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Author name code: canfield
ADS astronomy entries on 2022-09-14
author:"Canfield, Richard C."
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Title: It Takes a Village
Authors: Canfield, Richard C.
2022SoPh..297...94C Altcode:
My parents taught me the value of a good education. My studies at the
state universities of Michigan and Colorado and postgraduate studies
at the University of Utrecht built on an interest in astronomy that
dated back to high school. These institutions enabled me to have a
rewarding fifty-year career focused on the physics of the Sun. My work
combined research and education at the High Altitude Observatory,
the University of Utrecht, the Sacramento Peak Observatory, the
University of California San Diego, the University of Hawaii, and
Montana State University. My professional interests ranged from
spectroscopic diagnostics and radiative transfer, especially of the
flaring solar chromosphere, to the helicity of magnetic fields of
active regions in the chromosphere, corona, and interplanetary medium,
part of what is now called heliophysics and space weather. I am honored
to have been recognized for my efforts as a scientific leader, mentor,
and teacher. I am lucky to have lived at a time when access to space
led the field of solar physics to grow dramatically, including global
studies of solar activity, the heliosphere, and space weather.
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Title: Performance of Major Flare Watches from the Max Millennium
Program (2001 - 2010)
Authors: Bloomfield, D. S.; Gallagher, P. T.; Marquette, W. H.;
Milligan, R. O.; Canfield, R. C.
2016SoPh..291..411B Altcode: 2015arXiv151204518B; 2016SoPh..tmp....1B
The physical processes that trigger solar flares are not well
understood, and significant debate remains around processes governing
particle acceleration, energy partition, and particle and energy
transport. Observations at high resolution in energy, time, and
space are required in multiple energy ranges over the whole course of
many flares to build an understanding of these processes. Obtaining
high-quality, co-temporal data from ground- and space- based instruments
is crucial to achieving this goal and was the primary motivation for
starting the Max Millennium program and Major Flare Watch (MFW) alerts,
aimed at coordinating observations of all flares ≥ X1 GOES X-ray
classification (including those partially occulted by the limb). We
present a review of the performance of MFWs from 1 February 2001 to
31 May 2010, inclusive, which finds that (1) 220 MFWs were issued
in 3407 days considered (6.5 % duty cycle), with these occurring in
32 uninterrupted periods that typically last 2 - 8 days; (2) 56%
of flares ≥ X1 were caught, occurring in 19 % of MFW days; (3)
MFW periods ended at suitable times, but substantial gain could have
been achieved in percentage of flares caught if periods had started
24 h earlier; (4) MFWs successfully forecast X-class flares with a
true skill statistic (TSS) verification metric score of 0.500, that is
comparable to a categorical flare/no-flare interpretation of the NOAA
Space Weather Prediction Centre probabilistic forecasts (TSS = 0.488).
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Title: Relationship between the photospheric Poynting flux and the
active region luminosity
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Fisher, George
H.; Hudson, Hugh S.; Welsch, Brian
2014AAS...22412349K Altcode:
How does energy radiated by active regions compare with magnetic energy
that propagates lower across the photosphere? This is a fundamental
question for energy storage and release in active regions, yet it is
presently poorly understood. In this work we quantify and compare
both energy terms using SDO observations of the active region (AR)
11520. To quantify the magnetic energy crossing the photosphere, or
the Poynting flux, we need to know both the magnetic field vector B and
electric field vector E as well. Our current electric field inversion
technique, PDFI, combines the Poloidal-Toroidal-Decomposition method
with information from Doppler measurements, Fourier local correlation
tracking (FLCT) results, and the ideal MHD constraint, to determine
the electric field from vector magnetic field and Doppler data. We
apply the PDFI method to a sequence of Helioseismic and Magnetic
Imager (HMI/SDO) vector magnetogram data, to find the electric-field
and hence the Poynting-flux evolution in AR 11520. We find that most
of the magnetic energy in this AR is injected in the range of $10^7$
to $10^8$ $ergs/{cm^2 s}$, with the largest fluxes reaching $10^{10}$
$ergs/{cm^2 s}$. Integrating over the active region this yields a
total energy of order $10^{28}$ ergs/s. To quantify the active region
luminosity, we use EUV Variability Experiment (EVE) and Atmospheric
Imaging Assembly (AIA) spectrally resolved observations. We find the
active region luminosity of order $10^{28}$ ergs/s. We compare derived
magnetic and radiated energy fluxes on different temporal and spatial
scales and estimate their uncertainties. We also discuss the roles
that potential/non-potential and emerging/shearing terms play in the
total magnetic energy budget.
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Title: Estimating active region luminosity using EVE/SDO observations
Authors: Kazachenko, Maria D.; Hudson, H. S.; Fisher, G. H.; Canfield,
R. C.
2013SPD....44...44K Altcode:
Do solar active regions typically radiate more coronal energy during
flares than the quiescent periods between them? This is a fundamental
question for storage and release models of flares and active regions,
yet it is presently poorly answered by observations. The EUV Variability
Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides
spectrally resolved observations of the Sun in the "Sun-as-a-point
source" mode. It covers a wide range of temperatures and thus allows
a detailed study of thermal emissions. Here we present two approaches
for computing the active region luminosity, using EVE observations of
fourteen Fe lines (FeIX-FeXXIV). In the first approach, we analyze EVE
data in a time-series sense, when only one active region is present on
the disk; this allows us to subtract the background due to the quiet
sun and get the contribution from the active region alone. In the
second approach, we analyze correlations of the radiative signatures
with proxy indices (total solar magnetic and Poynting fluxes) during
several months of data, when multiple active regions are present
on the solar disk. We discuss capabilities of the two approaches,
and what we can learn from them.Abstract (2,250 Maximum Characters):
Do solar active regions typically radiate more coronal energy during
flares than the quiescent periods between them? This is a fundamental
question for storage and release models of flares and active regions,
yet it is presently poorly answered by observations. The EUV Variability
Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides
spectrally resolved observations of the Sun in the "Sun-as-a-point
source" mode. It covers a wide range of temperatures and thus allows
a detailed study of thermal emissions. Here we present two approaches
for computing the active region luminosity, using EVE observations of
fourteen Fe lines (FeIX-FeXXIV). In the first approach, we analyze EVE
data in a time-series sense, when only one active region is present on
the disk; this allows us to subtract the background due to the quiet
sun and get the contribution from the active region alone. In the
second approach, we analyze correlations of the radiative signatures
with proxy indices (total solar magnetic and Poynting fluxes) during
several months of data, when multiple active regions are present on
the solar disk. We discuss capabilities of the two approaches, and
what we can learn from them.
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Title: Twisting and Writhing with George Ellery Hale
Authors: Canfield, Richard C.
2013SPD....4410201C Altcode:
Early in his productive career in astronomy, George Ellery Hale
developed innovative instrumentation that allowed him to image
the magnetically-dominated solar chromosphere. Among the solar
phenomena he discovered were sunspot vortices, which he attributed
to storms akin to cyclones in our own atmosphere. Much more recently,
physicists discovered a quantity that is very well conserved in ideal
magnetohydrodynamics: magnetic helicity. Our contemporary understanding
of Hale's vortices as a consequence of large-scale twist in sunspot
magnetic fields hinges on this conservation. I will review the crucial
role that this property plays in the hemispheric and solar cycle
dependences of Hales vortices, as well as solar flares and CMEs.
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Title: Twisting and Writhing with George Ellery Hale
Authors: Canfield, Richard C.
2013AAS...22210601C Altcode:
Early in his productive career in astronomy, George Ellery Hale
developed innovative solar instrumentation that allowed him to make
narrow-band images. Among the solar phenomena he discovered were sunspot
vortices, which he attributed to storms akin to cyclones in our own
atmosphere. Using the concept of magnetic helicity, physicists and
mathematicians describe the topology of magnetic fields, including
twisting and writhing. Our contemporary understanding of Hale's
vortices as a consequence of large-scale twist in sunspot magnetic
fields hinges on a key property of helicity: conservation. I will
describe the critical role that this property plays, when applied to
twist and writhe, in a fundamental aspect of global solar magnetism:
the hemispheric and solar cycle dependences of active region electric
currents with respect to magnetic fields. With the advent of unbroken
sequences of high-resolution magnetic images, such as those presently
available from the Helioseismic and Magnetic Imager on Solar Dynamics
Observatory, the flux of magnetic helicity through the photosphere can
be observed quantitatively. As magnetic flux tubes buoy up through the
convection zone, buffeted and shredded by turbulence, they break up
into fragments by repeated random bifurcation. We track these rising
flux fragments in the photosphere, and calculate the flux of energy and
magnetic helicity there. Using a quantitative model of coronal currents,
we also track connections between these fragments to calculate the
energy and magnetic helicity stored at topological interfaces that
are in some ways analogous to the storage of stress at faults in
the Earth's crust. Comparison of these values to solar flares and
interplanetary coronal mass ejections implies that this is the primary
storage mechanism for energy and magnetic helicity released in those
phenomena, and suggests a useful tool for quantitative prediction of
geomagnetic storms.
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Title: Predictions of Energy and Helicity in Four Major Eruptive
Solar Flares
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Longcope, Dana
W.; Qiu, Jiong
2012SoPh..277..165K Altcode: 2011arXiv1104.3593K
In order to better understand the solar genesis of interplanetary
magnetic clouds (MCs), we model the magnetic and topological properties
of four large eruptive solar flares and relate them to observations. We
use the three-dimensional Minimum Current Corona model (Longcope, 1996,
Solar Phys.169, 91) and observations of pre-flare photospheric magnetic
field and flare ribbons to derive values of reconnected magnetic flux,
flare energy, flux rope helicity, and orientation of the flux-rope
poloidal field. We compare model predictions of those quantities to
flare and MC observations, and within the estimated uncertainties of
the methods used find the following: The predicted model reconnection
fluxes are equal to or lower than the reconnection fluxes inferred
from the observed ribbon motions. Both observed and model reconnection
fluxes match the MC poloidal fluxes. The predicted flux-rope helicities
match the MC helicities. The predicted free energies lie between the
observed energies and the estimated total flare luminosities. The
direction of the leading edge of the MC's poloidal field is aligned
with the poloidal field of the flux rope in the AR rather than the
global dipole field. These findings compel us to believe that magnetic
clouds associated with these four solar flares are formed by low-corona
magnetic reconnection during the eruption, rather than eruption of
pre-existing structures in the corona or formation in the upper corona
with participation of the global magnetic field. We also note that since
all four flares occurred in active regions without significant pre-flare
flux emergence and cancelation, the energy and helicity that we find
are stored by shearing and rotating motions, which are sufficient to
account for the observed radiative flare energy and MC helicity.
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Title: Predictions of Energy and Helicity in Four Major Eruptive
Solar Flares
Authors: Kazachenko, Maria; Canfield, Richard C.; Longcope, Dana W.;
Qiu, Jiong
2011shin.confE...4K Altcode:
In order to better understand the solar genesis of interplanetary
magnetic clouds (MCs), we model the magnetic and topological properties
of four large eruptive solar flares and relate them to observations. We
use the three-dimensional Minimum Current Corona model (Longcope in
Solar Phys. 169, 91, 1996) and observations of pre-flare photospheric
magnetic field and flare ribbons to derive values of reconnected
magnetic flux, flare energy, flux rope helicity, and orientation of
the flux rope poloidal field. We compare model predictions of those
quantities to flare and MC observations and within the estimated
uncertainties of the methods used find the following. The predicted
model reconnection fluxes are equal to or lower than the reconnection
fluxes inferred from the observed ribbon motions. Both observed and
model reconnection fluxes match the MC poloidal fluxes. The predicted
flux-rope helicities match the MC helicities. The predicted free
energies lie between the observed energies and the estimated total
flare luminosities. The direction of the leading edge of the MC's
poloidal field is aligned with the poloidal field of the flux rope in
the AR rather than the global dipole field. These findings compel us to
believe that magnetic clouds associated with these four solar flares are
formed by low-corona magnetic reconnection during the eruption, rather
than eruption of pre-existing structures in the corona or formation in
the upper corona with participation of the global magnetic field. We
also note that since all four flares occurred in active regions without
significant pre-flare flux emergence and cancelation, the energy and
helicity that we find are stored by shearing and rotating motions,
which are sufficient to account for the observed radiative flare energy
and MC helicity.
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Title: Predictions Of Energy And Helicity In Four Major Eruptive
Solar Flares
Authors: Kazachenko, Maria; Canfield, R. C.; Longcope, D. W.; Qiu, J.
2011SPD....42.2218K Altcode: 2011BAAS..43S.2218K
In order to better understand the solar genesis of interplanetary
magnetic clouds (MCs) we model the magnetic and topological properties
of four large eruptive solar flares and relate them to observations. We
use the three-dimensional Minimum Current Corona model and observations
of pre-flare photospheric magnetic field and flare ribbons to derive
values of reconnected magnetic flux, flare energy, flux rope helicity
and orientation of the flux rope poloidal field. We compare model
predictions of those quantities to flare and MC observations and within
the estimated uncertainties of the methods used find the following. The
predicted model reconnection fluxes are equal to or lower than the
observed reconnection fluxes from the ribbon motions. Both observed and
model reconnection fluxes match the MC poloidal fluxes. The predicted
flux rope helicities match the MC helicities. The predicted free
energies lie between the observed energies and the estimated total
flare luminosities. The direction of the leading edge of the MC's
poloidal field is aligned with the poloidal field of the flux rope in
the AR rather than the global dipole field. These findings compel us to
believe that magnetic clouds associated with these four solar flares are
formed by low-corona magnetic reconnection during the eruption, rather
than eruption of pre-existing structures in the corona or formation in
the upper corona with participation of the global magnetic field. We
also note that since all four flares occurred in active regions without
significant pre-flare flux emergence and cancellation, the energy and
helicity we find are stored by shearing and rotating motions, which
are sufficient to account for the observed radiative flare energy and
MC helicity.
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Title: Sunspot Rotation, Flare Energetics, and Flux Rope Helicity:
The Halloween Flare on 2003 October 28
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Longcope, Dana
W.; Qiu, Jiong
2010ApJ...722.1539K Altcode:
We study the X17 eruptive flare on 2003 October 28 using Michelson
Doppler Imager observations of photospheric magnetic and velocity
fields and TRACE 1600 Å images of the flare in a three-dimensional
model of energy buildup and release in NOAA 10486. The most dramatic
feature of this active region is the 123° rotation of a large positive
sunspot over 46 hr prior to the event. We apply a method for including
such rotation in the framework of the minimum current corona model of
the buildup of energy and helicity due to the observed motions. We
distinguish between helicity and energy stored in the whole active
region and that released in the flare itself. We find that while the
rotation of a sunspot contributes significantly to the energy and
helicity budgets of the whole active region, it makes only a minor
contribution to that part of the region that flares. We conclude
that in spite of the fast rotation, shearing motions alone store
sufficient energy and helicity to account for the flare energetics
and interplanetary coronal mass ejection helicity content within their
observational uncertainties. Our analysis demonstrates that the relative
importance of shearing and rotation in this flare depends critically
on their location within the parent active region topology.
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Title: Sunspot Rotation, Eruptive Flare Energetics And Flux Rope
Helicity: Topology Matters.
Authors: Kazachenko, Maria; Canfield, R.; Longcope, D.; Qiu, J.
2010AAS...21632003K Altcode: 2010BAAS...41..911K
We study the role of rotation in the flare energy and helicity budget
of two active regions: NOAA 10486 and NOAA 10759. Using MDI and TRACE
observations of photospheric magnetic and velocity fields in those
active regions we build a topological model of their three-dimensional
coronal magnetic field. In both active regions a fast rotating sunspot
is observed. We apply a method for including such rotation in the
framework of the minimum current corona model (MCC, Longcope 1996) to
the buildup of energy and helicity associated with the X17.2 eruptive
flare on 2003 October 28 (the Halloween flare) and M8.0 eruptive flare
on 2005 May 13. We find that including the sunspot rotation in the model
changes the total flare thermal energy and flux rope helicity by only
10% for the Halloween flare, but by more than 200% for the 2005 May
13 flare. While for the Halloween flare shearing motions alone store
sufficient energy and helicity to account for the flare energetics and
ICME helicity content within their observational uncertainties, for the
2005 May 13 flare it is the rotation that dominates. We demonstrate
that the relative importance of shearing and rotation in those two
flares depends critically on their location within the parent active
region topology.
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Title: Sunspot Rotation, Flare Energetics, and Flux Rope Helicity:
The Eruptive Flare on 2005 May 13
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Longcope, Dana
W.; Qiu, Jiong; Des Jardins, Angela; Nightingale, Richard W.
2009ApJ...704.1146K Altcode:
We use the Michelson Doppler Imager and TRACE observations of
photospheric magnetic and velocity fields in NOAA 10759 to build a
three-dimensional coronal magnetic field model. The most dramatic
feature of this active region is the 34° rotation of its leading
polarity sunspot over 40 hr. We describe a method for including such
rotation in the framework of the Minimum Current Corona model. We
apply this method to the buildup of energy and helicity associated
with the eruptive flare of 2005 May 13. We find that including
the sunspot rotation almost triples the modeled flare energy
(1.0 × 10<SUP>31</SUP> erg) and flux rope self-helicity (-7.1 ×
10<SUP>42</SUP> Mx<SUP>2</SUP>). This makes the results consistent with
observations: the energy derived from GOES is 1.0 × 10<SUP>31</SUP>
erg, the magnetic cloud helicity from WIND is -5 × 10<SUP>42</SUP>
Mx<SUP>2</SUP>. Our combined analysis yields the first quantitative
picture of the helicity and energy content processed through a flare
in an active region with an obviously rotating sunspot and shows that
rotation dominates the energy and helicity budget of this event.
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Title: Sunspot Rotation, Flare Energetics and Flux Rope Helicity:
The Eruptive Flare on 2005 May 13
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Longcope, Dana
W.; Qiu, Jiong; DesJardins, Angela; Nightingale, Richard W.
2009shin.confE..53K Altcode:
We use MDI and TRACE observations of photospheric magnetic and elocity
fields in NOAA 10759 to build a three-dimensional coronal magnetic
field model. The most dramatic feature of this active region is the
34 degree rotation of its leading polarity sunspot over 40 hours. We
describe a method for including such rotation in the framework of
the minimum current corona (MCC) model. We apply this method to the
buildup of energy and helicity associated with the eruptive flare
of 2005 May 13. We find that including the sunspot rotation almost
triples the modeled flare energy (-1.0 ×10^{31}ergs) and flux rope self
helicity (-7.1 ×10^{42}, Mx^2). This makes the results consistent with
observations: the energy derived from GOES is -1.0×10^{31} ergs, the
magnetic cloud helicity from WIND is -5 ×10^{42}, Mx^2. Our combined
analysis yields the first quantitative picture of the helicity and
energy content processed through a flare in an active region with
an obviously rotating sunspot and shows that rotation dominates the
energy and helicity budget of this event.
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Title: Sunspot Rotation, Flare Energetics and Flux Rope Helicity:
The Eruptive Flare on 2005 May 13
Authors: Kazachenko, Maria; Canfield, R. C.; Longcope, D. W.; Qiu,
J.; DesJardins, A.; Nightingale, R. W.
2009SPD....40.2013K Altcode:
We use MDI and TRACE observations of photospheric magnetic and velocity
fields in NOAA 10759 to build a three-dimensional coronal magnetic
field model. The most dramatic feature of this active region is the
34 degree rotation of its leading polarity sunspot over 40 hours. We
describe a method for including such rotation in the framework of
braiding and spinning in a magnetic charge topology (MCT) model. We
apply this method to the buildup of energy and helicity associated with
the eruptive flare of 2005 May 13. We find that adding rotation almost
triples the modeled flare energy (-1.0×10<SUP>31</SUP>ergs) and flux
rope self helicity (-7.1×10<SUP>42</SUP> Mx<SUP>2</SUP>). This makes
the results consistent with observations: the energy derived from GOES
is -1.0×10<SUP>31</SUP>ergs, the magnetic cloud helicity from WIND is
-5×10<SUP>42</SUP> Mx<SUP>2</SUP>. Our combined analysis yields the
first quantitative picture of the helicity and energy content processed
through a flare in an active region with an obviously rotating sunspot
and shows that rotation dominates the energy and helicity budget of
this event.
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Title: Reconnection in Three Dimensions: The Role of Spines in Three
Eruptive Flares
Authors: Des Jardins, Angela; Canfield, Richard; Longcope, Dana;
Fordyce, Crystal; Waitukaitis, Scott
2009ApJ...693.1628D Altcode: 2009ApJ...693.1628J
In order to better understand magnetic reconnection and particle
acceleration in solar flares, we compare the RHESSI hard X-ray
(HXR) footpoint motions of three flares with a detailed study of the
corresponding topology given by a Magnetic Charge Topology model. We
analyze the relationship between the footpoint motions and topological
spine lines and find that the examined footpoint sources move along
spine lines. We present a three-dimensional topological model in
which this movement can be understood. As reconnection proceeds,
flux is transferred between the reconnecting domains, causing the
separator to move. The movement of the separator's chromospheric ends,
identified with the HXR footpoints, is along those spine lines on
which the separator ends.
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Title: Signatures of Magnetic Stress Prior to Three Solar Flares
Observed by RHESSI
Authors: des Jardins, Angela; Canfield, Richard; Longcope, Dana;
McLinden, Emily; Dillman, Amanda
2009ApJ...693..886D Altcode: 2009ApJ...693..886J
We examine the hard X-ray (HXR) footpoint sources of three flares,
as observed by RHESSI, in combination with the topology given by the
extrapolation of line-of-sight magnetograms into the corona. Assuming
the HXR footpoint sources are chromospheric consequences of magnetic
reconnection that takes place on separators, we further assume a
relationship between the buildup of energy in stressed coronal magnetic
fields and the measurement of the change in separator flux per unit
length. We find that the value of this quantity is larger for the
separators that connect the HXR footpoint sources than the quantity for
the separators that do not. Therefore, we conclude that we are able to
understand the location of HXR sources observed in flares in terms of
a physical and mathematical model of the topology of the active region.
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Title: Modeling and measuring the flux and helicity ejected by the
two-ribbon flare on 2005-05- 13
Authors: Kazachenko, M.; Canfield, R. C.; Longcope, D. W.; Qiu, J.
2008AGUSMSP43A..08K Altcode:
In this work we study an eruptive flare event in order to quantitatively
understand flux and helicity transfer through reconnection in the
associated coronal flux rope formation. Quantitative observational
studies of solar flare reconnection have been made by a number of
research groups (Poletto and Kopp, 1986, Fletcher and Hudson 2001,
Qiu and Yurchyshyn, 2005). However, their work does not allow one
to predict, from observations, both the flux and twist that coronal
reconnection contributes to interplanetary flux ropes. Our hypothesis
is that the flux and helicity associated with eruptive solar flares
is created through a sequence of magnetic reconnections. Longcope
et al. (2007) introduced a topological method of studying flux rope
formation in 3D. In our study we use MDI, SOHO and TRACE data. We
apply two methods to derive the reconnection sequence: (1) the flaring
sequence from the TRACE observations of ribbon brightening (Qiu et al,
2007) and (2) the reconnection sequence from the topological model of
the coronal field based on the Minimum Current Corona model (Longcope,
2001). From the topological model we calculate the toroidal flux and
total helicity of the flux rope. We study in detail the M8.0 flare
in active region NOAA 10759, 13-May-2005 16:13UT. The total magnetic
flux of the active region is 1.7 ·10 22 Mx. From the photospheric
magnetogram evolution we determine that 1.9 · 1042 Mx2 of magnetic
helicity has been injected into the active region during the 40-hour
build-up prior to the flare. From the domain flux evolution we show that
reconnection in the model (2) must occur in a specific sequence which
would produce a twisted flux rope containing significantly less flux
and helicity than the whole active region. The reconnection sequence
from the model (2) compares favorably with the one inferred from the
observation sequence (1). However, the topological analysis might be
sensitive to the beginning of the buildup time, so its choice will
be discussed.
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Title: On the Solar Cycle Variation of the Hemispheric Helicity Rule
Authors: Pevtsov, A. A.; Canfield, Richard C.; Sakurai, T.; Hagino, M.
2008ApJ...677..719P Altcode:
We study the statistical significance of observed temporal variations
of the solar active-region hemispheric helicity rule, as measured by the
latitudinal gradient of the best-fit linear force-free-field parameter,
dα/dvarphi . Using data from four different vector magnetographs,
we compute and compare average annual dα/dvarphi values for these
instruments for 19 years from solar cycles 21, 22, and 23. We find that
although every instrument shows the "wrong" sign for the hemispheric
rule in some years, there is no agreement among the instruments on
which years are abnormal. None of the four data sets shows annual
values of dα/dvarphi departing from the hemispheric helicity rule
by more than 3 σ. We conclude that because the hemispheric helicity
rule is a weak tendency with significant scatter, an annual subset of
active regions is likely to produce statistically unreliable results.
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Title: Hinode XRT observations of a long-lasting coronal sigmoid
Authors: McKenzie, D. E.; Canfield, R. C.
2008A&A...481L..65M Altcode:
Aims:Coronal sigmoids are important sources of eruptions into
interplanetary space, and a handful of models have been proposed
to explain their characteristic S shape. However, the coronal X-ray
images available to date have generally not had sufficient resolution to
distinguish between these models. The goal of the present investigation
is to determine whether the new observations from Hinode can help
us to make such a distinction. <BR />Methods: We present the first
observations of a persistent coronal sigmoid obtained with the Hinode
X-Ray Telescope (XRT). The excellent angular resolution of XRT (1 arcsec
per pixel) and the sigmoid's location near disk center combined to
provide an unprecedented view of the formation and eruption of this
phenomenon. We compared the observed morphology with expectations
inferred from two popular models of sigmoid formation, the bald-patch
separatrix surface model and the kinking flux rope model. <BR />Results:
The images during the pre-eruptive phase show that the overall S
shape of the sigmoid comprises two separate J-shaped bundles of many
loops. The straight sections of the two J patterns lie anti-parallel to
one another in the middle of the S, on opposite sides of the magnetic
polarity inversion line. The images during the eruptive phase reveal
that, before any soft X-ray flaring begins, a diffuse linear structure
almost as long as the sigmoid lifts off from the middle of the S. It
shows slight clockwise rotation. The X-ray flare begins with the
appearance of a sheared arcade of short loops, in the area centered
between the two J-shaped patterns of the sigmoid. <BR />Conclusions:
Taken together, the observational findings provide strong support for
the bald-patch separatrix surface model for this sigmoid.
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Title: Twisted solar active region magnetic fields as drivers of
space weather: Observational and theoretical investigations
Authors: Nandy, Dibyendu; Mackay, Duncan H.; Canfield, Richard C.;
Martens, P. C. H.
2008JASTP..70..605N Altcode:
The properties and dynamics of magnetic fields on the Sun's photosphere
and outer layers--notably those within solar active regions--govern
the eruptive activity of the Sun. These photospheric magnetic
fields also act as the evolving lower boundary of the Sun-Earth
coupled system. Quantifying the physical attributes of these magnetic
fields and exploring the mechanisms underlying their influence on the
near-Earth space environment are of vital importance for forecasting
and mitigating adverse space weather effects. In this context, we
discuss here a novel technique for measuring twist in the magnetic
field lines of solar active regions that does not invoke the force-free
field assumption. Twist in solar active regions can play an important
role in flaring activity and the initiation of CMEs via the kink
instability mechanism; we outline a procedure for determining this
solar active region eruptive potential. We also discuss how twist in
active region magnetic fields can be used as inputs in simulations of
the coronal and heliospheric fields; specifically, we explore through
simulations, the formation, evolution and ejection of magnetic flux
ropes that originate in twisted magnetic structures. The results and
ideas presented here are relevant for exploring the role of twisted
solar active region magnetic fields and flux ropes as drivers of space
weather in the Sun-Earth system.
---------------------------------------------------------
Title: Signatures of Magnetic Stress Prior to Three Solar Flares
Observed by RHESSI
Authors: Des Jardins, A. C.; Canfield, R. C.; Longcope, D. W.
2007AGUFMSH13A1098D Altcode:
In order to better understand the location and evolution of magnetic
reconnection, which is thought to be the energy release mechanism in
solar flares, we combine the analysis of hard X-ray (HXR) sources
observed by RHESSI with a three-dimensional, quantitative magnetic
charge topology (MCT) model. We examine the location of reconnection
by assuming a relationship between the build-up of energy in stressed
coronal magnetic fields and the measurement of the change in separator
flux per unit length. We find that the value of this quantity is
larger on the separators that connect the HXR footpoint sources than
the value on the separators that do not. Therefore, we conclude the
MCT model gives useful insight into the relationship between sites of
HXR emission and the topology of flare productive active regions.
---------------------------------------------------------
Title: Yohkoh SXT Full-Resolution Observations of Sigmoids: Structure,
Formation, and Eruption
Authors: Canfield, Richard C.; Kazachenko, Maria D.; Acton, Loren W.;
Mackay, D. H.; Son, Ji; Freeman, Tanya L.
2007ApJ...671L..81C Altcode:
We study the structure of 107 bright sigmoids using full-resolution
(2.5" pixels) images from the Yohkoh Soft X-Ray Telescope (SXT)
obtained between 1991 December and 2001 December. We find that none of
these sigmoids are made of single loops of S or inverse-S shape; all
comprise a pattern of multiple loops. We also find that all S-shaped
sigmoids are made of right-bearing loops and all inverse-S-shaped
sigmoids of left-bearing loops, without exception. We co-align the SXT
images with Kitt Peak magnetograms to determine the magnetic field
directions in each sigmoid. We use a potential-field source surface
model to determine the direction of the overlying magnetic field. We
find that sigmoids for which the relative orientation of these two
fields has a parallel component outnumber antiparallel ones by more than
an order of magnitude. We find that the number of sigmoids per active
region varies with the solar cycle in a manner that is consistent with
this finding. Finally, those few sigmoids that are antiparallel erupt
roughly twice as often as those that are parallel. We briefly discuss
the implications of these results in terms of formation and eruption
mechanisms of flux tubes and sigmoids.
---------------------------------------------------------
Title: Solar Active Region Flux Fragmentation, Subphotospheric Flows,
and Flaring
Authors: Canfield, Richard C.; Russell, Alexander J. B.
2007ApJ...662L..39C Altcode:
We explore the properties of the fragmentation of magnetic flux in solar
active regions. We apply gradient-based tessellation to magnetograms
of 59 active regions to identify flux fragments. First, we find that
the distribution function of flux fragments in these regions is highly
consistent with lognormal form, which is the most direct evidence
yet obtained that repeated random bifurcation dominates fragmentation
and coalescence in all active regions. Second, we apply nonparametric
statistical methods to the variance of the lognormal distribution of
fragment flux, the flare X-ray energy output of the active regions,
and kinetic helicity measurements in the upper convection zone to
show that there is no significant statistical relationship between
the amount of fragmentation of an active region's flux at photospheric
levels and the amplitude of either its average kinetic helicity density
in the upper convection zone or its X-ray flare energy output.
---------------------------------------------------------
Title: Hinode/XRT Observations of a Coronal Sigmoid
Authors: McKenzie, David E.; Canfield, R. C.
2007AAS...210.7208M Altcode: 2007BAAS...39Q.180M
We present the first observations of an X-ray sigmoid made with
the Hinode X-Ray Telescope, co-aligned with those of TRACE and
SoHO/MDI. XRT's extraordinary angular resolution (1 arcsec/pixel)
and the sigmoid's location near disk center combined to provide an
unprecedented view of the formation and eruption of this phenomenon. XRT
observed the sigmoid over several days, with cadences as high as 1 image
per 10--30 seconds. The first motions associated with eruption of the
sigmoid started at 0600UT on 12-Feb-2007; the first brightening of the
ensuing X-ray arcade was seen at 0740UT. <P />The images during the
pre-eruptive phase, which ends with the onset of large-scale motions,
show:<ul><li>The overall S shape of the sigmoid is not
defined by any single X-ray loop. Rather, many individual loops
collectively comprise an S-shaped pattern.<li>The S shape is
comprised of two separate J shapes, whose straight sections lie
anti-parallel to one another in the middle of the S, on opposite
sides of the magnetic polarity inversion line. <li>During
the several-day span of the XRT observation, the S shape gradually
becomes better defined.</ul>The images during the eruptive
phase show:<ul><li>Approximately 100 minutes before any
soft X-ray flaring begins, a diffuse linear structure, almost as long
as the sigmoid, lifts off from the middle of the S. It shows slight
clockwise rotation.<li>The X-ray flare begins with the appearance
of a sheared arcade of short loops, in the area centered between the
two J-shaped patterns of the sigmoid. <li>Within 16 hours of
the start of the flare, no S shape remains.</ul>Taken together,
these features provide strong support for the Bald-Patch Separatrix
Surface model of sigmoids put forth by Titov & Demoulin (1999).
---------------------------------------------------------
Title: The REU Program in Solar Physics at Montana State University
Authors: Martens, Petrus C.; Canfield, R. C.; McKenzie, D. M.
2007AAS...210.8012M Altcode: 2007BAAS...39Q.189M
The Solar Physics group at Montana State University has organized
an annual summer REU program in Solar Physics, Astronomy, and Space
Physics since 1999, with NSF funding since 2003. The number of
students applying and being admitted to the program has increased
every year, and we have been very successful in attracting female
participants. A great majority of our REU alumni have chosen career
paths in the sciences, and, according to their testimonies, our REU
program has played a significant role in their decisions. From the
start our REU program has had an important international component
through a close collaboration with the University of St. Andrews in
Scotland. <P />In our poster we will describe the goals, organization,
scientific contents, international aspects, and results, and present
statistics on applications, participants, gender balance, and diversity.
---------------------------------------------------------
Title: A New Technique For Measuring The Twist Of Photospheric
Active Regions Without Recourse To The Force-Free-Field Equation:
Reconfirming The Hemispheric Helicity Trend
Authors: Nandy, Dibyendu; Calhoun, A.; Windschitl, J.; Canfield,
R. C.; Linton, M. G.
2007AAS...210.2402N Altcode: 2007BAAS...39..128N
The twist component of magnetic helicity in solar active regions is
known to be an important indicator of sub-photospheric flux tube
dynamics and solar eruptive activity. Traditionally, estimates
of the parameter alpha -- appearing in the force-free-field
equation -- has been used to infer the twist of photospheric active
regions. However, the photosphere is not force-free and this has
lead to recent concerns on the validity of using the alpha parameter
for determining photospheric active region twist. We have devised a
new flux-tube-fitting technique for determining the twist of active
regions without recourse to the force-free-field equation. This method
assumes that the underlying active region flux system is cylindrically
symmetric and uniformly twisted. By using this new technique, on a
statistically compelling number of photospheric active region vector
magnetograms, we re-confirm the hemispheric helicity rule independent
of the force-free-field assumption. This research has been supported
in parts by a NASA Living With a Star grant NNG05GE47G. A.C. and
J.W. were supported by a NSF Research Experience for Undergraduates
grant ATM-0243923 to Montana State University. M.G.L. acknowledges
support from NASA and the Office of Naval Research.
---------------------------------------------------------
Title: Relating RHESSI Footpoints to Reconnection: the Importance
of Spines and Separators
Authors: Des Jardins, A.; Canfield, R.; Longcope, D.; McLinden, E.;
Fordyce, C.; Waitukaitis, S.
2006AGUFMSH23A0349D Altcode:
In order to improve the understanding of both flare initiation and
evolution, we take advantage of powerful new topological methods
and the high spatial resolution of RHESSI to examine where magnetic
reconnection takes place in flare-producing solar active regions. We
use the MPOLE (http://solar.physics.montana.edu/dana/mpole/) software to
extrapolate the observed line of sight photospheric magnetic field into
the corona. MPOLE is a suite of IDL programs that implements the Minimum
Current Corona Model (Longcope 1996). Recently it has been improved to
use a hierarchy of topological features (Beveridge 2006). The coronal
extrapolation gives the location of topological features such as poles,
nulls, separatricies, separators, and spine lines. For several flares
well observed by RHESSI and MDI, we examine the locations of flare HXR
emission in the context of these topological features. Two noteworthy
relationships are found. First, when footpoints move, they move along
spine lines. Second, when separators significantly change over the
course of a flare, only those associated with the flare footpoints do
so. In this poster, we present observations supporting the relationship
between spine lines and footpoint tracks, demonstrate the importance
of separator analysis in the study of flares, explore uncertainties
in the MPOLE and RHESSI analyses, and survey possible interpretations
of the reported results. This work is supported by NASA.
---------------------------------------------------------
Title: Magnetic Topology of the 29 October 2003 X10 flare
Authors: Des Jardins, Angela C.; Canfield, R.; Longcope, D.
2006SPD....37.1311D Altcode: 2006BAAS...38..242D
In order to improve the understanding of both flare initiation and
evolution, we take advantage of powerful new topological methods
and the high spatial resolution of RHESSI to examine where magnetic
reconnection takes place in flare-producing solar active regions. Up
to this time, such studies have been carried out on a very small
number of active regions. According to present ideas, reconnection
is expected to occur at either a separatrix or separator topological
feature. We use the powerful X10 flare on 29 October 2003 (peak: 20:49
UT, location: (80”, 275”)) as a test of the ability to interpret the
topological location of reconnection. The 29 October 2003 flare was well
observed by RHESSI and MDI, occurred near the sun's central meridian,
and thus is thus a prime candidate for a study on the topological
location of magnetic reconnection. In this flare study, we use the
MPOLE (http://solar.physics.montana.edu/dana/mpole/) software to
extrapolate from the photospheric magnetic field, as observed by MDI,
to a coronal field. MPOLE is a suite of IDL programs implementing the
Minimum Current Corona Model (Longcope 1996) and currently includes a
new method that uses a hierarchy of topological features (Beveridge
2006). The extrapolation gives the location of topological features
such as poles, nulls, separatricies, separators, and spine lines. We
examine the flare emission observed by RHESSI in the context of these
topological features. In the case of the 29 October 2003 flare, we
find a relationship between the spine lines and the temporal evolution
of the HXR flare footpoints. In this poster, we present observations
supporting the relationship, explore uncertainties in the consistency
between MPOLE and RHESSI data, and survey possible results.This work
is supported by NASA.
---------------------------------------------------------
Title: Evolution of magnetic fields and energetics of flares in
active region 8210
Authors: Régnier, S.; Canfield, R. C.
2006A&A...451..319R Altcode:
To better understand eruptive events in the solar corona, we combine
sequences of multi-wavelength observations and modelling of the
coronal magnetic field of NOAA AR 8210, a highly flare-productive
active region. From the photosphere to the corona, the observations
give us information about the motion of magnetic elements (photospheric
magnetograms), the location of flares (e.g., Hα, EUV or soft X-ray
brightenings), and the type of events (Hα blueshift events). Assuming
that the evolution of the coronal magnetic field above an active
region can be described by successive equilibria, we follow in time
the magnetic changes of the 3D nonlinear force-free (nlff) fields
reconstructed from a time series of photospheric vector magnetograms. We
apply this method to AR 8210 observed on May 1, 1998 between 17:00 UT
and 21:40 UT. We identify two types of horizontal photospheric motions
that can drive an eruption: a clockwise rotation of the sunspot,
and a fast motion of an emerging polarity. The reconstructed nlff
coronal fields give us a scenario of the confined flares observed in
AR 8210: the slow sunspot rotation enables the occurence of flare
by a reconnection process close to a separatrix surface whereas
the fast motion is associated with small-scale reconnections but no
detectable flaring activity. We also study the injection rates of
magnetic energy, Poynting flux and relative magnetic helicity through
the photosphere and into the corona. The injection of magnetic energy
by transverse photospheric motions is found to be correlated with
the storage of energy in the corona and then the release by flaring
activity. The magnetic helicity derived from the magnetic field and
the vector potential of the nlff configuration is computed in the
coronal volume. The magnetic helicity evolution shows that AR 8210 is
dominated by the mutual helicity between the closed and potential fields
and not by the self helicity of the closed field which characterizes
the twist of confined flux bundles. We conclude that for AR 8210 the
complex topology is a more important factor than the twist in the
eruption process.
---------------------------------------------------------
Title: REU program in Solar Physics at Montana State University
Authors: Martens, P. C.; Canfield, R. C.; McKenzie, D. M.
2005AGUFMED31A1202M Altcode:
I will present an overview of the REU program in Solar Physics and Space
Weather that has existed since 1999 at Montana State University, since
2003 with NSF support. I will briefly describe the goals, organization,
scientific contents and results, and present statistics on applications,
participants, gender balance, and diversity. This will be concluded
by an overview of our plans for the future,
---------------------------------------------------------
Title: Evidence of Small Scale Reconnection in a Moving Feature
Authors: Régnier, S.; Canfield, R. C.
2005ESASP.600E..94R Altcode: 2005dysu.confE..94R; 2005ESPM...11...94R
No abstract at ADS
---------------------------------------------------------
Title: Describing Coronal Magnetic Fields by Successive Force-Free
Equilibia
Authors: Régnier, S.; Canfield, R. C.
2005ESASP.596E..13R Altcode: 2005ccmf.confE..13R
No abstract at ADS
---------------------------------------------------------
Title: Self and mutual magnetic helicities in coronal magnetic
configurations
Authors: Régnier, S.; Amari, T.; Canfield, R. C.
2005A&A...442..345R Altcode:
Together with the magnetic energy, the magnetic helicity is an
important quantity used to describe the nature of a magnetic field
configuration. In the following, we propose a new technique to
evaluate various components of the total magnetic helicity in the
corona for an equilibrium reconstructed magnetic field. The most
meaningful value of helicity is the total relative magnetic helicity
which describes the linkage of the field lines even if the volume
of interest is not bounded by a magnetic surface. In addition if the
magnetic field can be decomposed into the sum of a closed field and
a reference field (following , Berger 1999 in Magnetic Helicity in
Space and Laboratory Plasmas, ed. M. R. Brown, R. C. Canfield, &
A. A. Pevtsov, 1), we can introduce three other helicity components:
the self helicity of the closed field, the mutual helicity between
the closed field and the reference field, and the vacuum helicity
(self helicity of the reference field). To understand the meaning of
those quantities, we derive them from the potential field (reference)
and the force-free field computed with the same boundary conditions
for three different cases: a single twisted flux tube derived from the
extended Gold-Hoyle solutions, a simple magnetic configuration with
three balanced sources and a constant distribution of the force-free
parameter, and the AR 8210 magnetic field observed from 17:13 UT to
21:16 UT on May 1, 1998. We analyse the meaning of the self and mutual
helicities: the self and mutual helicities correspond to the twist and
writhe of confined flux bundles, and the crossing of field lines in
the magnetic configuration respectively. The main result is that the
magnetic configuration of AR 8210 is dominated by the mutual helicity
and not by the self helicity (twist and writhe). Our results also show
that although not gauge invariant the vacuum helicity is sensitive to
the topological complexity of the reference field.
---------------------------------------------------------
Title: Spatial Relationship between Twist in Active Region Magnetic
Fields and Solar Flares
Authors: Hahn, Michael; Gaard, Stacy; Jibben, Patricia; Canfield,
Richard C.; Nandy, Dibyendu
2005ApJ...629.1135H Altcode:
Twisted magnetic field lines in solar active regions constitute stressed
flux systems, the reconnection of which can release the stored (excess)
magnetic energy in the form of solar flares. Using co-registered
photospheric vector magnetograms and chromospheric Hα images for 29
flares, we explore the spatial relationship between these flares and
the magnetic topology of the active regions in which they occur. We
find two dominant trends. First, flares are preferentially initiated in
subregions that have a high gradient in twist. Second, flare initiation
occurs close to chirality inversion lines (which separate regions with
twist of opposite handedness). Our results demonstrate that magnetic
helicity, as manifested in the twist parameter, plays an important
role in magnetic reconnection and solar flaring activity.
---------------------------------------------------------
Title: Self and Mutual Helicities in Coronal Magnetic Configurations
Authors: Regnier, S.; Canfield, R. C.
2005AGUSMSP33A..04R Altcode:
Together with the magnetic energy, the magnetic helicity is an
important quantity used to describe the nature of a magnetic field
configuration. The most meaningful value of helicity is the relative
magnetic helicity (relative to a reference field) which describes
the linkage of the field lines even if the volume of interest is not
bounded by a magnetic surface. In addition if the magnetic field can
be decomposed into the sum of a closed field and a reference field
(following Berger 1999), we can introduce three other helicity values:
the self helicity of the closed field, the mutual helicity between
the closed field and the reference field, and the vacuum helicity
(self helicity of the reference field). To understand the meaning of
those quantities, we derive them from the potential field (reference)
and the nonlinear force-free field computed with the same boundary
conditions for three different cases: (i) a single twisted flux tube
derived from the extended Gold-Hoyle solutions, (ii) a simple magnetic
configuration with three balanced sources and a constant distribution of
the force-free parameter, and (iii) the AR 8210 magnetic field observed
at 19:40 UT on May 1, 1998. The self and mutual helicities corresponds
to the twist and writhe of confined flux bundles, and the crossing
of field lines in the magnetic configuration respectively. The vacuum
helicity is interpreted as a measure of the topological complexity of
the field.
---------------------------------------------------------
Title: The Relationship Between Active Region Twist & Solar
Flaring Activity
Authors: Nandy, D.; Hahn, M.; Gaard, S.; Jibben, P.; Canfield, R. C.
2005AGUSMSP23B..06N Altcode:
Twisted magnetic field lines in solar active regions constitute stressed
flux systems -- the reconnection of which can release the stored
(excess) energy in the form of solar flares. The explosive release of
energy through such flares, beyond contributing to the heating of the
solar corona, can sometimes affect the near-Earth Space environment and
trigger geomagnetic storms. Here we explore the relationship between
solar flares and the pre-flare magnetic topology (characterized by the
twist α in the magnetic fields lines) of the active regions in which
the flares originate. We have discovered that flares are preferentially
initiated in sub-regions that have an high gradient in twist and
lie close to chirality inversion lines (which separate regions with
twist of opposite handedness). Our results imply that the topology of
magnetic field lines -- as characterized by the twist parameter α --
plays an important role in magnetic reconnection and flaring events.
---------------------------------------------------------
Title: On a Cyclic Variation of the Hemispheric Helicity Rule
Authors: Pevtsov, A. A.; Hagyard, M. J.; Blehm, Z.; Smith, J. E.;
Canfield, R. C.; Sakurai, T.; Hagino, M.
2005HiA....13..140P Altcode:
We report the result of a study of magnetic helicity in solar active
regions during 1980-2000 (cycles 21-23). Using the vector magnetograms
from four different instruments (Haleakala Stokes Polarimeter Marshall
Space Flight Center Mitaka Solar Flare Telescope and Okayama Observatory
Solar Telescope) we calculated the force-free parameter alpha as
in Pevtsov et al. (1995). We use alpha as the proxy for current
helicity. For each instrument we computed a gradient dalpha/dL as
the linear fit of alpha versus latitude L using annual subsets of
data. The hemispheric helicity rule (negative/positive helicity in
northern/southern hemisphere) can be expressed in terms of this gradient
as dalpha/dL < 0. We find that each instrument exhibits change in
sign of this gradient for some years which implies that the hemispheric
helicity rule may not hold in some phases of a solar cycle (see Hagino
and Sakurai 2002). However we do not see consistency between different
instruments in regards to years disobeying the rule. The disagreement
may be due to difference in observations and/or insufficient number of
magnetograms in some years. We conclude that the present data sets do
not allow to make statistically significant inference about possible
cyclic variation of the hemispheric helicity rule.
---------------------------------------------------------
Title: Helicity of Magnetic Clouds and Their Associated Active Regions
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A.
2005HiA....13..132L Altcode:
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is the
relationship between the topology of these clouds and the associated
active region? For our purposes magnetic clouds can be modeled
adequately by a cylindrical force-free magnetic configuration (Lepping
1990). We have modeled the magnetic field topology of 14 magnetic
clouds and their associated active regions to determine values of
the force-free field parameter for both as well as total currents and
fluxes. We find that the number of turns of the magnetic field in the
full length of the cloud is typically an order of magnitude greater
than the same quantity in the associated active region. This finding
compels us to reject models of flux rope formation that do not invoke
magnetic reconnection and helicity conservation.
---------------------------------------------------------
Title: Of Tilt and Twist
Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca
A.; Howard, Robert F.; Pevtsov, Alexei A.
2005HiA....13..135H Altcode:
Using Haleakala Stokes Polarimeter active-region vector magnetograms
and Mt. Wilson Observatory full-disk longitudinal magnetograms we
measure both the overall twist (using the force-free-field parameter
alpha) and tilt of 368 active regions. This dataset clearly shows two
well-known phenomena Joy's law and the hemispheric helicity rule as well
as a lesser-known twist-tilt relationship which is the point of this
work. Those regions that closely follow Joy's law show no twist-tilt
relationship as expected if the twist originates from convective
buffeting of initially untwisted and unwrithed flux tubes within the
convection zone through the Sigma effect. Those regions that strongly
depart from Joy's law show significantly larger than average twist
and a very strong twist-tilt relationship. These properties suggest
that the twist-tilt relationship in these regions is due to kinking of
flux tubes that are initially highly twisted but not strongly writhed
perhaps as a result of dynamo action.
---------------------------------------------------------
Title: How is Magnetic Energy Stored and Released?
Authors: Régnier, S.; Canfield, R. C.
2004ESASP.575..255R Altcode: 2004soho...15..255R
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Field Topology of Sigmoids
Authors: Son, J. H.; Canfield, R. C.; Acton, L. W.
2004AAS...205.1004S Altcode: 2004BAAS...36R1349S
Sigmoids are studied due to their eruptive nature, which affects the
Earth and the space atmosphere. The shape of the sigmoid (S-shaped or
inverse S-shaped) is an indicator of eruption. The origin of this shape
has been the topic of many research papers. One such paper by Fan and
Gibson, The Emergence of a Twisted Magnetic Flux Tube Into a Preexisting
Coronal Arcade, appeared in 2003. Fan and Gibson argue that a sigmoid
with left-handed twist has left-handed writhe, which gives the sigmoid
its S-shape and right-handed twist the inverse S-shape. Our study
determined that there is no correlation between a sigmoid's handedness
and shape as claimed in the paper by Fan and Gibson. Doing a statistical
study observing the topology of the sigmoid using the data from Yohkoh
Soft X-ray Telescope, we classified each sigmoid by its shape, twist,
and magnetic field lines. We found that 23% of our data was right-handed
and S-shaped, 33% was left-handed and S-shaped, 22% was right-handed and
inverse S-shaped, and 22% was left-handed and inverse-S shaped. Thus,
we found no systematic relationship between the handedness and shape
of the sigmoid -- in disagreement with Fan and Gibson.
---------------------------------------------------------
Title: On the Tilt and Twist of Solar Active Regions
Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca
A.; Nandy, Dibyendu; Howard, Robert F.; Pevtsov, Alexei A.
2004ApJ...611.1149H Altcode:
Tilt and twist are two measurable characteristics of solar active
regions that can give us information about subsurface physical
processes associated with the creation and subsequent evolution of
magnetic flux tubes inside the Sun. Using Mees Solar Observatory active
region vector magnetograms and Mount Wilson Observatory full-disk
longitudinal magnetograms, we measure the magnetic twist and tilt
angles of 368 bipolar active regions. In addition to two well-known
phenomena, Joy's law and the hemispheric helicity rule, this data set
also shows a lesser known twist-tilt relationship, which is the focus
of this study. We find that those regions that closely follow Joy's
law do not show any twist-tilt dependence. The dispersion in tilt
angles and the dispersion in twist are also found to be uncorrelated
with each other. Both of these results are predicted consequences of
convective buffeting of initially untwisted and unwrithed flux tubes
through the Σ-effect. However, we find that regions that strongly
depart from Joy's law show significantly larger than average twist
and very strong twist-tilt dependence-suggesting that the twist-tilt
relationship in these regions is due to the kinking of flux tubes that
are initially highly twisted, but not strongly writhed. This implies
that some mechanism other than the Σ-effect (e.g., the solar dynamo
itself or the process of buoyancy instability and flux tube formation)
is responsible for imparting the initial twist (at the base of the
solar convection zone) to the flux tubes that subsequently become
kink-unstable.
---------------------------------------------------------
Title: Twist Propagation in Hα Surges
Authors: Jibben, Patricia; Canfield, Richard C.
2004ApJ...610.1129J Altcode:
We have studied Mees Solar Observatory Hα spectroheliogram and Doppler
velocity movies of surges in 11 active regions. We used these movies
to observe the surges' rotating motion, direction of propagation,
and the implied handedness of that motion. We were able to coregister
movies containing 47 surges with Haleakala Stokes Polarimeter vector
magnetograms. We could hence determine the direction of twist stored
in the magnetic field at the point of origin of each surge. We found
(with a 99% confidence) that the direction of observed spin of these
surges is consistent with the relaxation of the stored twist in the
magnetic field. Magnetic reconnection of twisted flux tubes with their
less twisted surroundings can account for the production and rotating
motion of these surges.
---------------------------------------------------------
Title: Photospheric and Coronal Currents in Solar Active Regions
Authors: Burnette, Andrew B.; Canfield, Richard C.; Pevtsov, Alexei A.
2004ApJ...606..565B Altcode:
Using photospheric line-of-sight magnetograms from the National
Solar Observatory (NSO) Kitt Peak and coronal X-ray images from the
Yohkoh Soft X-Ray Telescope (SXT), we have determined the value of
the constant α of the linear force-free field model (∇XB=αB)
that gives the best visual fit to the overall coronal X-ray structure
(α<SUB>c</SUB>) of 34 flare-productive active regions of relatively
simple bipolar morphology. Vector magnetograms for 24 of these
active regions are available from the Haleakala Stokes Polarimeter
at Mees Solar Observatory. For each of them, we determine the single
best-fit value of α in the photosphere (α<SUB>p</SUB>) by three
quite different methods and show that these methods give statistically
consistent values. By combining this data set with that of the NSO
and SXT, we are able to compare for the first time quantitatively and
statistically the observed values of α in the photosphere and corona
of these regions. We find that the distribution of α<SUB>p</SUB> and
α<SUB>c</SUB> values is fully consistent with the hypothesis that
the overall twist density of the magnetic fields of active regions,
as measured by the linear force-free field parameter α, is the same
in the photosphere and the corona. We therefore conclude that the
electric currents that create the nonpotential structure of such solar
coronal active regions are of subphotospheric origin and pass without
significant modification through the photosphere.
---------------------------------------------------------
Title: Helicity of magnetic clouds and their associated active regions
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A.
2004JGRA..109.5106L Altcode:
In this work we relate the magnetic and topological parameters of twelve
interplanetary magnetic clouds to associated solar active regions. We
use a cylindrically symmetric constant-α force-free model to derive
field line twist, total current, and total magnetic flux from in situ
observations of magnetic clouds. We compare these properties with those
of the associated solar active regions, which we infer from solar
vector magnetograms. Our comparison of fluxes and currents reveals:
(1) the total flux ratios Φ<SUB>MC</SUB>/Φ<SUB>AR</SUB> tend to be of
order unity, (2) the total current ratios I<SUB>MC</SUB>/I<SUB>AR</SUB>
are orders of magnitude smaller, and (3) there is a statistically
significant proportionality between them. Our key findings in comparing
total twists αL are that (1) the values of (αL)<SUB>MC</SUB> are
typically an order of magnitude greater than those of (αL)<SUB>AR</SUB>
and (2) there is no statistically significant sign or amplitude
relationship between them. These findings compel us to believe that
magnetic clouds associated with active region eruptions are formed by
magnetic reconnection between these regions and their larger-scale
surroundings, rather than simple eruption of preexisting structures
in the corona or chromosphere.
---------------------------------------------------------
Title: Magnetic energy and magnetic helicity budget in AR 8210:
What are the sources of flaring activity?
Authors: Régnier, S.; Canfield, R. C.
2004IAUS..223..297R Altcode: 2005IAUS..223..297R
The active region 8210 (AR 8210) observed on May 1, 1998 is the site of
numerous flares. By studying a time series (from 17:00 UT to 21:40 UT)
of reconstructed coronal magnetic configurations, we give a scenario of
the eruptive phenomena in AR 8210 involving the rotation of the sunspot
and the complex topology in a reconnection process. We also study the
time evolution of the energy and of the helicity budget. We compute the
free energy in the corona, the magnetic energy rate due to transverse
photospheric motions. We conclude that the photospheric motions are
related to flaring activities and occur before the injections of energy
into the corona. In terms of magnetic helicity, we are able to derived
the relative magnetic helicity (relative to the potential field) and
the helicity of the potential field configuration. The vacuum helicity
(or helicity of the potential field) is constant during the time
period and characterizes the complex topology. For this time period,
the relative magnetic helicity does not show obvious changes related
to the flaring activity.
---------------------------------------------------------
Title: Detection of a Taylor-like Plasma Relaxation Process in the
Sun and its Implication for Coronal Heating
Authors: Nandy, Dibyendu; Hahn, Michael; Canfield, Richard C.;
Longcope, Dana W.
2004IAUS..223..473N Altcode: 2005IAUS..223..473N
The relaxation dynamics of a magnetized plasma system is a subject
of fundamental importance in MHD - with applications ranging from
laboratory plasma devices like the Toroidal Field Pinch and Spheromaks
to astrophysical plasmas, stellar flaring activity and coronal
heating. Taylor in 1974 proposed that the magnetic field in a plasma
(of small but finite resistivity) relaxes to a minimum energy state,
subject to the constraint that its total magnetic helicity is conserved
(Woltjer 1958), such that the final magnetic field configuration is a
constant alpha (linear) force-free field - where alpha is a quantity
describing the twist in magnetic field lines. However, a clear signature
of this mechanism in astrophysical plasmas remained undetected. Here
we report observational detection of a relaxation process, similar
to what Taylor (1974, 1986) envisaged, in the magnetic fields of
flare-productive solar active regions. The implications of this result
for magnetic reconnection and the coronal heating problem are discussed.
---------------------------------------------------------
Title: The Active Region 8210: Observations, Coronal Magnetic Fields
and Energetics
Authors: Regnier, S.; Canfield, R. C.
2003AGUFMSH22A0174R Altcode:
The active region 8210 observed on May 1, 1998 is the site of several
flares (3 C-class flares from 17:00 UT to 22:00 UT and one M-class flare
at 22:40 UT). In this study, we analyse the causes and consequences
of these flares inside the coronal magnetic configurations: sunspot
rotation, moving features, cancellation of flux. The time evolution
of AR 8210 from observations (magnetograms, Hα , EUV, Soft X-rays)
and the nonlinear force-free reconstructed magnetic fields reveals
that the sites of activity are related to the topological skeleton
(null points, separatrix surfaces, separators): field lines crossing
a separatrix surface reconnect in an other connectivity domain and
produce an Hα brightening at the footpoints. We also determine the free
magnetic energy budget (difference between nonlinear and potential field
magnetic energy) and the relative magnetic helicity. The photospheric
increase (or decrease) of magnetic flux is related to the evolution
of the magnetic energy in the corona above the active region as well
as to the occurence of flares. The main photospheric changes occur
between the times of flaring activity. AR 8210 is a case study for
the Solar MURI project.
---------------------------------------------------------
Title: Detection of a Taylor-like Plasma Relaxation Process in the Sun
Authors: Nandy, Dibyendu; Hahn, Michael; Canfield, Richard C.;
Longcope, Dana W.
2003ApJ...597L..73N Altcode:
The relaxation dynamics of a magnetized plasma system is a subject of
fundamental importance in magnetohydrodynamics-with applications ranging
from laboratory plasma devices such as the toroidal-field pinch and
spheromaks to astrophysical plasmas, stellar flaring activity, and
coronal heating. Taylor in 1974 proposed that the magnetic field in
a plasma, subject to certain constraints, relaxes to a minimum energy
state such that the final magnetic field configuration is a constant α
(linear) force-free field-where α is a quantity describing the twist in
magnetic field lines. While Taylor's theory was remarkably successful in
explaining some intriguing results from laboratory plasma experiments,
a clear signature of this mechanism in astrophysical plasmas remained
undetected. Here we report observational detection of a relaxation
process, similar to what Taylor envisaged, in the magnetic fields of
flare-productive solar active regions. The implications of this result
for magnetic reconnection and the coronal heating problem are discussed.
---------------------------------------------------------
Title: Preflare Phenomena in Eruptive Flares
Authors: Des Jardins, Angela C.; Canfield, Richard C.
2003ApJ...598..678D Altcode:
We report the results of a statistical study of the relationship
between eruptive solar flares and an observed Hα preflare phenomenon
we call moving blueshift events (MBSEs). The Hα data were gathered
using the Mees Solar Observatory CCD imaging spectrograph (MCCD). The
16 events in our data set were observed by both the MCCD and the
Yohkoh Soft X-Ray Telescope, typically for at least 3 hr prior to
the flare and in some cases repeatedly for several days prior to the
flare. The data set contains both eruptive and noneruptive flares,
without bias. Focusing on 3 hr periods before and after the flares,
we found that the average rate of MBSEs prior to the flares was ~5
times greater prior to the 11 eruptive flares than prior to the five
noneruptive ones. Also, the average rate of MBSEs dropped by a factor
of ~6 after the eruptive flares. Earlier studies inferred that MBSEs
reflect motions that originate in the readjustment of magnetic fields
after magnetic reconnection. From the high correlation between eruptive
flares and preflare MBSEs in the several hours prior to such events,
we conclude that reconnection in the chromosphere or low corona plays
an important role in establishing the conditions that lead to solar
flare eruptions.
---------------------------------------------------------
Title: What Is the Role of the Kink Instability in Solar Coronal
Eruptions?
Authors: Leamon, Robert J.; Canfield, Richard C.; Blehm, Zachary;
Pevtsov, Alexei A.
2003ApJ...596L.255L Altcode:
We report the results of two simple studies that seek observational
evidence that solar coronal loops are unstable to the MHD kink
instability above a certain critical value of the total twist. First,
we have used Yohkoh soft X-ray telescope image sequences to measure the
shapes of 191 X-ray sigmoids and to determine the histories of eruption
(evidenced by cusp and arcade signatures) of their associated active
regions. We find that the distribution of sigmoid shapes is quite
narrow and the frequency of eruption does not depend significantly on
shape. Second, we have used Mees Solar Observatory vector magnetograms
to estimate the large-scale total twist of active regions in which
flare-related signatures of eruption are observed. We find no evidence
of eruption for values of large-scale total twist remotely approaching
the threshold for the kink instability.
---------------------------------------------------------
Title: On the origin of activity in solar-type stars
Authors: Canfield, Richard C.
2003AdSpR..32..985C Altcode:
The magnetic flux of solar coronal active regions is thought to
originate in strong toroidal magnetic fields generated by a dynamo at
the base of the convection zone. Once generated, this magnetic flux
rises through the convection zone as discrete buoyant flux tubes,
which may be formed into S2-shaped loops by their interaction with
convective: cells and strong downdrafts. The loops are prevented from
fragmentation by twist and curvature of their axes, which are writhed by
the Coriolis effect and helical convective turbulence. These Σ-shaped
loops emerge through the photosphere to form dipolar sunspot pairs and
coronal active regions. These regions' free energy, relative magnetic
helicity, and tendency to flare and erupt reflect the convection
zone phenomena that dominate their journey to the surface, in which
helical convective turbulence appears to play a primary role. Recent
research leads me to suggest a new paradigm for activity in solar-type
stars with deep-seated (tachocline) dynamos. In the present paradigm,
dynamo models are expected to explain the distribution of activity
in the H-R diagram, as reflected in mean chromospheric emission in
lower main-sequence stars. In the new paradigm, dynamo action simply
generates the flux that is necessary, but not sufficient, for such
activity, and the amplitude of activity depends; most importantly on
the kinetic helicity and turbulence of convection zone flows.
---------------------------------------------------------
Title: Force-free Fields in Active Regions: Magnetic configurations
and Energetics
Authors: Regnier, S.; Canfield, R. C.; Amari, T.
2003SPD....34.0103R Altcode: 2003BAAS...35..805R
To determine the 3D configuration of solar active regions and to define
boundary conditions for MHD codes, we reconstruct the coronal magnetic
field from photospheric measurements. For that, we consider the active
region in an equilibrium state. Three hypotheses are then often used:
the potential field (no electric current), the linear force-free field
(the current density is α times the magnetic field, α is a constant),
the nonlinear force-free field (α is a function of space). We here
compare those three models in terms of connectivity changes and
energetics for two different active regions: AR 8151 and AR 8210. AR
8151 shows dramatical changes between these models whereas AR 8210
configuration stays close to the potential field. The structure of the
filament and of the sigmoid observed in AR 8151 can only be determined
in the nonlinear force-free field: both structures are identified with
twisted flux tubes with ∼ 0.5-0.6 turns. Interestingly, the filament
is a right-handed structure whereas the sigmoid is left-handed! This
work is a part of the Solar MURI project.
---------------------------------------------------------
Title: Magnetic Cloud and Active Region Topology Compared
Authors: Canfield, R. C.; Leamon, R. J.; Jones, S. L.; Lambkin, K.;
Lundberg, B.
2003SPD....34.0518C Altcode: 2003BAAS...35..817C
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is
the relationship between the topology of these clouds and the
associated active region? For our purposes magnetic clouds can be
modeled adequately by a cylindrical force-free magnetic configuration
(Lepping, 1990). We have modeled the magnetic field topology of 14
magnetic clouds and their associated active regions to determine
values of the force-free field parameter for both, as well as total
currents and fluxes. We find that the number of turns of the twisted
magnetic field in the full length of the cloud is typically an order of
magnitude greater than the same quantity across the associated active
region. This finding compels us to reject models of flux rope formation
that do not invoke magnetic reconnection and helicity conservation.
---------------------------------------------------------
Title: On a Cyclic Variation of the Hemispheric Helicity Rule.
Authors: Pevtsov, Alexei A.; Hagyard, Mona J.; Blehm, Zachary; Smith,
James E.; Canfield, Richard C.; Sakurai, Takashi; Hagino, Masaoki
2003IAUJD...3E..35P Altcode:
We report the result of a study of magnetic helicity in solar active
regions during 1980-2000 (cycles 21-23). Using the vector magnetograms
from four different instruments (Haleakala Stokes Polarimeter Marshall
Space Flight Center Mitaka Solar Flare Telescope and Okayama Observatory
Solar Telescope) we calculated the force-free parameter alpha as
in Pevtsov et al. (1995). We use alpha as the proxy for current
helicity. For each instrument we computed a gradient dalpha/dL as
the linear fit of alpha versus latitude L using annual subsets of
data. The hemispheric helicity rule (negative/positive helicity in
northern/southern hemisphere) can be expressed in terms of this gradient
as dalpha/dL < 0. We find that each instrument exhibits change in
sign of this gradient for some years which implies that the hemispheric
helicity rule may not hold in some phases of a solar cycle (see Hagino
and Sakurai 2002). However we do not see consistency between different
instruments in regards to years disobeying the rule. The disagreement
may be due to difference in observations and/or insufficient number of
magnetograms in some years. We conclude that the present data sets do
not allow to make statistically significant inference about possible
cyclic variation of the hemispheric helicity rule.
---------------------------------------------------------
Title: Of Twist and Tilt
Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca
A.; Howard, Robert F.; Pevtsov, Alexei A.
2003IAUJD...3E..27H Altcode:
Using Haleakala Stokes Polarimeter active-region vector magnetograms
and Mt. Wilson Observatory full-disk longitudinal magnetograms we
measure both the overall twist (using the force-free-field parameter
alpha) and tilt of 368 active regions. This dataset clearly shows two
well-known phenomena Joy's law and the hemispheric helicity rule as well
as a lesser-known twist-tilt relationship which is the point of this
work. Those regions that closely follow Joy's law show no twist-tilt
relationship as expected if the twist originates from convective
buffeting of initially untwisted and unwrithed flux tubes within the
convection zone through the Sigma effect. Those regions that strongly
depart from Joy's law show significantly larger than average twist
and a very strong twist-tilt relationship. These properties suggest
that the twist-tilt relationship in these regions is due to kinking of
flux tubes that are initially highly twisted but not strongly writhed
perhaps as a result of dynamo action
---------------------------------------------------------
Title: Magnetic Cloud and Active Region Topology Compared
Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.;
Lundberg, Brian
2003IAUJD...3E..24L Altcode:
Magnetic clouds are closely associated with Coronal Mass Ejections
(CMEs). Most CMEs are associated with active regions. What is the
relationship between the topology of these clouds and the associated
active region? For our purposes magnetic clouds can be modeled
adequately by a cylindrical force-free magnetic configuration (Lepping
1990). We have modeled the magnetic field topology of 14 magnetic
clouds and their associated active regions to determine values of
the force-free field parameter for both as well as total currents and
fluxes. We find that the number of turns of the magnetic field in the
full length of the cloud is typically an order of magnitude greater
than the same quantity in the associated active region. This finding
compels us to reject models of flux rope formation that do not invoke
magnetic reconnection and helicity conservation.
---------------------------------------------------------
Title: The Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI)
Authors: Lin, R. P.; Dennis, B. R.; Hurford, G. J.; Smith, D. M.;
Zehnder, A.; Harvey, P. R.; Curtis, D. W.; Pankow, D.; Turin, P.;
Bester, M.; Csillaghy, A.; Lewis, M.; Madden, N.; van Beek, H. F.;
Appleby, M.; Raudorf, T.; McTiernan, J.; Ramaty, R.; Schmahl, E.;
Schwartz, R.; Krucker, S.; Abiad, R.; Quinn, T.; Berg, P.; Hashii,
M.; Sterling, R.; Jackson, R.; Pratt, R.; Campbell, R. D.; Malone,
D.; Landis, D.; Barrington-Leigh, C. P.; Slassi-Sennou, S.; Cork, C.;
Clark, D.; Amato, D.; Orwig, L.; Boyle, R.; Banks, I. S.; Shirey,
K.; Tolbert, A. K.; Zarro, D.; Snow, F.; Thomsen, K.; Henneck,
R.; Mchedlishvili, A.; Ming, P.; Fivian, M.; Jordan, John; Wanner,
Richard; Crubb, Jerry; Preble, J.; Matranga, M.; Benz, A.; Hudson,
H.; Canfield, R. C.; Holman, G. D.; Crannell, C.; Kosugi, T.; Emslie,
A. G.; Vilmer, N.; Brown, J. C.; Johns-Krull, C.; Aschwanden, M.;
Metcalf, T.; Conway, A.
2002SoPh..210....3L Altcode:
RHESSI is the sixth in the NASA line of Small Explorer (SMEX)
missions and the first managed in the Principal Investigator mode,
where the PI is responsible for all aspects of the mission except
the launch vehicle. RHESSI is designed to investigate particle
acceleration and energy release in solar flares, through imaging and
spectroscopy of hard X-ray/gamma-ray continua emitted by energetic
electrons, and of gamma-ray lines produced by energetic ions. The
single instrument consists of an imager, made up of nine bi-grid
rotating modulation collimators (RMCs), in front of a spectrometer
with nine cryogenically-cooled germanium detectors (GeDs), one behind
each RMC. It provides the first high-resolution hard X-ray imaging
spectroscopy, the first high-resolution gamma-ray line spectroscopy,
and the first imaging above 100 keV including the first imaging of
gamma-ray lines. The spatial resolution is as fine as ∼ 2.3 arc sec
with a full-Sun (≳ 1°) field of view, and the spectral resolution
is ∼ 1-10 keV FWHM over the energy range from soft X-rays (3 keV)
to gamma-rays (17 MeV). An automated shutter system allows a wide
dynamic range (>10<SUP>7</SUP>) of flare intensities to be handled
without instrument saturation. Data for every photon is stored in a
solid-state memory and telemetered to the ground, thus allowing for
versatile data analysis keyed to specific science objectives. The
spin-stabilized (∼ 15 rpm) spacecraft is Sun-pointing to within ∼
0.2° and operates autonomously. RHESSI was launched on 5 February
2002, into a nearly circular, 38° inclination, 600-km altitude orbit
and began observations a week later. The mission is operated from
Berkeley using a dedicated 11-m antenna for telemetry reception and
command uplinks. All data and analysis software are made freely and
immediately available to the scientific community.
---------------------------------------------------------
Title: Non-constant-α force-free field of active region NOAA 8210
Authors: Régnier, S.; Amari, T.; Canfield, R. C.
2002ESASP.505...65R Altcode: 2002IAUCo.188...65R; 2002solm.conf...65R
We investigate the 3D coronal magnetic configuration of the active
region NOAA 8210 (AR8210). This active region observed on May 1, 1998
is the site of numerous flares. Using the non-constant-α force-free
hypothesis, we determine the coronal magnetic field of AR8210. The
EIT/SOHO observations and the reconstructed magnetic configuration
suggest that the initiation of the eruptive events is related to the
existence of a complex topology (e.g. separatrix surfaces). From some
characteristic parameters before and after the eruptions, we note
that the magnetic energy (the free magnetic budget) decreases by 28%
(55%, respectively).
---------------------------------------------------------
Title: Properties of magnetic clouds and geomagnetic storms associated
with eruption of coronal sigmoids
Authors: Leamon, Robert J.; Canfield, Richard C.; Pevtsov, Alexei A.
2002JGRA..107.1234L Altcode:
We study 46 solar coronal eruptions associated with sigmoids seen
in images from the Yohkoh Soft X-ray Telescope (SXT). We relate
the properties of the sigmoids to in situ measurements at 1 AU and
geomagnetic storms. Our primary result is that erupting sigmoids tend
to produce geoeffective magnetic clouds (MCs): 85% of the erupting
sigmoidal structures studied spawned at least a "moderate" (|Dst| ≥
50 nT) geomagnetic storm. A collateral result is that MCs associated
with sigmoids do not show the same solar-terrestrial correlations
as those associated with filaments and, as such, form a distinct
class of events. First, rather than reversing with the global solar
dipole (at solar maximum), the leading field in MCs weakly (2:1)
shows a solar cycle (Hale polarity) based correlation (reversing at
solar minimum). Second, whereas the handedness of MCs associated with
filament eruptions is strongly (95%) related to their launch hemisphere,
that of MCs associated with sigmoid eruptions is only weakly (∼70%)
so related. Finally, we are unaware of any model of the magnetic fields
of sigmoids and their eruption that gives a useful prediction of the
leading field orientation of their associated MC.
---------------------------------------------------------
Title: The Twist and Tilt of Active Region Magnetic Fields
Authors: Holder, Z. A.; McMullen, R. A.; Canfield, R. C.; Howard,
R. F.; Pevtsov, A. A.
2002AAS...200.0305H Altcode: 2002BAAS...34..642H
We combine two large datasets to study the formation of the overall
twist that is present in solar active-region magnetic fields. For
purposes of discussion, we adopt a simplified model in which the
magnetic flux bundles that form active regions start as axisymmetric
toroids, without intrinsic twist, and rise in Ω -shaped loops through
the convection zone, acquiring writhe through the effect of the Coriolis
force on the large-scale flows within them, as well as buffeting by
turbulent convection. The tilt of active regions with respect to the
equator is an observable manifestation of such writhe, at photospheric
levels. Owing to magnetic helicity conservation, we expect this tilt
to be related to twist of the fields of these same regions. Using Mees
Solar Observatory active-region vector magnetograms and Mount Wilson
Observatory full-disk longitudinal magnetograms, we have measured both
the tilt (Mount Wilson) and twist (Mees) of their magnetic fields,
on active-region scales. This dataset clearly shows two well-known
phenomena, Joy's law and the hemispheric handedness rule. In this
paper we present the relationship between twist and tilt and estimate
the extent to which that relationship is due to a mutual dependence of
tilt and twist on latitude. We then compare our observational results
to the simplified model.
---------------------------------------------------------
Title: What is the role of the kink instability in eruption of
X-ray sigmoids?
Authors: Leamon, R.; Canfield, R.; Blehm, Z.; Pevtsov, A.
2002AGUSMSH32D..03L Altcode:
Observers see ample evidence of helical structures in erupting solar
filaments, X-ray sigmoids and CMEs. It has been argued that the total
amount of twist in a given loop is a factor in its MHD stability
[Priest, 1984]. A simple model illustrates this point. Consider a
cylindrical force-free magnetic field with constant α = T /L, where
L is the length of the tube and T is the total twist contained within
it. The tube is stable to the MHD kink instability for total twist
below a critical value T<SUB>c</SUB> ~ 2 π . Rust and Kumar [1996]
compared the shape of 49 transient, bright sigmoid structures to the
signature of a helically kinked flux rope. From a study of the aspect
ratios of these transient sigmoid brightenings, they inferred that the
cause of CMEs is the eruption of an unstable, kinked magnetic field. We
have analyzed 155 X-ray sigmoids in the the Yohkoh SXT data, measuring
the angle γ at which the sigmoid crosses its central axis and the
length of the sigmoid along that axis (which is not identical to L,
but is closely related to it). In a simple 2D force-free analysis,
Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying
that sin γ is a measure of the total twist T. By simple visual
inspection of the Yohkoh SXT movies, we have identified well-known
signatures of eruption, i.e., X-ray cusps and arcades. We find no
relationship between the frequency of occurrence of such signatures
of eruption and sin γ . {Pevtsov, A. A.}, {Canfield, R. C.}, and
{McClymont, A. N.}, Astrophys J., 481, 973, 1997. {Priest, E. R.},
{Solar Magneto-Hydrodynamics}, {Reidel: Dordrecht}, {1984}. {Rust,
D. M.}, and {Kumar, A.}, Astrophys J., 464, L199, 1996.
---------------------------------------------------------
Title: What is the role of the kink instability in eruption of
X-ray sigmoids?
Authors: Canfield, R. C.; Leamon, R. J.; Blehm, Z.; Pevtsov, A. A.
2002AAS...200.2001C Altcode: 2002BAAS...34..672C
Observers see ample evidence of helical structures in erupting solar
filaments, X-ray sigmoids and CMEs. It has been argued that the total
amount of twist in a given loop is a factor in its MHD stability
[Priest, 1984]. A simple model illustrates this point. Consider
a cylindrical force-free magnetic field with constant α = T /L,
where L is the length of the tube and T is the total twist contained
within it. The tube is stable to the MHD kink instability for total
twist below a critical value T<SUB>c</SUB> ~ 2 π . Rust and Kumar
[1996] compared the shape of 49 transient, bright sigmoid structures
to the signature of a helically kinked flux rope. From a study of the
aspect ratios of these transient sigmoid brightenings, they inferred
that the cause of CMEs is the eruption of an unstable, kinked magnetic
field. We have analyzed 191 X-ray sigmoids in the the Yohkoh SXT data,
measuring the angle γ at which the sigmoid crosses its central axis
and the length of the sigmoid along that axis (which is not identical
to L, but is closely related to it). In a simple 2D force-free analysis,
Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying that
sin γ is a measure of the total twist T. By simple visual inspection
of the Yohkoh SXT movies, we have identified well-known signatures of
eruption, i.e., X-ray cusps and arcades. We find no relationship between
the frequency of occurrence of such signatures of eruption and sin γ .
---------------------------------------------------------
Title: Importance of flux emergence as triggers
Authors: Canfield, Richard
2002ocnd.confE...4C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Active region magnetic flux systems
Authors: Canfield, R.
2002cosp...34E.688C Altcode: 2002cosp.meetE.688C
Solar active regions form where and when the tops of bundles of
magnetic flux, shaped like the Greek letter Omega, emerge into the
solar atmosphere. The last decade has witnessed considerable progress
in the understanding of the transport of these flux systems through the
convection zone and their emergence into the visible atmosphere. In
particular, observations with magnetographs and coronal imagers have
drawn attention to the relevance of twist in these magnetic fields to
both the convection zone transport of Omega loops and their eruption,
in the form of coronal mass ejections. In this talk I will review
these magnetic field observations and relevant theoretical models.
---------------------------------------------------------
Title: Solar magnetic fields and geomagnetic events
Authors: Pevtsov, Alexei A.; Canfield, Richard C.
2001JGR...10625191P Altcode:
Some interplanetary studies lead one to expect that the toroidal fields
of individual active regions are directly related to their heliospheric
structure. Other studies conclude that the large-scale solar dipolar
field is more important. We have carried out two studies that bear on
these apparently conflicting views. We first studied geomagnetic events
temporally associated with the eruption of 18 individual coronal X-ray
sigmoids, which occurred while the large-scale solar dipolar magnetic
field pointed southward. We found that if a coronal flux rope model is
used to interpret magnetic structure, eruptions with a southward leading
magnetic field are associated with stronger geomagnetic storms, but
those with a northward leading field are associated with more storms. We
next studied three full magnetic cycles, solar cycles 17-22. We examined
the temporal variation of the ratio of the geomagnetic A<SUB>p</SUB>
index to the sunspot number. We found no statistically compelling
fluctuations of this quantity on solar cycle time scales that are in
phase with the reversal of active region polarities. On the other hand,
we found a weak tendency for fluctuations that are in phase with the
reversal of the large-scale solar dipole field. From these two studies
we infer that the magnetic structure of individual active regions
plays a role in geomagnetic events, but their geoeffectiveness is
complicated by asymmetries in the leading and following magnetic field
and density. We conclude that simple cycle-dependent generalizations
have only statistical significance, and cannot dependably be used to
predict the geomagnetic effects of a given solar eruption.
---------------------------------------------------------
Title: Preflare Phenomena in Eruptive Flares
Authors: Colman, A. M.; Canfield, R. C.
2001AGUSM..SH22A03C Altcode:
We report the results of a statistical study of the relationship
between eruptive solar flares and an observed pre-flare phenomenon we
call blue shift events (BSEs). BSEs are believed to be the result of
magnetic reconnections in the chromosphere. Data for the study, Hα
CCD spectrograph images, were recorded at Mees Solar Observatory in
Hawaii. In order for a flare to be chosen for our study, it had to be
well observed by both the Mees Solar Observatory and Yohkoh. Therefore,
the dataset studied contains both eruptive and non-eruptive flares,
without bias. Once we finished analyzing each flare event for BSEs,
we determined whether or not the flare was eruptive. Out of 16 events
observed, the average rate of BSEs was five times greater prior to
eruptive flares than prior to non-eruptive ones. Also, the rate of
BSEs prior to eruptive flares was six times greater than after the
flares. From this high correlation, we conclude that reconnections in
the lower corona play a role in solar flare eruptions.
---------------------------------------------------------
Title: Properties of Magnetic Clouds Resulting from Eruption of
Coronal Sigmoids
Authors: Leamon, R. J.; Canfield, R. C.; Pevtsov, A. A.
2001AGUSM..SH31C08L Altcode:
We study over 40 eruptions which originated with coronal sigmoids seen
in Yohkoh SXT images, with subsequently observed in situ magnetic
clouds (MCs) and geomagnetic storms at 1~AU. We correlate solar and
interplanetary features so as to infer terrestrial event properties
from their solar sources. A collateral result from studying this
database is that CMEs and MCs resulting from erupting sigmoids seem
not to adhere to rules such as leading B<SUB>z</SUB> versus solar
dipole orientation and, as such, form a distinct class of events. %
Instead of a large-scale dipole rule, we find there is a weak (3:2)
solar cycle (Hale polarity)-based rule for leading interplanetary
field in MCs. We find that the helicity of magnetic clouds is much more
strongly correlated (>90%) with launch hemisphere than the 60--70%\
rule of photospheric active region helicity. This rule appears to hold
for all CMEs, taking the 28 years of events of Bothmer &\ Rust
[“Coronal Mass Ejections,” AGU Monograph Series 99, 139, 1997]. %
At least half of Bothmer &\ Rust's events are associated with
disparitions brusques, outside active regions. We therefore suggest
that active region sigmoids and disappearing filaments are the origins
of two different classes of CMEs.
---------------------------------------------------------
Title: Twist Propagation in Hα Surges
Authors: Jibben, P.; Canfield, R. C.
2001AGUSM..SP51B08J Altcode:
Hα surges are straight or slightly curved ejections that reach
heights of 200 Mm and typically last 10-30 minutes. The surge material
either fades or returns into the chromosphere along the trajectory
of accent. It has been proposed that reconnection of magnetic fields
accounts for Hα surges [2,3]. Previous observations demonstrated
Hα surges are seen in the early stages of flux emergence [1]. We
have studied 11 active regions, selected for surge activity, with
observations from the Mees Solar Observatory's CCD Imaging Spectrograph
and Haleakala Stokes Polarimeter (HSP). The spectroheliograms were
made into movies showing Hα line center and the corresponding Doppler
velocities from the shift in the \ha\ absorption line center. The
direction of stored twist in the magnetic field is determined from
the force-free field parameter, α , where ∇ x B =\ α B, computed
from HSP vector magnetograms. The magnetogram and velocity data were
coregistered and the relationship between the surge spin and the stored
twist in the magnetic field was recorded. Statistical analysis of the
data found with a 99% confidence level that the direction of observed
spin of the surge is consistent with the relaxation of the stored twist
in the magnetic field at the point where the surge originated. [1]
Kurowaka, H. & Kawai, G 1993, The Magnetic and Velocity Fields
of Solar Active Regions, ed. H. Zirin, G. Ai, & H. Wang, ASP
Conf. Ser., 46, 507. [2] Roy, J.-R. 1973, Solar Physics, 28, 95. [3]
Rust, D. M. 1968, Structure and Development of Solar Active Regions,
ed. K. O. Kiepenheuer, IAU Symposium 35, p 77.
---------------------------------------------------------
Title: Hemispheric Helicity Trend for Solar Cycle 23
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Latushko, Sergei M.
2001ApJ...549L.261P Altcode:
Applying the same methods we used in solar cycle 22, we study active
region vector magnetograms, full-disk X-ray images, and full-disk
line-of-sight magnetograms to derive the helicity of solar magnetic
fields in the first 4 years of solar cycle 23. We find that these
three data sets all exhibit the same two key tendencies-significant
scatter and weak hemispheric asymmetry-as were observed in solar cycle
22. This supports the interpretation of these tendencies as signatures
of the writhing of magnetic flux by turbulence in the convection zone.
---------------------------------------------------------
Title: Solar Active Regions
Authors: Canfield, R.
2000eaa..bookE2023C Altcode:
Solar active regions form where the tops of loops of magnetic flux,
shaped like the Greek letter omega (Ω), emerge into the solar
atmosphere where they can be seen. These Ω loops are thought to be
generated by the solar dynamo, located deep within the Sun (see DYNAMOS:
SOLAR AND STELLAR). The appearance of active regions depends greatly
on the radiation used to image them, as well as the angle at...
---------------------------------------------------------
Title: Vector Magnetic Fields, Sub-surface Stresses and Evolution
of Magnetic Helicity
Authors: Canfield, R. C.; Pevtsov, A. A.
2000JApA...21..213C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Structures as Tracers of Sub-surface Processes
Authors: Pevtsov, A. A.; Canfield, R. C.
2000JApA...21..185P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Max Millennium/Whole Sun Month Observations of a Sigmoid Region
(AR 8668)
Authors: Zarro, D. M.; Canfield, R. C.; Nitta, N.; Myers, D. C.;
Gregory, S. E.; Qiu, J.; Alexander, D.; Hudson, H. S.; Thompson,
B. J.; LaBonte, B. J.
2000SPD....31.0236Z Altcode: 2000BAAS...32..817Z
We report on observations of a sigmoidal region AR 8668 obtained
during the Whole Sun Month #3 campaign and Max Millennium Coordinated
Observing Program #2. The observations pertain to the period 1999
August 16-17 during which several GOES B and C class flares occurred
in AR 8668. Near simultaneous observations were obtained by SOHO (EIT
195 Angstroms/ and MDI full-disk magnetograms), TRACE 171 Angstroms/,
Yohkoh SXT, Big Bear (Hα ), and Mees (IVM vector magnetograms). The
multi-wavelength nature of these data, combined with their overlapping
spatial and temporal coverages, provide a unique opportunity to study
the magnetic topology and flaring evolution of twisted flux structures
associated with sigmoids. An objective of this study is to co-align
images and magnetograms obtained before and during the observed flares,
and compare the results with inferences from the topological model of
Titov and Demoulin, A&A 351, 707 (1999). We will present examples
of these coalignments and identify sites of magnetic energy release
that are associated with topological features (e.g. separatrices)
predicted by this model.
---------------------------------------------------------
Title: Simultaneous Hα and X-ray Observations of Prominence Eruption
and Disappearance
Authors: Tonooka, H.; Matsumoto, R.; Miyaji, S.; Martin, S. F.;
Canfield, R. C.; Reardon, K.; McAllister, A.; Shibata, K.
2000AdSpR..26..473T Altcode:
Prominence eruptions or disappearances observed with an Hα limb
filtergraph can be classified into 3 categories, the eruptive
prominence, the quasi-eruptive prominence, and the disappearing
prominence. We investigated their mechanism by comparing the results
of simultaneous observations by Yohkoh SXT and Hα. We found that soft
X-ray features change in both eruptive prominences and quasieruptive
prominences, whereas no significant change takes place in disappearing
prominences.In one prominence eruption event soft X-ray cusp structure
suggests that the reconnection point is just below the Hα prominence
---------------------------------------------------------
Title: The HESSI Coordinated Data Analysis Flare Archive
Authors: Zarro, D. M.; Canfield, R. C.; Csillaghy, A.
1999AAS...194.7703Z Altcode: 1999BAAS...31..960Z
In preparation for the NASA HESSI mission and in conjunction with
the Max Millenium Program, the current capabilities of the Synoptic
Data Archive at the NASA/GSFC Solar Data Analysis Center (SDAC) will
be enhanced. This Flare Archive will provide two distinct functions
with the same database: (1) a WWW interface to synoptic datasets
(e.g. daily images) for planning coordinated observations with HESSI;
(2) a central, searchable archive of ground-based observatory (GBO)
and space-based datasets for convenient joint analysis. Examples
of datasets that the ideal HESSI Flare Archive will benefit from
including are: Datasets & Source Full Disk Coalignment Img. &
Sac Peak, BBSO, NSO (SOLIS) Hα /Optic. Spect. (inc. Polariz.) &
Mees, Meudon Soft/Hard X-ray, EUV Img. & SXI, SXT, HXT, EIT,
TRACE Soft/Hard X-ray Lightcurve & GOES, BCS, BATSE Microwave
Img/Spect. & OVRO, Nobeyama, Zurich Radio (mm, meter, decimeter)
& BIMA, Zurich, Nancay, Izmiran Magnetograms (inc. Vector) &
BBSO, MDI, Mees, Mitaka, MSFC, KPNO Current capabilities of the Synoptic
Data Archive will be demonstrated, and methods for integrating some of
the above ancillary datasets with HESSI observations will be described.
---------------------------------------------------------
Title: Max Millennium Program in 1999/2000
Authors: Canfield, R. C.
1999AAS...194.8006C Altcode: 1999BAAS...31..965C
The primary goal of the Max Millennium program is to understand particle
acceleration and explosive energy release in solar flares. Elements
of the program are ground-based solar observation, data analysis,
and theory. We will work closely with the NASA HESSI mission and other
NASA and NOAA spacecraft during the period of high solar activity from
1999 -- 2004. A comprehensive outline of the Max Millennium program
is on the WWW at http://solar.physics.montana.edu/max_millennium/
Although the HESSI instrument views the whole Sun, many ground-based
instruments have a limited field of view. In order to put together a
compelling dataset, it is important to have comprehensive observations
of a given flare. Experience shows that the effectiveness of instruments
at Ground-Based Observatories (GBOs) with a limited field of view
depends on: Definition of GBO campaigns and targets of opportunity
Web access to GBO and spacecraft data Documentation and evaluation of
current solar conditions Definition and Web posting of GBO plans and
targets Web archive of operational GBO data During the coming year
the emphasis of the Max Millennium program will be on the development
and testing of capabilities for coordination of ground and space-based
solar flare observations and data analysis.
---------------------------------------------------------
Title: Sigmoidal morphology and eruptive solar activity
Authors: Canfield, Richard C.; Hudson, Hugh S.; McKenzie, David E.
1999GeoRL..26..627C Altcode:
Soft X-ray images of solar active regions frequently show S- or
inverse-S (sigmoidal) morphology. We have studied the Yohkoh Soft
X-Ray Telescope video movie for 1993 and 1997. We have classified
active regions according to morphology (sigmoidal or non-sigmoidal)
and nature of activity (eruptive or non-eruptive). As well, we have
used NOAA sunspot areas for each region as a measure of size. We find
that regions are significantly more likely to be eruptive if they are
either sigmoidal or large.
---------------------------------------------------------
Title: Magnetic helicity attracts interdisciplinary participation
at chapman conference
Authors: Canfield, R. C.; Pevtsov, A. A.
1999EOSTr..80...13C Altcode:
During the last 5 years interest in magnetic helicity has grown
dramatically in solar physics as a result of improved capabilities to
measure and image magnetic fields. Magnetic helicity was introduced by
K. Moffatt in the late 1950s as a topological invariant that describes
the complexity of a magnetic field. The topological aspect of helicity
is readily visualized in a Moebius strip, in which the system of
interest is closed and helicity takes two forms, the writhing of the
central axis of the strip and the twisting of the edges of the strip
about that axis.In many plasmas (but not in atmospheres like that
of Earth, for example), helicity is conserved, just as the sum of
twist and writhe is conserved in a Moebius strip. Mathematically, it
is related to linking integrals, which K. F. Gauss employed to study
asteroid paths on the sky. In the late 1970s the concept of magnetic
helicity was introduced in laboratory plasma physics, turbulence theory,
space physics, and statistical theory.
---------------------------------------------------------
Title: Magnetic Helicity in Space and Laboratory Plasmas
Authors: Brown, Michael R.; Canfield, Richard C.; Pevtsov, Alexei A.
1999GMS...111.....B Altcode: 1999mhsl.conf.....B
Using the concept of magnetic helicity, physicists and mathematicians
describe the topology of magnetic fields: twisting, writhing, and
linkage. Mathematically, helicity is related to linking integrals,
which Gauss introduced in the 19th century to describe the paths
of asteroids in the sky. In the late 1970s the concept proved to
be critical to understand laboratory plasma experiments on magnetic
reconnection, dynamos, and magnetic field relaxation. In the late 1980s
it proved equally important in understanding turbulence in the solar
wind and the interplanetary magnetic field. During the last five years
interest in magnetic helicity has grown dramatically in solar physics,
and it will continue to grow as observations of vector magnetic fields
become increasingly sophisticated.
---------------------------------------------------------
Title: High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer
mission for the next (2000) solar maximum
Authors: Lin, Robert P.; Hurford, Gordon J.; Madden, Norman W.;
Dennis, Brian R.; Crannell, Carol J.; Holman, Gordon D.; Ramaty,
Reuven; von Rosenvinge, Tycho T.; Zehnder, Alex; van Beek, H. Frank;
Bornmann, Patricia L.; Canfield, Richard C.; Emslie, A. Gordon; Hudson,
Hugh S.; Benz, Arnold; Brown, John C.; Enome, Shinzo; Kosugi, Takeo;
Vilmer, Nicole; Smith, David M.; McTiernan, Jim; Hawkins, Isabel;
Slassi-Sennou, Said; Csillaghy, Andre; Fisher, George; Johns-Krull,
Chris; Schwartz, Richard; Orwig, Larry E.; Zarro, Dominic; Schmahl,
Ed; Aschwanden, Markus; Harvey, Peter; Curtis, Dave; Pankow, Dave;
Clark, Dave; Boyle, Robert F.; Henneck, Reinhold; Michedlishvili,
Akilo; Thomsen, K.; Preble, Jeff; Snow, Frank
1998SPIE.3442....2L Altcode:
The primary scientific objective of the High Energy Solar Spectroscopic
Imager (HESSI) Small Explorer mission selected by NASA is to investigate
the physics of particle acceleration and energy release in solar
flares. Observations will be made of x-rays and (gamma) rays from
approximately 3 keV to approximately 20 MeV with an unprecedented
combination of high resolution imaging and spectroscopy. The HESSI
instrument utilizes Fourier- transform imaging with 9 bi-grid rotating
modulation collimators and cooled germanium detectors. The instrument
is mounted on a Sun-pointed spin-stabilized spacecraft and placed
into a 600 km-altitude, 38 degrees inclination orbit.It will provide
the first imaging spectroscopy in hard x-rays, with approximately
2 arcsecond angular resolution, time resolution down to tens of ms,
and approximately 1 keV energy resolution; the first solar (gamma)
ray line spectroscopy with approximately 1-5 keV energy resolution;
and the first solar (gamma) -ray line and continuum imaging,with
approximately 36-arcsecond angular resolution. HESSI is planned for
launch in July 2000, in time to detect the thousands of flares expected
during the next solar maximum.
---------------------------------------------------------
Title: The Eruptive Flare of 15 November 1991: Preflare Phenomena
Authors: Canfield, Richard C.; Reardon, Kevin P.
1998SoPh..182..145C Altcode:
We present and interpret observations of the preflare phase of the
eruptive flare of 15 November, 1991 in NOAA AR 6919. New flux emerged
in this region, indicated by arch filaments in Hα and increasing
vertical flux in vector magnetograms. With increasing frequency
before the eruption, transient dark Hα fibrils were observed that
crossed Hα bright plage and the magnetic inversion line to extend
from the region of flux emergence to the filament, whose eruption was
associated with the flare. These crossing fibrils were dynamic, and
were often associated with sites of propagating torsional motion. These
sites propagated from the region of flux emergence into the filament
flux system. We interpret these morphological and dynamic features in
terms of relaxation after magnetic reconnection episodes which create
longer field lines within the filament flux system, as envisioned in
the tether cutting model, and transfer twist to it, as well.
---------------------------------------------------------
Title: Helicity of Solar Active-Region Magnetic Fields
Authors: Canfield, Richard C.; Pevtsov, Alexei A.
1998ASPC..140..131C Altcode: 1998ssp..conf..131C
No abstract at ADS
---------------------------------------------------------
Title: On the Origin of Helicity in Active Region Magnetic Fields
Authors: Pevtsov, A. A.; Canfield, R. C.
1998ASSL..229...85P Altcode: 1998opaf.conf...85P
No abstract at ADS
---------------------------------------------------------
Title: Soft X-Ray Features of Prominence Eruption and Disappearance
Authors: Tonooka, H.; Matsumoto, R.; Miyaji, S.; Martin, S. F.;
Canfield, R. C.; Reardon, K.; McAllister, A.; Shibata, K.
1998ASSL..229..371T Altcode: 1998opaf.conf..371T
No abstract at ADS
---------------------------------------------------------
Title: The High Energy Solar Spectroscopic Imager (HESSI): A Small
Explorer for the Start of the New Millennium
Authors: Holman, G. D.; Lin, R. P.; Dennis, B. R.; Crannell, C. J.;
Ramaty, R. R.; Rosenvinge, T. T.; Canfield, R. C.; Emslie, A. G.;
Hudson, H. S.; Hurford, G. J.; Madden, N. W.; van Beek, H. F.; Benz,
A.; Bornmann, P. L.; Brown, J. C.; Enome, S.; Kosugi, T.; Vilmer,
N.; Zehnder, A.
1997AAS...191.7416H Altcode: 1997BAAS...29R1326H
The High Energy Solar Spectroscopic Imager (HESSI) has been selected
for launch in mid 2000, at the peak of the solar activity cycle. The
primary scientific objective of HESSI is to understand particle
acceleration and explosive energy release in the magnetized plasma at
the Sun. HESSI will provide the first high-spectral-resolution x-ray and
gamma -ray images of the Sun. It will obtain the first imaging above
100 keV, the first imaging of solar gamma -ray lines, and the first
high-resolution spectroscopy of solar gamma -ray lines, including the
first determination of line shapes. In two years HESSI is expected to
obtain observations of tens of thousands of microflares, thousands of
hard x-ray flares, and of order a hundred gamma -ray line flares. HESSI
will also monitor and provide high-spectral-resolution observations of
cosmic and terrestrial hard x-ray and gamma -ray transients, as well
as imaging of the Crab Nebula. HESSI's high spectral, spatial, and
temporal resolution and dynamic range will allow the first detailed
studies of the evolution of both accelerated particles and hot,
thermal plasma in solar flares.
---------------------------------------------------------
Title: The Solar-B Mission
Authors: Antiochos, Spiro; Acton, Loren; Canfield, Richard; Davila,
Joseph; Davis, John; Dere, Kenneth; Doschek, George; Golub, Leon;
Harvey, John; Hathaway, David; Hudson, Hugh; Moore, Ronald; Lites,
Bruce; Rust, David; Strong, Keith; Title, Alan
1997STIN...9721329A Altcode:
Solar-B, the next ISAS mission (with major NASA participation), is
designed to address the fundamental question of how magnetic fields
interact with plasma to produce solar variability. The mission has
a number of unique capabilities that will enable it to answer the
outstanding questions of solar magnetism. First, by escaping atmospheric
seeing, it will deliver continuous observations of the solar surface
with unprecedented spatial resolution. Second, Solar-B will deliver the
first accurate measurements of all three components of the photospheric
magnetic field. Solar-B will measure both the magnetic energy driving
the photosphere and simultaneously its effects in the corona. Solar-B
offers unique programmatic opportunities to NASA. It will continue an
effective collaboration with our most reliable international partner. It
will deliver images and data that will have strong public outreach
potential. Finally, the science of Solar-B is clearly related to the
themes of origins and plasma astrophysics, and contributes directly
to the national space weather and global change programs.
---------------------------------------------------------
Title: What Is the Spatial Relationship between Hard X-Ray Footpoints
and Vertical Electric Currents in Solar Flares?
Authors: Li, Jing; Metcalf, Thomas R.; Canfield, Richard C.; Wülser,
Jean-Pierre; Kosugi, Takeo
1997ApJ...482..490L Altcode:
We examine the spatial relationship between solar hard X-ray sources
observed with the Hard X-Ray Telescope aboard Yohkoh and photospheric
electric currents observed at Mees Solar Observatory. In 1993, Canfield
et al. concluded that energetic electron precipitation tends to occur
at the edge of sites of high vertical current. They did not, however,
have a direct diagnostic of particle precipitation; they used Hα
Stark-wing emission as a proxy. In this paper, we analyze hard X-ray
images and vector magnetograms of six flares of M/X X-ray class to reach
two basic conclusions. First, we confirm that electron precipitation
avoids sites of high vertical current density at photospheric levels,
preferentially occurring adjacent to these current channels. Hence, we
conclude that our observations rule out flare models in which nonthermal
electrons are accelerated within the large-scale active-region current
systems that are observed by present vector magnetographs. Second,
at conjugate magnetic footpoints the stronger hard X-ray emission is
associated with smaller vertical current density and weaker magnetic
field. This result is consistent with a “cornucopia”-shaped magnetic
morphology in which precipitating electrons are preferentially deflected
away from the narrower footpoint by magnetic mirroring.
---------------------------------------------------------
Title: The Solar Flare Dynamics Imager: A Low-Cost Mission for This
Solar Maximum
Authors: Wulser, J. -P.; Bruner, M. E.; Strong, K. T.; Canfield,
R. C.; Culhane, J. L.; Mariska, J. T.; Polidan, R.
1997SPD....28.0232W Altcode: 1997BAAS...29R.898W
The Solar Flare Dynamics Imager (SolFDI) is a very low-cost flare
mission proposed for this upcoming solar maximum. It is based on a small
solar EUV telescope/spectrograph for Spartan Lite, NASA's new ejectable
hitchhiker spacecraft. The experiment's main scientific objective is
to investigate the spatial, temporal, and velocity structure of the
upflowing hot plasma frequently observed in soft X-ray lines during
solar flares. Past observations were spatially unresolved, and the
nature of these plasma flows, and their relationship with the impulsive
phase flare energy release are not well understood. The second objective
is to image the spatial and velocity structure of eruptive flares. Such
observations can ultimately reveal the true three-dimensional geometry
of the eruptive component of the flare. The Solar Flare Dynamics
Imager will observe flares in a few selected extreme ultraviolet lines,
including a high temperature Fe XXIV line. The instrument uses normal
incidence multilayer coated optics to provide simultaneous imaging and
spectroscopy in these lines with good spatial, spectral, and temporal
resolution. The instrument is designed to fit within the envelope
of the Spartan Lite ejectable hitchhiker spacecraft. Spartan Lite is
smaller, and costs a fraction of a SMEX spacecraft. But if launched
into the upcoming solar maximum, its 6-12 month mission duration would
be sufficient to achieve SolFDI's scientific objectives.
---------------------------------------------------------
Title: NOAA 7926: A Kinked, Submerging Omega -loop ?
Authors: Pevtsov, Alexei A.; Canfield, Richard C.
1997SPD....28.0238P Altcode: 1997BAAS...29..900P
Using vector magnetograms and X-ray images, we study the evolution
of decaying active region NOAA AR 7926. This active region had
bipolar structure with non-Hale polarity. Observations suggest
that the following polarity of this active region was in fact the
leading polarity of active region NOAA AR 7918 on the previous solar
rotation. Analyzing the rotation rate of both active regions and the
topology of their magnetic field, we conclude that they belong to a
single magnetic system resembling a kinked Omega loop. During the first
rotation the upper part of the loop was exposed, forming the bipolar
active region of normal (Hale) polarity. The rest of the Omega loop
had emerged on the time by the second rotation, giving the appearance
of non-Hale polarity. The major soft X-ray coronal loops of NOAA AR
7926 closely relate to the weak magnetic field in the middle part of
the region. In that area, the photospheric field stayed concave-down
in the course of dissipation of the active region, and the coronal
loops decreased their length. We also find that coronal loops decrease
their height derived using E and W limb observations of the two active
regions NOAA AR 7926 and NOAA AR 7918. Hence, we concluded that the
magnetic field of the active region submerged under the photosphere.
---------------------------------------------------------
Title: On the Subphotospheric Origin of Coronal Electric Currents
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; McClymont,
Alexander N.
1997ApJ...481..973P Altcode:
Using photospheric vector magnetograms from the Haleakala Stokes
Polarimeter and coronal X-ray images from the Yohkoh Soft X-Ray
Telescope (SXT), we infer values of the force-free field parameter α
at both photospheric and coronal levels within 140 active regions. We
determine the value of α for a linear force-free field that best
fits each magnetogram in a least-squares sense. We average values
from all available magnetograms to obtain a single mean photospheric
α-value <α<SUB>p</SUB>> for each active region. From the SXT
images we estimate α in the corona by determining (π/L) sin γ for
individual loops, where γ is the observed shear angle of X-ray loops
of length L. We then average these values of α to obtain a single
coronal α value, <α<SUB>c</SUB>>, for each active region. <P
/>In active regions for which the photospheric α-map is predominantly
of one sign, we find that the values of <α<SUB>p</SUB>> and
<α<SUB>c</SUB>> are well correlated. Only for active regions in
which both signs of α are well represented, and in which our method of
analysis therefore breaks down, are the values of <α<SUB>p</SUB>>
and <α<SUB>c</SUB>> poorly correlated. The former correlation
implies that coronal electric currents typically extend down to at
least the photosphere. However, other studies imply subphotospheric
origin of the currents, and even current systems, that are observed in
the photosphere. We therefore conclude that the currents responsible
for sinuous coronal structures are of subphotospheric origin.
---------------------------------------------------------
Title: Coronal Structure as a Diagnostic of the Solar Dynamo
Authors: Sandborgh, S.; Canfield, R. C.; Pevtsov, A. A.
1997SPD....28.0151S Altcode: 1997BAAS...29..888S
This paper is motivated by the discovery of large-scale structures
in the distribution of twist of magnetic fields with solar longitude
and latitude. These structures are observed to persist for many
solar rotations (Pevtsov and Latushko, BAAS 27, 978, 1995; Pevtsov,
Canfield, and Metcalf, 4th SOHO Workshop: Helioseismology, Asilomar,
2-6 April 1995; Pevstov, Canfield, and Glatzmaier, Geophysical and
Astrophysical Convection, NCAR, 10-13 October 1995). The large scale of
these patterns, in space and time, implies that they are a deep-seated
phenomenon, presumably that of the solar dynamo itself. Recent
observations of twist and tilt of active regions (Pevstov and Canfield,
Yohkoh Fifth Anniversary Symposium, Yoyogi, 6-8 November 1996, and
Canfield and Pevtsov, this meeting) and the relationship between
photospheric and coronal manifestations of twist (Pevstov, Canfield,
and McClymont, ApJ 481, in press) confirm this conclusion. The Yohkoh
Soft X-Ray Telescope images from the first five years of operations
often clearly show the presence of topologically distinct regions. We
have developed and used IDL software that allows us to identify and
transfer to Carrington coordinates the boundaries of these systems,
which we identify with magnetic flux systems. In this paper we present
the results of our studies of these systems over many solar rotations,
and relate them to the previously discovered persistent large-scale
structures in the distribution of twist of active region magnetic
fields with longitude and latitude.
---------------------------------------------------------
Title: On the Origin of Helicity in Active Region Magnetic Fields
Authors: Canfield, Richard C.; Pevtsov, Alexei A.
1997SPD....28.1705C Altcode: 1997BAAS...29..921C
The magnetic helicity of flux tubes consists of twist and writhe. If
flux bundles at the base of the convection zone are simple axisymmetric
toroids, and rise in omega-shaped loops through the convection zone,
they acquire writhe through the effect of the Coriolis force on flows
within them. The tilt of active regions with respect to the equator is
an observable manifestation of this writhe, at photospheric levels. As
a consequence of helicity conservation, we expect active regions to
acquire twist to compensate for this writhe. The non-zero curl of
the large-scale magnetic fields in active-region vector magnetograms
is the observable manifestation of twist. Recent observations have
revealed many interesting properties of the helicity of solar
magnetic fields. Hemispheric preferences exist: active region
fields predominantly have left-handed topology in the Northern
hemisphere. Prominence structures also predominantly have left-handed
writhe in the Northern hemisphere. Large-scale structures have been
observed to exist in the distribution of both twist and writhe with
longitude and latitude, and to persist for many solar rotations. To
study the physical origin of these properties, we have used a dataset
of about 100 active regions for which vector magnetograms were obtained
at Mees Solar Observatory. We have measured both the overall tilt and
the overall twist of these active regions. The dataset clearly shows
Joy's law, the well-known dependence of tilt on latitude, as well as
the hemispheric dependence of twist. However, our analysis shows that
twist and tilt are not related as they should be if both twist and
tilt are a consequence of the Coriolis force. Hence, we conclude that
the twist seen in active regions is the consequence of a deep-seated
phenomenon, presumably that of the solar dynamo itself.
---------------------------------------------------------
Title: Erratum: "The imaging vector magnetograph at Haleakala"
[Sol. Phys., Vol. 168, No. 2, p. 229 - 250 (Oct 1996)].
Authors: Mickey, D. L.; Canfield, R. C.; Labonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
1997SoPh..170..455M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Reconnection and Helicity in a Solar Flare
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Zirin, Harold
1996ApJ...473..533P Altcode:
Using X-ray images, Hα images, and vector magnetograms, we have
studied the evolution of the coronal structure and magnetic field of
NOAA Active Region 7154 during 1992 May 5-12. A two-ribbon 4B/M7.4
flare associated with an Hα filament eruption was observed on May 8,
15:13-19:16 UT. An interesting feature of the region was a long,
twisted X-ray structure, which formed shortly before the flare
and disappeared after it, being replaced by a system of unsheared
postflare loops. Neither the X-ray nor Hα morphology nor the photo
spheric magnetic field shows any indication of gradual buildup of
nonpotential energy prior to the flare. Rather, the long structure
appears to result from the reconnection of two shorter ones just tens
of minutes before the filament eruption and flare. <P />Using vector
magnetograms and X-ray morphology, we determine the helicity density
of the magnetic field using the force-free field parameter α. The
observations show that the long structure retained the same helicity
density as the two shorter structures, but its greater length implies
a higher coronal twist. The measured length and α value combine to
imply a twist that exceeds the threshold for the MHD kink instability
in a force-free cylindrical flux tube. We conclude that theoretical
studies of such simple models, which have found that the MHD kink
instability does not lead to global dissipation, do not adequately
address the physical processes that govern coronal magnetic fields.
---------------------------------------------------------
Title: High-Energy Solar Spectroscopic Imager (HESSI)
Authors: Dennis, Brian R.; Lin, Robert P.; Canfield, Richard C.;
Crannell, Carol J.; Emslie, A. Gordon; Holman, Gordon D.; Hudson,
Hugh H.; Hurford, Gordon J.; Ling, James C.; Madden, Norman W.;
Ramaty, Reuven
1996SPIE.2804..228D Altcode:
The primary scientific objective of the High Energy Solar Spectroscopic
Imager (HESSI) is to understand particle acceleration and explosive
energy release in the magnetized plasmas at the Sun. HESSI will provide
the first hard X-ray imaging spectroscopy, the first high-resolution
spectroscopy of solar gamma-ray lines from a spacecraft, the first
imaging above 100 keV, and the first imaging of solar gamma- ray
lines. The gamma-ray imaging spectroscopy will provide the first
information on the spatial distribution of energetic (>1 MeV)
protons, heavy ions, and relativistic electrons, and the first
information on the angular distribution of the energetic ions. It
will also provide detailed information on elemental abundances for
both the accelerated ions and the ambient ions in the interaction
region. HESSI uses Fourier-transform imaging spectroscopy to cover
the broad energy range from soft X-rays (2 keV) to gamma-rays (20 MeV)
with spatial resolutions down to 2 arcseconds and spectral resolutions
down to 1 keV. This capability is achieved with 12 bi-grid rotating
modulation collimators located in front of a corresponding set of 12
pairs of cooled germanium and silicon (Si(Li)) detectors to provide
the wide spectral coverage. HESSI has been selected by NASA as an
alternate Medium-class Explorer (MIDEX) mission, for launch in the
year 2000. If it does not get funded as a flight mission, it will be
descoped and proposed at a Small Explorer mission for launch in 2000
at half the MIDEX cost.
---------------------------------------------------------
Title: The Imaging Vector Magnetograph at Haleakala
Authors: Mickey, D. L.; Canfield, R. C.; LaBonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
1996SoPh..168..229M Altcode:
We describe an instrument we have built and installed at Mees Solar
Observatory on Haleakala, Maui, to measure polarization in narrow-band
solar images. Observations in Zeemansensitive photospheric lines have
been made for nearly all solar active regions since the instrument
began operations in 1992. The magnetograph includes a 28-cm aperture
telescope, a polarization modulator, a tunable Fabry-Pérot filter,
CCD cameras and control electronics. Stokes spectra of a photospheric
line are obtained with 7 pm spectral resolution, 1 arc sec spatial
resolution over a field 4.7 arc min square, and polarimetric precision
of 0.1%. A complete vector magnetogram observation can be made every
eight minutes. The flexibility of the instrument encourages diverse
observations: besides active region magnetograms we have made, for
example, composite vector magnetograms of the full solar disk, and
Hα polarization movies of flaring regions.
---------------------------------------------------------
Title: What is the spatial relationship between hard x-ray footpoints
and vertical electric currents?
Authors: Li, Jing; Metcalf, Thomas R.; Canfield, Richard C.; Wülser,
Jean-Pierre; Kosugi, Takeo
1996AIPC..374..336L Altcode: 1996hesp.conf..336L
We examine the spatial relationship between solar flare hard x-ray
emission sites observed with the HXT aboard Yohkoh and photospheric
electric currents observed at Mees Solar Observatory. Canfield et
al. (3) concluded that nonthermal electron precipitation tends to
occur at the edges of sites of high vertical current, not at their
maxima. They did not, however, have very direct observations of the
electron precipitation, since they used Hα Stark wing emission. In
this work we compare hard x-ray images and vertical current maps in six
large M/X-class flares. Our results confirm that electron precipitation
sites avoid regions of strong photospheric vertical currents in large
flares, and that magnetic mirroring strongly influences the relative
HXR brightness of conjugate footpoints.
---------------------------------------------------------
Title: H alpha Surges and X-Ray Jets in AR 7260
Authors: Canfield, Richard C.; Reardon, Kevin P.; Leka, K. D.; Shibata,
K.; Yokoyama, T.; Shimojo, M.
1996ApJ...464.1016C Altcode:
We discuss nine events, observed simultaneously as jets in X-rays and
surges in Hα, which are associated with moving magnetic bipoles. The
X-ray jets share many features with those discovered by Yohkoh in active
regions, emerging flux regions, and X-ray bright points (see paper by
Shibata et al.); in particular, they originate near one end of a pair of
small flaring loops. The Hα surges are adjacent to the X-ray jets. At
the bases of these surges we observe both blueshifts (initially) and
redshifts (1-2 minutes later). All the observed surges spin in a sense
consistent with the relaxation of the twist stored in the magnetic
fields of the moving magnetic bipoles. Newly discovered phenomena
include footpoint convergence and moving-blueshift features. <P
/>We develop a model of the role of magnetic reconnection in these
events. This model explains the temporal and spatial relationship
between the jets and surges, the role of the moving bipoles, the
flaring X-ray loops and their converging Hα footpoints, the Hα
moving-blueshift features, the direction and amount of spin of the
surges, and the relative temporal development of the Hα redshifts
and blueshifts.
---------------------------------------------------------
Title: Evidence for Current-carrying Emerging Flux
Authors: Leka, K. D.; Canfield, R. C.; McClymont, A. N.; van
Driel-Gesztelyi, L.
1996ApJ...462..547L Altcode:
To determine the relationship between electric currents and magnetic
flux in emerging sunspots, we use observations of the morphology,
proper motion, magnetic flux, and currents associated with several
well-observed growing bipoles. Our target was NOAA Active Region 7260,
which included a preexisting large spot and a fast-growing area of new
magnetic flux. Magnetic bipoles in this region are well documented
by X-ray images from the Yohkoh spacecraft and optical images and
vector magnetograms from several ground-based observatories. <P />In
this paper we show that (1) the Hα and X-ray structures associated
with these bipoles do not agree with potential-field extrapolations
of magnetograms; (2) proper motions imply that the flux bundles that
make up these new bipoles are twisted before they emerge; (3) these
new bipoles are cospatial with significant vertical electric currents;
(4) the morphology, proper motion, and measured currents of these
bipoles all imply the same sense of twist; (5) this sense of twist
is the same as the large-scale twist of the preexisting large spot;
and (6) the increase of these currents, as new flux emerges, is not
consistent with their generation by photospheric motions. <P />We
conclude that the new magnetic flux that emerged in this active region
carried currents generated below the photosphere.
---------------------------------------------------------
Title: The High Energy Solar Spectroscopic Imager - HESSI
Authors: Dennis, B. R.; Crannell, C. J.; Holman, G. D.; Ramaty,
R.; von Rosenvinge, T. T.; Benz, A.; Bornmann, P. L.; Brown, J. C.;
Canfield, R. C.; Emslie, A. G.; Enome, S.; Kosugi, T.; Hudson, H. S.;
Hurford, G. J.; Lin, R. P.; Ling, J. C.; Madden, N. W.; van Beek,
H. F.; Vilmer, N.
1996AAS...188.7016D Altcode: 1996BAAS...28..941D
HESSI will investigate the physics of particle acceleration and energy
release in solar flares through an unprecedented combination of high
resolution imaging and spectroscopy of X-rays and gamma rays from 2
keV to 20 MeV during the next solar maximum. It uses Fourier-transform
imaging with 12 bi-grid modulation collimators and cooled germanium and
silicon detectors mounted on a Sun-pointed spin-stabilized spacecraft in
a low-altitude equatorial orbit. HESSI will carry out the first imaging
spectroscopy in hard X-rays with 2 arcseconds angular resolution, time
resolution to tens of ms, and ~ 1 keV energy resolution; the first
gamma-ray line spectroscopy from a spacecraft with ~ 1 keV energy
resolution; and the first gamma-ray line and continuum imaging with
20 arcseconds angular resolution.
---------------------------------------------------------
Title: Magnetic Chirality and Coronal Reconnection
Authors: Pevtsov, A. A.; Canfield, R. C.; McClymont, A. N.
1996AAS...188.3503P Altcode: 1996BAAS...28..871P
We have used Mees Solar observatory vector magnetograms and
Yohkoh Soft X-Ray Telescope images to study the role of magnetic
chirality (handedness) in the trans-equatorial reconnection of
active regions. Transequatorial reconnections are identified using
SXT images. The chirality of the active regions is inferred from
vector magnetograms and SXT images. Our results indicate that active
regions reconnect preferentially with others of the same chirality. We
have identified the 9 closest pairs of active regions separated by
up to +/- 20° in latitude and longitude. All six pairs of active
regions having the same sign of chirality showed transequatorial
connection. All three pairs of active regions of opposite chirality
indicated no inter-connection. Less close pairs of active regions,
with separation up to +/- 40° in latitude and +/- 20° in longitude,
showed the same tendency: 15 of 17 regions with the same chirality were
inter-connected in the corona, and 8 of 10 regions having the opposite
chirality did not show inter-connection. We explain this result with
a simple model of current-system closure.
---------------------------------------------------------
Title: H alpha Surges and X-ray Jets in AR7260
Authors: Canfield, R. C.; Reardon, K. P.; Leka, K. D.; Shibata, K.;
Yokoyama, T.; Shimojo, M.
1996mpsa.conf...49C Altcode: 1996IAUCo.153...49C
No abstract at ADS
---------------------------------------------------------
Title: A Search for Asymmetric Flows in Young Active Regions
Authors: Cauzzi, G.; Canfield, R. C.; Fisher, G. H.
1996ApJ...456..850C Altcode:
We have studied the temporal evolution of photospheric velocities
in young active regions that show evidence of ongoing magnetic
flux emergence. We searched for asymmetries in the vertical plasma
flows between the leading and following legs of the magnetic flux
tubes. Such asymmetries are predicted in models of flux tubes rising
in the convection zone (see the recent work of Fan, Fisher, &
DeLuca). These models, which successfully describe several aspects of
active region formation, predict plasma flows from the leading to the
following leg of a magnetic flux loop, driven by the Coriolis force
acting on the rising loop. These flows contribute to an excess of
gas pressure in the following leg with respect to the leading one. <P
/>Our results show a predominance of downflow in the leading part of
three young regions with respect to the following part, contrary to
the model predictions. The observed asymmetries, obtained by averaging
over the totality of the magnetic structures, range from 60 to 150 m
s<SUP>-1</SUP>. Their real value, however, could be higher if the age
and effective magnetic filling factor were taken into account. The flow
asymmetry seems to disappear when the active regions enter a phase
of magnetic stability. <P />We suggest two possible interpretations
of these results in terms of the dynamics of emerging magnetic flux
tubes as the most plausible ones. One possibility is that the rising
flux tube experiences severe fragmentation during the last stages of
emergence through the convection zone. After fragmentation, the greater
effect of aerodynamic drag strongly reduces the rise speed of the
smaller flux tubes and hence the Coriolis force that drives the flows
from the leading to the following leg of the magnetic loop. Since the
higher gas pressure present in the following leg is no longer balanced,
it will then drive a flow in the opposite direction, i.e., from the
following to the leading side. Estimates of these pressure-driven
flow velocities are consistent with the observed values. A second
possibility is that the asymmetric flows originate from a preexisting
superrotational velocity within high-field strength toroidal flux
rings near the base of the solar convection zone. As pointed out
in the recent work of Moreno-Insertis, Schussler, & Ferriz-Mas,
such superrotational velocities are required to maintain toroidal flux
rings in dynamical equilibrium.
---------------------------------------------------------
Title: Magnetic Chirality and Coronal Reconnection
Authors: Canfield, Richard C.; Pevtsov, Alexei A.; McClymont,
Alexander N.
1996ASPC..111..341C Altcode: 1997ASPC..111..341C
The authors have used Mees Solar Observatory vector magnetograms
and Yohkoh Soft X-ray Telescope images to study the role of magnetic
chirality in the trans-equatorial reconnection of active regions. They
conclude that active regions reconnect preferentially with others of
the same chirality. They explain this result with a simple model of
the closure of their current systems.
---------------------------------------------------------
Title: YOHKOH SXT Observations of Prominence Eruption and
Disappearance
Authors: Tonooka, H.; Matsumoto, R.; Miyaji, S.; Martin, S. F.;
Canfield, R. C.; Reardon, K.; McAllister, A.; Shibata, K.
1996mpsa.conf..493T Altcode: 1996IAUCo.153..493T
No abstract at ADS
---------------------------------------------------------
Title: Coordinated X-ray and Hα Observations of Eruptive Flares
Authors: Wülser, J. -P.; Canfield, R. C.; Sakao, T.; Acton, L. W.
1995SPD....26.1315W Altcode: 1995BAAS...27..990W
No abstract at ADS
---------------------------------------------------------
Title: Latitudinal Variation of Helicity of Photospheric Magnetic
Fields
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R.
1995ApJ...440L.109P Altcode:
Using a 1988-1994 data set of original photospheric vector magnetograms
as well as published data, we have studied the average magnetic
helicity of 69 diverse active regions, adopting the linear force-free
field parameter alpha as a measure. This average value was determined
by minimizing the differences between the computed constant-alpha
force-free and observed horizontal magnetic fields. The average
magnetic helicity shows a sign difference at the 2 sigma level in
opposite hemispheres. In our data set, 76% of the active regions in
the northern hemisphere have negative helicity, and 69% in the southern
hemisphere, positive. Although the data show considerable variation from
one active region to the next, the data set as a whole suggest that
the magnitude of the average helicity increases with solar latitude,
starting at zero near the equator, reaches a maximum near 15 deg - 25
deg in both hemispheres, and drops back toward smaller values avove 35
deg - 40 deg. Qualitative comparison with published models shows that
such latitudinal variation of the average magnetic helicity may result
from either turbulent convective motions or differential rotation,
although our studies of rotating sunspots lead us to favor the former.
---------------------------------------------------------
Title: The 1991 October 24 Flare: A Challenge for Standard Models
Authors: de La Beaujardiere, J. -F.; Canfield, R. C.; Hudson, H. S.;
Wulser, J. -P.; Acton, L.; Kosugi, T.; Masuda, S.
1995ApJ...440..386D Altcode:
The M9.8 solar flare of 1991 October 24 22:30 UT presents several
interesting characteristics: (1) energy release starts high in
the corona; (2) the primary chromospheric ribbons are initially
well separated and do not move apart at an observable rate; (3) no
evidence is found for an erupting filament or other driver. To explain
this flare, we consider several canonical flare models, including a
filament eruption, a confined filament eruption, current interruption,
and interacting loops. We conclude that none of these scenarios
unequivocally explains this flare. Two possibilities which cannot be
ruled out are (1) the eruption of a filament unobservable in H-alpha
which starts high in the corona and produces no ribbon motions smaller
than our detection threshold and no perceptible expansion of the coronal
X-ray source, and (2) energy release due to spontaneous, propagating
reconnection which allows the system to essentially brighten in place.
---------------------------------------------------------
Title: Is the Solar Chromospheric Magnetic Field Force-free?
Authors: Metcalf, Thomas R.; Jiao, Litao; McClymont, Alexander N.;
Canfield, Richard C.; Uitenbroek, Han
1995ApJ...439..474M Altcode:
We use observations of the Na I lambda 5896 spectral line, made with
the Stokes Polarimeter at Mees Solar Observatory, to measure the
chromospheric vector magnetic field in NOAA active region 7216. We
compute the magnetic field from observations of the Stokes parameters
at six wavelengths within this spectral line using a derivative method
and calculate the height dependence of the net Lorentz force in the
photosphere and low chromosphere. We conclude that the magnetic field
is not force-free in the photosphere, but becomes force-free roughly
400 km above the photosphere.
---------------------------------------------------------
Title: The Magnetic Evolution of the Activity Complex AR:7260 -
a Roadmap
Authors: Leka, K. D.; Canfield, R. C.; Mickey, D. L.; van
Driel-Gesztelyi, L.; Nitta, N.; Sakurai, T.; Ichimoto, K.
1994SoPh..155..301L Altcode:
The active region NOAA 7260 rotated onto the north solar hemisphere
as a mature bipole: a dominant negative-polarity sunspot with trailing
plage and scattered small spots in attendance. The dominantp spot itself
had strong magnetic fields and covered almost 400 × 10<SUP>−6</SUP>
of a solar hemisphere. For a period of seven days beginning 14 August,
1992 this active region displayed rapid and drastic evolution: no fewer
than 50 magnetic bipoles emerged in the area trailing the large sunspot,
increasing the region's magnetic flux by more than 10<SUP>22</SUP>
Mx. This new group of sunspots formed a complexβγδ configuration
with twoδ spots and a high degree of magnetic shear.
---------------------------------------------------------
Title: Transient Microwave Brightenings in Solar Active Regions:
Comparison between VLA and YOHKOH Observations
Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994ApJ...437..522G Altcode:
We report observations of transient microwave (2 cm) brightenings
and their relationship with brightenings in soft X-rays. The peak
flux of the microwave brightenings observed by the Very Large Array
(VLA) is smaller than the previously reported fluxes by two orders
of magnitude. The microwave sources were highly polarized (up to
100%) and were situated on the periphery of a sunspot umbra. Among
the many transients observed in X-rays by Yohkoh, two were observed
simultaneously in microwaves. The microwave sources were found to
be closer to the umbra of the sunspot than were the X-ray loops. It
seems that the microwave sources are located at the footpoints of
the looplike X-ray transients. Using the combined VLA, Yohkoh, and
Mees data set, we determine the physical parameters of the loop in
which the brightenings occur. We find that an increase in emission
measure accompanied by small-scale heating can account for the X-ray
brightening. The microwave emission can be interpreted as thermal
gyroresonance or nonthermal gyrosynchrotron processes during the X-ray
brightening. The magnetic field in the microwave-source region is
found to be 1200-1800 G. The observations also provide evidence for
temperature gradient in the coronal loops.
---------------------------------------------------------
Title: The NASA High-Energy Solar Physics Mission (HESP)
Authors: Dennis, B. R.; Emslie, A. G.; Canfield, R.; Doschek, G.;
Lin, R. P.; Ramaty, R.
1994AIPC..294..230D Altcode: 1994hesp.conf..230D
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in our understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. HESP's primary strawman instrument, the High Energy
Imaging Spectrometer (HEISPEC), will provide X-ray and gamma-ray
imaging spectroscopy, i.e., high-resolution spectroscopy at each
spatial point in the image. It has the following unique capabilities:
(1) high-resolution (~keV) spectroscopy from 2 keV-20 MeV to resolve
flare gamma-ray lines and sharp features in the continuum; (2) hard
X-ray imaging with 2` angular resolution and tens of millisecond
temporal resolution, commensurate with the travel times and stopping
distances for the accelerated electrons; (3) gamma-ray imaging with 4-8`
resolution with the capability of imaging in specific lines or continuum
regions; (4) moderate resolution measurements of energetic (20 MeV to
~1 GeV) gamma-rays and neutrons. <P />Addtional strawman instruments
include a Bragg crystal spectrometer for diagnostic information
and a soft X-ray/XUV/UV imager to map the flare coronal magnetic
field and plasma structure. The HESP mission also includes extensive
ground-based observational and supporting theory programs. Recently,
the HESP mission has been adapted to “lightsats”-lighter, smaller,
cheaper spacecraft that can be built faster-and the baseline plan now
includes two Taurus-class and one Pegasus-class spacecraft. A launch
by the end of the year 2000 is desirable to be in time for the next
solar activity maximum.
---------------------------------------------------------
Title: A search for low-energy protons in a solar flare from October
1992: Preliminary results
Authors: Metcalf, T.; Mickey, D.; Canfield, R.; Wülser, J. -P.
1994AIPC..294...59M Altcode: 1994hesp.conf...59M
We give preliminary results from the first use of the University of
Hawaii's new Imaging Vector Magnetograph (IVM) to search for linear
polarization in the H-alpha spectral line during solar flares. Such
polarization has previously been interpreted as impact polarization
from 100 keV protons impacting the chromosphere. The new data set has
several advantages over previous data. First, the field of view is
substantially larger than that used by Metcalf et al., and, second,
the temporal resolution (16 s) is a factor of two better than that
previously obtained. We show a preliminary comparison between the flare
Hα polarization and hard X-rays observed with the Compton Observatory.
---------------------------------------------------------
Title: H_alpha and X-ray Signatures of Chromospheric Heating Observed
in Solar Flares
Authors: Wuelser, J. -P.; Canfield, R. C.; Sakao, T.; Masuda, S.;
Kosugi, T.; Tsuneta, S.
1994kofu.symp..195W Altcode:
We have studied the spatial and temporal relationship between
thermal and non-thermal energy transport, and the chromospheric
response in solar flares. H_alpha imaging spectra from Mees Solar
Observatory provided the information on the heating and dynamics in the
chromosphere, soft X-ray images from Yohkoh provided the conditions
of the thermal plasma in the corona, and hard X-ray data from Yohkoh
provided the diagnostics of the non-thermal particles. We present
some preliminary results for several large flares, and discuss their
implications for the chromospheric flare heating mechanism.
---------------------------------------------------------
Title: Study of Active Region Magnetic Field Structures Using VLA
Radio, YOHKOH X-ray and MEES Optical Observations
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.;
Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J.
1994kofu.symp..347G Altcode:
We report on the observation of compact magnetic flux tubes from the
boundary between the umbra and penumbra of a large sunspot in AR 7135
on April 24, 1992. The structure and geometry of one such flux tube
was determined using the coordinated observations obtained by the
Very Large Array, the Yohkoh Soft X-ray Telescope and the Mees Solar
Observatory. From radio observations we infer that the magnetic field
of the flux tube at the spot-side footpoint is ~ 1300-1800 G.
---------------------------------------------------------
Title: Electric Currents and Coronal Heating in NOAA Active Region
6952
Authors: Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey,
D. L.; Wulser, J. -P.; Martens, P. C. H.; Tsuneta, S.
1994ApJ...428..860M Altcode:
We examine the spatial and temporal relationship between coronal
structures observed with the soft X-ray telescope (SXT) on board the
Yohkoh spacecraft and the vertical electric current density derived from
photospheric vector magnetograms obtained using the Stokes Polarimeter
at the Mees Solar Observatory. We focus on a single active region:
AR 6952 which we observed on 7 days during 1991 December. For 11
independent maps of the vertical electric current density co-aligned
with non-flaring X-ray images, we search for a morphological
relationship between sites of high vertical current density in the
photosphere and enhanced X-ray emission in the overlying corona. We
find no compelling spatial or temporal correlation between the sites of
vertical current and the bright X-ray structures in this active region.
---------------------------------------------------------
Title: Electron precipitation and mass motion in the 1991 June 9
white-light flare
Authors: de La Beaujardiere, J. -F.; Canfield, R. C.; Metcalf, T. R.;
Hiei, E.; Sakurai, T.; Ichimoto, K.
1994SoPh..151..389D Altcode:
We use Hα line profiles as a diagnostic of mass motion and
nonthermal electron precipitation in the white-light flare (WLF) of
1991 June 9 01:34 UT. We find only weak downflow velocities (≈10 km
s<SUP>−1</SUP>) at the site of white-light emission, and comparable
velocities elsewhere.We also find that electron precipitation is
strongest at the WLF site. We conclude that continuum emission in this
flare was probably caused by nonthermal electrons and not by dynamical
energy transport via a chromospheric condensation.
---------------------------------------------------------
Title: Patterns of Helicity in Solar Active Regions
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R.
1994ApJ...425L.117P Altcode:
Using 46 vector magnetograms from the Stokes Polarimeter of Mees
Solar Observatory (MSO), we studied patterns of local helicity
in three diverse solar active regions. From these magnetograms
we computed maps of the local helicity parameter alpha =
J<SUB>z</SUB>/B<SUB>z</SUB>. Although such maps are noisy, we
found patterns at the level approximately 2 to 3 sigma<SUB>J(sub
z</SUB>), which repeat in successive magnetograms for up to
several days. Typically, the alpha maps of any given active region
contain identifiable patches with both positive and negative values
of alpha. Even within a single sunspot complex, several such alpha
patches can often be seen. We followed 68 alpha patches that could be
identified on at least two successive alpha maps. We found that the
persistence fraction of such patches decrease exponentially, with a
characteristic time approximately 27 hr.
---------------------------------------------------------
Title: A Purely Polarized S-Component at 17 GHz
Authors: Shibasaki, Kiyoto; Enome, Shinzo; Nakajima, Hiroshi; Nishio,
Masanori; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Kawashima, Susumu; Bushimata, Takeshi; Shinohara,
Noriyuki; Koshiishi, Hideki; Shiomi, Yasuhiko; Irimajiri, Yoshihisa;
Leka, K. D.; Canfield, Richard C.
1994PASJ...46L..17S Altcode:
A purely polarized bright radio source was found at 17 GHz by the
Nobeyama Radioheliograph. This source was associated with a large
sunspot. The source structure of this S-component was resolved due to
high spatial resolution of the radioheliograph. A soft X-ray image of
this active region taken by Yohkoh Satellite shows no counterpart for
the radio source. Emission mechanism of the radio source is identified
as gyroresonance. Magnetic field of the sunspot was measured by the
Haleakala Vector Magnetograph at Mees Solar Observatory. The field
strength at the half power level of the radio source was 2000 gauss
at the photospheric level. This corresponds to the third harmonic
layer. A bright soft X-ray loop, whose footpoint is at the penumbra
of the large sunspot, can also be seen in the radio map. This loop
is strongly curved, to form a part of spiral, which reflects strong
electric current. Vector magnetogram shows strong rotation of the
transverse field in the sunspot, which also corresponds to strong
electric current. Due to this current and also to the density and the
temperature enhancement near the X-ray loop, the radio peak is shifted
toward the loop and has no dip.
---------------------------------------------------------
Title: Radio Imaging Observations of the Evolution of Thermal and
Nonthermal Sources during a Gradual Solar Burst
Authors: Nishio, Masanori; Nakajima, Hiroshi; Enome, Shinzo; Shibasaki,
Kiyoto; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Bushimata, Takeshi; Kawashima, Susumu; Shinohara,
Noriyuki; Irimajiri, Yoshihisa; Choi, Yong-Seok; Koshiishi, Hideki;
Shiomi, Yasuhiko; Metcalf, Thomas R.; Canfield, Richard C.
1994PASJ...46L..11N Altcode:
With the Nobeyama Radioheliograph, evolution of thermal and nonthermal
radio sources was observed during a gradual solar radio burst. Two
thermal sources were located near the top of an arcade-like soft X-ray
structure observed by the Yohkoh satellite, while a nonthermal source
was observed near the foot points of the arcade-like structure. During
the early phase of the burst, an elongated structure was observed
connecting one of the thermal sources and the nonthermal source. The
elongation started from the location of the nonthermal source and
gradually progressed to the thermal source placed just radially above
the nonthermal source with the velocity of about 170 km s(-1) . These
observations imply that the thermal source and the nonthermal source
are connected by a single magnetic loop, and that the elongation of
the source structure is an indication of chromospheric evaporation by
radio imaging observations. The energetics of the thermal and nonthermal
sources was analyzed using the radio and soft X-ray data. We suggest
that a continuous supply of accelerated electrons for about 1000 s
can maintain the hot plasma observed at the foot points of the loop.
---------------------------------------------------------
Title: Multispectral Observations of Chromospheric Evaporation in
the 1991 November 15 X-Class Solar Flare
Authors: Wuelser, Jean-Pierre; Canfield, Richard C.; Acton, Loren W.;
Culhane, J. Leonard; Phillips, Andrew; Fludra, Andrzej; Sakao, Taro;
Masuda, Satoshi; Kosugi, Takeo; Tsuneta, Saku
1994ApJ...424..459W Altcode:
We analyze simultaneous H(alpha) images and spectra (from Mees
Solar Observatory), and soft and hard X-ray images and spectra (from
YOHKOH) during the early phase of an X1.5/3B flare. We investigate
the morphological relationship between chromospheric downflows,
coronal upflows, and particle precipitation sites, and the energetic
relationship between conductive heating, nonthermal particle heating,
and the chromospheric response. We find that the observations
consistently fit the chromospheric evaporation model. In particular,
we demonstrate that the observed upflowing coronal and downflowing
chromospheric plasma components originate in the same locations,
and we show that our unique set of optical and X-ray observations
can clearly distinguish between conductively driven and electron beam
driven evaporation.
---------------------------------------------------------
Title: Rapid Sunspot Motion Associated with Large Solar Flares
Authors: Reardon, K. W.; Canfield, R. C.; McClymont, A. N.; Hudson,
H. S.
1994ASPC...68..336R Altcode: 1994sare.conf..336R
No abstract at ADS
---------------------------------------------------------
Title: Filament Tether Cutting Before a Major Eruptive Flare
Authors: Canfield, R. C.; Blais, K. A.; Reardon, K. P.; Acton, Loren;
Kurokawa, H.
1994ASPC...68..411C Altcode: 1994sare.conf..411C
No abstract at ADS
---------------------------------------------------------
Title: Evidence for Twisted Emerging Flux in NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.
1994ASPC...68..145L Altcode: 1994sare.conf..145L
No abstract at ADS
---------------------------------------------------------
Title: Photospheric Magnetic Field Measurement Errors and the Inferred
Properties of Coronal Magnetic Fields
Authors: Klimchuk, James A.; Canfield, Richard C.
1994ASPC...68..233K Altcode: 1994sare.conf..233K
No abstract at ADS
---------------------------------------------------------
Title: The NASA High Energy Solar Physics (HESP) mission for the
next solar maximum.
Authors: Lin, R. P.; Dennis, B. R.; Ramaty, R.; Emslie, A. G.;
Canfield, R.; Doschek, G.
1994GMS....84..283L Altcode:
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in the understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. Recently, the HESP mission has been adapted to Lightsats,
lighter, smaller, cheaper spacecraft: the baseline HESP mission now
includes two Pegasus-class spacecraft. A launch by the end of the year
2000 is desirable to be in time for the next solar activity maximum.
---------------------------------------------------------
Title: The X Flare of 15 November, 1991: Preflare Flux Emergence,
Heating and Filament Eruption
Authors: Canfield, R. C.; Blais, K. A.; McClymont, A. N.; Metcalf,
T. R.; Reardon, K. P.; Wülser, J. -P.; Acton, L. W.; Kurokawa, H.;
Hirayama, T.
1994xspy.conf..153C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostics of Twisted Flux Emergence (noaa AR7260)
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Anwar, B.; Canfield,
R. C.; Hudson, H. S.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.;
Kurokawa, H.
1994xspy.conf...25L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flares in Active Region NOAA 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Sakurai,
T.; Shibata, K.; Ichimoto, K.; Canfield, R. C.; Wülser, J. -P.;
Metcalf, T. R.; Mickey, D. L.
1994xspy.conf..111N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα and X-Ray Signatures of Chromospheric Evaporation Observed
during the Early Phase of the 15 November 1991 Flare
Authors: Wülser, J. -P.; Canfield, R. C.; Acton, L. W.; Culhane,
J. L.; Phillips, A.; Fludra, A.; Sakao, T.; Masuda, S.; Kosugi, T.
1994xspy.conf...75W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electric Currents and Coronal Structures in NOAA Active
Region 6952
Authors: Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey,
D. L.; Wülser, J. -P.; Tsuneta, S.
1994xspy.conf...51M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar imaging vector magnetograph
Authors: Canfield, Richard C.
1993huha.rept.....C Altcode:
This report describes an instrument which has been constructed at the
University of Hawaii to make observations of the magnetic field in solar
active regions. Detailed knowledge of active region magnetic structures
is crucial to understanding many solar phenomena, because the magnetic
field both defines the morphology of structures seen in the solar
atmosphere and is the apparent energy source for solar flares. The
new vector magnetograph was conceived in response to a perceived
discrepancy between the capabilities of X ray imaging telescopes to
be operating during the current solar maximum and those of existing
magnetographs. There were no space-based magnetographs planned for
this period; the existing ground-based instruments variously suffered
from lack of sensitivity, poor time resolution, inadequate spatial
resolution or unreliable sites. Yet the studies of flares and their
relationship to the solar corona planned for the 1991-1994 maximum
absolutely required high quality vector magnetic field measurements. By
'vector' measurements we mean that the observation attempts to deduce
the complete strength and direction of the field at the measurement
site, rather than just the line of sight component as obtained by a
traditional longitudinal magnetograph. Knowledge of the vector field
permits one to calculate photospheric electric currents, which might
play a part in heating the corona, and to calculate energy stored in
coronal magnetic fields as the result of such currents. Information
about the strength and direction of magnetic fields in the solar
atmosphere can be obtained in a number of ways, but quantitative data
is best obtained by observing Zeeman-effect polarization in solar
spectral lines. The technique requires measuring the complete state
of polarization at one or more wavelengths within a magnetically
sensitive line of the solar spectrum. This measurement must be done
for each independent spatial point for which one wants magnetic field
data. All the measurements need to be done in a time short compared to
the time scale for changes of the solar features being observed. Were it
possible, one would want to record all the needed data simultaneously,
since temporal variation of atmospheric seeing degrades both the
image and the polarization sensitivity. Since the measurements must
span four dimensions, two spatial plus polarization and wavelength,
we had some freedom to design the instrument to favor some dimensions
over others in terms of simultaneity. Our earlier instrument, the
Haleakala Stokes Polarimeter, records a range of wavelengths spanning
two spectral lines in each reading, but requires two seconds to
determine the polarization state and obtains spatial information only
by assembling a long sequence of measurements at single locations on
the sun. The new instrument sacrifices spectral detail and accuracy
in favor of greatly improved imaging characteristics. The scientific
goals for this instrument were to measure surface magnetic fields with
enough accuracy to permit calculations of photospheric currents, but
with a field of view covering an entire typical active region, high
spatial resolution, and a fast enough temporal cadence for detecting
flare-associated changes in magnetic structures.
---------------------------------------------------------
Title: The NASA high energy solar physics (HESP) mission for the
next solar maximum
Authors: Lin, R. P.; Dennis, B. R.; Emslie, A. G.; Ramaty, R.;
Canfield, R.; Doschek, G.
1993AdSpR..13i.401L Altcode: 1993AdSpR..13..401L
The NASA High Energy Solar Physics (HESP) mission offers the opportunity
for major breakthroughs in our understanding of the fundamental energy
release and particle acceleration processes at the core of the solar
flare problem. HESP's primary strawman instrument, the High Energy
Imaging Spectrometer (HEISPEC), will provide X-ray and γ-ray imaging
spectroscopy, i.e., high-resolution spectroscopy at each spatial
point in the image. It has the following unique capabilities; (1)
high-resolution (~keV) spectroscopy from 2 keV - 20 MeV to resolve flare
gamma-ray lines and sharp features in the continuum; (2) hard X-ray
imaging with 2” angular resolution and tens of millisecond temporal
resolution, commensurate with the travel and stopping distances and
times for the accelerated electrons; (3) gamma-ray imaging with 4”-8”
resolution with the capability of imaging in specific lines or continuum
regions; (4) moderate resolution imaging of energetic (20 MeV to ~1 GeV)
gamma-rays and neutrons. Additional strawman instruments include a Bragg
crystal spectrometer for diagnostic information and a soft X-ray/XUV/UV
imager to map the flare coronal magnetic field and plasma structure. The
HESP mission also includes extensive ground-based observational and
supporting theory programs. Presently HESP is planned for a FY 1995 new
start and late 1999 launch, in time for the next solar activity maximum.
---------------------------------------------------------
Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. I. Introduction and Methods
Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Fan,
Yuhong; Leka, K. D.; McClymont, A. N.; Metcalf, Thomas R.; Mickey,
Donald L.; Wuelser, Jean-Pierre; Lites, Bruce W.
1993ApJ...411..362C Altcode:
Electric current systems in solar active regions and their spatial
relationship to sites of electron precipitation and high-pressure
in flares were studied with the purpose of providing observational
evidence for or against the flare models commonly discussed in the
literature. The paper describes the instrumentation, the data used, and
the data analysis methods, as well as improvements made upon earlier
studies. Several flare models are overviewed, and the predictions
yielded by each model for the relationships of flares to the vertical
current systems are discussed.
---------------------------------------------------------
Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. II. NOAA Active Region 5747
(1989 October)
Authors: Leka, K. D.; Canfield, Richard C.; McClymont, A. N.; de La
Beaujardiere, J. -F.; Fan, Yuhong; Tang, F.
1993ApJ...411..370L Altcode:
The paper describes October 1989 observations in NOAA Active Region 5747
of the morphology of energetic electron precipitation and high-pressure
coronal flare plasmas of three flares and their relation to the
vector magnetic field and vertical electric currents. The H-alpha
spectroheliograms were coaligned with the vector magnetograms using
continuum images of sunspots, enabling positional accuracy of a few
arcsec. It was found that, during the gradual phase, the regions of
the H-alpha flare that show the effects of enhanced pressure in the
overlying corona often encompass extrema of the vertical current
density, consistent with earlier work showing a close relationship
between H-alpha emission and line-of-sight currents. The data are
also consistent with the overall morphology and evolution described
by erupting-filament models such as those of Kopp and Pneuman (1976)
and Sturrock (1989).
---------------------------------------------------------
Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. III. NOAA Active Region 6233
(1990 August)
Authors: de La Beaujardiere, J. -F.; Canfield, Richard C.; Leka, K. D.
1993ApJ...411..378D Altcode:
We investigate the spatial relationship between vertical electric
currents and flare phenomena in NOAA Active Region 6233, which
was observed 1990, August 28-31 at Mees Solar Observatory. The two
flares studied are the 1N/M1.8 flare on August 28, 22:30 UT and the
1N/M1.6 flare on August 29, 20:35 UT. Using Stokes polarimetry we
make magnetograms of the region and compute the vertical current
density. Using H-alpha imaging spectroscopy we identify sites
of intense nonthermal electron precipitation or of high coronal
pressure. The precipitation in these flares is barely strong enough
to be detectable. We find that both precipitation and high pressure
tend to occur near vertical currents, but that neither phenomenon
is cospatial with current maxima. In contrast with the conclusion
of other authors, we argue that these observations do not support a
current-interruption model for flares, unless the relevant currents are
primarily horizontal. The magnetic morphology and temporal evolution of
these flares suggest that an erupting filament model may be relevant,
but this model does not explicitly predict the relationship between
precipitation, high pressure, and vertical currents.
---------------------------------------------------------
Title: The Confined Two-Ribbon Flare of 1991 October 24
Authors: de La Beaujardiere, J. F.; Canfield, R. C.; Hudson, H. S.;
Wuelser, J. -P.; Kosugi, T.; Masuda, S.; Acton, L. W.
1993BAAS...25.1178D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electric Currents and Coronal Structures in NOAA Active
Region 6952
Authors: Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey,
D. L.; Martens, P. C. H.; Tsuneta, S.
1993BAAS...25.1179M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα Impact Polarization Observations in Solar Flares
Authors: Mickey, D. L.; Metcalf, T.; Canfield, R. C.; Wuelser, J. -P.
1993BAAS...25.1223M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Filament Tether Cutting Before a Major Eruptive Flare
Authors: Canfield, R. C.; Blais, K. A.; McClymont, A. N.; Metcalf,
T. R.; Reardon, K. P.; Wuelser, J. -P.; Acton, L. W.; Kurokawa, H.
1993BAAS...25.1188C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Magnetograph Comparison Workshop
Authors: Jones, H.; Bogart, R.; Canfield, R.; Chapman, G.; Henney,
C.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet, V.;
Rabin, D.; Ulrich, R.; Walton, S.
1993BAAS...25.1216J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for Twisted Emerging Flux: NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.; Anwar,
B.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.
1993BAAS...25R1187L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Invited Talk: (The NASA High Energy Solar Physics (HESP)
Mission for the Next Solar Maximum)
Authors: Lin, R. P.; Dennis, B. R.; Ramaty, R.; Emslie, A. G.;
Canfield, R.; Doschek, G.
1993BAAS...25.1180L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated Spectral and Temporal H alpha Observations of a
Solar Flare
Authors: de La Beaujardiere, J. -F.; Kiplinger, Alan L.; Canfield,
Richard C.
1992ApJ...401..761D Altcode:
We report simultaneous observations of a flare (1991 January 11 18:25
UT) with a combination of spectra and high time resolution images in
H-alpha. The Mees Solar Observatory CCD Imaging Spectrograph obtains
spectra and spectroheliograms with a repetition rate of 14 s. These data
permit the identification of sites of nonthermal electron precipitation
or of high coronal pressure. We observe extremely strong electron
precipitation in this flare; we find reasonable agreement between the
observed profiles and theoretical precipitation spectra. We discuss the
possibility that the spectra classed as precipitation signatures are
in fact the result of a projection effect, and we indicate limitations
of the one-dimensional theoretical models.
---------------------------------------------------------
Title: Joint vector magnetograph observations at BBSO, Huairou
Station and Mees Solar Observatory
Authors: Wang, Haimin; Varsik, John; Zirin, Harold; Canfield, Richard
C.; Leka, K. D.; Wang, Jingxiu
1992SoPh..142...11W Altcode:
Joint vector magnetograph observations were carried out at Big Bear
Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou),
and Mees Solar Observatory (MSO) in late September 1989. Comparisons of
vector magnetograms obtained at the three stations show a high degree
of consistency in the morphology of both longitudinal and transverse
fields. Quantitative comparisons show the presence of noise, cross-talk
between longitudinal field and transverse field, Faraday rotation
and signal saturation effects in the magnetograms. We have tried to
establish how the scatter in measurements from different instruments
is apportioned between these sources of error.
---------------------------------------------------------
Title: The X Flare of 1991 November 15: Coordinated Mees/Yohkoh
Observations
Authors: Canfield, Richard C.; Hudson, Hugh S.; Leka, K. D.; Mickey,
Donald L.; Metcalf, Thomas R.; Wuelser, Jean-Pierre; Acton, Loren W.;
Strong, Keith T.; Kosugi, Takeo; Sakao, Taro; Tsuneta, Saku; Culhane,
J. Leonard; Phillips, Andrew; Fludra, Andrzej
1992PASJ...44L.111C Altcode:
This is a preliminary report on two unique new results from coordinated
observations at Mees Solar Observatory and Yohkoh of the X1.5 flare
of 1991 November 15, using vector magnetograms, Hα imaging spectra,
X-ray images, and X-ray spectra. First, we find a close spatial
relationship between Hα redshifts and X-rays from a flare loop and
its footpoints at a time of large X-ray blueshifts. Second, we find
that impulsive-phase hard X-rays originate in regions that are near,
but not coincident with, the peaks of the vertical electrical current
density distribution in AR 6919.
---------------------------------------------------------
Title: The YOHKOH mission for high-energy solar physics
Authors: Acton, L.; Tsuneta, S.; Ogawara, Y.; Bentley, R.; Bruner, M.;
Canfield, R.; Culhane, L.; Doschek, G.; Hiei, E.; Hirayama, T. Hudson,
H.; Kosugi, T.; Lang, J.; Lemen, J.; Nishimura, J.; Makishima, K.;
Uchida, Y.; Watanabe, T.
1992Sci...258..618A Altcode: 1992Sci...258..591A
Data on solar flare mechanisms and the sun's corona will be generated
by Japan's Yohkoh satellite's X-ray imaging sensors and X-ray and
gamma-ray spectrometers. It is noted that the X-ray corona above active
regions expands, in some cases almost continually, in contradiction of
the widely accepted model of magnetohydrostatic equilibrium in such
regions. Flaring X-ray bright points have been discovered to often
involve ejecta into an adjacent, much larger and fainter magnetic loop,
which brightens along its length at speeds up to 1000 km/sec.
---------------------------------------------------------
Title: Hard X-Ray Imaging Observations by YOHKOH of the 1991 November
15 Solar Flare
Authors: Sakao, Taro; Kosugi, Takeo; Masuda, Satoshi; Inda, Mika;
Makishima, Kazuo; Canfield, Richard C.; Hudson, Hugh S.; Metcalf,
Thomas R.; Wuelser, Jean-P.; Acton, Loren W.; Ogawara, Yoshiaki
1992PASJ...44L..83S Altcode:
We report on hard X-ray imaging observations of the 1991 November 15
flare with the HXT instrument aboard {Yohkoh}. Distributions of the hard
X-ray sources at various stages of the flare, together with an overlay
of the white-light flare, are presented. Attention is concentrated on
the behavior of hard X-ray sources during the impulsive phase. The
hard X-ray source appeared initially as a single source near the
magnetic neutral line, then evolved into a double-source shape with the
separation increasing with time. We believe that this is evidence for a
multiple loop system flaring successively with a rising energy-release
site. At the minima between the individual spikes of the time profile,
the hard X-rays at 20--30 keV were concentrated near the apex of the
flaring loop, whereas the hard X-rays above 30 keV originated from the
footpoints. These observations are compared with the existing models.
---------------------------------------------------------
Title: CELIAS: charge, element and isotope analysis system for the
SOHO mission.
Authors: Hovestadt, D.; Geiss, J.; Gloeckler, G.; Axford, W. I.;
Balsiger, H.; Bochsler, P.; Bürgi, A.; Canfield, R.; Coplan, M.;
Dinse, H.; Galvin, A. B.; Gliem, F.; Gringauz, K. I.; Grünwaldt, H.;
Hilchenbach, M.; Hsieh, K. C.; Ipavich, F. M.; Judge, D.; Klecker,
B.; Kühne, M.; Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.;
Neugebauer, M.; Möbius, E.; Reiche, K. V.; Scholer, M.; Wilken, B.
1992ESASP.346..343H Altcode: 1992ssts.rept..343H
The status and further development as well as first calibration of the
CELIAS experiment on SOHO is presented. CELIAS is designed to measure
the mass, ionic charge, and energy of low and high speed solar wind of
suprathermal ions and of low energy flare particles. Through analysis
of the elemental and isotopic abundances (the ionic charge state and
velocity distributions of ions originating on the solar atmosphere),
the investigation focuses on studying the plasma processes in various
temporal and spatial scales in the solar chromosphere, transition zone,
and corona. Additionally, the CELIAS experiment includes the Solar EUV
Monitor (SEM). This unit, which consists of an EUV transmission grating
spectrometer and three isolated silicon photodiodes as detectors,
is described. The three mass and charge discriminating sensors based
on the time of flight technique are also described.
---------------------------------------------------------
Title: The X10 Flare of 1991 June 9: White Light, H-alpha, Magnetic
Fields, and Electric Currents
Authors: de La Beaujardiere, J. -F.; Canfield, R. C.; Metcalf, T. R.;
Hiei, E.; Sakurai, T.; Ichimoto, K.
1992AAS...180.4108D Altcode: 1992BAAS...24..795D
We present observations by several instruments of the white-light
flare (WLF) of 1991 June 9 01:34 UT. A white-light image from the
National Astronomical Observatory of Japan indicates the location
of the WLF within the active region (NOAA 6659). Stokes polarimetry
from Mees Solar Observatory (University of Hawai`i) yields a vector
magnetogram and a map of the vertical electric currents. Also from
Mees comes Hα imaging spectroscopy, which is an indicator of such
specific chromospheric processes as nonthermal electron precipitation,
high coronal pressure, and mass motion. Both Mees instruments provide
continuum images, allowing coregistration of the various datasets. The
white-light emission arises from an extended area including both
sunspot umbra and penumbra. The active region magnetic field is strongly
nonpotential and has numerous vertical electric current channels. The
WLF is situated in an area of relatively low current density at the
edge of the strongest current in the active region, and the nearby
magnetic neutral line is highly sheared. The WLF site shows electron
precipitation, but only in its penumbral portion; stronger magnetic
mirroring in the umbra may inhibit precipitation there. Also, the
precipitation is not especially strong (relative to that observed
elsewhere in this flare), suggesting that the electron-beam model
for WLFs is not appropriate in this case. Also, the lack of strong
redshifts argues against a dynamical energy transport model.
---------------------------------------------------------
Title: November 15, 1991 X Flare -- The Movie: Hα , Soft X-rays,
and Hard X-rays and Magnetic Fields
Authors: Wulser, J. -P.; Acton, L.; Sakao, T.; Canfield, R.; Kosugi,
T.; Slater, G.; Strong, K.; Tsuneta, S.
1992AAS...180.3003W Altcode: 1992BAAS...24..775W
The X1.5/3B flare on 1991 November 15, 22:33 UT was well observed
by the Hα Imaging Spectrograph and the Vector Magnetograph
(Stokes Polarimeter) at Mees Solar Observatory, and by the Soft-
and Hard X-ray Telescopes (SXT and HXT) aboard YOHKOH. We have
combined this multispectral dataset into a series of temporally and
spatially co-aligned video movies and analyzed the morphological
and temporal relationships of the various flare emissions. The
earliest manifestations of this flare include unresolved preflare SXR
brightenings very close to the magnetic neutral line and preflare
motions of filaments seen in Hα . In the flare core, SXR and Hα
emission show moving and rotating coronal structures which we interpret
as a successive brightening of adjacent loops during the main phase
of the flare. The HXR source shows much more dramatic variability
than the SXR source, and they are clearly not cospatial. On the other
hand, there is a close spatial relationship between the HXR and Hα
blue wing emission sites. The Hα , HXR, and SXR images all point to
acceleration and heating in a region that starts close to the neutral
line and moves outward during each HXR burst and during the gradual
phase. Spectacular mass ejections are seen in both SXR and Hα , with
clear unwinding of tightly coiled structures, acceleration of X-ray
and Hα material to velocities of order 1000 km/s, and a striking
thermal bifurcation between hot and cold plasma.
---------------------------------------------------------
Title: Electric Currents and Coronal Structures in Two Flare-
Productive Active Regions, AR 6850 and AR 6952
Authors: Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey,
D. L.; Strong, K. T.; Tsuneta, S.
1992AAS...180.3004M Altcode: 1992BAAS...24R.775M
In this study, we examine the spatial and temporal relationship between
coronal structures observed with the Soft X-Ray Telescope (SXT) on
board the YOHKOH spacecraft and vertical electric currents derived
from vector magnetograms obtained at the Mees Solar Observatory,
Haleakala, Hawaii. We have focused on two active regions, AR 6850
(October 1991) and AR 6952 (December 1991). In both active regions,
we observed significant current structures which persisted over time
scales of days. The SXR emitting coronal structures, however, changed
on much shorter time scales, indicating that there is no compelling,
direct spatial and temporal relationship between the non-flaring SXR
structures and the long-lived electric current systems. We have seen
at least one case (in AR 6952) where a SXR brightening was associated
spatially with a change in the vertical electric current. In this case,
the the vertical current dissipated between December 8, 00:35 UT and
the next observation at 00:48 UT on December 9, leaving a bright SXR
structure which was observed at 24:27 UT on December 8. Hence, although
more data must be analyzed to make a compelling case, it is possible
that the SXR emission is related more closely to changes in the electric
current systems rather than simply to the presence of these currents.
---------------------------------------------------------
Title: The Haleakala Imaging Vector Magnetograph
Authors: Mickey, D. L.; Canfield, R. C.; Labonte, B. J.; Metcalf, T. R.
1992AAS...180.4005M Altcode: 1992BAAS...24..793M
The Imaging Vector Magnetograph, now in daily use at Mees Solar
Observatory, Haleakala, Hawaii, extends our capabilities in the
measurement of solar vector magnetic fields by providing high
spatial and temporal resolution, together with extended area
coverage. The instrument is based on a fast-readout CCD camera as
its primary detector, a tunable air-spaced Fabry-Perot filter for
spectral selection, and variable nematic liquid-crystal retarders
for polarization selection. A 28 cm aperture reflecting telescope
provides an image the size of a large active region; it is coupled
to the magnetograph in a configuration compact enough to mount on
the Observatory's 3.6 m equatorial spar. The assembly can be pointed
independently of the spar to select a region of interest, so the
telescope is always used on-axis. A tip-tilt image stabilizer corrects
for image displacement due to spar shake or large-scale atmospheric
turbulence. A workstation-based computer control system, incorporating
separate processors for user interface, process management and device
control, permits accurate process timing along with a flexible user
interface. The latter is implemented in an X-windows framework, so that
in fact we have found it quite reasonable to operate the instrument
from an X terminal at a remote location. The raw data images are
stored on 8mm tape for off-line processing, or can be reduced in a
few minutes using the instrument's built-in array processor to provide
near-real-time magnetograms. Instrument operational parameters can be
adjusted in several ways to favor spatial resolution, spatial field,
temporal resolution or magnetic sensitivity, but typically we have
a 4.5 x 4.5 arcminute field, 1 arcsecond spatial sampling, and an
observation interval of five minutes. Initial solar observations
showing current capabilities will be presented.
---------------------------------------------------------
Title: Co-Registered High-Time-Resolution Images and Spectra of the
1991 January 11 18:25 UT flare.
Authors: de La Beaujardiere, J. -F.; Kiplinger, A. L.; Canfield, R. C.
1992AAS...180.4506D Altcode: 1992BAAS...24..803D
The 1B/M1.0 flare of 1991 January 11 18:25 UT was simultaneously
observed in Hα by two complementary instruments. Spectra and
spectroheliograms were obtained from the Mees Solar Observatory
CCD Imaging Spectrograph (MCCD) at the University of Hawai`i, while
line-center and blue-wing (-1.3 Angstroms) images were made at 0.1
s time resolution by the NASA/GSFC High-Speed Hα Camera (HSHC)
at the University of Colorado at Boulder. >From the MCCD data we
identify sites showing the spectral signatures of nonthermal electron
precipitation, high coronal pressure, or mass motions. We detect strong
precipitation, and find reasonable agreement between the observed
line profiles and theoretical precipitation spectra. We consider the
possibility that the observed spectra actually arise from a projection
effect and we indicate limitations of the one-dimensional theoretical
models. We also observe redshifted emission which may be the signature
of a chromospheric condensation, and we compare the downflow velocity
with that predicted by the numerical model of Fisher. The slowing-down
time of the observed downflow is about four times longer than in the
model, perhaps because of the superposition of several unresolved
condensations.
---------------------------------------------------------
Title: SPAM: A Canned Internet-Accessible Database of Interest to
Solar Flare Researchers
Authors: Canfield, R. C.; Hudson, H. S.; Kiernan, E.; Metcalf, T. R.;
Wulser, J. -P.
1992AAS...180.5103C Altcode: 1992BAAS...24..813C
We have established a searchable database, called SPAM (Spectroscopy
and Polarimetry at Mees), which contains logs of observations made at
Mees Solar Observatory (Haleakala, Maui). Of more general interest,
the database also includes the Events List and Region Report from
the Space Environment Laboratory (Boulder). Logs from YOHKOH are
currently being added. Hence, SPAM can be used to determine, for
example, whether Mees has vector magnetograms of a certain NOAA AR
or whether YOHKOH has certain types of observations in specified time
ranges. As well, it can be used to search the SEL database for flares
with selected attributes. Included logs (and searchable attributes, in
addition to date, day of year, and time) are: Mees Solar Observatory Log
(instrument, NOAA AR, data type, observing setup), SEL Event List (NOAA
AR, X-ray Class), SEL Region Report (NOAA AR), YOHKOH Orbit Summary,
YOHKOH SXT Quiet Mode PFI Observations (latitude, longitude, X-ray and
optical image size), YOHKOH Flare Observations (latitude, longitude,
specific channel counts or ratios). SPAM runs on a Sun workstation at
Mees Solar Observatory, and is available over Internet. Simply access
(e.g., telnet) koa.ifa.hawaii.edu (128.171.167.1) from any vt100,
Sun, or xterm emulator. Log on as spam (lower case); there is no
password. New users are asked to read release notes and hints.
---------------------------------------------------------
Title: Soft X-ray Blueshifts and Hα Redshifts in the November 15,
1991 X-Class Flare
Authors: Wulser, J. -P.; Acton, L.; Canfield, R.; Culhane, L.; Fludra,
A.; Masuda, S.; Phillips, A.; Sakao, T.
1992AAS...180.1805W Altcode: 1992BAAS...24..755W
We analyzed simultaneous Hα line profile observations (from Mees Solar
Observatory), CaXIX line profile observations (from the Bragg Crystal
Spectrometer aboard YOHKOH), and soft- and hard X-ray images (from SXT
and HXT on YOHKOH) of the November 15, 1991 X-class flare. The observed
CaXIX emission shows strong blueshifts very early in the flare. The soft
X-ray images suggest that this blueshifted emission originates from
one or more of three localized soft X-ray bright points. At the same
time, the Hα line profile shows redshifted and blueshifted emission
in several locations. Two Hα redshift kernels are associated with the
two brightest soft X-ray sources. On the basis of their relationship
to the magnetic neutral line and their subsequent development, we
conclude that these Hα redshift kernels are the footpoints of a
single loop, which initially exhibits two soft X-ray bright points
in the loop legs. The results suggest that chromospheric evaporation
is the responsible mechanism for the observed Hα redshifts and CaXIX
blueshifts in the early stage of the flare. The independent hard X-ray
(HXT) and Hα observations both indicate that this chromospheric
evaporation is not associated with strong non-thermal electron
precipitation. The third soft X-ray bright point, the faintest of the
three, is not associated with redshifted Hα emission. This bright spot
develops into a connection between the second Hα redshift kernel,
and another Hα kernel with strong blueshifts. The Hα blueshift is
associated with a mass ejection phenomenon.
---------------------------------------------------------
Title: Ground-Based Context Observations for the High Energy Solar
Physics (HESP) Mission
Authors: Canfield, R. C.; Hurford, G.
1992AAS...180.3305C Altcode: 1992BAAS...24..780C
The core instrument in the HESP strawman payload is an X-ray and
gamma-ray imaging spectrometer. Physical interpretation of this
instrument's data will require a knowledge of the magnetic and thermal
context in which the radiating ions and electrons are accelerated
and thermalized. Many of the required observations can effectively
and economically be made with ground-based optical and radio imagers,
spectrometers, and magnetographs. For these reasons, the HESP Science
Study Group has included ground-based instruments and observations
as an integral part of the baseline HESP mission. The nature of
HESP's needs for ground-based instrumentation is well understood
as the result of continuing experience with collaborative use of
ground-based instruments in coordination with long-duration balloons,
SMM, and YOHKOH. Ground-based instruments relevant to HESP include
magnetographs (both longitudinal/full disk and vector/active-region),
optical and microwave high-resolution imagers and imaging spectrographs,
and coronagraphs. The key to a successful HESP mission is adequate
ground-based support in three respects: (1) a capability for
observations with the appropriate spatial, spectral, and temporal
resolution, and polarimetric accuracy, from the point of view of the
HESP scientific requirements; (2) sufficiently extensive coordinated
ground-based coverage so that complementary data for HESP-selected
events is likely to be available throughout the mission; (3) adequate
support and the mechanisms so that reduced ground-based data is
conveniently available as an integral part of the HESP data base.
---------------------------------------------------------
Title: The Center-to-Limb Dependence of Flare Hα Redshift Velocities
Authors: Blais, K. A.; Canfield, R. C.
1992AAS...180.4103B Altcode: 1992BAAS...24Q.794B
It is well known that impulsive phase flare spectra show redshifts
in Hα and blueshifts in soft X-ray lines. Various authors have
argued that this is a consequence of chromospheric evaporation and
momentum balance. During the Solar Maximum Mission it was found
that a center-to-limb dependence exists in X-ray blueshifts. This is
understood to imply that the motions of the X-ray emitting material have
a significant radial preference. If this is true, and the motions are
due to chromospheric evaporation (so momentum balance should obtain
in the observed Hα and X-ray plasmas), we should expect to see a
center-to-limb dependence in Hα redshifts, as well. In this paper we
present the results of a statistical study of the Hα spectra of ~
35 flares observed with the CCD Imaging Spectrograph at Mees Solar
Observatory. For purposes of comparison of Hα to the X-ray data,
we have spatially averaged the spectrum of each flare, subtracted off
the preflare spectrum, and determined the line-of-sight velocity of the
usually redshifted component as a function of time using a two-Gaussian
fit. We force one component to appear in the preflare line center,
and determine the maximum observed velocity of the second (shifted)
component for each flare. No center-to-limb dependence is obvious when
we plot these velocities as a function of the usual direction cosine mu
= cos theta . But when we compare this velocity to a modeled one based
on the chromospheric evaporation model, a relationship emerges between
the observed and modeled velocity. Finally, the relationship is improved
still further when we take disk position into account, using a linear mu
relation. We conclude that the center-to-limb dependence of Hα Doppler
shifts in these flares supports the chromospheric evaporation model. As
well, we infer that there is considerable statistical departure from
strictly radial motion due to non-radial magnetic field geometry in
the chromosphere at the sites of these flares.
---------------------------------------------------------
Title: Electric Currents and Hard X-ray Images in the X Class Flare
of November 15, 1991
Authors: Metcalf, T. R.; Sakao, T.; Acton, L. W.; Canfield, R. C.;
Hudson, H. S.; Inda, M.; Kosugi, T.; Wulser, J. P.
1992AAS...180.3005M Altcode: 1992BAAS...24..776M
We present co-aligned observations of hard x-rays observed with the
Hard X-ray Telescope (HXT) on board the YOHKOH spacecraft and vertical
electric currents derived from a vector magnetogram obtained at the
Mees Solar Observatory, Haleakala, Hawaii. Previous work comparing
the wings of the Hα line to vertical electric currents has suggested
that electron precipitation in flares occurs at the edges of these
currents. The Stark wings of Hα were interpreted as a signature of
non-thermal electrons penetrating the relatively dense chromosphere and
used as a proxy for direct observation of the non-thermal electrons. The
hard X-rays used in this study provide a direct determination of
the locations of the electron energy losses. In the X class flare
of November 15, 1991, we find the same relation between hard X-ray
emission and vertical electric currents as was found between Hα Stark
wing emission and vertical currents: the hard x-ray emission occurs
predominantly at the edges of the vertical current sites, and not
spatially on top of these currents. Canfield, R. C., de La Beaujardiere,
J., and Leka, K. D., in “The Physics of Solar Flares", ed. Culhane and
Jordan, The Royal Society, London, 1991 Canfield, R. C., Leka, K. D.,
and Wulser,J. P., in “Flare Physics in Solar Activity Maximum 22",
ed. Uchida, Canfield, Watanabe, and Hiei, Springer-Verlag, Berlin, 1991
---------------------------------------------------------
Title: Search for evidence of low energy protons in solar flares.
Authors: Metcalf, Thomas R.; Wuelser, Jean-Pierre; Canfield, Richard
C.; Hudson, Hugh S.
1992NASCP3137..536M Altcode: 1992como.work..536M
We searched for linear polarization in the H alpha line using the
Stokes Polarimeter at Mees Solar Observatory and present observations
of a flare from NOAA active region 6659 which began at 01:30 UT on
14 Jun. 1991. Our dataset also includes H alpha spectra from the Mees
charge coupled device (MCCD) imaging spectrograph as well as hard x ray
observations from the Burst and Transient Source Experiment (BATSE)
instrument on board the Gamma Ray Observatory (GRO). The polarimeter
scanned a 40 x 40 inch field of view using 16 raster points in a 4 x
4 grid. Each scan took about 30 seconds with 2 seconds at each raster
point. The polarimeter stopped 8.5 inches between raster points and
each point covered a 6 inch region. This sparse sampling increased
the total field of view without reducing the temporal cadence. At
each raster point, an H alpha spectrum with 20 mA spectral sampling is
obtained covering 2.6 A centered on H alpha line center. The preliminary
conclusions from the research are presented.
---------------------------------------------------------
Title: Energetics and Dynamics in a Large Solar Flare of 1989 March
Authors: Wulser, Jean-Pierre; Canfield, Richard C.; Zarro, Dominic M.
1992ApJ...384..341W Altcode:
Solar Maximum Mission X-ray observations and National Solar
Observatory/Sacramento Peak H alpha spectra are combined in a large
(X1.2) solar flare to test predictions of chromospheric heating and
evaporation by nonthermal thick-target electrons. It is demonstrated
that the ratio of H alpha flare energy flux to the energy flux deposited
by thick-target electrons obeys a power-law dependence on electron
heating flux, with a slope that is consistent with that predicted by a
thick-target electron transport and heating model in a 1D hydrostatic
atmosphere. It is concluded that the thick-target model satisfactorily
accounts for the observed magnitude of chromospheric H alpha emission,
and the amplitudes and timing of oppositely directed plasma motions
during the impulsive phase of this X flare.
---------------------------------------------------------
Title: The Practical Application of the Magnetic Virial Theorem
Authors: Klimchuk, J. A.; Canfield, R. C.; Rhoads, J. E.
1992ApJ...385..327K Altcode:
The magnetic energy of solar active regions is computed via the
application of the magnetic virial theorem together with vector
magnetograph data. In order to investigate how errors in the vector
magnetograph measurements produce errors in the virial theorem
energy, the effects of realistic errors on known magnetic fields are
simulated numerically. These include errors due to random polarization
noise, crosstalk between different polarization signals, systematic
polarization bias, and seeing-induced crosstalk. Analytical expressions
for the energy errors which apply under certain idealized conditions are
derived. The results are useful for evaluating the ability of vector
magnetographs to provide suitable data for the accurate determination
of magnetic energies using the virial theorem.
---------------------------------------------------------
Title: Inferring Chromospheric Flare Heating from Hydrogen-Line Wings
Authors: Gayley, K. G.; Canfield, R. C.
1991ApJ...380..660G Altcode:
Strong flare heating that penetrates deeply into the solar chromosphere
is examined, and a simple model that is supported by a numerical
radiative transfer simulation is applied to study how elevated free
electron densities produce markedly increased Stark emission in the
wings of hydrogen Lyman and Balmer lines. The proportionality that
exists between the observed Stark wing intensity and the total energy
deposition in the partially ionized layer is calculated for various
Lyman and Balmer lines. It is concluded that when the effects of
background opacity sources on the wing enhancements are not important,
the magnitude of the nonthermal heating that penetrates the chromosphere
may be inferred from the observed line wings. It is predicted that
Ly-alpha extended wings will exhibit enhancement of Stark shape,
even when inherent damping wing opacity exceeds Stark wing opacity
over the entire absorption profile.
---------------------------------------------------------
Title: The Mees CCD imaging spectrograph
Authors: Penn, Matthew J.; Mickey, Donald L.; Canfield, Richard C.;
Labonte, Barry J.
1991SoPh..135..163P Altcode:
The Mees CCD (MCCD) instrument is an imaging spectroscopy device which
uses the 25 cm coronagraph telescope and the 3.0 m Coudé spectrograph
at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works
with resolving power up to R ≈ 200 000 with significant throughput
from λ3934 Å (CaII K) to λ ≈ 10 000 Å. A fast guiding active
mirror stabilizes the image during observations. A rapidly writing
magnetic tape storage system allows observations to be recorded
at 256 kbytes s<SUP>−1</SUP>. Currently, the MCCD is used for
imaging spectroscopy of solar flares at λ6563 Å (Hα), and velocity
measurements of umbral oscillations; future plans include emission
line studies of active region coronae, and photospheric studies of
solar oscillations.
---------------------------------------------------------
Title: Flare Energy Release: Observational Consequences and Signatures
Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Leka, K. D.
1991RSPTA.336..381C Altcode:
It is generally accepted, but not yet compellingly demonstrated, that
the energy released in solar flares is stored in stressed magnetic
fields. Little is known, at present, about how the most obvious
manifestations of flare energy release - heating, mass motion, magnetic
field reconfiguration and particle acceleration - are related to the
spatial distribution of free energy within those fields. To address
this issue we have underway at Mees Solar Observatory a programme of
simultaneous polarimetric and spectroscopic observations that allow
us to explore the spatial relation between active region currents,
flare particle acceleration and flare heating. In this paper we
discuss several days observations of two flare-productive active
regions. By using the Haleakala Stokes polarimeter, we observed
the spatial distribution of the Stokes profiles of two photospheric
Fe<SUP>I</SUP> lines, from which we inferred the spatial distribution
of the vector magnetic field and the vertical current density. In
flares that were observed on the same days, we then compared the
locations of vertical currents to the sites of non-thermal electron
precipitation and high coronal pressure inferred from Hα line profiles
and spectroheliograms obtained with the Mees charge coupled device
imaging spectrograph. Without exception we found that the sites of
significant energetic electron precipitation into the chromosphere
were at the edges of regions of vertical current, not within them. In
contrast, we found that the footpoints of high-pressure flare plasmas
during the main phase of the observed flares all coincided very well
with such currents.
---------------------------------------------------------
Title: The Magnetic Morphology of High-Pressure Plasmas in Three
October 1989 (AR5747) Flares
Authors: Leka, K. D.; Canfield, R. C.
1991BAAS...23.1066L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Derivation of Vector Magnetic Fields from Stokes Profiles:
Derivative versus Least Squares Fitting Techniques
Authors: Metcalf, T. R.; Canfield, R. C.; Mickey, D. L.
1991BAAS...23.1054M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energetics and Dynamics in an Explosive Flare of March 1989
Authors: Zarro, D. M.; Wüsler, J. -P.; Canfield, R. C.
1991BAAS...23..924Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Practical Application of the Magnetic Virial Therom:
Analytical Results
Authors: Rhoads, J. E.; Klimchuk, J. A.; Canfield, R. C.
1991BAAS...23.1055R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electric Currents and Flares in Solar Active Regions
Authors: Canfield, R. C.
1991BAAS...23.1025C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Current Systems and Particle Precipitation in AR 6233
Authors: de La Beaujardière, J. -F.; Canfield, R. C.
1991BAAS...23.1031D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Practical Application of the Magnetic Virial Theorm:
Simulated Magnetograph Observations
Authors: Klimchuk, J. A.; Canfield, R. C.; Rhoads, J. E.
1991BAAS...23.1031K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα Imaging Spectroscopy during the Max '91 Campaign
Authors: de La Beaujardière, J. -F.; Blais, K. A.; Canfield, R. C.
1991BAAS...23.1071D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Linear Hα Polarization in Flares
Authors: Metcalf, T. R.; Wulser, J. P.; Canfield, R. C.
1991BAAS...23.1073M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Study of Solar Flare Energy Transport Based on Coordinated
H alpha and X-Ray Observations
Authors: Canfield, Richard C.; Wulser, Jean-Pierre; Zarro, Dominic M.;
Dennis, Brian R.
1991ApJ...367..671C Altcode:
The temporal evolution of the ratio between H-alpha to nonthermal hard
X-ray emission was investigated using coordinated H-alpha and hard- and
soft-X-ray observations of five solar flares (on May 7, June 23, June
24, and June 25, 1980 and on April 30, 1985). These observations were
used to estimate the emitted flare energy flux F(H-alpha) in H-alpha,
the flux of F(2O) energy deposited by nonthermal electrons with energies
above 20 keV, and the pressure p(c) of soft X-ray-emitting plasma as
functions of time during the impulsive phase of each flare. It was found
that the F(H-alpha)/F(2O) ratio shows a power-law dependence on F(2O),
with a slope that differs slightly from that predicted by the static
thick-target model of solar transport. Results also indicate that the
power-law dependence is modified by hydrostatic pressure effects.
---------------------------------------------------------
Title: The derivation of vector magnetic fields from Stokes profiles:
derivative versus least squares fitting techniques.
Authors: Metcalf, T. R.; Canfield, R. C.; Mickey, D. L.; Lites, B. W.
1991sopo.work..376M Altcode:
The authors present a comparison of solar magnetic fields calculated
using the weak field equations of Jefferies, Lites, and Skumanich
and the least squares fitting method of Skumanich and Lites. The two
calculations used Fe I 6302 data from June, 1985, and are found to
agree quite well up to at least 1200 G.
---------------------------------------------------------
Title: Chromospheric Plasma Motions in the X 1.2 Flare of 1536 UT
1989 March 11
Authors: Zarro, D. M.; Wülser, J. -P.; Canfield, R. C.
1991max..conf...77Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar astronomy
Authors: Rosner, Robert; Noyes, Robert; Antiochos, Spiro K.; Canfield,
Richard C.; Chupp, Edward L.; Deming, Drake; Doschek, George A.;
Dulk, George A.; Foukal, Peter V.; Gilliland, Ronald L.
1991aap..reptR....R Altcode:
An overview is given of modern solar physics. Topics covered include
the solar interior, the solar surface, the solar atmosphere, the Large
Earth-based Solar Telescope (LEST), the Orbiting Solar Laboratory, the
High Energy Solar Physics mission, the Space Exploration Initiative,
solar-terrestrial physics, and adaptive optics. Policy and related
programmatic recommendations are given for university research and
education, facilitating solar research, and integrated support for
solar research.
---------------------------------------------------------
Title: Flare Physics in Solar Activity Maximum 22
Authors: Uchida, Yutaka; Canfield, Richard C.; Watanabe, Tetsuya;
Hiei, Eijiro
1991LNP...387.....U Altcode: 1991fpsa.conf.....U
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Response During the Gamma Ray Flare on March
10, 1989
Authors: Wülser, J. -P.; Canfield, R. C.; Rieger, E.
1991max..conf..149W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Practical Application of the Magnetic Virial Theorem
Authors: Klimchuk, J. A.; Canfield, R. C.; Rhoads, J. E.
1991LNP...387..219K Altcode: 1991fpsa.conf..219K
We have performed simulated vector magnetograph observations to study
the effects of random and systematic magnetic field measurement errors
on the magnetic energies that may be estimated using the virial theorem.
---------------------------------------------------------
Title: Flare energy release: observational consequences and
signatures.
Authors: Canfield, R. C.; de La Beaujardiere, J. -F.; Leka, K. D.
1991psf..conf..381C Altcode:
At Mees Solar Observatory a programme is underway of simultaneous
polarimetric and spectroscopic observations that allow to explore
the spatial relation between active region currents, flare particle
acceleration and flare heating. The authors discuss several days
observations of two flare-productive active regions. They compared the
locations of vertical currents to the sites of non-thermal electron
precipitation and high coronal pressure inferred from Hα line profiles
and spectroheliograms. Without exception they found that the sites
of significant energetic electron precipitation into the chromosphere
were at the edges of regions of vertical current, not within them. In
contrast, they found that the footpoints of high-pressure flare plasmas
during the main phase of the observed flares all coincided very well
with such currents.
---------------------------------------------------------
Title: Magnetic Morphology of Nonthermal Electron Precipitation
During Three Flares in a Highly Nonpotential Active Region
Authors: Canfield, Richard C.; Leka, K. D.; Wülser, Jean-Pierre
1991LNP...387...96C Altcode: 1991fpsa.conf...96C
NOAA Active region 5747, during its October 1989 transit across
the solar disk, showed highly nonpotential photospheric vector
magnetic field structure and produced many solar flares, three of
which we observed at Mees Solar Observatory. After resolution of
the 180° ambiguity, we determined the photospheric distribution of
the vertical current density. We then compared the locations of the
major current systems to sites of nonthermal electron precipitation
inferred from H profiles of three flares observed using the Mees CCD
Imaging Spectrograph. We found that the sites of energetic electron
precipitation are at the edges of these currents, not at their peaks.
---------------------------------------------------------
Title: Flare Heating and Ionization of the Low Solar
Chromosphere. II. Observations of Five Solar Flares
Authors: Metcalf, Thomas R.; Canfield, Richard C.; Saba, Julia L. R.
1990ApJ...365..391M Altcode:
Two neutral Mg spectral lines formed in the temperature-minimum
region and the low chromosphere, at 4571 and 5173 A, are used to
quantify the changes in the atmospheric structure as a function
of time during five solar flares. Eight proposed flare heating and
ionization mechanisms and predictions of the effects of each on the
temperature minimum region are discussed. Two Mg spectral observations
made at the National Solar Observatory (Sacramento Peak), along with
observations of hard and soft X-rays from the SMM and GOES satellites,
are compared to the predictions of the eight proposed mechanisms. The
initial effects in all five flares are consistent with backwarming by
enhanced Balmer- and Paschen-continuum radiation originating in the
upper chromosphere. Extended heating observed in two of the flares
is most likely due to UV irradiation. In all cases heating by the
dissipation of nonreversed electric currents, collisions with an
electron or proton beam, irradiation by soft X-rays, and dissipation
of Alfven waves are eliminated.
---------------------------------------------------------
Title: H alpha Spectra of Dynamic Chromospheric Processes in Five
Well-observed X-Ray Flares
Authors: Canfield, Richard C.; Penn, Matthew J.; Wulser, Jean-Pierre;
Kiplinger, Alan L.
1990ApJ...363..318C Altcode:
Simultaneous H-alpha and hard X-ray (HXR) spectra were obtained for five
solar flares to determine the relationship of H-alpha profiles and the
nonthermal part of the flare represented by the hard X-ray burst. All
five flares exhibited impulsive-phase redshifted H-alpha in emission,
which was temporarily and spatially associated with intense HXR emission
and broad impulsive-phase H-alpha wings. A few small regions within
two flares showed a blueshifted H-alpha emission which appeared only
early in the impulsive phase and was temporally correlated with the
HXR emission but not with broad H-alpha wings. Finally, there were
both redshifted and blueshifted absorption spectra with properties
fully consistent with those known for erupting and untwisting filaments.
---------------------------------------------------------
Title: Flare Heating and Ionization of the Low Solar Chromosphere
Authors: Metcalf, T. R.; Canfield, R. C.
1990BAAS...22Q.891M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Mass Motions in the X1 Flare of 1533 UT 11
March 1989
Authors: Canfield, R. C.; Zarro, D. M.; Wülser, J. -P.
1990BAAS...22..824C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Vertical Currents in a Flare-Productive Active Region
Authors: Fan, Y.; Canfield, R. C.; McClymont, A. N.
1990BAAS...22..827F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Capabilities of the MCCD System at Mees Solar Observatory
Authors: Penn, M. J.; Mickey, D. L.; Canfield, R. C.
1990BAAS...22..880P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric response during the gamma ray flare on March
10, 1989.
Authors: Wülser, J. -P.; Canfield, R. C.; Rieger, E.
1990BAAS...22..890W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα Flare Observations with the Mees CCD Imaging Spectrograph
Authors: Canfield, R. C.; Mickey, D. L.; Penn, M. J.; Wülser, J. -P.
1990BAAS...22..809C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Response During the Gamma Ray Flare on March
10, 1989
Authors: Wülser, J. -P.; Canfield, R. C.; Rieger, E.
1990BAAS...22R.890W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Morphology of Chromospheric Particle Precipitation
in Three October 1989 (AR 5747) Flares
Authors: Leka, K. D.; Canfield, R. C.; Wülser, J. -P.; Fan, Y.
1990BAAS...22..824L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated Optical and Hard X-ray Flare Observations: A GRO
Guest Investigator Proposal
Authors: Metcalf, T. R.; Wülser, J. P.; Canfield, R. C.
1990BAAS...22..791M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare Heating and Ionization of the Low Solar
Chromosphere. I. Inversion Methods for MG i lambda lambda 4571
and 5173
Authors: Metcalf, Thomas R.; Canfield, Richard C.; Avrett, Eugene H.;
Metcalf, Frederic T.
1990ApJ...350..463M Altcode:
Various methods of inverting solar Mg I 4571 and 5173 spectral line
observations are examined to find the best method of using these lines
to calculate the vertical temperature and electron density structure
around the temperature minimum region. Following a perturbation
analysis by Mein (1971), a Fredholm integral equation of the first
kind is obtained which can be inverted to yield these temperature and
density structures as a function of time. Several inversion methods are
tested and compared. The methods are used to test data as well as to a
subset of observations of these absorption lines taken on February 3,
1986 before and during a solar flare. A small but significant increase
is found in the temperature and a relatively large increase in the
electron density during this flare. The observations are inconsistent
with heating and ionization by an intense beam of electrons and with
ionization by UV photoionization of Si I.
---------------------------------------------------------
Title: Momentum Balance in Four Solar Flares
Authors: Canfield, Richard C.; Zarro, Dominic M.; Metcalf, Thomas R.;
Lemen, James R.
1990ApJ...348..333C Altcode:
Solar Maximum Mission soft X-ray spectra and National Solar Observatory
(Sacramento Peak) H-alpha spectra were combined in a study of high-speed
flows during the impulsive phase of four solar flares. In all events,
a blue asymmetry (indicative of upflows) was observed in the coronal Ca
XIX line during the soft X-ray rise phase. In all events a red asymmetry
(indicative of downflows) was observed simultaneously in chromospheric
H-alpha. These oppositely directed flows were concurrent with impulsive
hard X-ray emission. Combining the velocity data with estimates of the
density based on emission measurements and volume estimates, it is shown
that for the impulsive phase as a whole the total momentum of upflowing
soft X-ray plasma equaled that of the downflowing H-alpha plasma, to
within an order of magnitude, in all four events. Only the chromospheric
evaporation model predicts equal total momentum in the upflowing soft
X-ray-emitting and downflowing H-alphba-emitting materials.
---------------------------------------------------------
Title: On the Stability of Proton Beams against Resonant Scattering
by Alfven Waves in Solar Flare Loops
Authors: Tamres, David H.; Melrose, D. B.; Canfield, Richard C.
1989ApJ...342..576T Altcode:
The growth of Alfven waves in magnetized hydrogen plasma at flare-loop
densities and magnetic field strengths driven by a dilute population of
streaming protons in the energy range 10-1000 keV is investigated. The
streaming distribution induces wave growth principally through resonant
interactions between forward-moving protons and forward-propagating
waves. All other factors constant, the maximum growth rate increases
with mean beam energy and with increased narrowness of the beam
distribution. The frequency of the most rapidly growing waves
is inversely related to the mean beam energy. Under typical flare
conditions, thermal damping when mean energy equals the Alfven speed
effectively stabilizes proton beams of moderate collimation. At beam
energies only one order of magnitude larger, thermal damping under
flare loop conditions is insufficient to prevent highly restrictive
upper limits on the beam-to-background proton density ratio for even
mildly collimated proton beams.
---------------------------------------------------------
Title: On the stability of super-Alfvénic proton beams in solar
flare loops.
Authors: Tamres, D. H.; Melrose, D. B.; Canfield, R. C.
1989BAPS...34.1284T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: H alpha Redshifts as a Diagnostic of Solar Flare Heating
Authors: Zarro, Dominic M.; Canfield, Richard C.
1989ApJ...338L..33Z Altcode:
The dynamics of chomospheric condensations formed during chromospheric
evaporation are studied using coordinated X-ray and H-alpha observations
of five solar flares. It is shown that the peak downflow velocity
of condensations predicted by simple hydrodynamic compression of the
chromosphere is in good agreement with empirical downflow velocities
implied by impulsive phase H-alpha red wing Doppler shifts. It is found
that the H-alpha wing redshift provides a diagnostic of the pressure
excess in the evaporating region and the coronal energy flux driving
chromospheric evaporation. Because preflare coronal pressures derived
for each of the flares are high, it is suggested that the chromosphere
succeeds in radiating excess flare heat energy without undergoing
explosive chromospheric evaporation.
---------------------------------------------------------
Title: Hα Imaging Spectroscopy of Three of the March 1989 X Flares
Authors: Wuelser, J. -P.; Canfield, R. C.
1989BAAS...21R.835W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energetics of Hα and Hard X-Ray Emission in Solar Flares
Authors: Canfield, R. C.; Zarro, D. M.; Wuelser, J. -P.; Dennis, B. R.
1989BAAS...21..846C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Imaging vector Magnetograph for the Next Solar Maximum
Authors: Mickey, D. L.; Canfield, R. C.
1989BAAS...21..863M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lyα Fermi Acceleration in Chromospheric Shocks
Authors: Gayley, K. G.; Canfield, R. C.
1989BAAS...21..851G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An imaging vector magnetograph for the next solar maximum.
Authors: Canfield, R. C.; Mickey, D. L.
1989GMS....54...37C Altcode: 1989sspp.conf...37C
The authors describe the conceptual design of a new imaging vector
magnetograph that combines a modest solar telescope with a rotating
quarter-wave plate, an acousto-optic tunable prefilter as a blocker for
a servo-controlled Fabry-Perot etalon, charge-coupled device cameras,
and a rapid digital tape recorder. Its high spatial resolution (0.5
arc sec pixel size) over a large field-of-view (4 by 5 arc min) is
expected to be sufficient to significantly measure, for the first
time, the magnetic energy dissipated in major solar flares. Its
millisecond tunability and wide spectral range (5000 - 7000 Å)
enable nearly simultaneous vector magnetic field measurements in
the gas-pressure-dominated photosphere and magnetically-dominated,
chromosphere, as well as effective co-alignment with Solar-A's X-ray
images.
---------------------------------------------------------
Title: Chromospheric downflows as a diagnostic of solar flare heating.
Authors: Zarro, D. M.; Canfield, R. C.
1989sasf.confP.203Z Altcode: 1989IAUCo.104P.203Z; 1988sasf.conf..203Z
Using coordinated X-ray and Hα observations of five solar flares,
the authors investigate the dynamics of chromospheric condensations
formed during chromospheric evaporation. They show that the peak
downflow velocity of condensations predicted by simple hydrodynamic
compression of the chromosphere is in good agreement with empirical
downflow velocities implied by impulsive phase Hα redwing Doppler
shifts. This agreement indicates that the Hα wing redshift provides a
useful diagnostic of the pressure excess in the evaporating region and,
hence, the energy flux driving chromospheric evaporation.
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1989epos.conf..225C Altcode:
The work of this group was concerned with how the energy released
in a solar flare is transported through the solar atmosphere before
escaping in the form of radiant and mechanical energy.
---------------------------------------------------------
Title: An imaging vector magnetograph for the next solar maximum
Authors: Mickey, D. L.; Labonte, B. J.; Canfield, R. C.
1989dots.work..324M Altcode:
Researchers describe the conceptual design of a new imaging vector
magnetograph currently being constructed at the University of
Hawaii. The instrument combines a modest solar telescope with a
rotating quarter-wave plate, an acousto-optical tunable prefilter
as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras,
and on-line digital image processing. Its high spatial resolution (1/2
arcsec pixel size) over a large field of view (5 by 5 arcmin) will be
sufficient to significantly measure, for the first time, the magnetic
energy dissipated in major solar flares. Its millisecond tunability
and wide spectral range (5000 to 7000 A) enable nearly simultaneous
vector magnetic field measurements in the gas-pressure-dominated
photosphere and magnetically-dominated chromosphere, as well as
effective co-alignment with Solar-A's X ray images. Researchers
expect to have the instrument in operation at Mees Solar Observatory
(Haleakala) in early 1991. They have chosen to use tunable filters
as wavelength-selection elements in order to emphasize the spatial
relationships between magnetic field elements, and to permit
construction of a compact, efficient instrument. This means that
spectral information must be obtained from sequences of images, which
can cause line profile distortions due to effects of atmospheric seeing.
---------------------------------------------------------
Title: Max 1991: Flare Research at the Next Solar Maximum. Workshop 1:
Scientific Objectives
Authors: Canfield, Richard C.; Dennis, Brian R.
1988fnsm.work.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An imaging vector magnetograph for the next solar maximum
Authors: Canfield, Richard C.; Mickey, Donald L.
1988fnsm.work...81C Altcode:
Measurements of the vector magnetic field in the solar atmosphere
with high spatial and temporal resolution over a large field of view
are critical to understanding the nature and evolution of currents
in active regions. Such measurements, when combined with the thermal
and nonthermal X-ray images from the upcoming Solar-A mission, will
reveal the large-scale relationship between these currents and sites
of heating and particle acceleration in flaring coronal magnetic flux
tubes. The conceptual design of an imaging vector magnetograph that
combines a modest solar telescope with a rotating quarter-wave plate,
an acousto-optical tunable prefilter as a blocker for a servo-controlled
Fabry-Perot etalon, CCD cameras, and a rapid digital tape recorder are
described. Its high spatial resolution (1/2 arcsec pixel size) over a
large field of view (4 x 5 arcmin) will be sufficient to significantly
measure, for the first time, the magnetic energy dissipated in major
solar flares. Its millisecond tunability and wide spectra range (5000 to
8000 A) enable nearly simultaneous vector magnetic field measurements
in the gas-pressure-dominated photosphere and magnetically dominated
chromosphere, as well as effective co-alignment with Solar-A's X-ray
images.
---------------------------------------------------------
Title: The Dependence of Hα Redshifts on Coronal Heating in Solar
Flares
Authors: Zarro, D. M.; Canfield, R. C.
1988BAAS...20.1028Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Imaging Vector Magnetograph for the Next Solar Maximum
Authors: Canfield, R. C.; Mickey, D. L.
1988BAAS...20..745C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of the Temperature Structure of the Temperature
Minimum Region during Solar Flares
Authors: Metcalf, T. R.; Metcalf, F. T.; Canfield, R. C.; Avrett, E. H.
1988BAAS...20..688M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Momentum Balance in Four Solar Flares
Authors: Canfield, R. C.; Zarro, D. M.; Metcalf, T. R.; Lemen, J. R.
1988BAAS...20..688C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Stability of Superof-Alfvénic Proton Beams in Solar
Flare Loops
Authors: Tamres, D. H.; Melrose, D. B.; Canfield, R. C.
1988BAAS...20..739T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Explosive Plasma Flows in a Solar Flare
Authors: Zarro, Dominic M.; Canfield, Richard C.; Strong, Keith T.;
Metcalf, Thomas R.
1988ApJ...324..582Z Altcode:
Solar Maximum Mission soft X-ray data and Sacramento Peak Observatory
H-alpha observations are combined in a study of the impulsive phase of
a solar flare. A blue asymmetry, indicative of upflows, was observed
in the coronal Ca XIX line during the soft X-ray rise phase. A red
asymmetry, indicative of downflows, was observed simultaneously in
chromospheric H-alpha emitted from bright flare kernels during the
period of hard X-ray emission. Combining the velocity data with a
measurement of coronal electron density, it is shown that the impulsive
phase momentum of upflowing soft X-ray-emitting plasma equalled that
of the downflowing H-alpha-emitting plasma to within one order of
magnitude. In particular, the momentum of the upflowing plasma was 2 x
10 to the 21st g cm/s while that of the downflowing plasma was 7 x 10
to the 21st g cm/s, with a factor of 2 uncertainty on each value. This
equality supports the explosive chromospheric evaporation model of
solar flares, in which a sudden pressure increase at the footprint of
a coronal loop produces oppositely directed flows in the heated plasma.
---------------------------------------------------------
Title: Coordinated soft X-ray and Hα observations of solar flares
Authors: Zarro, D. M.; Canfield, R. C.; Metcalf, T. R.; Lemen, J. R.
1988AdSpR...8k.149Z Altcode: 1988AdSpR...8..149Z
We have analyzed a unique set of four solar flares for which coordinated
soft X-ray Ca XIX and Hα spectral observations were obtained during
the impulsive phase. In all events, a blue asymmetry (indicative of
upflows) was observed in the coronal Ca XIX line during the soft X-ray
rise phase. In all events, a red asymmetry (indicative of downflows)
was observed simultaneously in chromospheric Hα at spatial locations
associated with enhanced flare heating. Combining the velocity data with
estimates of the evaporated mass based on soft X-ray emission measure,
we demonstrate that the impulsive phase momentum of upflowing soft
X-ray plasma equalled that of the downflowing Hα plasma, to within an
order of magnitude. This equality supports the explosive chromospheric
evaporation model of solar flares - the only model that predicts equal
momentum content in upflowing coronal and downflowing chromospheric
plasmas. <P />under contract with Lockheed Palo Alto Research Laboratory
---------------------------------------------------------
Title: Max '91: Flare research at the next solar maximum
Authors: Dennis, Brian; Canfield, Richard; Bruner, Marilyn; Emslie,
Gordon; Hildner, Ernest; Hudson, Hugh; Hurford, Gordon; Lin, Robert;
Novick, Robert; Tarbell, Ted
1988STIN...8814919D Altcode:
To address the central scientific questions surrounding solar
flares, coordinated observations of electromagnetic radiation and
energetic particles must be made from spacecraft, balloons, rockets,
and ground-based observatories. A program to enhance capabilities
in these areas in preparation for the next solar maximum in 1991 is
recommended. The major scientific issues are described, and required
observations and coordination of observations and analyses are
detailed. A program plan and conceptual budgets are provided.
---------------------------------------------------------
Title: Impulsive H alpha Diagnostics of Electron-Beam--heated Solar
Flare Model Chromospheres
Authors: Canfield, Richard C.; Gayley, Kenneth G.
1987ApJ...322..999C Altcode:
Time-dependent H-alpha profiles were computed for the dynamic model
atmospheres of Fisher, Canfield, and McClymont (1985) simulating the
effects of an intense impulsively initiated power-law beam of electrons
incident on the chromosphere. The temporal response of H-alpha arises
from three separate physical mechanisms, whose relative importance
varies over the line profile. The fastest variations (typically less
than 0.1 s for the explosive heating discussed here) arise from energy
imbalance; these are apparent on chromospheric heating and cooling
time scales and have their greatest amplitude at line center. Slower
variations arise from ionization imbalance and are most apparent in the
blue wing. The slowest variations arise from hydrodynamic effects and
are related to the formation of a chromospheric condensation; these
are most apparent in the red wing. These results provide a basis for
the design and analysis of observations of H-alpha, in coordination
with hard X-rays or microwaves, to test mechanisms of energy transport
in solar flares.
---------------------------------------------------------
Title: The H alpha Spectral Counterparts of Solar Hard X-Rays
Microflares
Authors: Canfield, Richard C.; Metcalf, Thomas R.
1987ApJ...321..586C Altcode:
X-ray observations have revealed energetically significant numbers
of very small hard X-ray bursts, termed microflares by Lin et al. The
authors have simultaneously observed the Hα counterparts of serveral
of these microflares. It is found that microflares occur in regions
that are also productive of larger flares, suggesting that they may be
components of the larger flare event. All but the weakest miroflares
show pronounced impulsive-phase red asymmetry in Hα. Their energetics,
interpreted using the thick-target nonthermal model of electron
transport, implies that these events are substantially underresolved at
the authors' spatial resolution and have a true area of 10<SUP>15</SUP>-
10<SUP>16</SUP>cm<SUP>-2</SUP>.
---------------------------------------------------------
Title: Alfvén Wave Growth Driven by Streaming Protons in Coronal
Loops
Authors: Tamres, D. H.; Melrose, D. B.; Canfield, R. C.
1987BAAS...19R.943T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Explosive Mass Motions in the Flare of 1456 UT 7 May 1980
Authors: Canfield, Richard C.; Zarro, Dominic M.
1987BAAS...19..921C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A novel observational test of momentum balance in a solar flare
Authors: Canfield, Richard C.; Metcalf, Thomas R.; Strong, Keith T.;
Zarro, Dominic M.
1987Natur.326..165C Altcode:
A unique combination of Solar Maximum Mission X-ray spectra and
Sacramento Peak Observatory Hα imaging spectra has enabled us,
for the first time, to measure and compare momentum values of
upflowing and downflowing plasmas during the impulsive phase
of a solar flare. We observed the well-known blue asymmetry of
X-ray spectral lines<SUP>1</SUP>, indicative of upflow, in the
coronal Ca XIX line. We simultaneously observed the red asymmetry
of H<SUP>α</SUP> line profiles, indicative of downflow, in bright Ha
kernels. We find that, to within observational uncertainty, the momentum
transported by the upflowing X-ray plasma was the same as that of the
downflowing H<SUP>α</SUP> material. Of the several physical mechanisms
advanced<SUP>2</SUP> to explain the observed blue asymmetry of X-ray
lines, only explosive chromospheric evaporation predicts oppositely
directed momenta of equal amplitude.
---------------------------------------------------------
Title: Alfven wave growth driven by streaming protons in coronal loops
Authors: Tamres, David H.; Melrose, D. B.; Canfield, Richard C.
1987SoPh..113..313T Altcode: 1982SoPh..113..313T
No abstract at ADS
---------------------------------------------------------
Title: Optical imaging spectroscopy
Authors: Canfield, R. C.
1987SoPh..113...95C Altcode: 1982SoPh..113...95C
No abstract at ADS
---------------------------------------------------------
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf..3.4C Altcode: 1986epos.confC...4C
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf.3.34C Altcode: 1986epos.confBC.34C
No abstract at ADS
---------------------------------------------------------
Title: Impulsive phase transport
Authors: Canfield, Richard C.; Bely-Dubau, Francoise; Brown, John C.;
Dulk, George A.; Emslie, A. Gordon; Enome, Shinzo; Gabriel, Alan H.;
Kundu, Mukul R.; Melrose, Donald; Neidig, Donald F.
1986epos.conf..3.1C Altcode: 1986epos.confC...1C
The transport of nonthermal electrons is explored. The thick-target
electron beam model, in which electrons are presumed to be accelerated
in the corona and typically thermalized primarily in the chromosphere
and photosphere, is supported by observations throughout the
electromagnetic spectrum. At the highest energies, the anisotropy
of gamma-ray emission above 10 MeV clearly indicates that these
photons are emitted by anisotropically-directed particles. The timing
of this high-energy gamma-radiation with respect to lower-energy
hard X-radiation implies that the energetic particles have short
life-times. For collisional energy loss, this means that they are
stopped in the chromosphere or below. Stereoscopic (two-spacecraft)
observations at hard X-ray energies (up to 350 keV) imply that these
lower-energy (but certainly nonthermal) electrons are also stopped deep
in the chromosphere. Hard X-ray images show that, in spatially resolved
flares whose radiation consists of impulsive bursts, the impulsive
phase starts with X-radiation that comes mostly from the foot-points
of coronal loops whose coronal component is outlined by microwaves.
---------------------------------------------------------
Title: Beam-induced Pressure Gradients in the Early Phase of
Proton-heated Solar Flares
Authors: Tamres, David H.; Canfield, Richard C.; McClymont, A. N.
1986ApJ...309..409T Altcode:
The pressure gradient induced in a coronal loop by proton beam
momentum deposition is calculated and compared with the thermal
pressure gradient arising from nonuniform deposition of beam energy;
it is assumed that the transfer of momentum and energy from beam to
target occurs via the Coulomb interaciton. Results are presented for
both a low mean energy and a high mean energy proton beam injected at
the loop apex and characterized by a power-law energy spectrum. The
present treatment takes account of the breakdown of the cold target
approximation for the low-energy proton beam in the corona, where the
thermal speed of target electrons exceeds the beam speed. It is found
that proton beam momentum deposition plays a potentially significant
role in flare dynamics only in the low mean energy case and only in
the corona, where it may dominate the acceleration of target material
for as long as several tens of seconds. This conclusion suggest that
the presence of low-energy nonthermal protons may be inferred from
velocity-sensitive coronal observations in the early impulsive phase.
---------------------------------------------------------
Title: Action and Reaction Observed in a Solar Flare
Authors: Zarro, D. M.; Canfield, R. C.; Strong, K. T.; Metcalf, T. R.
1986BAAS...18..966Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Solar Flare Extreme Ultraviolet to Hard X-Ray Ratio
Authors: McClymont, A. N.; Canfield, R. C.
1986ApJ...305..936M Altcode:
Simultaneous measurements of the peak 10-1030 A extreme ultraviolet
(EUV) flux enhancement and more than 10 keV hard X-ray (HXR) peak
flux of many solar flare bursts, ranging over about four orders
of magnitude in HXR intensity, are studied. A real departure from
linearity is found in the relationship between the peak EUV and HXR
fluxes in impulsive flare bursts. This relationship is well described
by a given power law. Comparison of the predictions of the impulsive
nonthermal thick-target electron beam model with observations shows
that the model satisfactorily predicts the observed time differences
between the HXR and EUV peaks and explains the data very well under
given specific assumptions. It is concluded that the high-energy
fluxes implied by the invariant area thick-target model cannot be
completely ruled out, while the invariant area model with smaller low
cutoff requires impossibly large beam densities. A later alternative
thick-target model is suggested.
---------------------------------------------------------
Title: Optical imaging spectroscopy
Authors: Canfield, R. C.
1986sfcp.nasa..120C Altcode:
During the recent solar maximum the combination of imaging and
spectroscopy in the visible part of the spectrum became a powerful tool
for observational study of flares primarily because of the development
of two-dimensional charge-coupled-device (CCD) arrays. In combination
with appropriate new operational methods, this has led to the ability
to observe, for the first time, the preflare and impulsive-phase
physical processes associated with spatially resolved features of
flare loops. As a result of concurrent theoretical developments,
modeling progressed from an empirical to a physical level. This made
it possible to interpret imaging spectra in terms of coronal pressure
and heat flux, particle beam heating, chromospheric evaporation,
and explosive chromospheric dynamics at the footpoints of flare
loops. There is clear potential for further advances in the near
future, taking advantage of improvements in digital recording speed
(approx. 10-fold), number of photosensitive elements per array
(approx. 10-fold), real-time data pre-reduction (potentially 10- to
100-fold), and using multiple CCD arrays. By the time of the next
solar maximum imaging spectroscopy is expected to achieve spatial
resolution or approx. arc 1 arc s, temporal resolution or approx. 5
s, and simultaneous critically-sampled spectroscopy of several lines
and continua. As a result, continued increase in our understanding
of the physical processes and configurations of solar flares in the
chromosphere, temperature minimum region, and photosphere can be
anticipated. Even greater progress toward a more global understanding
of flares will obviously come about when simultaneous optical, X-ray,
and gamma-ray imaging spectroscopy are possible.
---------------------------------------------------------
Title: H-α Response to Rapid Flare Heating Fluctuations
Authors: Gayley, K. G.; Canfield, R. C.
1986BAAS...18..698G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Role of Nonclassical Electron Transport in the Lower
Solar Transition Region
Authors: Owocki, S. P.; Canfield, R. C.
1986ApJ...300..420O Altcode:
One problem in solar physics is concerned with an understanding of the
observed brightness of the quiet solar atmosphere in spectral lines
which are formed in the lower solar transition region. The present
paper has the objective to examine the possibility that the observed
line emission results from nonclassical electron transport effects
which are associated with the inherently steep temperature gradients
in the solar transition region. The height variation of the electron
temperature is parameterized to enable correspondence with a variety
of one-dimensional constant pressure transition region models. The
models include empirical models, theoretical models, and the constant
classical heat fluxx model used by Shoub (1983). The electron velocity
distribution function is considered along with the effect on collisional
excitation and ionization rates, and effects on heat transport.
---------------------------------------------------------
Title: Impulsive phase chromospheric flare dynamics.
Authors: Canfield, Richard C.
1986lasf.conf...10C Altcode: 1986lasf.symp...10C
The study of the dynamics of chromospheric material in solar flares has
a long history, which is primarily observational. The author briefly
summarizes what was known on this topic prior to the recent solar
maximum, as a standard against which to measure recent work. Then
he discusses the most relevant theoretical work on chromospheric
aspects of impulsive phase dynamics and singles out chromospheric
spectroscopy that is different from older work in an important
respect: the Hα spectroscopy and imaging is accompanied by hard X-ray
and/or microwave spectroscopy (and in some cases, also imaging),
which uniquely pins down the temporal (and in some cases, spatial)
relationship of chromospheric dynamics to high-energy (nonthermal)
impulsive phase phenomena. Discussion of what a comparison of the new
theory and observation implies, and what it does not imply, is found,
leading to requirements for future progress in theory and observation.
---------------------------------------------------------
Title: Observations of chromospheric flare dynamics at the next
solar maximum specific recommendations of the Chromospheric Flare
Dynamics Group.
Authors: Canfield, R. C.; Gaizauskas, V.; Kurokawa, H.; Martin, S. F.;
Svestka, Z.
1986lasf.conf..489C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for explosive chromospheric evaporation in a solar
flare observed with SMM
Authors: Zarro, D. M.; Strong, K. T.; Canfield, R. C.; Metcalf, T.;
Saba, J. L. R.
1986AdSpR...6f.155Z Altcode: 1986AdSpR...6..155Z
Solar Maximum Mission soft X-ray data and Sacramento Peak Observatory
Hα observations are combined in a study of the impulsive phase
of a solar flare. A blue asymmetry, indicative of upflow motions,
was observed in the coronal Ca XIX line during the soft X-ray rise
phase. Hα redshifts, indicative of downward motions, were observed
simultaneously in bright flare kernels during the period of hard X-ray
emission. We show that, to within observational errors, the impulsive
phase momentum transported by the upflowing soft X-ray plasma is
equivalent to that of the downward moving chromospheric material.
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986NASCP2439....3C Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.
---------------------------------------------------------
Title: Impulsive phase explosive dynamics
Authors: Canfield, Richard C.
1986AdSpR...6f.167C Altcode: 1986AdSpR...6..167C
As the result of observational and theoretical research carried out
during the last solar cycle, we have seen a dramatic increase in our
physical understanding of explosive mass motions during the impulsive
phase. One of the major discoveries was the dramatic blueshift
of 10<SUP>7</SUP> K X-ray lines during the impulsive phase of many
solar flares. The temporal and spectral character of these blueshifts
is well observed, but their physical interpretation has been quite
controversial. Another interesting discovery made during the last
solar maximum was strong redshift of 10<SUP>4</SUP> K Hα emission
during the impulsive phase, which is closely temporally correlated
with X-ray and microwave emission. The evidence that redshifts are
a consequence of chromospheric explosions is quite strong-stronger,
in fact, than that for X-ray blueshifts because of better spatial
resolution. Theoretical hydrodynamic simulations of impulsive-phase
nonthermal electron transport, spanning the temperature range from
10<SUP>4</SUP> to 10<SUP>7</SUP> K, show upward-moving 10<SUP>7</SUP>
K material and downward-moving 10<SUP>4</SUP> K material caused by
chromospheric evaporation driven by either thermal conduction from
a hot flare corona and Coulomb heating by energetic flare electrons
of coronal origin. Of the various physical mechanisms that figure in
the controversies, only explosive chromospheric evaporation has been
shown to explain impulsive-phase Hα redshifts and X-ray blueshifts
in a simple and compelling manner.
---------------------------------------------------------
Title: Optical imaging spectroscopy.
Authors: Canfield, R. C.
1986NASCP2421..120C Altcode:
The author reviews the technological and operational advances, some
of the physical understanding that has come about as a result, and
the possibilities for the future.
---------------------------------------------------------
Title: The sensitivity of Hα profiles to rapid electron beam
fluctuations.
Authors: Canfield, Richard C.; Gayley, Kenneth G.
1986NASCP2449..249C Altcode: 1986rfsf.nasa..249C
The authors find an Hα response to an instantaneously initiated
intense beam of nonthermal electrons that is rapid compared to the
timescale associated with the propagation of these electrons over
characteristic flare loop dimensions. The amplitude and timescale
of this response vary over the Hα profile, and show effects which
arise from three different physical mechanisms. It is concluded that
observational efforts to detect impulsive Hα brightenings associated
with implusive hard X-ray or microwave bursts should initially focus
their attention on line center.
---------------------------------------------------------
Title: Ly-alpha and H-alpha emission by superthermal proton beams
Authors: Canfield, R. C.; Chang, C. -R.
1985ApJ...295..275C Altcode:
Simnett and Harrison (1984) have presented a model in which 100-1000 keV
protons are an energy transfer agent linking coronal mass ejections and
solar flares. Orrall and Zirker (1976) suggested that such protons,
incident upon the chromosphere, would produce nonthermal Ly-alpha
emission after charge exchange with ambient chromospheric hydrogen
atoms. The present investigation is concerned with a study of the
charge-exchange mechanism proposed by Orral and Zirker. The physical
theory of the formation of nonthermal Ly-alpha (and H-alpha) emission
is considered, taking into account photon emission, atomic transitions,
atomic equilibrium, the dominant atomic processes, and the stopping
of superthermal protons. Computational results presented by Orrall
and Zirker are extended.
---------------------------------------------------------
Title: On the Detectability of Kev-Mev Solar Protons Through Their
Nonthermal Lyman-Alpha Emission
Authors: Canfield, R. C.; Chang, C. R.
1985ICRC....4...86C Altcode: 1985ICRC...19d..86C
The intensity and timescale of nonthermal Doppler-shifted hydrogen
L alpha photon emission as diagnostics of 10 keV to 10 MeV protons
bombarding the solar chromosphere during flares are investigated. The
steady-state excitation and ionization balance of the proton beam
are determined, taking into account all important atomic interactions
with the ambient chromosphere. For a proton energy flux comparable to
the electron energy flux commonly inferred for large flares, L alpha
wing intensities orders of magnitude larger than observed nonflaring
values were found. Investigation of timescales for ionization and
charge exchange leads researchers to conclude that over a wide range
of values of mean proton energy and beam parameters, Doppler-shifted
nonthermal L alpha emission is a useful observational diagnostic of
the presence of 10 keV to 10 MeV superthermal proton beams in the
solar flare chromosphere.
---------------------------------------------------------
Title: The Importance of Proton Beam Pressure in Solar Flares
Authors: Tamres, D. H.; Canfield, R. C.; McClymont, A. N.
1985BAAS...17..634T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coulomb and Ohmic Flare Heating by Nonthermal Electrons
Authors: McClymont, A. N.; Canfield, R. C.; Brown, J. C.
1985BAAS...17..635M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Impulsive-Phase Chromospheric Dynamics in
Energetic-Electron-Heated Flare Kernels
Authors: Canfield, R. C.; Gunkler, T. A.; Fiplinger, A. T.
1985BAAS...17..628C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα Microflares at the Limit of Hard X-ray Detectability
Authors: Metcalf, T. R.; Canfield, R. C.
1985BAAS...17..644M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare Loop Radiative Hydrodynamics - Part Seven - Dynamics
of the Thick Target Heated Chromosphere
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1985ApJ...289..434F Altcode:
It is shown that hydrodynamic phenomena in the chromospheric portion
of the flaring solar atmosphere depend dramatically on whether
chromospheric evaporation by thick-target fast-electron heating is
"gentle" or "explosive." In the case of gentle evaporation, velocities
in the upper chromosphere are upward. In the case of explosive
evaporation, the overpressure of the evaporated material drives downward
motion in the residual flare chromosphere. The plasma driven downward
by explosive evaporation is cool and dense in comparison with the
chromospheric material ahead of it. We review previous discussions
of these "chromospheric condensations" and conclude that physical
understanding has been incomplete. We suggest that these condensations
are an inevitable consequence of compression of a thermally stable
heated plasma. We then investigate the nature of hydrodynamic waves
in a heated, strongly radiating, optically thin plasma. It is first
shown that acoustic waves in the flare chromosphere travel more slowly
than adiabatic or even isothermal sound waves. Next, a simple model
for the formation and propagation of chromospheric condensations is
developed. This model is based on the propagation of a compression
wave into the chromosphere, with quasi-steady equilibrium between flare
heating and radiative losses on each side of the compression front. We
derive jump conditions and accretion rates for the compression wave. We
find that this simple model agrees well with our numerical simulations.
---------------------------------------------------------
Title: Flare loop radiative hydrodynamics. V - Response to
thick-target heating. VI - Chromospheric evaporation due to heating
by nonthermal electrons. VII - Dynamics of the thick-target heated
chromosphere
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1985ApJ...289..414F Altcode:
The results of thick-target model simulations of the hydrodynamic and
radiative response of the solar-loop atmosphere to short bursts of
energetic nonthermal electrons are presented in extensive graphs and
diagrams and characterized in detail. The physical basis and numerical
techniques of the simulations, which continue the program initiated
by McClymont and Canfield (1983), are explored; the radiative-loss
approximations employed are compared with those of Ricchiazzi
(1982); the dynamics of coronal mass motion driven by chromospheric
evaporation are investigated; and gentle and explosive evaporation
regimes associated with upward and downward velocities in the upper
chromosphere, respectively, are differentiated. Consideration is
given to the propagation of hydrodynamic waves in heated strongly
radiating optically thin plasmas, the formation and propagation of
chromospheric condensations, and jump conditions and accretion rates
for the compression wave.
---------------------------------------------------------
Title: Flare Loop Radiative Hydrodynamics - Part Six - Chromospheric
Evaporation due to Heating by Nonthermal Electrons
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1985ApJ...289..425F Altcode:
The response of the solar chromosphere to flare heating by nonthermal
electrons is examined. A number of interesting phenomena appear in our
numerical solutions of the equations of hydrodynamics and radiative
transfer. Here we discuss one aspect of these results: the phenomenon
of chromospheric evaporation. We present results for a range of heating
fluxes and show how these may be understood in simple terms. Our major
conclusions are as follows: (1) There is an energy flux threshold for
"explosive" evaporation. Explosive evaporation occurs when the upper
chromosphere is unable to radiate the flare energy deposited there,
and is therefore heated rapidly to coronal temperatures. Energy fluxes
less than this threshold produce "gentle" evaporation, in which the
chromosphere is eaten away by conduction at a much slower rate. (2)
The expansion velocity of explosively evaporated plasma cannot exceed
∼ 2.35c<SUB>s</SUB> , where c<SUB>s</SUB> is the sound speed in the
evaporated material. (3) We derive a simple analytic model for the
temporal variation of velocity in explosively evaporated plasma. This
"gasbag" model, based on isothermal expansion of an impulsively
heated mass of plasma, is used successfully to reproduce our own
numerical results, as well as those of MacNeice et al. (1984). (4)
The lower transition region, in both gentle and explosive evaporation,
quickly reaches a quasisteady balance between conduction and radiation,
so that the conductive flux at 10<SUP>5</SUP> K is given by 3.42 x
10<SUP>5</SUP> P ergs cm <SUP>-2</SUP> s<SUP>-1</SUP>, where P(dyn
cm<SUP>-2</SUP>) is the pressure in the flare transition region. In the
case of explosive evaporation, a short powerful pulse of EUV radiation
is emitted from plasma with temperatures near 10<SUP>5</SUP> K during
the adjustment to this equilibrium.
---------------------------------------------------------
Title: Energetic electron heating and chromospheric evaporation
during a well-observed compact flare
Authors: Canfield, R. C.; Gunkler, T. A.
1985ApJ...288..353C Altcode:
A previous analysis of chromospheric evaporation in the solar flare of
May 7, 1980, in which it was shown that the chromospheric evaporation
can account for the thermal X-ray plasma of the flare, is extended. The
way the H-alpha profile should respond to thick-target nonthermal
electron heating is discussed using previous theoretical modelling. It
is shown that broad Stark wings are the theoretically expected response
above moderately high values of the input nonthermal electron energy
flux. The observed spatial and temporal behavior of H-alpha profiles and
hard X-rays during the impulsive phase is exmined, and it is concluded
that broad H-alpha wings are closely related observationally to hard
X-rays. Finally, it is shown that the observed width of impulsive-phase
H-alpha wings supports the thick-target nonthermal electron heating
model.
---------------------------------------------------------
Title: A consistent picture of coronal and chromospheric processes
in a well-observed solar flare
Authors: Gunkler, T. A.; Canfield, R. C.; Acton, L. W.; Kiplinger,
A. L.
1984ApJ...285..835G Altcode:
The solar flare of 15:22 UT on June 24, 1980 is analyzed using
simultaneous observations in hard X-rays, soft X-rays, and H-alpha line
profiles obtained from instruments aboard the Solar Maximum Mission
and ground-based instruments. The theoretical H-alpha profiles of
Canfield, Gunkler, and Ricchiazzi (1984) are used to analyze the
H-alpha data, and the work of Hummer and Rybicki (1968) is used to
provide qualitative velocity information. The soft X-ray data are
employed to obtain coronal measurements of parameters of interest,
while the flux and spectrum of the hard X-rays are used to calculate
the peak power of nonthermal electrons. Various flare phenomena are
studied, including heating of the chromosphere by nonthermal electrons,
enhanced coronal pressure, enhanced thermal conduction, chromospheric
evaporation and mass motion. It is shown that the observations strongly
suggest a scenario in which two large magnetic loop systems interact
to provide the flare energy.
---------------------------------------------------------
Title: The Role of Non-Classical Transport in the Formation of the
Ly-α Temperature Plateau
Authors: Owocki, S. P.; Canfield, R. C.; McClymont, A. N.
1984BAAS...16..992O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Hα Spectral Counterpart of Hard X-ray Microflares
Authors: Canfield, R. C.; Metcalf, T. R.
1984BAAS...16..891C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The H-alpha spectral signatures of solar flare nonthermal
electrons, conductive flux, and coronal pressure
Authors: Canfield, R. C.; Gunkler, T. A.; Ricchiazzi, P. J.
1984ApJ...282..296C Altcode:
During a solar flare, a number of mechanisms heat the chromosphere
above its preflare temperature. Ricchiazzi and Canfield (1983)
have modeled the response of the chromosphere to processes related
to energetic electrons, thermal conductivity, and enhanced coronal
pressure. The present investigation is concerned with the computation
of H-alpha profiles for various models, thus providing their H-alpha
spectral signatures. It is shown that H-alpha responds sensitively to
these processes. The investigation is based on static models of flare
chromospheres which have been obtained for two limiting assumptions,
taking into account hydrostatic equilibrium and the assumption that
the flare heating has just been turned on. After computing the model
atmospheres, theoretical H-alpha line profiles are generated for
each model.
---------------------------------------------------------
Title: The unimportance of beam momentum in electron-heated models
of solar flares
Authors: McClymont, A. N.; Canfield, R. C.
1984A&A...136L...1M Altcode:
In a previous letter to this journal, Brown and Craig (1984) called
attention to the possible importance of the hitherto neglected direct
collisional acceleration of flare atmospheres heated by particle
beams. For the case commonly believed to be of most physical interest -
electron-beam heating in closed flare loops - these arguments are found
to be incomplete. Both the early (impulsive) and late (equilibrium)
phases of the atmospheric response are treated self-consistently, and
in addition the intermediate phase (in which pressure equilibrium, but
not energetic equilibrium, has been established) is considered. It is
concluded that acceleration due to beam pressure is important for only
a few seconds after the electron beam is switched on and is unlikely to
have a significant influence on the global flare evolution. Brown and
Craig's conclusions should, however, be taken into account in models
of proton beam heating, because of the much higher momentum-to-energy
ratio of proton beams.
---------------------------------------------------------
Title: Studies of solar flares and coronal loops
Authors: Canfield, R. C.
1984ucsd.reptQ....C Altcode:
The objectives of this research were to improve our understanding
of solar flares and solar coronal loops. The specific approach to
the flare objective was to analyze and interpret solar flare data,
using theoretical methods developed as part of the research. The
specific approach to the coronal loop objective was to investigate
their thermal and magnetohydrodynamic stability for various physical
models. The principal result of the flare research was to demonstrate
that, in two well observed flares, the mechanism of chromospheric
evaporation accounts for the observed amount of flare X-ray plasma. The
dominant energy transport mechanism is thermal conduction. Heating by
energetic electrons is of secondary importance. The principal results
of the magnetohydrodynamic stability analyses were demonstrations by
the role of radiative energy loss, compressibility, magnetic field
line twist, foot point magnetic field line tying, and radial plasma
pressure gradient.
---------------------------------------------------------
Title: Chromospheric evaporation velocities in solar flares
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1984ApJ...281L..79F Altcode:
It is shown that the upper limit to chromospheric evaporation velocities
in solar flare loops is 2.35 C<SUB>s,</SUB> where C<SUB>s</SUB> is the
sound speed in the evaporated material. Upward velocities greater than
this limit would imply the existence of additional nonhydrodynamic
forces. Several hydrodynamic calculations are made of collisional
heat produced by nonthermal energetic electrons, and upward velocities
are found which are at the upper limit of large (less than 3 x 10 to
the 10th ergs/sec/sq cm) energy flux values. At more modest fluxes
(10 to the 10th or 10 to the 9th ergs/sec/sq cm) both thermal and
thick target models yield upward velocities which are within 10 to
20 percent of the upper limit. When both temperature and velocity of
the evaporated plasma are considered, the thermal model is found to
be the most consistent with recent observational data.
---------------------------------------------------------
Title: On the Formation of Temperature Plateaus in the Solar
Transition Region
Authors: Owocki, S. P.; McClymont, A. N.; Canfield, R. C.
1984BAAS...16..729O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum - a Static Model of Chromospheric Heating in Solar
Flares
Authors: Ricchiazzi, P. J.; Canfield, R. C.
1984ApJ...279..463R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron Beam Heating During a Well-Observed Compact Flare
Authors: Canfield, R. C.; Gunkler, T. A.
1984BAAS...16..544C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Lyman - α Emission by 3 KeV-300 MeV Protons
Authors: Chang, C. -R.; Canfield, R. C.
1984BAAS...16..535C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Evaporation in Flares Due to Heating by
Nonthermal Electrons
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1984BAAS...16..543F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational evidence for chromospheric footpoint penetration
of nonthermal electrons during two well-observed flares
Authors: Canfield, R. C.; Gunkler, T. A.; Kiplinger, A. L.
1984AdSpR...4g.255C Altcode: 1984AdSpR...4..255C
Recent advances have enabled simultaneous Hα and X-ray observations
with substantially improved spatial, spectral, and temporal
resolution. In this paper we study two events observed as part of a
coordinated observing program between the Solar Maximum Mission and
Sacramento Peak Observatory: the flares of 1456 UT, 7 May 1980 and
1522 UT, 24 June 1980. Using recently-developed physical models of
static flare chromospheres, and corresponding theoretical Hα line
profiles, we can distinguish effects of intense nonthermal electron
heating from those of high conduction and pressure from the overlying
flare corona. Both flares show the signature of intense chromospheric
heating by fast electrons, temporally correlated with X-ray light curves
at E > 27keV, and spatially associated with X-ray emission sites at
E >62; 16 keV. Interpreting the Hα line profile observations using
the theoretical Hα line profiles, we infer values of the thick-target
input power contained in nonthermal electrons that are observationally
indistinguishable (within a factor of 2-3) from those inferred from
the X-ray data. Although these events are small, the energy flux values
are large: of order 10<SUP>11</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>
above 20 keV.
---------------------------------------------------------
Title: Probabilistic radiative transfer.
Authors: Canfield, R. C.; McClymont, A. N.; Puetter, R. C.
1984mrt..book..101C Altcode: 1984mrt..conf..101C
The authors have developed a computationally efficient method for highly
nonlinear problems in which radiative transfer is an important aspect
of the heating and cooling of the medium. This paper summarizes all
essential aspects of the method. The authors derive an approximate
probabilistic radiative transfer equation for one-dimensional
plane-parallel atmospheres of finite or semi-infinite extent, for both
spectral lines and bound-free continua. They also discuss boundary
conditions, accuracy, escape probabilities, and practical aspects of
complete linearization, which is a key element of the method.
---------------------------------------------------------
Title: Hα Signatures of Impulsive Flare Heating by Energetic
Nonthermal Electrons and Thermal Conduction
Authors: Canfield, R. C.; Gunkler, T. A.; Ricchiazzi, P. J.
1983BAAS...15Q.918C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A static model of chromospheric heating in solar flares
Authors: Ricchiazzi, P. J.; Canfield, R. C.
1983ApJ...272..739R Altcode:
The response of the solar chromosphere to flare processes, namely
nonthermal electrons, thermal conduction, and coronal pressure,
is modeled. Finite difference methods employing linearization and
iteration are used in obtaining simultaneous solutions to the equations
of steady-state energy balance, hydrostatic equilibrium, radiative
transfer, and atomic statistical equilibrium. The atmospheric response
is assumed to be confined to one dimension by a strong vertical magnetic
field. A solution is obtained to the radiative transfer equation for
the most important optically thick transitions of hydrogen, magnesium,
and calcium. The theoretical atmospheres discussed here are seen as
elucidating the role of various physical processes in establishing
the structure of flare chromospheres. At low coronal pressures,
conduction is found to be more important than nonthermal electrons
in establishing the position of the transition region. Only thermal
conduction can adequately account for the chromospheric evaporation in
compact flares. Of the mechanisms considered, only nonthermal electrons
bring about significant heating below the flare transition region.
---------------------------------------------------------
Title: A Consistent Picture of Coronal and Chromospheric Processes
in a Well-Observed Flare
Authors: Gunkler, T. A.; Canfield, R. C.; Acton, L. W.; Kiplinger,
A. L.
1983BAAS...15Q.919G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Maximum Upward Velocities of Chromospheric Evaporation
in Flares
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1983BAAS...15..918F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare loop radiative hydrodynamics. IV - Dynamic evolution
of unstable semiempirical loop models
Authors: An, C. -H.; Canfield, R. C.; Fisher, G. H.; McClymont, A. N.
1983ApJ...267..421A Altcode:
The evolution of the unstable solar atmosphere into the nonlinear phase,
in response to various perturbations, is followed. The initial dynamic
evolution of the atmosphere follows the predictions of linear stability
analysis. In the nonlinear phase, rapid changes are confined to the
transition region; these changes are manifested as a propagation
of the transition region through the plasma, i.e., chromospheric
evaporation or condensation. Global evolution therefore proceeds on
the coronal conductive time scale. The rate of propagation of the
transition region is determined by the imbalance between the energy
supplied by thermal conduction from the corona and radiative cooling
within the transition region itself. Flow velocities in the lower
corona during evaporation or condensation are, in the cases studied,
of order 3 km/s. The observed dynamic evolution is consistent with the
existence of relatively long-lived coronal loops whose brightnesses
vary on the evaporative time scale.
---------------------------------------------------------
Title: Chromospheric Evaporation in Flare Loops Heated Impulsively
by Nonthermal Electrons
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1983BAAS...15..708F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The H-alpha Spectral Signature of Several Flare Processes
Authors: Gunkler, T. A.; Canfield, R. C.; Ricchiazzi, P. J.
1983BAAS...15Q.697G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emission from Flare Loops Heated Impulsively by Nonthermal
Electrons
Authors: Canfield, R. C.; Fisher, G. H.; McClymont, A. N.
1983BAAS...15R.708C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive EUV and Hard X-ray Flare Emission
Authors: McClymont, A. N.; Canfield, R. C.; Fisher, G. H.
1983BAAS...15R.711M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare loop radiative hydrodynamics. I - Basic methods
Authors: McClymont, A. N.; Canfield, R. C.
1983ApJ...265..483M Altcode:
The study presented here has two goals. The first is to examine the
role of energy transport mechanisms in flare dynamics, for instance,
thermal cone conduction in the corona and radiative transfer in the
chromosphere. The second is to provide diagnostics of flare energization
processes by predicting the evolutionary behavior of concurrent
emissions from all regions of the flaring atmosphere. To attain these
ends, a numerical method is developed for the simultaneous solution
of thy continuity, momentum, and energy equations; the time-dependent
atomic rate equations describing ionization and excitation; and the
radiative transfer equations. With the physical model and computational
methods used here, all components of the plasma move as a single
fluid and in the initial studies are assumed to have a common kinetic
temperature. The plasma is constrained to move in one dimension along
the axis of a loop of nonuniform cross section, the geometry of which
is defined by a sufficiently strong magnetic field.
---------------------------------------------------------
Title: Flare loop radiative hydrodynamics. III - Nonlocal radiative
transfer effects
Authors: Canfield, R. C.; Fisher, G. H.; McClymont, A. N.
1983ApJ...265..507C Altcode:
The study has three goals. The first is to demonstrate that processes
exist whose intrinsic nonlocal nature cannot be represented by local
approximations. The second is to elucidate the physical nature and
origins of these nonlocal processes. The third is to suggest that the
methods and results described here may prove useful in constructing
semiempirical models of the chromosphere by means more efficient than
trial and error. Matrices are computed that describe the effect of a
temperature perturbation at an arbitrary point in the loop on density,
hydrogen ionized fraction, total radiative loss rate, and radiative loss
rate of selected hydrogen lines and continua at all other points. It
is found that the dominant nonlocal radiative transfer effects can
be separated into flux divergence coefficient effects and upper level
population effects. The former are most important when the perturbation
takes place in a region of significant opacity. Upper level population
effects arise in both optically thick and thin regions in response to
nonlocal density, ionization, and interlocking effects.
---------------------------------------------------------
Title: Flare Loop Radiative Hydrodynamics - Part Two - Thermal
Stability of Empirical Models
Authors: McClymont, A. N.; Canfield, R. C.
1983ApJ...265..497M Altcode:
The importance of loop structures in the corona, both for flares and
for the quiet Sun, has stimulated considerable attention to questions
of their thermal stability. Previous studies have focused attention on
the coronal part of the loop. In this paper we examine loop stability by
treating the entire observable loop, from its photospheric footpoints
to its coronal apex. This approach allows the chromosphere and corona
to interact naturally, thus avoiding possibly artificial boundary
conditions imposed at transition region footpoints. <P />We develop
a numerical eigenfunction method for the study of stability, which
is based on the methods discussed in a previous paper. For exemplary
purposes, we have applied these methods to several loop models based on
semiempirical model chromospheres, under the assumption that the rate
of ambient energy input per unit mass of plasma depends only on column
depth. Our principal study is of a loop model based on the semiempirical
model F of Vernazza, Avrett, and Loeser. <P />We find that this loop
model has one unstable eigenmode, with a growth time of 2 minutes. This
mode appears in the transition region, centered on the peak of
the optically thin radiative loss function at T ≍ 10<SUP>5</SUP>
K. However, we provide evidence that suggests that this instability
may not be a feature of real loops. More importantly, we find that (1)
this atmosphere is stable to the hydrogen-induced radiative instability
of optically thin gases at temperatures around 10<SUP>4.3</SUP> K; (2)
were it not for radiative transfer effects, this atmosphere would be
dramatically unstable, with growth times in the range 1 ≤ r ≤ 18 s;
and (3) the stability when radiative transfer is taken into account can
be understood primarily as a result of the reduction of the peak in the
radiative loss rate at 10<SUP>4.3</SUP> K, due to hydrogen, that would
exist if the chromosphere were optically thin. This reduction is due to
the significant optical depth, and consequent low escape probability,
of radiation of the dominant coolant, Lyα, at upper temperatures.
---------------------------------------------------------
Title: Chromospheric evaporation in a well-observed compact flare
Authors: Acton, L. W.; Leibacher, J. W.; Canfield, R. C.; Gunkler,
T. A.; Hudson, H. S.; Kiplinger, A. L.
1982ApJ...263..409A Altcode:
Hudson and Ohki (1972) pointed out that the increase of the soft
X-ray emission measure during flares might be accounted for in two
different ways, either by 'coronal condensation', or by what they termed
'chromospheric rarefaction', now more commonly called 'chromospheric
evaporation'. They ruled out coronal condensation on the basis of
cornal mass content arguments. Moore et al. (1980) found it highly
probable that the bulk of the mass of the soft X-ray emitting plasma is
supplied during the rise phase by chromospheric evaporation from the
feet of the soft X-ray loops. On the other hand, Cheng et al. (1981)
argued that chromospheric evaporation is not important as a source
of soft X-ray plasma. The present investigation is concerned with
an event in which direct chromospheric observations contradict the
conclusions reached by Cheng et al. Up to now chromospheric evaporation
has always been an inference, without compelling positive evidence. In
the current investigation, observations are considered which constitute
such evidence.
---------------------------------------------------------
Title: A Static Model of Chromospheric Heating in Solar Flares
Authors: Canfield, R. C.; Ricchiazzi, P. J.
1982BAAS...14..898C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical quasar emission-line ratios. VI - A probabilistic
radiative transfer equation for finite slab atmospheres
Authors: Puetter, R. C.; Hubbard, E. N.; Ricchiazzi, P. J.; Canfield,
R. C.
1982ApJ...258...46P Altcode:
Previous papers in this series have been based on an approximation
in which the line ratios were inferred from those computed for
a semi-infinite cloud model. In this paper we present a superior
method, which permits the treatment of the emission-line clouds as
slab atmospheres of finite thickness. In common with our previous
semi-infinite approach, it is based on photon escape probabilities,
yet it recognizes the important distinction between the photon escape
probability and the flux divergence. This distinction is neglected in
all existing models of energy balance in QSO emission-line clouds. This
neglect can lead to order of magnitude errors in the cooling rates,
casting doubt on the results of past models. <P />The present method
reduces to the previous one in the semi-infinite case. It not only
produces the correct source function S<SUB>∞</SUB> at the surface of
a semi-infinite atmosphere S<SUB>∞</SUB>(τ-0) = ɛ<SUP>1/2</SUP>B
for a constant Planck function B and photon destruction probability
ɛ, but it derives the empirical relationship S<SUB>T</SUB>(τ=0) ≍
ɛ<SUP>1/2</SUP>S∞(τ=T) proposed by Avrett and Hummer relating the
source function at the surface of a finite slab of optical thickness T
to the source function at τ = T in a semi-infinite slab. We show that
the method provides a solution that departs from the exact solution
by at most a few tens of percent in cases of physical interest, while
retaining all the advantages of the previous method.
---------------------------------------------------------
Title: Erratum - Theoretical Quasar Emission-Line Ratios - Part
Three - Flux Divergence and Photon Escape
Authors: Canfield, R. C.; Puetter, R. C.; Ricchiazzi, P. J.
1982ApJ...256..798C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar flare studies
Authors: Canfield, R. C.
1982ucsd.rept.....C Altcode:
The primary objective of the research described in this report
was increased understanding of solar flares. In the course of the
research, many tasks were carried out, which achieved not only the
primary objective, but also secondary objectives in related areas. The
research program started with active participation in the Skylab Solar
Flare Workshop. New observations of solar flare spectra were obtained
and interpreted in terms of basic solar flare mechanisms. It was
shown that the basic process by which the X-ray radiation of flares
is created is by heating the flare plasma to temperatures of about
ten million degrees, through evaporation of the chromosphere. This
process is driven both by beams of accelerated electrons and by
thermal conduction. However, in the major flare for which data were
interpreted, the principal energy release mechanism was found to be
thermal in nature, implying that most of the flare energy is released
in the form of heat, and not charged particles. Theoretical modeling
methods were developed for understanding the spectra solar flares. These
methods were applied to flare loop dynamics. The spectral signatures
of both chromospheric evaporation and beams of accelerated electrons
were established. Finally, a theorectical program of theoretical
magnetohydrodynamic stability studies was begun.
---------------------------------------------------------
Title: A qualitative interpretation of 7 August 1972 impulsive phase
flare Hα line profiles
Authors: Canfield, R. C.
1982SoPh...75..263C Altcode:
Tanaka's (1977) unique Hα profiles of the kernels of the 7 August 1972
flare were quantitatively interpreted by Brown et al. (1978; henceforth
BCR) in terms of a thick target electron beam model. They found
that this interpretation required beam inhomogeneity and/or partial
precipation and large (60-100 km s<SUP>−1</SUP>) macroturbulence. The
latter requirement is somewhat suspect, since the only independent
evidence also comes from efforts to understand the profiles of
optically thick chromospheric lines. Relationships between model
atmosphere parameters and line profile parameters calculated by Dinh
(1980) show that these requirements could be considerably reduced,
if not totally eliminated, if the actual chromospheric flare heating
mechanism were simultaneously capable of pushing the flare transition
region to greater column density and causing less heating of the
residual chromosphere than the BCR models. This then implies that the
chromosphere is heated primarily by a mechanism through which the
heating effects do not penetrate as far below the flare transition
region as is the case for a power-law spectrum of non-thermal electrons
whose parameters are chosen appropriate to the nonthermal thick target
interpretation of hard X-rays. Thermal conduction and optically thick
radiation are examples of such a mechanism.
---------------------------------------------------------
Title: Direct evidence for chromospheric evaporation in a
well-observed compact flare
Authors: Canfield, R. C.; Gunkler, T. A.; Hudson, H. S.; Acton, L. W.;
Leibacher, J. W.; Kiplinger, A. L.
1982AdSpR...2k.145C Altcode: 1982AdSpR...2..145C
Observations of the solar flare of May 7, 1980 using several Solar
Maximum Mission instruments are presented as an investigation of the
phenomenon of chromospheric evaporation. The total amount of plasma
at temperatures greater than 2 x 10 to the 6th K were determined from
the X-ray data, and the amount of plasma that was evaporated from
the chromosphere was determined from the H-alpha data. The H-alpha
profiles indicate that for the flare as a whole, at the time of peak
soft X-ray emission measure, the number of atoms evaporated from the
chromosphere was 7 x 10 to the 37th. The soft X-ray emission measure
of 1 x 10 to the 49th/cu cm, coupled with the flare volume estimate
of 10 to the 26th cu cm, indicates that there were 3 x 10 to the 37th
electrons in the soft X-ray plasma with temperatures greater than 2 x
10 to the 6th K. These results indicate that enough material had been
evaporated from the chromosphere to account for the X-ray plasma. Taken
together, the H-alpha, soft X-ray, and hard X-ray images indicate that
chromospheric evaporation is driven both by flare-accelerated electrons
during the impulsive phase and by conduction during the thermal phase.
---------------------------------------------------------
Title: The Lyman-alpha/H-alpha ratio in solar flares and quasars
Authors: Canfield, R. C.; Puetter, R. C.; Ricchiazzi, P. J.
1981ApJ...249..383C Altcode:
Constant temperature and density solar flare models are constructed
with temperature and hydrogen density values that reflect reasonable
nonlinear averages of those parameters in the depth dependent solar
flare chromosphere models of Lites and Cook (1979). Acceptable values
of the intensity ratios L-alpha/H-alpha and H-beta/H-alpha correspond
to temperatures from about 9000 to 13,000 K, and hydrogen densities from
10 to the 11th to 10 to the 15th cu cm. The H-alpha and Ly-alpha source
functions are thermalized at depths consistent with those inferred from
independent studies, although the observed Ly-alpha/H-alpha ratio does
not necessarily imply an electron temperature appropriate to the Planck
function ratio. It is also shown that the value of Ly-alpha/H-alpha
depends on the temperature, hydrogen density, and the optical depth
of the emitting chromospheric layer.
---------------------------------------------------------
Title: Theoretical quasar emission-line ratios. III - Flux divergence
and photon escape
Authors: Canfield, R. C.; Puetter, R. C.; Ricchiazzi, P. J.
1981ApJ...248...82C Altcode:
In this paper we develop a computationally useful version of the
probabilistic first-order differential radiative transfer equation
of Frisch and Frisch. This approximate radiative transfer equation
is especially appropriate for the evaluation of radiative transfer
effects in multilevel atomic systems due to its extreme computational
efficiency and reasonably accurate description of the physics of
radiation transfer. In particular, it recognizes the distinction between
the flux divergence coefficient, ρ, and the photon escape probability,
P<SUB>e</SUB>. We show that this distinction is crucial for calculations
that attempt to construct self-consistent energy balance models since
substitution of P<SUB>e</SUB> for ρ in such models leads to large
errors (of sign as well as magnitude) in the local cooling rate.
---------------------------------------------------------
Title: A Probabilistic Radiative Transfer Equation for Finite Slab
Models of QSO Emission Line Regions
Authors: Ricchiazzi, P. J.; Puetter, R. C.; Hubbard, E. N.; Canfield,
R. C.
1981BAAS...13..788R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Direct Evidence for Chromospheric Evaporation in a
Well-Observed Compact Flare
Authors: Canfield, R. C.; Acton, L. W.; Gunkler, T. A.; Hudson, H. S.;
Kiplinger, A. L.; Leibacher, J. W.
1981BAAS...13R.819C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-Local Effects of Radiative Transfer on Radiative
Hydrodynamic Stability
Authors: Fisher, G. H.; Canfield, R. C.; McClymont, A. N.
1981BAAS...13..846F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Models of Electron-Heated Solar Flare Chromospheres
Authors: Ricchiazzi, P. J.; Canfield, R. C.
1981BAAS...13..819R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-Linear Development of the Radiative Hydrodynamic
Instability in Empirical Solar Loop Models
Authors: An, C. -H.; Canfield, R. C.; McClymont, A. N.; Fisher, G. H.
1981BAAS...13..837A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Quasar Emission Line Ratios - Part Two - Hydrogen
Lyman-Alpha Balmer and Paschen Lines and the Balmer Continuum
Authors: Canfield, R. C.; Puetter, R. C.
1981ApJ...243..390C Altcode:
We explore the formation of the hydrogen La, Balmer, and Paschen lines
and the Balmer continuum in highly idealized QSO broad emission line
clouds (ELCs) of constant temperature and density irradiated by an
external source of power-law spectral form. We simultaneously solve
the equations governing excitation, ionization, and transfer of
both external and diffuse radiation fields. Our calculations show
that the typical observed broad emission line ratios of Lα/Hα,
Hβ/Hα, Pα/Hα, and Balmer continuum/Hα can be understood for
ELC conditions in the temperature range 7 × 10<SUP>3</SUP> ≲
T<SUB>e</SUB> ≲ 2 × 10<SUP>4</SUP> K, hydrogen density range
10<SUP>8</SUP> ≲ n<SUB>H</SUB> ≲ 10<SUP>12</SUP> cm<SUP>-3</SUP>,
and for external fluxes F ≲<SUP>-6</SUP> ergs cm<SUP>-2</SUP>
s<SUP>-1</SUP> Hz<SUP>-1</SUP> at the Lyman continuum limit. <P
/>Important results are: <P />1. The Lα/Hα ratio is very sensitive
to the optical thickness of the cloud at the optical thickness that
we think are appropriate for QSOs. <P />2. It is not necessary to
postulate dust either internal or external to the ELC. <P />3. The
ELCs are very optically thick; the Balmer lines and Pa originate
in a region for which the Lyman-limit optical depth τ<SUB>cl</SUB>
≳ 10<SUP>2</SUP>. <P />4. A very extended ionized zone results from
ionization from excited states. <P />5. The radiation from various
transitions arises from very extended and sometimes quite different
regions of the cloud. This renders a mean escape probability approach
inappropriate. <P />6. Predicted line ratios and cooling rates depend
critically on the functional form of the photon escape probability. <P
/>7. Acceptable values of the area covering factor and static energy
balance require temperatures somewhat in excess of 10<SUP>4</SUP> K.
---------------------------------------------------------
Title: Theoretical quasar emission line ratios. I - Transfer and
escape of radiation. II - Hydrogen L-alpha, Balmer, and Paschen lines,
and the Balmer continuum
Authors: Canfield, R. C.; Puetter, R. C.
1981ApJ...243..381C Altcode:
We describe a formalism for the solution of the frequency-integrated
radiative transfer equation and the atomic steady state equation
appropriate to an externally irradiated, semi-infinite medium. The
source functions are cast into equivalent two-level forms, and the
equations linking the emergent flux, the line center source function,
the flux divergence coefficient ρ, and the atomic steady state
equations are given. Asymptotic forms for scaling law solutions to
the radiative transfer equation are developed. Escape probabilities
appropriate to the above scaling law solutions are discussed for
subordinate lines, strongly interlocked resonance lines, weakly
interlocked resonance lines, and the bound-free continua.
---------------------------------------------------------
Title: A Method for Combined Hydrodynamics and Probabilistic
Radiative Transfer
Authors: McClymont, A. N.; Canfield, R. C.
1980BAAS...12..915M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: CCD Observations of the Profile of H-alpha Throughout the
Flare of 1456 UT 07 May 1980
Authors: Gunkler, T. A.; Canfield, R. C.
1980BAAS...12R.905G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Sufficient Condition for Evaluation of the Stability of
Solar Coronal Loops
Authors: An, C. -H.; McClymont, A. N.; Canfield, R. C.
1980BAAS...12..913A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observed Lα profiles for two solar flares: 14∶12 UT 15 June,
1973 and 23∶16 UT 21 January, 1974
Authors: Canfield, R. C.; van Hoosier, M. E.
1980SoPh...67..339C Altcode:
Photographic observations of the time development of the profile
of the Lα line of hydrogen during flares were obtained with the NRL
spectrograph on ATM. The profiles for the 15 June, 1973 and 21 January,
1974 flares reported here cover both core and wings of the line. The
time sequences begin before flare maximum, and continue well into the
decay phase. Careful attention has been given to photometry and absolute
calibration. In the case of the 15 June, 1973 flare, data are presented
both first-order corrected and uncorrected for incomplete filling of the
spectrograph slit by flaring material. Correction of the 21 January,
1974 flare was not possible. We discuss core symmetry and shift, and
show that our observations imply integrated flare Lα/Hα intensity
ratios within a factor of two of unity for these two flares.
---------------------------------------------------------
Title: A probabilistic approach to radiative energy loss calculations
for optically thick atmospheres - Hydrogen lines and continua
Authors: Canfield, R. C.; Ricchiazzi, P. J.
1980ApJ...239.1036C Altcode:
An approximate probabilistic radiative transfer equation and the
statistical equilibrium equations are simultaneously solved for a
model hydrogen atom consisting of three bound levels and ionization
continuum. The transfer equation for L-alpha, L-beta, H-alpha,
and the Lyman continuum is explicitly solved assuming complete
redistribution. The accuracy of this approach is tested by comparing
source functions and radiative loss rates to values obtained with
a method that solves the exact transfer equation. Two recent model
solar-flare chromospheres are used for this test. It is shown that
for the test atmospheres the probabilistic method gives values of the
radiative loss rate that are characteristically good to a factor of
2. The advantage of this probabilistic approach is that it retains a
description of the dominant physical processes of radiative transfer
in the complete redistribution case, yet it achieves a major reduction
in computational requirements.
---------------------------------------------------------
Title: Lα/Hα in Solar Flares and QSO's
Authors: Canfield, R. C.; Puetter, R. C.
1980BAAS...12..517C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line and Continuum Cooling in QSO Emission Line Regions
Authors: Canfield, R. C.; Puetter, R. C.; Ricchiazzi, P. J.
1980BAAS...12..536C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The implications of hydrogen emission line ratios in
quasi-stellar objects
Authors: Canfield, R. C.; Puetter, R. C.
1980ApJ...236L...7C Altcode:
The results of multilevel, depth-dependent, fully interlocked radiative
transfer calculations for hydrogen emission line strengths in a single
QSO emission line cloud (ELC) are summarized. The hydrogen-line forming
region of the ELC is found to be quite thick (tau<SUB>el</SUB> between
1,000 and 100,000), which is consistent with heating of a pure hydrogen
cloud by photoionization. Results indicate that the volume-averaged
escape probability approach introduces large errors by assuming,
in effect, that a single point in the ELC is representative of the
emergent radiation; that the influence of frequency redistribution on
the photon escape probability in resonance and subordinate lines must
be explicitly recognized, and that full consistency between excitation
and ionization processes must be maintained.
---------------------------------------------------------
Title: Radiative hydrodynamics of flares - Preliminary results and
numerical treatment of the transition region
Authors: McClymont, A. N.; Canfield, R. C.
1980IAUS...91..313M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The chromosphere and transition region
Authors: Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner,
G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.;
Henoux, J. -C.; Lites, B. W.
1980sfsl.work..231C Altcode: 1980sofl.symp..231C
The physical processes occurring as a result of the transfer of
energy and momentum from the primary solar flare energy release site
in the corona to the underlying chromosphere and transition region
during the course of the flare are investigated through a comparison
of theoretical models and observational data. Static, dynamic and
hydrodynamic models of the lower-temperature chromospheric flare are
reviewed. The roles of thermal conduction, radiation, fast particles
and mass motion in chromosphere-corona interactions are analyzed on
the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic
models of the chromospheric and upper photospheric responses to flares
are developed. The canonical model of chromospheric heating during
flares as a result of primary energy release elsewhere is found to be
justified in the chromosphere as a whole, although not entirely as the
temperature minimum, and a simplified model of horizontal chromospheric
flare structure based on results obtained is presented.
---------------------------------------------------------
Title: Radiative energy output of the 5 September 1973 flare
Authors: Canfield, R. C.; Cheng, C. -C.; Dere, K. P.; Dulk, G. A.;
McLean, D. J.; Schmahl, E. J.; Robinson, R. D., Jr.; Schoolman, S. A.
1980sfsl.work..451C Altcode: 1980sofl.symp..451C
Measurements of the radiative energy output of the solar flare of
Sept. 5, 1973, over a wavelength range of more than ten decades,
from below 1 A to above 1 m are presented. Observations of soft
X-rays (0.5-20 A), XUV and EUV lines (171-1863 A) and EUV continua
(1400-1960 A), H alpha radiation, visible lines and continua (3700-8700
A) and radio emission (centimeter to meter wavelengths) were obtained
concurrently by Skylab and ground-based instruments. Estimates of power
output at flare maximum are obtained for the observed wavelengths with
uncertainty of at least half an order of magnitude, due to corresponding
uncertainties in EUV and visible fluxes. Taking into account energy
radiated at unobserved wavelengths and the characteristic time of
the best-reduced data (the soft X-ray), calculations indicate a total
radiated flare energy of approximately 4 x 10 to the 29th erg.
---------------------------------------------------------
Title: The Thermal vs. Non-Thermal Flare Controversy: More Fuel for
the Fire
Authors: Canfield, R. C.
1979BAAS...11..650C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Formation of Lyman α, the Balmer and Paschen Lines
and the Balmer Continuum in Quasars
Authors: Canfield, R. C.; Puetter, R. C.
1979BAAS...11..670C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The implications of hydrogen emission-line ratios in
quasi-stellar objects.
Authors: Canfield, R. C.; Puetter, R. C.
1979PASP...91R.609C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Height Variation of Velocity and Temperature Fluctuations
in the Solar Photosphere
Authors: Keil, S. L.; Canfield, R. C.
1978A&A....70..169K Altcode:
Summary. The Vacuum Tower Telescope of Sacramento Peak Observatory is
used to observe intensity and velocity fluctuations in several Fe I
lines as functions of heliocentric angle. We derive the vertical and
horizontal components of the velocity fluctuations, using the technique
developed by Canfield (1976) to separate granular and oscillatory
velocities. We also find a set of height dependent temperature
perturbations which are capable of reproducing the observed intensity
fluctuations. The horizontal component of the granular velocity is found
to be between one and two km 1 greater than the vertical component
(depending on height in the atmosphere). A temperature perturbation
(constant with height) of 175 1 25 K in the upper layers of the
atmosphere [Tsooo 0.1] is sufficient to reproduce the intensity
fluctuations in the strong lines. In deeper layers the temperature
perturbations must increase rapidly with depth to reproduce the observed
intensity fluctuations in the continuum and weak lines. Key words: solar
atmosphere - solar velocity fluctuations - solar temperature structure
---------------------------------------------------------
Title: Indirect estimation of energy disposition by non-thermal
electrons in solar flares.
Authors: Hudson, H. S.; Canfield, R. C.; Kane, S. R.
1978SoPh...60..137H Altcode:
The broad-band EUV and microwave fluxes correlate strongly with hard
X-ray fluxes in the impulsive phase of a solar flare. This note presents
numerical aids for the estimation of the non-thermal electron fluxes
from these correlations, using the SFD (sudden frequency deviation)
ionospheric data to measure the EUV flux.
---------------------------------------------------------
Title: ATM evidence for a nonthermal proton/electron energy flux
ratio in solar flares.
Authors: Canfield, R. C.; Cook, J. W.
1978ApJ...225..650C Altcode:
An observational search has been carried out for asymmetry in the
wings of L-alpha during flares, produced by beams of nonthermal protons
injected into the chromosphere from the corona as suggested by Orrall
and Zirker (1976). The data base is the ATM/Skylab EUV spectrograms from
the NRL S082B spectrograph. The asymmetries expected to be present in
the normal thermal profile are discussed, and detailed consideration
is given to the flare that occurred at 1551 UT on August 9, 1973,
which was observed during the nonthermal phase. In this flare only
very small L-alpha asymmetries are observed, not large enough to be
statistically significant. It is shown that this result, combined
with microwave radio data for information on nonthermal electrons,
implies that the energy flux of nonthermal protons injected into the
chromosphere at energies above 20 keV is less than approximately 0.02
times that of electrons of the same energy range in the observed events.
---------------------------------------------------------
Title: A Probabilistic Approach to Radiative Energy Loss Calculations
for Optically Thick Atmospheres: Hydrogen Lines and Continua
Authors: Canfield, R. C.; Ricchiazzi, P. J.
1978BAAS...10..683C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Intensities of Lyman α, Balmer α and Paschen
α in QSO Clouds
Authors: Canfield, R. C.; Puetter, R. C.
1978BAAS...10R.691C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spatial structure in lines in the 3398 3526 å region at the
extreme limb: Observation, identification and interpretation
Authors: Canfield, R. C.; Pasachoff, J. M.; Stencel, R. E.; Beckers,
J. M.
1978SoPh...58..263C Altcode:
We have obtained spectrograms of high spatial and spectral resolution
of the extreme solar limb, using the vacuum tower telescope of
Sacramento Peak Observatory. We have identified emission lines in
the range 3398-3526 Å, and classified them according to intensity,
spatial structure (intensity variation), and profile. Some lines show
spatial intensity variation; others do not. We show that this effect
is related to the abundance of the element responsible for the line
and the mean lower-level excitation potential of interlocked lines. We
explain the effect in terms of radiative interlocking with other lines,
as well as the characteristic size of the volume contributing to the
mean intensity.
---------------------------------------------------------
Title: Hα profiles from electron-heated solar flares
Authors: Brown, John C.; Canfield, Richard C.; Robertson, Matthew N.
1978SoPh...57..399B Altcode:
We briefly review the status of models of optical flare heating
by electron bombardment. We recompute Brown's (1973a) flare
model atmospheres using considerably revised radiative loss
rates, based on Canfield's (1974b) method applied to α, Lα,
and H<SUP>−</SUP>. Profiles of α are computed and compared with
observation. The computed profiles agree satisfactorily with those
observed during the large 1972 August 7 flare, if spatial and velocity
inhomogeneities are assumed. The electron injection rate inferred
from α is one order of magnitude less than that inferred from hard
X-rays, for this event. This may be due to either (1) the neglect of
a mechanism that reduces the thick-target electron injection rate or
(2) failure to incorporate important radiative loss terms.
---------------------------------------------------------
Title: ATM Evidence for a Low Non-Thermal Proton/Electron Energy
Flux Ratio in Solar Flares.
Authors: Canfield, R. C.; Cook, J. W.
1978BAAS...10..441C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of the solar magnesium I spectrum. II. Sensitivity
of lambda 2852 to partial redistribution effects.
Authors: Canfield, R. C.; Cram, L. E.
1977ApJ...216..654C Altcode:
We have computed theoretical profiles of the Mg 1 A2852 resonance
line by using various models for the frequency redistribution of
the scattered radiation. We find that throughout the line core and
inner wings these profiles are highly sensitive to the assumed
extent of redistribution. In the line core the profile computed
allowing partial redistribution has emission peaks at AA + 0.1 A,
while the profile computed for complete redistribution has no peaks
at all. In the inner wings (0.1 < i AAI < 5.0 A) the residual
intensity with partial redistribution falls as much as a factor of 3
below the complete redistribution profiles. We conclude that partial
redistribution effects in the formation of this line must be taken into
account in subsequent calculations. Subject headings: line formation -
line profiles - radiative transfer - Sun: spectra - ultraviolet: spectra
---------------------------------------------------------
Title: Magnetic field reconnection in the flare of 18:28 UT 1975
August 10.
Authors: Canfield, R. C.; Fisher, R. R.
1976ApJ...210L.149C Altcode:
The letter discusses observations of the cited flare made with the
Sacramento Peak Observatory 512-diode array, which simultaneously
measures photospheric magnetic fields, photospheric and chromospheric
velocities, and chromospheric brightness in several lines. The
observations suggest triggering of the flare by emergence of new
magnetic flux, as well as the geometry of the reconnected field during
the flare. Implications of the present observations regarding the site
of the initial instability are discussed as well as the relationship
to X-ray observations.
---------------------------------------------------------
Title: The height variation of granular and oscillatory velocities.
Authors: Canfield, R. C.
1976SoPh...50..239C Altcode:
Previous observations of spatially-resolved vertical velocity variations
in ten lines of Fe I spanning the height range 0 ≲ h ≲ 1000 km
are re-analyzed using velocity weighting functions. The amplitudes and
scale heights of granular and oscillatory velocities are determined,
as well as those of the remaining unresolved velocities. I find that
the optimal representation of the amplitude of the outward-decreasing
granular velocities is an exponentially decreasing function of height,
with a scale height of 150 km and a velocity at zero height of 1.27 km
s<SUP>−1</SUP>. The optimal representation of the same quantities
for oscillatory velocities is an exponential increase with height,
with a scale height of 1100 km and a velocity at zero height of 0.35
km s<SUP>−1</SUP>. The remaining unresolved velocities decrease with
height, with a scale height of 380 km and a velocity at zero height
of 2.3 km s<SUP>−1</SUP>.
---------------------------------------------------------
Title: Emission lines in the wings of Ca II H and K. I. Initial
solar observations and implications.
Authors: Canfield, R. C.; Stencel, R. E.
1976ApJ...209..618C Altcode:
We apply solar observations to the problem of proper identification of
the atomic species and the mechanism of formation of emission lines
in the wings of the Ca ii H and K lines. Emission lines of both rare
earths and metals appear to be present in the Sun. Their behavior
in the solar spectrum implies that emission lines of metals will be
useful in studies of chromospheres of other stars in which they are
observed. Subject headings: line identifications - Sun: chromosphere -
Sun: spectra
---------------------------------------------------------
Title: Fine Structure Variations in High-Spatial-Resolution Solar
Spectra.
Authors: Pasachoff, J. M.; Canfield, R. C.; Stencel, R. E.; Beckers,
J. M.
1976BAAS....8..501P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Emission Lines in the Wings of Calcium H and K
Authors: Stencel, R. E.; Canfield, R. C.
1976BAAS....8..307S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for Magnetic Field Reconnection in the Flare
Process? Diode Array Observations of the 18:28 U.T. Flare, 10
August 1976
Authors: Fisher, R. R.; Canfield, R. C.
1976BAAS....8..374F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational evidence for unresolved motions in the solar
atmosphere
Authors: Canfield, R. C.; Beckers, J. M.
1976pmas.conf..291C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spatially resolved motions in stellar atmospheres
Authors: Beckers, J. M.; Canfield, R. C.
1976pmas.conf..207B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Motions in the solar atmosphere
Authors: Beckers, J. M.; Canfield, R. C.
1975STIN...7630135B Altcode:
The report presents two papers on observational evidence for large
and small scale motions in the solar atmosphere.
---------------------------------------------------------
Title: A model for the solar flare
Authors: Canfield, R. C.; Priest, E. R.; Rust, D. M.
1975STIN...7615007C Altcode:
It is suggested that many solar flares occur due to an interaction
between newly emerging magnetic flux and an active region filament. A
current sheet forms between the new and old flux and, when its
electric current density exceeds a critical value, rapid magnetic
fields reconnection takes place. Electrons are then accelerated
to high energies and follow the magnetic field lines down to the
chromosphere where they produce several (typically three) bright H
alpha knots. Magnetic energy is continuously released as reconnected
prominence fields are allowed to untwist. Two ribbons of H alpha
emission are produced by one or more of three mechanisms: energetic
particles, thermal conduction or shocks due to infalling material.
---------------------------------------------------------
Title: A simplified method for calculation of radiative energy loss
due to spectral lines.
Authors: Canfield, R. C.
1974ApJ...194..483C Altcode:
In problems of atmospheric structure, numerical complexity often
precludes exact treatment of the radiative transfer problem, making
approximate methods necessary. Such a method, outlined by the
author, makes it possible to estimate radiative losses in spectral
lines in atmospheres of nonnegligible optical depth. The technique
uses approximate solutions of the transfer equation to obtain source
functions and photon escape probabilities as a function of position in
the atmosphere. An example of the application of this method to hydrogen
excitation, ionization, and radiative losses in a solar flare model is
presented. The results are then compared with an exact calculation. The
method reduces computing time by over four orders of magnitude.
---------------------------------------------------------
Title: Analysis of the solar magnesium I spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
1974ApJ...194..733A Altcode:
Without assuming local thermodynamic equilibrium (LTE), we
simultaneously solve the equations of statistical equilibrium and
radiative transfer for a model Mg I atom that includes the lines 4571,
5172 (b2), and 2852 A, which we then compare with observations. From
this comparison we determine by trial and error an optimum model of
run with height of electron temperature, electron density, and total
hydrogen density, and microturbulent velocity in the solar atmosphere up
to approximately h = 1000 km. In addition, we show that the assumption
of LTE for the 4571 A source function is valid to a high degree of
precision.
---------------------------------------------------------
Title: Theoretical Hydrogen Spectra of Chromospheric Flares
Authors: Canfield, Richard C.
1974BAAS....6R.285C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A simplified method for computing radiative energy loss due
to spectral lines. 2: Programs for solar flare models
Authors: Canfield, R. C.
1974erp..reptQ....C Altcode:
The paper lists FORTRAN-IV programs that implement a simplified method
for computing radiative loss rates due to spectral lines. As it is
planned to apply these techniques to solar flare models, the programs
are set up to take into account Lyman alpha, Balmer-alpha and H-,
the principal contributors to radiative energy loss in solar flares.
---------------------------------------------------------
Title: Theoretical Chromospheric Flare Spectra. II: Hydrogen
Equilibrium for Brown's (1973) Models for Heating by Non-Thermal
Electrons
Authors: Canfield, Richard C.
1974SoPh...34..339C Altcode:
We obtain simultaneous solutions of the equations of radiative
transfer and statistical equilibrium for hydrogen excitation and
ionization. The model atom includes Lα, Lβ, Balmer-α and the Lyman,
Balmer and Paschen continua. The model atmospheres are these of Brown
(1973) representating the effects of heating by non-thermal electrons
on the Harvard-Smithsonian Reference Atmosphere.
---------------------------------------------------------
Title: A Non-L.T.E. Analysis of the Solar Mg I Spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
1974BAAS....6..220A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Chromospheric Flare Spectra. I: Hydrogen
Equilibrium for the Kinematic Flare-Shock Models of Nakagawa et
al. (1973)
Authors: Canfield, Richard C.; Athay, R. Grant
1974SoPh...34..193C Altcode:
We simultaneously solve the equations of radiative transfer and
statistical equilibrium for a model hydrogen atom including Lyman-α,
Lyman-β, Balmer-α and the Lyman, Balmer and Paschen continua. The
model atmospheres we use are the results of Nakagawa et al. (1973)
for a kinematic model of the chromospheric solar flare.
---------------------------------------------------------
Title: A non-L.T.E. analysis of the solar Mg I spectrum.
Authors: Altrock, R. C.; Canfield, R. C.
1974BAAS....6..219A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fluctuations of Brightness and Vertical Velocity at Various
Heights in the Photosphere
Authors: Canfield, Richard C.; Mehltretter, J. P.
1973SoPh...33...33C Altcode:
In a spectrogram of exceptionally high spatial resolution, brightness
and velocity fluctuations in seven weak to medium-strong Fe I lines
have been measured and analyzed. Heights of formation of these lines
have been computed using the Harvard-Smithsonian Reference Atmosphere
(Gingerich et al., 1972), taking into account departures from LTE.
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Title: A Scaling-law Approach to the Calculation of Radiative Losses
in Optically Thick Atmospheres.
Authors: Canfield, R. C.
1973BAAS....5..443C Altcode:
No abstract at ADS
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Title: Vertical Phase Variation and Mechanical Flux in the Solar
5-MINUTE Oscillation
Authors: Canfield, Richard C.; Musman, Steven
1973ApJ...184L.131C Altcode:
We have made observations of the solar five-minute oscillation that
allow measurement of the difference of phase between absorption
lines formed over a range of almost 1000 km in the photosphere
and chromosphere. We derive phase velocities, group velocities,
and mechanical fluxes. The amount of mechanical flux lost by the
five-minute oscillation matches the estimated chromospheric radiative
loss in quantity but has a different height distribution. This
difference implies that a change in the mode of energy propagation
may take place below 500 km. Subject headings:chromosphere, solar -
solar atmospheric motions
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Title: Observation and Interpretation of Phase Lags in the Five-Minute
Oscillation
Authors: Canfield, Richard C.; Musman, Steven
1973BAAS....5..269C Altcode:
No abstract at ADS
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Title: Observations of the Variation of Temperature with Latitude
in the Upper Solar Photosphere. 11. Magnetic-Field Comparison,
Implications for Solar-Oblateness Measurements, and Harmonic Analysis
Authors: Canfield, Richard C.
1973ApJ...179..643C Altcode:
It is shown that there is a close relationship between the
latitudinal variation of upper-photospheric temperature and that of
photospheric magnetic field. This correlation, when used with 1966
magnetic-field data, implies that very little of Dicke and Goldenberg's
solar-oblateness signal was due to pole-equator temperature differences
at small optical depths. In the Appendix, Legendre-polynomial
representations of the temperature-difference data are given. Subject
headings: atmospheres, solar - magnetic fields, solar - rotation, solar
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Title: Observations on the Relationship between the Latitudinal
Variations of Temperature and Magnetic Field
Authors: Canfield, R. C.
1972BAAS....4..378C Altcode:
No abstract at ADS
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Title: Observations of Photospheric Pole-Equator Temperature
Differences
Authors: Altrock, Richard C.; Canfield, Richard C.
1972SoPh...23..257A Altcode:
Using photoelectric methods we have repeated Plaskett's (1970)
measurements of poleequator temperature differences. We average many
limb-darkening scans to reduce statistical errors. We then analyze the
differences between the average polar and equatorial scans. Plaskett's
large poleequator temperature differences are not confirmed. Our data
yield a pole-equator temperature difference of 1.5K±0.6K, although
we cannot rule out systematic errors of 3-4 K.
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Title: Observations of the variation of temperature with latitude
in the upper solar photosphere.
Authors: Altrock, R. C.; Canfield, R. C.
1972BAAS....4..268A Altcode:
No abstract at ADS
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Title: Observations of the Variation of Temperature with Lattitude
in the Upper Solar Photosphere
Authors: Altrock, Richard C.; Canfield, Richard C.
1972ApJ...171L..71A Altcode:
We made photoelectric meridional and equatorial limb-darkening scans
during the period 15-22 June 1971, using a spectral region of 30 mA
width centered 0.77 A to the red of Ca II K3. The radiation observed
originates at r5000 10 . At the time of our observations the temperature
relative to the equatorial temperature was enhanced by 8 K + 2.5 K at
active-region latitudes and 5 K + 2 K at latitude 50 N.
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Title: A Measurement of the Non-Thermal Velocity in the Low
Chromosphere
Authors: Canfield, Richard C.
1971SoPh...20..275C Altcode:
I have determined horizontally averaged non-thermal velocities from
Jensen and Orrall's (1963) observations of Doppler widths of weak
rare-earth emission lines in the wings of H and K. Combining these
results with previous rare-earth line results, I conclude that this
velocity in the low chromosphere (300-600 km) is 2.0 ± 0.2 km/s,
and changes little with height.
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Title: Theory of formation of solar rare-earth lines.
Authors: Canfield, R. C.
1971BAAS....3Q.260C Altcode:
No abstract at ADS
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Title: Formation of Solar Rare-Earth Lines inside and outside H and K
Authors: Canfield, R. C.
1971A&A....10...64C Altcode:
The solar spectra of many lanthanide rare-earths consist entirely of
weak lines, and the atomic structure of the ions of interest in the
visible solar spectrum encourages interlocking effects. In this paper
calculations are made that mimic the essential features of these ions
in the solar atmosphere. It is shown that the mechanism of interlocking
via photo-excitations and de-excitations can quantitatively explain
the characteristic behavior of solar lines of rare-earth ions, both
in normal continuum regions in the visible spectrum and in the wings
of the H and K lines. Key words: rare-earth lines
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Title: Deviations from Local Thermodynamic Equilibrium in Weak
Complex Spectra
Authors: Canfield, R. C.
1971A&A....10...54C Altcode:
The equations of statistical equilibrium are solved for an atom
or ion whose energy level structure is complex and whose spectral
lines are all weak. Semi-empirical expressions are used to calculate
atomic cross-sections for idealized multi-level atoms. A linear
Planck function B(T) is assumed, i.e. there is no chromospheric
temperature rise in the atmospheric model. Solutions of the statistical
equilibrium equations are obtained for a variety of model atoms and
atmospheres. When interlocking via permitted radiative excitations and
de-excitations can take place, the source function is photo-excitation
controlled. As a result, LTE does not normally obtain. Calculations
made for atoms of up to 24 levels plus continuum demonstrate the
extent of representative deviations from LTE. Key words: interlocking -
weak-line source functions
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Title: Deviations from Local Thermodynamic Equilibrium in Weak
Complex Stellar Spectra
Authors: Canfield, Richard C.
1970BAAS....2Q.301C Altcode:
No abstract at ADS
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Title: On the Frequency Dependence of the Line Source Function
Authors: Canfield, Richard C.
1970SoPh...12...63C Altcode:
No abstract at ADS
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Title: A Self-Consistent Model Atmosphere Program with Applications
to Solar OI Resonance Lines
Authors: Athay, R. Grant; Canfield, R. C.
1970sfss.coll...65A Altcode: 1970IAUCo...2...65A
No abstract at ADS
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Title: Reversals of Selected CE II Solar Lines
Authors: Canfield, Richard C.
1969ApJ...157..425C Altcode:
Observations of six Ce ii lines in the solar spectrum show that
the lines reverse from absorption to emission on the disk, inside
the limb. Furthermore, the position of this reversal varies with
wavelength. Analysis implies that this behavior is due to the dominance
of the scattering term in the line source function. The absorption-line
profiles favor a non-thermal velocity field that is anisotropic. The
emission-line profiles require a horizontal non-thermal velocity of
2 0 ± 0.2 km sec', averaged over heights 0 < h < 400 km. The
equivalent widths and central intensities of the absorption lines
require a cerium abundance log = 1.4 ± 0.3 (log NH 12 0), and favor
the Bilderberg temperature distribution over that of Hoiweger
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Title: Computed Profiles for Solar Mg b and Na D Lines
Authors: Athay, R. Grant; Canfield, Richard C.
1969BAAS....1..272A Altcode:
No abstract at ADS
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Title: Computed Profiles for Solar MG b- and NA D-Lines
Authors: Athay, R. Grant; Canfield, Richard C.
1969ApJ...156..695A Altcode:
Profiles are computed for the Doppler cores of solar Mg b- and
Na D-lines for multilevel model atoms and for selected ranges of
chromospheric parameters. Comparison of computed and observed profiles
from center to limb on the solar disk yields the depth variation
of the horizontal and vertical components of microturbulence. The
two components are found to be of unequal amplitude for r~> 1O~
and pass through minima near r~ = 1O~. The profiles also suggest that
fle(Tc) at Tc = 104_106 obtained from eclipse data is more reasonable
than that of the Bilderberg model
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Title: Computed Profiles of Mg b and Na D Lines
Authors: Athay, R. G.; Canfield, R. C.
1968rla..conf..363A Altcode:
No abstract at ADS
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Title: Observation and Interpretation of Rare Earth Spectra.
Authors: Canfield, Richard C.
1968AJS....73Q..57C Altcode:
We have observed spectral lines of the rare earth ion Ce II in
the wavelength range 4000-4700 A. Photoelectric and photographic
observations cover the disk from its center to beyond the limb. The
height resolution of the observations near the limb is enhanced through
Fourier transform techniques. The residual spread function has 0.7-1.4
sec of arc half-width at half-maximum, and low-amplitude wings. The
observed chromospheric emission line profiles yield 2.0+0.1 km/ sec
non-thermal broadening velocities in the height range 0 <h <400
km. The observed Ce II lines reverse from absorption to emission on the
disk. The reversal height depends on wavelength. At shorter wavelengths
emission lines extend farther onto the disk. The center-limb variation
of absorption line equivalent widths is analyzed by Altrock's method
(Ph.D. thesis, University of Colorado, 1967). The ratio of the line-
to-continuum source functions S/B >1, and increases with decreasing
wavelength. This suggests that scattering contributes to the line source
function. Athay and Skumanich's method (Ann. Astrophys. 30, 669,1967)
is used with recent solar models to calculate pure absorption and pure
noncoherent scattering line profiles. Noncoherent scattering produces
better agreement with the observed profiles. The atmospheric parameters
that provide the best agreement with the observed absorption lines
are then applied to the extreme limb spectra. Using these parameters,
noncoherent scattering also correctly predicts both the existence of
emission lines on the disk and the observed wavelength dependence of
the reversal height.
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Title: Solar Extreme Limb Spectrum of the Rare-Earth Cerium.
Authors: Canfield, Richard Charles
1968PhDT.........3C Altcode:
No abstract at ADS
