Author name code: balasubramaniam
ADS astronomy entries on 2022-09-14
author:"Balasubramaniam, K."
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Title: Complex Structure of the Eastern Lobe of the Pictor A Radio
Galaxy: Spectral Analysis and X-Ray/Radio Correlations
Authors: Thimmappa, R.; Stawarz, Ł.; Pajdosz-Śmierciak, U.;
Balasubramaniam, K.; Marchenko, V.
Bibcode: 2021ApJ...921...44T
Altcode: 2021arXiv210311928T
Here we present detailed analysis of the distinct X-ray emission
features present within the eastern radio lobe of the Pictor A galaxy,
around the jet termination region, utilizing the data obtained from
the Chandra X-ray Observatory. Various emission features have been
selected for the study based on their enhanced X-ray surface brightness,
including five sources that appear pointlike, as well as three extended
regions, one characterized by a filamentary morphology. For those, we
perform a basic spectral analysis within the 0.5-7 keV range. We also
investigate various correlations between the X-ray emission features
and the nonthermal radio emission, utilizing the high-resolution radio
maps from the Very Large Array at gigahertz frequencies. The main
novel findings following from our analysis concern the newly recognized
bright X-ray filament located upstream of the jet termination region,
extending for at least 30 kpc (projected), and inclined with respect
to the jet axis. For this feature, we observe a clear anticorrelation
between the X-ray surface brightness and the polarized radio intensity,
as well as a decrease in the radio rotation measure with respect to the
surroundings. We speculate on the nature of the filament, in particular
addressing a possibility that it is related to the presence of a hot
X-ray-emitting thermal gas, only partly mixed with the nonthermal
radio/X-ray-emitting electrons within the lobe, combined with the
reversals in the lobe's net magnetic field.
Title: X-Ray Emission of the γ-ray-loud Young Radio Galaxy NGC 3894
Authors: Balasubramaniam, K.; Stawarz, Ł.; Cheung, C. C.; Sobolewska,
M.; Marchenko, V.; Thimmappa, R.; Król, D. Ł.; Migliori, G.;
Siemiginowska, A.
Bibcode: 2021ApJ...922...84B
Altcode: 2021arXiv210613193B
The radio source 1146+596 is hosted by the elliptical/S0 galaxy NGC
3894, with a low-luminosity active nucleus. The radio structure
is compact, suggesting a very young age for the jets in the
system. Recently, the source has been confirmed as a high-energy
(HE; >0.1 GeV) γ-ray emitter in the most recent accumulation of
Fermi Large Area Telescope data. Here we report on the analysis of
the archival Chandra X-ray Observatory data for the central part of
the galaxy, consisting of a single 40 ks long exposure. We have found
that the core spectrum is best fitted by a combination of an ionized
thermal plasma with a temperature of ≃0.8 keV, and a moderately
absorbed power-law component (photon index Γ = 1.4 ± 0.4, hydrogen
column density N H/1022 cm-2 = 2.4
± 0.7). We have also detected the iron Kα line at 6.5 ± 0.1 keV,
with a large equivalent width of ${1.0}_{-0.5}^{+0.9}$ keV. Based on
the simulations of Chandra's point-spread function, we have concluded
that while the soft thermal component is extended on the scale of the
galaxy host, the hard X-ray emission within the narrow photon energy
range 6.0-7.0 keV originates within the unresolved core (effectively
the central kiloparsec radius). The line is therefore indicative of
the X-ray reflection from a cold neutral gas in the central regions of
NGC 3894. We discuss the implications of our findings in the context
of the X-ray Baldwin effect. NGC 3894 is the first young radio galaxy
detected in HE γ-rays with the iron Kα line.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: Chandra View of the LINER-type Nucleus in the Radio-loud
Galaxy CGCG 292-057: Ionized Iron Line and Jet-ISM Interactions
Authors: Balasubramaniam, K.; Stawarz, L.; Marchenko, V.; Sobolewska,
M.; Cheung, C. C.; Siemiginowska, A.; Thimmappa, R.; Kosmaczewski, E.
Bibcode: 2020ApJ...905..148B
Altcode: 2020arXiv200603717B
We present an analysis of the new, deep (94 ksec) Chandra ACIS-S
observation of radio-loud active galaxy CGCG 292-057, characterized
by a LINER-type nucleus and a complex radio structure that indicates
intermittent jet activity. On the scale of the host galaxy bulge, we
detected excess X-ray emission with a spectrum best fit by a thermal
plasma model with a temperature of ∼0.8 keV. We argue that this
excess emission results from compression and heating of the hot diffuse
fraction of the interstellar medium displaced by the expanding inner,
∼20 kpc-scale lobes observed in this restarted radio galaxy. The
nuclear X-ray spectrum of the target clearly displays an ionized iron
line at ∼6.7 keV, and is best fitted with a phenomenological model
consisting of a power-law (photon index ≃ 1.8) continuum absorbed by a
relatively large amount of cold matter (hydrogen column density ≃0.7
× 1023 cm-2), and partly scattered (fraction
∼3%) by ionized gas, giving rise to a soft excess component and Kα
line from iron ions. We demonstrate that the observed X-ray spectrum,
particularly the equivalent width of Fe XXV Kα (of order 0.3 keV)
can in principle, be explained in a scenario involving a Compton-thin
gas located at the scale of the broad-lined region in this source and
photoionized by nuclear illumination. We compare the general spectral
properties of the CGCG 292-057 nucleus, with those of other nearby
LINERs studied in X-rays.
Title: Chandra Imaging of the Western Hotspot in the Radio Galaxy
Pictor A: Image Deconvolution and Variability Analysis
Authors: Thimmappa, R.; Stawarz, Ł.; Marchenko, V.; Balasubramaniam,
K.; Cheung, C. C.; Siemiginowska, A.
Bibcode: 2020ApJ...903..109T
Altcode: 2020arXiv200510350T
Here we present an analysis of the X-ray morphology and flux
variability of the particularly bright and extended western hotspot
in the nearest powerful (FR II-type) radio galaxy, Pictor A, based
on data obtained with the Chandra X-ray Observatory. The hotspot
marks the position where the relativistic jet, which originates in
the active nucleus of the system, interacts with the intergalactic
medium, at hundreds-of-kiloparsec distances from the host galaxy,
forming a termination shock that converts jet bulk kinetic energy to
internal energy of the plasma. The hotspot is bright in X-rays due to
the synchrotron emission of electrons accelerated to ultrarelativistic
energies at the shock front. In our analysis, we make use of several
Chandra observations targeting the hotspot over the last decades with
various exposures and off-axis angles. For each pointing, we study in
detail the point-spread function, which allows us to perform the image
deconvolution, and to resolve the hotspot structure. In particular,
the brightest segment of the X-ray hotspot is observed to be extended
in the direction perpendicular to the jet, forming a thin, ∼3 kpc
long, feature that we identify with the front of the reverse shock. The
position of this feature agrees well with the position of the optical
intensity peak of the hotspot, but is clearly offset from the position
of the radio intensity peak, located ∼1 kpc further downstream. In
addition, we measure the net count rate on the deconvolved images,
finding a gradual flux decrease by about 30% over the 15 yr timescale
of the monitoring.
Title: Chandra view on the active nucleus of CGCG 292-057: Jet-ISM
interactions
Authors: Balasubramaniam, K.; Stawarz, Ł.; Marchenko, V.;
Thimmappa, R.; Sobolewska, M.; Siemiginowska, A.; Cheung, C. C.;
Kozieł-Wierzbowska, D.; Jamrozy, M.
Bibcode: 2020IAUS..342..222B
Altcode:
We present the analysis of the 93 ksec Chandra ACIS-S data for the
galaxy CGCG 292-057 (z = 0.054), with complex radio structure indicative
of the intermittent jet activity. In order to characterize precisely
the spectrum of the unresolved low-luminosity active nucleus in the
source, we performed detailed MARX/PSF simulations and studied the
radial profile of the source region surface brightness. In this way,
we have detected an additional X-ray component extending from a few
up to ∼10 kpc from the unresolved core, which could be associated
with the hot gaseous medium compressed and heated (up to 0.9 keV) by
the expanding inner lobes of the radio galaxy. We modeled the X-ray
spectrum of the unresolved nucleus assuming various emission models,
including an absorbed power-law, a power-law plus thermal emission
component, and a two-temperature thermal plasma. The best fit was
however obtained assuming a power-law emission scattered by a hot
ionized gas, giving rise to the 6.7 keV iron line.
Title: Preliminary analysis of the X-ray emission from the central
regions of the Pictor A
Authors: Thimmappa, R.; Stawarz, Ł.; Balasubramaniam, K.; Marchenko,
V.
Bibcode: 2020IAUS..342..224T
Altcode:
Here we present some preliminary results of our analysis of the combined
Chandra observations of the Pictor A radio galaxy. All the available
Chandra data for the target, consisting of multiple pointings spanning
over 15 years and amounting to the total exposure time of 464 ks,
have been included in the analysis. We studied in detail the PSFs of
the core region in the individual pointings, as well as the radial
profile of the X-ray surface brightness of the source in the combined
dataset, in order to discriminate between the radiative output of the
unresolved core and the host galaxy. Based on these, we have performed
spectral modeling of the active nucleus, constraining its variability.
Title: Signatures of the Disk-Jet Coupling in the Broad-line Radio
Quasar 4C+74.26
Authors: Bhatta, G.; Stawarz, Ł.; Markowitz, A.; Balasubramaniam,
K.; Zola, S.; Zdziarski, A. A.; Jamrozy, M.; Ostrowski, M.; Kuzmicz,
A.; Ogłoza, W.; Dróżdż, M.; Siwak, M.; Kozieł-Wierzbowska, D.;
Debski, B.; Kundera, T.; Stachowski, G.; Machalski, J.; Paliya, V. S.;
Caton, D. B.
Bibcode: 2018ApJ...866..132B
Altcode: 2018arXiv180506957B
We explore the disk-jet connection in the broad-line radio quasar
4C+74.26, utilizing the results of multiwavelength monitoring of
the source. The target is unique in that its radiative output at
radio wavelengths is dominated by a moderately beamed nuclear jet,
at optical frequencies by the accretion disk, and in the hard X-ray
range by the disk corona. Our analysis reveals a correlation (local and
global significance of 96% and 98% respectively) between the optical and
radio bands, with the disk lagging behind the jet by 250 ± 42 days. We
discuss the possible explanation for this, speculating that the observed
disk and the jet flux changes are generated by magnetic fluctuations
originating within the innermost parts of a truncated disk, and that
the lag is related to a delayed radiative response of the disk when
compared with the propagation timescale of magnetic perturbations along
a relativistic outflow. This scenario is supported by re-analysis of
NuSTAR data, modeled in terms of a relativistic reflection from the disk
illuminated by the coronal emission, which returns an inner disk radius
{R}in}/{R}ISCO}={35}-16+40.
We discuss the global energetics in the system, arguing that while the
accretion proceeds at the Eddington rate, with the accretion-related
bolometric luminosity L bol ∼ 9 × 1046 erg
s-1 ∼ 0.2L Edd, the jet total kinetic energy L
j ∼ 4 × 1044 erg s-1, inferred
from the dynamical modeling of the giant radio lobes in the source,
constitutes only a small fraction of the available accretion power.
Title: Constraining Disk-Jet Connection in the Radio Source 4C+74.26
Authors: Bhatta, G.; Stawarz, L.; Zola, S.; Ostrowski, M.;
Balasubramaniam, K.; Zdziarski, A.; Markowitz, A.; Kuzmicz, A.;
Jamrozy, M.; MAXI Team
Bibcode: 2017xru..conf..254B
Altcode:
We present our results of multi-wavelength analysis of the source
4C+74.26, one of the largest known sources associated with a quasar
activity, with an aim to investigate the disk-jet connection in
AGNs. While in blazar sources the disk/corona component is outshined
by strongly beamed jet emission and in radio galaxies it is typically
heavily absorbed by the circumnuclear dust, in this radio-loud AGN we
see directly the disk (optical), disk corona and disk outflows (X-rays),
and relativistic jet (radio). In addition, all these components
are bright enough to be monitored on a regular basis. Therefore,
it presents an unique opportunity to explore the disk-jet connection
in radio sources. We studied multi-frequency cross-correlation in the
source using optical, radio and Swift/BAT long-term observations. The
results reveal a significant correlation between the optical and the
radio emissions in the sense that optical emission lags behind the radio
emission by about 250 days. However, as the Swift/BAT observations
were found to be mostly dominated by Poisson noise, they were were
binned in a 30-day bin before cross-correlating with optical and radio
observations. In addition, spectral analysis of the NuSTAR observations
was used to constrain the disk and the coronal properties of the source.
Title: Chandra view on the active nucleus of the restarted radio
galaxy CGCG 292-057
Authors: Balasubramaniam, K.; Stawarz, L.; Sobolewska, M.;
Siemiginowska, A.; Cheung, C.; Goyal, A.; Koziel-Wierzbowska, D.
Bibcode: 2017xru..conf..251B
Altcode:
Here we present an analysis of the 90ksec Chandra ACIS-I data for the
galaxy CGCG 292-057 (z = 0.054), which is a remarkable system showing
at optical wavelengths, strong evidence for a relatively recent merger
event. Radio images reveal a similarly complex picture, with a pair
of compact young/inner radio lobes confined to the host galaxy, and
embedded within larger-scale old/outer radio lobes characterized by
the X-shaped morphology. The active nucleus in the system is clearly
detected in the newly obtained Chandra data. We model the X-ray
spectrum of the core assuming various emission models, including an
absorbed power-law, a power-law plus thermal emission component, and
a two-temperature thermal plasma. The best fit was however obtained
assuming a model consisting of a power-law emission scattered by a
hot ionized gas (giving rise to the 6.7 keV iron line). We discuss
our results in a general context of the jet-ISM interaction in a
post-merger AGN with an intermittent jet activity.
Title: Relationships Between Sequential Chromospheric Brightening
and the Corona
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; Gilbert,
H. R.
Bibcode: 2017IAUS..327..117K
Altcode: 2017arXiv170403835K
The chromosphere is a complex region that acts as an intermediary
between the magnetic flux emergence in the photosphere and the magnetic
features seen in the corona. Large eruptions in the chromosphere of
flares and filaments are often accompanied by ejections of coronal mass
off the sun. Several studies have observed fast-moving progressive
trains of compact bright points (called Sequential Chromospheric
Brightenings or SCBs) streaming away from chromospheric flares that
also produce a coronal mass ejection (CME). In this work, we review
studies of SCBs and search for commonalties between them. We place
these findings into a larger context with contemporary chromospheric
and coronal observations. SCBs are fleeting indicators of the
solar atmospheric environment as it existed before their associated
eruption. Since they appear at the very outset of a flare eruption,
SCBs are good early indication of a CME measured in the chromosphere.
Title: Dynamic Loading Assembly for Testing Actuators of Segmented
Mirror Telescope
Authors: Deshmukh, Prasanna Gajanan; Parihar, Padmakar;
Balasubramaniam, Karthik A.; Mishra, Deepta Sundar; Mahesh, P. K.
Bibcode: 2017JAI.....650006D
Altcode:
Upcoming large telescopes are based on Segmented Mirror Telescope (SMT)
technology which uses small hexagonal mirror segments placed side by
side to form the large monolithic surface. The segments alignment
needs to be maintained against external disturbances like wind,
gravity, temperature and structural vibration. This is achieved by
using three position actuators per segment working at few-nanometer
scale range along with a local closed loop controller. The actuator
along with a controller is required to meet very stringent performance
requirements, such as track rates up to 300nm/s (90mN/s) with tracking
errors less than 5nm, dynamical forces of up to ±40N, ability to reject
disturbances introduced by the wind as well as by mechanical vibration
generated in the mirror cell, etc. To conduct these performance tests in
more realistic manner, we have designed and developed a Dynamic Loading
Assembly (DLA) at Indian Institute of Astrophysics (IIA), Bangalore. DLA
is a computer controlled force-inducing device, designed in a modular
fashion to generate different types of user-defined disturbances in
extremely precise and controlled manner. Before realizing the device,
using a simple spring-mass-damper-based mathematical model, we ensured
that the concept would indeed work. Subsequently, simple concept was
converted into a detailed mechanical design and parts were manufactured
and assembled. DLA has static and dynamic loading capabilities up to
250N and 18N respectively, with a bandwidth sufficient to generate wind
disturbances. In this paper, we present various performance requirements
of SMT actuators as well as our effort to develop a dynamic loading
device which can be used to test these actuators. Well before using
DLA for meaningful testing of the actuator, the DLA itself have gone
through various tests and improvements phases. We have successfully
demonstrated that DLA can be used to check the extreme performance
of two different SMT actuators, which are expected to track the
position/force with a few nanometer accuracy.
Title: The Origin of Sequential Chromospheric Brightenings
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; Gilbert,
H. R.
Bibcode: 2017SoPh..292...72K
Altcode: 2017arXiv170403828K
Sequential chromospheric brightenings (SCBs) are often observed in the
immediate vicinity of erupting flares and are associated with coronal
mass ejections. Since their initial discovery in 2005, there have
been several subsequent investigations of SCBs. These studies have
used differing detection and analysis techniques, making it difficult
to compare results between studies. This work employs the automated
detection algorithm of Kirk et al. (Solar Phys. 283, 97, 2013) to
extract the physical characteristics of SCBs in 11 flares of varying
size and intensity. We demonstrate that the magnetic substructure
within the SCB appears to have a significantly smaller area than the
corresponding Hα emission. We conclude that SCBs originate in the
lower corona around 0.1 R⊙ above the photosphere, propagate
away from the flare center at speeds of 35 -85 kms−1, and
have peak photosphere magnetic intensities of 148 ±2.9 G. In light
of these measurements, we infer SCBs to be distinctive chromospheric
signatures of erupting coronal mass ejections.
Title: Timing signatures of solar flares
Authors: Balasubramaniam, K. S.; Lynch, C.; Henry, T.; Nitta, N.;
Hurlburt, N. E.; Slater, G. L.
Bibcode: 2016AGUFMSH43E..02B
Altcode:
We compare the timing signatures of solar flares observed with the GOES
X-ray and the SDO/AIA instruments between the years 2010-2015. From
this comparison we find that: (i) the rise-time of flares (time
difference from the background to peak) is inversely correlated with
the solar cycle, i.e. longer lasting rise times occur during the
solar minimum. This implies that a higher thermal state of the outer
solar atmosphere, during solar maximum, is far more receptive to being
heated than during a solar minimum. (ii) From an analysis of rise-times,
statistically, we find that 171 A appears to detect the earliest flares,
providing clues to fact that this might be layer where reconnections
are first triggered. We discuss the implications of these and other
statistical results in terms of forecasting of solar flares.
Title: Comparing SSN Index to X-Ray Flare and Coronal Mass Ejection
Rates from Solar Cycles 22 - 24
Authors: Winter, L. M.; Pernak, R. L.; Balasubramaniam, K. S.
Bibcode: 2016SoPh..291.3011W
Altcode: 2016arXiv160500503W; 2016SoPh..tmp...77W
The newly revised sunspot-number series allows for placing historical
geoeffective storms in the context of several hundred years of solar
activity. Using statistical analyses of the Geostationary Operational
Environmental Satellites (GOES) X-ray observations from the past
≈30 years and the Solar and Heliospheric Observatory (SOHO) Large
Angle and Spectrometric Coronagraph (LASCO) Coronal Mass Ejection
(CME) catalog (1996 - present), we present sunspot-number-dependent
flare and CME rates. In particular, we present X-ray flare rates as
a function of sunspot number for the past three cycles. We also show
that the 1 - 8 Å X-ray background flux is strongly correlated with
sunspot number across solar cycles. Similarly, we show that the CME
properties (e.g. proxies related to the CME linear speed and width) are
also correlated with sunspot number for Solar Cycles 23 and 24. These
updated rates will enable future predictions for geoeffective events
and place historical storms in the context of present solar activity.
Title: Sunspot Numbers from ISOON: A Ten-Year Data Analysis
Authors: Balasubramaniam, K. S.; Henry, T. W.
Bibcode: 2016SoPh..291.3123B
Altcode: 2016arXiv160207741B; 2016SoPh..tmp...40B
Sunspot numbers are important tracers of historical solar activity. They
are important in predicting the oncoming solar maximum, in the
design of lifetimes of space assets, and in assessing the extent
of solar-radiation impact on the space environment. Historically,
sunspot numbers have been obtained visually from sunspot drawings. The
availability of digital images from the US Air Force Improved Solar
Optical Observing Network (ISOON) prototype telescope concurrent to
observer-dependent sunspot numbers recorded at the National Solar
Observatory (NSO) has provided a basis for comparing sunspot numbers
determined from the two methods. We compare sunspot numbers from visual
and digital methods observed nearly simultaneously. The advantages of
digital imagery are illustrated.
Title: Towards a Physics-Based Flare Irradiance Model
Authors: Hock-Mysliwiec, R. A.; Klimchuk, J. A.; Eparvier, F. G.;
Woods, T. N.; Balasubramaniam, K. S.
Bibcode: 2016usc..confE..46H
Altcode:
The Extreme UltraViolet (EUV) irradiance from solar flares is a critical
driver of short term variability in the Earth's upper atmosphere. The
EUV Variability Experiment (EVE) onboard NASA's Solar Dynamics
Observatory (SDO) has been making moderate spectral resolution (0.1
nm), high time cadence (10 s) measurements of the solar EUV irradiance
(5-105 nm) since 2010. A key observation from EVE is that flares of the
same magnitude at one wavelength (e.g. GOES XRS) have different peak
intensities and time profiles in other wavelengths. As it is impractical
to measure the entire EUV spectrum with sufficient spectral resolution
and temporal cadence to capture these differences for space weather
operations, the next generation of flare irradiance models must be
able to capture these variations. We have developed a framework for
a physics-based flare irradiance model based on the EBTEL model. At
present, this Multi-Strand Flare Irradiance Model (MS-FIM) is able to
predict EUV lightcurves over a range of coronal temperatures given the
lightcurves from two EVE lines as inputs. In this paper, we present an
overview of the Multi-Strand Flare Irradiance Model as well as initial
results showing its ability to predict the irradiances for a diverse
range of flares, including EUV late phase flares. We also describe
preliminary efforts to drive the model with parameters derived from
images of the flaring region instead of EUV lightcurves.
Title: Timing signatures of large scale solar eruptions
Authors: Balasubramaniam, K. S.; Hock-Mysliwiec, Rachel; Henry,
Timothy; Kirk, Michael S.
Bibcode: 2016SPD....47.1301B
Altcode:
We examine the timing signatures of large solar eruptions resulting
in flares, CMEs and Solar Energetic Particle events. We probe solar
active regions from the chromosphere through the corona, using data from
space and ground-based observations, including ISOON, SDO, GONG, and
GOES. Our studies include a number of flares and CMEs of mostly the M-
and X-strengths as categorized by GOES. We find that the chromospheric
signatures of these large eruptions occur 5-30 minutes in advance of
coronal high temperature signatures. These timing measurements are
then used as inputs to models and reconstruct the eruptive nature of
these systems, and explore their utility in forecasts.
Title: Comparing Digital Sunspot Number Counts to the New
International Sunspot Numbers
Authors: Balasubramaniam, K. S.; Henry, Timothy
Bibcode: 2016SPD....47.1202B
Altcode:
The International Sunspot Numbers (ISN; Version 2) have been
recently (2015) revised at the Sunspot Index and Long Term
Solar Observations maintained at Royal Observatory of Belgium
(http://www.sidc.be/silso/datafiles). ISN is a reconciled aggregate
over several ground-based observatories, mostly using hand-drawn sunspot
recordings. We make a detailed 10-year comparisons between the Improved
Solar Observing Optical Network’s prototype digital data (2002-2011)
and the ISN V1 (Version 1; pre-2015), and ISN V2. Over the ~ 10-year
period, ISN V1 underestimates the sunspot number counts by up to 40%
while the ISN V2 overestimates by a similar amount. We also compare
the hand-drawn data from a single telescope at the National Solar
Observatory with the digital data and ISN numbers. These comparisons
reveal caveats that need to be taken into account, as sunspot numbers
are used to forecast both the solar cycle and the near term climatology
of solar cycle impacts on the space environment.
Title: The Origin of Sequential Chromospheric Brightening
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, Jason;
Gilbert, Holly
Bibcode: 2016SPD....47.0104K
Altcode:
Sequential Chromospheric Brightenings (SCBs) are often observed in the
immediate vicinity of erupting flares and are associated with coronal
mass ejections. When SCBs are observed, they routinely appear before the
peak emission of the flare and several hours before the first detection
of a coupled CME. Since their initial discovery in 2005, there have been
several subsequent investigations of SCBs. In each case, these sudden,
small-scale brightenings provide vital clues regarding the mechanisms
of large-scale energy release in the solar atmosphere. We make use
of an automated detection algorithm developed by Kirk et al. (2013)
to extract the physical qualities of SCBs in 11 flares of varying size
and intensity. Using complementary magnetic field measurements, we also
model the potential field beneath these brightenings. We conclude that
SCBs originate in the lower corona around 0.1 R⊙ above
the photosphere, propagate away from the flare center at speeds 35 -
85 km s-1, and have typical photosphere magnetic intensities
257± 37 G. In light of these measurements, we conclude that SCBs are
distinctive chromospheric signatures of erupting coronal mass ejections.
Title: In-progress X-ray Flare Forecasting
Authors: Balasubramaniam, K. S.; Winter, L. M.
Bibcode: 2015AGUFMSM41A2462B
Altcode:
Solar X-ray flares release intense amounts of radiation and can be
associated with subsequent changes in the geomagnetic field as well as
a large influx of solar energetic particles. From analyses of 50,000
flares detected with the NOAA GOES satellites over the past 40 years,
Winter & Balasubramaniam (2015) introduced a flare phase diagram
where X-ray observables indicating flare temperature and background
solar activity levels can be used to separate flares of different peak
flux. We present results from adapting this method into a real-time
forecast tool. Real-time GOES X-ray observations are used to predict
expected flare class, with updates made every 1-minute. KSB, in
part by the Air Force Office of Scientific Research on "the Physics
of Coupled Flares and CME Systems". LM was supported by AER, and in
part by a contract supported by AFRL/RV
Title: Solar Flare, CME, and Proton Event Rates Correlated with
Sunspot Number
Authors: Winter, L. M.; Balasubramaniam, K. S.; Pernak, R.
Bibcode: 2015AGUFMSH23C2454W
Altcode:
The newly revised sunspot number series allows for placing historical
geoeffective storms in the context of several hundred years of solar
activity. Using statistical analyses of the GOES X-ray and differential
particle observations from the past ~30 years and the SOHO/LASCO
CME catalog (1996-present), we present sunspot number dependent
predictions for expected flare, SEP, and CME rates. In particular,
we present X-ray flare rates as a function of sunspot number for the
past three cycles. We also show, as in the attached figure, that the
1-8 Angstrom background flux is strongly correlated with sunspot number
across solar cycles. Similarly, we show that the CME properties (e.g.,
velocity and width) are also correlated with sunspot number for cycles
23 and 24. Finally, SEP rates and background proton flux levels are also
scaled to sunspot number. These rates will enable future predictions
for geoeffective events and place historical storms in context of
present solar activity.
Title: Using the maximum X-ray flux ratio and X-ray background to
predict solar flare class
Authors: Winter, L. M.; Balasubramaniam, K.
Bibcode: 2015SpWea..13..286W
Altcode: 2015arXiv150400294W
We present the discovery of a relationship between the maximum ratio
of the flare flux (namely, 0.5-4 Å to the 1-8 Å flux) and nonflare
background (namely, the 1-8 Å background flux), which clearly separates
flares into classes by peak flux level. We established this relationship
based on an analysis of the Geostationary Operational Environmental
Satellites X-ray observations of ∼ 50,000 X, M, C, and flares derived
from the NOAA/Space Weather Prediction Center flares catalog. Employing
a combination of machine learning techniques (K-nearest neighbors
and nearest centroid algorithms) we show a separation of the observed
parameters for the different peak flaring energies. This analysis is
validated by successfully predicting the flare classes for 100% of the
X-class flares, 76% of the M-class flares, 80% of the C-class flares,
and 81% of the B-class flares for solar cycle 24, based on the training
of the parametric extracts for solar flares in cycles 22-23.
Title: MorePITA - an automated Moreton wave detector
Authors: Pérez-Suárez, David; Long, David; Balasubramaniam,
Karatholuvu S.
Bibcode: 2015TESS....140318P
Altcode:
Globally-propagating waves in the solar chromosphere (commonly called
Moreton waves) have been observed for more than 50 years, but are
typically identified and characterised by eye, leading to significant
user bias. The Moreton Pulse Identification and Tracking Algorithm
(MorePITA) is a new technique based on the Coronal Pulse Identification
and Tracking Algorithm (CorPITA) but tuned to detect Moreton waves using
ground based H-alpha observations. We present a preliminary analysis
of two events observed by two different Hα telescopes (ISOON and GONG)
and compare the results with the equivalent detections made by CorPITA
applied to SDO/AIA observations.
Title: A Phase Diagram for Solar Flares
Authors: Balasubramaniam, K. S.; Winter, Lisa; Pernak, Rick
Bibcode: 2015TESS....131101B
Altcode:
Using the data from the NOAA/GOES X-ray observations of ~50,000 flares,
we develop a Phase Diagram for solar flares. Such a Solar Flare Phase
Diagram helps to trace the underlying energy structure of solar flares,
and provides a prediction framework. The temperature (maximum ratio of
short (0.5 - 4 A) to long band (1-8 A) band) and background solar x-ray
radiation (at 1-8 A band) forms the basis of the phase diagram. Using
the phase diagram and relevant statistical analysis, we derive insights
into the eruptive nature of flares during the solar-cycle ramp (ramp
up to and ramp down from solar maximum) phases and peak phase of the
solar cycle.
Title: Towards Predicting Solar Flares
Authors: Winter, Lisa; Balasubramaniam, Karatholuvu S.
Bibcode: 2015TESS....130216W
Altcode:
We present a statistical study of solar X-ray flares observed using
GOES X-ray observations of the ~50,000 fares that occurred from 1986
- mid-2014. Observed X-ray parameters are computed for each of the
flares, including the 24-hour non-flare X-ray background in the 1-8 A
band and the maximum ratio of the short (0.5 - 4 A) to long band (1-8
A) during flares. These parameters, which are linked to the amount
of active coronal heating and maximum flare temperature, reveal a
separation between the X-, M-, C-, and B- class fares. The separation
was quantified and verified through machine-learning algorithms (k
nearest neighbor; nearest centroid). Using the solar flare parameters
learned from solar cycles 22-23, we apply the models to predict flare
categories of solar cycle 24. Skill scores are then used to assess the
success of our models, yielding correct predictions for ~80% of M-,
C-, and B-class flares and 100% correct predictions for X-flares. We
present details of the analysis along with the potential uses of our
model in flare forecasting.
Title: Qualities of Sequential Chromospheric Brightenings Observed
in Hα and UV Images
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, Jason;
McAteer, R. T. James
Bibcode: 2014ApJ...796...78K
Altcode: 2014arXiv1411.4069K
Chromospheric flare ribbons observed in Hα appear well-organized
when first examined: ribbons impulsively brighten, morphologically
evolve, and exponentially decay back to pre-flare levels. Upon closer
inspection of the Hα flares, there is often a significant number
of compact areas brightening in concert with the flare eruption but
are spatially separated from the evolving flare ribbon. One class of
these brightenings is known as sequential chromospheric brightenings
(SCBs). SCBs are often observed in the immediate vicinity of erupting
flares and are associated with coronal mass ejections. In the past
decade there have been several previous investigations of SCBs. These
studies have exclusively relied upon Hα images to discover and analyze
these ephemeral brightenings. This work employs the automated detection
algorithm of Kirk et al. to extract the physical qualities of SCBs in
observations of ground-based Hα images and complementary Atmospheric
Imaging Assembly images in He II, C IV, and 1700 Å. The metadata
produced in this tracking process are then culled using complementary
Doppler velocities to isolate three distinguishable types of SCBs. From
a statistical analysis, we find that the SCBs at the chromospheric
Hα layer appear earlier and last longer than their corresponding
signatures measured in AIA. From this multi-layer analysis, we infer
that SCBs are spatially constrained to the mid-chromosphere. We also
derive an energy budget to explain SCBs which have a postulated energy
of not more than 0.01% of the total flare energy.
Title: In-Progress flare Forecasting of the Peak and Fall of X-Ray
Flares
Authors: Balasubramaniam, K. S.; Winter, L. M.
Bibcode: 2014AGUFMSM31A4152B
Altcode:
In-progress flare forecasting aims to predict the properties of an
eminent flare, given only the first few observations during the initial
rise phase. We present initial stages of a new model to forecast
the rise and fall times and the peak flux level of X-ray flares. Our
model is based upon a statistical analysis of the properties of M-
and X- class flares occurring over the past three solar cycles. In a
similar statistical analysis to the automated method of Aschwanden &
Freeland (2012), we analyze the 1-min GOES X-ray data, detecting flares
and characterizing the shape of the rising flare. We also determine
the characteristics of the fall from peak and characterize the X-ray
background, using techniques similar to those presented in Hock,
Woodraska, and Woods (2013). Our analysis includes both the softer
(1-8 Angstrom) and harder (0.5-4 Angstrom) energy X-ray channels from
observations from 1986-present.
Title: Estimate of Solar Maximum using the 1-8 Å GOES X-ray
Measurements
Authors: Winter, L. M.; Balasubramaniam, K. S.
Bibcode: 2014AGUFMSM31A4153W
Altcode:
We present an alternate method of determining the progression of the
solar cycle through an analysis of the solar X-ray background. Our
results are based on the NOAA GOES X-ray data in the 1-8 Angstrom band
from 1986 - present, covering solar cycles 22, 23, and 24. The X-ray
background level tracks the progression of the solar cycle through
its maximum and minimum. Using the X-ray data, we can therefore
make estimates of the solar cycle progression and date of so- lar
maximum. Based upon our analysis, we conclude that the Sun reached
its hemisphere-averaged maximum in Solar Cycle 24 in late 2013. This
agrees with the NOAA prediction of a maximum in Fall 2013.
Title: Estimate of Solar Maximum Using the 1-8 Å Geostationary
Operational Environmental Satellites X-Ray Measurements
Authors: Winter, L. M.; Balasubramaniam, K. S.
Bibcode: 2014ApJ...793L..45W
Altcode: 2014arXiv1409.2763W
We present an alternate method of determining the progression of the
solar cycle through an analysis of the solar X-ray background. Our
results are based on the NOAA Geostationary Operational Environmental
Satellites (GOES) X-ray data in the 1-8 Å band from 1986 to the
present, covering solar cycles 22, 23, and 24. The X-ray background
level tracks the progression of the solar cycle through its maximum
and minimum. Using the X-ray data, we can therefore make estimates of
the solar cycle progression and the date of solar maximum. Based upon
our analysis, we conclude that the Sun reached its hemisphere-averaged
maximum in solar cycle 24 in late 2013. This is within six months of
the NOAA prediction of a maximum in spring 2013.
Title: Magnetic Field Changes in SDO/HMI Line-of-sight Magnetograms
during Large Solar Flares
Authors: Balasubramaniam, K. S.; Hock, Rachel
Bibcode: 2014AAS...22412305B
Altcode:
Photospheric magnetic fields are often used to study the topology
of a flaring active region as well as to predict when a flare will
happen. We examined SDO/HMI line-of-sight magnetograms for forty flares
(M5.0 or larger) from 2010 to 2013. Using the full-resolution (0.5
arcsecond/pixel) and high time cadence (45-second), observations, we
identified three types of changes in line-of-sight magnetic flux near
the flaring region during large solar flares: First, discreet jumps
or steps in the line-of-sight magnetic flux are often observed when
examining magnetograms before and after the flare. Second, spikes or
rapid and transient changes lasting just a few minutes occur during the
rise of the flare, coinciding with the impulsive phase. Finally, in a
few flares, moderate-scale waves in magnetograms, similar to Moreton
or EIT waves, are seen propagating away from the flaring region. In
this study, we provide statistics on these different apparent magnetic
flux changes as well as offer possible physical explanations.
Title: Chromospheric Mass Motions and Intrinsic Sunspot Rotations
for NOAA Active Regions 10484, 10486, and 10488 Using ISOON Data
Authors: Hardersen, Paul S.; Balasubramaniam, K. S.; Shkolyar, Svetlana
Bibcode: 2013ApJ...773...60H
Altcode: 2013arXiv1306.3132H
This work utilizes Improved Solar Observing Optical Network continuum
(630.2 nm) and Hα (656.2 nm) data to: (1) detect and measure intrinsic
sunspot rotations occurring in the photosphere and chromosphere,
(2) identify and measure chromospheric filament mass motions, and
(3) assess any large-scale photospheric and chromospheric mass
couplings. Significant results from 2003 October 27-29, using the
techniques of Brown et al., indicate significant counter-rotation
between the two large sunspots in NOAA AR 10486 on October 29, as well
as discrete filament mass motions in NOAA AR 10484 on October 27 that
appear to be associated with at least one C-class solar flare.
Title: The evolution of solar activity across the visible solar disk
Authors: Balasubramaniam, K. S.; Hock, R. A.
Bibcode: 2013SPD....44...69B
Altcode:
It is well known that large solar flares do not occur in isolation. Once
an active region produces a flare, the probability of another flares
increase dramatically. Using data from NASA's Solar Dynamics Observatory
(SDO) and the US Air Force's Improved Solar Observing Optical Network
(ISOON), we are able to examine all layers of the solar atmosphere and
isolate active regions as they transit the solar disk. By studying the
fluctuations in lightcurves and magnetic flux before, during, and after
solar flares, we seek to understand the patterns of activity during
phases of the active region evolution. In this study, we examined the
month of February 2011. During that time, there were fifteen numbered
NOAA Active Regions, which produced over 100 flares greater than C1.0,
including the first X-class flare of Solar Cycle 24.
Title: Failed filament eruption inside a coronal mass ejection in
active region 11121
Authors: Kuridze, D.; Mathioudakis, M.; Kowalski, A. F.; Keys, P. H.;
Jess, D. B.; Balasubramaniam, K. S.; Keenan, F. P.
Bibcode: 2013A&A...552A..55K
Altcode: 2013arXiv1302.5931K
Aims: We study the formation and evolution of a failed filament
eruption observed in NOAA active region 11121 near the southeast limb on
November 6, 2010.
Methods: We used a time series of SDO/AIA 304,
171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as
ROSA and ISOON Hα images to study the erupting active region.
Results: We identify coronal loop arcades associated with a quadrupolar
magnetic configuration, and show that the expansion and cancellation
of the central loop arcade system over the filament is followed by
the eruption of the filament. The erupting filament reveals a clear
helical twist and develops the same sign of writhe in the form of
inverse γ-shape.
Conclusions: The observations support the
"magnetic breakout" process in which the eruption is triggered by
quadrupolar reconnection in the corona. We propose that the formation
mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic
helical kink instability. The eruption has failed because of the
large-scale, closed, overlying magnetic loop arcade that encloses
the active region. Movies are available in electronic form at
http://www.aanda.org
Title: An Automated Algorithm to Distinguish and Characterize Solar
Flares and Associated Sequential Chromospheric Brightenings
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; McNamara,
B. J.; McAteer, R. T. J.
Bibcode: 2013SoPh..283...97K
Altcode: 2011arXiv1108.1384K; 2011SoPh..tmp..345K
We present a new automated algorithm to identify, track, and
characterize small-scale brightening associated with solar eruptive
phenomena observed in Hα. The temporal, spatially localized changes in
chromospheric intensities can be separated into two categories: flare
ribbons and sequential chromospheric brightenings (SCBs). Within each
category of brightening we determine the smallest resolvable locus of
pixels, a kernel, and track the temporal evolution of the position and
intensity of each kernel. This tracking is accomplished by isolating
the eruptive features, identifying kernels, and linking detections
between frames into trajectories of kernels. We fully characterize the
evolving intensity and morphology of the flare ribbons by observing
the tracked flare kernels in aggregate. With the location of SCB and
flare kernels identified, they can easily be overlaid on complementary
data sets to extract Doppler velocities and magnetic-field intensities
underlying the kernels. This algorithm is adaptable to any dataset to
identify and track solar features.
Title: Solar Hα Oscillations from Intensity and Doppler Observations
Authors: Jackiewicz, Jason; Balasubramaniam, K. S.
Bibcode: 2013ApJ...765...15J
Altcode: 2013arXiv1301.2825J
Chromospheric wave activity around flares and filaments has been a
research focus for years, and could provide indirect measurements of
local conditions that are not otherwise accessible. One interesting
observed phenomenon is oscillations in filaments, activated by distant
flares and the large-scale waves they produce. Characteristics of
these oscillations, such as periods, amplitudes, and lifetimes, can
provide unique information about the filament. We measure oscillation
properties in flares and filaments from Hα chromospheric data using a
new method that provides important spatial and frequency content of the
dynamics. We apply the method to two flare events where filaments are
observed to oscillate and determine their properties. We find strong
oscillatory signal in flaring active regions in the chromosphere
over a range of frequencies. Two filaments are found to oscillate
without any detectable chromospheric wave acting as an activation
mechanism. We find that filaments oscillate with periods of tens of
minutes, but variations are significant at small spatial scales along
the filamentary region. The results suggest that there is a frequency
dependence of the oscillation amplitude, as well as a spatial dependence
along single filaments that is more difficult to quantify. It also
appears that the strength of the oscillations does not necessarily
depend on the strength of the trigger, although there are other
possible effects that make this conclusion preliminary. Applications
of this technique to other events and different data sets will provide
important new insights into the local energy densities and magnetic
fields associated with dynamic chromospheric structures.
Title: Sequential Chomospheric Brightening: An Automated Approach
to Extracting Physics from Ephemeral Brightening
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; McAteer,
R. T. J.; McNamara, B. J.
Bibcode: 2012ASPC..463..267K
Altcode: 2012arXiv1203.1277K
We make a comparison between small scale chromospheric brightenings
and energy release processes through examining the temporal evolution
of sequential chromospheric brightenings (SCBs), derive propagation
velocities, and propose a connection of the small-scale features to
solar flares. Our automated routine detects and distinguishes three
separate types of brightening regularly observed in the chromosphere:
plage, flare ribbon, and point brightenings. By studying their distinct
dynamics, we separate out the flare-associated bright points commonly
known as SCBs and identify a propagating Moreton wave. Superimposing
our detections on complementary off-band images, we extract a Doppler
velocity measurement beneath the point brightening locations. Using
these dynamic measurements, we put forward a connection between point
brightenings, the erupting flare, and overarching magnetic loops. A
destabilization of the pre-flare loop topology by the erupting flare
directly leads to the SCBs observed.
Title: Insights into Using SDO Data for Active Region Specification
and Real-time Event Monitoring
Authors: Hock, R. A.; Balasubramaniam, K. S.; Amezcua, A.; Bogart,
R. S.; Eparvier, F. G.; Hoeksema, J. T.; Jones, A. R.; Woodraska,
D.; Woods, T. N.
Bibcode: 2012AGUFMSH13A2279H
Altcode:
NASA's Solar Dynamics Observatory (SDO) launched in February 2010
provides unprecedented capabilities to capture the spatial, temporal,
and spectral evolution of the Sun. While SDO is primarily a science
mission, the data it produces has the potential to be used for space
weather operations. Here, we present two ways data from SDO could
be used to supplement current space weather capabilities. Presently,
active regions are numbered and classified at the beginning of each
day. High-cadence white light images and magnetograms from Helioseismic
and Magnetic Imager (HMI) onboard SDO have the potential to provide
automated and continuous specification of active regions. To demonstrate
the capabilities of SDO, we analyzed a month-long sequence of HMI images
starting 1 February 2011. We were able to automatically identify and
track all fifteen active regions present on the solar disk during the
month. We were also able to characterize the active region, including
its location, longitudinal extent, sunspot number and area, as well as
approximate the McIntosh classification. In addition to specification
of active regions, SDO has the capability to monitor solar events in
near real-time. SDO's EUV Variability Experiment (EVE) provides near
real-time flare intensity and location in the soft x-rays. Here, we
present a comparison of flare intensities and locations from EVE and
NOAA over the first two years of the SDO mission.
Title: Diagnosis of Flow and Magnetic Fields Using Simultaneous
Spectro-Polarimetry of Photospheric Fe I and Chromospheric Mg I lines
Authors: Deng, N.; Choudhary, D. P.; Balasubramaniam, K. S.
Bibcode: 2012ASPC..454..229D
Altcode:
We present a study of active region (AR) NOAA 9661 using simultaneous
spectro-polarimetric observations of photospheric Fe I (630.25 and
630.15 nm) and chromospheric Mg I b2 (517.27 nm) lines
obtained with the HAO/NSO Advanced Stokes Polarimeter (ASP). SIR
(Stokes Inversion based on Response function) code was applied to
the Stokes spectra of Fe I line pair and Mg I line, thus providing
magnetic field vectors at the photosphere and low chromosphere. We
quantitatively compared the magnetic field at the two heights and
obtained reasonable results. Doppler velocities were extracted from
both Stokes I and V profiles of the three spectral lines, which reveal
strong red shifts in the penumbra near the magnetic neutral line.
Title: Beckers Effect in a Fabry-Pérot Imaging Interferometer and
Its Effects on Magnetic Field Measurements
Authors: Robinson, Brian; Balasubramaniam, K.; Gary, G.
Bibcode: 2012AAS...22020623R
Altcode:
The Beckers effect and its impact on the optical performance of a
triple-etalon Fabry-Pérot imaging spectral interferometer, such
as that intended for use in the Advanced Technology Solar Telescope
visible tunable filter, are analyzed in terms of its impacts on line
profiles and spatial resolution. In this multi-etalon design, the
interferometer is mounted in a telecentric beam. The Beckers effect
refers to the pupil apodization in this configuration caused by the
dependence of the spectral transmittance of Fabry-Pérot etalons on the
angle of incidence of impinging rays. We find that the effect on the
imaging and spectral performance can be significant even for the high
F-number intermediate images required for narrowband imaging. We go on
to explore the impact on Stokes line profiles at 6303Å as well as the
cross-talk caused by the degraded point spread function, and analyze
the resultant error in the calculated magnetic fields. We gratefully
acknowledge the National Science Foundation and the National Solar
Observatory for their support of this work.
Title: Properties of Sequential Chromospheric Brightenings and
Associated Flare Ribbons
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, Jason;
McAteer, R. T. James; Milligan, Ryan O.
Bibcode: 2012ApJ...750..145K
Altcode: 2012arXiv1203.1271K
We report on the physical properties of solar sequential chromospheric
brightenings (SCBs) observed in conjunction with moderate-sized
chromospheric flares with associated Coronal mass ejections. To
characterize these ephemeral events, we developed automated procedures
to identify and track subsections (kernels) of solar flares and
associated SCBs using high-resolution Hα images. Following the
algorithmic identification and a statistical analysis, we compare
and find the following: SCBs are distinctly different from flare
kernels in their temporal characteristics of intensity, Doppler
structure, duration, and location properties. We demonstrate that
flare ribbons are themselves made up of subsections exhibiting
differing characteristics. Flare kernels are measured to have a mean
propagation speed of 0.2 km s-1 and a maximum speed of 2.3 km
s-1 over a mean distance of 5 × 103 km. Within
the studied population of SCBs, different classes of characteristics
are observed with coincident negative, positive, or both negative and
positive Doppler shifts of a few km s-1. The appearance of
SCBs precedes peak flare intensity by ≈12 minutes and decay ≈1 hr
later. They are also found to propagate laterally away from flare center
in clusters at 45 km s-1 or 117 km s-1. Given
SCBs' distinctive nature compared to flares, we suggest a different
physical mechanism relating to their origin than the associated
flare. We present a heuristic model of the origin of SCBs.
Title: Abrupt Changes in the Photospheric Magnetic Structures and
H-alpha Chromosphere during the 2006 December 6 X6.5 Flare
Authors: Petrie, Gordon; Balasubramaniam, K. S.; Burtseva, O.; Pevtsov,
A. A.
Bibcode: 2012AAS...22020406P
Altcode:
The active region NOAA 10930 produced the last X-class flares of Solar
Cycle 23, including one at 18:29 UT on December 6. Here we investigate
the relationships between signatures of this flare observed in the
photospheric magnetic field and white light and continuum intensity, and
H-alpha chromosphere. We use GONG 1-minute magnetograms and continuum
intensity images and (1-minute?) ISOON white-light and H-alpha images to
show that (1) the sunspot penumbral area and mean intensity decreased
abruptly during the flare; (2) the magnetic field changed in large,
contiguous patterns inside and immediately outside the southern and
western penumbra resulting in a more vertical penumbral field on
average; (3) H-alpha brightenings were observed to begin around the
GOES start time, the earliest occurring near the sunspot and later
brightenings progressively further north and south of the center of
the active region near magnetic neutral lines; and (4) most of the
detected photospheric flux cancellation (75%) occurred during the flare,
and the remainder before the flare.
Title: An Insight Into Atmospheric Structure Through Compact
Chromospheric Brightenings
Authors: Kirk, Michael S.; Balasubramaniam, K.; Jackiewicz, J.;
McAteer, R.
Bibcode: 2012AAS...22012406K
Altcode:
Compact chromospheric brightenings have a range of intensities,
Doppler velocities, and magnetic field strength each giving clues to
their physical origin. One type of compact brightening, sequential
chromospheric brightening (SCB), has several properties of small-scale
chromospheric evaporation. SCBs appear adjacent to two ribbon flares
with associated halo CMEs. This work presents a definition of SCBs
constrained by a statistical analysis of several chromospheric flaring
events. From this definition of SCBs, we extract physical qualities of
SCBs and correlate these qualities with data gathered from additional
layers of the solar atmosphere. Using these dynamic measurements, we
suggest a connection between compact brightenings, the erupting flare,
and overarching magnetic loops.
Title: Insights Into Categorization Of Solar Flares Using Principal
Component Analysis
Authors: Balasubramaniam, K. S.; Norquist, D. C.
Bibcode: 2012AAS...22020446B
Altcode:
Using time sequences of solar chromospheric images acquired using the
USAF/NSO Improved Solar Observing Network (ISOON) prototype telescope,
we have applied principal component analysis (PCA) to time-series of
both erupting and non-erupting active regions. Our primary purpose is
to develop an advanced data driven model for solar flare prediction
using machine learning algorithms, with principal components as the
input. Using the principal components we show a clear separation in the
Eigen vectors. Eigen vectors fall into three major flaring categories:
weak flares (GOES peak intensity < C4.0; intermediary flares (GOES
peak intensity between C4.0 and C8.0) and, strong flares (GOES peak
intensity > C8.0). In this paper, we will provide insights into
implications for the underlying physical mechanisms that describe
these three distinct categories. This work funded by the U. S. Air
Force Office of Scientific Research (AFOSR).
Title: Direct Comparison Of A Moreton Wave, EUV Wave And CME
Authors: White, Stephen M.; Cliver, E.; Balasubramaniam, K.
Bibcode: 2012AAS...22020412W
Altcode:
The first period of major solar activity in the current cycle,
due to AR 11158 in mid February 2011, produced a sequence of solar
flares exhibiting both Moreton waves in H-alpha images and "EIT-waves"
seen in EUV images. Given the rarity of Moreton waves, this offers an
excellent opportunity to compare the properties of the two phenomena
with simultaneous observations. We focus on the event of 17:24 UT on
February 14, which was well-observed by a number of observatories. We
find a strong link between the Moreton wave, the EUV wave and the CME
in this event. The Moreton wave has the same speed as the EUV wave, but
it lags behind the leading edge of the EUV wave. A vertical signature
is seen in the H-alpha Doppler images. STEREO observations of the
CME indicate that initially the vertical speed of the disturbance was
not as high as the EUV wave speed, and the CME rapidly decelerates on
merging with a rising loop system. We interpret the results in light
of current models for such disturbances.
Title: Chromospheric Explosions: Linking Observations Toward a
Physical Model
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, J.;
McAteer, R. T. J.; McNamara, B. J.
Bibcode: 2012AAS...21922408K
Altcode:
Bright points are observed routinely in every layer of the Sun. One type
of bright point, called sequential chromospheric brightening (SCB),
is coincident with flares and is thought to represent a chromospheric
foot-point of a magnetic field line that extends into the corona. These
field lines are energized during a CME-causing eruption leading
to the brightening we observe. We extract physical measurements of
chromospheric flares and SCBs using an automated feature detection
suite. Correlating these results with complementary data from the
corona, we identify the spatio-temporal relationship between coronal
loops and SCBs. We explore a coronal origin for SCBs and put forth an
explicatory model.
Title: The Solar Decimetric Spike Burst of 2006 December 6: Possible
Evidence for Field-aligned Potential Drops in Post-eruption Loops
Authors: Cliver, E. W.; White, S. M.; Balasubramaniam, K. S.
Bibcode: 2011ApJ...743..145C
Altcode:
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density (~106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak 1.4
GHz emission did not occur during the flare impulsive phase but rather
~45 minutes later, in association with post-eruption loop activity
seen in Hα and by the Hinode EUV Imaging Spectrometer. During the
Waves/LASCO era, three other delayed bursts with peak intensities
>105 sfu in the 1.0-1.6 GHz (L-band) frequency range
have been reported that appear to have characteristics similar to the
December 6 burst. In each of these three cases, high-frequency type
IV bursts were reported in a range from ~150 to ~1500 MHz. Assuming
a common ECM emission mechanism across this frequency range implies
a broad span of source heights in the associated post-eruption loop
systems. Difficulties with an ECM interpretation for these events
include the generation of the lower frequency component of the type
IVs and the long-standing problem of escape of the ECM emission from
the loops. Magnetic-field-aligned potential drops, analogous to those
observed for Earth's auroral kilometric radiation, could plausibly
remove both of these objections to ECM emission.
Title: Mapping the Dynamics of Chromospheric Flares
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.;
Mcateer, R.
Bibcode: 2011AGUFMSH51B2003K
Altcode:
Brightening in the chromosphere comes in three different flavors:
plage, flare ribbon, and point. These types of brightening are all
characterized by intensity above the background but have different
dynamics causing the increased intensity. We have developed an automated
software suite to identify and track both ribbon and point brightening
associated with moderate sized flares observed in H alpha. Superposing
our detections on complementary datasets, we produce a three-dimensional
velocity map of flare ribbons, and a Doppler velocity measurement
beneath the point brightening detections. These dynamic measurements
allow us to postulate a physical connection between point brightening,
the erupting flare, and coronal loops.
Title: The Disappearing Solar Filament of 2003 June 11: A Three-body
Problem
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Cliver, E. W.;
Martin, S. F.; Panasenco, O.
Bibcode: 2011ApJ...743..202B
Altcode:
The eruption of a large quiescent filament on 2003 June 11 was preceded
by the birth of a nearby active region—a common scenario. In this
case, however, the filament lay near a pre-existing active region
and the new active region did not destabilize the filament by direct
magnetic connection. Instead it appears to have done so indirectly
via magnetic coupling with the established region. Restructuring
between the perturbed fields of the old region and the filament
then weakened the arcade overlying the midpoint of filament, where
the eruption originated. The inferred rate (~11° day-1)
at which the magnetic disturbance propagates from the mature region
to destabilize the filament is larger than the mean speed (~5º-6°
day-1) but still within the scatter obtained for Bruzek's
empirical relationship between the distance from a newly formed
active region to a quiescent filament and the time from active region
appearance to filament disappearance. The higher propagation speed in
the 2003 June 11 case may be due to the "broadside" (versus ''end-on")
angle of attack of the (effective) new flux to the coronal magnetic
fields overlying a central section of the axis of the filament.
Title: Figure testing and calibration of the ISOON Fabry-Perot etalons
Authors: Robinson, Brian; Balasubramaniam, K. S.; Justice, Jerry;
Pitts, Frank
Bibcode: 2011SPIE.8148E..0AR
Altcode: 2011SPIE.8148E...9R
We present the methods and results for the figure testing and spectral
calibration of the narrow- and wide-band etalons for the Improved Solar
Observing Optical Network's dual-etalon tunable imaging filters. The
ISOON system comprises a distributed network of ground-based patrol
telescopes that gather full-disk data for the monitoring of solar
activity and for the development of more reliable space weather
models. The etalon figure testing consists mainly of testing the
cavity flatness and coating uniformity of each etalon. For this
testing a series of exposures is taken as the etalon is tuned through
a stable spectral line and a full-aperture line profile correlation
method is employed to map the variations in the effective cavity
thickness. Calibration of the etalons includes absolute calibration of
the cavity mean spacing change corresponding to a controller step and
calibration of plate parallelism and spacing settings for each spectral
region of interest. Developmental acceptance testing and calibration
procedures were performed in a laboratory environment using a HeNe laser
source. A calibration method that uses illumination in the telluric
lines is also described. This latter method could be used to conduct
calibration in the field without the use of an artificial light source.
Title: Ground-based synoptic instrumentation for solar observations
Authors: Balasubramaniam, K. S.; Pevtsov, Alexei
Bibcode: 2011SPIE.8148E..09B
Altcode: 2011SPIE.8148E...8B
We will describe the status of current ground-based solar spectroscopic
and imaging instruments used in solar observations. We will describe the
advantages and disadvantages of using these two classes of instruments
with examples drawn from the Improved Solar Optical Observing Network
(ISOON) and Synoptic Long Term Investigations of the Sun (SOLIS)
Network. Besides instrumental requirements and lessons learned
from existing ground-based instruments, this talk will also focus
on the future needs and requirements of ground-based solar optical
observations.
Title: Small-scale Hα jets in the solar chromosphere
Authors: Kuridze, D.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.;
Christian, D. J.; Keenan, F. P.; Balasubramaniam, K. S.
Bibcode: 2011A&A...533A..76K
Altcode: 2011arXiv1108.1043K
Aims: High temporal and spatial resolution observations from
the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength
imager on the Dunn Solar Telescope are used to study the velocities
of small-scale Hα jets in an emerging solar active region.
Methods: The dataset comprises simultaneous imaging in the Hα
core, Ca ii K, and G band, together with photospheric line-of-sight
magnetograms. Time-distance techniques are employed to determine
projected plane-of-sky velocities.
Results: The Hα images
are highly dynamic in nature, with estimated jet velocities as high
as 45 km s-1. These jets are one-directional, with their
origin seemingly linked to underlying Ca ii K brightenings and G-band
magnetic bright points.
Conclusions: It is suggested that the
siphon flow model of cool coronal loops is suitable for interpreting our
observations. The jets are associated with small-scale explosive events,
and may provide a mass outflow from the photosphere to the corona.
Title: Estimating Flaring Probability from High-Cadence Images of
the Solar Chromosphere
Authors: Norquist, Donald C.; Balasubramaniam, K.
Bibcode: 2011SPD....42.2217N
Altcode: 2011BAAS..43S.2217N
We applied principal component analysis to 8-10 hour sequences of
chromospheric Hα images of selected solar active regions as observed
by the U. S. Air Force Improved Solar Optical Observation Network
(ISOON) telescope at Sacramento Peak, NM at one-minute intervals. A
covariance matrix of all combinations of image time pairs was computed
from the picture element Hα intensities from each image sequence,
and eigenvalues and eigenvectors were computed. Computation of
explained variance from the eigenvalues indicated that 99.9% of the
characteristics were represented by the first 50 eigenvectors or
so. The leading eigenvectors were matched at each image time with
a flare category indicator deduced from coincident active region
area-average Hα intensity and 1-8 Å GOES X-ray flux measurements
at one-minute intervals. Multivariate discriminant analysis (MVDA)
was applied to the eigenvector elements and flaring indicators from
a training set of image sequences to compute a vector of coefficients
whose linear combination with the eigenvector predictors maximizes the
distinction among flaring groups. The discriminant function, computed
from the dot product of the coefficients with the eigenvectors of an
independent ISOON case, is used to compute the probability of each
flaring group at each measurement time. Flare category indicators from
independent case times are used to assess the flaring probability
estimates. Multivariate logistic regression (MVLR) was also applied
to the subset of eigenvectors in the training data, and the derived
coefficients were also dotted with the independent eigenvalues to
generate a separate flaring probability estimate. A total of 47 ISOON
image sequences were available for training and flaring probability
estimation. Preliminary results showed that the MVLR was competitive
with MVDA in skill of diagnosing flaring probability. If this approach
shows promise in a diagnostic mode, efforts will be made to extend it
to short-term (1-3 hour) prognostic mode.
Title: Analysis Of Sunspot Number Counts, Sunspot Area, And Sunspot
Irradiance Deficit: 2002-2011
Authors: Balasubramaniam, K. S.; Henry, T.
Bibcode: 2011SPD....42.0301B
Altcode: 2011BAAS..43S.0301B
Sunspot numbers have been traditionally associated with strength of
solar activity, and feed into a variety of space weather forecast
models. We present a detailed analysis of (i) sunspot
number counts, (ii) sunspot area, (iii) their component umbral
and penumbral intensities, and (iv) sunspot irradiance deficit as
measured from 5-minute cadence true continuum images observed with the
USAF/AFRL's Improved Solar Observing Optical Network (ISOON) prototype
telescope. The data were acquired from December 2002 - present. These
measures are obtained, semi-automatically. We relate these observed
measures to the daily NOAA/SWPC Sunspot Numbers, and International
Sunspot Numbers, and trace the intra-day fluctuations in sunspot
numbers to its component constituents. With higher data cadence of
modern instruments, we relate the advantages and disadvantages of
automating the process. We trace inherent fluctuations in sunspot
numbers to the underlying solar activity, and relate them to the solar
eruptive process. This work was supported by the Air Force Office
of Scientific Research (AFOSR)
Title: Connecting Ephemeral Chromospheric Brightenings to Coronal
Loops
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, J.;
McAteer, J.; Milligan, R.
Bibcode: 2011SPD....42.1732K
Altcode: 2011BAAS..43S.1732K
Sequential chromospheric brightenings (SCBs) flanking solar flares
represent chromospheric foot-points of magnetic field lines that
extend into the corona. During the eruption of a solar flare related
CME, these field lines are considered to be energized in sequence
by magnetic re-connection, as coronal fields separate from the solar
surface. Using automated procedures to extract physical measurements
of chromospheric flares and SCBs, we superpose these features onto
coronal EUV images and trace the spatio-temporal relationship between
coronal loops and SCBs. We postulate a physical connection for SCBs
and their coronal counterparts and estimate an energy budget.
Title: The Great Decimetric Solar Spike Burst of 2006 December 6:
Possible Evidence for Field-aligned Potential Drops in Post-eruption
Loops
Authors: Cliver, Edward W.; White, S. M.; Balasubramaniam, K. S.
Bibcode: 2011SPD....42.2223C
Altcode: 2011BAAS..43S.2223C
A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare
on 2006 December 6 had the highest peak flux density ( 106
sfu) of any event yet recorded at this frequency. The decimetric event
characteristics during the brightest emission phase (numerous intense,
short-lived, narrow-band bursts that overlapped to form a continuous
spectrum) suggest electron cyclotron maser (ECM) emission. The peak
1.4 GHz emission did not occur during the flare impulsive phase
but rather 45 minutes later, in association with post-eruption loop
activity seen in H-alpha and by Hinode EIS. During the Waves/LASCO era,
three other delayed bursts with peak intensities >105
sfu in the 1.0-1.6 GHz (L-band) frequency range have been reported
and appear to have characteristics similar to the December 6 burst. In
each of these three cases type IV bursts were reported in a range from
150 to 1500 MHz. Assuming a common ECM emission mechanism across this
frequency range implies a broad span of source heights in the associated
post-eruption loop systems. Difficulties with an ECM interpretation for
these events include the generation of the lower frequency component
of the type IVs and the long-standing problem of escape of the ECM
emission from the loops. Magnetic-field-aligned potential drops,
analogous to those observed for Earth's auroral kilometric radiation,
could plausibly remove both of these objections to ECM emission.
Title: Intrinsic Sunspot Rotations and Energetic Events
Authors: Hardersen, Paul S.; Balasubramaniam, K.; Shkolyar, S.; Zak, B.
Bibcode: 2011SPD....42.1716H
Altcode: 2011BAAS..43S.1716H
The intrinsic rotation of sunspots is considered to play a role
in the magnetic energy buildup leading to solar eruptions. Much of
sunspot intrinsic rotational measurements are made from photospheric
observations via white-light imaging and refers to rotation of the
photospheric layers. This paper presents a pilot project to investigate
measures of intrinsic sunspot rotations at both the photosphere
(true-continuum) and chromosphere (H-alpha) in an effort to understand
their coupling in these layers. The data used in this research
are obtained from the USAF/AFRL/NSO Improved Solar Observing Optical
Network (ISOON) prototype telescope at the National Solar Observatory,
Sunspot, New Mexico. ISOON images from 2003 October 27-29 include
NOAA active regions 10484, 10486, 10487, 10488, 10490, 10491, and
10492. These active regions, during the mentioned time period, were
a source of intensive solar eruptions and include a 4B/X17.2-class
solar flare in NOAA Active Region 10486 (Ambastha 2007; Kazachenko et
al., 2010). For each sunspot within an active region, a circular
aperture is chosen to enclose the sunspot. The aperture is centered on
the umbra and the sunspot is "uncurled” into a two-dimensional plot of
radial distance, in pixels, versus angular distance, in degrees. This
procedure follows the technique of Balasubramaniam (2002) and Brown
et al. (2003) and will yield intrinsic sunspot rotational velocities
through time for variable distances from the umbral center. We present
our initial comparisons of photospheric and chromospheric rotational
characteristics, the extent of coupling between the photosphere
and chromosphere, and rotational characteristics as a function of
sunspot size, age, solar latitude, and classification. Determining
the rotational nature of a large number of sunspots as a function of
various sunspot characteristics can lead to a greater understanding
of the effects of intrinsic sunspot rotations on the occurrences of
solar flares.
Title: Solar Oscillations And Acoustic Power Measured In H-alpha
Authors: Jackiewicz, Jason; Balasubramaniam, K.; McAteer, R.;
Jefferies, S. M.
Bibcode: 2011SPD....42.1731J
Altcode: 2011BAAS..43S.1731J
We present initial studies of the evidence of acoustic power in H alpha
data observed with the ISOON telescope. Uninterrupted times series
were obtained at 1-minute cadence of the H alpha intensity and Doppler
velocity signals of both quiet and active regions on the Sun. Spatial
and temporal power maps show enhanced contributions from a flaring
active region that is a strong function of frequency. Cross-correlations
and wave travel times are computed and give indications of the presence
of running waves below the acoustic cut-off frequency.
Title: Characterizing Chromospheric Flares and Sequential Brightenings
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, J.;
McAteer, J.; Milligan, R.
Bibcode: 2011SPD....42.2201K
Altcode: 2011BAAS..43S.2201K
Solar sequential chromospheric brightenings (SCBs) are typically
observed in conjunction with flares that have associated coronal mass
ejections (CMEs). To characterize these ephemeral events, we developed
automated procedures to identify and track subsections of large solar
flares and the SCBs using the ISOON telescope's H-alpha data. This
software package extracts physical quantities such as temporal variation
of flare and SCB intensities, apparent proper motion of the moving
ribbons, and the speed of SCB intensity propagation. Overlying the
extracted features onto complementary datasets, we obtain underlying
Doppler velocity and magnetic intensity measurements. We demonstrate
that flare ribbons can be fully characterized by subdividing them
into discrete flare kernels. We also present evidence that SCBs are
a different class of brightening than the flare ribbons.
Title: Development of a Statistical Diagnostic Scheme for Flare
Probability
Authors: Balasubramaniam, K. S.; Norquist, D. C.
Bibcode: 2010AGUFMSH43B1820B
Altcode:
Principal Component Analysis was applied to selected sequences of
Hydrogen-alpha images of solar active regions observed by the Improved
Solar Optical Observation Network (ISOON) telescope at Sacramento
Peak, NM at one-minute intervals. Resulting eigenvalues were used to
determine the explained variance by the corresponding eigenvectors with
elements for each ISOON measurement time. The subset of eigenvectors
accounting for 99.9% of the variance were used as the source of the
variable data in an application of multivariate discriminant analysis
using the Fisher’s Linear Discriminant (FLD) algorithm applied
to two groups. Independently obtained GOES x-ray flux measurements
at one-minute intervals for the same measurement times were used to
determine which group (non-flaring or flaring) the measurement time
was assigned to, using a flux threshold based on the background x-ray
flux from the day prior to the day of analysis. The product of the
FLD algorithm applied to the eigenvectors from several selected ISOON
measurement sequences was the discriminant vector (DV) consisting of
coefficients for each of the subset eigenvector elements. The DV was
then applied to same subset of eigenvector elements for an independent
ISOON sequence to diagnose the value of the FLD function, which was
used to determine the probability of flaring (0 - no likelihood of
flaring, 1 - full likelihood of flaring) at each independent sequence
measurement time. Results showed that for many of the image times,
the diagnosed flaring probability was able to indicate the presence
of flaring at the correct times of the image sequence. This flare/no
flare diagnostic scheme, if successfully projected forward in time,
might serve as a basis for short-term flare probability predictions.
Title: Properties of Solar Flares and Associated Sequential
Chromospheric Brightenings
Authors: Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; McNamara,
B. J.
Bibcode: 2010AGUFMSH43B1816K
Altcode:
Solar sequential chromospheric brightenings (SCBs) are observed
in conjunction with coronal mass ejection (CME) related flares. We
present results from automated procedures to identify characteristics
of large solar flares and flare associated SCBs. These procedures
extract physical quantities: temporal variation of flare kernel and
SCB relative intensities, relative energies of the bright kernels of
the flare, apparent proper motion of the moving ribbons and the rate
of SCB propagation. In two events, we observe multiple bursts of SCBs
as a function of time and distance. We present evidence that SCBs are a
different class of brightening than the flare ribbons and can be divided
into two distinct types. The propagation speeds of SCBs are comparable
to emerging CME speeds. We also observe an exponential decrease in
the SCB intensity as a function of time and distance from the flare
peak. The apparent motions of the flare ribbons are quantified and
related to the locus of propagating brightening in coronal loops. We
analyze H-α Doppler images and relate them to measured flare and
SCB characteristics.
Title: Solar Active Region Classification and Flare Forecasting
Authors: Crown, M.; Balasubramaniam, K. S.; Cooley, K.; Daniels, A.;
Mara, J.; Valdez, M.
Bibcode: 2010AGUFMSM54A..07C
Altcode:
There are two sunspot classification systems that are currently being
used to forecast the probability of a solar active region flaring,
the Mount Wilson magnetic classification system and the Modified Zurich
classification system. Once a solar active region emerges on the visible
solar disk, it is classified using both of these systems. An individual
active region's flaring probability is produced using a well-known
table of probabilities (based on the Modified Zurich system), and
these probabilities are modified using rules of thumb based on the
Mount Wilson system information. A study has been conducted taking
solar cycle 23 active regions, re-classifying these regions, and then
using the look-up table and legacy rule to provide a probability. These
probabilities were then compared to actual flare rates. The presentation
will discuss the issues with current classification systems, why look-up
table flare forecasting does not work, and where improvements to the
current classification systems can be made.
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
Bibcode: 2010ApJ...723..587B
Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s-1 ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.
Title: On the Doppler Shift and Asymmetry of Stokes Profiles of
Photospheric Fe I and Chromospheric Mg I Lines
Authors: Deng, Na; Prasad Choudhary, Debi; Balasubramaniam, K. S.
Bibcode: 2010ApJ...719..385D
Altcode: 2010arXiv1006.3579D
We analyzed the full Stokes spectra using simultaneous measurements
of the photospheric (Fe I 630.15 and 630.25 nm) and chromospheric
(Mg I b 2 517.27 nm) lines. The data were obtained with
the High Altitude Observatory/National Solar Observatory (HAO/NSO)
advanced Stokes polarimeter, about a near disk center sunspot region,
NOAA AR 9661. We compare the characteristics of the Stokes profiles
in terms of Doppler shifts and asymmetries among the three spectral
lines, helping us to better understand the chromospheric lines and
the magnetic and flow fields in different magnetic regions. The main
results are: (1) for the penumbral area observed by the photospheric Fe
I lines, Doppler velocities derived from Stokes I (ν i )
are very close to those derived from linear polarization profiles
(νlp) but significantly different from those derived from
Stokes V profiles (νzc), thus providing direct and strong
evidence that the penumbral Evershed flows are magnetized and mainly
carried by the horizontal magnetic component; (2) the rudimentary
inverse Evershed effect observed by the Mg I b 2 line
provides qualitative evidence on its formation height that is around
or just above the temperature minimum region; (3) νzc
and νlp in the penumbrae and νzc in the pores
generally approach their ν i observed by the chromospheric
Mg I line, which is not the case for the photospheric Fe I lines; (4)
the outer penumbrae and pores show similar Stokes V asymmetry behavior
that tend to change from positive values in the photosphere (Fe I lines)
to negative values in the low chromosphere (Mg I line); (5) the Stokes
V profiles in plage regions are highly asymmetric in the photosphere
and more symmetric in the low chromosphere; and (6) strong redshifts
and large asymmetries are found around the magnetic polarity inversion
line within the common penumbra of the δ spot. We offer explanations
or speculations to the observed discrepancies between the photospheric
and chromospheric lines in terms of the three-dimensional structure
of the magnetic and velocity fields. This study thus emphasizes the
importance of spectropolarimetry using chromospheric lines.
Title: Sunspot Characteristics Associated with Solar Flares
Authors: Kasper, Devin; Balasubramaniam, K. S.
Bibcode: 2010AAS...21542202K
Altcode: 2010BAAS...42..291K
Solar flares, as seen in the chromosphere and corona, mostly occur
in regions of sunspot activity as identified in the photosphere. The
purpose of this study was to understand and identify characteristics
of sunspots leading to solar flares. The parameters examined were the
penumbral area, umbral area, mean penumbral intensity, mean umbral
intensity and irradiance reduction due to sunspots. The temporal
fluctuations of these parameters were explored to identify their
relationship to the flaring situation. Trends were identified before
and after solar flares. The study concluded that while the penumbral
area, umbral area and irradiance showed promise as possible parameters
for predicting solar flares, particularly M-class flares. This poster
will discuss the results of these analyses and presents a basis from
which future work can be developed.
Title: Understanding the Physics of Sequential Chromospheric
Brightenings of the Sun Through Automated Recognition
Authors: Kirk, Michael S.; Balasubramaniam, K. S.; Jackiewicz, J.;
McNamara, B. J.
Bibcode: 2010AAS...21542206K
Altcode: 2010BAAS...42..292K
Wave-like disturbances are observed propagating along chromospheric
network lines in conjunction with energetic events such as solar flares,
prominence eruptions, and coronal mass ejections. These disturbances
are called sequential chromospheric brightenings (SCBs) and are thought
to be magnetic in origin. An automated method has been developed to
detect and track SCBs and the associated flare ribbons. Using H-alpha
images from the Improved Solar Observing Optical Network (ISOON)
telescope during previously identified SCB events in 2005, we have
developed an automated tracking algorithm that identifies and follows
the SCB event as well as the evolving flare ribbons. With bright-point
detection and tracking fully automated, we will be able to efficiently
identify and track both the evolution of the SCBs which are seen as
precursors to mass ejections, and the evolution of the ribbons within
the flare itself. From the classified bright-points and other available
observations, we will be able to characterize the flare's physical
nature: speed, distance traveled, changing brightness, and magnetic
field intensity. This poster presents the methodology developed to
measure these parameters. The ultimate objective of this work is to use
real-time image analysis in conjunction with this automated recognition
technique to characterize SCBs thereby giving some indication of the
nature of the subsequent solar eruption.
Title: The Variation of Solar Chromospheric H-alpha Plage 2002-2009
Authors: Balasubramaniam, K. S.
Bibcode: 2009AGUFMSH11A1492B
Altcode:
Solar Chromospheric Plages in H-alpha represent a thermal dissipative
response to the underlying magnetic field. In this study we track the
daily variation of active region and quiet-sun plages areas and the
underlying magnetic fields, during 2002-2009. In this poster, we present
the methodology used to understand this variation as a function of the
magnetic field. We present variations of plage intensities and ares over
the solar cycle and examine their cyclical and non-cyclical patterns.
Title: Observations of Large-Scale Dynamic Bubbles in Prominences
Authors: de Toma, G.; Casini, R.; Berger, T. E.; Low, B. C.; de Wijn,
A. G.; Burkepile, J. T.; Balasubramaniam, K. S.
Bibcode: 2009ASPC..415..163D
Altcode:
Solar prominences are very dynamic objects, showing continuous motions
down to their smallest resolvable spatial and temporal scales. However,
as macroscopic magnetic structures, they are remarkably stable during
their quiescent phase. We present recent ground-based and Hinode
observations of large-scale bubble-like, dynamic sub-structures that
form within and rise through quiescent prominences without disrupting
them. We investigate the similarities and differences of the Hinode
and ground-based observations and discuss their implications for models
of prominences.
Title: Automated Characterization of Sequential Chromospheric
Brightenings
Authors: Kirk, M. S.; Balasubramaniam, K. S.
Bibcode: 2009AGUFMSH23A1524K
Altcode:
Solar sequential chromospheric brightenings (SCBs) are noticed in
conjunction with energetic events such as solar flares, prominence
eruptions, and coronal mass ejections. A new automated method for
detecting and tracking SCBs and the associated flare ribbons is
presented. Using a series of H-α images taken by the Improved Solar
Observing Optical Network (ISOON) telescope during two SCB events
in May 2005, we have developed an automated tracking algorithm that
follows the SCB event as well as the evolving flare ribbons. With a
bright-point detection and tracking fully automated, we will be able
to efficiently identify and track both the evolution of the SCBs which
are seen as precursors to the flare and the evolution of the ribbons
within the flare itself. The tracked points allow us to characterize
each of the flare's components: speed, distance traveled, and changing
brightness. Automated recognition and characterization of SCBs will
eventually allow real-time image analysis of active regions for SCBs
which can give some indication of the nature of the flare to follow.
Title: Predictability of Solar Flares
Authors: Mares, Peter; Balasubramaniam, K. S.
Bibcode: 2009APS..APR.E1027M
Altcode:
Solar flares are significant drivers of space weather. With the
availability of high cadence solar chromospheric and photospheric data
from the USAF's Optical Solar PAtrol Network (OSPAN; photosphere and
chromosphere imaging) Telescope and the Global Oscillations Network
Group (GONG; photosphere magnetic imaging), at the National Solar
Observatory, we have gained insights into potential uses of the data for
solar flare prediction. We apply the Principal Component Analysis (PCA)
to parameterize the flaring system and extract consistent observables
at solar chromospheric and photospheric layers that indicate a viable
recognition of flaring activity. Rather than limiting ourselves to a
few known indicators of solar activity, PCA helps us to characterize
the entire system using several tens of variables for each observed
layer. The components of the Eigen vectors derived from PCA help us
recognize and quantify innate characteristics of solar flares and
compare them. We will present an analysis of these results to explore
the viability of PCA to assist in predicting solar flares.
Title: The Solar Moreton Wave Of 6 December 2006: Evidence For A
CME Driver
Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Cliver, E. W.;
Neidig, D. F.; Petrie, G. J. D.
Bibcode: 2009SPD....40.3703P
Altcode:
We analyze ground- and space-based observations of the major eruptive
flare and associated Moreton wave of 6 December 2006. The Moreton wave
spanned 270° in azimuth and exhibited a variable speed time profile
as it propagated away from the source region. The Hα wave traveled
1.2 Rsun from the S06E63 site of the eruption and white-light flare
toward the southwest in 15 minutes where it disrupted a large quiescent
filament. A preceding coronal wave was observed in a single He 10830 Å
image. Potential field analysis of the active region magnetic fields
and a comparison of ISOON images of the eruptive flare in line-center
Hα with off-band images of the wave indicate that the Moreton wave
was driven by a coronal mass ejection.
Title: Erupting Chromospheric Filaments
Authors: Balasubramaniam, K. S.; Cliver, E.; Pevtsov, A.; Martin,
S.; Panasenco, O.
Bibcode: 2009SPD....40.1010B
Altcode:
Erupting filaments are commonly associated with coronal mass
ejections. They represent the chromospheric structures most closely tied
to the underlying photospheric magnetic fields. We present an analysis
of the eruption of an unusually large filament on the SE quadrant of the
solar disc on 2003 June 11. The data are drawn from USAF/NSO Improved
Solar Observing Optical Network, Solar and Heliospheric Observatory,
and ground-based telescopes at NSO. The filament rises with an initial
slow speed of 6-7 km/s over a period of 2 hours and later erupts by
rapidly accelerating to 170 km/s second in the following 30 minutes. The
filament eruption is accompanied by a flare in a neighboring active
region. We trace morphological and topological changes in the filament
and overlying arcade before and during its eruption, and interpret
these changes in terms of physical structure of the filament and whole
filament system. The destabilization of the filament and its overlying
coronal arcade are related to interactions with a new emerging active
region, and adjacent active region.
Title: Great geomagnetic storm of 9 November 1991: Association with
a disappearing solar filament
Authors: Cliver, E. W.; Balasubramaniam, K. S.; Nitta, N. V.; Li, X.
Bibcode: 2009JGRA..114.0A20C
Altcode: 2009JGRA..11400A20C
We attribute the great geomagnetic storm on 8-10 November 1991 to a
large-scale eruption that encompassed the disappearance of a ~25° solar
filament in the southern solar hemisphere. The resultant soft X-ray
arcade spanned ~90° of solar longitude. The rapid growth of an active
region lying at one end of the X-ray arcade appears to have triggered
the eruption. This is the largest geomagnetic storm yet associated with
the eruption of a quiescent filament. The minimum hourly Dst value of
-354 nT on 9 November 1991 compares with a minimum Dst value of -161
nT for the largest 27-day recurrent (coronal hole) storm observed
from 1972 to 2005 and the minimum -559 nT value observed during the
flare-associated storm of 14 March 1989, the greatest magnetic storm
recorded during the space age. Overall, the November 1991 storm ranks
15th on a list of Dst storms from 1905 to 2004, surpassing in intensity
such well-known storms as 14 July 1982 (-310 nT) and 15 July 2000
(-317 nT). We used the Cliver et al. and Gopalswamy et al. empirical
models of coronal mass ejection propagation in the solar wind to
provide consistency checks on the eruption/storm association.
Title: Forecasting Frontiers Part I: Solar Drivers of Space Weather
Observations
Authors: Johnston, J. C.; Balasubramaniam, K. S.; Fry, C. D.; Kuchar,
T. A.; Webb, D. F.
Bibcode: 2008AGUFMSA51A1532J
Altcode:
The new AFRL Space Weather Forecasting Laboratory (SWFL) seeks to
understand, explore and research the elements involved in developing
a successful program of space situational awareness. Originating
with the primary solar drivers, space weather envelops a continuum
of critically connected heliospheric, ionospheric and thermospheric
regimes. Within each regime, a successful space weather awareness and
forecast situation requires a multi- pronged effort that spans areas
of reliable monitoring, data acquisition and its timely availability,
fusing of the data with physical, heuristic and numerical models, and
timely now-cast and forecast abilities. In this presentation we will
address solar drivers. We will illustrate the need for monitoring solar
surface phenomena. Within the realm of solar drivers, eruptive solar
activity comprises of primarily flares and mass ejections, which are,
in turn, driven by local physical conditions of constantly competing
magnetic, hydrodynamic and thermodynamic forces. These physical
conditions span the entire solar atmosphere from below the visible solar
photosphere through chromosphere to corona. We will address the need for
timely monitoring of physical conditions leading to these phenomena and
the diagnostic potential of various seemingly heterogeneous physical
quantities connected to the resultant eruptive activity. A discussion
of time-scales of phenomena, and resources/tools required for timely
monitoring, cadence, tolerances to latency in data availability,
testing/evaluation of physical and data models and the viability of
a deterministic now-cast and forecast models will be covered.
Title: Challenges to Solar Flare Prediction
Authors: Balasubramaniam, K. S.
Bibcode: 2008AGUFMSA41B..01B
Altcode:
Solar flares are a significant driver of violent space weather. With
the availability of high cadence photospheric and chromospheric data
from the USAF's Optical Solar PAtrol Network (OSPAN) Telescope at the
National Solar Observatory, we have gained insights into potential
uses of the data for solar flare prediction. We will consider the need
for timeliness and high cadence data. Using examples of active region
temporal evolutionusing measurements of the solar photosphere and its
magnetic fields,chromosphere and corona, we will explore the promises
for forecasting the onset of solar flares.
Title: Challenges to Solar Flare Prediction
Authors: Balasubramaniam, K. S.
Bibcode: 2008AGUFMSA41B0100J
Altcode:
Solar flares are a significant driver of violent space weather. With
the availability of high cadence photospheric and chromospheric data
from the USAF's Optical Solar PAtrol Network (OSPAN) Telescope at the
National Solar Observatory, we have gained insights into potential
uses of the data for solar flare prediction. We will consider the need
for timeliness and high cadence data. Using examples of active region
temporal evolution using measurements of the solar photosphere and its
magnetic fields,chromosphere and corona, we will explore the promises
for forecasting the onset of solar flares.
Title: Dual Height Spectropolarimetry Observations of Active Region
NOAA 9662
Authors: Choudhary, D.; Deng, N.; Balasubramaniam, K.
Bibcode: 2008AGUSMSP31B..06C
Altcode:
We present the results of the spectropolarimetry observations of
active region NOAA 9664 observed in spectral lines FeI 6302 and
Mgb2 5872 A. These spectral lines originate at photospheric and
lower chromospheric heights of solar atmosphere, respectively. The
active region was situated near the disk center at the time of our
observations. Among several interesting features, we observe three
compact, down-flow regions (each about two seconds in size) which
are near the magnetic neutral line. The Stokes V profiles at these
locations are normal in chromosphere but anomalous in photosphere. The
corresponding Stokes I profiles are symmetric in chromosphere and
highly asymmetric in the photosphere. We present the results of
bisector analysis of these profiles and discuss their significance in
the evolution of sunspot structure.
Title: Eruption Characteristics of a Large Filament
Authors: Balasubramaniam, K. S.
Bibcode: 2008AGUSMSP43A..05B
Altcode:
Erupting filaments are often precursors to mass ejections. We present
chromospheric observations of a large erupting filament observed on
November 7, 2003. Using trajectory tracking algorithms, we follow the
dynamics of this eruption over several hours, in an effort to understand
the structural reorganization of filaments during an eruption. This
analysis provides clues to the magnetic structure of filaments, and
a model for the expansion of conical structures containing twisted
magnetic fields.
Title: Evershed Flow, Oscillations, and Sunspot Structure
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Olmschenk, S.
Bibcode: 2008ASPC..383..279B
Altcode:
Using high resolution spectroscopy at high cadence, we probe
oscillatory properties of the Evershed effect flows. We employ
Doppler measurements in several spectral lines to show that the
Evershed flow is modulated at periods lasting a few tens of minutes,
at the photosphere and chromosphere. The phase of this modulation is
always outward propagating irrespective of whether the spectral line
originates in the photosphere or chromosphere. From a power-spectrum
analysis, we show that periods of peak power shift to longer periods as
magnetic field strength increases (going from the umbra to the outer
penumbra), at photospheric levels. At the chromosphere the periods
shift to longer periods as the magnetic field shifts from stronger to
weaker fields. An analysis of these phenomena and their influence on
the sunspot structure will be presented.
Title: Subsurface and Atmospheric Influences on Solar Activity
Authors: Howe, R.; Komm, R. W.; Balasubramaniam, K. S.; Petrie,
G. J. D.
Bibcode: 2008ASPC..383.....H
Altcode:
No abstract at ADS
Title: Evolution strategies optimization of the multiple Fabry-Perót
imaging interferometer for the advanced technology solar telescope
Authors: Robinson, Brian; Gary, G. Allen; Balasubramaniam, K. S.
Bibcode: 2008OptEn..47j3002R
Altcode:
No abstract at ADS
Title: Chromospheric observations of erupting filaments with the
Optical Solar Patrol Network (OSPaN) telescope
Authors: Cliver, Edward; Balasubramaniam, K. S.; Cliver, E. W.;
Engvold, O.; Pevtsov, A.; Martin, S.; Panasenco, O.
Bibcode: 2008cosp...37..562C
Altcode: 2008cosp.meet..562C
Using AFRL/NSO OSPaN telescope chromospheric images, we present movies
and analyses of the eruption of a quiescent filament (11 June 2003)
and an active region filament (13 May 2005). In both cases, widely
separated regions of the solar surface were affected by the eruptions,
either via the Moreton waves they generated (inferred from winking
filaments) or through direct magnetic connection (manifested by
sequential chromospheric brightenings). We investigate the topology
of the magnetic fields in which these eruptions occur and use Doppler
measurements to understand the dynamics of the eruptions.
Title: Sunspot Numbers and Sunspot Irradiance Reductions as Obtained
with OSPAN Semi- automatic Analysis
Authors: Balasubramaniam, K. S.; Neidig, D. F.; Radick, R. R.;
Henry, T.
Bibcode: 2007AGUFMSH13A1108B
Altcode:
The USAF/AFRL Optical Solar PAtrol Network telescope (OSPAN) acquires
true continuum solar images (0.08 Å bandwidth) in the optical
region(6303.15 Å). OSPAN analysis software includes semi-automatic
routines for measuring (1) sunspot counts, which we compare with
counts obtained by traditional methods, and (2) solar irradiance
reductions due tosunspot blocking. We present measurements of the
variation of irradiance reductions as a function of the solar cycle,
including examples of irradiance reduction due to sunspot activity
during solarcycle maximum. This work was supported by US Air Force
Office of Scientific Research (AFOSR).
Title: Semiempirical Models of the Solar Atmosphere. II. The Quiet-Sun
Low Chromosphere at Moderate Resolution
Authors: Fontenla, J. M.; Balasubramaniam, K. S.; Harder, J.
Bibcode: 2007ApJ...667.1243F
Altcode:
We present a new, one-dimensional model of the solar
atmosphere (called SRPM 305) at moderate angular resolution
(~1''-2''). Key characteristics of the SRPM 305
model include (1) a minimum temperature of ~3800 K at a gas pressure
of ~80 dyne cm-2 and (2) a rapid temperature rise above the
temperature-minimum layer that results in substantial overionization
of most elements when compared with LTE calculations. The model
calculations reproduce the ~4300 K minimum brightness temperature of
the UV continuum (between 1400-1500 Å) observed by SUMER and the ~4400
K observed minimum radio-continuum brightness temperature (between
wavelengths 0.01 and 100 mm). Neither the UV nor the radio continuum
bear on the low-temperature minimum value because their broad intensity
contribution functions cause the higher temperatures of the upper
chromospheric layers to effectively hide the low minimum temperature
region. The SRPM 305 model reproduces the observed intensities of CO
lines at 4.466 μm, at both the disk center and near the limb, by using
C and O abundances consistent with recent literature low values. The
model also reproduces observed intensities of C I spectral lines at
5381 and 8337 Å, CH lines at about 4306 Å, the CN band head at 3883
Å, and the O I lines at 7772, 7774, and 7776 Å, respectively. Using
the SRPM 305 model, we find no significant abundance variations
between the photosphere and the low chromosphere. Consequently,
the single-component model presented here matches several apparently
contradictory observations and thereby resolves the controversy about
the temperature minimum value.
Title: Multiheight Properties of Moving Magnetic Features
Authors: Choudhary, Debi Prasad; Balasubramaniam, K. S.
Bibcode: 2007ApJ...664.1228C
Altcode:
We report on spectropolarimetric and dynamical properties of a moving
magnetic feature (MMF) around a disk-center sunspot observed using
photospheric (Fe I λλ6301.5 and 6302.5) and lower chromospheric
(Mg b2 λ5172.7) lines. We find that there are 33%
fewer MMFs at the lower chromosphere compared to the photosphere,
implying a sophisticated magnetic field geometry of tight low-level
loops. A majority of bipolar MMFs are oriented with their neutral
line perpendicular to the radial direction. Their ``spot-ward''
component has the same polarity as the sunspot. The magnetic filling
factor is larger for all types of MMFs situated closer to the spot
than those situated further away. Bipolar MMFs have a larger filling
factor compared to the unipolar ones. Comparison of dI/dλ and Stokes V
profile suggests a large magnetic filling factor within the MMFs in the
photosphere. Traversing individual MMFs, the Stokes V profiles vary from
normal antisymmetric structures to multilobed anomalous profiles. The
chromospheric counterpart of multilobed and anomalous photospheric MMF
Stokes V profiles are normal and antisymmetric. This suggests that
magnetic loops corresponding to MMFs in the lower atmosphere are of
mixed polarity and perhaps twisted while they are relatively relaxed
in the corresponding upper atmosphere. The temporal evolution of the
MMFs shows a transition between anomalous and normal Stokes V profiles.
Title: Chromospheric Heating and Low-Chromosphere Modeling
Authors: Fontenla, J. M.; Balasubramaniam, K. S.; Harder, J.
Bibcode: 2007ASPC..368..499F
Altcode:
Updated modeling of the ``quiet'' Sun low chromosphere based on existing
observations show that at least all the data we examined in detail
is consistent with a single model that has a very low temperature
minimum and a sharp temperature increase above it. Such a model
explains simultaneously the deep CO lines observed on the disk and
off the limb, as well as the UV and radio continua and thus solves
the controversy regarding the minimum temperature without resorting
to ``bifurcation''. This results simply from considering both: the
spatial extent of the intensity contribution functions, and non-LTE. The
model also shows that the structure of the low-chromosphere cannot be
unambiguously inferred from any simple diagnostic but rather needs
to be examined by forward modeling with consideration of full-NLTE
radiative transfer and observations at many wavelengths. In addition,
the characteristics of this model are consistent with the magnetic
heating of the chromosphere. The mechanism proposed consists of small
scale magnetic fields and sudden triggering of their free-energy
dissipation by a plasma instability starting at the base of the
chromospheric plateau. As a result of such a mechanism a complex spatial
structure would result in the upper chromosphere that can hardly be
explained in terms of shocks but instead shows magnetic patterns.
Title: Moreton Waves And Filament Eruptions
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.
Bibcode: 2007AAS...210.2504B
Altcode: 2007BAAS...39..131B
Moreton waves are traditionally associated with large flares, and may
accompany filament and mass ejections. Using high-spectral resolution
and high cadence full-disk chromospheric imaging measurements, we track
two exceptional Moreton waves (2003 October 29 and 2006 December 6)
to understand the nature of this phenomenon. We employ arguments drawn
from spectroscopy, wave propagation and formation of prominences to
affirm the location of Moreton waves to coronal heights. We present
evidence that the Moreton wave sweeps filamentary material and thus
became visible in chromospheric spectral line. We suggest a model to
describe the associations between the flares, filament eruptions and
coronal mass ejections.
Title: Spectropolarimetric Signatures of Down-flows About Magnetic
Boundaries
Authors: Choudhary, Debi P.; Balasubramaniam, K.
Bibcode: 2007AAS...210.4504C
Altcode: 2007BAAS...39..160C
We analyze spectropolarimetric signatures across magnetic boundaries
of opposite polarities at the photosphere. HAO/NSO Advanced Stokes
Polarimeter measurements were made at the NSO/Dunn Solar Telescope
of photospheric spectral lines (FeI 6301.2 A and 6302.3 A). These
observations (NOAA 9662; 2001 October 16-17) about a corridor of a
magnetic inversion line near the edge of a disk-center sunspot show
strong red-asymmetry. Several (at least six) such discrete and compact
sites of both polarities, near these magnetic neural lines, show such
red-asymmetry. Strong down-flows associated with these unusual Stokes
polarization profiles are associated with these asymmetries. We discuss
detailed properties and possible origin of the observed profiles.
Title: Are Moreton Waves Coronal Phenomena?
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.
Bibcode: 2007ApJ...658.1372B
Altcode:
We report on permeability characteristics of the upper solar atmosphere
due to the progression of a Moreton wave. An exceptional Moreton wave
is tracked to cover most of the Sun, following an unusually large
solar X-ray flare observed on 2003 October 29. Using Hα intensity
and Doppler measurements, the Moreton wave is tracked for as long as
12 minutes. Moving outward, the wave circumnavigates strong-field
active regions. The wave sweeps through solar magnetic neutral
lines, disrupting material from filament and filament channels,
thereby accentuating the visibility of the wave. We establish that
the requirement for the visibility of a Moreton wave is the necessary
presence of higher density material in the layers of the corona, besides
reaffirming that Moreton waves are observed only when the speed of the
disturbance exceeds Mach 2. We suggest that the cause can be a removal
of significant amount of material from the solar upper atmosphere due
to a coronal mass ejection.
Title: Sequential chromospheric brightenings: The case for
chromospheric evaporation
Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Hock, Rachel A.
Bibcode: 2007AdSpR..39.1781P
Altcode:
Sequential chromospheric brightenings (SCBs [Balasubramaniam, K.S.,
Pevtsov, A.A., Neidig, D.F., Cliver, E.W., Thompson, B.J., Young, C.A.,
Martin, S.F., & Kiplinger, A., 630, 1160, 2005.]) are observed
in conjunction with some strong solar flares, prominence eruptions,
and coronal mass ejections (CMEs). SCBs are seen as wave-like trains
of increased brightening of chromospheric network elements propagating
away from the site of eruption (flare/CME). Although network magnetic
field usually has mixed polarity, only areas of one (prevailing)
polarity are seen as SCBs; there are no brightenings in neighboring
network elements of opposite (minor) polarity. This polarity rule,
relative timing of SCBs in respect to beginning of flare/CME, and
their location in respect to overall topology of each event suggest
that SCBs may be caused by high energy particles precipitating from
the reconnection site at the tail of CME. In this work we use TRACE,
SOHO/MDI, and H-alpha OSPAN data to demonstrate that indeed SCB
locations exhibit several properties of chromospheric evaporation.
Title: Multi-Line Spectro-Polarimetry of Filaments
Authors: Balasubramaniam, K. S.; Sankarasubramanian, K.; Pevtsov, A. A.
Bibcode: 2006ASPC..358...68B
Altcode:
We present a spectro-polarimetric study of magnetic structures
supporting quiescent filaments, using the combined DLSP-Phase I and
ASP observations. The observations were performed using the spectral
lines Fe I 6301.5 Å and 6302.5 Å at the photospheric level, and Mg
I 5172.7 Å and H I 6562.8 Å (Hα) at the chromospheric level. Using
non-linear, force-free extrapolation models, we reconstruct the 3D
magnetic loop-geometry and compare the viability of the magnetic
filament dips as the true location of the filaments, as seen in Hα.
Title: 3-D Structure of Sunspots Using Imaging Spectroscopy
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2006ASPC..354..237B
Altcode:
We use the Interferometric BIdimensional Spectrometer (IBIS) of the
INAF/Arcetri Astrophysical Observatory and installed at the National
Solar Observatory (NSO) Dunn Solar Telescope, to understand the
structure of sunspots. Using the spectral lines Fe I 6301.5 Å, Fe II
7224.4 Å, and Ca II 8542.6 Å, we examine the spectroscopic variation
of sunspot penumbral and umbral structures at the heights of formation
of these lines. These high resolution observations were acquired on
2004 July 30 -- 31, of active region NOAA 10654, using the high order
NSO adaptive optics system. We map the spatio-temporal variation of
Doppler signatures in these spectral lines, from the photosphere to
the chromosphere. From a 70-minute temporal average of individual
32-second cadence Doppler observations we find that the averaged
velocities decrease with height. They are about 3.5 times larger in the
deeper photosphere (Fe II 7224.4 Å; height-of-formation ≈ 50 km)
than in the upper photosphere Fe I 6301.5 Å; height-of-formation
≈ 350 km), There is a remarkable coherence of Doppler signals
over the height difference of 300 km. From a high-speed animation
of the Doppler sequence we find evidence for what appears to be
ejection of high speed gas concentrations from edges of penumbral
filaments into the surrounding granular photosphere. The Evershed
flow persists a few arcseconds beyond the traditionally demarcated
penumbra-granulation boundary. We present these and other results and
discuss the implications of these measurements for sunspot models.
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: Challenges for Chromospheric Spectropolarimetry
Authors: Balasubramaniam, K. S.
Bibcode: 2006IAUJD...3E..76B
Altcode:
The solar chromosphere is the most immediate and intermediary layer
where competitive magnetic forces begin to dominate their thermodynamic
counterparts. The chromosphere quickly responds to magnetic energy
release processes, and is one of the early indicators of this energy
release. Hence, understanding the nature of the magnetic field at
the chromospheric layer is vital. Measurements of the chromospheric
magnetic field, via spectropolarimetry polarimetry are necessary to
constrain 3-D models of the magnetic field geometry via extrapolation
methods. In this presentation we will describe the challenges for
measuring and inferring the chromospheric magnetic field in solar-disk
measurements. Examples of spectropolarimetric measurements in the
spectral lines of CaII 8542 Å and HI 6563 Å will be illustrated.
Title: Dynamical properties of moving magnetic features of sunspots
Authors: Choudhary, Debi P.; Balasubramaniam, K. S.
Bibcode: 2006IAUJD...3E..74C
Altcode:
We have observed the active region NOAA 9662 on 16 and 17 October 2001
using the Advanced Stokes Polarimeter (ASP) at Richard B. Dunn Solar
Telescope of National Solar Observatory. The ASP recorded all the full
Stokes profiles in photospheric FeI 630.2 nm and Chromospheric Mgb2
517.2 nm lines simultaneously. During our observations, the active
region was located near the centre of solar disk. Combining the high
resolution magnetograms obtained with the Michelson Doppler Imager
on-board the Solar Heliospheric observatory; we determine the dynamical
properties of moving magnetic features (MMF) around the prominent
leading spots of the active region. In this paper we summarize the
three dimensional structure of the MMFs and their photospheric and
chromospheric dynamical properties.
Title: Evidence for a Siphon Flow Ending near the Edge of a Pore
Authors: Uitenbroek, H.; Balasubramaniam, K. S.; Tritschler, A.
Bibcode: 2006ApJ...645..776U
Altcode:
Observations of NOAA AR 9431, taken with the Vacuum Tower at Kitt
Peak on 2001 April 18 in the Ca II 854.21 nm line in both circular
polarizations, show evidence for a strong supersonic downflow ending
near the edge of a magnetic pore. The observed supersonic motion is
interpreted as a siphon flow along a magnetic loop connecting a patch
of weaker field to the pore of opposite polarity in the same active
region. The 854.21 nm line data reveal the upflow at one footpoint of
the loop, as well as the acceleration of the flow toward the footpoint
at the pore, where the flow reaches line-of-sight velocities of well
over 20 km s-1, substantially larger than the critical
speed. Numerical radiative transfer modeling of the 854.21 nm line
indicates the presence of a strong discontinuity in the flow velocity,
which we interpret as evidence for a tube shock in the downwind leg
of the siphon.
Title: Dynamical Properties Of Moving Magnetic Features Of Sunspots
Authors: Choudhary, Debi P.; Balasubramaniam, K.
Bibcode: 2006SPD....37.3404C
Altcode: 2006BAAS...38..259C
We have observed the active region NOAA 9662 on 16 and 17 October 2001
using the Advanced Stokes Polarimeter (ASP) at Richard B. Dunn Solar
Telescope of National Solar Observatory. The ASP recorded all the full
Stokes profiles in photospheric FeI 630.2 nm and Chromospheric Mgb2
517.2 nm lines simultaneously. During our observations, the active
region was located near the center of solar disk. Combining the high
resolution magnetograms obtained with the Michelson Doppler Imager
on-board the Solar Heliospheric observatory; we determine the dynamical
properties of moving magnetic features (MMF) around the prominent
leading spots of the active region. In this paper we summarize the
three dimensional structure of the MMFs and their photospheric and
chromospheric dynamical properties.
Title: Imaging Spectroscopy Of Sunspots Using IBIS
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2006SPD....37.0712B
Altcode: 2006BAAS...38..229B
We use the Interferometric BIdimensional Spectrometer (IBIS) of
the INAF/Arcetri Astrophysical Observatory and installed at the
National Solar Observatory (NSO) Dunn Solar Telescope, to understand
the structure of sunspots. These high resolution observations were
acquired on 2004 July 30-31, of active region NOAA 10654, using the
high order NSO adaptive optics system. We map the spatio-temporal
variation of the penumbral Doppler signatures in three spectral
lines, FeI 6301.5 Å, FeII 7224.4 Å, and CaII 8542.6 Å, from the
photosphere to the chromosphere. From a 70-minute temporal average
of individual 32-second cadence Doppler observations we find that
the averaged velocities decrease with height, about 3.5 times larger
in the deeper photosphere (FeII 7224.4 Å height-of-formation ≈50
km) than in the upper photosphere FeI 6301.5 Å height-of-formation
≈350 km), There is a remarkable coherence of Doppler signals over
the height difference of 300 km. From a high-speed animation of the
Doppler sequence we find evidence for what appears to be ejection of
high speed gas concentrations from edges of penumbral filaments into
the surrounding granular photosphere. The Evershed flow persists a few
arcseconds beyond the traditionally demarcated penumbra-granulation
boundary. We present these and other results and discuss implications
of these measurements for sunspot models.
Title: The Great Geomagnetic Storm of 9 November 1991: Origin in a
Disappearing Solar Filament
Authors: Cliver, E. W.; Nitta, N.; Balasubramaniam, K.; Li, X.
Bibcode: 2006AGUSMSH43A..06C
Altcode:
The largest geomagnetic storms are characteristically associated with
major solar flares. The great storm of 9 November 1991 (Dst = -375 nT)
provides an exception to this rule of thumb. It is ranked tenth of the
largest Dst storms from 1932-2002, surpassing in intensity such well
known events as 14 July 1982 and 16 July 2000. The November 1991 storm
can be traced to a large disappearing solar filament from the southeast
quadrant late on 5 November. The filament was located outside of an
active region and its disappearance was well observed in both H-alpha
and soft X-rays. The associated long-duration 1-8 Angstrom event had a
C5 peak. This solar-terrestrial event indicates that neither a large
complex active region nor an intense solar flare is a requirement
for even first rank geomagnetic storms, thus providing insight to the
physics of such events while making their prediction more difficult.
Title: Advanced technology solar telescope multiple Fabry-Pérot
interferometer telecentric optical design
Authors: Robinson, Brian M.; Balasubramaniam, K. S.; Gary, Gilmer A.
Bibcode: 2006OptEn..45b3001R
Altcode:
We present four preliminary designs for a telecentric optical
train supporting the Advanced Technology Solar Telescope (ATST)
multiple Fabry-Pérot interferometer (MFPI), which is to be used as
an imaging spectrometer and imaging spectropolarimeter. The point
of departure for all three designs is the F/40 telecentric image
at the Coudé focus of the ATST. The first design, representing the
high-spectral-resolution mode of operation, produces an intermediate
F/300 telecentric image within the triple étalon system and a 34-arcsec
field of view (FOV). The second design, intermediate between high- and
low-spectral-resolution modes of operation, produces an intermediate
F/150 telecentric image at the étalons and a 1.1-arcmin FOV. The
third and fourth designs each represent a low-resolution mode of
operation, producing an F/82 telecentric image at the étalons and
a 2-arcmin FOV. Each design results in good telecentricity and image
quality. Departures from telecentricity at the intermediate image plane
cause field-dependent shifts of the bandpass peak, which are negligible
compared to the bandpass FWHM. The root mean square (rms) geometric spot
sizes at the final image plane fit well within the area of a camera
pixel, which is itself in accordance with the Nyquist criterion, half
the width of the 28-µm-wide resolution element (as determined from
the diffraction limit of the ATST). For each configuration, we also
examine the impact that the Beckers effect (the pupil apodization
caused by the angle-dependent amplitude transmittance of the MFPI)
has on the image quality of the MFPI instrument.
Title: Sequential Chromospheric Brightenings as Signature of
Chromospheric Evaporation
Authors: Pevtsov, A.; Balasubramaniam, K.
Bibcode: 2006cosp...36.3671P
Altcode: 2006cosp.meet.3671P
Sequential Chromospheric Brightennings SCBs Balasubramaniam et
al 2005 are observed in conjunction with some strong solar flares
prominence eruptions and coronal mass ejections CMEs SCBs are seen as
wave-like trains of increased brightenning of chromospheric network
elements propagating away from the site of eruption flare CME Although
network magnetic field usually has mixed polarity only areas of one
polarity prevailing or unbalanced field are seen as SCBs there are no
brightenings in neighboring network elements of opposite minor polarity
This polarity rule relative timing of SCBs in respect to beginning
of flare CME and their location in respect to overall topology of
each event suggest that SCBs may be caused by high energy particles
precipitating from the reconnection site at the tail of CME In this work
we use TRACE SOHO MDI and H-alpha ISOON data to demonstrate that indeed
SCB locations exhibit several properties of chromospheric evaporation
Title: Large scale solar chromospheric eruptive activity - a signature
of magnetic reconnection
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Hock,
R. A.
Bibcode: 2006ilws.conf...65B
Altcode:
A new class of large-scale solar chromospheric eruptive activity,
sequential chromospheric brightenings (SCBs), has been reported by
Balasubramaniam et al. (2005). SCBs are chromospheric network points
(outside of active regions) that sequentially brighten over a narrow
path of chromospheric network points. SCBs appear as single or multiple
trains of brightenings, the underlying magnetic poles of each train
having the same (negative or positive) polarity. SCBs may be associated
with the following phenomena: solar flares, filament eruptions, CMEs,
disappearing transequatorial loops, Moreton and EIT waves. We present
an understanding of SCBs and their place in respect to these related
eruptive phenomena.
Title: Case Study of A Sequential Chromospheric Brightening (SCB)
Associated with May 6, 2005 event.
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Hock, R. A.
Bibcode: 2005AGUFMSH13A0282B
Altcode:
A sequential chromospheric brightening on May 6, 2005 was accompanied
by a long duration event, LDE (16:00 - 23:00 UT). Using data from ISOON/
H-alpha, TRACE (171 A), and SOHO/MDI (magnetograms) missions, we present
a detailed sequential study of this event that includes large scale
coronal disturbances(TRACE 171 A), ribbon-ed flares (ISOON & TRACE),
large scale motion of magnetic fields (SOHO/MDI), filament eruptions
(ISOON & TRACE), flares, and post-flare loops (TRACE). This event
presents a good example in the continuity of events comprising an
LDE. We present a model of the eruptive process of this LDE.
Title: High Resolution Optical Spectroscopy, Spectropolarimetry and
Spectral Imaging of Filament and Flaring Atmospheres
Authors: Keil, S. L.; Balasubramaniam, K. S.
Bibcode: 2005AGUFMSH41B1129K
Altcode:
Narrow-band spectral imaging, and Zeeman Stokes polarimetry of the
photosphere and chromosphere helps to understand the nature of twisted
magnetic fields and their propagation into the chromosphere. We will
discuss high resolution, multi-spectral diagnostics using optical
spectroscopy, imaging and spectropolarimetric techniques as applied
to filament and flaring atmospheres. We trace the twists in magnetic
fields through the trail of evidence it leaves at various levels of the
atmosphere, as it propagates upward of the photosphere. The diagnostic
tools used for this purpose include magnetic and velocity fields at
the photosphere and lower chromosphere (Hα), and velocities in the
upper chromosphere (Ca II~K line). We deduce the structure of magnetic
fields, their relationship to the formation of the filament structure,
and magnetic channels.
Title: ISOON H-alpha Survey of Sequential Chromospheric Brightenings
Authors: Hock, R.; Balasubramaniam, K. S.; Pevtsov, A. A.
Bibcode: 2005AGUFMSH13A0281H
Altcode:
Balasubramaniam et al. (2005, ApJ, 630, 1160) described a new
phenomenon, sequential chromospheric brightenings (SCBs), associated
with eruption of a transequatorial loop and a CME. We present a
detailed survey of SCBs between December 2000 - May 2005. From this
survey we have identified 17 SCBs observed during this period. We
discuss the relationship between SCBs, and filament eruptions,
coronal mass ejections (CME), and flares. The data were drawn from
ISOON, SOHO/LASCO, and NOAA/GOES, and RHESSI missions. We find that:
all SCBs are accompanied by filament eruption or disappearance; SCBs
are more likely to be longer in duration than associated flares;
and a large fraction of the SCBs (71%) are associated with CMEs.
Title: Sequential Chromospheric Brightenings beneath a Transequatorial
Halo Coronal Mass Ejection
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Cliver,
E. W.; Thompson, B. J.; Young, C. A.; Martin, S. F.; Kiplinger, A.
Bibcode: 2005ApJ...630.1160B
Altcode:
Analyses of multiwavelength data sets for a solar eruption at ~21:30
UT on 2002 December 19 show evidence for the disappearance of a
large-scale, transequatorial coronal loop (TL). In addition, coronal
manifestations of the eruption (based on SOHO EIT and LASCO images)
include large-scale coronal dimming, flares in each associated active
region in the northern and southern hemispheres, and a halo CME. We
present detailed observations of the chromospheric aspects of this
event based on Hα images obtained with the ISOON telescope. The
ISOON images reveal distant flare precursor brightenings, sympathetic
flares, and, of most interest herein, four nearly cospatial propagating
chromospheric brightenings. The speeds of the propagating disturbances
causing these brightenings are 600-800 km s-1. The inferred
propagating disturbances have some of the characteristics of Hα
and EIT flare waves (e.g., speed, apparent emanation from the flare
site, subsequent filament activation). However, they differ from
typical Hα chromospheric flare waves (also known as Moreton waves)
because of their absence in off-band Hα images, small angular
arc of propagation (<30°), and their multiplicity. Three of
the four propagating disturbances consist of a series of sequential
chromospheric brightenings of network points that suddenly brighten in
the area beneath the TL that disappeared earlier. SOHO MDI magnetograms
show that the successively brightened points that define the inferred
propagating disturbances were exclusively of one polarity, corresponding
to the dominant polarity of the affected region. We speculate that
the sequential chromospheric brightenings represent footpoints of
field lines that extend into the corona, where they are energized in
sequence by magnetic reconnection as coronal fields tear away from
the chromosphere during the eruption of the transequatorial CME. We
report briefly on three other events with similar narrow propagating
disturbances that were confined to a single hemisphere.
Title: Triple Fabry-Pérot Imaging Interferometer for High Resolution
Solar Spectroscopy using the ATST
Authors: Robinson, B. M.; Gary, G. A.; Balasubramaniam, K. S.
Bibcode: 2005AGUSMSP34A..05R
Altcode:
We present a telecenrically mounted triple Fabry-Pérot imaging
interferometer for the NSOs Advanced Technology Solar Telescope
(ATST). It consists of three Fabry-Pérot etalons and the feed and
imaging optics. This system provides high throughput, flexibility
and breadth of operation when compared to other spectroscopic
imaging systems. It can operate in four distinct modes: as a
spectro-polarimeter, a filter-vector magnetograph, an intermediate-band
imager, and broadband high-resolution imager. In the proposed
telecentric mount configuration, the transmittance of the etalon system
is not a function of position in the field, so that instantaneous
spectroscopic measurements can be performed across the entire field
of view; however, the transmission peak of the interferometer is
broadened. Mitigation of this broadening requires a low F# image at
the etalons. Together with the requirement that the field of view be
large enough to observe large-scale processes in the solar atmosphere,
this limitation dictates that the diameter of the etalons have a large
aperture. Specifically, for a spectrographic passband full-width at
half-maximum (FWHM) of around 2 pm, and entrance pupil diameter of 4 m,
and a field of view of 35", the required etalon diameter is around 200
mm. This is beyond the size of current Fabry-Pérot etalons and near
the current projected limit of manufacturability. The development
of this instrument will bring these large etalons to realization
and take Fabry-Pérot imaging interferometry to the next level of
operational capability within telescopes of large aperture. This
instrument will provide spectral, spatial, and temporal resolution
which is not currently available to large aperture solar astronomy,
but which is necessary, in conjunction with the new class telescopes,
to the continuing discovery of laws that govern the dynamics of the sun
and the earth-sun connection. The resolution afforded by higher aperture
telescopes and instrumentation will give scientists new insight into
the magnetohydrodynamic processes occurring on the Sun via simultaneous
spectral and spatial measurements across the entire field of view. We
will describe the optical train supporting the filter system and the
expected imaging performance. We will analyze the effects of spectral
resolution of the instrument due etalon spacing parameters, optical
configuration, and the plate defect finesse. We present calculations of
the pupil apodization for three modes of operation and the consequences
for the imaging and spectroscopic performance of the system; and a
treatment of noise contributions from the parasitic off-band spectral
orders and ghost images arising from multiple reflections within the
etalon system.
Title: First-Light Instrumentation for the Advanced Technology
Solar Telescope
Authors: Rimmele, T.; Balasubramaniam, K.; Berger, T.; Elmore, D.;
Gary, A.; Keller, C.; Kuhn, J.; Lin, H.; Mickey, D.; Pevtsov, A.;
Robinson, B.; Sigwarth, M.; Soccas-Navarro, H.
Bibcode: 2005AGUSMSP34A..03R
Altcode:
The 4m Advanced Technology Solar Telescope (ATST) is the next
generation ground based solar telescope. In this paper we provide
an overview of the ATST post-focus instrumentation. The majority of
ATST instrumentation is located in an instrument Coude lab facility,
where a rotating platform provides image de-rotation. A high order
adaptive optics system delivers a corrected beam to the Coude lab
facility. Alternatively, instruments can be mounted at the Nasmyth
focus. For example, instruments for observing the faint corona
preferably will be mounted at Nasmyth where maximum throughput
is achieved. In addition, the Nasmyth focus has minimum telescope
polarization and minimum stray light. We give an overview of the
initial set of first generation instruments: the Visible-Light
Broadband Imager (VLBI), the Visible Spectro-Polarimeter (ViSP),
the Near-IR Spectro-Polarimeter (NIRSP), which includes a coronal
module, and the Visible Tunable Filter. We also discuss the unique and
efficient approach to the ATST instrumentation, which builds on the use
of common components such as detector systems, polarimetry packages
and various opto-mechanical components. For example, the science
requirement for polarimetric sensitivity (10-5 relative to intensity)
and accuracy (5'10-4 relative to intensity) place strong constraints
on the polarization analysis and calibration units. Consequently,
these systems are provided at the facility level, rather than making
it part of the requirement for each instrument.
Title: Photospheric and Chromospheric structure of Sunspots using
IBIS.
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2005AGUSMSP11A..04B
Altcode:
We use the Interferometric BIdimensional Spectrometer (IBIS) of the
INAF/Arcetri Astrophysical Observatory and installed at the National
Solar Observatory's (NSO) Dunn Solar Telescope, to understand the
structure of sunspots. Using the spectral lines FeI 6301.5Å, FeII
7224.4Å and CaII 8542.6Å, we examine the spectroscopic variation of
sunspot penumbral and umbral structures about the heights of formation
of these lines. Simultaneous white-light imaging data helps us to
register and track the images. We map the spatio-temporal variation
of Doppler signatures in these spectral lines, from the photosphere
to the chromosphere, and discuss the implication of these variations
for sunspot models. These high resolution observations were acquired
on 2004 July 30-31, on a sunspot NOAA 10654, using the higher order
NSO adaptive optics system.
Title: Spectro-polarimetry of the G band
Authors: Uitenbroek, H.; Balasubramaniam, K.; Tritschler, A.
Bibcode: 2005AGUSMSP41B..03U
Altcode:
Narrow-band filter imaging in the G band at 430 nm has been used to
track the evolution of small-scale magnetic field elements for more
than two decades. Because of the presence of many lines of the CH
molecule, and the relatively high contrast at this short wavelength
the G-band region is exceptionally suitable for this task. However,
despite the frequent use of G-band brightness as magnetic field proxy
it has not yet been well established what the precise mechanism is that
makes the small scale magnetic elements appear bright. In particular,
it is unclear why there is no one-to-one correlation between G-band
brightness and magnetic field, as established from co-spatial
magnetograms in atomic lines. To obtain a better understanding of
the elusive G-band brightening mechanism we obtained high spatial-
and spectral resolution spectra of the G-band region in Stokes I and V
at the Dunn Solar Telescope on Sacramento Peak. We use the molecular
Zeeman effect to determine line-of-sight magnetic field strength
directly in the CH lines that provide most of the opacity in the G
band, avoiding difficulties with co-aligning images and magnetograms
taken seperately. We compare our observations with radiative transfer
modeling of the Stokes profiles in snapshots of a magneto-hydrodynamic
simulation of solar convection.
Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
J.; Balasubramaniam, K. S.
Bibcode: 2005ApJ...621L.145L
Altcode:
We report on spectropolarimetric observations of Hα in prominences
made with the Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires and the High Altitude Observatory/Advanced
Stokes Polarimeter. Stokes Q and U show the expected profile shape from
resonance scattering polarization and the Hanle effect. In contrast,
most of the time, Stokes V does not show the antisymmetric profile shape
typical of the Zeeman effect but a profile that indicates the presence
of strong atomic orientation in the hydrogen levels, to an extent that
cannot be explained by invoking the alignment-to-orientation transfer
mechanism induced by the prominence magnetic field. We found that the
largest signal amplitudes of Stokes V (comparable to that of Stokes
Q and U) could be produced by a process of selective absorption of
circularly polarized radiation from the photosphere, which requires
that the prominence be in the vicinity of an active region. Although
recent observations of active region filaments indicate such a
selective absorption mechanism as a plausible explanation of the
anomalous signals observed, the particular set of conditions that
must be met suggest that a different explanation may be required
to explain the almost ubiquitous symmetric V signal observed in Hα
prominences. Therefore, we speculate that an alternative mechanism
inducing strong atomic orientation at the observed level could be due
to the presence of electric fields inducing an electric Hanle effect
on Hα. Although we are still working toward a careful modeling of
this effect, including both electric and magnetic fields, we present
some preliminary considerations that seem to support this possibility.
Title: PCA-Interpolation Methods for Inversion of Solar Stokes
Profiles. I. Inversion of Photospheric Profiles
Authors: Eydenberg, M. S.; Balasubramaniam, K. S.; López Ariste, A.
Bibcode: 2005ApJ...619.1167E
Altcode:
We present a method for the analysis of solar Stokes profiles based on
the technique of principal component analysis (PCA). We consider the
development of a PCA/interpolation technique for obtaining estimates of
the solar magnetic field vector when the underlying physical parameter
distribution is not well determined. Unlike previous applications
of PCA, we consider separate distributions of the PCA components as
applied to the source of the underlying plasma, namely, the umbra,
penumbra, and quiet photosphere. We also isolate the PCA for the Fe I
λ6301.5 line. In some previous work, PCA was applied to the entire
6300-6305 Å spectral region that includes the telluric lines. The
method is tested on photospheric (Fe I λ6301.5) observations of NOAA
Active Region 9240 and compared with the results of the traditional
High Altitude Observatory Milne-Eddington inversion code. We also
consider a PCA-perturbation analysis of the data and how it can assist
the interpretation of the results, discuss current challenges faced by
the inversion codes, and suggest important areas for future development.
Title: Asymmetric Stokes-V Profiles at the Penumbral Boundary of
a Sunspot
Authors: Choudhary, D. P.; Balasubramaniam, K. S.; Suematsu, Y.
Bibcode: 2004ASPC..325..137C
Altcode:
We present the spectropolarimetric measurements of a sunspot
situated near central meridian disk passage. The sunspot was of
positive polarity with several opposite polarity magnetic elements
at and beyond the penumbral boundary. The Hα images of the sunspot
show bright emission regions near the penumbral boundary towards the
sun-center, which was of opposite polarity to the main spot. Doppler
velocities determined by measuring the center-of-gravity (COG) of the
Stokes-I profile, in general, agree with Evershed flow. In addition,
it shows strong flows in the penumbra. The velocities derived from
zero-crossing wavelengths of Stokes-V profiles show strong downflows
at the penumbral boundary. Double-lobed Stokes-V profiles are observed
at locations where penumbral fibrils terminate coinciding with Hα
plages. Double lobed profiles have an unshifted component similar to
the Stokes-V profiles of the sunspot penumbra and a shifted component
with a velocity of about 5 kmps. The amplitude of the second component
increases along the penumbral fibril as a function of the distance from
the center of the sunspot. In this paper we present the preliminary
results and propose to observe with the SolarB Solar Optical Telescope
(SOT) for understanding the nature of emerging flux near the sunspots.
Title: Spectro-polarimetry of the G band
Authors: Uitenbroek, H.; Balasubramaniam, K. S.
Bibcode: 2004AAS...205.4302U
Altcode: 2004BAAS...36.1411U
Narrow-band filter imaging in the G band at 430 nm has been used to
track the evolution of small-scale magnetic field elements for more
than two decades. Because of the presence of many lines of the CH
molecule, and the relatively high contrast at this short wavelength
the G-band region is exceptionally suitable for this task. Howeve,
despite the frequent use of G-band brightness as magnetic field proxy
it has not yet been well established what the precise mechanism is that
makes the small scale magnetic elements appear bright. In particular,
it is unclear why there is no one-to-one correlation between magnetic
field and G-band brightness, as has been established from co-spatial
magnetograms in atomic lines. To obtain a better understanding
of the elusive G-band brightening mechanism we obtained high spatial-
and spectral resolution spectra of the G-band region in Stokes I and V
at the Dunn Solar Telescope on Sacramento Peak. We use the molecular
Zeeman effect to determine line-of-sight magnetic field strength
directly in the CH lines that provide most of the opacity in the G
band, avoiding difficulties with co-aligning images and magnetograms
taken seperately. We compare our observations with radiative transfer
modeling of the Stokes profiles in snapshots of a magneto-hydrodynamic
simulation of solar convection.
Title: Temporal Variations in the Evershed Flow
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Olmschenk, S.
Bibcode: 2004AGUFMSH13A1141B
Altcode:
We present results of an analysis of the temporal Doppler variations
of the Evershed flow. Doppler shifts were calculated from a unique,
high-resolution data set of 39 spectral lines, spanning the photosphere
and chromosphere. Our results indicate a quasi-periodic structure
of the Evershed flow with a typical period between 18-24 minutes in
the photosphere and 12-18 minutes in the chromosphere. We discuss the
implications of these results for both the siphon flow and the moving
flux tube models.
Title: Optical design for a Fabry-Perot image interferometer for
solar observations
Authors: Moretto, Gilberto; Gary, G. Allen; Balasubramaniam, K. S.;
Rimmele, Thomas R.
Bibcode: 2004SPIE.5492.1773M
Altcode:
We outline here a preliminary optical design study for a telecentric
tunable Fabry-Perot etalon system. The first result of the optical
optimization into a design, which delivers performance image quality
and telecentricity, is presented here. Bearing in mind the possible
use of such a study design - as a possible instrument for the Advanced
Technology Solar Telescope (ATST) - we also show that a hybrid design
strategy delivers a compact design that will fit inside the ATST's
Coude optical tables.
Title: Instrumentation for the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Hubbard, Robert P.; Balasubramaniam,
K. S.; Berger, Tom; Elmore, David; Gary, G. Allen; Jennings, Don;
Keller, Christoph; Kuhn, Jeff; Lin, Haosheng; Mickey, Don; Moretto,
Gilberto; Socas-Navarro, Hector; Stenflo, Jan O.; Wang, Haimin
Bibcode: 2004SPIE.5492..944R
Altcode:
The 4-m aperture Advanced Technology Solar Telescope (ATST) is the
next generation ground based solar telescope. In this paper we provide
an overview of the ATST post-focus instrumentation. The majority of
ATST instrumentation is located in an instrument Coude lab facility,
where a rotating platform provides image de-rotation. A high order
adaptive optics system delivers a corrected beam to the Coude lab
facility. Alternatively, instruments can be mounted at Nasmyth or
a small Gregorian area. For example, instruments for observing the
faint corona preferably will be mounted at Nasmyth focus where maximum
throughput is achieved. In addition, the Nasmyth focus has minimum
telescope polarization and minimum stray light. We describe the set of
first generation instruments, which include a Visible-Light Broadband
Imager (VLBI), Visible and Near-Infrared (NIR) Spectropolarimeters,
Visible and NIR Tunable Filters, a Thermal-Infrared Polarimeter &
Spectrometer and a UV-Polarimeter. We also discuss unique and efficient
approaches to the ATST instrumentation, which builds on the use of
common components such as detector systems, polarimetry packages and
various opto-mechanical components.
Title: Statistical Properties of Superpenumbral Whorls around Sunspots
Authors: Balasubramaniam, K. S.; Pevtsov, Alexei; Rogers, Joey
Bibcode: 2004ApJ...608.1148B
Altcode:
We study properties of 897 superpenumbral fibrils using Hα Big Bear
Solar Observatory (BBSO) and photospheric magnetic field National
Solar Observatory/Kitt Peak (NSO/KP) data of 139 sunspots between
2000 July and 2001 April. From this low-resolution data, we find
that about one-third of all superpenumbral fibrils begin inside the
penumbra. The typical length of fibrils is 2.7 times the sunspot
white-light penumbral radius. A majority of the fibrils are curved,
i.e., 67% of them exhibit bow-extent/footpoint separation greater than
0.1. Both clockwise and counterclockwise fibrils are typically present
within the same superpenumbra. We show that the topology of fibrils is
clearly affected by distribution of magnetic fields around the sunspot.
Title: Physical Properties of Structures about Sunspots
Authors: Balasubramaniam, K. S.
Bibcode: 2004AAS...204.2001B
Altcode: 2004BAAS...36..685B
Through a series of spectroscopic and polarimetric observations
spanning the photosphere and chromosphere, we diagnose the physical
and magnetic structure about sunspots. The relevant data were obtained
with the HAO Advanced Stokes Polarimeter in conjunction with the NSO
Dunn Solar Telescope's horizontal Littrow spectrograph and the UBF
filter, using the spectral lines: FeI λ λ 6301.5, 5320.5 Å, Hα ,
and CaII 3933.6 Å. We examine the dynamic character of evolving active
region filaments and examine the physical characteristics that influence
these structures from the photosphere though the upper chromosphere. We
characterize the atmospheric structures about sunspots in the presence
of magnetic null points and twisted magnetic fields. Signatures of
magnetic reconnection - the spectral ``chromospheric red-shift spur"
will be demonstrated. The National Solar Observatory is operated
by the Association of Universities Research in Astronomy, Inc. (AURA),
for the National Science Foundation.
Title: Promises and Pitfalls of Solar Hα Zeeman Spectropolarimetry
Authors: Balasubramaniam, K. S.; Christopoulou, E. B.; Uitenbroek, H.
Bibcode: 2004ApJ...606.1233B
Altcode:
Zeeman spectropolarimetry of the solar disk in the Hα line is a
daunting, yet promising diagnostic for measuring solar chromospheric
magnetic fields. As a demonstration of its potential we used the
National Solar Observatory (NSO)/High Altitude Observatory (HAO)
Advanced Stokes Polarimeter to obtain simultaneous measurements
of polarimetric signals from the photosphere in the Fe I 6301.5,
6302.5 Å lines and from the chromosphere in Hα. With these
measurements, we explore the promises and pitfalls of Hα Zeeman
spectropolarimetry. Remarkable features observed in Hα include
a reversal of Zeeman polarity in the emission core across flaring
active regions and highly redshifted and smeared Stokes V profiles in
prominences. We reproduce the Hα Zeeman reversals using radiative
transfer diagnostics, and we compare photospheric and chromospheric
line-of-sight magnetic fields.
Title: Synergy of Research and EPO Programs at NSO
Authors: Balasubramaniam, K. S.; Keil, S. L.; Penn, M. J.; Dooling,
D.; Piano, P.; Diehl, J.; Hunter, R.
Bibcode: 2003AGUFMED51C1215B
Altcode:
The National Solar Observatory with its facilities at Sunspot, NM and
Tucson, AZ runs an extensive education and public outreach effort. Much
of these efforts are coupled research and education efforts aimed
across a spectrum that spans through school teachers, school students,
undergraduate and graduate researchers, and the public. In this paper,
we will describe the benefits and challenges the NSO program faces,
and future prospects of these programs.
Title: Chirality of Chromospheric Filaments
Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Rogers, Joey W.
Bibcode: 2003ApJ...595..500P
Altcode:
We use the chromospheric full-disk Hα observations to study the
chirality of 2310 filaments from 2000-2001. For each filament,
we identify the spine and its barbs and determine the filament
chirality as fraction of dextral/sinistral barbs of the total number
of barbs. We find that 80.2% (558 out of 696) of quiescent filaments
in the northern hemisphere are dextral and 85.5% (633 out of 740)
of filaments in southern hemisphere are sinistral, in agreement with
the well-known hemispheric helicity rule. Our data also show that the
active-region filaments follow the same rule, though the hemispheric
dependence is weaker: 74.9% (338 out of 451) of active-region filaments
in the northern hemisphere are dextral, and 76.7% (297 out of 387)
of filaments in the southern hemisphere are sinistral. We show that
quiescent filaments formed on leading and returning arms of the same
switchback exhibit the same chirality. We also investigate a possible
change in the hemispheric rule with polarity reversal of the polar
field, and we find no such change.
Title: Chirality of Chromospheric Filaments
Authors: Pevtsov, A. A.; Balasubramaniam, K. S.; Rogers, J. W.
Bibcode: 2003SPD....34.0709P
Altcode: 2003BAAS...35..821P
We use the chromospheric full disk Hα observations
to study chirality (sign of helicity) of 2310 filaments from
2000--2001. For each filament we identify the spine and its barbs
and determine the filament chirality as fraction of dextral/sinistral
barbs of total number of barbs. We find that 80.2% (558 out of 696)
of quiescent filaments in northern hemisphere are dextral, and 85.5%
(633 out of 740) of filaments in southern hemisphere are sinistral,
in agreement with well known hemispheric helicity rule. Our data
also show that the active region filaments follow the same rule,
though the hemispheric dependence is weaker; 74.9% (338 out of 451) of
active region filaments in northern hemisphere are dextral, and 76.7%
(297 out of 387) of filaments in southern hemisphere are sinistral. We
show that quiescent filaments formed on leading and returning arms of
the same switch-back exhibit the same chirality. We also investigate
a possible change in the hemispheric rule with polarity reversal of
the polar field and we find no such change.
Title: Signatures of Large Scale Coronal Eruptive Activity, Associated
Flares, and Propagating Chromospheric Disturbances
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.;
Cliver, E. W.; Young, C. A.; Martin, S. F.; Kiplinger, A. L.
Bibcode: 2003SPD....34.0505B
Altcode: 2003BAAS...35..814B
Analyses of multi-wavelength data sets on 2002 December 19 at
approximately 2150 UT show evidence of a large-scale, transequatorial
coronal eruption associated with simultaneous flares in active
regions in both hemispheres. The coronal manifestations (based on
EIT, LASCO, and TRACE images) include a large coronal dimming,
an opening/restructuring of magnetic fields, the formation of a
transient coronal hole, and a halo CME. In the chromosphere, ISOON
H-alpha images show distant flare precursor brightenings and several
sympathetic flares. Originating near the main flare is a rapidly
propagating (800 km/s), narrowly channeled disturbance detectable as a
sequential brightening of numerous pre-existing points in the H-alpha
chromospheric network. This disturbance is not a chromospheric Moreton
wave, but it does produce a temporary activation of a transequatorial
filament. This filament does not erupt nor do any other filaments
in the vicinity. MDI magnetograms show that the brightened network
points are all of the same polarity (the dominant polarity among the
points in the disturbance's path), suggesting that the affected field
lines extend into the corona where they are energized in sequence
as the eruption tears away. Three other similar eruptive events
(non-transequatorial) that we studied, while they are less impressive,
show most of the same phenomena including distant sympathetic flares and
a propagating disturbance showing close adherence to the monopolarity
rule. Two of these events do include filament eruptions near the main
flare. We conclude that the observations of these four events are
consistent with large scale coronal eruptive activity that triggers
nearly simultaneous surface activity of various forms separated by
distances on the same scale as the coronal structures themselves. A
filament eruption at the main flare site appears not to be a necessity
in this type of eruptive activity.
Title: Multiple Etalon Systems for the Advanced Technology Solar
Telescope
Authors: Gary, G. A.; Balasubramaniam, K. S.; Sigwarth, Michael
Bibcode: 2003SPIE.4853..252G
Altcode:
Multiple etalon systems are discussed that meet the science requirements
for a narrow-passband imaging system for the 4-meter National Solar
Observatory (NSO)/Advance Technology Solar Telescope (ATST). A
multiple etalon system can provide an imaging interferometer that
works in four distinct modes: as a spectro-polarimeter, a filter-vector
magnetograph, an intermediate-band imager, and broadband high-resolution
imager. Specific dual and triple etalon configurations are described
that provide a spectrographic passband of 2.0-3.5 pm and reduce
parasitic light levels to 10-4 as required for precise
polarization measurement, e.g., Zeeman measurements of magnetic
sensitive lines. A TESOS-like (Telecentric Etalon SOlar Spectrometer)
triple etalon system provides a spectral purity of 10-5. The
triple designs have the advantage of reducing the finesse requirement
on each etalon; allow the use of more stable blocking filters, and have
very high spectral purity. A dual-etalon double-pass (Cavallini-like)
system can provide a competing configuration. Such a dual-etalon design
can provide high contrast. The selection of the final focal plane
instrument will depend on a trade-off between an ideal instrument and
practical reality. The trade study will include the number of etalons,
their aperture sizes, complexities of the optical train, number of
blocking filters, configuration of the electronic control system,
computer interfaces, temperature controllers, etalon controllers,
and their associated feedback electronics. The heritage of single and
multiple etalon systems comes from their use in several observatories,
including the Marshall Space Flight Center (MSFC) Solar Observatory,
Sacramento Peak Observatory (NSO), and Kiepenheuer-Institut für
Sonnenphysik (KIS, Germany), Mees Solar Observatory (University of
Hawaii), and Arcetri Astrophysical Observatory (Italy). The design
of the ATST multiple etalon system will benefit from the experience
gained at these observatories.
Title: Vorticity patterns of sunspot H α whirls
Authors: Pevtsov, A. A.; Balasubramaniam, K. S.; Rogers, W. J.
Bibcode: 2003AdSpR..32.1905P
Altcode:
We study vorticity patterns of 897 superpenumbral filaments (in 142
sunspots) using Hα (BBSO) observations from July 2000 - April 2001. A
majority (69%) of filaments show noticeable curvature in clockwise (CW)
or counter-clockwise (CCW) sense. 73% of all sunspots contain both CW
and CCW filaments in their superpenumbrae. Only 27% of sunspots have
all their superpenumbral filaments twisted in the same direction. The
average sunspot vorticity exhibits well-known hemispheric preference,
but the dependence is weaker than in the previous studies: 34 (54%)
out of 63 sunspots in the northern hemisphere exhibit CCW pattern of
superpenumbral whirls, and 45 (69%) of 65 sunspots in the southern
hemisphere show CW pattern. We suggest that the local distribution
of magnetic fields around sunspots may affect the curvature of
superpenumbral filaments and, hence, weaken the hemispheric helicity
rule.
Title: Simultaneous Chromospheric and Photospheric Spectropolarimetry
of a Sunspot
Authors: Balasubramaniam, K. S.; Christopoulou, E. B.; Uitenbroek, H.
Bibcode: 2003ASPC..286..227B
Altcode: 2003ctmf.conf..227B
No abstract at ADS
Title: Spectroscopy and Polarimetry of Sunspots
Authors: Balasubramaniam, K. S.; Eydenberg, M. S.
Bibcode: 2003ASPC..307..358B
Altcode:
No abstract at ADS
Title: High Resolution Imaging Spectroscopy of Sunspots
Authors: Balasubramaniam, K. S.; Titus, T.; Gary, G. Allen
Bibcode: 2003ASPC..286..259B
Altcode: 2003ctmf.conf..259B
No abstract at ADS
Title: Helicity patterns on the sun
Authors: Pevtsov, A. A.; Balasubramaniam, K. S.
Bibcode: 2003AdSpR..32.1867P
Altcode:
Solar magnetic fields exhibit hemispheric preference for negative
(positive) helicity in northern (southern) hemisphere. The hemispheric
helicity rule, however, is not very strong, — the patterns of
mixed helicity were observed at different spatial scales in each
hemisphere. Helicity patterns on scales larger than the size of typical
active region were observed in distribution of active regions with
abnormal (for a give hemisphere) helicity, in large-scale photospheric
magnetic fields and coronal flux systems. We review the observations
of large-scale patterns of helicity in solar atmosphere and their
possible relationship with (sub-)photospheric processes.
Title: Multi-wavelength Structure of an Active Region Filament
Authors: Balasubramaniam, K. S.; Kucera, T. A.; McAllister, A. H.
Bibcode: 2002AGUFMSH52A0469B
Altcode:
In this work we will compare the structure of active region filaments
near a sunspot, in a number of wavelengths. The data were obtained
from three sources on June 20, 2001 between 14:00 and 16:00 NSO/SP,
photospheric and chromospheric observations of intensities (G-Band),
and spectroscopy (Hα, MgI 5172 Å, and CaI 6122 Å) to determine
velocities, and magnetic fields; TRACE observations at 1600Å continuum,
and coronal measurements in 171 Å; SOHO/EIT coronal observations in
Fe XII 195A, SOHO/CDS spectroscopic observations in spectral lines --
SiXII 520.66 Å, OIV 554.52 Å, NeVI 562.80 Å, HeI 584.33 Å, OIII
599.59 Å, HeII 303.78 Å, MgIX 368.07 Å, MgX 624.94 Å, OV 629.73
Å, SiXII 520.66 Å, OIV 554.52 Å, NeVI 562.80 Å, HeI 584.33 Å,
OIII 599.59 Å, HeII 303.78 Å, MgIX 368.07 Å, MgX 624.94 Å, OV
629.73 Å; and SOHO/MDI magnetic and intensity images. The common FOV
covers about 100 arcseconds. We will present the evolutionary nature of
the photospheric magnetic field, the the corresponding chromospheric
velocities and the coronal variations of this filament region. During
the initial period of the observations, this active region filament
system is disrupted by an adjoining solar flare. The structure and
dynamics of the filament system during this eruption will be traced.
Title: Imaging Spectroscopy of a Sunspot: Thermal and Velocity
Structure
Authors: Balasubramaniam, K. S.
Bibcode: 2002ApJ...575..553B
Altcode:
The purpose of this paper is (1) to confirm and establish the working of
a dual-etalon Fabry-Pérot imaging spectroscopy system at the National
Solar Observatory/Sacramento Peak Dunn Solar Telescope and (2) to use
this system to extend previous work by many authors and understand the
structure and dynamics of sunspots. A detailed investigation of the
thermal and velocity structure in an isolated sunspot, using the Fe I
5576 Å spectral line, is presented. The concept of flowless maps is
incorporated, to separate velocity and intensity effects. The resulting
intensities are used to generate thermal maps of the sunspot along
the height of formation of a spectral line, followed by a thermal
span map. The thermal span in penumbral regions is in the range
of 1350-1580 K. It is a factor of 2 smaller in the umbra. Using
spectral line bisectors, we extend the concept of a velocity span
to a sunspot, following Gray. The velocity span is used to study the
velocity gradients across a sunspot. The velocity span maximizes in
the middle of the sunspot penumbra and falls off on either side. The
Doppler-neutralized mean bisectors from the disk-side and limb-side
penumbra show more sharply inclined gradients, when compared with the
C-shaped photospheric bisectors. The mean umbral bisectors show sharp,
<-shaped profiles. In most of the penumbra, the individual bisectors
are sharply inclined, with a shape of ``/'' or ``\,'' indicative of
a highly suppressed convective flow. The intensity and velocity data
show that a new family of penumbral filaments rises in the middle
penumbra. Bisector intensity-velocity relationships display opposite
gradients in the inner and outer penumbra, showing the rising and
falling parts of curved penumbral flux tubes. Some clustering of the
bisector intensity-velocity relationship is perhaps due to the fluted
nature of flux tubes.
Title: The Diagnostic Potential of the CaII 8542 spectral line for
Stokes I, V Spectropolarimetry
Authors: Balasubramaniam, K. S.; Uitenbroek, H.; Havey, J. W.;
Jones, H.
Bibcode: 2002AAS...200.3807B
Altcode: 2002BAAS...34R.699B
The number of available spectral lines to probe magnetic fields in the
solar chromosphere from the ground is practically limited to resonance
lines of hydrogen, calcium, sodium and magnesium and the multiplets of
helium. The range of heights over which each these spectral lines form
extends over several hundred kilometers and temperatures over several
hundreds of degrees, in a significantly non-local thermodynamic
equilibrium atmosphere. In this paper we explore the diagnostic
potential of the CaII 8542 A spectral line and the inference of active
region magnetic and velocity fields. We will provide a NLTE analysis of
the radiative transfer of this spectral line in the presence of magnetic
fields and compare theoretical and measured spectral line profiles
(observed using the NSO/KP Vacuum Telescope), to infer magnetic field
strengths using the center-of-gravity separation of the Stokes (I+V),
(I-V) components, and using the weak field approximation.
Title: Vorticity patterns of sunspot H-alpha whirls
Authors: Pevtsov, A.; Balasubramaniam, K.; Rogers, J.
Bibcode: 2002cosp...34E1105P
Altcode: 2002cosp.meetE1105P
We study vorticity patterns of 1003 superpenumbral filaments using H
(BBSO) data of 145 sunspots observed from July 2000 - April 2001. A
majority (67%) of filaments show noticeable curvature in clockwise (CW)
or counter-clockwise (CCW) sense. The 75% of all sunspots contain both
CW and CCW filaments in their superpenumbrae. Only 25% of sunspots have
all their superpenumbral filaments twisted in the same direction. The
average sunspot vorticity exhibits well known hemispheric preference,
but the dependence is weaker than in previous studies. The 42 (58%)
out of 73 sunspots in the northern hemisphere exhibit CCW pattern of
superpenumbral whirls. The 43 (61%) of 70 sunspots in the southern
hemisphere show CW pattern. The weak hemispheric asymmetry suggests
that the mechanisms with strong hemispheric dependency (e.g., Coriolis
force, solar differential rotation) may not play a dominant role in
the hemispheric chirality (helicity) rule. Mr. J. Rogers was supported
by the 2001 NSF/RET Program at NSO/SP.
Title: Spectral Diagnostics of Chromospheres-A Signature of Emergent
Magnetic Flux
Authors: Balasubramaniam, K. S.
Bibcode: 2001ApJ...557..366B
Altcode:
The chromospheres of the Sun and solar-like stars respond to the
underlying magnetic activity. The spectral lines of singly ionized
calcium (e.g., Ca II K at 3933 Å) exhibit single or double reversals
and serve as diagnostic tools for the magnetic activity. We present
observations showing that the Ca II K spectral line may exhibit
reversals in addition to the well-known K1, K2, and K3 components,
when observed with high angular and spectral resolution. These Ca II K
spectral line anomalies occur when small-scale, subarcsecond magnetic
fields emerge through the chromosphere. The anomalous profiles originate
at locations that are cospatial with Hα brightening at footpoints of
dark active region fibrils, or active region filaments. The photospheric
magnetic field is bipolar (small opposite polarity magnetic nodules)
or has neutral lines at cospatial locations where the spectral lines
are anomalous. Small-scale reconnective processes can cause these
anomalous profiles. From a simultaneous time series of magnetic field
data, we find that the emerging magnetic flux is associated with
these profiles. The additional reversals primarily occur redward of
the familiar K3 absorption trough, implying chromospheric downflow
velocities that lead to the formation of shocks. The magnitude of the
Doppler shift is of the order 40-50 km s-1. We present
evidence to suggest that a combination of subresolution elements,
each of which has regular profiles with large relative Doppler shifts
could explain the formation of some of these profiles. A heuristic
model that combines buoyant magnetic fields, convective collapse,
gas evacuation, shock formation, heating, and a multicomponent model
atmosphere can reproduce these profiles.
Title: Small Scale Dynamics in an Emerging Flux Region
Authors: Sigwarth, M.; Balasubramaniam, K.
Bibcode: 2001AGUSM..SP41B05S
Altcode:
Unusual Stokes spectra measured with the HAO/NSO Advanced Stokes
Polarimeter ASP in a young active region with ongoing flux emergence
indicate upward and downward moving shock fronts in the photosphere. The
data cover the evolution of the region over 1.25 hours. The found flows
are mainly located in magnetic fields only and occur on very small
spatial scales. We present results from the analysis of individual
Stokes profiles and from the inversion of the full Stokes vector in
order to investigate the magnetic field topology and the dynamics that
leads to the observed profiles. First results indicate that rising
flux tubes with the onset of shocked down drafts can explain some of
the observed spectra.
Title: Solar Seeing Seven Ways From Sunday
Authors: Hill, F.; Balasubramaniam, K. S.; Beckers, J. M.; Briggs,
J. W.; Hegwer, S.; Radick, R. R.; Rimmele, T. R.; Richards, K.;
Denker, C.
Bibcode: 2001AGUSM..SP21B03H
Altcode:
The Advanced Technology Solar Telescope (ATST) site survey will be
carried out with a Solar Differential Image Motion Monitor (S-DIMM)
and a six-scintillometer SHAdow BAnd Ranging (SHABAR) array. This
device will provide estimates of the Fried parameter, R0,
derived from the differential motion measurements of two images of the
same cut across the solar limb formed by two 45 mm diameter telescope
apertures 225 mm apart, and an estimate of the height dependence of the
index of refraction structure parameter, Cn2, from
the co-variance of the signals from an array of 6 scintillometers with
15 baseline separations. It will also provide a cloud cover measurement
and RMS scintillation signal. In preparation for the survey, we compare
estimates of daytime solar seeing obtained simultaneously from seven
different instruments. The observations were made at NSO/Sacramento
Peak during the period January 26 - February 5, 2001 under a variety of
seeing and transparency conditions ranging from poor to excellent. The
seven instruments were: 1. a S-DIMM/SHABAR mounted at the top of
the Dunn Solar Tower (DST) 2. an identical S-DIMM/SHABAR mounted at
ground level 3. the NSO/SP Adaptive Optics wavefront sensor providing
subaperature image motion measurements 4. a Dalsa camera providing
bursts of high-speed images for spectral ratio seeing estimates 5. a
Xedar camera obtaining granulation images for contrast and differential
stretching measurements 6. a Seykora scintillometer mounted in the
DST 7. a video camera recording a movie of the visual quality of the
image The analysis of this data set will provide the first direct
comparison of this many simultaneous solar seeing measurements, test
the ATST site survey system, and verify the SHABAR measurement of the
seeing height profile.
Title: Structure and Dynamics of a Sunspot Penumbra using Imaging
Spectroscopy
Authors: Balasubramaniam, K. S.; Sigwarth, M.
Bibcode: 2001AGUSM..SP41C07B
Altcode:
We present high angular resolution measurements and analysis of a
sunspot penumbra using imaging spectroscopy with the NSO Dual-FP system
(DPF), simultaneous Hα and G-Band measurements. These measurements
were made using the NSO Low-order Adaptive Optics system at the Richard
B. Dunn Solar Telescope. The DFP was used to acquire the spectral images
using the FeI 5576 Å Zeeman insensitive spectral line to map the upper
photospheric layers. The dynamic signatures of the penumbra are analyzed
using the Doppler maps of the sunspot. We present FLOW-LESS maps of the
sunspot to examine the thermal structure of the sunspot. Using spectral
line asymmetries, we probe the dynamical structure of the penumbrae
at different heights. We also examine the structural properties of
the penumbra using high-resolution high-speed images in Hα , and the
G-band. We discuss the impacts of these measurements on the current
models of sunspot penumbrae.
Title: Understand spectroheliograms - insight from spectral line
analysis
Authors: Smaldone, L. A.; Scognamiglio, O.; Balasubramaniam, K. S.
Bibcode: 2001MmSAI..72..553S
Altcode:
In an effort to seek newer diagnostic tools for monitoring the solar
activity, we have reconstructed spectroheliograms in various spectral
lines in the range 3900-3940 Angstroms (around the Ca II K line), from
high spatial and spectral resolution measurements. In active regions,
we find that the spectroheliogram features in a number of spectral lines
are similar to the Ca II K1v spectroheliogram features. In plages, on
the contrary, only spectroheliograms in a few spectral lines correlate
with the Ca II K1v. In plages, we get the best correlation with the
Si I 3905. From these measurements we develop contrast functions to
isolate various active phenomena as seen in Ca II, and compare its
formation contribution of relative velocities, magnetic fields and
intensity as seen in Fe I and Si I spectral lines. These indicators
provide much insight into the formation of Ca II K line.
Title: Dynamics of solar magnetic elements
Authors: Sigwarth, M.; Balasubramaniam, K. S.; Knölker, M.;
Schmidt, W.
Bibcode: 1999A&A...349..941S
Altcode:
We present observational results that demonstrate a strong increase in
the dynamic behavior of magnetic elements at the solar photosphere,
when observed at high spatial and temporal resolution. The HAO/NSO
Advanced Stokes Polarimeter was used to obtain an extensive set of
high resolution Stokes-V spectra from network, intranetwork and active
region magnetic fields at a low noise level. We performed a statistical
analysis of Doppler shifts and asymmetries of the V spectra of FeI
630.15 and 630.25 nm to obtain information on the dynamics of magnetic
elements of different sizes. The spatial resolution of 0.8-1 arcsec in
combination with high polarimetric precision allowed us to investigate
Stokes-V spectra of magnetic elements down to a size of ~ 150 km. The
Doppler velocity within magnetic elements as well as the amplitude and
area asymmetries of the Stokes-V profiles show a strong dependence on
the size of the magnetic elements as well as on the granular velocity
in their vicinity. Applying an absolute velocity calibration we find
that the smallest magnetic features have velocities of up to 5 km s(-1)
in both up- and downflows whereas for larger elements or clusters of
several flux tubes the velocities become smaller and more uniform. The
V-profile asymmetries are larger (both positive and negative) for
small fill fraction than for higher fill fraction within the resolution
element. Averaged over all individual profiles, there remains a positive
amplitude and area asymmetry and a downflow exceeding 0.5 km s(-1)
. The properties of spatially and temporally integrated V profiles are
consistent with results from FTS-observations. Our observations are
in qualitative agreement with results from numerical MHD simulations.
Title: Simultaneous 2-D Spatial Spectra Using a Microlens Array
Authors: Balasubramaniam, K. S.; Suematsu, Y.; Smaldone, L. A.;
Yoshimura, K.; Hegwer, S.; Otani, H.
Bibcode: 1999AAS...194.9306B
Altcode: 1999BAAS...31R.989B
Simultaneous spatial spectra of extended solar structures, at a high
spatial resolution and temporal cadence is important to track and
understand the physics of dynamical evolutionary phenomena. Replacing
the slit of a conventional spectrograph with a micro-lens array will
then help to capture simultaneous spatial spectra using a large format
CCD camera. Such a technique will be useful to study small structures
(a few arcseconds across) such as Ellerman bombs, kernels of flares,
filamentary evolution and spicules. At the NSO/Richard B. Dunn Solar
Telescope, we have used a micro-lens array (0.6 mm pitch, 50 x 50
lens-lets) to observe structures with a spatial sampling of 0.24
arcseconds in Hα \ spectral line. The spectral sampling is 0.93
Angstroms/pixel over a 10- Angstroms bandwidth. The field-of-view
is however limited to about 12 arcseconds. We have also explored the
microlens array the observations to magnetic spectral lines such as
FeI 6301.5 and FeI 6302.5 Angstroms for variation of line-of-sight
of subarcsecond magnetic fields. We present initial results from an
engineering observational experiment at the Dunn Solar Telescope.
Title: High Resolution Solar Physics: Theory, Observations, and
Techniques
Authors: Rimmele, T. R.; Balasubramaniam, K. S.; Radick, R. R.
Bibcode: 1999ASPC..183.....R
Altcode: 1999hrsp.conf.....R
No abstract at ADS
Title: Simultaneous High Resolution Spectroscopy of the Photosphere
and Chromosphere
Authors: Balasubramaniam, K.; Bianda, M.
Bibcode: 1999ASPC..183..132B
Altcode: 1999hrsp.conf..132B
No abstract at ADS
Title: High Resolution Observations of the Dynamics of Magnetic
Elements
Authors: Sigwarth, M.; Balasubramaniam, K.; Knölker, M.
Bibcode: 1999ASPC..183...36S
Altcode: 1999hrsp.conf...36S
No abstract at ADS
Title: Velocities in Solar Pores
Authors: Keil, S. L.; Balasubramaniam, K. S.; Smaldone, L. A.;
Reger, B.
Bibcode: 1999ApJ...510..422K
Altcode:
We use high spatial and spectral resolution filtergrams to examine the
three-dimensional morphology and velocity fields associated with solar
pores in a region of newly emerged magnetic flux. The observed amplitude
of the horizontal surface velocities decreases near the pores. Most of
the pores exhibit a downflow in the surrounding region. Time-averaged
line-of-sight velocities in and near the pores increased with the
strength of the associated magnetic field. The LOS velocities are
such that the maximum downflow is not centered about the continuum
intensity and sometimes traces an annulus ringlike structure around
the pore. From a time sequence of continuum images, it appears that
some pores shed flux at the photospheric level. ``Cork movies'' of the
surface velocities show that the ``corks'' are advected toward weak
downflows near the pore locations and that the loci of the advected
corks trace boundaries that resemble mesogranular and supergranular
flows. We analyze the vertical velocity structure in pores and show that
the downflow decreases exponentially with height, with a scale height
that is a factor of 2 smaller than the photospheric scale height for
granules. The line-of-sight flow associated with the pores appears
to expand with height. Our observations are compared with previous
measurements of flows in and around pores that were based on both
spectrograms and filtergrams. Finally, we provide a phenomenological
description for pores.
Title: Dynamical Motions as Precursors to Activity
Authors: Keil, S.; Balasubramaniam, K.; Milano, L.; Bayliss, A.;
Jones, J.; Clark, J.
Bibcode: 1999ASPC..183..540K
Altcode: 1999hrsp.conf..540K
No abstract at ADS
Title: Nineteenth NSO/SP International Workshop on High-Resolution
Solar Physics:Theory, Observations, and Techniques
Authors: Rimmele, Thomas; Balasubramaniam, K. S.; Radick, Richard
Bibcode: 1999PASP..111..127R
Altcode:
No abstract at ADS
Title: H alpha Synoptic Observations of Flare-Filament Eruption
Complex 1997 April 6 - 7
Authors: Balasubramaniam, K. S.; Milano, L.; Keil, S. L.
Bibcode: 1998ASPC..140..189B
Altcode: 1998ssp..conf..189B
No abstract at ADS
Title: A Search for Systematic Periodicities in Solar Flares
Authors: Balasubramaniam, K. S.; Radick, R. R.; Fox, J.
Bibcode: 1998ASPC..140..415B
Altcode: 1998ssp..conf..415B
No abstract at ADS
Title: Synoptic Solar Physics -- 18th NSO/Sacramento Peak Summer
Workshop
Authors: Balasubramaniam, K. S.; Harvey, Jack; Rabin, D.
Bibcode: 1998ASPC..140.....B
Altcode: 1998ssp..conf.....H
No abstract at ADS
Title: The USAF Improved Solar Observing Optical Network (ISOON)
and its Impact on Solar Synoptic Data Bases
Authors: Neidig, D.; Wiborg, P.; Confer, M.; Haas, B.; Dunn, R.;
Balasubramaniam, K. S.; Gullixson, C.; Craig, D.; Kaufman, M.; Hull,
W.; McGraw, R.; Henry, T.; Rentschler, R.; Keller, C.; Jones, H.;
Coulter, R.; Gregory, S.; Schimming, R.; Smaga, B.
Bibcode: 1998ASPC..140..519N
Altcode: 1998ssp..conf..519N
No abstract at ADS
Title: Stokes Profile Asymmetries in Solar Active Regions
Authors: Balasubramaniam, K. S.; Keil, S. L.; Tomczyk, S.
Bibcode: 1997ApJ...482.1065B
Altcode:
Asymmetries in Stokes polarization spectral line profiles can be
attributed to the existence of gradients in the velocity (and magnetic
field) over the line-forming region. Models that solve the Stokes
radiative transfer equations have incorporated both line-of-sight
gradients and gradients perpendicular to the line of sight over the
resolution element to produce the observed asymmetries. There have been
only a few systematic studies of how these Stokes profile asymmetries
vary across spatial structures and as a function of the amplitude of the
velocity and magnetic fields, and very little statistical information
is available. We present observational results from high spectral and
spatial resolution Stokes V profile measurements made in an active
region located near disk center and present correlations between the
amplitude of the Stokes V asymmetry, the magnetic field strength, and
line shifts and line asymmetries observed in the Stokes I profile. In
regions where the field strength exceeds a few hundred gauss, we find
a good correlation between the amplitude of the measured asymmetry
in Stokes V and the observed shifts of the Stokes I profile. We also
find a correlation between the asymmetry of the Stokes I profile and
the amplitude of the Stokes V profile asymmetry.
Title: ISOON: The Improved Solar Observing Optical Network
Authors: Neidig, D.; Confer, M.; Wiborg, P.; Dunn, R.; Balasubramaniam,
K. S.; Frederick, R.; Kutzman, R.; Soli, R.; Keller, C.; Gullixson,
C.; Alios, Inter
Bibcode: 1997SPD....28.0224N
Altcode: 1997BAAS...29..897N
Efforts are under way to replace the existing SOON system, which was
designed in the 1970s, with a new system (ISOON) based on a fully
tunable narrow-band filter and CCD detector. ISOON would feature
autonomous, rapid-cadence solar imaging and remote operation at four
sites, and would transmit solar images in near real time to central
facilities at Falcon AFB and Boulder CO, for use in space weather
forecasting. The ISOON technical approach is to retain the front
end of the existing SOON telescope, but replace the optical bench,
birefringent filter, and spectrograph with a dual Fabry-Perot filter
system and secondary optics contained in a single pod. ISOON data
products will include full-disk H-alpha, continuum, and line-of-sight
magnetograms on 1-arcsecond pixels. High- resolution images (limited
field, 0.3-arcsecond pixels) would be available via a future upgrade
in the secondary optics. ISOON will also be capable of acquiring
vector magnetic field images via a software upgrade to be added at a
future time.
Title: Multiple Reversals in CA II K Profiles
Authors: Balasubramaniam, K. S.
Bibcode: 1997SPD....28.0105B
Altcode: 1997BAAS...29..880B
The Ca II K spectral line serves as a diagnostic for plasma properties,
activity levels and magnetic influence of the chromosphere in the Sun
and stars. Traditionally, the K line exhibits a double reversal with
well identified spectral features, K1, K2 and K3. This research note
presents observations to show that the K line exhibits multiple spectral
reversals in addition to the well known features. These multiple
reversals are seen only at high spatial and spectral resolution, in
solar active regions. The locations of these multiple reversals are
cospatial with local H-alpha brightenings that appear at foot-points of
dark active region H-alpha fibrils (or active region filaments). The
magnetic field structure at the photosphere at the spatial locations
where these multiple reversals are observed, are either bipoles (small
opposite polarity magnetic nodules) or neutral lines. A compendium
of Ca II K spectral lines are presented to demonstrate the nature of
these these multiple reversals.
Title: Near Infrared Vector Magnetograph Development
Authors: Gullixson, Craig; Balasubramaniam, K. S.; Keil, Stephen
Bibcode: 1997SPD....28.0226G
Altcode: 1997BAAS...29..897G
We have developed a two etalon, narrow-band, tunable infrared filter
system and are using it to make solar vector magnetograms in the Fe
I lines at 1.5648 microns. We present results on the spectral and
polarization resolution of the filter system and show maps of the
magnetic field in both quiet regions of the solar atmosphere and
in a region with a growing sunspot. We will discuss the magnetic
sensitivity of the instrument. This system is a prototype instrument
for a operational vector magnetograph that will monitor the evolution
of solar magnetic fields preceding solar activity.
Title: Velocities in Solar Pores
Authors: Balasubramaniam, K. S.; Keil, S. L.; Smaldone, L. A.
Bibcode: 1996AAS...188.0203B
Altcode: 1996BAAS...28..820B
We investigate the three dimensional structure of solar pores and
their surroundings using high spatial and spectral resolution data. We
present evidence that surface velocities decrease around pores with
a corresponding increase in the line-of-sight (LOS) velocities. LOS
velocities in pores increase with the strength of the magnetic
field. Surface velocities show convergence toward a weak downflow which
appear to trace boundaries resembling meso-granular and super granular
flows. The observed magnetic fields in the pores appear near these
boundaries. We analyze the vertical velocity structure in pores and show
that they generally have downflows decreasing exponentially with height,
with a scale height of about 90 km. Evidence is also presented for the
expanding nature of flux tubes. Finally we describe a phenomenological
model for pores. This work was supported by AFOSR Task 2311G3. LAS was
partially supported by the Progetto Nazionale Astrofisica e Fisica
Cosmica of MURST and Scambi Internazionali of the Universita degli
Studi di Napoli Frederico II. National Solar Observatory, NOAO, is
operated for the National Science Foundation by AURA, Inc.
Title: Design Considerations for a Near Infrared Imaging Vector
Magnetograph
Authors: Gullixson, C. A.; Keil, S. L.; Balasubramaniam, K. S.
Bibcode: 1996AAS...188.5603G
Altcode: 1996BAAS...28R.911G
We present a preliminary design for an imaging vector magnetograph at
15648 Angstroms. This instrument is intended as a potential source
of vector magnetic field measurments for the USAF and NOAA solar
activity prediction programs. It will consist of a blocking filter, two
Fabry-Perot Etalons in tandem, a near-IR (10000 -- 17000 Angstroms)
camera and associated polarization optics. Initial test results
of the optical characteristics of this instrument and its expected
performance characteristics will be described. We are exploring designs
for operational vector magnetographs in the near-IR as a way to simplify
vector magnetic field measurements while improving their accuracy. This
work was supported by AFOSR Task 2311G3. National Solar Observatory,
NOAO, is operated for the National Science Foundation by AURA, Inc.
Title: Solar drivers of the interplanetary and terrestrial
disturbances
Authors: Balasubramaniam, K. S.; Keil, Stephen L.; Smartt, Raymond N.
Bibcode: 1996ASPC...95.....B
Altcode: 1996sdit.conf.....B
No abstract at ADS
Title: Book-Review : Solar Active Region Evolution: Comparing Models
with Observations
Authors: Balasubramaniam, K. S.; Simon, G. W.; Andrews, A. D.
Bibcode: 1996IrAJ...23..119B
Altcode:
No abstract at ADS
Title: A search for large-scale photospheric flows as drivers of
mass ejections
Authors: Balasubramaniam, K. S.; Keil, S. L.
Bibcode: 1996ASPC...95..189B
Altcode: 1996sdit.conf..189B
No abstract at ADS
Title: Preliminary Results of the Analysis of CAII K Spectroheliograms
Authors: Kariyappa, R.; Pap, J. M.; Balasubramaniam, K. S.; Kuhn, J. R.
Bibcode: 1995ESASP.376b.429K
Altcode: 1995help.confP.429K; 1995soho....2..429K
No abstract at ADS
Title: Restored Solar Velocity Measurements Obtained from the May 10,
1994 Annular Solar Eclipse
Authors: Keil, S. L.; Balasubramaniam, K. S.; Ljungberg, S. K.;
Smaldone, L. A.; Rimmele, T. R.
Bibcode: 1995SPD....26..202K
Altcode: 1995BAAS...27..951K
No abstract at ADS
Title: Stokes Profile Asymmetries in Active Regions
Authors: Balasubramaniam, K. S.; Keil, S. L.; Tomczyk, S.; Bernasconi,
P.
Bibcode: 1995SPD....26..205B
Altcode: 1995BAAS...27..951B
No abstract at ADS
Title: A Search for Periodicities in Solar H-alpha Flares
Authors: Radick, R. R.; Balasubramaniam, K. S.
Bibcode: 1995SPD....26.1322R
Altcode: 1995BAAS...27..992R
No abstract at ADS
Title: Magneto-Optic Effects on FeI 1.56 Micron Line
Authors: Balasubramaniam, K. S.; Petry, C. E.
Bibcode: 1995itsa.conf..369B
Altcode:
No abstract at ADS
Title: Removing Instrumental Polarization from Infrared Solar
Polarimetric Observations
Authors: Kuhn, J. R.; Balasubramaniam, K. S.; Kopp, G.; Penn, M. J.;
Dombard, A. J.; Lin, H.
Bibcode: 1994SoPh..153..143K
Altcode:
Full Stokes polarimetry is obtained using the National Solar
Observatory Vacuum Tower Telescope at Sacramento Peak while observing
the magnetically sensitive infrared FeI line at wavelength of 1.56μ. A
technique is described which makes use of the high magnetic resolution
in this spectral range to remove instrumental polarization from observed
StokesQ, U, andV line profiles.
Title: Latitude Dependence of Solar Activity From a Statistical
Study of Flares from 1938 to 1992
Authors: Balasubramaniam, K. S.; Regan, Jennifer
Bibcode: 1994ASPC...68...17B
Altcode: 1994sare.conf...17B
No abstract at ADS
Title: Active Region Development: Results from the JHU/APL Vector
Magnetograph
Authors: Rust, D. M.; Murphy, G.; Balasubramaniam, K. S.; Gullixson,
C. A.; Henry, T.; Coulter, R. L.; Keil, S. L.
Bibcode: 1994ASPC...68..263R
Altcode: 1994sare.conf..263R
No abstract at ADS
Title: Dynamics of Small Flux Tubes
Authors: Reger, Bernard; Keil, Stephen L.; Smaldone, Luigi A.; Cauzzi,
Gianna; Balasubramaniam, K. S.
Bibcode: 1994ASPC...68..157R
Altcode: 1994sare.conf..157R
No abstract at ADS
Title: Simultaneous Filter and Spectrograph Observations of Active
Regions with the Advanced Stokes Polarimeter
Authors: Tomczyk, S.; Balasubramaniam, K. S.; Keil, Stephen L.
Bibcode: 1994ASPC...68..262T
Altcode: 1994sare.conf..262T
No abstract at ADS
Title: Observations of Active Region Dynamics: Preflare Flows and
Field Observations
Authors: Keil, Stephen L.; Balasubramaniam, K. S.; Bernasconi, Pietro;
Smaldone, Luigi A.; Cauzzi, Gianna
Bibcode: 1994ASPC...68..265K
Altcode: 1994sare.conf..265K
No abstract at ADS
Title: Solar active region evolution: comparing models with
observations
Authors: Balasubramaniam, K. S.; Simon, George W.
Bibcode: 1994ASPC...68.....B
Altcode: 1994sare.conf.....B
No abstract at ADS
Title: On the calibration of line-of-sight magnetograms
Authors: Cauzzi, G.; Smaldone, L. A.; Balasubramaniam, K. S.; Keil,
S. L.
Bibcode: 1993SoPh..146..207C
Altcode:
Inference of magnetic fields from very high spatial, spectral, and
temporal resolution polarized images is critical in understanding the
physical processes that form and evolve fine scale structures in the
solar atmosphere. Studying high spectral resolution data also helps
in understanding the limits of lower resolution spectral data. We
compare three different methods for calibrating the line-of-sight
component of the magnetic field. Each method is tested for varying
degrees of spectral resolution on both synthetic line profiles computed
for known magnetic fields and real data. The methods evaluated are:
(a) the differences in the center of gravity of the right and left
circular components for different spectral resolution, (b) conversion
of circular polarization, at particular wavelengths, to magnetic
fields using model-dependent numerical solutions to the equations of
polarized radiative transfer, and (c) the derivative method using
the weak field approximation. Each method is applied to very high
spatial and spectral resolution circular polarization images of an
active region, acquired in the FeI 5250 å Zeeman-sensitive spectral
line. The images were obtained using the 20 må pass-band tunable
filter at NSO/Sacramento Peak Observatory Vacuum Tower Telescope. We
find that the center-of-gravity separation offers the best way of
inferring the longitudinal magnetic field.
Title: Vector Magnetography of a Large Sunspot
Authors: Rust, D. M.; Murphy, G. A.; Blanchette, J. J.; Cauzzi, C.;
Keil, S.; Balasubramaniam, K. S.
Bibcode: 1993BAAS...25.1205R
Altcode:
No abstract at ADS
Title: C Class Flares: Dynamics at Multiple Heights in the Solar
Atmosphere
Authors: Balasubramaniam, K. S.; Keil, S. L.
Bibcode: 1993BAAS...25R1214B
Altcode:
No abstract at ADS
Title: Calibrations of the JHU/APL-NSO-USAF Vector Magnetograph
Authors: Balasubramaniam, K. S.; Keil, S. L.
Bibcode: 1993BAAS...25.1205B
Altcode:
No abstract at ADS
Title: A comparison of vector magnetograms from the marshall space
flight center and mees solar observatory
Authors: Ronan, R. S.; Orrall, F. Q.; Mickey, D. L.; West, E. A.;
Hagyard, M. J.; Balasubramaniam, K. S.
Bibcode: 1992SoPh..138...49R
Altcode:
We compare completely independent vector magnetic field measurements
from two very different polarimetric instruments. The Marshall Space
Flight Center's imaging vector magnetograph is based on a birefringent
filter, routinely measuring all four Stokes parameters integrated over
the filter bandpass (1/8 Å) which is tunable across the FeI λ5250
line in 10 mÅ steps. The Haleakala Stokes Polarimeter of the Mees
Solar Observatory (MSO) is based on a spectrometer, routinely measuring
all four Stokes parameters of the FeI λ6302.5 line simultaneously and
then spatially scanning to build up a vector magnetogram. We obtained
active region magnetic field data with both the Marshall Space Flight
Center (MSFC) and MSO systems on five days during June 1985. After
interpolating the MSFC vector fields onto the more coarse spatial grid
of MSO we make a point-by-point comparison of the two vector fields for
data obtained on two of these days (June 8 and 9). From this comparison
we conclude: (1) the spatially-averaged line-of-sight components
agree quite well; (2) although the MSO spatial grid is coarser, the
quality of the MSO image is better than that of the MSFC data because
of better seeing conditions; (3) the agreement between the transverse
magnitudes is affected by the poor image quality of the MSFC data; and
(4) if the effects of Faraday rotation caused by including line-center
linear polarization in the method of analysis are taken into account,
the azimuths show good agreement within the scatter in the data caused
by the averaging process.
Title: Vector Magnetic Fields in Sunspots. I. Stokes Profile Analysis
Using the Marshall Space Flight Center Magnetograph
Authors: Balasubramaniam, K. S.; West, E. A.
Bibcode: 1991ApJ...382..699B
Altcode:
The Marshall Space Flight Center (MSFC) vector magnetograph is a tunable
filter magnetograph with a bandpass of 125 mA. Results are presented
of the inversion of Stokes polarization profiles observed with the MSFC
vector magnetograph centered on a sunspot to recover the vector magnetic
field parameters and thermodynamic parameters of the spectral line
forming region using the Fe I 5250.2 A spectral line using a nonlinear
least-squares fitting technique. As a preliminary investigation, it is
also shown that the recovered thermodynamic parameters could be better
understood if the fitted parameters like Doppler width, opacity ratio,
and damping constant were broken down into more basic quantities like
temperature, microturbulent velocity, or density parameter.
Title: Blending Influence of Fe I 5250.6 Å Spectral Line on the
Fe I 5250.2 Å Spectral Line and Its Implication for Polarization
Measurements
Authors: Balasubramaniam, K. S.
Bibcode: 1991BAAS...23.1054B
Altcode:
No abstract at ADS
Title: Stokes profile analysis of a sunspot using the MSFC
magnetograph.
Authors: Balasubramaniam, K. S.; West, E. A.; Hagyard, M. J.
Bibcode: 1991sopo.work..213B
Altcode:
Stokes filtergrams of a sunspot (AR 4662: June 9, 1985) have been
observed using the MSFC magnetograph. The authors present the analysis
of the resulting Stokes profiles to recover the vector magnetic field
and other physical parameters of the sunspot using the nonlinear
least square inversion. An intercomparison of the results with the
MSFC vector magnetographs is presented.
Title: A lunar based solar observatory rationale and concepts
Authors: Davis, John M.; Balasubramaniam, K. S.; Gary, G. A.; Moore,
Ronald L.
Bibcode: 1990AIPC..207..567D
Altcode: 1990am...proc..567D
The rationale for a lunar solar observatory is described and the
requirements for various candidate instruments are developed. The unique
characteristics of the lunar surface, its stability, low seismicity,
and long unobstructed paths make it an ideal site for a large, high
performance optical telescope. The capabilities of such an instrument is
used, as an example (1) for the science that might be achieved from the
lunar surface, (2) to identify the magnitude of the instrumentation,
and (3) to indicate the technologies that must be developed if such
an observatory is to become a reality.
Title: A Demonstration of How Crosstalk Affects the Polarization
Measurements of the MSFC Vector Magnetograph
Authors: West, E. A.; Balasubramaniam, K. S.
Bibcode: 1990BAAS...22..840W
Altcode:
No abstract at ADS
Title: Polarization studies of Zeeman affected spectral lines using
the MSFC magnetograph
Authors: Balasubramaniam, K. S.; West, E. A.
Bibcode: 1990SPIE.1317..356B
Altcode:
The Marshall Space Flight Center (MSFC) vector magnetograph records
polarization images of absorption lines that are sensitive to magnetic
fields. A method is presented for analyzing the Stokes spectral-line
profiles of a photospheric Fe I absorption line (5250.2 A) which
is influenced by the Zeeman effect. Using nonlinear least-square
optimization, the observed Stokes profiles are compared with those
generated from the theoretical solution of the polarized radiative
transfer equations. The optimization process accounts for the spectral
convolution of the source and the MSFC vector magnetograph. The
resulting physical properties of the active region producing the
polarized light are discussed.
Title: Stokes polarimetry and the measurement of vector magnetic
fields in solar active regions
Authors: Balasubramaniam, K. S.
Bibcode: 1988PhDT.......240B
Altcode:
No abstract at ADS
Title: Asymmetry of Stokes Profiles across a Sunspot; Measurements
Authors: Balasubramaniam, K. S.
Bibcode: 1987rfsm.conf..131B
Altcode:
The author has attempted to measure the symmetries in Stokes V profiles
across a sunspot using the lines Fe I λ6301.5 Å (g = 1.667) and Fe
I λ6302.5 Å (g = 2.5) and present some preliminary results.
Title: Measurement of solar magnetic fields.
Authors: Bhattacharyya, J. C.; Balasubramaniam, K. S.
Bibcode: 1986KodOB...6...30B
Altcode:
The paper reviews several methods of estimation of solar magnetic fields
so far employed. The possibility of measurement of the vector magnetic
fields by using two dimensional detector arrays is discussed. A program
for vector measurements of strong fields around solar active regions
is described and an experiment for determining the errors in these
measurements is discussed.
Title: Measurement of Vector Magnetic Fields - Part One - Theoretical
Approach to the Instrumental Polarization of the Kodaikanal Solar
Tower
Authors: Balasubramaniam, K. S.; Venkatakrishnan, P.; Bhattacharyya,
J. C.
Bibcode: 1985SoPh...99..333B
Altcode:
The observations of Stokes line profiles require an accurate knowledge
of the instrumental polarisation caused by optical components in the
path of the light beam. In this context we present a theoretical
approach to the instrumental polarisation caused by the 3-mirror
coelostat system of the Kodaikanal Solar Tower.