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Author name code: meyer-karen
ADS astronomy entries on 2022-09-14
author:"Meyer, Karen A."
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Title: Defining the Middle Corona
Authors: West, Matthew J.; Seaton, Daniel B.; Wexler, David B.;
Raymond, John C.; Del Zanna, Giulio; Rivera, Yeimy J.; Kobelski,
Adam R.; DeForest, Craig; Golub, Leon; Caspi, Amir; Gilly, Chris R.;
Kooi, Jason E.; Alterman, Benjamin L.; Alzate, Nathalia; Banerjee,
Dipankar; Berghmans, David; Chen, Bin; Chitta, Lakshmi Pradeep; Downs,
Cooper; Giordano, Silvio; Higginson, Aleida; Howard, Russel A.; Mason,
Emily; Mason, James P.; Meyer, Karen A.; Nykyri, Katariina; Rachmeler,
Laurel; Reardon, Kevin P.; Reeves, Katharine K.; Savage, Sabrina;
Thompson, Barbara J.; Van Kooten, Samuel J.; Viall, Nicholeen M.;
Vourlidas, Angelos
2022arXiv220804485W Altcode:
The middle corona, the region roughly spanning heliocentric altitudes
from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential
physical transitions and processes that govern the behavior of
coronal outflow into the heliosphere. Eruptions that could disrupt
the near-Earth environment propagate through it. Importantly, it
modulates inflow from above that can drive dynamic changes at lower
heights in the inner corona. Consequently, this region is essential
for comprehensively connecting the corona to the heliosphere and for
developing corresponding global models. Nonetheless, because it is
challenging to observe, the middle corona has been poorly studied by
major solar remote sensing missions and instruments, extending back to
the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent
advances in instrumentation, observational processing techniques,
and a realization of the importance of the region, interest in the
middle corona has increased. Although the region cannot be intrinsically
separated from other regions of the solar atmosphere, there has emerged
a need to define the region in terms of its location and extension
in the solar atmosphere, its composition, the physical transitions
it covers, and the underlying physics believed to be encapsulated by
the region. This paper aims to define the middle corona and give an
overview of the processes that occur there.
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Title: The Effect of Internal Gravity Waves on Cloud Evolution in
Substellar Atmospheres
Authors: Parent, Amy; Falconer, Ruth E.; Meyer, Karen A.; Stark,
Craig R.
2021csss.confE.147P Altcode:
Substellar objects exhibit photometric variability which is believed to
be caused by a number of processes such as magnetically-driven spots
or inhomogeneous cloud coverage. Recent substellar models have shown
that turbulent flows and waves, including internal gravity waves,
may play an important role in dust cloud evolution. The aim of this
paper is to investigate the effect of internal gravity waves on
dust cloud nucleation and dust growth, and whether observations of
the resulting cloud structures could be used to recover atmospheric
density information. For a simplified atmosphere in two dimensions, we
numerically solve the governing fluid equations to simulate the effect
on dust nucleation and mantle growth as a result of the passage of an
internal gravity wave. Furthermore, we derive an expression that relates
the properties of the wave-induced cloud structures to observable
parameters in order to deduce the atmosphere density. Numerical
simulations show that the density, pressure and temperature variations
caused by gravity waves lead to an up to 20-fold increase of the
dust nucleation rate and an up to 80% increase of the dust growth
rate in the linear regime. These variations lead to banded areas in
which dust formation is much more pronounced. We show that internal
gravity waves in substellar atmospheres lead to banded cloud structures
similar to those observed on Earth. Using the proposed method, potential
observations of banded clouds could be used to estimate the atmospheric
density of substellar objects.
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Title: Investigation of the Middle Corona with SWAP and a Data-Driven
Non-Potential Coronal Magnetic Field Model
Authors: Meyer, Karen A.; Mackay, Duncan H.; Talpeanu, Dana-Camelia;
Upton, Lisa A.; West, Matthew J.
2020SoPh..295..101M Altcode: 2020arXiv200702668M
The large field-of-view of the Sun Watcher using Active Pixel System
detector and Image Processing (SWAP) instrument onboard the PRoject for
Onboard Autonomy 2 (PROBA2) spacecraft provides a unique opportunity
to study extended coronal structures observed in the EUV in conjunction
with global coronal magnetic field simulations. A global non-potential
magnetic field model is used to simulate the evolution of the global
corona from 1 September 2014 to 31 March 2015, driven by newly emerging
bipolar active regions determined from Helioseismic and Magnetic
Imager (HMI) magnetograms. We compare the large-scale structure of
the simulated magnetic field with structures seen off-limb in SWAP EUV
observations. In particular, we investigate how successful the model
is in reproducing regions of closed and open structures, the scale of
structures, and compare the evolution of a coronal fan observed over
several rotations. The model is found to accurately reproduce observed
large-scale, off-limb structures. When discrepancies do arise they
mainly occur off the east solar limb due to active regions emerging on
the far side of the Sun, which cannot be incorporated into the model
until they are observed on the Earth-facing side. When such "late"
active region emergences are incorporated into the model, we find that
the simulated corona self-corrects within a few days, so that simulated
structures off the west limb more closely match what is observed. Where
the model is less successful, we consider how this may be addressed,
through model developments or additional observational products.
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Title: The effect of internal gravity waves on cloud evolution in
sub-stellar atmospheres
Authors: Parent, A.; Falconer, R. E.; Lee, E. K. H.; Meyer, K. A.;
Stark, C. R.
2020A&A...635A.159P Altcode: 2020arXiv200210379P
Context. Sub-stellar objects exhibit photometric variability,
which is believed to be caused by a number of processes, such as
magnetically-driven spots or inhomogeneous cloud coverage. Recent
sub-stellar models have shown that turbulent flows and waves,
including internal gravity waves, may play an important role in cloud
evolution. <BR /> Aims: The aim of this paper is to investigate the
effect of internal gravity waves on dust nucleation and dust growth,
and whether observations of the resulting cloud structures could be
used to recover atmospheric density information. <BR /> Methods: For
a simplified atmosphere in two dimensions, we numerically solved the
governing fluid equations to simulate the effect on dust nucleation
and mantle growth as a result of the passage of an internal gravity
wave. Furthermore, we derived an expression that relates the properties
of the wave-induced cloud structures to observable parameters in order
to deduce the atmospheric density. <BR /> Results: Numerical simulations
show that the density, pressure, and temperature variations caused
by gravity waves lead to an increase of the dust nucleation rate by
up to a factor 20, and an increase of the dust mantle growth rate by
up to a factor 1.6, compared to their equilibrium values. Through an
exploration of the wider sub-stellar parameter space, we show that
in absolute terms, the increase in dust nucleation due to internal
gravity waves is stronger in cooler (T dwarfs) and TiO<SUB>2</SUB>-rich
sub-stellar atmospheres. The relative increase, however, is greater in
warm (L dwarf) and TiO<SUB>2</SUB>-poor atmospheres due to conditions
that are less suited for efficient nucleation at equilibrium. These
variations lead to banded areas in which dust formation is much more
pronounced, similar to the cloud structures observed on Earth. <BR />
Conclusions: We show that internal gravity waves propagating in the
atmosphere of sub-stellar objects can produce banded clouds structures
similar to that observed on Earth. We propose a method with which
potential observations of banded clouds could be used to estimate the
atmospheric density of sub-stellar objects.
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Title: The effect of internal gravity waves on cloud evolution in
sub-stellar atmospheres
Authors: Parent, Amy; Falconer, Ruth; Meyer, Karen; Stark, Craig R.
2019ESS.....432910P Altcode:
Substellar objects exhibit photometric variability which is believed to
be caused by a number of processes such as magnetically-driven spots
or inhomogeneous cloud coverage. Recent substellar models have shown
that turbulent flows and waves, including internal gravity waves,
may play an important role in dust cloud evolution. The aim of this
paper is to investigate the effect of internal gravity waves on
dust cloud nucleation and dust growth, and whether observations of
the resulting cloud structures could be used to recover atmospheric
density information. For a simplified atmosphere in two dimensions, we
numerically solve the governing fluid equations to simulate the effect
on dust nucleation and mantle growth as a result of the passage of an
internal gravity wave. Furthermore, we derive an expression that relates
the properties of the wave-induced cloud structures to observable
parameters in order to deduce the atmosphere density. Numerical
simulations show that the density, pressure and temperature variations
caused by gravity waves lead to an up to 600-fold increase of the
dust nucleation rate and an up to 80% increase of the dust growth
rate in the linear regime. These variations lead to banded areas in
which dust formation is much more pronounced. We show that internal
gravity waves in substellar atmospheres lead to banded cloud structures
similar to those observed on Earth. Using the proposed method, potential
observations of banded clouds could be used to estimate the atmospheric
density of substellar objects.
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Title: Nonlinear Force-free Field Modeling of Solar Coronal Jets in
Theoretical Configurations
Authors: Meyer, K. A.; Savcheva, A. S.; Mackay, D. H.; DeLuca, E. E.
2019ApJ...880...62M Altcode:
Coronal jets occur frequently on the Sun, and may contribute
significantly to the solar wind. With the suite of instruments
available now, we can observe these phenomena in greater detail
than ever before. Modeling and simulations can assist further with
understanding the dynamic processes involved, but previous studies
tended to consider only one mechanism (e.g., emergence or rotation)
for the origin of the jet. In this study we model a series of idealized
archetypal jet configurations and follow the evolution of the coronal
magnetic field. This is a step toward understanding these idealized
situations before considering their observational counterparts. Several
simple situations are set up for the evolution of the photospheric
magnetic field: a single parasitic polarity rotating or moving in a
circular path; as well as opposite polarity pairs involved in flyby
(shearing), cancellation or emergence; all in the presence of a uniform,
open background magnetic field. The coronal magnetic field is evolved in
time using a magnetofrictional relaxation method. While magnetofriction
cannot accurately reproduce the dynamics of an eruptive phase, the
structure of the coronal magnetic field, as well as the buildup of
electric currents and free magnetic energy are instructive. Certain
configurations and motions produce a flux rope and allow the significant
buildup of free energy, reminiscent of the progenitors of so-called
blowout jets, whereas other, simpler configurations are more comparable
to the standard jet model. The next stage is a comparison with observed
coronal jet structures and their corresponding photospheric evolution.
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Title: The Role of Small-Scale Processes in Solar Active Region Decay
Authors: Meyer, Karen; Mackay, Duncan
2017SPD....4810106M Altcode:
Active regions are locations of intense magnetic activity on the Sun,
whose evolution can result in highly energetic eruptive phenomena
such as solar flares and coronal mass ejections (CMEs). Therefore,
fast and accurate simulation of their evolution and decay is essential
in the prediction of Space Weather events. In this talk we present
initial results from our new model for the photospheric evolution
of active region magnetic fields. Observations show that small-scale
processes appear to play a role in the dispersal and decay of solar
active regions, for example through cancellation at the boundary
of sunspot outflows and erosion of flux by surrounding convective
cells. Our active region model is coupled to our existing model for
the evolution of small-scale photospheric magnetic features. Focusing
first on the active region decay phase, we consider the evolution of
its magnetic field due to both large-scale (e.g. differential rotation)
and small-scale processes, such as its interaction with surrounding
small-scale magnetic features and convective flows.This project is
funded by The Carnegie Trust for the Universities of Scotland, through
their Research Incentives Grant scheme.
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Title: Solar Coronal Jets: Observations, Theory, and Modeling
Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.;
Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.;
DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.;
Meyer, K.; Dalmasse, K.; Matsui, Y.
2016SSRv..201....1R Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R
Coronal jets represent important manifestations of ubiquitous solar
transients, which may be the source of significant mass and energy
input to the upper solar atmosphere and the solar wind. While
the energy involved in a jet-like event is smaller than that of
"nominal" solar flares and coronal mass ejections (CMEs), jets
share many common properties with these phenomena, in particular,
the explosive magnetically driven dynamics. Studies of jets could,
therefore, provide critical insight for understanding the larger,
more complex drivers of the solar activity. On the other side of the
size-spectrum, the study of jets could also supply important clues on
the physics of transients close or at the limit of the current spatial
resolution such as spicules. Furthermore, jet phenomena may hint to
basic process for heating the corona and accelerating the solar wind;
consequently their study gives us the opportunity to attack a broad
range of solar-heliospheric problems.
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Title: Modeling the Sun’s Small-scale Global Photospheric Magnetic
Field
Authors: Meyer, K. A.; Mackay, D. H.
2016ApJ...830..160M Altcode:
We present a new model for the Sun’s global photospheric magnetic
field during a deep minimum of activity, in which no active regions
emerge. The emergence and subsequent evolution of small-scale magnetic
features across the full solar surface is simulated, subject to the
influence of a global supergranular flow pattern. Visually, the
resulting simulated magnetograms reproduce the typical structure
and scale observed in quiet Sun magnetograms. Quantitatively, the
simulation quickly reaches a steady state, resulting in a mean field
and flux distribution that are in good agreement with those determined
from observations. A potential coronal magnetic field is extrapolated
from the simulated full Sun magnetograms to consider the implications
of such a quiet photospheric magnetic field on the corona and inner
heliosphere. The bulk of the coronal magnetic field closes very low
down, in short connections between small-scale features in the simulated
magnetic network. Just 0.1% of the photospheric magnetic flux is found
to be open at 2.5 R <SUB>⊙</SUB>, around 10-100 times less than that
determined for typical Helioseismic and Magnetic Imager synoptic map
observations. If such conditions were to exist on the Sun, this would
lead to a significantly weaker interplanetary magnetic field than is
currently observed, and hence a much higher cosmic ray flux at Earth.
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Title: The Sun's Magnetic Field During a Grand Minimum of Activity
Authors: Meyer, Karen; Mackay, Duncan
2014AAS...22411205M Altcode:
During a grand minimum of solar activity, no sunspots are observed
on the photosphere, but what might the Sun's magnetic field look
like? One possibility is that there would be no active regions or larger
scale magnetic activity. We have extended our photospheric model for
small-scale magnetic flux evolution to cover the full Sun. As an initial
study, we consider how the surface magnetic field of the Sun would look
if only smaller-scale magnetic features were allowed to emerge. We also
consider the resultant coronal and inner heliospheric magnetic fields,
and discuss potential consequences of such fields for Earth.
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Title: Analyzing an IRIS Blowout jet via Magnetofrictional Simulation
Authors: Savcheva, Antonia; Tian, Hui; Meyer, Karen
2014AAS...22432310S Altcode:
The imaging spectrograph, IRIS, offers unprecedented spatial and
temporal resolution of small-scale phenomena, which allows the
study of their spectral properties in the chromosphere and transition
region. This study present IRIS observations of a blowout coronal jet,
demonstrating the ability of IRIS to detect reconnection effects in
the low atmosphere in the available suite of spectral lines. We present
Doppler velocity and non-thermal width (NTW) maps of the jet and their
evolution in time. We interpret the results using MHD simulations of
jets. In addition, we present a data-driven magnetofrictional simulation
of the same jet and match the magnetic and current structure of the
jet to the observed NTW maps. We infer the height of the null point
and the extent of the region showing reconnection effects. We discuss
the implications of understanding reconnection effects in conjunction
with NTW maps.
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Title: Data-constrained Magnetofrcitional Simulation of a Flux Rope
Build-up in a Sigmoidal Active Region
Authors: Savcheva, Antonia Stefanova; Mackay, D.; Meyer, K.; Gibb,
G.; DeLuca, E.
2014shin.confE...3S Altcode:
We present a data-constrained magnetofrictional (MF) simulation of
the evolution over two days of the sigmoidal active region from 6-7
Dec 2007. The lower boundary condition is supplied by a series of
line-of-sight (LoS) namgnetograms from MDI, but for the first time the
initial condition is taken from a data-constrained non-linear force-free
(NLFFF) model of the active region early on Dec 6. The NLFFF model is
produced with the flux rope insertion method and is constrained by a LoS
magnetogram, filament path from STEREO, and coronal loops from XRT. The
initial condition is that of a sheared arcade and as time progresses
the photospheric evolution builds a flux rope, which becomes unstable
a few hours before the actual observed eruption. We show field lines
and current density distributions over time and compare them to XRT
images. We present the evolution of the free and potential energy and
relative helicity in the region. We compare our results to a previous
a simulation starting from a potential field as initial condition.
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Title: Simulating the Formation of a Sigmoidal Flux Rope in AR10977
from SOHO/MDI Magnetograms
Authors: Gibb, G. P. S.; Mackay, D. H.; Green, L. M.; Meyer, K. A.
2014ApJ...782...71G Altcode:
The modeling technique of Mackay et al. is applied to simulate the
coronal magnetic field of NOAA active region AR10977 over a seven day
period (2007 December 2-10). The simulation is driven with a sequence
of line-of-sight component magnetograms from SOHO/MDI and evolves
the coronal magnetic field though a continuous series of non-linear
force-free states. Upon comparison with Hinode/XRT observations, results
show that the simulation reproduces many features of the active region's
evolution. In particular, it describes the formation of a flux rope
across the polarity inversion line during flux cancellation. The flux
rope forms at the same location as an observed X-ray sigmoid. After five
days of evolution, the free magnetic energy contained within the flux
rope was found to be 3.9 × 10<SUP>30</SUP> erg. This value is more
than sufficient to account for the B1.4 GOES flare observed from the
active region on 2007 December 7. At the time of the observed eruption,
the flux rope was found to contain 20% of the active region flux. We
conclude that the modeling technique proposed in Mackay et al.—which
directly uses observed magnetograms to energize the coronal field—is
a viable method to simulate the evolution of the coronal magnetic field.
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Title: Solar Magnetic Carpet III: Coronal Modelling of Synthetic
Magnetograms
Authors: Meyer, K. A.; Mackay, D. H.; van Ballegooijen, A. A.; Parnell,
C. E.
2013SoPh..286..357M Altcode: 2013arXiv1303.1342M
This article is the third in a series working towards the construction
of a realistic, evolving, non-linear force-free coronal-field model
for the solar magnetic carpet. Here, we present preliminary results of
3D time-dependent simulations of the small-scale coronal field of the
magnetic carpet. Four simulations are considered, each with the same
evolving photospheric boundary condition: a 48-hour time series of
synthetic magnetograms produced from the model of Meyer et al. (Solar
Phys.272, 29, 2011). Three simulations include a uniform, overlying
coronal magnetic field of differing strength, the fourth simulation
includes no overlying field. The build-up, storage, and dissipation of
magnetic energy within the simulations is studied. In particular, we
study their dependence upon the evolution of the photospheric magnetic
field and the strength of the overlying coronal field. We also consider
where energy is stored and dissipated within the coronal field. The
free magnetic energy built up is found to be more than sufficient to
power small-scale, transient phenomena such as nanoflares and X-ray
bright points, with the bulk of the free energy found to be stored low
down, between 0.5 - 0.8 Mm. The energy dissipated is currently found
to be too small to account for the heating of the entire quiet-Sun
corona. However, the form and location of energy-dissipation regions
qualitatively agree with what is observed on small scales on the
Sun. Future MHD modelling using the same synthetic magnetograms may
lead to a higher energy release.
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Title: A Non-Linear Force-Free Field Model for the Solar Magnetic
Carpet
Authors: Meyer, Karen; Mackay, D.; van Ballegooijen, A.; Parnell, C.
2013SPD....4430201M Altcode:
The magnetic carpet is defined to be the small-scale photospheric
magnetic field of the quiet-Sun. Recent high resolution, high cadence
observations have shown that although small-scale, the magnetic carpet
is far from 'quiet', it is continually evolving in a complex and
dynamic manner. I will present a two-component model for the dynamic
evolution of the Sun's magnetic carpet. The first component is a 2D
model for the photospheric evolution of the small-scale solar magnetic
field, that reproduces many observed parameters. The basic evolution of
magnetic elements within the model is governed by a supergranular flow
profile. In addition, magnetic elements may evolve through the processes
of emergence, cancellation, coalescence and fragmentation. The synthetic
magnetograms produced by the 2D model are then applied as photospheric
boundary data to drive the continuous evolution of a 3D non-linear
force-free coronal field. We studied the resultant complex, small-scale
coronal magnetic field, in particular the energetics of the field.
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Title: The Storage and Dissipation of Magnetic Energy in the Quiet
Sun Corona Determined from SDO/HMI Magnetograms
Authors: Meyer, K. A.; Sabol, J.; Mackay, D. H.; van Ballegooijen,
A. A.
2013ApJ...770L..18M Altcode:
In recent years, higher cadence, higher resolution observations
have revealed the quiet-Sun photosphere to be complex and rapidly
evolving. Since magnetic fields anchored in the photosphere extend
up into the solar corona, it is expected that the small-scale
coronal magnetic field exhibits similar complexity. For the first
time, the quiet-Sun coronal magnetic field is continuously evolved
through a series of non-potential, quasi-static equilibria, deduced
from magnetograms observed by the Helioseismic and Magnetic Imager
on board the Solar Dynamics Observatory, where the photospheric
boundary condition which drives the coronal evolution exactly
reproduces the observed magnetograms. The build-up, storage, and
dissipation of magnetic energy within the simulations is studied. We
find that the free magnetic energy built up and stored within the
field is sufficient to explain small-scale, impulsive events such
as nanoflares. On comparing with coronal images of the same region,
the energy storage and dissipation visually reproduces many of the
observed features. The results indicate that the complex small-scale
magnetic evolution of a large number of magnetic features is a key
element in explaining the nature of the solar corona.
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Title: High-resolution wide-band fast Fourier transform spectrometers
Authors: Klein, B.; Hochgürtel, S.; Krämer, I.; Bell, A.; Meyer,
K.; Güsten, R.
2012A&A...542L...3K Altcode: 2012arXiv1203.3972K
We describe the performance of our latest generations of sensitive
wide-band high-resolution digital fast Fourier transform spectrometer
(FFTS). Their design, optimized for a wide range of radio astronomical
applications, is presented. Developed for operation with the GREAT
far infrared heterodyne spectrometer on-board SOFIA, the eXtended
bandwidth FFTS (XFFTS) offers a high instantaneous bandwidth of
2.5 GHz with 88.5 kHz spectral resolution and has been in routine
operation during SOFIA's Basic Science since July 2011. We discuss
the advanced field programmable gate array (FPGA) signal processing
pipeline, with an optimized multi-tap polyphase filter bank algorithm
that provides a nearly loss-less time-to-frequency data conversion with
significantly reduced frequency scallop and fast sidelobe fall-off. Our
digital spectrometers have been proven to be extremely reliable and
robust, even under the harsh environmental conditions of an airborne
observatory, with Allan-variance stability times of several 1000 s. An
enhancement of the present 2.5 GHz XFFTS will duplicate the number
of spectral channels (64k), offering spectroscopy with even better
resolution during Cycle 1 observations.
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Title: Solar Magnetic Carpet II: Coronal Interactions of Small-Scale
Magnetic Fields
Authors: Meyer, K. A.; Mackay, D. H.; van Ballegooijen, A. A.
2012SoPh..278..149M Altcode: 2012arXiv1211.3924M
This paper is the second in a series of studies working towards
constructing a realistic, evolving, non-potential coronal model for
the solar magnetic carpet. In the present study, the interaction of
two magnetic elements is considered. Our objectives are to study
magnetic energy build-up, storage and dissipation as a result of
emergence, cancellation, and flyby of these magnetic elements. In
the future these interactions will be the basic building blocks of
more complicated simulations involving hundreds of elements. Each
interaction is simulated in the presence of an overlying uniform
magnetic field, which lies at various orientations with respect to the
evolving magnetic elements. For these three small-scale interactions,
the free energy stored in the field at the end of the simulation ranges
from 0.2 - 2.1×10<SUP>26</SUP> ergs, whilst the total energy dissipated
ranges from 1.3 - 6.3×10<SUP>26</SUP> ergs. For all cases, a stronger
overlying field results in higher energy storage and dissipation. For
the cancellation and emergence simulations, motion perpendicular
to the overlying field results in the highest values. For the flyby
simulations, motion parallel to the overlying field gives the highest
values. In all cases, the free energy built up is sufficient to explain
small-scale phenomena such as X-ray bright points or nanoflares. In
addition, if scaled for the correct number of magnetic elements for
the volume considered, the energy continually dissipated provides a
significant fraction of the quiet Sun coronal heating budget.
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Title: A non-linear force-free field model for the solar magnetic
carpet
Authors: Meyer, Karen A.
2012PhDT.......460M Altcode:
The magnetic carpet is defined to be the small-scale photospheric
magnetic field of the quiet Sun. Observations of the magnetic carpet
show it to be highly dynamic, where the time taken for all flux
within the magnetic carpet to be replaced is on the order of just
a few hours. The magnetic carpet is continually evolving due to the
Sun's underlying convection and the interaction of small-scale magnetic
features with one another. Due to this, the small-scale coronal field
of the magnetic carpet is also expected to be highly dynamic and
complex. Previous modelling has shown that much of the flux from the
magnetic carpet is stored along low-lying closed connections between
magnetic features. This indicates that significant coronal heating
could occur low down in the small-scale corona. In this thesis, a new
two-component magnetic field model is developed for the evolution
of the magnetic carpet. A 2D model is constructed to realistically
simulate the evolution of the photospheric field of the magnetic carpet,
where many of the parameters for the model are taken from observational
studies. The photospheric model contains a granular and supergranular
flow profile to describe the motion of the small-scale magnetic
features, and includes the processes of flux emergence, cancellation,
coalescence and fragmentation. This 2D model then couples to a 3D
model as the lower boundary condition, which drives the evolution of
the coronal field through a series of non-linear force-free states,
via a magnetofrictional relaxation technique. We first apply the
magnetofrictional technique to consider the coronal evolution of three
basic small-scale photospheric processes: emergence, cancellation
and flyby. We consider the interaction of the magnetic features with
an overlying coronal magnetic field, and quantify magnetic energy
build-up, storage and dissipation. The magnetofrictional technique is
then applied to synthetic magnetograms produced from the 2D model, to
simulate the evolution of the coronal field in a situation involving
many hundreds of magnetic features. We conduct a preliminary analysis
of the resultant 3D simulations, considering the magnetic energy stored
and dissipated, as well as regions of enhanced velocity and electric
current density within the coronal volume. The simulations show that
the so-called 'quiet Sun' is not quiet and a significant amount of
complex interactions take place.
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Title: A non-linear force-free field model for the solar magnetic
carpet
Authors: Meyer, Karen Alison
2012PhDT.......542M Altcode:
No abstract at ADS
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Title: Solar Magnetic Carpet I: Simulation of Synthetic Magnetograms
Authors: Meyer, K. A.; Mackay, D. H.; van Ballegooijen, A. A.; Parnell,
C. E.
2011SoPh..272...29M Altcode: 2011SoPh..tmp..294M; 2011SoPh..tmp..198M; 2011SoPh..tmp..319M;
2011SoPh..tmp..267M; 2011arXiv1108.1080M
This paper describes a new 2D model for the photospheric evolution
of the magnetic carpet. It is the first in a series of papers
working towards constructing a realistic 3D non-potential model
for the interaction of small-scale solar magnetic fields. In the
model, the basic evolution of the magnetic elements is governed by a
supergranular flow profile. In addition, magnetic elements may evolve
through the processes of emergence, cancellation, coalescence and
fragmentation. Model parameters for the emergence of bipoles are based
upon the results of observational studies. Using this model, several
simulations are considered, where the range of flux with which bipoles
may emerge is varied. In all cases the model quickly reaches a steady
state where the rates of emergence and cancellation balance. Analysis
of the resulting magnetic field shows that we reproduce observed
quantities such as the flux distribution, mean field, cancellation
rates, photospheric recycle time and a magnetic network. As expected,
the simulation matches observations more closely when a larger, and
consequently more realistic, range of emerging flux values is allowed
(4×10<SUP>16</SUP> - 10<SUP>19</SUP> Mx). The model best reproduces
the current observed properties of the magnetic carpet when we take
the minimum absolute flux for emerging bipoles to be 4×10<SUP>16</SUP>
Mx. In future, this 2D model will be used as an evolving photospheric
boundary condition for 3D non-potential modeling.
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Title: Fast Fourier Transform Spectrometer
Authors: Klein, B.; Krämer, I.; Hochgürtel, S.; Güsten, R.; Bell,
A.; Meyer, K.; Chetik, V.
2009stt..conf..199K Altcode:
No abstract at ADS
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Title: Submillimeter heterodyne arrays for APEX
Authors: Güsten, R.; Baryshev, A.; Bell, A.; Belloche, A.; Graf, U.;
Hafok, H.; Heyminck, S.; Hochgürtel, S.; Honingh, C. E.; Jacobs, K.;
Kasemann, C.; Klein, B.; Klein, T.; Korn, A.; Krämer, I.; Leinz,
C.; Lundgren, A.; Menten, K. M.; Meyer, K.; Muders, D.; Pacek, F.;
Rabanus, D.; Schäfer, F.; Schilke, P.; Schneider, G.; Stutzki, J.;
Wieching, G.; Wunsch, A.; Wyrowski, F.
2008SPIE.7020E..10G Altcode:
We report on developments of submillimeter heterodyne arrays for
high resolution spectroscopy with APEX. Shortly, we will operate
state-of-the-art instruments in all major atmospheric windows accessible
from Llano de Chajnantor. CHAMP+, a dual-color 2×7 element heterodyne
array for operation in the 450 μm and 350 μm atmospheric windows
is in operation since late 2007. With its state-of-the-art SIS
detectors and wide tunable local oscillators, its cold optics with
single sideband filters and with 3 GHz of processed IF bandwidth per
pixel, CHAMP+ does provide outstanding observing capabilities. The
Large APEX sub-Millimeter Array (LAsMA) is in the final design phase,
with an installation goal in 2009. The receiver will operate 7 and 19
pixels in the lower submillimeter windows, 285-375 GHz and 385-520 GHz,
respectively. The front-ends are served by an array of digital wideband
Fast Fourier Transform spectrometers currently processing up to 32×1.5
(optionally 1.8) GHz of bandwidth. For CHAMP+, we process 2.8 GHz of
instantaneous bandwidth (in 16.4 k channels) for each of the 14 pixels.
---------------------------------------------------------
Title: CHAMP: A powerful submm Heterodyne Array
Authors: Kasemann, C.; Heyminck, S.; Bell, A.; Belloche, A.;
Castenholz, C.; Güsten, R.; Hafok, H.; Henseler, A.; Hochgürtel,
S.; Klein, B.; Klein, T.; Krämer, I.; Korn, A.; Meyer, K.; Muders,
D.; Pacek, F.; Schäafer, F.; Schneider, G.; Wieching, G.; Baryshev,
A.; Hesper, R.; Zijlstra, T.; Lodewijk, C. F. J.; Klapwijk, T. M.
2008stt..conf..166K Altcode:
No abstract at ADS
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Title: Minor Planet Observations [671 Stony Ridge]
Authors: Brewster, S. C.; Hoff, J. M.; Sable, P. K.; Hadlen, D.;
Martin, S.; Meyer, K.; Sable, P.; Sloman, C.; Sousa, J.; Sousa, L.
2004MPC..52895...6B Altcode:
No abstract at ADS
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Title: Sun-Earth Day 2004: Venus Transit
Authors: Thieman, J. R.; Odenwald, S.; Cline, T.; Lewis, E.; Mayo,
L.; Ng, C.; Meyer, K.
2003AGUFMED12E..02T Altcode:
The NASA Sun-Earth Connection Education Forum annually promotes an
event called Sun-Earth Day. For Sun-Earth Day 2004 SECEF has selected
the transit of Venus as the theme. Opportunities are available
to prepare for the viewing of this event. The event last occurred
in 1882, so no one alive today has ever witnessed the transit of
Venus. Through parallax measurements, it allowed astronomers to
define, for the first time, a fairly accurate number for the A.U. and
therefore, the distance to all the other known planets. The website
http://sunearth.gsfc.nasa.gov/sunearthday has been developed to
provide the necessary resources and opportunities for participation in
Sun-Earth Day. This is the fourth year that we offer new and exciting
space science. This year in particular the content area crosses all of
space sciences offering activities and resources for every classroom and
museum event. The goal is to involve as much of the student population
and the public in this event as possible and to help them understand
the immense importance and excitement surrounding this and previous
transits. Through engaging activities focused on US and world history,
technology, math, and astronomy, classrooms and museums can create
their own event or participate in one of the opportunities we make
available. Comparisons of Venus with the Earth and Mars, calculations
of the distances to nearby stars, and the use of transits to identify
extra-solar planets will all add to the excitement of this cosmic
occurrence.
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Title: Space Science Education Resource Directory
Authors: Betrue, R.; Miner, E.; Lowes, L.; Meyer, K.; Rosendhal, J.;
Morrow, C.
2000DPS....32.6541B Altcode: 2000BAAS...32.1647B
One of the more difficult tasks facing educators (and others involved
in education and public outreach) is that of identifying, finding,
and accessing existing NASA science resources that meet their specific
needs. NASA's OSS EPO Support Network has assembled a NASA Space
Science Education resource Directory to assist interested individuals
(including planetary scientists) to identify and download desired
electronic products funded by NASA. This presentation will describe
and demonstrate the system, which was unveiled in early October 2000
through a NASA Press Release; the Resource Directory is located at URL
http://teachspacescience.stsci.edu. We are investigating solutions to
the difficult issue of efficient distribution of hard copy resources. We
hope to have a live computer demonstration of the Directory at the
NASA Space Science EPO booth at the Conference. Comments and feedback
on the Directory structure and contents will be solicited and welcome.
---------------------------------------------------------
Title: The Sun-Earth Connection Education Forum -Helping NASA Missions
and Scientists Participate in Education and Public Outreach
Authors: Hawkins, I.; Vondrak, R.; Meyer, K.; Thieman, J.
1999AAS...194.7021H Altcode: 1999BAAS...31..941H
The Sun-Earth Connection Education Forum (SECEF) is one of four national
centers of space science education and outreach funded by NASA's
Office of Space Science (OSS). SECEF acts as a central clearinghouse of
information and coordination, facilitating the effective archiving and
dissemination of education and public outreach materials from NASA SEC
missions and scientists. SECEF also helps coordinate participation of
SEC missions at national education conferences, such as the National
Science Teachers Association and the Association of Science and
Technology Centers. SECEF is working with the other three OSS theme
Education Forums (Solar System Exploration, Origins, and Structure and
Evolution of the Universe) to develop an on-line resource directory
for EPO products for teachers and the general public. SECEF is also
leveraging high visibility public events, such as the 1998 Total
Solar Eclpise Webcast in partnership with the Exploratorium museum,
to highlight SEC research and the people responsible for the science
discoveries. Our poster will describe in more detail how SECEF can serve
the NASA SEC community in the context of EPO, show a short video of the
Eclipse '98 Webcast, and describe how scientists can become involved
in the upcoming Eclipse '99 Webcast from the Black Sea and Turkey. This
will be the best looking poster at the meeting - don't miss it!
---------------------------------------------------------
Title: CHAMP: the Carbon Heterodyne Array of the MPIfR
Authors: Guesten, Rolf; Ediss, Geoffrey A.; Gueth, F.; Gundlach,
K. H.; Hauschildt, H.; Kasemann, Christoph; Klein, Thomas; Kooi,
Jacob W.; Korn, A.; Kramer, I.; Leduc, Henry G.; Mattes, H.; Meyer,
K.; Perchtold, E.; Pilz, M.
1998SPIE.3357..167G Altcode:
A 16-element SIS heterodyne array for operation in the 625 micrometer
atmospheric window is under development at the MPIfR. The array consists
of 2 X 8 elements with closest feasible spacing of the pixels on the
sky ((root)2 (DOT) (Theta) (subscript mb)). The L.O. tuning range
covers the astronomically important CI and the CO(4-3) transitions,
and an IF bandwidth of 2 GHz (1200 kms(superscript -1)) will permit
mapping of extragalactic systems. For best system sensitivity the
design allows for cold optics ( 15K) and single-sideband operation. The
frontend will be linked to a flexible autocorrelator, with a maximum
bandwidth of 2 GHz (2048 channels) for each of the 16 modules. In
the high-resolution mode, 500 MHz of bandwidth can be operated with
8192 channels of 61 kHz spectral resolution. System components are
currently undergoing final integration and critical evaluation in
our laboratories. First astronomical commissioning is scheduled for
later this year. The sensitivity expected with CHAMP, for e.g. carbon
studies, will be unparalleled. With the full array in SSB operation
the mapping speed will be enhanced by a factor of 50 - 100 compared
to current single-pixel detectors.
---------------------------------------------------------
Title: Molecular gas in the Galactic center region. I. Data from a
large scale C<SUP>18</SUP>O(J = 1-->0) survey
Authors: Dahmen, G.; Huettemeister, S.; Wilson, T. L.; Mauersberger,
R.; Linhart, A.; Bronfman, L.; Tieftrunk, A. R.; Meyer, K.;
Wiedenhoever, W.; Dame, T. M.; Palmer, E. S.; May, J.; Aparici, J.;
Mac-Auliffe, F.
1997A&AS..126..197D Altcode: 1997A&AS..125....1D
A large scale survey of the Galactic center region in the
C<SUP>18</SUP>O(J = 1 --> 0) transition is presented. This survey
was obtained with the 1.2m Southern Millimeter-Wave Telescope (SMWT)
at the Cerro Tololo Interamerican Observatory (CTIO) near La Serena,
Chile. It covers the region -1.05d <= l <= +3.6d and -0.9d <=
b <= +0.75d with a grid spacing of 9', i.e. the sampling is at full
FWHP beamwidth. 357 positions were in total observed. After reviewing
the instrumentation of the 1.2m SMWT, the observing techniques,
and the methods used in the data reduction, the data of the survey
are presented and morphologically described. In addition, data of the
HNCO(5_{0,5}-4_{0,4}) line are presented, which was also included in the
large bandwidth of the spectrometer. <SUP>12</SUP>CO(1-0) measurements
performed for comparison purposes are presented and compared with other
<SUP>12</SUP>CO results. The maps of the C<SUP>18</SUP>O(1-0) survey
demonstrate that there are great differences between the distribution
of the optically thin C<SUP>18</SUP>O(1-0) emission and the usually
optically thick <SUP>12</SUP>CO(1-0) emission.
---------------------------------------------------------
Title: The Molecular Gas in the Galactic Center Region based on C-18
O Measurements
Authors: Dahmen, C.; Huttemeister, S.; Wilson, T. L.; Mauersberger, R.;
Linhart, A.; Bronfman, L.; Tieftrunk, A. R.; Meyer, K.; Wiedenhover,
W.; Dame, T. M.; Palmer, E. S.; May, J.; Aparici, J.; Macauliffe, F.
1996ASPC..102...54D Altcode: 1996gace.conf...54D
No abstract at ADS
---------------------------------------------------------
Title: An Innovative Concept for Secondary Batteries Applicable
Particularly to Small Satellites
Authors: Meyer, K.; Mickan, J.; Kieb, K.
1995ESASP.369..623M Altcode: 1995esp..conf..623M
No abstract at ADS
---------------------------------------------------------
Title: A C<SUP>18</SUP>O survey of the Galactic center.
Authors: Dahmen, G.; Henkel, C.; Hüttemeister, S.; Lemme, C.; Linhart,
A.; Mauersberger, R.; Meyer, K.; Tieftrunk, A.; Wiedenhöver, W.;
Wilson, T. L.; Aparici, J.; Bronfman, L.; May, J.; Dame, T.; Palmer, S.
1993AGAb....9..162D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A 1 GHz bandwidth acousto-optical spectrometer for airborne
submillimetre astronomy
Authors: Schwaab, G. W.; Meyer, K.; Roeser, H. P.; van der Wal, P.;
Wattenbach, R.; Wiedenhoever, W.
1989JPhE...22..510S Altcode:
A modular easily transportable acoustooptical spectrometer (AOS)
designed for airborne submillimeter astronomical observations is
described. The large bandwidth (992 MHz) of the AOS, combined with
high resolution (1.7 MHz), make it possible to observe astronomical
transitions within a wide variety of spectral widths. The AOS provides
its own data acquisition and handling system, enabling on-line data
reduction and a high degree of flexibility. The AOS was flown aboard
the Kuiper Airborne Observatory in September 1988. Even in the noisy,
shaky, and thermally unstable environment encountered by the AOS its
performance was comparable to that in the laboratory. A diagram of
the electrooptical part of the AOS is included.
---------------------------------------------------------
Title: Infrared detector arrays with multiplexing cryogenic read-out
electronics for ISOPHOT.
Authors: Engemann, D.; Faymonville, R.; Felten, R.; Frenzl, O.; Meyer,
K.; Sohn, A.; Dierickx, B.; Vermeiren, J.
1989InfPh..29..235E Altcode:
Cryogenic Read out Electronic circuits (CRE) are developed in a CMOS
technology for the multiplexing operation at temperatures around 4K and
below of extrinsic photoconducting detectors and detector arrays of
Ge and Si in the Infrared Space Observatory (ISO) instrument ISOPHOT
covering a wavelength region between 10-200 μm. Measurements on the
66 elements spectroscopic array ISOPHOT S2 show performance data of
an NEP around 4×10<SUP>-17</SUP>W/√Hz and a voltage responsivity
of 10<SUP>14</SUP>V/Ws at low background operation.
---------------------------------------------------------
Title: Tests of low background Si:Ga-Infrared-Detector-Arrays with
Cold Multiplexer Readout Circuits
Authors: Weitzel, L.; Wolf, J.; Grözinger, U.; Lemke, D.; Raymonville,
R.; Frenzl, O.; Meyer, K.; Dierickx, B.; Vermeiren, J.
1989AGAb....3..129W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: 2.5. Discussions at the Weil der Stadt symposium
Authors: Krafft, F.; Meyer, K.; Sticker, B.
1975VA.....18...53K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Discussion at the Weil der Stadt Symposium.
Authors: Krafft, F.; Meyer, K.; Sticker, B.
1975kfhy.conf...53K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Object Lowell Observatory
Authors: Esclangon, M. E.; de Grandchamp; Canavaggia; Mineur; Barbier;
Baade, W.; Shapley, H.; Leuschner, A. O.; Bower, E. C.; Whipple,
F. L.; Meyer
1930IAUC..268....1E Altcode:
Observations. In Circulaire No. 8 D (Service des informations rapides)
M. E. Esclangon, Director of the observatory Paris, publishes the
following observations made at Paris observatory (Equatorial of the
Carte du Ciel; observers: de Grandchamp, Canavaggia, Mineur, Barbier;
computers: Mineur, Canavaggia, Barbier): 1930 U.T. R.A. (1930.0)
Decl. March 26 21h32m5 7 15 31.17 +22 8 17.8 27 21 35.0 7 15 31.09 +22
8 24.4 28 21 44.0 7 15 30.63 +22 8 26.4 31 21 7.0 7 15 30.21 +22 8 40.7
April 3 20 7.0 7 15 30.77 +22 8 50.2 Dr. W. Baade at the observatory
Bergedorf sends the following positions: 1930 U.T. R.A. (1930.0)
Decl. March 30 19h47m 4s 7 15 30.23 +22 8 33.6 April 3 23 6 20 7
15 30.84 +22 8 48.8 We have received the following telegram from
Prof. Shapley: "Leuschner telegraphs preliminary investigation Lowell
observatory object by Bower and Whipple results in group of solutions
giving approximate present distance forty one astronomical units
inclination 17 deg. longitude node 109 deg. Observations chiefly
by Meyer Lick Observatory March 16th to April 4th are accurately
represented by orbits varying from near circle to parabola with
perihelion distance 17 astronomical units." An Observation Circular from
the Lowell Observatory of 1930 March 13 gives details about the search
for a transneptunian planet, the discovery of the new object on plates
of 1930 Jan. 21, 23 and 29 and about the observations since that time.
