, H.
Bibcode: 2006SoPh..235..147Y
Altcode:
We studied the M7.9 flare on April 9, 2001 that occurred within a
δ-sunspot of active region NOAA 9415. We used a multi-wavelength
data set, which includes Yohkoh, TRACE, SOHO, and ACE spacecraft
observations, Potsdam and Ondřejov radio data and Big Bear Solar
Observatory (BBSO) images in order to study the large-scale structure
of this two-ribbon flare that was accompanied by a very fast coronal
mass ejection (CME). We analyzed light curves of the flare emission as
well as the structure of the radio emission and report the following:
the timing of the event, i.e., the fact that the initial brightenings,
associated with the core magnetic field, occurred earlier than the
remote brightening (RB), argue against the break-out model in the
early phase of this event. We thus conclude that the M7.9 flare and
the CME were triggered by a tether-cutting reconnection deep in the
core field connecting the δ-spot and this reconnection formed an
unstable flux rope. Further evolution of the erupted flux rope could
be described either by the "standard" flare model or a break-out
type of the reconnection. The complex structure of flare emission
in visible, X-ray, and radio spectral ranges point toward a scenario
which involves multiple reconnection processes between extended closed
magnetic structures.
Title: Flux Rope Model of the 2003 October 28-30 Coronal Mass Ejection
and Interplanetary Coronal Mass Ejection
Authors: Krall, J.; Yurchyshyn, V. B.; Slinker, S.; Skoug, R. M.;
Chen, J.
Bibcode: 2006ApJ...642..541K
Altcode:
A numerical model of an erupting solar flux rope is shown to reproduce
both quantitative near-Sun properties of the 2003 October 28 coronal
mass ejection and the timing, strength, and orientation of the fields
measured in situ at 1 AU. Using a simple erupting flux rope model, we
determine the best-fit parameters for this event. Our analysis shows
that the orientation of the magnetic axis of the flux rope in this
case rotates smoothly through approximately 50° as the flux rope apex
expands from the solar surface to 1 AU. Using a global magnetospheric
simulation code, we further show that the resulting model solar wind
properties at 1 AU produce a magnetospheric response comparable to
that computed using the actual solar wind data.
Title: The Rate of Emergence of Magnetic Dipoles in Coronal Holes
and Adjacent Quiet-Sun Regions
Authors: Abramenko, V. I.; Fisk, L. A.; Yurchyshyn, V. B.
Bibcode: 2006ApJ...641L..65A
Altcode:
Observations from the Michelson Doppler Imager and the EUV Imaging
Telescope on the Solar and Heliospheric Observatory are analyzed to
determine the rate of emergence of new magnetic flux in coronal holes
and in surrounding regions on the quiet Sun. Coronal holes are regions
where the open magnetic flux of the Sun, the component that forms the
heliospheric magnetic field, is concentrated. It is determined that
the rate of emergence of new magnetic flux is systematically lower,
by a factor of ~2, in coronal holes relative to the surrounding quiet
Sun. This result is consistent with a prediction in a recent model for
the transport of open magnetic flux on the Sun, which demonstrated
that open flux tends to accumulate and concentrate in regions where
the rate of emergence of new magnetic flux is a local minimum.
Title: Relationship between the magnetic field of interplanetary
ejecta and their solar sources
Authors: Yurchyshyn, V.
Bibcode: 2006cosp...36..677Y
Altcode: 2006cosp.meet..677Y
Solar coronal mass ejections CMEs are a principal link that connects
the chain of events in the solar atmosphere interplanetary space and
the earth s magnetic environment The occurrence of earth-directed
CMEs is well associated with geomagnetic disturbances that can impose
large negative interplanetary magnetic fields IMF across the dayside
magnetosphere at 1 AU and large pressure-produced compressions of the
dayside magnetopause Such geomagnetic storms can be the sources of
impaired and even disrupted technological systems flying in space and
operating on the earth s surface Recent research from our group has
demonstrated that the size of a geomagnetic storm as measured by the
geomagnetic index Dst appears to be well associated with the expansion
speed of the halo CME that triggered the storm The relationship was
found to be more pronounced for very fast ejecta v 1000 km s In addition
we obtained new and original results that demonstrate the relationship
between magnetic fields of the solar source of a coronal eruption and
magnetic fields of the interplanetary ejecta In this presentation
we will investigate the very real possibility that the polarity of
IMF near 1 AU can be deduced from key solar data -- photospheric
magnetograms coronal images and the observed configurations of CMEs
near the Sun This information is critical together with data on the
CME arrival time velocity and plasma density for assessing geospace
disturbances that might result from the solar eruption This research
also contributes to deeper understandings of the
Title: Observed pre flare characteristics of active region magnetic
fields
Authors: Yurchyshyn, V.
Bibcode: 2006cosp...36..676Y
Altcode: 2006cosp.meet..676Y
I will present data and results on observations of flare-related
magnetic conditions in solar active regions The following topics will
be discussed Static non-potential magnetic characteristics before
flares such as magnetic gradients shear and twist 2 spatio-temporal
dynamics of the photospheric magnetic flux such as flows and flux
emergence 3 evolution of magnetic structures leading to and following
flares A special attention will be payed to new approaches to quantify
complexity of the photospheric magnetic fields in terms of intermittency
magnetic power spectra and probability distribution functions Discovered
correlation between the parameters and the flare activity in active
regions provides new insights into understanding of the nature
of magnetic coupling between the sub-photospheric layers where the
magnetic field is generated and the corona where eruptions occur
Title: Magnetic Structure of Halo CMEs and Corresponding ICMEs
Authors: Krall, J.; Yurchyshyn, V. B.; Chen, J.
Bibcode: 2005AGUFMSH13A0300K
Altcode:
The detailed connection between a halo coronal mass ejection (CME)
and its corresponding ``interplanetary CME'' (ICME) is an area of
active study. Using the erupting flux rope model [1-2], we present
model/data comparisons for multiple CME/ICME events near the sun
(using coronagraph image data) and in the heliosphere (using in situ
measurements). We find that the near-Sun magnetic configuration, as
obtained from a match of the model to the observed halo-CME morphology,
is closely related to the ICME magnetic configuration, as determined
by matching the model ICME to the in situ magnetic field and plasma
measurements. The differences between the near-Sun flux-rope orientation
parameters and the near-Earth orientation parameters are noted in each
case. These indicate that, typically, the apex of the flux rope is
deflected by 5-10 degrees as the flux rope expands outwards to 1 AU. [1]
Chen, J. 1996, JGR, 101, 27499 [2] Krall, J. et al., 2000, ApJ, 539, 964
Title: Continuation of the SHINE Campaign Studies: Eruption on May
13, 2005
Authors: Yurchyshyn, V.; Liu, C.
Bibcode: 2005AGUFMSH13A0274Y
Altcode:
We will present data on a well observed eruptive flare that occurred
on May 13, 2005 in NOAA AR 0759. This typical two-ribbon flare was
associated with a fast CME and caused an intense geomagnetic storm
(Dst < -259nT) on early May 15th. The magnetic structure of this
flare, the position of the AR, flare duration, filament activation,
sigmoidal appearance in Halpha and coronal images, association with
a CME and coronal dimming as well as interplanetary characteristics
are strikingly similar to those of the 1997 May 12 SHINE campaign
event. Because the solar and heliospheric background conditions for
the May 12 1997 eruption were relatively simple, this event became
a key event in many collaborative campaigns such as SHINE-GEM-CEDAR,
MURI, and CISM. The biggest problem is that the 1997 event was not well
observed and many essential data sets are not available. Therefore,
various simulations, methods, inferences and theoretical ideas which
arose from this campaign study could not be satisfactory tested against
observations. It is thus, essential to continue these focused event
oriented studies. The recent May 13 flare was well covered by Big Bear
Solar Observatory (Halpha images and vector magnetograms) as well as
SOHO, TRACE, RHESSI and ACE satellites. In this presentation we will
discuss the structure of the May 13, 2005 eruption and analyze the
flare light curves produced by Halpha and X- ray sources. We will also
present vector magnetic field data and flow maps. We will analyze the
evolution of the AR magnetic field (flux emergence and cancellation;
magnetic gradients; magnetic flux change) and compare them to the flare
activity and interplanetary data on the associated magnetic cloud that
was observed at 1AU. Finally we will discuss our findings in terms of
the existing CME models and provide observational restrains to modelers.
Title: Magnetic Reconnection Flux and Coronal Mass Ejection Velocity
Authors: Qiu, Jiong; Yurchyshyn, Vasyl B.
Bibcode: 2005ApJ...634L.121Q
Altcode:
We explore the relationship between the total reconnection flux
ψrec estimated from flare observations and the velocity
VCME of coronal mass ejections (CMEs) observed with the
Large Angle and Spectrometric Coronagraph (LASCO) Experiment. Our
study includes 13 events with varying magnetic configurations in
source regions. It is shown that VCME is proportional to
ψrec, with a linear cross-correlation of 89% and confidence
level greater than 99.5%. This result confirms the importance of
magnetic flux transferred by magnetic reconnection in the early stage
of fast CMEs. On the other hand, the CME velocity and kinematic energy
are probably independent of magnetic configurations of source regions.
Title: Evolution of Barb Angle and Filament Eruption
Authors: Su, J. T.; Liu, Y.; Zhang, H. Q.; Kurokawa, H.; Yurchyshyn,
V.; Shibata, K.; Bao, X. M.; Wang, G. P.; Li, C.
Bibcode: 2005ApJ...630L.101S
Altcode:
Hα observations of a quiescent U-shaped filament were obtained at Big
Bear Solar Observatory and at Hida Observatory with the Flare Monitoring
Telescope. The filament was located in the southern hemisphere on
1998 November 4. We study the evolution of the angle of a barb with
respect to the axis of the filament and find the evolution can be
divided into two phases: a rise from the acute phase to the obtuse
phase and a fall. Thus, this indicates that the chirality of this barb
changes with time. Moreover, in the process of evolution, we find that
interconnection of the part of the filament bearing the barb with the
whole filament became either weakened or strengthened. We impute the
final eruption of the filament to the chirality evolution of the barb.
Title: Structure of magnetic fields in NOAA active regions 0486 and
0501 and in the associated interplanetary ejecta
Authors: Yurchyshyn, Vasyl; Hu, Qiang; Abramenko, Valentyna
Bibcode: 2005SpWea...3.8C02Y
Altcode:
Spectacular burst of solar activity in October-November 2003, when large
solar spots and intense solar flares dominated the solar surface for
many consecutive days, caused intense geomagnetic storms. In this paper
we analyze solar and interplanetary magnetic fields associated with the
storms in October-November 2003. We used space- and ground-based data in
order to compare the orientations of the magnetic fields on the solar
surface and at 1 AU as well as to estimate parameters of geomagnetic
storms during this violent period of geomagnetic activity. Our study
further supports earlier reports on the correlation between the
coronal mass ejection speed and the strength of the magnetic field in
an interplanetary ejecta. A good correspondence was also found between
directions of the helical magnetic fields in interplanetary ejecta and
in the source active regions. These findings are quite significant in
terms of their potential to predict the severity of geomagnetic activity
1-2 days in advance, immediately after an Earth directed solar eruption.
Title: Magnetic structures of active regions and their link to
coronal mass ejections
Authors: Yurchyshyn, V.
Bibcode: 2005AGUSMSH51C..03Y
Altcode:
olar coronal mass ejections (CMEs) are a principal link that connects
the chain of events in the solar atmosphere, interplanetary space and
the earth's magnetic environment. The central objective of our study is
to advance our understanding of physical processes in CMEs and related
phenomena, including their ultimate origin, precursors and near sun
evolution as well as their link to the interplanetary phenomena. Earlier
studies unanimously suggest that there is a straightforward relationship
between the magnetic fields of erupted filaments and magnetic clouds at
1AU. However, the situation is more complicated and less understood
in the case of eruptions from solar active regions. We combined
photospheric magnetograms, chromospheric and coronal images as well
as solar wind data of high spatial and temporal resolution in order
to i) determine the basic characteristics of the initial pre-eruption
magnetic configuration in an active region and ii) find a link between
these characteristics and the magnetic fields in interplanetary CMEs
(ICMEs) at 1AU. Our results show a good correspondence between the
directions of the helical magnetic fields in interplanetary ejecta
and in the source active regions. We will also demonstrate how the
combination of the solar surface and solar wind data may be used to
discriminate between different CME models and to predict the sign of
the interplanetary magnetic field at 1AU.
Title: Towards Real-Time Automated Prediction of Geo-Magnetic Storms
Based on Observations of Source Regions of Halo CMEs
Authors: Song, H.; Yurchyshyn, V.; Wang, H.
Bibcode: 2005AGUSMSP23A..01S
Altcode:
Halo Coronal Mass Ejections (CMEs), originating near disk center,
are possible sources of large geomagnetic storms. Our goal is to
predict geomagnetic activities automatically and in real time based
on the observations of source regions of CMEs. We have achieved the
following two steps: (1) We studied the magnetic structure of a number
of famous active regions that produced large flares (X5 or larger), and
found a close correlation between magnetic gradient and magnetic shear;
and magnetic gradient could be even a better proxy to predict where a
major flare might occur. Therefore, we can avoid complication of using
vector magnetograms to derive magnetic shear. (2) We investigated the
relationship between geoeffectiveness and the orientation of magnetic
field in source active regions. Based on the flaring neutral lines
detected by step (1), we extrapolated the magnetic structure in active
region with three-dimensional (3D) numerical models. We started with
the potential field model. We attempt to find relationship between the
the orientation of magnetic field in the source region and the hourly
averaged ACE measurements of the Bz component of the interplanetary
magnetic fields, that is believed to be the indicator of geomagnetic
storms.
Title: On the Relationship Among Magnetic Twist, Reconnection Rate
and Acceleation in Solar Eruptions
Authors: Jing, J.; Yurchyshyn, V.; Qiu, J.; Xu, Y.; Wang, H.
Bibcode: 2005AGUSMSP44A..03J
Altcode:
We investigate the statistical correlation between the magnetic
twist and properties of solar eruptions such as acceleration of
eruptive filaments and magnetic reconnection rate of corresponding
two-ribbon flares. We anticipate to provide observational evidence
for, or against, the speculation that increasing magnetic twist
is more likely giving rise to the violent solar eruptions. The
magnetic twist is characterized by the linear force-free (LFFF)
magnetic field constant α. We adopt a method for the reconstruction
of the LFFF magnetic field in a bounded domain that was described in
Abramenko and Yurchishin (1996). The best-fit value of α is selected
so that the extrapolated field gives the closest match to the coronal
observations. The magnetic reconnection rate of two-ribbon flares, in
terms of electric field inside the reconnecting current sheet(RCS) and
flux change rate involved in magnetic reconnection in the low corona,
is derived by measuring the expansion of flare ribbons across the the
magnetic field. Based our limited events studied so far, there appears
to be a tendency that the magnetic field with higher α shows higher
filament acceleration and magnetic reconnection rate.
Title: Photospheric sources of very fast coronal mass ejections
Authors: Yurchyshyn, V.; Yashiro, S.; Gopalswamy, N.
Bibcode: 2005AGUSMSH51C..04Y
Altcode:
We identified photospheric sources for 39 very fast (v > 1100
km/s) front-side coronal mass ejections that erupted between 1999 and
2001. For our study we used data on CMEs and their sources provided
by the CME Catalog, SOHO spacecraft (LASCO, EIT, MDI), Big Bear Solar
Observatory (Halpha, magnetograms), Mount Wilson Observatory (sunspot
drawings) and Joint USAF/NOAA active region summary. Our results are
as follows. We distinguished three different groups of active regions
which are responsible for very fast CMEs: 1) Complex delta spots (21
events). This group of active regions is characterized by the presence
of at least two large opposite polarity sunspots located close to
each other. 2) Simple delta spots (8 events). A typical configuration
of this type consists of one large twisted tadpole-shaped sunspot,
surrounded by many small satellite-sunspots. 3) Extended magnetic
regions, which consist of two adjacent decaying active regions or a
new active region emerging inside a decaying active region.
Title: Statistical Distributions of Speeds of Coronal Mass Ejections
Authors: Yurchyshyn, V.; Yashiro, S.; Abramenko, V.; Wang, H.;
Gopalswamy, N.
Bibcode: 2005ApJ...619..599Y
Altcode:
We studied the distribution of plane-of-sky speeds determined for
4315 coronal mass ejections (CMEs) detected by the Large Angle and
Spectrometric Coronagraph Experiment on board the Solar and Heliospheric
Observatory (SOHO LASCO). We found that the speed distributions
for accelerating and decelerating events are nearly identical and
to a good approximation they can be fitted with a single lognormal
distribution. This finding implies that, statistically, there is no
physical distinction between the accelerating and the decelerating
events. The lognormal distribution of the CME speeds suggests that
the same driving mechanism of a nonlinear nature is acting in both
slow and fast dynamical types of CMEs.
Title: Magnetic Flux Ropes from the Sun to 1 AU*
Authors: Krall, J.; Yurchyshyn, V. B.; St. Cyr, O. C.; Chen, J.
Bibcode: 2004AGUFMSH22A..07K
Altcode:
Any practical model of the dynamics of a coronal mass ejection (CME)
and its interplanetary counterpart (ICME) must conform to available
observational constraints from sun and to the earth; the upcoming
STEREO mission will add significantly to those constraints. We present
model/data comparisons for specific CME/ICME events near the sun
(using coronagraph image data) and in the heliosphere (using in situ
measurements) to show that the flux rope model of Chen and Krall[1-2]
provides an accurate physics-based characterization of flux-rope
CMEs over this range. We further show that quantitative results,
such as the field energy required for eruption, depend on specific
aspects of the flux rope geometry, such as the ratio (length/width)
of the elliptical shape traced out by the flux-rope axis. It is this
geometry that will be determined, for the first time, by STEREO. [1]
Chen, J. 1996, JGR, 101, 27499 [2] Krall, J. et al., 2000, ApJ, 539,
964 *Work supported by ONR, NASA and NSF
Title: On the Relation between Filament Eruptions, Flares, and
Coronal Mass Ejections
Authors: Jing, Ju; Yurchyshyn, Vasyl B.; Yang, Guo; Xu, Yan; Wang,
Haimin
Bibcode: 2004ApJ...614.1054J
Altcode:
We present a statistical study of 106 filament eruptions, which were
automatically detected by a pattern recognition program implemented
at Big Bear Solar Observatory using Hα full-disk data from 1999
to 2003. We compare these events with Geostationary Operational
Environmental Satellite soft X-ray time profiles, solar-geophysical
data (SGD) solar event reports, Michelson Doppler Imager magnetograms,
and Large Angle and Spectrometric Coronagraph (LASCO) data to determine
the relationship between filament eruptions and other phenomena of solar
activity. (1) Excluding eight events with no corresponding LASCO data,
55% or 56% of 98 events were associated with coronal mass ejections
(CMEs). (2) Active region filament eruptions have a considerably
higher flare association rate of 95% compared to quiescent filament
eruptions with 27%, but a comparable CME association rate, namely, 43%
for active region filament eruptions and 54% for quiescent filament
eruptions. (3) 54% or 68% of 80 disk events were associated with new
flux emergence. In addition, we derived the sign of magnetic helicity
and the orientation of the magnetic field associated with seven halo
CMEs and demonstrated that the geoeffectiveness of a halo CME can be
predicted by these two parameters.
Title: On the Temporal Relationship between Hα Filament Eruptions
and Soft X-Ray Emissions
Authors: Schuck, P. W.; Chen, J.; Schwartz, I. B.; Yurchyshyn, V.
Bibcode: 2004ApJ...610L.133S
Altcode:
A technique for investigating the temporal relationship between
Hα filament eruptions and soft X-ray flux is presented. The method
is fast, simple, based on statistical measures, and requires no a
priori knowledge regarding the location of the filaments on the solar
disk. The method is used to study the filament eruption associated
with a coronal mass ejection and the M-class flare that originated
from NOAA Active Region 9163 on 2000 September 12. The technique
provides a quantitative determination of the temporal relationship
between changes in the Hα filament and soft X-ray flux. We conclude
that the filament eruption begins 2 hr prior to the first detectable
enhancement in soft X-ray flux.
Title: Topological changes of the photospheric magnetic field inside
active regions: A prelude to flares?
Authors: Sorriso-Valvo, Luca; Carbone, Vincenzo; Veltri, Pierluigi;
Abramenko, Valentina I.; Noullez, Alain; Politano, Hélène; Pouquet,
Annick; Yurchyshyn, Vasyl
Bibcode: 2004P&SS...52..937S
Altcode:
The detection of magnetic field variations as a signature of flaring
activity is one of the main goals in solar physics. Past efforts gave
apparently no unambiguous observations of systematic changes. In the
present study, we discuss recent results from observations that scaling
laws of turbulent current helicity inside a given flaring active region
change in response to large flares in that active region. Such changes
can be related to the evolution of current structures by a simple
geometrical argument, which has been tested using high Reynolds number
direct numerical simulations of the MHD equations. Interpretation
of the observed data within this picture indicates that the change
in scaling behavior of the current helicity seems to be associated
with a topological reorganization of the footpoint of the magnetic
field loops, namely with the dissipation of small scales structures
in turbulent media.
Title: Coronal ejecta in October - November of 2003 and predictions
of the associated geomagnetic events
Authors: Yurchyshyn, V.
Bibcode: 2004AAS...204.0217Y
Altcode: 2004BAAS...36..670Y
Recently we found that the Bz component in the interplanetary
magnetic field is correlated with the projected speed of coronal mass
ejections (CME). The relationship is better pronounced for very fast
ejecta with speeds higher than 1200 km/s, while slower events display
larger scatter. In turn, the Bz in IMF is correlated with
the intensity of the Dst index of geomagnetic activity. Based on this
result we are elaborating a procedure to routinely predict the magnitude
of the Bz and the intensity of geomagnetic storms 1-2 days
in advance by measuring speeds of halo CMEs as they propagate across
the LASCO C3 field of view. Here we present our predictions made for
9 halo CMEs ejected during the period of violent solar activity in
October-November 2003. The comparison between the predicted values of
the Bz and the Dst index and the observed data shows that we
were abble to satisfactory predict all three major geomagnetic events
when the Dst index decreased below -300 nT.
Title: Characterizing Solar Surface Turbulence
Authors: Schuck, P.; Chen, J.; Schwartz, I.; Yurchyshyn, V.
Bibcode: 2004AAS...204.3711S
Altcode: 2004BAAS...36..710S
The identification and characterization of solar surface turbulence
is particularly important for understanding the dynamics associated
with eruptive phenomena. In this paper, we present a wavelet
analysis for characterizing surface turbulence associated with solar
eruptions. By definition, solar eruptions represent impulsive events
rather than a statistical steady state and the analysis of impulsive
events requires both time and frequency localization for proper
robust characterization. Thus, the wavelet (time-frequency) basis
represents integral ingredient for the analysis. In this paper,
H-α turbulence on the solar disk is characterized by estimating the
local-frequency-wavenumber distribution (local dispersion relation)
of the fluctuations. The local frequency wavenumber distribution is
computed by generalizing established two-point multi-scale wavelet
interferometric techniques [1-3] for the multipoint data represented
by solar images. The local-wavenumber-distribution produces robust
estimates for the phase velocities of fluctuations in the sequence
of solar images. [1] J. L. Pinçon, P. M. Kintner, P. W. Schuck
and C. E. Seyler, Observation and analysis of lower hybrid solitary
structures as rotating eigenmodes, \textit{J. Geophys. Res.},
\textbf{102}, 17283\--17296, 1997. [2] P. W. Schuck, C. E. Seyler,
J. L. Pinçon, John Bonnell, and P. M. Kintner, Theory, simulation and
observation of discrete eigenmodes associated with lower hybrid solitary
structures, \textit{J. Geophys. Res.}, \textbf{103}, 6935\--6953,
1998. [3] J. W. Bonnell, P. W. Schuck, J.\--L. Pinçon,
C. E. Seyler, and P. M. Kintner, Observation of bound states and
counter\--rotating lower hybrid eigenmodes in the auroral ionosphere,
\textit{Phys. Rev. Lett.}, \textbf{80}, 5734\--5737, 1998. Work
Supported by ONR
Title: Traces of the Dynamic Current Sheet during a Solar Flare
Authors: Ji, Haisheng; Wang, Haimin; Goode, Philip R.; Jiang, Yunchun;
Yurchyshyn, V.
Bibcode: 2004ApJ...607L..55J
Altcode:
High-cadence and high-resolution time sequences of far Hα
off-band images provide a unique tool to study the evolution of
the fine structure of flare kernels. The fine structure contains
important information on flare topology and the triggering
mechanism. In this Letter, we concentrate on the rapid changes
of the relative positions of two conjugate flare footpoints. In
order to carry out this study with the highest physical precision,
we use rc=ΣrjIj/ΣIj
(Ij is the Hα brightness at rj) to compute the
centroid of an Hα bright kernel region caused by solar flares. Using
this, we probe the fine temporal structures connected to the distance
between the centroids of two conjugate kernels of an M2.3 flare. The
flare, which occurred on 2002 September 9 in NOAA Active Region 0105,
was observed at Big Bear Solar Observatory at the far off-band center
wavelength of H α-1.3 Å, with a cadence of ~40 ms. The flare was also
observed by RHESSI. The time profile of the separation distance shows
an excellent anticorrelation to that of the hard X-ray (HXR) emissions
in 25-50 keV, which exhibit a number of separate spikes (the linear
Pearson correlation coefficient is found to be ~-0.83). The separation
between the two centroids decreases at the rising periods of four HXR
spikes, then it increases after the peak time of the flare to show
the expected separation motion. The most obvious decreasing, which
occurred during the first HXR peak, was confirmed by corresponding
images. This implies that during the impulsive phases, the energy
transported from the corona is deposited increasingly inwardly between
the two kernels. This new and perhaps surprising tendency for the
energy deposition can be explained as being caused by current sheet
pinch motions, which, at the same time, enhance the magnetic energy
reconnection rate to produce the observed HXR spikes.
Title: Magnetic Field, Hα, and RHESSI Observations of the 2002 July
23 Gamma-Ray Flare
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna;
Spirock, Thomas J.; Krucker, Säm
Bibcode: 2004ApJ...605..546Y
Altcode:
In this paper we examine two aspects of the 2002 July 23 gamma-ray flare
by using multiwavelength observations. First, the data suggest that the
interaction of the erupted field with an overlying large-scale coronal
field can explain the offset between the gamma-ray and the hard X-ray
sources observed in this event. Second, we pay attention to rapid and
permanent changes in the photospheric magnetic field associated with
the flare. MDI and BBSO magnetograms show that the following magnetic
flux had rapidly decreased by 1×1020 Mx immediately after
the flare, while the leading polarity was gradually increasing for
several hours after the flare. Our study also suggests that the changes
were most probably associated with the emergence of new flux and the
reorientation of the magnetic field lines. We interpret the magnetograph
and spectral data for this event in terms of the tether-cutting model.
Title: Evidence of Rapid Flux Emergence Associated with the M8.7
Flare on 2002 July 26
Authors: Wang, Haimin; Qiu, Jiong; Jing, Ju; Spirock, Thomas J.;
Yurchyshyn, Vasyl; Abramenko, Valentina; Ji, Haisheng; Goode,
Phillip R.
Bibcode: 2004ApJ...605..931W
Altcode:
In this paper, we present a detailed study of the M8.7 flare
that occurred on 2002 July 26 using data from the Big Bear Solar
Observatory (BBSO), Ramaty High Energy Solar Spectroscopic Imager
(RHESSI), the Transition Region and Coronal Explorer (TRACE), and the
Solar and Heliospheric Observatory (SOHO). This flare has interesting
properties similar to a number of flares that we studied previously,
such as a rapid increase of magnetic flux in one polarity and an
increase in transverse fields and magnetic shear associated with the
flare. However, this event had the most comprehensive observations; in
particular, the high-resolution high-cadence BBSO vector magnetograph
observations. At the time of the flare, across the flare neutral
line, there was a sudden emergence of magnetic flux at the rate
of 1020 Mx hr-1 in both the longitudinal and
transverse components. The emerging flux mostly occurred at the sites
of the flare. It was very inclined and led to impulsively enhanced
shear in the magnetic fields. We discuss these observations in the
context of magnetic reconnection triggered by rapid flux emergence. It
is also possible that the new flux signifies flare-related change in
the field line inclination.
Title: Correlation between speeds of coronal mass ejections and the
intensity of geomagnetic storms
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna
Bibcode: 2004SpWea...2.2001Y
Altcode:
We studied the relationship between the projected speed of coronal
mass ejections (CMEs), determined from a sequence of Solar and
Heliospheric Observatory/Large Angle and Spectrometric Coronagraph
Experiment (SOHO/LASCO) images, and the hourly averaged magnitude of
the Bz component of the magnetic field in an interplanetary
ejecta, as measured by the Advanced Composition Explorer (ACE)
magnetometer in the Geocentric Solar Magnetospheric Coordinate System
(GSM). For CMEs that originate at the central part of the solar
disk we found that the intensity of Bz is correlated with
the projected speed of the CME, Vp. The relationship is
more pronounced for very fast ejecta (Vp > 1200 km/s),
while slower events display larger scatter. We also present data which
support earlier conclusions about the correlation of Bz
and the Dst index of geomagnetic activity. A possible application of
the results to space weather forecasting is discussed.
Title: The earthshine spectrum
Authors: Montañés Rodriguez, P.; Pallé, E.; Goode, P. R.; Hickey,
J.; Qiu, J.; Yurchyshyn, V.; Chu, M. C.; Kolbe, E.; Brown, C. T.;
Koonin, S. E.
Bibcode: 2004AdSpR..34..293M
Altcode:
Since 1998 the Earthshine Project has been a collaborative effort
between Big Bear Solar Observatory/New Jersey Institute of Technology
and California Institute of Technology. Cyclic spectroscopic
observations of the dark and bright sides of the moon (or earthshine
and moonshine, respectively) have been carried out in the visible
region at Palomar Observatory. From these data, the ratio of the
earthshine to moonshine characterizes the globally averaged Earth's
spectrum. Information concerning the search for extra-solar, terrestrial
planets can be also obtained from these observations.
Title: The Earthshine Project: update on photometric and spectroscopic
measurements
Authors: Pallé, E.; Montañés Rodriguez, P.; Goode, P. R.; Qiu,
J.; Yurchyshyn, V.; Hickey, J.; Chu, M. -C.; Kolbe, E.; Brown, C. T.;
Koonin, S. E.
Bibcode: 2004AdSpR..34..288P
Altcode:
The Earthshine Project is a collaborative effort between Big Bear
Solar Observatory (New Jersey Institute of Technology) and the
California Institute of Technology. Our primary goal is the precise
determination of a global and absolutely calibrated albedo of the Earth
and the characterization of its synoptic, seasonal and inter-annual
variability. Photometric observations of the Earth's reflectance have
been regularly carried out during the past 4 years. The up-to-date
synoptic, seasonal and long-term variation in the Earth's albedo
are reported in this paper, together with a comparison to model
albedos using modern cloud satellite data and Earth Radiation Budget
Experiment scene models. The Earth's albedo has a major role in
determining the Earth's climate. The possibility of a response of
this parameter to solar activity is also discussed. Simultaneously,
spectrometric observations of the earthshine have been carried out
at Palomar Observatory. The main goals and first results of those
observations are also presented.
Title: On the time coincidence between \boldmath{Hα
}-filament eruptions and soft X-ray emissions
Authors: Schuck, P. W.; Chen, J.; Schwartz, I.; Yurchyshyn, V.
Bibcode: 2003AGUFMSH22B..05S
Altcode:
The interrelationships among coronal mass ejections, solar flares,
and filament eruptions have been a long standing issue in solar
physics. In particular, timing and spatial relationships among such
eruptive phenomena play a key role in understanding any possible
causality among them. Presently, observational ambiguities often
result from insufficient temporal and spatial resolution. However,
we expect that observational capabilities will continue to improve,
and in the near future, produce large volumes of solar data with
high time-cadence and spatial resolution. We present a technique for
quantitatively characterizing dynamics in Hα -data. We
report on the result of applying this technique to a sequence of 1-min
Hα -images from the Kanzelhöhe Solar Observatory. We
chose Hα -data for our initial application because many
solar eruptive phenomena have observable signatures in chromospheric
dynamics and long periods of Hα -observations are readily
available. The data set contains quiescent filaments and a filament
eruption accompanied by a two-ribbon flare. The analysis reveals
the spatially and temporally correlated phenomena on the Hα
-solar disk. The Hα -dynamics are compared with
variations in the integrated soft X-ray flux detected by the GOES 8
satellite. Work supported by ONR, NSF ATM 0205157, and ATM 9903515.
Title: Photospheric Sources of Very Fast (>1100 km/s) CMEs Between
1999 and 2001
Authors: Yurchyshyn, V.
Bibcode: 2003AGUFMSH22B..06Y
Altcode:
We identified photospheric sources for 39 very fast (faster then
1100 km/s) front-side coronal mass ejections, which occurred between
1999 and 2001. For our study we used data on CMEs and their sources
provided by the CME Catalog, SOHO spacecraft (LASCO, EIT, MDI), Big
Bear Solar Observatory (Hα, magnetograms), Mount Wilson Observatory
(sunspot drawings) and Joint USAF/NOAA active region summary. We
distinguished three different groups of active regions which are
responsible for very fast CMEs: 1) Complex delta spots (delta spots
with a Mt. Wilson classification of beta gamma). This group of active
regions (21 events) can be represented by active regions 9393 and 9415
and is characterized by the presence of at least two large opposite
polarity sunspots located close to each other. 2) Simple delta spots
(8 events). A typical configuration of this type can be represented
by active regions 8375 and 9236 and consists of one large twisted
tadpole-shaped sunspot, surrounded by many small satellite-sunspots. 3)
Extended magnetic regions, which consist of two adjacent decaying active
regions or a new active region emerging inside a decaying active region
(active regions 9046 and 9085). In this presentation we will discuss in
detail the evolution and the type of the magnetic structures which are
responsible for very fast CMEs originating from delta-configurations.
Title: Signature of an Avalanche in Solar Flares as Measured by
Photospheric Magnetic Fields
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
Bibcode: 2003ApJ...597.1135A
Altcode:
We analyzed time variations of turbulent parameters of the photospheric
magnetic field of four active regions obtained during the course of
major solar flares using longitudinal magnetograms from the Big Bear
Solar Observatory and from SOHO/MDI full-disk measurements. Analysis of
the data indicated that, before each flare, the degree of intermittency
of the magnetic field had been increasing for 6-33 minutes and reached
a maximum value approximately 3-14 minutes before the peak of the
hard X-ray emission for each event. This result seems to suggest the
existence in an active region of a turbulent phase prior to a solar
flare. We also found that the maximum of the correlation length of
the magnetic energy dissipation field tends to follow (or to occur
nearly simultaneously) with the peak of the hard X-ray emission. The
data suggest that the peak in the correlation length might be a trace
of an avalanche of coronal reconnection events. We discuss the results
in the framework of the concept of self-organized criticality.
Title: Themis, BBSO, MDI and trace observations of a filament eruption
Authors: Contarino, L.; Romano, P.; Yurchyshyn, V. B.; Zuccarello, F.
Bibcode: 2003SoPh..216..173C
Altcode:
We describe a filament destabilization which occurred on 5 May 2001 in
NOAA AR 9445, before a flare event. The analysis is based on Hα data
acquired by THEMIS operating in IPM mode, Hα data and magnetograms
obtained at the Big Bear Solar Observatory, MDI magnetograms and 171 Å
images taken by TRACE. Observations at 171 Å show that ∼ 2.5 hours
before the flare peak, the western part of the EUV filament channel
seems to split into two parts. The bifurcation of the filament in the
Hα line is observed to take place ∼ 1.5 hours before the flare peak,
while one thread of the filament erupts ∼10 min before the peak of
the flare. Our analysis of longitudinal magnetograms shows the presence
of a knot of positive flux inside a region of negative polarity, which
coincides with the site of filament bifurcation. We interpret this
event as occurring in two steps: the first step, characterized by the
appearance of a new magnetic feature and the successive reconnection
in the lower atmosphere between its field lines and the field lines
of the old arcade sustaining the filament, leads to a new filament
channel and to the observed filament bifurcation; the second step,
characterized by the eruption of part of the filament lying on the
old PIL, leads to a second reconnection, occurring higher in the corona.
Title: Cancellations and structures in the solar photosphere:
signature of flares
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
Bibcode: 2003AIPC..679..695S
Altcode:
The topological properties of the typical current structures in
a turbulent magnetohydrodynamic flow can be measured using the
cancellations analysis. In two-dimensional numerical simulations, this
reveals current filaments being the most typical current structures. The
observations of the topology of photospheric current structures within
active regions shows that modifications occur correspondingly with
strong flares.
Title: Sunshine, Earthshine and Climate Change: II. Solar Origins
of Variations in the Earth's Albedo
Authors: Goode, P. R.; Pallé, E.; Yurchyshyn, V.; Qiu, J.; Hickey,
J.; Rodriguez, P. Montañés; Chu, M. -C.; Kolbe, E.; Brown, C. T.;
Koonin, S. E.
Bibcode: 2003JKAS...36S..83G
Altcode:
No abstract at ADS
Title: Signature of Avalanche in Solar Flares as Measured by
Photospheric Magnetic Fields
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
Bibcode: 2003SPD....34.1507A
Altcode: 2003BAAS...35..831A
Turbulent/fractal parameters of the longitudinal magnetic field,
Bz, for four powerful solar flares were analyzed utilizing
the correlation length, l, of the magnetic energy dissipation
field and the scaling exponent, b, which characterizes the measure
of intermittency of the Bz structure. We select a set of
four two-ribbon flares, which were followed by coronal mass ejections,
for the study of magnetic structure. During the course of each flare,
we found a peak in b which was followed by a peak in l in all of the
cases studied in this paper. These two peaks were separated by the time
interval tl during which a rapid growth of the soft X-ray
and Hα flux occurred. The peak in b was preceded by a time period
tb during which b increased gradually. For all of the flares
tb was longer than the time interval tl. The
maximum of l occurred nearly simultaneously, within an accuracy of
about 2-5 minutes, with the maximum of the hard X-ray emission. For
the four flares considered in this paper, we concluded that the more
impulsive and/or more powerful a flare is, the shorter the b growth
time, tb, and the l growth time, tl, are. In
the framework of the theory of non-linear dissipative processes,
these results may be interpreted as follows. Before a solar flare
occurs there is a significant increase in the number of magnetic field
discontinuities (b increasing), which is followed by an avalanche
(increase of the correlation length) of magnetic energy dissipation
events. The avalanche event occupies the entire active region from the
corona to the photosphere. Our study indicates that the more abrupt
is the avalanche, the stronger and/or more impulsive a flare is. The
time profiles of an avalanche is either Gaussian, which satisfies
the logistic avalanche model, or exponential with an abrupt drop,
which satisfies the exponential avalanche model. The driving time,
tb, was longer than the avalanching time, tl,
for all of the events. This qualitatively agrees with the requirements
of the self-organized criticality theory. This work was supported
by NSF-ATM 0076602, 0205157, 9903515 and NASA NAG5-12782 grants.
Title: Rapid Changes in the Longitudinal Magnetic Field Associated
with the July 23, 2002 γ -ray Flare
Authors: Yurchyshyn, V. B.; Wang, H.; Abramenko, V. I.; Spirock,
T. J.; Krucker, S.
Bibcode: 2003SPD....34.1508Y
Altcode: 2003BAAS...35Q.832Y
In this paper we analyze and discuss rapid changes of the magnetic field
associated with the July 23, 2002 γ -ray flare. MDI magnetic flux
profiles and BBSO vector magnetograms showed that immediately after
the flare the leading polarity had increased by 2*E20Mx,
while the following polarity decreased only by 1*E20Mx. The
observed changes were permanent and not caused by variations in seeing
or changes in the line profile, which we used to measure the magnetic
field. In this active region we distinguish two separate locations,
which show the most dramatic changes in the magnetic field. The
first location showed an increase in the magnetic field strength
and a new penumbra area and it was associated with emergence of new
magnetic flux. At the second location the position of the neutral
line had changed and it coincided with the footpoints of a rapidly
growing post-flare loop system. Linear force-free field simulations
showed that the re-orientation of the magnetic field during the flare
was capable of producing the observed changes in the total magnetic
flux. We also discuss a possible magnetic configuration responsible
for the flare. This work was supported in part by NSF ATM-0086999 and
ATM-0205157 and under NASA NAG5-10910 NAG5-12782 grants.
Title: Chromospheric Dynamics: An Examination of Spatio-temporal
Phenomena in \boldmathHα -Data
Authors: Schuck, P. W.; Chen, J.; Schwartz, I. .; Yurchyshyn, V.
Bibcode: 2003SPD....34.1612S
Altcode: 2003BAAS...35..834S
The interrelationships among coronal mass ejections, solar flares,
and filament eruptions have been a long standing issue in solar
physics. In particular, timing and spatial relationships among such
eruptive phenomena play a key role in understanding any possible
causality among them. Presently, observational ambiguities often
result from insufficient temporal and spatial resolution. However,
we expect that observational capabilities will continue to improve,
and in the near future, produce large volumes of solar data with high
time-cadence and spatial resolution. We have developed a method of
identifying and extracting coherent structures from multi-dimensional
sequences of data. The technique is general and may be applied to
sequences of solar images in any frequency (e.g., white light, X-rays,
UV), magnetograms, and other astrophysical and laboratory data. The
spatio-temporal dynamics revealed using this method can provide a
new, improved quantitative understanding of coherent and eruptive
phenomena. We report on the result of applying this technique to a
sequence of 1-min Hα -images from the Kanzelhöhe Solar
Observatory. We chose Hα -data for our initial application
because many solar eruptive phenomena have observable signatures in
chromospheric dynamics and long periods of Hα -observations
are readily available. The data set contains quiescent filaments
and a filament eruption accompanied by a two-ribbon flare. The
analysis reveals the spatially and temporally correlated phenomena and
self-similar structures on the solar disk in extraordinary detail. Work supported by ONR, NSF ATM 0205157, and ATM 9903515.
Title: How directions and helicity of erupted solar magnetic fields
define geoeffectiveness of coronal mass ejections
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna
Bibcode: 2003AdSpR..32.1965Y
Altcode:
In this study we report on the relationship between the projected speed
of CMEs, measured at 20R from SOHO/LASCO images, and the hourly averaged
magnitude of the southwardly directed magnetic field, B z,
at the leading edge of interplanetary ejecta, as measured by the ACE
magnetometer. We found that those CMEs that originate at the central
part of the solar disk ( r < 0.6 R⊙) are the most
geoeffective and the intensity of B z is an exponential
function of the CME's speeds. We propose an approach to estimate the
strength of the southward IMF at least one day in advance, immediately
after a CME started. The predicted value of the B z
component can be then used to estimate the intensity of a geomagnetic
storm caused by the eruption. The prediction method is based on the
correlation between the speeds of CMEs and magnitudes of the southward
IMF as well as the fact that the orientation and chirality of the
erupted solar filaments correspond to the orientation and chirality
of interplanetary ejecta.
Title: Cancellations analysis of photospheric magnetic structures
and flares
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
Bibcode: 2003MmSAI..74..631S
Altcode:
The topological properties of the typical current structures in
a turbulent magnetohydrodynamic flow can be measured using the
cancellations analysis. In two-dimensional numerical simulations, this
reveals current filaments being the most typical current structures. The
observations of the topology of photospheric current structures within
active regions shows that modifications occur correspondingly with
strong flares.
Title: A process of low-lying magnetic reconnection observed by
THEMIS, BBSO and TRACE
Authors: Contarino, L.; Romano, P.; Zuccarello, F.; Yurchyshyn, V. B.
Bibcode: 2003MmSAI..74..647C
Altcode:
We describe the results obtained from the study of a filament eruption
associated to a two-ribbon flare, occurred in NOAA AR 9445 on May 5,
2001. We interpret the event in a two-step reconnection scenario. The
first reconnection takes place in the lower atmosphere and is due to a
slow, but continuous, magnetic flux cancellation near the filament. The
second reconnection, which is explosive and takes place in the corona,
is caused by the eruption of the filament which triggers a two-ribbon
flare. The analysis is based on Hα data acquired by THEMIS operating
in IPM mode, Hα data and magnetograms obtained at the Big Bear Solar
Observatory, and 171 Å images taken by TRACE.
Title: Optical and EUV observation of a filament destabilization
and pre-eruption reconnection
Authors: Contarino, L.; Romano, P.; Zuccarello, F.; Yurchyshyn, V. B.
Bibcode: 2002ESASP.506..573C
Altcode: 2002ESPM...10..573C; 2002svco.conf..573C
Filament eruption occurring prior to solar flares or CME may be
related to changes in the magnetic field structure in and around
the filament. In particular, when the magnetic field topology is
characterized by great complexity, or new magnetic flux emerges in
the surrouding of the main arcade supporting the filament, a so-called
pre-eruption reconnection is likely to take place. In this framework,
using both ground-based (THEMIS and BBSO) and satellite (TRACE)
images and BBSO magnetograms, we have followed a filament eruption
occurred in AR 9445 on May 5, 2001, before a two-ribbon flare. Our
analysis has shown that the event was characterized by the following
steps: a) presence of a knot of positive polarity inside the region of
negative polarity where the arcade loops were anchored; b) appearance
of a bright knot in Hα images at the same location where the positive
polarity knot was observed; c) spread of the filament into two threads
and bifurcation near the Hα bright knot; d) eruption of part of the
filament and two-ribbon flare; e) EUV post-flare loops anchored in a
region near the Hα bright knot. The interpretation of these phenomena
in terms of a pre-eruption, low-lying magnetic reconnection, followed
by a post-eruption, high-lying reconnection, is discussed.
Title: Rapid Changes of Magnetic Fields Associated with Six X-Class
Flares
Authors: Wang, Haimin; Spirock, Thomas J.; Qiu, Jiong; Ji, Haisheng;
Yurchyshyn, Vasyl; Moon, Yong-Jae; Denker, Carsten; Goode, Philip R.
Bibcode: 2002ApJ...576..497W
Altcode:
In this paper, we present the results of the study of six X-class
flares. We found significant changes in the photospheric magnetic
fields associated with all of the events. For the five events in 2001,
when coronagraph data were available, all were associated with halo
coronal mass ejections. Based on the analyses of the line-of-sight
magnetograms, all six events had an increase in the magnetic flux
of the leading polarity of order of a few times 1020 Mx
while each event had some degree of decrease in the magnetic flux
of the following polarity. The flux changes are considered impulsive
because the ``changeover'' time, which we defined as the time to change
from preflare to postflare state, ranged from 10 to 100 minutes. The
observed changes are permanent. Therefore, the changes are not due
to changes in the line profile caused by flare emissions. For the
three most recent events, when vector magnetograms were available,
two showed an impulsive increase of the transverse field strength
and magnetic shear after the flares, as well as new sunspot area in
the form of penumbral structure. One of the events in this study was
from the previous solar cycle. This event showed a similar increase
in all components of the magnetic field, magnetic shear, and sunspot
area. We present three possible explanations to explain the observed
changes: (1) the emergence of very inclined flux loops, (2) a change
in the magnetic field direction, and (3) the expansion of the sunspot,
which moved some flux out of Zeeman saturation. However, we have no
explanation for the polarity preference; i.e., the flux of leading
polarity tends to increase while the flux of following polarity tends
to decrease slightly.
Title: Evidence of a Flux-Rope Model for Corona Mass Ejections Based
on Observations of the Limb Prominence Eruption on 2002 January 4
Authors: Yurchyshyn, Vasyl B.
Bibcode: 2002ApJ...576..493Y
Altcode:
We report on a prominence eruption as seen in Kanzelhöhe Solar
Observatory Hα images, Solar and Heliospheric Observatory (SOHO) EUV
Imaging Telescope (EIT) 195 Å images, and coronal SOHO Large Angle
Spectrometric Coronograph C2 images. Our data favor the flux-rope
model for coronal mass ejections (CMEs), which suggests that a flux
rope is formed long before the eruption. Our conclusion is based on a
three-part structure of the pre-erupted configuration of the magnetic
field and on the fact that the first Hα, SOHO EIT 195 Å brightenings
occurred some 15 minutes after the filament began to ascend. The data
also clearly demonstrate two rarely observed components of the standard
flare model: (1) magnetic loops that overlay the pre-erupted filament
and (2) magnetic field lines stretched vertically by the ascending
filament. These field lines are compressed horizontally and move
toward each other where they reconnect to form an apparently growing
post-flare loop system.
Title: Scaling Behavior of Structure Functions of the Longitudinal
Magnetic Field in Active Regions on the Sun
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
Bibcode: 2002ApJ...577..487A
Altcode:
In the framework of a refined Kolmogorov hypothesis, the scaling
behavior of the Bz-component of the photospheric
magnetic field is analyzed and compared with flaring activity in
solar active regions. We use Solar and Heliospheric Observatory
Michelson Doppler Imager, Huairou (China), and Big Bear measurements
of the Bz-component in the photosphere for nine active
regions. We show that there is no universal behavior in the scaling
of the Bz-structure functions for different active
regions. Our previous study has shown that scaling for a given active
region is caused by intermittency in the field, ɛ(B)(x),
describing the magnetic energy dissipation. When intermittency is
weak, the Bz field behaves as a passive scalar in the
turbulent flow, and the energy dissipation is largely determined by
the dissipation of kinetic energy in the active regions with low flare
productivity. However, when the field ɛ(B)(x) is highly
intermittent, the structure functions behave as transverse structure
functions of a fully developed turbulent vector field, and the scaling
of the energy dissipation is mostly determined by the dissipation of the
magnetic energy (active regions with strong flaring productivity). Based
on this recent result, we find that the dissipation spectrum of the
Bz-component is strongly related to the level of flare
productivity in a solar active region. When the flare productivity is
high, the corresponding spectrum is less steep. We also find that during
the evolution of NOAA Active Region 9393, the Bz dissipation
spectrum becomes less steep as the active region's flare activity
increases. Our results suggest that the reorganization of the magnetic
field at small scales is also relevant to flaring: the relative fraction
of small-scale fluctuations of magnetic energy dissipation increases
as an active region becomes prone to producing strong flares. Since
these small-scale changes seem to begin long before the start of a
solar flare, we suggest that the relation between scaling exponents,
calculated by using only measurements of the Bz-component,
and flare productivity of an active region can be used to monitor and
forecast flare activity.
Title: Flare Activity and Magnetic Helicity Injection by Photospheric
Horizontal Motions
Authors: Moon, Y. -J.; Chae, Jongchul; Choe, G. S.; Wang, Haimin;
Park, Y. D.; Yun, H. S.; Yurchyshyn, Vasyl; Goode, Philip R.
Bibcode: 2002ApJ...574.1066M
Altcode:
We present observational evidence that the occurrence of homologous
flares in an active region is physically related to the injection of
magnetic helicity by horizontal photospheric motions. We have analyzed
a set of 1 minute cadence magnetograms of NOAA AR 8100 taken over a
period of 6.5 hr by the Michelson Doppler Imager on board the Solar
and Heliospheric Observatory. During this observing time span, seven
homologous flares took place in the active region. We have computed
the magnetic helicity injection rate into the solar atmosphere by
photospheric shearing motions and found that a significant amount of
magnetic helicity was injected during the observing period. In a strong
M4.1 flare, the magnetic helicity injection rate impulsively increased
and peaked at the same time as the X-ray flux. The flare X-ray flux
integrated over the X-ray emission time strongly correlates with the
magnetic helicity injected during the flaring interval. The integrated
X-ray flux is found to be a logarithmically increasing function of
the injected magnetic helicity. Our results suggest that injection of
helicity and abrupt increase of helicity magnitude play a significant
role in flare triggering.
Title: Solar activity monitoring and forecasting capabilities at
Big Bear Solar Observatory
Authors: Gallagher, P. T.; Denker, C.; Yurchyshyn, V.; Spirock, T.;
Qiu, J.; Wang, H.; Goode, P. R.
Bibcode: 2002AnGeo..20.1105G
Altcode:
The availability of full-disk, high-resolution Ha
Title: Topological changes of the photospheric magnetic field inside
active regions: a prelude to flares
Authors: Sorriso-Valvo, L.; Carbone, V.; Abramenko, V.; Yurchyshyn,
V.; Noullez, A.; Politano, H.; Pouquet, A.; Veltri, P.
Bibcode: 2002astro.ph..7244S
Altcode:
The observations of magnetic field variations as a signature of flaring
activity is one of the main goal in solar physics. Some efforts in
the past give apparently no unambiguous observations of changes. We
observed that the scaling laws of the current helicity inside a given
flaring active region change clearly and abruptly in correspondence with
the eruption of big flares at the top of that active region. Comparison
with numerical simulations of MHD equations, indicates that the change
of scaling behavior in the current helicity, seems to be associated to a
topological reorganization of the footpoint of the magnetic field loop,
namely to dissipation of small scales structures in turbulence. It is
evident that the possibility of forecasting in real time high energy
flares, even if partially, has a wide practical interest to prevent
the effects of big flares on Earth and its environment.
Title: Rapid Changes in the Longitudinal Magnetic Field Related to
the 2001 April 2 X20 Flare
Authors: Spirock, Thomas J.; Yurchyshyn, Vasyl B.; Wang, Haimin
Bibcode: 2002ApJ...572.1072S
Altcode:
Big Bear Solar Observatory observed the X20 flare that occurred at
approximately 21:50 UT on 2001 April 2 with its standard complement of
instruments. In this paper, we discuss the evolution of high-resolution
and high-cadence longitudinal magnetograph observations in the region
of the flare. The data reveal that there was a significant increase
in the magnetic field on the limbward side of the neutral line of the
active region at the location of the flare, while the magnetic field
on the side of the neutral line closer to the disk center remained
constant. We discuss possible rearrangements in the active region's
magnetic field that could lead to the observed changes.
Title: Limb Prominence Eruption on 11 August 2000 as Seen From Ground-
and Space-Based Observations
Authors: Shakhovskaya, A. N.; Abramenko, V. I.; Yurchyshyn, V. B.
Bibcode: 2002SoPh..207..369S
Altcode:
We report on a prominence eruption as seen in Hα with the Crimean
Lyot coronagraph, the global Hα network, and coronal images from
the LASCO C2 instrument on board SOHO. We observed an Hα eruption
at the northwest solar limb between 07:38:50 UT and 07:58:29 UT on
11 August 2000. The eruption originated in a quiet-Sun region and
was not associated with an Hα filament. No flare was associated with
the eruption, which may indicate that, in this case, a flux rope was
formed prior to the eruption of the magnetic field. The Hα images
and an Hα Dopplergram show a helical structure present in the erupted
magnetic field. We suggest that the driving mechanism of the eruption
may be magnetic flux emergence or magnetic flux injection. The limb
Hα observations provide missing data on CME speed and acceleration
in the lower corona. Our data show that the prominence accelerated
impulsively at 5.5 km s−2 and reached a speed slightly
greater than 800 km s−1 in a narrow region (h<0.14
R⊙) above the solar surface. The observations presented
here also imply that, based only on a CME's speed and acceleration,
it cannot be determined whether a CME is the result of a flare or an
eruptive prominence.
Title: Scaling Behavior of Structure Functions of the Longitudinal
Magnetic Field in Active Regions on the Sun
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
Bibcode: 2002AAS...200.0309A
Altcode: 2002BAAS...34..643A
In the framework of a refined Kolmogorov's hypotheses, the scaling
behavior of the BZ--component of the photospheric magnetic
field is analyzed and compared with flaring activity in solar active
regions. We used SOHO/MDI, Huairou (China) and Big Bear measurements
of the Bz-component in the photosphere for nine active
regions. We show that there is no universal behavior in the scaling
of the Bz-structure functions for different active
regions. Scaling for a given active region is caused by intermittency
in the field, ǎrepsilon(B)(ěc x), of magnetic energy
dissipation. When intermittency is weak, the Bz-field
behaves as a passive scalar in the turbulent flow and the energy
dissipation is largely determined by the dissipation of kinetic energy
in active regions with low flare productivity. However, when the field
ǎrepsilon(B)(ěc x) is highly intermittent, the structure
functions behave as transverse structure functions of a fully developed
turbulent vector field and the scaling of the energy dissipation is
mostly determined by the dissipation of the magnetic energy (active
regions with strong flaring productivity). We found that the spectrum
of dissipation of the Bz component is strongly related
to the level of flare productivity of a solar active region. When
the flare productivity is high, the corresponding spectrum is less
steep. We also found that during the evolution of an NOAA AR 9393 the
Bz dissipation spectrum becomes less steep as the active
region's flare activity increases. We suggest that the relation between
scaling exponents and flare productivity of an active region enables
us to monitor and forecast flare activity using only measurements of
the Bz component of the photospheric magnetic field. This
work was supported in part by the Ukrainian Ministry of Science and
Education, NSF-ATM (0076602 and 0086999) and NASA (9682 and 9738)
grants. SOHO is a project of international cooperation between ESA
and NASA.
Title: Orientation of Magnetic Fields in Erupted Solar Filaments
and Geoeffectiveness of Coronal Mass Ejections
Authors: Yurchyshyn, V. B.
Bibcode: 2002AAS...200.3606Y
Altcode: 2002BAAS...34..693Y
Coronal mass ejections (CMEs) are often associated with erupted magnetic
fields or disappeared chromospheric filaments. The majority of CMEs
headed directly toward the earth (halo CMEs) are observed at 1AU as
magnetic clouds (MC). The 3D structure of a MC can be represented by a
force-free flux rope. When CMEs reach the earth, they may or may not
cause magnetic storms. The geoeffectiveness of CMEs depends on the
orientation of the magnetic field in them. In our previous study we
showed that the direction of the axial field in a MC and its helicity
are consistent with the direction of the axial field and helicity of
the erupted filaments. We also suggested that geoeffectiveness of
a CME can be forecasted by using daily Big Bear Solar Observatory
full disk Hα and SOHO EIT 195Å images and SOHO/MDI magnetograms,
as well. Here we continue to study the orientation of magnetic
fields in CMEs and its correlation with the occurrence of geomagnetic
storms. The study includes 11 earth directed CMEs for which photospheric
sources were reliably defined. Our results further demonstrate that
the geoeffectiveness of a CME can be predicted by considering the
orientation of the CME's magnetic fields. This work was supported in
part by ATM-0076602, ATM-9903515 and NASA (NAG5-9682) grants. SOHO is
a project of international cooperation between ESA and NASA.
Title: Flare Activity and Magnetic Helicity Injection By Photospheric
Horizontal Motions
Authors: Moon, Y. -J.; Chae, J.; Choe, G.; Wang, H.; Park, Y. D.;
Yun, H. S.; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2002AAS...200.2002M
Altcode: 2002BAAS...34..673M
We present observational evidence that the occurrence of homologous
flares in an active region is physically related to the injection
of magnetic helicity by horizontal photospheric motions. We have
analyzed a set of 1 minute cadence magnetograms of NOAA AR 8100 taken
over a period of 6.5 hours by Michelson Doppler Imager (MDI) on board
Solar and Heliospheric Observatory (SOHO). During this observing time
span, seven homologous flares took place in the active region. We have
computed the magnetic helicity injection rate into the solar atmosphere
by photospheric shearing motions, and found that a significant amount
of magnetic helicity was injected during the observing period. In a
strong M4.1 flare, the magnetic helicity injection rate impulsively
increased and peaked at the same time as the X-ray flux did. The flare
X-ray flux integrated over the X-ray emission time strongly correlates
with the magnetic helicity injected during the flaring interval. The
integrated X-ray flux is found to be a logarithmically increasing
function of the injected magnetic helicity. Our results suggest that
injection of helicity and abrupt increase of helicity magnitude play
a significant role in flare triggering. This work has been supported
by NASA grants NAG5-10894 and NAG5-7837, by MURI grant of AFOSR, by
the US-Korea Cooperative Science Program (NSF INT-98-16267), by NRL
M10104000059-01J000002500 of the Korean government, and by the BK 21
project of the Korean government.
Title: Core and Large-Scale Structure of the 2000 November 24 X-Class
Flare and Coronal Mass Ejection
Authors: Wang, Haimin; Gallagher, Peter; Yurchyshyn, Vasyl; Yang,
Guo; Goode, Philip R.
Bibcode: 2002ApJ...569.1026W
Altcode:
In this paper, we present three important aspects of the X1.8 flare
and the associated coronal mass ejection (CME) that occurred on 2000
November 24: (1) The source of the flare is clearly associated with
a magnetic channel structure, as was noted in a study by Zirin &
Wang , which is due to a combination of flux emergence inside the
leading edge of the penumbra of the major leading sunspot and proper
motion of the sunspot group. The channel structure provides evidence for
twisted flux ropes that can erupt, forming the core of a CME, and may
be a common property of several superactive regions that have produced
multiple X-class flares in the past. (2) There are actually three flare
ribbons visible. The first can be seen moving away from the flare site,
while the second and third make up a stationary ribbon near the leader
spot. The moving ribbons could be due to a shock associated with the
erupting flux rope or due to the interaction of erupting rope and the
surrounding magnetic fields. In either case, the ribbon motion does
not fit the classical Kopp-Pneuman model, in which the separation
of ribbons is due to magnetic reconnection at successively higher
and higher coronal altitudes. (3) From the coronal dimming observed
with the EUV Imaging Telescope (EIT), the CME involved a much larger
region than the initial X-class flare. By comparing high-resolution
full-disk Hα and EIT observations, we found that a remote dimming
area is cospatial with the enhanced Hα emission. This result is
consistent with the recent model of Yokoyama & Shibata that some
dimming areas near footpoints may be due to chromospheric evaporation.
Title: Space Weather: The Scientific Forecast
Authors: Wang, H.; Gallagher, P. T.; Yurchyshyn, V.
Bibcode: 2002stma.conf..375W
Altcode:
No abstract at ADS
Title: How directions and helicity of the magnetic field in erupted
solar filaments define geoeffectiveness of coronal mass ejections?
Authors: Yurchyshyn, V.
Bibcode: 2002cosp...34E1426Y
Altcode: 2002cosp.meetE1426Y
Coronal mass ejections (CMEs) are often associated with erupted magnetic
fields or disappeared chromospheric filaments. The majority of CMEs
headed directly toward the earth (halo CMEs) are observed at 1AU as
magnetic clouds (MC). The 3D structure of a MC can be represented by a
force-free flux rope. When CMEs reach the earth, they may or may not
cause magnetic storms. The geoeffectiveness of CMEs depends on the
orientation of the magnetic field in them. In our previous study we
showed that the direction of the axial field in a MC and its helicity
are consistent with the direction of the axial field and helicity of
the erupted filaments. We also suggested that geoeffectiveness of
a CME can be forecasted by using daily Big Bear Solar Observatory
full disk H and SOHO EIT 195Å images and SOHO/MDI magnetograms,
as well. Here we continue to study the orientation of magnetic
fields in CMEs and its correlation with the occurrence of geomagnetic
storms. The study includes earth directed CMEs for which photospheric
sources were reliably defined. Our results further demonstrate that
the geoeffectiveness of a CME can be predicted by considering the
orientation of the CME's magnetic fields. This work was supported in
part by ATM-0076602, ATM-9903515 and NASA (NAG5-9682) grants. SOHO is
a project of international cooperation between ESA and NASA.
Title: Analysis of Cancellations of Photospheric Current Helicity
and Flares Forecasting
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
Bibcode: 2002EGSGA..27.3215S
Altcode:
The observations of magnetic field variations as a signature of flaring
activity is one of the main goal in solar physics. Some efforts in
the past give apparently no unambigu- ous observations of changes. We
observed that the scaling laws of the current helicity inside a given
flaring active region change clearly and abruptly before the eruption
of big flares at the top of that active region. Comparison with
numerical simulations of MHD equations, indicates that the change of
scaling behavior in the current helicity, seems to be associated to a
topological reorganization of the footpoint of the magnetic field loop,
namely to dissipation of small scales structures in turbulence. It is
evident that the possibility of forecasting in real time high energy
flares, even if partially, has a wide practical interest to prevent
the effects of big flares on Earth and its environment.
Title: Orientation of the Magnetic Fields in Interplanetary Flux
Ropes and Solar Filaments
Authors: Yurchyshyn, Vasyl B.; Wang, Haimin; Goode, Philip R.; Deng,
Yuanyong
Bibcode: 2001ApJ...563..381Y
Altcode:
Coronal mass ejections (CMEs) are often associated with erupting
magnetic structures or disappearing filaments. The majority of CMEs
headed directly toward the Earth are observed at 1 AU as magnetic
clouds-the region in the solar wind where the magnetic field strength
is higher than average and there is a smooth rotation of the magnetic
field vectors. The three-dimensional structure of magnetic clouds can
be represented by a force-free flux rope. When CMEs reach the Earth,
they may or may not cause magnetic storms, alter Earth's magnetic field,
or produce the phenomena known as auroras. The geoeffectiveness of a
solar CME depends on the orientation of the magnetic field in it. Two
M-class solar flares erupted on 2000 February 17. The second flare
occurred near a small active region, NOAA Active Region 8872. This
eruption was accompanied by a halo CME. However, the February 17 CME did
not trigger any magnetic activity when it arrived at the Earth. Another
powerful flare, on 2000 July 14, was also associated with a halo CME,
which caused the strongest geomagnetic activity of solar cycle 23. Using
ACE measurements of the interplanetary magnetic fields, we study the
orientation of the magnetic flux ropes in both sets of magnetic clouds
and compare them with the orientation of the solar magnetic fields
and disappearing filaments. We find that the direction of the axial
field and helicity of the flux ropes are consistent with those of
the erupted filaments. Thus, the geoeffectiveness of a CME is defined
by the orientation and structure of the erupted filament and by its
magnetic helicity as well. We also suggest that the geoeffectiveness
of a CME can be forecasted using daily full-disk Hα and Yohkoh images
and MDI magnetograms as well.
Title: Photospheric Plasma Flows Around a Solar Spot
Authors: Yurchyshyn, Vasyl B.; Wang, Haimin
Bibcode: 2001SoPh..203..233Y
Altcode:
We study photospheric plasma flows in an active region NOAA 8375, by
using uninterrupted high-resolution SOHO/MDI observations (137 intensity
images, 44 hours of observations). The active region consists of a
stable large spot and many small spots and pores. Analyzing horizontal
flow maps, obtained with local correlation tracking technique, we
found a system of stable persistent plasma flows existing in the
active region. The flows start on either side of the sunspot and
extend over 100'' to the east. Our measurements show that the speed
of small sunspots and pores, averaged over 44 hours, was about 100 m
s−1, which corresponds to root-mean-square longitudinal
drifts of sunspots of 0.67°-0.76° day−1. We conclude
that these large-scale flows are due to faster proper motion of the
large sunspot relative to the ambient photospheric plasma. We suggest
that the flows may be a good carrier to transport magnetic flux from
eroding sunspots into the outer part of an active region.
Title: Inter-Active Region Connection of Sympathetic Flaring on 2000
February 17
Authors: Wang, Haimin; Chae, Jongchul; Yurchyshyn, Vasyl; Yang, Guo;
Steinegger, Michael; Goode, Philip
Bibcode: 2001ApJ...559.1171W
Altcode:
We have analyzed high-resolution Hα full disk data from Big
Bear Solar Observatory (BBSO); magnetograph and EUV data from the
Michelson Doppler Imager, Large Angle and Spectrometric Coronagraph,
and Extreme Ultraviolet Imaging Telescope on board SOHO; and Yohkoh
soft X-ray data of 2000 February 17. Two sympathetic M-class solar
flares erupted in succession in NOAA Active Region 8869 and 8872,
respectively. The eruption from AR 8872 was followed by an extremely
symmetric halo coronal mass ejection (CME). We demonstrate the loop
activation, which appears to be the consequence of the first flare in
AR 8869 and the cause of the second flare in AR 8872. The activation
started in the form of a surge just after a filament eruption and its
associated flare in AR 8869. The surge quickly turned into a set of
disturbances that propagated at a speed of about 80 km s-1
toward the other active region AR 8872. The second flare followed in
less than an hour after the arrival of the disturbances at AR 8872. The
moving disturbances appeared in absorption in both Hα and EUV 195
Å images. The disturbances may represent mass transfer, which had
a significant velocity component perpendicular to the field lines
and, hence, caused the transport of field lines. In this case, the
disturbances may be considered to be a special kind of surge, which we
may call a ``sweeping closed-loop surge.'' We also demonstrated large
area dimmings associated with the CME in three active regions. The
dimming started from AR 8869 and AR 8872 and was extended to AR 8870,
which was on the opposite side of the solar equator. We believe that
both the activation of inter-active region loops and the large-scale
dimming are the signatures of large-scale restructuring associated
with the CME.
Title: Parameters of the Turbulent Magnetic Field in the Solar
Photosphere: Power Spectrum of the Line-of-Sight Field
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Goode, P. R.
Bibcode: 2001ARep...45..824A
Altcode:
Ground-based (Big Bear Solar Observatory) and extra-atmospheric
(SOHO/MDI) measurements of the photospheric line-of-sight magnetic field
of one active and two quiet regions are used to calculate power spectra
of the field, taking into account the characteristic function for the
diffraction limit of the telescope resolution. At high frequencies, the
physically meaningful linear interval in the spectrum extends to a wave
number of k=4.6 Mm-1 (spatial scale l=1.4 Mm) for the quiet regions and
k=3.35 Mm-1 (l=1.9 Mm) for the active region. A high-frequency spectral
break at k≥3 Mm-1 is associated with the characteristic telescope
function; the position of the break and the spectral slope beyond the
break do not reflect the turbulent state of the field. As the field
recording improves, the break shifts toward higher frequencies. The
spectral indices in the physically meaningful linear interval are
substantially different for the active and quiet regions: in the active
region (NOAA 8375), the spectrum behaves as E(k)≈k -1.7 (very close
to the Kolmogorov index, -5/3) in the interval 0.78≤k≤3.35 Mm-1,
while in the quiet regions E(k)≈k -1.3 for 0.77≤k≤4.57 Mm-1. This
difference can be explained by the additional effect of a small-scale
turbulent dynamo in the unperturbed photosphere. In this case, this
mechanism can generate at least 6% of the magnetic energy of the
photospheric line-of-sight field in quiet regions.
Title: Magnetic Flux Cancellation Observed in the Sunspot Moat
Authors: Yurchyshyn, Vasyl B.; Wang, Haimin
Bibcode: 2001SoPh..202..309Y
Altcode:
In this paper we study the evolution of magnetic fields of a 1F/2.4C
solar flare and following magnetic flux cancellation. The data are Big
Bear Solar Observatory and SOHO/MDI observations of active region NOAA
8375. The active region produced a multitude of subflares, many of them
being clustered along the moat boundary in the area with mixed polarity
magnetic fields. The study indicates a possible connection between the
flare and the flux cancellation. The cancellation rate, defined from
the data, was found to be 3×1019 Mx h−1. We
observed strong upward directed plasma flows at the cancellation
site. Suggesting that the cancellation is a result of reconnection
process, we also found a reconnection rate of 0.5 km s−1,
which is a significant fraction of Alfvén speed. The reconnection
rate indicates a regime of fast photospheric reconnection happening
during the cancellation.
Title: Magnetic Power Spectra Derived from Ground and Space
Measurements of the Solar Magnetic Fields
Authors: Abramenko, V.; Yurchyshyn, V.; Wang, H.; Goode, P. R.
Bibcode: 2001SoPh..201..225A
Altcode:
We study magnetic power spectra of active and quiet regions by using
Big Bear Solar Observatory and SOHO/MDI measurements of longitudinal
magnetic fields. The MDI power spectra were corrected with Gaussian
Modulation Transfer Function. We obtained reliable magnetic power
spectra in the high wave numbers range, up to k=4.6 Mm−1,
which corresponds to a spatial scale l=1.4 Mm. We find that the
occurrence of the spectral discontinuity at high wave numbers,
k≥3 Mm−1, largely depends on the spatial resolution
of the data and it appears at progressively higher wave numbers as
the resolution of the data improves. The spectral discontinuity in
the raw spectra is located at wave numbers about 3 times smaller
than wave numbers, corresponding to the resolution of the data, and
about 1.5-2.0 times smaller in the case of the noise- and-resolution
corrected spectra. The magnetic power spectra for active and quiet
regions are different: active-region power spectra are described as
∼k−1.7, while in a quiet region the spectrum behaves
as ∼k−1.3. We suggest that the difference can be
due to small-scale dynamo action in the quiet-Sun photosphere. Our
estimations show that the dynamo can generate more than 6% of the
observed magnetic power.
Title: Earthshine observations of the Earth's reflectance
Authors: Goode, P. R.; Qiu, J.; Yurchyshyn, V.; Hickey, J.; Chu,
M. -C.; Kolbe, E.; Brown, C. T.; Koonin, S. E.
Bibcode: 2001GeoRL..28.1671G
Altcode:
Regular photometric observations of the moon's “ashen light”
(earthshine) from the Big Bear Solar Observatory (BBSO) since December
1998 have quantified the earth's optical reflectance. We find large
(∼5%) daily variations in the reflectance due to large-scale weather
changes on the other side of the globe. Separately, we find comparable
hourly variations during the course of many nights as the earth’s
rotation changes that portion of the earth in view. Our data imply
an average terrestrial albedo of 0.297±0.005, which agrees with
that from simulations based upon both changing snow and ice cover and
satellite-derived cloud cover (0.296±0.002). However, we find seasonal
variations roughly twice those of the simulation, with the earth being
brightest in the spring. Our results suggest that long-term earthshine
observations are a useful monitor of the earth's albedo. Comparison
with more limited earthshine observations during 1994-1995 show a
marginally higher albedo then.
Title: Magnetic Power Spectra Derived From Photospheric Magnetic
Fields
Authors: Abramenko, V. I.; Yurchyshyn, V.; Wang, H.; Goode, P. R.
Bibcode: 2001AGUSM..SP41C04A
Altcode:
We study magnetic power spectra of active and quiet regions by using
Big Bear Solar Observatory and SOHO/MDI measurements of longitudinal
magnetic fields. The MDI power spectra were corrected with Gaussian
Modulation Transfer Function. We obtained reliable magnetic power
spectra in the high wave numbers range, up to k=4.6 Mm-1,
which corresponds to a spatial scale l=1.4 Mm. We find that the
occurrence of the spectral discontinuity at high wavenumbers, k >=
3 Mm-1, largely depends on the spatial resolution of the data
and it appears at progressively higher wave numbers as the resolution
of the data improves. The spectral discontinuity in the raw spectra
is located at wave numbers about 3 times smaller than wavenumbers,
corresponding to the resolution of the data, and about 1.5 -- 2.0 times
smaller in the case of the noise-and-resolution corrected spectra. The
magnetic power spectra for active and quiet regions are different:
active region power spectra are described as ~ k-1.7,
while in a quiet region the spectrum behaves as ~ k-1.3. We
suggest, that the difference can be due to small-scale dynamo action
in the quiet sun photosphere. Our estimations show that the dynamo
can generate more than 6% of the observed magnetic power.
Title: Inter-Active Region Connection of Sympathetic Flaring on 2000
February 17
Authors: Wang, H.; Chae, J.; Yurchyshyn, V.; Yang, G.; Steinegger,
M.; Goode, P. R.
Bibcode: 2001AGUSM..SP42A03W
Altcode:
We have analyzed high resolution Hα full disk data from Big Bear
Solar Observatory (BBSO), magnetograph and EUV data from MDI, LASCO
and EIT on board SOHO, and Yohkoh soft X-ray data of February 17,
2000. Two sympathetic M-class solar flares erupted in succession
in NOAA 8869 and 8872, respectively. The eruption from AR 8872 was
followed by an extremely symmetric halo CME. We demonstrate a new
kind of loop activation, which appears to be the consequence of
the first flare in AR 8869 and the cause of the second flare in
AR 8872. The activation started in the form of a surge just after
a filament eruption and its associated flare in AR 8869. The surge
quickly turned into a set of disturbances that propagated at a speed of
about 80 km/s toward the other active region AR 8872. The second flare
followed in less than an hour after the arrival of the disturbances
at AR 8872. The moving disturbances appeared in absorption in both
Hα and EUV 195A images. The disturbances may represent mass transfer
which had a significant velocity component perpendicular to the field
lines and, hence, caused the transport of field lines. In this case,
the disturbances may be considered to be a special kind of surge,
which we may call a "sweeping closed-loop surge". Alternatively, the
disturbances may represent fronts of compressive magnetohydrodynamic
waves that were driven by the surge. We also demonstrated large area
dimmings associated with the CME in three active regions. The dimming
started from ARs 8869 and 8872, and was extended to AR 8870 which was
on the opposite side of the solar equator. We believe that both the
activation of inter-active region loops and the large scale dimming are
the signatures of large scale re-structuring associated with the CME.
Title: Orinetation of the Magnetic Fields in Interplanetary Flux
Ropes and Solar Filaments
Authors: Yurchyshyn, V.; Wang, H.; Goode, P. R.; Deng, Y.
Bibcode: 2001AGUSM..SH61A02Y
Altcode:
Coronal mass ejections are often associated with erupting magnetic
structures or disappearing filaments. Majority of CMEs headed directly
toward the earth are observed at 1AU as magnetic clouds --- region in
the solar wind where the magnetic field strength is higher than average
and smooth rotation of the magnetic field vectors. The 3D structure
of magnetic clouds can be represented by force-free flux rope. When a
CME reaches the earth, it may or may not cause magnetic storms, alter
Earth's magnetic field or produce the phenomena known as auroras. The
geoeffectiveness of a solar CME depends on the orientation of the
magnetic field in it. Two M-class solar flares erupted on February
17, 2000. The second flare occurred near a small active region NOAA
8872. The eruption was accompanied by a halo CME. However the February
17 CME did not trigger any magnetic activity at the time it arrived at
the earth. Another powerful flare on July 14, 2000 was also associated
with a halo CME, which caused strongest geomagnetic activity in the
solar cycle 23. Using ACE measurements of the interplanetary magnetic
fields we study the orientation of the magnetic flux ropes in both
magnetic clouds and compare it to the orientaion of solar magnetic
fields and disappearing filaments. We find that the direction of
the axial filed in the flux ropes and their helicity are consistent
with the direction of the axial field and helicity of the erupted
filaments. Thus, the geoeffectiveness of a CME is defined by the
orientation and structure of the erupted filament and by its magnetic
helicity as well. We also suggest that geoeffectiveness of a CME can
be forecasted using daily full disk Hα and Yohkoh images and MDI
magnetograms as well.
Title: On the Correlation Between the Orientation of Moving Magnetic
Features and the Large-Scale Twist of Sunspots
Authors: Yurchyshyn, V.; Wang, H.; Goode, P. R.
Bibcode: 2001AGUSM..SP41C03Y
Altcode:
We present new results on the nature of moving magnetic features
(MMFs) deduced from Big Bear Solar Observatory observations of the
longitudinal magnetic fields of two large solar spots. MMFs are small
magnetic bipoles that move outward, across the moat of an eroding
sunspot. We find that MMFs are not randomly oriented. To wit, in 21
out of 28 (75%) MMF pairs, the magnetic element having the polarity
of the sunspot was located farther from the sunspot. Furthermore,
there is a correlation between the orientation of the bipole and that
of the twist in a sunspot. For the two nearly round sunpots we studied,
we found that the bipoles were rotated counterclockwise in the case of a
clockwise twisted sunspot and clockwise for a spot with counterclockwise
twist. We also found a correlation between the orientation of MMF
bipole and the amount of twist in the spot. The MMF bipoles around
the highly twisted sunspot are oriented nearly tangential to the edge
of the sunspot; while in the slightly twisted sunspot the bipoles are
oriented nearly radially, so that they point back to the spot.
Title: On the Correlation between the Orientation of Moving Magnetic
Features and the Large-Scale Twist of Sunspots
Authors: Yurchyshyn, Vasyl B.; Wang, Haimin; Goode, Philip R.
Bibcode: 2001ApJ...550..470Y
Altcode:
We present new results on the nature of moving magnetic features
(MMFs) deduced from Big Bear Solar Observatory observations of the
longitudinal magnetic fields of two large solar spots. MMFs are small
magnetic bipoles that move outward across the moat of an eroding
sunspot. We find that MMFs are not randomly oriented. To wit, in 21
out of 28 (75%) MMF pairs, the magnetic element having the polarity
of the sunspot was located farther from the sunspot. Furthermore,
there is a correlation between the orientation of the bipole and that
of the twist in a sunspot. For the two nearly round sunpots we studied,
we found that the bipoles were rotated counterclockwise in the case of a
clockwise twisted sunspot and clockwise for a spot with counterclockwise
twist. We also found a correlation between the orientation of MMF
bipole and the amount of twist in the spot. The MMF bipoles around
the highly twisted sunspot are oriented nearly tangential to the edge
of the sunspot, while in the slightly twisted sunspot the bipoles are
oriented nearly radially so that they point back to the spot.
Title: Magnetic Topology in 1998 November 5 Two-Ribbon Flare as
Inferred from Ground-based Observations and Linear Force-free Field
Modeling
Authors: Yurchyshyn, V. B.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko,
V. I.
Bibcode: 2000ApJ...540.1143Y
Altcode:
We analyzed the three-dimensional structure of the linear force-free
magnetic field. A longitudinal magnetogram of Active Region NOAA
8375 has been used as the photospheric boundary condition. The 1998
November 5 2B/M8.4 two-ribbon flare can be explained in the framework
of quadrupolar reconnection theory: the interaction of two closed
magnetic loops that have a small spatial angle. The energy derived from
soft X-ray telescope (SXT)/Yohkoh data (3-6×1030 ergs)
is 1 order of magnitude higher than the lower limit of flare energy
predicted by Melrose's model. The latter estimation was made using
the linear force-free extrapolation. It was suggested that, taking
into account the nonlinear character of the observed magnetic field,
we can increase the lower limit of the magnetic energy stored in the
studied magnetic configuration. The revealed magnetic configuration
allows us to understand the observed location and evolution of the flare
ribbons and the additional energy released during the gradual phase
of the flare, as well. Besides, reconnection of closed magnetic loops
can logically explain the connection between a two-ribbon flare and a
giant X-ray postflare arch, which usually is observed after the flare
onset. We emphasize that unlike the Kopp and Pneuman configuration,
the model discussed here does not necessarily require destabilization
and opening of the magnetic field.
Title: Flare-Related Changes of an Active Region Magnetic Field
Authors: Yurchyshyn, V. B.; Abramenko, V. I.; Carbone, V.
Bibcode: 2000ApJ...538..968Y
Altcode:
It was shown recently that current helicity, calculated
using the photospheric magnetic field vector measurements,
possesses a well-pronounced scaling behavior. The sign
singularity of two-dimensional structures of current helicity,
hc=Bz˙(∇XB)z, can be studied by
introducing a signed measure and by calculating the power-law exponent,
the cancellation exponent κ. The time variations of the cancellation
exponent seem to be related to flare activity of an active region
(AR). Periods of enhanced flaring are accompanied by a drop and
subsequent rise of the cancellation exponent. Here we focus on the
changes in the vortex structure of the photospheric magnetic field
during the transition of an active region from low flaring to enhanced
flaring state. We analyzed variations of the cancellation exponent,
helicity imbalance, and total electric current in four flaring active
regions and one quiet one. We show that the transition of an active
region from a low flaring state to an enhanced one is always accompanied
(in this study, the corresponding time interval is less than 2 hr)
by the 30%-45% decrease of the cancellation exponent. In two active
regions, a reliable 13%-22% decrease of the total electric current took
place, and in three active regions the helicity imbalance changed. This,
possibly, implies a reinforcement of the anticoriolis twist of the whole
magnetic configuration. For comparison, the decrease of κ in the quiet
active region does not exceed 10%. This can be interpreted as a real
preflare reorganization of the vortex structure of the photospheric
magnetic field: a combination of the exhausting of small-scale eddies
along with the reinforcement of the total anticoriolis twist of the
magnetic structure.
Title: Energy Release in an Impulsive Flare
Authors: Qiu, J.; Wang, H.; Yurchyshyn, V. B.; Goode, P. R.;
BBSO/NJIT Team
Bibcode: 2000SPD....31.0258Q
Altcode: 2000BAAS...32..821Q
We analyze the multi-spectral observations on an impulsive short-lived
flare event, and demonstrate that the flare consisted of several
flaring components with different evolution profiles, morphologies,
energy spectra, and magnetic configurations. These observations suggest
that the magnetic energy was released in this event in several ways. (1)
Two hard X-ray components were observed by Yohkoh HXT. One component was
brightened and reached its emission maximum more slowly than the other
component by > 15 seconds, and the spectrum of the slow component
was much softer than the fast component. The coordinated high resolution
ground-based observations from Big Bear Solar Observatory (BBSO) further
demonstrate that these two hard X-ray components were each co-aligned
with complicated Hα and magnetic field structures. Therefore, the two
hard X-ray components should come from different magnetic reconnection
processes at different locations. (2) Accompanying the flare, we find
both hot and cool mass ejections. The cool mass ejection was related
to the fast-varying non-thermal flare component, while the hot mass
ejection was related to the flare component which exhibited a strong
heating process. The hot mass ejection, or bright surge, also led
to a long-lasting (for at least a few hours) bright EUV loop. Such
observation offers a strong evidence that both pre-flare and post-flare
heating of the chromospheric material occurred at the root of the
bright surge. (3) We study the magnetic field configurations of the
flare components, and propose that both the non-thermal and thermal
components of the flare, together with the cool and hot surges, were
produced by the magnetic reconnection of the large scale over-lying
open field lines with the low-lying magnetic loops, while the gradual
and thermal flare components and bright surge were located in the area
of magnetic quadrupolar structures where moving magnetic features and
flux cancellation were observed. The observations suggest that the
proper motions in the region of the quadrupolar structure may enhance
electric current along the separatrix and neutral point, and produce
heating via current dissipation in the quadrupolar areas in the lower
atmosphere both before and after the fast reconnection occurred.
Title: Earthshine and the Earth's Reflectivity
Authors: Goode, P. R.; Hickey, J.; Qiu, J.; Yurchyshyn, V. B.; Koonin,
S. E.; Brown, T.; Kolbe, E.; Chu, M.
Bibcode: 2000SPD....3102121G
Altcode: 2000BAAS...32..833G
The earth's climate is driven by the net sunlight reaching
the earth, which depends on the solar irradiance and the earth's
reflectivity. Changes in the the solar irradiance have been well-studied
for twenty years, but the degree of variation in the earth's albedo
is not so clear. We have been measuring the earthshine from Big Bear
Solar Observatory (BBSO) since December 1998. Earthshine, or "ashen
light", is sunlight reaching the eye of a nighttime observer after
being successively reflected from the day side of the earth, and the
dark face of the moon. The ratio of reflected light from the dark
part of the moon to that from the bright part provides an absolutely
calibrated, large scale measure of the earth's albedo. We have solved
the long-standing problem of determining the scattering of sunlight
from the moon as a function of lunar phase. Earthshine measurements
of the earth's albedo are complementary to those from satellites. We
find the earth's albedo varies by 20% with season, and by as much at
5% from night to night. We put contemporaneous cloud cover data into
a scene model and calculate a good agreement with our observations,
but we also find some interesting differences. Using the scene model
and monthly averaged cloud cover data from ISCCP, we find between 1986
and 1990 (solar minimum to near solar maximum) that the change in the
net irradiance into the climate system is several times larger from
the varying albedo than from the varying solar irradiance. The two
changes are in phase.
Title: Magnetic Topology in November 5, 1998 Two-Ribbon Flare as
Inferred from Ground-Based Observations and Linear Force-Free Field
Modeling
Authors: Yurchyshyn, V. B.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko,
V. I.
Bibcode: 2000SPD....31.0153Y
Altcode: 2000BAAS...32..810Y
We analyzed the 3D structure of the linear force-free magnetic field in
an active region. A longitudinal magnetogram of AR NOAA 8375 has been
used as the photospheric boundary condition. The Nov 5, 1998 2B/M8.4
two-ribbon flare can be explained in the framework of quadrupolar
reconnection theory: the interaction of two closed magnetic loops which
have a small spatial angle. The energy derived from SXT/YOHKOH data (3
- 6 x 1030 ergs) is one order of magnitude higher than the
lower limit of flare energy predicted by Melrose's model. The latter
estimation was made using the linear force-free extrapolation. It is
suggested that by taking into account the non-linear character of the
observed magnetic field we can increase the lower limit of the magnetic
energy stored in the studied magnetic configuration. The revealed
magnetic configuration allows us to understand the observed location
and evolution of the flare ribbons and the additional energy released
during the gradual phase of the flare, as well. Also, the reconnection
of closed magnetic loops can logically explain the connection between
a two-ribbon flare and the giant X-ray post-flare arch which usually
is observed after flare onset. We emphasize that unlike the Kopp and
Pneuman configuration, the model discussed here doesn't necessarily
need destabilization and opening of the magnetic field. This work was
supported in part by NSF-ATM (97-14796) and NASA (NAG5-4919) grants.
Title: Magnetic Topology in November 5, 1998 Two-Ribbon Flare as
Inferred from Ground-Based Observations and Linear Force-Free Field
Modeling
Authors: Yurchyshyn, V.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko,
V. I.
Bibcode: 2000ESASP.463..463Y
Altcode: 2000sctc.proc..463Y
No abstract at ADS
Title: Magnetic Power Spectra in the Solar Photosphere derived from
Ground and Space based Observations
Authors: Abramenko, V.; Yurchyshyn, V. B.
Bibcode: 2000ESASP.463..273A
Altcode: 2000sctc.proc..273A
No abstract at ADS
Title: On the Correlation between the Orientation of Moving Magnetic
Features and the Large-Scale Twist of Sunpots
Authors: Yurchyshyn, V.; Wang, Haimin; Goode, Philip R.
Bibcode: 2000ESASP.463..459Y
Altcode: 2000sctc.proc..459Y
No abstract at ADS
Title: Flare Associated Changes in the Helicity of the Solar
Magnetic Field
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Carbone, V.
Bibcode: 1999ESASP.448..679A
Altcode: 1999mfsp.conf..679A; 1999ESPM....9..679A
No abstract at ADS
Title: The Changes of the Current Helicity Scaling Prior to a Strong
Solar Flare
Authors: Yurchyshyn, V. B.; Abramenko, V. I.; Carbone, V.
Bibcode: 1999AAS...194.5404Y
Altcode: 1999BAAS...31..909Y
Recently it has been shown (Abramenko et al., Sol. Phys. 178) the
current helicity calculated by the photospheric magnetic field vector
possesses a well pronounced scaling behavior. The sign-singularity of
the 2D structures of current helicity can be studied by introducing the
signed measure and by calculating some power-law exponent: cancellation
exponent kappa . The time variations of the cancellation exponent
seem to be related to flare activity of an active region: the periods
of enhanced flaring are accompanied by a drop and subsequent rise of
the cancellation exponent (Abramenko et al., A&A. 334). Here we
continue to study the flare-related changes of cancellation exponent
paying special attention to the preflare situation. We have found
that the significant decrease of kappa begins 1-3 hours prior to
a strong flare. The reduce of the kappa means the changes in the
transverse magnetic field structure. The preflare energy release
produced by small-scale currents dissipation seems to supply observed
preflare energetic phenomena such as preflare flocculi brightening and
enhanced X-ray and microwave emission. So we are able to conclude that
small-scale energy release in the transverse photospheric magnetic
field take place prior to a strong flare. As soon as the evaluation
of kappa needs only the calibrated vector magnetogram and some minutes
for calculations the preflare drop of the cancellation exponent could
be used for the short-time prediction of strong flares.
Title: Evidence of preflare small-scale energy release on the basis
of the magnetic field fractal analysis.
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Carbone, V.
Bibcode: 1999joso.proc..188A
Altcode:
The preflare changes in the complexity of the photospheric magnetic
fields were studied. The two-dimensional structures of the current
helicity of magnetic field were analyzed using the method of fractal
analysis. It was shown that several hours prior to a strong flare the
decreasing of the cancellation exponent of current helicity begins. This
result assumes the preflare dissipation of small-scale photospheric
electric currents and should be used for the short-time prediction of
strong flares.
Title: Magnetic fields and electric current in the filament of active
region NOAA 7597, in connection with two-ribbon flare.
Authors: Yurchyshyn, V. B.
Bibcode: 1999joso.proc..107Y
Altcode:
By comparing the orientation of the photospheric transverse magnetic
field with that of chromospheric fibrils the author shows that they
significantly differ. It seems that the active region filament matches
to the inversion polarity configuration.