Author name code: martens
ADS astronomy entries on 2022-09-14
author:"Martens, Petrus C.H." OR author:"Martens, Piet"
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Title: Machine Learning-based Prediction of Solar Energetic Particle
Events Using GOES Proton and X-ray Time Series Data.
Authors: Rotti, Sumanth; Martens, Petrus
Bibcode: 2022cosp...44.1182R
Altcode:
Solar Energetic Particle (SEP) events are sudden enhancements in space
around Earth's radiation environment, often associated with eruptions
such as solar flares and coronal mass ejections (CMEs). SEPs determine
the dosage exposure on astronauts and spacecraft equipment outside the
Earth's magnetosphere, while proton events >100MeV can penetrate
the Earth's upper atmosphere. Hence, reliable predictions of SEPs are
vital to mitigate space weather hazards for space travel. This work
uses machine learning (ML) models for a binary classification problem
addressing the prediction >10 MeV SEP events from a time-series
perspective. We developed an integrated catalog of 342 SEP events
observed between 1986 and 2017. Furthermore, we have carefully chosen
temporally overlapping >M1.0 class flares that have NOT given rise
to a SEP event. The balanced data set between positive and negative
samples provides an advantage with binary classifiers by allowing the
hyper-plane to pass through the decision boundary such that it is not
shifted to favor one particular class. We experiment with ML models such
as support vector machine (SVM), decision trees, and time series forest
(TSF) classifiers to predict SEPs. We consider the X-ray and proton
fluxes from the Geostationary Operational Environmental Satellites
(GOES). Furthermore, we examine the correlations of these fluxes and the
correlations that happen across all the proton channels. This strategy
offers a new perspective in establishing predictions for geo-effective
SEP events arising from a large flare. The motivation behind this
work to use ML is that the models can learn and make decisions based
on observational data and issue quicker forecasts to improve upon the
results of the existing statistical models.
Title: Global network of cosmic ray muon detectors for terrestrial
and space weather monitoring and climate studies
Authors: He, Xiaochun; Martens, Petrus; Sadykov, Viacheslav; Sarsour,
Murad; Connors, Megan; Chien, Yang-Ting; Ashok, Ashwin; Perera, Unil;
Tiwari, Chetan; Mikler, Armin
Bibcode: 2022cosp...44.1562H
Altcode:
Driven by the advancements in particle detection technologies, in
recent years, there has been a growing interest in using cosmic rays,
particularly muon particles, for many practical applications - ranging
from tomography to space and earth weather monitoring. The challenge
in space and earth weather monitoring on a global scale using cosmic
rays is to deploy many efficient and affordable detectors that can
provide accurate correlations between cosmic ray flux variations and
weather conditions. A low-cost and portable muon particle detector has
been developed at Georgia State University (GSU) based on expertise
accumulated while working on the sPHENIX Experiment at Brookhaven
National Lab. The key components include three plastic scintillators
(20cm x 20xm x 1cm) embedded with wavelength shifting fibers and a
Raspberry PI readout. The success of this project requires international
collaborations and partnerships, to jointly develop cosmic ray detector
network and create a global education outreach of climate studies. In
this talk, we will present the detector design (including simulation
studies) and preliminary results from prototype detectors collecting
data on GSU campus. We would also like to take this opportunity to
share our long-term plan and solicit a broader participation in this
project worldwide.
Title: Exploratory Analysis of Magnetic Polarity Inversion Line
Metadata and Eruptive Characteristics of Solar Active Regions
Authors: Aydin, Berkay; Georgoulis, Manolis K.; Martens, Petrus;
Angryk, Rafal A.; Ji, Anli; Khasayeva, Nigar
Bibcode: 2022cosp...44.3223A
Altcode:
Magnetic polarity inversion lines (PILs) detected in solar active
regions and features engineered from them have been recognized as
one of the essential features for predicting key characteristics of
explosive and eruptive instabilities, such as solar flares and coronal
mass ejections. We have built a systematic and comprehensive dataset
of polarity inversion lines from line-of-sight magnetograms in HMI
Active Region Patches (HARPs) data series. Our dataset covers the
series ranging from May 2010 to December 2021. The dataset includes
PIL-related binary masks of rasters (i.e., thinned PIL, the region
of polarity inversion (RoPI), and the convex hull of PIL) as well as
time series metadata extracted from these masks. We will introduce
this multi-modal solar dataset and present some key results of our
first exploratory analysis. We will further highlight relationships
between the time evolution characteristics of magnetic PILs and provide
an empirical analysis and predictive heuristics to demonstrate the
usefulness of multi-modal PIL data in forecasting solar flares, both
confined and eruptive. In particular, we will show the similarities and
differences between pre-flare series of eruptive and confined flares
and explore the relationships between PIL characteristics and the
cumulative flare index. While this line of work is just starting, we
emphasize the use of machine-learning-ready datasets for both physical
and operational purposes, from understanding the key ingredients
of the pre-instability phase in active regions to assigning fully
validated forecast probabilities for major solar events that largely
shape heliospheric space weather.
Title: Integrated Geostationary Solar Energetic Particle Events
Catalog: GSEP
Authors: Rotti, Sumanth; Aydin, Berkay; Georgoulis, Manolis K.;
Martens, Petrus C.
Bibcode: 2022arXiv220412021R
Altcode:
We present a catalog of solar energetic particle (SEP) events covering
solar cycles 22, 23 and 24. We correlate and integrate three existing
catalogs based on Geostationary Operational Environmental Satellite
(GOES) integral proton flux data. We visually verified and labeled
each event in the catalog to provide a homogenized data set. We have
identified a total of 341 SEP events of which 245 cross the space
weather prediction center (SWPC) threshold of a significant proton
event. The metadata consists of physical parameters and observables
concerning the possible source solar eruptions, namely flares and
coronal mass ejections for each event. The sliced time series data
of each event, along with intensity profiles of proton fluxes in
several energy bands, have been made publicly available. This data set
enables researchers in machine learning (ML) and statistical analysis
to understand the SEPs and the source eruption characteristics useful
for space weather prediction.
Title: Revisiting the Solar Research Cyberinfrastructure Needs:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena;
Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal;
Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens,
Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov,
Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L.
Bibcode: 2022arXiv220309544N
Altcode:
Solar and Heliosphere physics are areas of remarkable data-driven
discoveries. Recent advances in high-cadence, high-resolution
multiwavelength observations, growing amounts of data from realistic
modeling, and operational needs for uninterrupted science-quality data
coverage generate the demand for a solar metadata standardization and
overall healthy data infrastructure. This white paper is prepared as
an effort of the working group "Uniform Semantics and Syntax of Solar
Observations and Events" created within the "Towards Integration of
Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research
Coordination Network (@HDMIEC RCN), with primary objectives to discuss
current advances and identify future needs for the solar research
cyberinfrastructure. The white paper summarizes presentations and
discussions held during the special working group session at the
EarthCube Annual Meeting on June 19th, 2020, as well as community
contribution gathered during a series of preceding workshops and
subsequent RCN working group sessions. The authors provide examples
of the current standing of the solar research cyberinfrastructure, and
describe the problems related to current data handling approaches. The
list of the top-level recommendations agreed by the authors of the
current white paper is presented at the beginning of the paper.
Title: Filament Chirality Detection using Machine Learning
Authors: Venkataramanasastry, Aparna; Rotti, Sumanth; Martens, Petrus
Bibcode: 2021AGUFMSH55A1821V
Altcode:
Space weather monitoring and prediction efforts are growing in
importance with the increasing interest in commercialization of the
space sector and as it opens space for public. From our previous
analysis (Aparna & Martens, 2020) of about 2 solar cycles of
CME and ICME data we have shown that the CME Bz can be predicted by
monitoring the regions of eruptions or the chromospheric filaments on
the Sun. This analysis requires manual identification of chirality
in the cases of filament eruptions and the skew of the overlying
arcade fields in active regions where filaments might not be visible
or may not be fully formed. Once the chirality is obtained, we get
the axial field direction of the polarity inversion line of that
region using photospheric magnetograms. Hence, so far, we have been
manually determining the chiralities of these filaments. Due to the
potential of this method in determining a non-geo-effective CME from
a geo-effective one while a filament is still on the Sun, further
efforts in automating the process seems worthwhile. As a first step,
we automate the filament chirality identification using computer
vision. We use chromospheric filament data between 2003 and 2013 from
Helio Research, Inc., run by Mrs. Sara Martin - one of the pioneers in
filament chirality and filament eruptions research, taken in the center
line of Halpha and its red and blue wings. The images have a resolution
of 0.9 per pixel with a narrow field of view. We use LabelBox1, a
proprietary online tool to label the various features in the images
and Google Cloud2 for storing and easy access to our images. We will
present the details of the machine learning algorithm that we use for
classifying the images and the results from our model at the AGU 2021
Fall meeting. References Aparna, V., & Martens, P. C. H., 2020ApJ,
897, 68 1https://labelbox.com 2https://cloud.google.com/edu/
Title: Prediction of Solar Energetic Particle Events Based on GOES
Proton, Electron and X-ray Fluxes Time Series Data Using Machine
Learning Techniques.
Authors: Rotti, Sumanth; Martens, Petrus
Bibcode: 2021AGUFMSH15B2036R
Altcode:
Solar Energetic Particle (SEP) event is a sudden enhancement in space
around Earth's radiation environment that is often associated with
solar eruptions such as flares and coronal mass ejections (CMEs). SEPs
determine the dosage exposure on astronauts and spacecraft equipment
outside the Earth's magnetosphere, while proton events >100MeV can
penetrate the Earth's upper atmosphere. Hence, reliable predictions
of SEPs are vital to mitigate space weather hazards for space
travel. In this work, we address the prediction >10 MeV SEP
events from a multivariate time series perspective using machine
learning (ML) models. Between 1997 and 2020, we have identified 348
SEP events using available catalogs. Furthermore, we have carefully
chosen 348 temporally overlapping >M1.0 class flares that have
NOT given rise to a SEP event. Here, we experiment with ML models
such as support vector machine (SVM) and time series forest (TSF)
classifiers to predict SEPs under a binary classification problem
domain. We consider the X-ray, electron, and proton fluxes from the
Geostationary Operational Environmental Satellites (GOES). Furthermore,
we examine the correlations of these fluxes and the correlations that
happen across all the proton and electron channels. This strategy
offers a new perspective in establishing predictions for geo-effective
SEP events arising from a large flare. Also, the balanced data set
between positive and negative samples gives an advantage to binary
classifiers by allowing the hyper-plane to pass through the decision
boundary such that it is not shifted to favor one particular class. The
motivation behind this work to use ML is that the models can learn and
make decisions based on observational data and issue quicker forecasts
to improve upon the results of the existing statistical models.
Title: New initiatives from the Solar Data Analysis Center
Authors: Ireland, Jack; Amezcua, Arthur; Davey, Alisdair; Inglis,
Andrew; Mansky, Edmund; Martens, Petrus; Oien, Niles; Spencer,
Jennifer; Yashiro, Seiji
Bibcode: 2021AGUFMSH55A1823I
Altcode:
We describe new initiatives undertaken by the Solar Data Analysis Center
(SDAC) to better support the solar physics community. The role of the
SDAC is to support the scientific analysis of solar physics data. The
SDAC has begun a new effort to catalog solar physics data resources from
around the web. The purpose of this effort is to more fully understand
the breadth of solar physics data that are available, to provide a
place where users from solar physics and other disciplines can search
a curated catalog of data resources, and to inform the development of
new SDAC capabilities that are aligned with NASA's Heliophysics Digital
Resource Library initiative. Resources that are in scope include solar
physics data from NASA (and non-NASA) supported missions and instruments
(both current and historical), rocket and balloon experiments, cubesats
and smallsats, and ground based instruments and facilities (for example,
eclipse observations). Also in scope are online resources that describe
solar features and events (for example, the HEK and the CDAW list
of CMEs), and solar physics related data products which are not the
primary data products of NASA solar physics missions/instruments:
for example, the Helioviewer JPEG2000 image files and machine learning
ready datasets fall in to this category. Another new initiative under
development is the regular testing of the command-line Virtual Solar
Observatory (VSO) clients. We are developing a VSO testing capability
that performs automated data searches using the same SunPy, Solarsoft
and VSO code that the solar physics community uses on a daily basis. The
purpose of this testing capability is to capture important diagnostic
information of the data search and download functionality of the VSO,
SunPy and Solarsoft. This information will be used to improve the VSO,
SunPy and Solarsoft. Finally, we describe some recent updates to the
capabilities of the VSO, including newly available datasets.
Title: Solar evolution and extrema: current state of understanding
of long-term solar variability and its planetary impacts
Authors: Nandy, Dibyendu; Martens, Petrus C. H.; Obridko, Vladimir;
Dash, Soumyaranjan; Georgieva, Katya
Bibcode: 2021PEPS....8...40N
Altcode:
The activity of stars such as the Sun varies over timescales
ranging from the very short to the very long—stellar and planetary
evolutionary timescales. Experience from our solar system indicates that
short-term, transient events such as stellar flares and coronal mass
ejections create hazardous space environmental conditions that impact
Earth-orbiting satellites and planetary atmospheres. Extreme events
such as stellar superflares may play a role in atmospheric mass loss
and create conditions unsuitable for life. Slower, long-term evolutions
of the activity of Sun-like stars over millennia to billions of years
result in variations in stellar wind properties, radiation flux, cosmic
ray flux, and frequency of magnetic storms. This coupled evolution of
star-planet systems eventually determines planetary and exoplanetary
habitability. The Solar Evolution and Extrema (SEE) initiative of the
Variability of the Sun and Its Terrestrial Impact (VarSITI) program of
the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) aimed
to facilitate and build capacity in this interdisciplinary subject
of broad interest in astronomy and astrophysics. In this review, we
highlight progress in the major themes that were the focus of this
interdisciplinary program, namely, reconstructing and understanding
past solar activity including grand minima and maxima, facilitating
physical dynamo-model-based predictions of future solar activity,
understanding the evolution of solar activity over Earth's history
including the faint young Sun paradox, and exploring solar-stellar
connections with the goal of illuminating the extreme range of activity
that our parent star—the Sun—may have displayed in the past,
or may be capable of unleashing in the future.
Title: Which Verification Metrics Are Appropriate for Rare-Event
Classification Problems?
Authors: Ahmadzadeh, Azim; Kempton, Dustin; Martens, Petrus; Angryk,
Rafal
Bibcode: 2021AGUFMSH53A..05A
Altcode:
Strong solar flares are indeed rare events, which make the
flare classification task a rare-event problem. Solar energetic
particle events are even rarer space weather events as only a few
instances of them are recorded each year. With the unprecedented
growth in employment of Machine Learning algorithms for rare-event
classification/forecast problems, a proper evaluation of rare-event
models becomes a necessary skill for domain experts to have. This task
remains to be an outstanding challenge as both the learning process and
the metrics used for quantitative verification of models can easily
obscure or skew the true performance of models and yield misleading
and biased results. To help mitigate this effect we introduce a
bounded semimetric space that provides a generic representation for
any deterministic performance verification metric. This space, named
Contingency Space, can be easily visualized and shed light on models
performance as well as on the metrics distinct behavior. An arbitrary
models performance can be mapped to a unique point in this space,
which allows comparison of multiple models at the same time, for a given
metric. Using this geometrical setting we show the difference between a
metrics interpretation of performance and the true performance of the
model. Using this perspective, models which are seemingly different
but practically identical, or only marginally different, can be easily
spotted. By tracking down a learners performance at each epoch, we
can also compare different learners learning paths, which provides a
deeper understanding of the utilized algorithms and their challenge
in the learning process. Moreover, in the Contingency Space, a given
verification metric can be represented by a geometrical surface,
which allows a visual comparison between different metrics---a task
that without this concept could be done only by the tedious algebraic
comparison of metrics formulae. Moreover, using such a surface,
for the first time we can see and quantify the impact of scarcity
of data (intrinsic to rare-even problems) on different metrics. This
extra knowledge provides us with the information we need to choose an
appropriate metric for evaluation of our rare-event models.
Title: Using CME Progenitors to Assess CME Geoeffectiveness
Authors: Mundra, Kashvi; Aparna, V.; Martens, Petrus
Bibcode: 2021ApJS..257...33M
Altcode: 2020arXiv201102123M
There have been a few previous studies claiming that the effects of
geomagnetic storms strongly depend on the orientation of the magnetic
cloud portion of coronal mass ejections (CMEs). Aparna & Martens,
using halo-CME data from 2007 to 2017, showed that the magnetic field
orientation of filaments at the location where CMEs originate on the
Sun can be used to credibly predict the geoeffectiveness of the CMEs
being studied. The purpose of this study is to extend their survey
by analyzing the halo-CME data for 1996-2006. The correlation of
filament axial direction on the solar surface and the corresponding
Bz signatures at L1 are used to form a more extensive analysis
for the results previously presented by Aparna & Martens. This
study utilizes Solar and Heliospheric Observatory Extreme-ultraviolet
Imaging Telescope 195 Å, Michelson Doppler Imager magnetogram images,
and Kanzelhöhe Solar Observatory and Big Bear Solar Observatory
Hα images for each particular time period, along with ACE data for
interplanetary magnetic field signatures. Utilizing all these, we
have found that the trend in Aparna & Martens' study of a high
likelihood of correlation between the axial field direction on the
solar surface and Bz orientation persists for the data between 1996
and 2006, for which we find a match percentage of 65%.
Title: Improved Measurements of the Sun's Meridional Flow and
Torsional Oscillation from Correlation Tracking on MDI and HMI
Magnetograms
Authors: Mahajan, Sushant S.; Hathaway, David H.; Muñoz-Jaramillo,
Andrés; Martens, Petrus C.
Bibcode: 2021ApJ...917..100M
Altcode: 2021arXiv210707731M
The Sun's axisymmetric flows, differential rotation, and meridional
flow govern the dynamics of the solar magnetic cycle, and a variety of
methods are used to measure these flows, each with its own strengths
and weaknesses. Flow measurements based on cross-correlating images of
the surface magnetic field have been made since the 1970s that require
advanced numerical techniques that are capable of detecting movements
of less than the pixel size in images of the Sun. We have identified
several systematic errors in addition to the center-to-limb effect that
influence previous measurements of these flows and propose numerical
techniques that can minimize these errors by utilizing measurements
of displacements at several time lags. Our analysis of line-of-sight
magnetograms from the Michelson Doppler Imager on the ESA/NASA Solar
and Heliospheric Observatory and the Helioseismic and Magnetic Imager
on the NASA Solar Dynamics Observatory shows long-term variations in
the meridional flow and differential rotation over two sunspot cycles
from 1996 to 2020. These improved measurements can serve as vital
inputs for solar dynamo and surface flux transport simulations.
Title: Updates To The Virtual Solar Observatory
Authors: Ireland, J.; Amezcua, A.; Davey, A.; Hourcle, J.; Mansky,
E.; Martens, P.; Oien, N.; Spencer, J.
Bibcode: 2021AAS...23821302I
Altcode:
The Virtual Solar Observatory (VSO) is a community-driven tool that
allows users to seamlessly search for data from multiple, geographically
distributed solar data providers. In this presentation we will describe
the latest updates to the VSO, including newly available data sets,
and the adoption and use of REST (REpresentational State Transfer)
and TAP (Table Access Protocol) methods that expand the reach of the
VSO. We will also describe the VSO's support for data providers written
in Python, and the VSO's interaction with the SunPy Project to bring
access to solar data via a SunPy VSO client. Finally, we will briefly
outline how the VSO will contribute to NASA's Heliophysics Digital
Resource Library.
Title: Data Benchmarking for Solar Flare, CME and SEP Event
Forecasting: Different Prediction and Verification Needs, Unified
Authors: Georgoulis, Manolis K.; Martens, Petrus; Aydin, Berkay;
Ahmadzadeh, Azim; Kempton, Dustin J.; Angryk, Rafal A.
Bibcode: 2021cosp...43E2357G
Altcode:
In this synergistic, interdisciplinary work we convey two principles
that we consider central to improving space weather forecast
capabilities of current and future modeling efforts: first, that
data, model and performance verification tasks are equally important
and should be treated on equal footing. Second, that the solar end
of adverse space weather, comprising flares, coronal mass ejections
(CMEs) and Solar Energetic Particle (SEP) events should be viewed and
treated as a single, albeit multi-faceted, physical problem, rather
than as a set of standalone problems corresponding to each facet. We
present paradigms for both of these principles: first, we discuss a
solar flare benchmark dataset in which the data are fully verified
and we have taken steps to verify different forecast models and their
performance. We show that unverified models lead to much degraded
performance. Second, we outline the main aspects of a methodology to
forecast SEP events in terms of temporal profile and peak proton flux
starting from forecasting their source eruptions in the Sun. Performance
needs dictate the introduction of two modeling tiers, one for eruption
forecasting and projected SEP properties and another for updated,
forecast SEP properties in case of SEP-eligible eruptions. This practice
enables a dual validation of the performance for both tiers, at the
same time constraining applicable uncertainties that could otherwise
render the overall task untenable. Benefits of this approach in terms
of both operations-to-research and research-to-operations are profound
and can lead to both an improved physical understanding of vast swaths
of the heliosphere, along with future prediction services combining
computational efficiency with proven, quantifiable value.
Title: Filament Bz and IMF Bz - A Relation
Authors: Venkataramanasastry, Aparna; Martens, Petrus
Bibcode: 2021cosp...43E1046V
Altcode:
An ICME (interplanetary coronal mass ejection) magnetic field
orientation plays an important role in determining if it will cause
a geo-magnetic storm upon impact with the Earth's magnetosphere. A
southward pointing filament field at the CME causes the maximum
impact geomagnetic storms on Earth and potentially damage power grids,
satellites and astronauts in space. We conduct a survey using halo-CMEs
from 2007-2017 to observe the correlation between the direction of the
axial magnetic field of the source region on the Sun and the enhancement
in the interplanetary magnetic field (IMF) near the Earth from these
CMEs. We see a significant correlation between the direction of the
axial field of the filament and that of the IMF near Earth. We find
that about 86% of the times the magnetic field orientation of a CME is
retained after the eruption. We conclude that this method can be used
for effectively predicting space weather related events. The above
analysis involves visually determining filament chirality to obtain
the axial field direction. We investigate this further with vector
magnetograms of the source regions to determine if they give the same
field orientation as that obtained using chirality. This will further
confirm the chirality method and is also useful for automating space
weather predictions. At the Earth we use flux rope fitting techniques to
get the exact orientation of the IMF. Vector magnetograms from SDO/HMI
are used for obtaining the axial magnetic field of filaments for a
subset (from 2010-2017) of the data used in the previous study which
ranged from 2007-2017. ACE data is used for understanding the IMF at L1.
Title: Coronal Sigmoids and Chromospheric Filaments - A relation?
Authors: Venkataramanasastry, Aparna; Georgoulis, Manolis K.;
Martens, Petrus
Bibcode: 2021cosp...43E1765V
Altcode:
Sigmoids are forward (S-shaped) or inverse (Z-shaped) features
on the Sun that are seen at coronal heights in X-ray or high
temperature extreme ultraviolet (EUV) wavelengths. The sharpest
and brightest of them are highly eruptive. They usually deform or
disappear via coronal mass ejections. This makes it important to
understand X-ray sigmoids because of their relevance for space-weather
forecasting purposes. Chromospheric filaments are generally observed
as absorption features in H$\alpha$ wavelengths. In this work, we
observe chromospheric filaments lying under the sigmoids in order to
correlate the chiralities of the two features. We expect that if the
formation mechanisms of filaments and sigmoids are similar then they
should have same chirality. We have conducted a joint survey of the
sigmoids and the underlying filaments between 2007 and 2017. We use
Hinode soft and hard X-ray data for sigmoid images and GONG H$\alpha$
data for the filaments. We find a total of 84 sigmoids with filaments
within the said time period. Among these we have 41 forward and
43 inverse sigmoids. In the 41 forward sigmoids, 8 (20%) filaments
are dextral, 21 (50%) are sinistral and 12 (30%) ambiguous. In the
inverse sigmoids, 16 filaments (37%) are dextral, 13 (30%) sinistral
and 14 (33%) ambiguous. It is evident from this analysis that there
is no clear correspondence between filament chirality and the sigmoid
handedness. This result warrants further investigation. We therefore
perform calculations of magnetic helicity in the photospheric regions
that encloses the footprints of sigmoids and filaments to primarily
obtain the sign of their helicities. For many of the cases mentioned
above, we use SHARP (Space-weather HMI Active Region Patch) vector
magnetograms to serve as the photospheric boundary condition to which we
apply the linear force-free magnetic helicity and energy formulations
of Georgoulis \& LaBonte (2007). We will report on the findings
of this study during the 43rd COSPAR General Assembly. References
Georgoulis, M. K. \& LaBonte, B. J., ApJ, 2007, 671, 1034
Title: A Catalog of Solar Flare Events Observed by the SOHO/EIT
Authors: Rotti, Sumanth A.; Martens, Petrus C. H.; Aydin, Berkay
Bibcode: 2020ApJS..249...20R
Altcode: 2020arXiv200705586R
We have compiled a catalog of solar flares (SFs) as observed by the
Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and
Heliospheric Observatory (SOHO) spacecraft and the Geostationary
Operational Environmental Satellites (GOES) spacecraft over a span
from 1997 to 2010. During mid-1998, the cadence of EIT images was
revised from two images per day to 12 minutes. However, the low temporal
resolution causes significant data gaps in capturing much of the flaring
phenomenon. Therefore, we monitor possible errors in flare detection by
flare parameters such as temporal overlap, observational wavelength,
and considering full field-of-view images. We consider the GOES flare
catalog as the primary source. We describe the technique used to enhance
the GOES detected flares using the extreme ultraviolet image captured
by the EIT telescope. In order to detect brightenings, we subtract
the images with a maximum cadence of 25 minutes. We have downloaded
and analyzed the EIT data via the Virtual Solar Observatory. This flare
data set from the SOHO/EIT period proves indispensable to the process of
the SF predictions as the instrument has covered most of Solar Cycle 23.
Title: Solar Filaments and Interplanetary Magnetic Field Bz
Authors: Aparna, V.; Martens, Petrus C.
Bibcode: 2020ApJ...897...68A
Altcode:
The direction of the axis of an interplanetary coronal mass ejection
(ICME) plays an important role in determining if it will cause a
geomagnetic disturbance in the Earth's magnetosphere upon impact. Long
period southward-pointing ICME fields are known to cause significant
space weather impacts and thus geomagnetic storms. We present an
extensive analysis of CME-ICME directionality using 86 halo-CMEs
observed between 2007 and 2017 to compare the direction of the source
filament axial magnetic field on the Sun and the direction of the
interplanetary magnetic field near the Earth at the L1 Lagrangian
point. Excluding 12 cases that were too ambiguous to determine,
for the remaining 74 ICMEs, we find an agreement in terms of the
northward/southward orientation of Bz between ICMEs and
their CME source regions in 85% of cases. Some of the previous studies
discussed here have obtained an agreement of 77% and 55%. We therefore
suggest that our method can be meaningful as a first step in efficiently
predicting geoeffective ICMEs by observing and analyzing the source
regions of CMEs on the Sun.
Title: Machine Learning in Heliophysics and Space Weather Forecasting:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov,
Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin;
Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh,
Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen,
Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale;
Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland,
Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu,
Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus;
McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey;
Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie
Bibcode: 2020arXiv200612224N
Altcode:
The authors of this white paper met on 16-17 January 2020 at the New
Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that
brought together a group of heliophysicists, data providers, expert
modelers, and computer/data scientists. Their objective was to discuss
critical developments and prospects of the application of machine and/or
deep learning techniques for data analysis, modeling and forecasting
in Heliophysics, and to shape a strategy for further developments in
the field. The workshop combined a set of plenary sessions featuring
invited introductory talks interleaved with a set of open discussion
sessions. The outcome of the discussion is encapsulated in this white
paper that also features a top-level list of recommendations agreed
by participants.
Title: Multivariate time series dataset for space weather data
analytics
Authors: Angryk, Rafal A.; Martens, Petrus C.; Aydin, Berkay; Kempton,
Dustin; Mahajan, Sushant S.; Basodi, Sunitha; Ahmadzadeh, Azim; Cai,
Xumin; Filali Boubrahimi, Soukaina; Hamdi, Shah Muhammad; Schuh,
Michael A.; Georgoulis, Manolis K.
Bibcode: 2020NatSD...7..227A
Altcode:
We introduce and make openly accessible a comprehensive, multivariate
time series (MVTS) dataset extracted from solar photospheric vector
magnetograms in Spaceweather HMI Active Region Patch (SHARP) series. Our
dataset also includes a cross-checked NOAA solar flare catalog that
immediately facilitates solar flare prediction efforts. We discuss
methods used for data collection, cleaning and pre-processing of the
solar active region and flare data, and we further describe a novel
data integration and sampling methodology. Our dataset covers 4,098
MVTS data collections from active regions occurring between May 2010 and
December 2018, includes 51 flare-predictive parameters, and integrates
over 10,000 flare reports. Potential directions toward expansion of the
time series, either "horizontally" - by adding more prediction-specific
parameters, or "vertically" - by generalizing flare into integrated
solar eruption prediction, are also explained. The immediate tasks
enabled by the disseminated dataset include: optimization of solar flare
prediction and detailed investigation for elusive flare predictors or
precursors, with both operational (research-to-operations), and basic
research (operations-to-research) benefits potentially following in
the future.
Title: Forecasting Space Weather Hazards for Astronauts in Deep Space
Authors: Martens, P. C.; Filali Boubrahimi, S.; Aydin, B.; Angryk, R.
Bibcode: 2019AGUFMSH34B..08M
Altcode:
Astronauts on interplanetary missions, often far off from the Earth-Sun
line, will be subject to high energy solar energetic particle (SEP)
events from solar eruptive flares. Protective measures can be taken
but they require alerts of tens of minutes ahead, longer in case of
extravehicular or off-base activities. We have developed a SEP
early warning algorithm based on data from the GOES instruments alone
(Filali-Boubrahimi et al. 2018). Applied to the same original SEP events
as UMASEP, developed by Núñez (2015) we get slightly better results,
using the Decision Tree classifier. We have now extended the
training, testing, and verification database to all GOES observed SEP
events in cycles 23 and 24, complemented with a similar sized database
of non-SEP events, during minor flares and flare-quiet intervals. We
are testing these data with a variety of classifiers, such as Support
Vector Machines, Dynamic Time Warping, and Neural Networks, to find
the best possible predictor for the largest possible (but still small)
benchmark data set. We will present the results focusing on the
accuracy of forecasts and further data that are needed to improve
the forecasts to the level that is required for interplanetary manned
flight. This research is supported by the NASA Space Radiation
Analysis Group at JSC. Núñez, M. 2015, Space Weather, 13,
807-819, doi:10.1002/2015SW001256. Soukaina Filali Boubrahimi,
Berkay Aydin, Petrus Martens, and Rafal Angryk, 2018, IEEE International
Conference on Big Data, pp. 2533-2542, https://arxiv.org/pdf/1712.01402.
Title: The SOHO/EIT solar flare catalog
Authors: Rotti, S.; Martens, P. C.
Bibcode: 2019AGUFMSH31E3341R
Altcode:
In this work, we attempt to produce a database of solar flares
detected by the Extreme ultraviolet Imaging Telescope (EIT) aboard
the Solar and Heliospheric Observatory (SOHO) in accordance to
the Geostationary Operational Environmental Satellite (GOES) flare
catalog. The flare detection effort for the pre-SDO (Solar Dynamics
Observatory) era available is only the GOES catalog with spatial and
temporal specifications along with an associated active region (AR)
number. The GOES system records flares through hard X-ray detectors and
provides flare location on the Sun using it's SXI (Solar X-ray Imager)
instrument (Bornmann et al., 1996). However, many flare locations
and/or AR numbers are unavailable in the GOES catalog. For machine
learning purposes, it is crucial to establish the correct locations
of solar flares in the GOES catalog with other space-borne instruments
(Aydin et al., 2019). Hence we choose the duration of EIT operations,
i.e., from 1996 to 2010, for analysis of an extensive data set from
the instrument. Considering the GOES flare catalog as the primary
source, the recorded peak time of the flare is used as a reference to
select the closest Extreme UltraViolet (EUV) image of the Sun from EIT
plus a consecutive one in order to detect brightenings. The follow-up
image to the peak time could be before or after the peak depending
on the temporally closest available. Although the cadence of EIT was
revised from two images per day to 12 minutes in mid-1998 until 2010
(ESA, 2017), this still causes significant data gaps in capturing much
of the flaring phenomenon. Therefore, we monitor possible errors in
flare detection by parameters such as temporal overlap, observational
wavelength, maximum cadence limit of 24 minutes, and considering only
full field of view (FOV) images. Over 12 years of EIT data has been
downloaded via the Virtual Solar Observatory (VSO). Nonetheless,
this flare data from the SOHO/EIT period proves essential to the
study of the solar atmosphere as the instrument has covered most of
Solar Cycle 23. The flare catalog will be part of a machine learning
benchmark dataset for solar flare prediction.
Title: Relationship between Chromospheric Filaments & IMF Bz - II
Authors: Venkataramanasastry, Aparna; Martens, Petrus
Bibcode: 2019shin.confE..25V
Altcode:
Space weather events such as Coronal Mass Ejections (CMEs) and Solar
Energetic Particle Events that are Earth-bound tend to have tremendous
impact on the power grids on Earth, astronauts and satellites in
space. Effective ways of predicting such events even before they
occur on the Sun are very helpful in avoiding or minimizing their
effects. Chromospheric filaments on the Sun can be used to act
as precursors to CMEs by utilizing the orientation of their axial
magnetic field to predict if the CME will reconnect with the Earth’s
magnetosphere. Aparna & Martens, 2018 (Abstract link here) for SHINE
yielded results that proved the above statement, in that the poloidal
component of the axial field of the filament had the same directionality
as that measured at L1 by using Bz and other plasma parameters from
the Mag instrument aboard Advanced Composition Explorer situated at
L1. The current study is directed towards using the direction of the
axial magnetic field with the aid of vector magnetograms along with flux
rope fitting techniques at L1 to obtain the orientation of the flux
rope there. Vector magnetograms from SDO/HMI are used for obtaining
the axial magnetic field of filaments for a subset (from 2010-2017)
of the data used in the previous study which ranged from 2007-2017.
Title: Machine Learning in Solar Eruption Forecasting: a Scene-Setting
Attempt
Authors: Georgoulis, Manolis K.; Martens, P. C.; Angryk, R. A.; Aydin,
B.; Ahmadzadeh, A.
Bibcode: 2019shin.confE..89G
Altcode:
Over the nearly three decades of space weather forecasting efforts,
increased awareness suggests that conventional solar physics may
not suffice to fully understand, and ultimately predict, eruptive
solar activity, particularly the rarest trio of major flare, coronal
mass ejection and solar energetic particle events. Both statistical
and computer science techniques and approaches, such as machine and
deep learning, seem apt to break ground in both pursuits, namely, in
enhancing physical understanding and in enabling forecasts reliable
enough to become practical. Like any promising new trend, however,
machine and deep learning methods entail major challenges. In this
brief account, we discuss a subset of these challenges whose efficient
tackling can spur further progress. These major issues became evident in
the framework of the European Union Flare Likelihood and Region Eruption
Forecasting (FLARECAST) project on solar flare forecasting. The most
substantial of them, that can easily mislead results, comparisons
and interpretation, include climatology and uncertainties thereof,
the construction of the training and test samples in machine learning
methods and the class imbalance problem that becomes conspicuous when
forecasting increasingly rare events. The above underline the need
for benchmarking standards against which new methods are to be tested,
verified and validated. We discuss a such benchmark, namely the Space
Weather data ANalytics (SWAN) benchmark dataset for flare prediction,
established at the Georgia State University Astroinformatics Cluster,
that aims to tackle climatology and the construction of training and
test samples. In addition, we show indicative, preliminary results
of efforts tackling the class imbalance problem on the GSU SWAN flare
prediction data.
Title: Work Done by Lorentz Force Drives Solar-Stellar Magnetic Cycles
Authors: Mahajan, Sushant Sushil; Nandy, Dibyendu; Martens, Petrus C.
Bibcode: 2019shin.confE.199M
Altcode:
Our theoretical analysis of the equations of magnetohydrodynamics
applied to the solar dynamo suggests that the work done by Lorentz force
is the source of magnetic energy inside the solar convection zone. The
action of Lorentz Force on poloidal field inside the convection zone
is expected to leave behind signs of magnetic tension which manifest
in the form of reduced latitudinal shear in differential rotation. We
show that these expected signs of magnetic tension are consistent
with the torsional oscillation profile of the Sun measured by three
different instruments and hence can be used to locate regions inside
the Sun where the magnetic field in sunspots originates.
Title: Hemispheric Preference and Cyclic Variation of Solar Filament
Chirality from 2000 to 2016
Authors: Hazra, Soumitra; Mahajan, Sushant S.; Douglas, William Keith,
Jr.; Martens, Petrus C. H.
Bibcode: 2018ApJ...865..108H
Altcode: 2017arXiv171105758H
It is well known that solar filaments are features in the solar
atmosphere that show a hemispheric preference in their chirality. The
hemispheric preference is such that the dextral chirality dominates in
the northern hemisphere while the sinistral chirality dominates in the
southern. Determining the strength and cyclic variation of the degree
of this hemispheric preference however, is challenging and tedious,
and thus, needs to be automated. In this paper, we follow Dr. Pietro
Bernasconi’s algorithm to detect filament chirality with two parallel
channels of application. The algorithm is applied to H-alpha images
with the “Advanced Automated Filament Detection and Characterization
Code” and the full algorithm (including the detection of filaments
and tracking) is explained to the human observer who determines the
chirality of the solar filament. We have conducted this exercise on the
data during the month of August from years 2000 to 2016 and we found
that 83% of our visually determined filaments follow the hemispheric
chirality preference, while 58% of automatically determined filaments
follow it. Our visually compiled results have over 90% agreement with
those of Pevtsov et al., yet the visually determined chiralities of
filaments disagree with the automated determinations significantly. We
find that the hemispheric preference remained the same between solar
cycles 23 and 24, but the preference is very difficult to determine
during the solar minimum of 2008-2010 primarily due to the absence
of filaments.
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
Bibcode: 2018arXiv181008728N
Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
Title: Data Handling and Assimilation for Solar Event Prediction
Authors: Martens, Petrus C.; Angryk, Rafal A.
Bibcode: 2018IAUS..335..344M
Altcode: 2017arXiv171201402M
The prediction of solar flares, eruptions, and high energy particle
storms is of great societal importance. The data mining approach
to forecasting has been shown to be very promising. Benchmark
datasets are a key element in the further development of data-driven
forecasting. With one or more benchmark data sets established,
judicious use of both the data themselves and the selection of
prediction algorithms is key to developing a high quality and robust
method for the prediction of geo-effective solar activity. We review
here briefly the process of generating benchmark datasets and developing
prediction algorithms.
Title: On the relationship between chromospheric filaments and IMF B
Authors: Venkataramanasastry, Aparna; Martens, Petrus
Bibcode: 2018shin.confE.224V
Altcode:
I present a poster that depicts a qualitative relationship between the
direction of the axial magnetic field of chromospheric filaments on
the Sun and the Interplanetary Magnetic Field axis of Earth-impacting
Coronal Mass Ejections (CMEs) that were caused due to the eruptions
of those filaments. I conduct analysis of a set of halo CMEs between
2007 and 2017 by comparing the axial magnetic field of CME producing
filaments determined using their chirality. Utilizing the magnetic
field measurements obtained from the Advanced Composition Satellite
(ACE), the variations in the interplanetary magnetic field (IMF) due
to the CME are analyzed. The arrival time of the CME is calculated in
a linear fashion according to the estimated speed. To quantitatively
establish a relation between the two, we use flux rope models to fit the
interplanetary magnetic field. This will suggest how the orientation
of the field is varying. In other words, obtaining the helicity at L1
will help determine how it has changed since it was at the Sun.
Title: Scene Setting Talk: Advancing Solar Activity Forecasts Through
Data Handling and Machine Learning
Authors: Martens, Petrus C.; Angryk, Rafal A.
Bibcode: 2018shin.confE.272M
Altcode:
To "Advance Solar Activity Forecasts Through Observations, Data
Assimilation and Machine Learning" solar physicists need to apply
knowledge and experience from other domains of science, in particular
data analytics, a subdiscipline of computer science. It is naive of
solar physicists to think they can become experts in this field by
simply scavenging the literature that appears pertinent. After all,
can we expect, say a chemist, to become an expert in solar flare
prediction by browsing the relevant literature? The way to make
progress in combining data mining and solar activity prediction is a
close collaboration between solar physicists and data mining experts -
unless, of course, one has the inclination to go for a second PhD in
computer science. The latter is actually not a bad idea for students:
we are developing a joint degree program for this purpose. The
solar-stellar informatics cluster at Georgia State University (GSU)
is such an interdisci-plinary effort between the departments of
Physics & Astronomy and Computer Science. The first and major
objective of this rapidly expanding group is the prediction of solar
flares and closely related phenomena such as Solar Energetic Particles
and Coronal Mass Ejections (CME's) using recently developed methods
of data mining. The primary requirement requirement for such
an undertaking is developing a clean and balanced database. We are
analyzing all available data and metadata produced during the Solar
Dynamics Observatory (SDO) mission with the goal of developing
a benchmark flare dataset, following the recommendation of the US
National Science and Technology Council. It is worth pointing
out here that this undertaking is neither trivial nor effortless. SDO
sends down of the order of 100,000 images per day, and from those
images we produce metadata on various solar phenomena (e.g. sunspots,
active regions, sigmoids, CME's) with automated feature recognition
modules (Martens et al. 2012). One cannot review all these images
and metadata by hand, so again automated methods had to be developed
to accomplish this task. Examples of features that are not useful for
flare prediction are sunspot or active region coordinates off the disk,
image data gaps for various reasons (explained or unexplained), gaps
in metadata caused for example by the relevant module being off-line,
etc. It is obvious that any flare prediction algorithm would be greatly
confused, say about the relation between flares and sigmoids, when
there are undeclared gaps in either sigmoid or flare coverage. The second step in our program is to use this benchmark data set
to test various classifiers to see which ones perform best for solar
flares. Here we not only use a snapshot of solar images and metadata,
but we also look at the evolution of various parameters. Already in
our first cursory analysis we found a strong and rather surprising
flare parameter that I will discuss in this introduction.
Title: The solar dynamo as an interplay of rotational shear and
magnetic field
Authors: Mahajan, Sushant Sushil; Nandy, Dibyendu; Martens, Petrus C.
Bibcode: 2018shin.confE.154M
Altcode:
No abstract at ADS
Title: Using DSG to build the capability of space weather forecasting
in deep space.
Authors: DeLuca, Edward; Golub, Leon; Korreck, Kelly; Savage, Sabrina
L.; McKenzie, David E.; Rachmeler, Laurel; Winebarger, Amy R.; Martens,
Petrus C.
Bibcode: 2018tess.conf22002D
Altcode:
The prospect of astronaut missions to deep space and off the
sun-earth line raises new challenges for space weather awareness
and forecasting. Combined efforts of the science and human flight
communities are needed to identify the requirements and identify
pathways that will allow us to address the requirements for protecting
human life and equipment, on a timescale consistent with the deep space
exploration program. <p class="p1" The Deep Space Gateway provides
a platform where we can develop, test and validate a combined space
weather instrumentation, analysis and forecasting system that can be
used when out of routine contact with near earth based assets. This
presentation will attempt to outline the bounds of the problem and start
the discussion about how to build an independent space weather program.
Title: Forecasting Space Weather Hazards for Astronauts in Deep Space
Authors: Martens, P. C.
Bibcode: 2018LPICo2063.3188M
Altcode:
Deep Space Gateway provides a unique platform to develop, calibrate,
and test a space weather forecasting system for interplanetary travel
in a real life setting. We will discuss requirements and design of
such a system.
Title: Using DSG to Build the Capability of Space Weather Forecasting
in Deep Space
Authors: DeLuca, E. E.; Golub, L.; Korreck, K.; Savage, S.; McKenzie,
D. D.; Rachmeler, L.; Winebarger, A.; Martens, P.
Bibcode: 2018LPICo2063.3050D
Altcode:
The prospect of astronaut missions to deep space and off the
Sun-Earth line raises new challenges for space weather awareness and
forecasting. We need to identify the requirements and pathways that
will allow us to protect human life and equipment.
Title: A Two Dimensional Prediction of Solar Cycle 25
Authors: Munoz-Jaramillo, A.; Martens, P. C.
Bibcode: 2017AGUFMSH13A2469M
Altcode:
To this date solar cycle most cycle predictions have focused on the
forecast of solar cycle amplitude and cycle bell-curve shape. However,
recent intriguing observational results suggest that all solar cycles
follow the same longitudinal path regardless of their amplitude,
and have a very similar decay once they reach a sufficient level
of maturity. Cast in the light of our current understanding, these
results suggest that the toroidal fields inside the Sun are subject
to a very high turbulent diffusivity (of the order of magnitude of
mixing-length estimates), and their equatorward propagation is driven
by a steady meridional flow. Assuming this is the case, we will revisit
the relationship between the polar fields at minimum and the amplitude
of the next cycle and deliver a new generation of polar-field based
predictions that include the depth of the minimum, as well as the
latitude and time of the first active regions of solar cycle 25.
Title: On the Prediction of >100 MeV Solar Energetic Particle
Events Using GOES Satellite Data
Authors: Filali Boubrahimi, Soukaina; Aydin, Berkay; Martens, Petrus;
Angryk, Rafal
Bibcode: 2017arXiv171203998F
Altcode:
Solar energetic particles are a result of intense solar events such as
solar flares and Coronal Mass Ejections (CMEs). These latter events all
together can cause major disruptions to spacecraft that are in Earth's
orbit and outside of the magnetosphere. In this work we are interested
in establishing the necessary conditions for a major geo-effective
solar particle storm immediately after a major flare, namely the
existence of a direct magnetic connection. To our knowledge, this is
the first work that explores not only the correlations of GOES X-ray
and proton channels, but also the correlations that happen across all
the proton channels. We found that proton channels auto-correlations
and cross-correlations may also be precursors to the occurrence of an
SEP event. In this paper, we tackle the problem of predicting >100
MeV SEP events from a multivariate time series perspective using easily
interpretable decision tree models.
Title: A Survery of the Correlation between Filament Chirality and
Sigmoid Handedness
Authors: V, A.; Hazra, S.; Martin, S. F.; Martens, P. C.
Bibcode: 2017AGUFMSH51C2498V
Altcode:
Sigmoid regions on the Sun are often the regions that cause Coronal
Mass Ejections (CMEs). Large CMEs most often have filaments that
erupt with them. This study focuses on the statistical relevance of
the shape of the sigmoid and the chirality of the filament residing in
these sigmoids. The study further extends to the relation between the
directionality of filaments and the Earth-directed CMEs. Sigmoid data
from Savcheva et al. (2014) between 2007 and 2012 and a compilation of
data using the HEK Sigmoid Sniffer (Martens et al. 2012) along with
Hinode XRT Soft X-ray images were used for analyzing data between
2013 and 2017. Hence this dataset consists of almost one solar cycle
of data. A similar study done previously by Martens et al. (2013)
analysed data for a solar cycle using an Advanced Automated Filament
Detection & Characterization Code (Bernasconi, Rust & Hakim
2005). Considering that automated chirality detection is not foolproof,
we present this study which uses manual determination of chirality
for accuracy using high resolution chromospheric images. Mainly full
disk images of soft X-ray obtained from Hinode XRT (X-Ray Telescope)
have been used to find and ensure the S or Z shape of sigmoids. H-alpha
images obtained from BBSO and Kanzelhohe Solar Observatory (KSO) are
used in determining the chirality of filaments. The resolutions of BBSO
and KSO data are 1k and 4k respectively. A comparison of the analysis of
the chirality of filaments using both data will be presented. Although
KSO gives a 4k resolution, it is still difficult to determine the
chirality of small filaments. For this reason, high resolution images of
H-alpha chromospheric filaments obtained from Helio Research and Solar
Observing Optical Network (SOON) have been used for further analysis
of chirality of those filaments that were undeterminable using the
BBSO or KSO full disk images. The results of the comparison using
the different resolutions are shown. The results of the correlation
between sigmoid shape and filament chirality are also shown. Further,
these results are used in determining the correlation with Earth
directed CMEs and those that cause geo-magnetic storms. Savacheva,
A. S., McKillop, S. C., McCauley, P. I., et al., 2014, 289Bernasconi,
P. N., Rust, D. M., & Hakim, D., 2005, Sol. Phys., 228, 97 Martens,
P., Yeates, A., & Pillai, K., 2013, IAU, 3000
Title: The Faint Young Sun and Faint Young Stars Paradox
Authors: Martens, Petrus C.
Bibcode: 2017IAUS..328..350M
Altcode: 2017arXiv170601016M
The purpose of this paper is to explore a resolution for the Faint Young
Sun Paradox that has been mostly rejected by the community, namely the
possibility of a somewhat more massive young Sun with a large mass loss
rate sustained for two to three billion years. This would make the young
Sun bright enough to keep both the terrestrial and Martian oceans from
freezing, and thus resolve the paradox. It is found that a large and
sustained mass loss is consistent with the well observed spin-down rate
of Sun-like stars, and indeed may be required for it. It is concluded
that a more massive young Sun must be considered a plausible hypothesis.
Title: Update on a Solar Magnetic Catalog Spanning Four Solar Cycles
Authors: Vargas-Acosta, Juan Pablo; Munoz-Jaramillo, Andres; Vargas
Dominguez, Santiago; Werginz, Zachary; DeLuca, Michael D.; Longcope,
Dana; Harvey, J. W.; Windmueller, John; Zhang, Jie; Martens, Petrus C.
Bibcode: 2017SPD....4811202V
Altcode:
Bipolar magnetic regions (BMRs) are the cornerstone of solar
cycle propagation, the building blocks that give structure to the
solar atmosphere, and the origin of the majority of space weather
events. However, in spite of their importance, there is no homogeneous
BMR catalog spanning the era of systematic solar magnetic field
measurements. Here we present the results of an ongoing project to
address this deficiency applying the Bipolar Active Region Detection
(BARD) code to magnetograms from the 512 Channel of the Kitt Peak
Vaccum Telescope, SOHO/MDI, and SDO/HMI.The BARD code automatically
identifies BMRs and tracks them as they are rotated by differential
rotation. The output of the automatic detection is supervised by a human
observer to correct possible mistakes made by the automatic algorithm
(like incorrect pairings and tracking mislabels). Extra passes are made
to integrate fragmented regions as well as to balance the flux between
BMR polarities. At the moment, our BMR database includes nearly 10,000
unique objects (detected and tracked) belonging to four separate solar
cycles (21-24).
Title: Hemispheric Preference and Cyclic Variation of Solar Filament
Chirality
Authors: Hazra, Soumitra; Mahajan, Sushant S.; Douglas, William;
Martens, Petrus C.
Bibcode: 2017SPD....4810617H
Altcode:
Although the hemispheric preference of magnetic topological features in
the solar atmosphere is a well-established fact, strength and cyclic
variation of the hemispheric rule is a debatable issue. In this work,
we study the chirality of 3480 solar filaments from 2000 to 2016. We
determine the chirality of filaments manually and compare with the
results obtained from the Advanced Automated Filament Detection
and Characterization Code (AAFDCC). We find that 83% of our manually
determined filaments follow the hemispheric chirality rule, while 58% of
automatically determined filamentsfollow the same. We also compare our
result with an other manually compiled list by Pevtsov et al. (2003). We
find that our list matches Pevtsovs manually compiled list with 90%
accuracy. We also find that the hemispheric chirality rule does not
vary from cycle to cycle. However, the strength of the hemispheric
preference decreases at the end and beginning phase of the solar cycle.
Title: Mi Gauss es su Gauss: Lessons from Cross-Calibrating 40 years
of Full Disk Magnetograms
Authors: Werginz, Zachary; Munoz-Jaramillo, Andres; Martens, Petrus
C.; Harvey, J. W.
Bibcode: 2017SPD....4811102W
Altcode:
Full-disk line-of-sight magnetograms from the Kitt Peak Vacuum Telescope
(KPVT) are a highly valuable, but underutilized, source of data for
understanding long-term solar variability. Here we present the results
of a project for obtaining a cross-callibrated series of magnetograms
spanning 40 years including KPVT (512 and SPMG), SOHO/MDI and SDO/HMI
magnetographs. The biggest challenge we face is empirically identifying
a calibration factor and estimate of uncertainty between instruments
with little temporal overlap.Here we propose a method that fragments
magnetograms into spherical quadrangles bounded by latitudes and
longitudes and calculates various information such as total area, mean
flux density, and distance from disk center. Our main assumption is that
the Sun does not change significantly over daily time periods.First
a magnetogram to be calibrated is differentially rotated to match
a reference magnetogram in time. Then the smaller magnetogram is
interpolated into the larger one to account for sub-pixel heliographic
coordinates. We then produce equally spaced bands of latitude and
longitude determined from a fragmentation parameter. These are used
to map out regions on each magnetogram that are expected to relay
the same information. Our efforts to cross-calibrate lead to results
that vary with fragmentation parameters, the difference in time of
selected magnetograms, and distance from disk center.Given that this
cross-callibrated series will be made publically available, we are
looking for constructive criticism, suggestions, and feedback. Please
join us in making these data as good as they can be.
Title: Addressing Systematic Errors in Correlation Tracking on
HMI Magnetograms
Authors: Mahajan, Sushant S.; Hathaway, David H.; Munoz-Jaramillo,
Andres; Martens, Petrus C.
Bibcode: 2017SPD....4820702M
Altcode:
Correlation tracking in solar magnetograms is an effective method to
measure the differential rotation and meridional flow on the solar
surface. However, since the tracking accuracy required to successfully
measure meridional flow is very high, small systematic errors have a
noticeable impact on measured meridional flow profiles. Additionally,
the uncertainties of this kind of measurements have been historically
underestimated, leading to controversy regarding flow profiles at
high latitudes extracted from measurements which are unreliable
near the solar limb.Here we present a set of systematic errors we
have identified (and potential solutions), including bias caused by
physical pixel sizes, center-to-limb systematics, and discrepancies
between measurements performed using different time intervals. We have
developed numerical techniques to get rid of these systematic errors
and in the process improve the accuracy of the measurements by an order
of magnitude.We also present a detailed analysis of uncertainties in
these measurements using synthetic magnetograms and the quantification
of an upper limit below which meridional flow measurements cannot be
trusted as a function of latitude.
Title: Solar Data Mining at Georgia State University
Authors: Angryk, R.; Martens, P. C.; Schuh, M.; Aydin, B.; Kempton,
D.; Banda, J.; Ma, R.; Naduvil-Vadukootu, S.; Akkineni, V.; Küçük,
A.; Filali Boubrahimi, S.; Hamdi, S. M.
Bibcode: 2016AGUFMSH11A2225A
Altcode:
In this talk we give an overview of research projects related to solar
data analysis that are conducted at Georgia State University. We will
provide update on multiple advances made by our research team on
the analysis of image parameters, spatio-temporal patterns mining,
temporal data analysis and our experiences with big, heterogeneous
solar data visualization, analysis, processing and storage. We will
talk about up-to-date data mining methodologies, and their importance
for big data-driven solar physics research.
Title: Development of a Homogenous Database of Bipolar Active Regions
Spanning Four Cycles
Authors: Munoz-Jaramillo, A.; Werginz, Z. A.; Vargas-Acosta, J. P.;
DeLuca, M. D.; Vargas-Dominguez, S.; Lamb, D. A.; DeForest, C. E.;
Longcope, D. W.; Martens, P.
Bibcode: 2016AGUFMSH11A2219M
Altcode:
The solar cycle can be understood as a process that alternates the
large-scale magnetic field of the Sun between poloidal and toroidal
configurations. Although the process that transitions the solar cycle
between toroidal and poloidal phases is still not fully understood,
theoretical studies, and observational evidence, suggest that this
process is driven by the emergence and decay of bipolar magnetic
regions (BMRs) at the photosphere. Furthermore, the emergence of
BMRs at the photosphere is the main driver behind solar variability
and solar activity in general; making the study of their properties
doubly important for heliospheric physics. However, in spite of their
critical role, there is still no unified catalog of BMRs spanning
multiple instruments and covering the entire period of systematic
measurement of the solar magnetic field (i.e. 1975 to present).In
this presentation we discuss an ongoing project to address this
deficiency by applying our Bipolar Active Region Detection (BARD)
code on full disk magnetograms measured by the 512 (1975-1993) and
SPMG (1992-2003) instruments at the Kitt Peak Vacuum Telescope (KPVT),
SOHO/MDI (1996-2011) and SDO/HMI (2010-present). First we will discuss
the results of our revitalization of 512 and SPMG KPVT data, then
we will discuss how our BARD code operates, and finally report the
results of our cross-callibration across instruments.The corrected
and improved KPVT magnetograms will be made available through the
National Solar Observatory (NSO) and Virtual Solar Observatory (VSO),
including updated synoptic maps produced by running the corrected KPVT
magnetograms though the SOLIS pipeline. The homogeneous active region
database will be made public by the end of 2017 once it has reached
a satisfactory level of quality and maturity. The Figure shows all
bipolar active regions present in our database (as of Aug 2016) colored
according to the instrument where they were detected. The image also
includes the names of the NSF-REU students in charge of the supervision
of the detection algorithm and the year in which they worked on the
catalog. Marker size is indicative of the total active region flux.
Title: A 2D Discrete Surface Flux Transport (DSFT) model applied to
polar and quiet sun regions.
Authors: Eckberg, J.; Kankelborg, C. C.; Martens, P.
Bibcode: 2016AGUFMSH31B2551E
Altcode:
We have developed a Surface Flux Transport simulation utilizing
a Semi-Lagrangian scheme to advect discrete magnetic flux
elements. Advection occurs due to the flow fields from supergranulation,
meridional flow, and differential rotation. Granular advection is
modeled using a time integrated effect which lowers the computational
cost of the simulation. We have incorporated observational, energetic
and geometric considerations in constructing the magnetic flux dynamics
of emergence, interaction, and fragmentation. Our model reproduces
observed distributions of magnetic flux in quiet sun and at the
poles. The variation of mean squared velocities with flux is also
reproduced. Our simulation clarifies which processes are essential in
reproducing the dynamics of solar magnetic flux balance.
Title: The best of both worlds: Using automatic detection and limited
human supervision to create a homogenous magnetic catalog spanning
four solar cycles
Authors: Muñoz-Jaramillo, Andres; Werginz, Zachary; Vargas-Acosta,
Juan Pablo; DeLuca, Michael; Windmueller, J. C.; Zhang, Jie; Longcope,
Dana; Lamb, Derek; DeForest, Craig; Vargas-Domínguez, Santiago;
Harvey, Jack; Martens, Piet
Bibcode: 2016bida.conf.3194M
Altcode: 2022arXiv220311908M
Bipolar magnetic regions (BMRs) are the cornerstone of solar
variability. They are tracers of the large-scale magnetic processes
that give rise to the solar cycle, shapers of the solar corona,
building blocks of the large-scale solar magnetic field, and significant
contributors to the free-energetic budget that gives rise to flares and
coronal mass ejections. Surprisingly, no homogeneous catalog of BMRs
exists today, in spite of the existence of systematic measurements of
the magnetic field since the early 1970's. The purpose of this work is
to address this deficiency by creating a homogenous catalog of BMRs
from the 1970's until the present. For this purpose, in this paper
we discuss the strengths and weaknesses of the automatic and manual
detection of BMRs and how both methods can be combined to form the basis
of our Bipolar Active Region Detection (BARD) code and its supporting
human supervision module. At present, the BARD catalog contains more
than 10,000 unique BMRs tracked and characterized during every day
of their observation. Here we also discuss our future plans for the
creation of an extended multi-scale magnetic catalog combining the
SWAMIS and BARD catalogs.
Title: Developing a Solar Magnetic Catalog Spanning Four Cycles
Authors: Werginz, Zachary; Munoz-Jaramillo, Andres; DeLuca, Michael
D.; Vargas Acosta, Juan Pablo; Vargas Dominguez, Santiago; Zhang,
Jie; Longcope, Dana; Martens, Petrus C.
Bibcode: 2016SPD....4740502W
Altcode:
Bipolar magnetic regions (BMRs) are the cornerstone of solar
cycle propagation, the building blocks that give structure to the
solar atmosphere, and the origin of the majority of space weather
events. However, in spite of their importance, there is no homogeneous
BMR catalog spanning the era of systematic solar magnetic field
measurements. Here we present the results of an ongoing project to
address this deficiency applying the Bipolar Active Region Detection
(BARD) code to magnetograms from the 512 Channel of the Kitt Peak Vaccum
Telescope, SOHO/MDI, and SDO/HMI.The BARD code automatically identifies
BMRs and tracks them as they are rotated by differential rotation. The
output of the automatic detection is supervised by a human observer
to correct possible mistakes made by the automatic algorithm (like
incorrect pairings and tracking mislabels). Extra passes are made to
integrate fragmented regions as well as to balance the flux between
BMR polarities. At the moment, our BMR database includes 6,885 unique
objects (detected and tracked) belonging to four separate solar cycles
(21-24).
Title: A large-scale dataset of solar event reports from automated
feature recognition modules
Authors: Schuh, Michael A.; Angryk, Rafal A.; Martens, Petrus C.
Bibcode: 2016JSWSC...6A..22S
Altcode:
The massive repository of images of the Sun captured by the Solar
Dynamics Observatory (SDO) mission has ushered in the era of Big Data
for Solar Physics. In this work, we investigate the entire public
collection of events reported to the Heliophysics Event Knowledgebase
(HEK) from automated solar feature recognition modules operated by
the SDO Feature Finding Team (FFT). With the SDO mission recently
surpassing five years of operations, and over 280,000 event reports
for seven types of solar phenomena, we present the broadest and most
comprehensive large-scale dataset of the SDO FFT modules to date. We
also present numerous statistics on these modules, providing valuable
contextual information for better understanding and validating of the
individual event reports and the entire dataset as a whole. After
extensive data cleaning through exploratory data analysis, we
highlight several opportunities for knowledge discovery from data
(KDD). Through these important prerequisite analyses presented here,
the results of KDD from Solar Big Data will be overall more reliable
and better understood. As the SDO mission remains operational over
the coming years, these datasets will continue to grow in size and
value. Future versions of this dataset will be analyzed in the general
framework established in this work and maintained publicly online for
easy access by the community.
Title: Heating Profiles of Coronal Loops
Authors: Plowman, Joseph; Kankelborg, Charles C.; Martens, Petrus C.
Bibcode: 2016SPD....47.0328P
Altcode:
We analyze the temperature and density profiles of coronal
loops, as a function of their length, using data from SDO/AIA and
Hinode/EIS. The analysis considers the location of the heating along
the loop's length, and we conduct a more throrough investigation of our
previous preliminary result that heating is concentrated near the loop
footpoints. The work now features a larger selection of coronal loops,
compared to our previous presentations, and examines their scale-height
temperatures to ascertain the extent to which they are hydrostatic.
Title: Observing Sun-like Stars
Authors: Martens, Petrus C.; White, Russel J.
Bibcode: 2016SPD....47.1104M
Altcode:
The Sun represents only one realization of the many possibilities for
stellar dynamos. In order to fully understand the physics of solar and
stellar magnetism we need to study in full detail the magnetic cycles of
stars that are very much like the Sun . To do this we need a telescope
that can resolve the disks of nearby solar type stars. Georgia State's
University Center for High Resolution Astronomy (CHARA) array is a
diffraction limited interferometer with a baseline of over 300 m,
located on Mount Wilson. It is the highest resolution telescope in
the visible and infrared currently in operation. CHARA has resolved
the disks of larger stars and observed starspots. We will describe an
ongoing observing program for nearby Sun-like stars to determine with
great accuracy the basic parameters of these stars and the presence of
starspots on their surfaces. Combined with the decades long observations
of Mount Wilson and Lowell Observatories of stellar cycles the data
obtained will act as a powerful constraint on solar and stellar dynamo
models and simulations.
Title: Predicting the Interplanetary Magnetic Field using Approaches
Based on Data Mining and Physical Models
Authors: Riley, P.; Russell, C. T.; de Koning, C. A.; Biesecker, D. A.;
Linker, J.; Owens, M. J.; Lugaz, N.; Martens, P.; Angryk, R.; Reinard,
A.; Ulrich, R. K.; Horbury, T. S.; Pizzo, V. J.; Liu, Y.; Hoeksema, T.
Bibcode: 2015AGUFMSH14A..06R
Altcode:
An accurate prediction of the interplanetary magnetic field, and,
in particular, its z-component (Bz) is a crucial capability for any
space weather forecasting system, and yet, thus far, it has remained
largely elusive (a point exemplified by the fact that no prediction
center currently provides a forecast for Bz). In this presentation,
we discuss the various physical processes that can produce non-zero
values of Bz and summarize a selection of promising approaches that may
ultimately lead to reliable forecasts of Bz. We describe the first steps
we have taken to develop a framework for assessing these techniques,
and show preliminary results of their efficacy.
Title: Contextualizing Solar Cycle 24: Report on the Development of
a Homogenous Database of Bipolar Active Regions Spanning Four Cycles
Authors: Munoz-Jaramillo, A.; Werginz, Z. A.; DeLuca, M. D.;
Vargas-Acosta, J. P.; Longcope, D. W.; Harvey, J. W.; Martens, P.;
Zhang, J.; Vargas-Dominguez, S.; DeForest, C. E.; Lamb, D. A.
Bibcode: 2015AGUFMSH33D..06M
Altcode:
The solar cycle can be understood as a process that alternates the
large-scale magnetic field of the Sun between poloidal and toroidal
configurations. Although the process that transitions the solar cycle
between toroidal and poloidal phases is still not fully understood,
theoretical studies, and observational evidence, suggest that this
process is driven by the emergence and decay of bipolar magnetic
regions (BMRs) at the photosphere. Furthermore, the emergence of
BMRs at the photosphere is the main driver behind solar variability
and solar activity in general; making the study of their properties
doubly important for heliospheric physics. However, in spite of their
critical role, there is still no unified catalog of BMRs spanning
multiple instruments and covering the entire period of systematic
measurement of the solar magnetic field (i.e. 1975 to present).In
this presentation we discuss an ongoing project to address this
deficiency by applying our Bipolar Active Region Detection (BARD)
code on full disk magnetograms measured by the 512 (1975-1993) and
SPMG (1992-2003) instruments at the Kitt Peak Vacuum Telescope (KPVT),
SOHO/MDI (1996-2011) and SDO/HMI (2010-present). First we will discuss
the results of our revitalization of 512 and SPMG KPVT data, then we
will discuss how our BARD code operates, and finally report the results
of our cross-callibration.The corrected and improved KPVT magnetograms
will be made available through the National Solar Observatory (NSO)
and Virtual Solar Observatory (VSO), including updated synoptic maps
produced by running the corrected KPVT magnetograms though the SOLIS
pipeline. The homogeneous active region database will be made public
by the end of 2017 once it has reached a satisfactory level of quality
and maturity. The Figure shows all bipolar active regions present in
our database (as of Aug 2015) colored according to the sign of their
leading polarity. Marker size is indicative of the total active region
flux. Anti-Hale regions are shown using solid markers.
Title: Solar image parameter data from the SDO: Long-term curation
and data mining
Authors: Schuh, M. A.; Angryk, R. A.; Martens, P. C.
Bibcode: 2015A&C....13...86S
Altcode:
The Solar Dynamics Observatory (SDO) mission captures thousands
of images of the Sun per day, motivating the need for efficient and
effective storage, representation, and search over a massive repository
of data. This work investigates the general-purpose image parameter
data produced by the SDO Feature Finding Team's trainable module, which
operates at a fixed six minute cadence over all AIA channels. The data
contains ten numerical measures computed for each image cell over a 64
× 64 grid for each image. We analyze all available data and metadata
produced over the first three years and present comprehensive statistics
and outliers while validating the cleanliness and usability of the data
source for future research. We then utilize a database of automated
solar event reports to create large-scale region-labeled datasets
available to the public. We highlight the new-found potential for
data-driven discovery by presenting several best-case labeling scenarios
that establish a baseline for comparing machine learning classification
and attribute (image parameter) evaluation results. Future work focuses
on continued dataset curation and spatiotemporal data mining.
Title: Special Section: Management, Search and Analysis of Solar
Astronomy Big Data
Authors: Angryk, Rafal A.; Csillaghy, André; Martens, Petrus C.
Bibcode: 2015A&C....13...85A
Altcode:
Astronomy and Computing is very proud to announce a new topical issue
devoted to the Management, Search and Analysis of Solar Astronomy
Big Data.
Title: The Minimum of Solar Cycle 23: As Deep as It Could Be?
Authors: Muñoz-Jaramillo, Andrés; Senkpeil, Ryan R.; Longcope,
Dana W.; Tlatov, Andrey G.; Pevtsov, Alexei A.; Balmaceda, Laura A.;
DeLuca, Edward E.; Martens, Petrus C. H.
Bibcode: 2015ApJ...804...68M
Altcode: 2015arXiv150801222M
In this work we introduce a new way of binning sunspot group data
with the purpose of better understanding the impact of the solar
cycle on sunspot properties and how this defined the characteristics
of the extended minimum of cycle 23. Our approach assumes that
the statistical properties of sunspots are completely determined
by the strength of the underlying large-scale field and have no
additional time dependencies. We use the amplitude of the cycle
at any given moment (something we refer to as activity level) as a
proxy for the strength of this deep-seated magnetic field. We find
that the sunspot size distribution is composed of two populations:
one population of groups and active regions and a second population
of pores and ephemeral regions. When fits are performed at periods
of different activity level, only the statistical properties of the
former population, the active regions, are found to vary. Finally,
we study the relative contribution of each component (small-scale
versus large-scale) to solar magnetism. We find that when hemispheres
are treated separately, almost every one of the past 12 solar minima
reaches a point where the main contribution to magnetism comes from
the small-scale component. However, due to asymmetries in cycle phase,
this state is very rarely reached by both hemispheres at the same
time. From this we infer that even though each hemisphere did reach
the magnetic baseline, from a heliospheric point of view the minimum
of cycle 23 was not as deep as it could have been.
Title: The Minimum of Solar Cycle 23: As Deep as It Could Be?
Authors: Munoz-Jaramillo, Andres; Senkpeil, Ryan; Longcope, Dana;
Tlatov, Andrey; Pevtsov, Alexei A.; Balmaceda, Laura; DeLuca, Edward
E.; Martens, Petrus C.
Bibcode: 2015TESS....130803M
Altcode:
After a lull lasting more than 60 years of seemly uniform solar minima,
the solar minimum of solar cycle 23 came as a great surprise due to its
depth, duration, and record lows in a wide variety of solar activity
indices and solar wind properties. One of the consequence of such an
event is the revival of the interest in extreme minima, grand minima,
and the identification of a solar basal state of minimum magnetic
activity.In this presentation we will discuss a new way of binning
sunspot group data, with the purpose of better understanding the impact
of the solar cycle on sunspot properties, and how this defined the
characteristics of the extended minimum of cycle 23. Our main result
is centered around the fact that the sunspot size distribution is
composed of two populations, a population of groups and active regions,
and second of pores and ephemeral regions. We find that only the
properties of the former population, the active regions, is found to
vary with the solar cycle, while the propeties of pores and ephemeral
regions does not.Taking advantage of our statistical characterization
we probe the question of the solar baseline magnetism. We find that,
when hemispheres are treated separately, almost every one of the past
12 solar minima reaches such a point. However, due to asymmetries in
cycle phase, the basal state is very rarely reached by both hemispheres
at the same time. From this we infer that, even though each hemisphere
did reach the magnetic baseline, from a heliospheric point of view
the minimum of cycle 23 was not as deep as it could have been.
Title: Exploring the Solar-stellar connection with the CHARA Array
Authors: Martens, Petrus C.; McAlister, Hal; White, Russel
Bibcode: 2015TESS....110505M
Altcode:
It is well understood that in order to better understand solar
magnetism it is of key importance that we have detailed data on
magnetic activity of stars that are very much like our Sun. Georgia
State's University Center for High Resolution Astronomy's (CHARA)
Array is a diffraction limited interferometer with a baseline of
over 300 m, located on Mount Wilson. CHARA has resolved the disk of
larger early-type stars and observed starspots. It has the potential of
detecting spots (and eclipsing exoplanets) on nearby solar-type stars,
and thus adding significant in-depth magnetic cycle information to
the long time series of chromospheric data from MWO and Lowell.We will
describe the main characteristics of CHARA, highlight science results,
and describe our plans to contribute to the renewed effort from the
NASA Heliophysics division to study the solar-stellar connection,
with the goal of improving long-term solar activity forecasts.URL:
http://www.chara.gsu.edu/
Title: Small-scale and Global Dynamos and the Area and Flux
Distributions of Active Regions, Sunspot Groups, and Sunspots:
A Multi-database Study
Authors: Muñoz-Jaramillo, Andrés; Senkpeil, Ryan R.; Windmueller,
John C.; Amouzou, Ernest C.; Longcope, Dana W.; Tlatov, Andrey G.;
Nagovitsyn, Yury A.; Pevtsov, Alexei A.; Chapman, Gary A.; Cookson,
Angela M.; Yeates, Anthony R.; Watson, Fraser T.; Balmaceda, Laura A.;
DeLuca, Edward E.; Martens, Petrus C. H.
Bibcode: 2015ApJ...800...48M
Altcode: 2014arXiv1410.6281M
In this work, we take advantage of 11 different sunspot group,
sunspot, and active region databases to characterize the area
and flux distributions of photospheric magnetic structures. We
find that, when taken separately, different databases are better
fitted by different distributions (as has been reported previously
in the literature). However, we find that all our databases can be
reconciled by the simple application of a proportionality constant,
and that, in reality, different databases are sampling different
parts of a composite distribution. This composite distribution
is made up by linear combination of Weibull and log-normal
distributions—where a pure Weibull (log-normal) characterizes the
distribution of structures with fluxes below (above) 1021Mx
(1022Mx). Additionally, we demonstrate that the Weibull
distribution shows the expected linear behavior of a power-law
distribution (when extended to smaller fluxes), making our results
compatible with the results of Parnell et al. We propose that this is
evidence of two separate mechanisms giving rise to visible structures
on the photosphere: one directly connected to the global component of
the dynamo (and the generation of bipolar active regions), and the other
with the small-scale component of the dynamo (and the fragmentation of
magnetic structures due to their interaction with turbulent convection).
Title: First Science Results from Solar Data Mining Using Automated
Feature Detection
Authors: Martens, P. C.
Bibcode: 2014AGUFMSH34A..07M
Altcode:
The SDO Feature Finding Team (FFT) has produced 16 automated feature
tracking modules for data from SDO, LASCO, and ground-based H-alpha
observatories. The metadata produced by those modules and others are
available from the Heliophysics Events Knowledgebase (HEK) and the
Virtual Solar Observatory (VSO). Having metadata available for large
amounts of events and phenomena, obtained with consistent detection
criteria unlike catalogs produced by human observers, allows researchers
to effectively search solar data for patterns. I will show a number
of science results obtained recently. Not surprisingly several of the
patterns are well known (e.g. flares occur mostly in active regions),
but some really surprising new trends have been discovered as well,
in at least one case upending scientific consensus. These results
show the power and promise that systematic feature recognition and
data mining holds for solar physics.
Title: A Comparative Evaluation of Automated Solar Filament Detection
Authors: Schuh, M. A.; Banda, J. M.; Bernasconi, P. N.; Angryk, R. A.;
Martens, P. C. H.
Bibcode: 2014SoPh..289.2503S
Altcode: 2014SoPh..tmp...34S
We present a comparative evaluation for automated filament detection
in Hα solar images. By using metadata produced by the Advanced
Automated Filament Detection and Characterization Code (AAFDCC)
module, we adapted our trainable feature recognition (TFR) module to
accurately detect regions in solar images containing filaments. We
first analyze the AAFDCC module's metadata and then transform it into
labeled datasets for machine-learning classification. Visualizations
of data transformations and classification results are presented and
accompanied by statistical findings. Our results confirm the reliable
event reporting of the AAFDCC module and establishes our TFR module's
ability to effectively detect solar filaments in Hα solar images.
Title: Feature Finding for Solar Physics
Authors: Martens, Petrus C.
Bibcode: 2014simi.conf...25M
Altcode:
NASA's Solar Dynamics Observatory (SDO) data repository dwarfs the
archives of all previous solar physics missions put together. The
traditional methods of analyzing data-analyzing the images by hand -
would simply not work and NASA tasked my Feature Finding Team (FFT)
with developing automated feature recognition modules for solar
phenomena likely to be observed by SDO. Having the derived metadata
now available on-line enables to conduct statistical studies involving
large sets of events that would be impossible now with traditional
means. First we developed some existing and new task-specific
solar feature finding modules to be 'pipe-line' ready for the stream
of SDO data. Secondly, we took it upon us to develop an entirely new
'trainable' module that would be capable of identifying different types
of solar phenomena starting from a limited number of user-provided
examples. Next I will focus on our most innovative 'trainable'
module, developed mostly at MSU in collaboration with Prof. Angryk and
his students at the Computer Science department there. TFirst, there
is the strong similarity between solar and medical X-ray images with
regard to their texture, which allowed us to apply some advances made
in medical image recognition. Second, we found that there is a strong
similarity between the way our trainable module works and the way our
brain recognizes images. The brain can quickly recognize similar images
from key characteristics, just as our code does. We conclude that our
approach represents the beginning of a more human-like procedure for
computer image recognition.
Title: Insights on the solar dynamo from stellar observations
Authors: Egeland, Ricky; Martens, Petrus C.; Judge, Philip G.
Bibcode: 2014AAS...22421105E
Altcode:
A successful dynamo model should not only explain the broad
characteristics of the magnetic field cycle for the Sun (22-year sunspot
cycle with polarity reversals, migration of active latitudes toward
the poles throughout the cycle, and Joy’s law), but should also be
able to explain the cycling behavior observed in Solar-analog stars,
which are very close to the Sun in essential characteristics. Our aim
is to develop a set of constraints on dynamo models from the observed
behavior of solar-analog stars obtained from a number of long-running
synoptic surveys of cycling activity (Mount Wilson Observatory HK
survey, Lowel Observatory Solar-Stellar Spectrograph, and the Fairborn
Observatory Automatic Photoelectric Telescope survey), in conjuncture
with stellar rotation and differential rotation data obtained by the
Kepler Mission and other sources. By carefully piecing together the
best data available today, we will provide an improved understanding
of the parameter space in which Solar-like dynamos operate.
Title: Statistical Constraints on Joy's Law
Authors: Amouzou, Ernest C.; Munoz-Jaramillo, Andres; Martens, Petrus
C.; DeLuca, Edward E.
Bibcode: 2014AAS...22421829A
Altcode:
Using sunspot data from the observatories at Mt. Wilson and Kodaikanal,
active region tilt angles are analyzed for different active region
sizes and latitude bins. A number of similarly-shaped statistical
distributions were fitted to the data using maximum likelihood
estimation. In all cases, we find that the statistical distribution
best describing the number of active regions at a given tilt angle is a
Laplace distribution with the form (2β)-1*exp(-|x-μ|/β),
with 2° ≤ μ ≤ 11°, and 10° ≤ β ≤ 40°.
Title: From the Tachocline Into the Heliosphere: Coupling a 3D
kinematic dynamo to the CCMC
Authors: Munoz-Jaramillo, Andres; Yeates, Anthony R; Martens, Petrus
C.; DeLuca, Edward E.
Bibcode: 2014AAS...22421103M
Altcode:
During the last decade, axisymmetric kinematic dynamo models have
contributed greatly to our understanding of the solar cycle. However,
with the advent of more powerful computers the limitation to axisymmetry
has been lifted. Here we present a 3D kinematic dynamo model where
active regions are driven by velocity perturbations calibrated to
reproduce observed active region properties (including the size and
flux of active regions, and the distribution of tilt angle with
latitude), resulting in a more consistent treatment of flux-tube
emergence in kinematic dynamo models than artificial flux deposition. We
demonstrate how this technique can be used to assimilate active region
observations obtained from the US National Solar Observatory/Kitt Peak
(NSO/KP) synoptic magnetograms and how our model couples naturally
with heliospheric models, paving the way for the simultaneous study
of the evolution of the magnetic field in the solar interior as well
as its impact on the heliosphere.
Title: Hemispheric Patterns in Filament Chirality and Sigmoid Shape
over the Solar Cycle
Authors: Martens, Petrus C.; Yeates, Anthony R.; Pillai, Karthik G.
Bibcode: 2014IAUS..300..135M
Altcode:
The motivation for our research was to study the correlation between
the chirality of filaments and the handedness (S- or Z-shape) of
sigmoids. It was assumed that sigmoids would mostly coincide with
filaments and that the S-shaped sigmoids would correlate well with
filaments of sinistral chirality, which we found that to be at best
a very weak relation. Since we had a full solar cycle of filament
metadata at hand it was easy to verify the supposedly known hemispheric
preference of filament chirality. We discovered that the hemispheric
chirality rule was confirmed for the epoch where a thorough manual
study had been performed, but that at other phases of the solar cycle
the rule seems to disappear and sometimes even reverse.
Title: Helioseismic Perspective of the Solar Dynamo
Authors: Muñoz-Jaramillo, A.; Martens, P. C. H.; Nandy, D.
Bibcode: 2013ASPC..478..271M
Altcode:
Helioseismology has been, without a doubt, one of the greatest
contributors to our understanding of the solar cycle. In particular,
its results have been critical in the development of solar dynamo
models, by providing modelers with detailed information about the
internal, large scale flows of solar plasma. This review will
give a historical overview of the evolution of our understanding of the
solar cycle, placing special emphasis on advances driven by helioseismic
results. We will discuss some of the outstanding modeling issues, and
discuss how Helioseismology can help push our understanding forward
during the next decade.
Title: Steps Toward a Large-Scale Solar Image Data Analysis to
Differentiate Solar Phenomena
Authors: Banda, J. M.; Angryk, R. A.; Martens, P. C. H.
Bibcode: 2013SoPh..288..435B
Altcode:
We detail the investigation of the first application of several
dissimilarity measures for large-scale solar image data analysis. Using
a solar-domain-specific benchmark dataset that contains multiple
types of phenomena, we analyzed combinations of image parameters with
different dissimilarity measures to determine the combinations that
will allow us to differentiate between the multiple solar phenomena from
both intra-class and inter-class perspectives, where by class we refer
to the same types of solar phenomena. We also investigate the problem
of reducing data dimensionality by applying multi-dimensional scaling
to the dissimilarity matrices that we produced using the previously
mentioned combinations. As an early investigation into dimensionality
reduction, we investigate by applying multidimensional scaling (MDS)
how many MDS components are needed to maintain a good representation
of our data (in a new artificial data space) and how many can be
discarded to enhance our querying performance. Finally, we present a
comparative analysis of several classifiers to determine the quality
of the dimensionality reduction achieved with this combination of
image parameters, similarity measures, and MDS.
Title: Fast Differential Emission Measure Inversion of Solar
Coronal Data
Authors: Plowman, Joseph; Kankelborg, Charles; Martens, Petrus
Bibcode: 2013ApJ...771....2P
Altcode: 2012arXiv1204.6306P
We present a fast method for reconstructing differential emission
measures (DEMs) using solar coronal data. The method consists of a
fast, simple regularized inversion in conjunction with an iteration
scheme for removal of residual negative emission measure. On average,
it computes over 1000 DEMs s-1 for a sample active region
observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics
Observatory, and achieves reduced chi-squared of order unity with no
negative emission in all but a few test cases. The high performance of
this method is especially relevant in the context of AIA, which images
of order one million solar pixels per second. This paper describes the
method, analyzes its fidelity, compares its performance and results with
other DEM methods, and applies it to an active region and loop observed
by AIA and by the Extreme-ultraviolet Imaging Spectrometer on Hinode.
Title: Filament Chirality over an Entire Cycle Determined with an
Automated Detection Module -- a Neat Surprise!
Authors: Martens, Petrus C.; Yeates, A. R.; Mackay, D.; Pillai, K. G.
Bibcode: 2013SPD....4410104M
Altcode:
Using metadata produced by automated solar feature detection modules
developed for SDO (Martens et al. 2012) we have discovered some trends
in filament chirality and filament-sigmoid relations that are new
and in part contradict the current consensus. Automated detection
of solar features has the advantage over manual detection of having
the detection criteria applied consistently, and in being able to
deal with enormous amounts of data, like the 1 Terabyte per day that
SDO produces. Here we use the filament detection module developed by
Bernasconi, which has metadata from 2000 on, and the sigmoid sniffer,
which has been producing metadata from AIA 94 A images since October
2011. The most interesting result we find is that the hemispheric
chirality preference for filaments (dextral in the north, and v.v.),
studied in detail for a three year period by Pevtsov et al. (2003)
seems to disappear during parts of the decline of cycle 23 and during
the extended solar minimum that followed. Moreover the hemispheric
chirality rule seems to be much less pronounced during the onset
of cycle 24. For sigmoids we find the expected correlation between
chirality and handedness (S or Z) shape but not as strong as expected.
Title: Effects of a Meridional Flow Counter-Cell on the Solar
Activity Cycle
Authors: Amouzou, Ernest C.; Martens, P. C.
Bibcode: 2013SPD....44..110A
Altcode:
The effects of varying the latitudinal extent and peak flow speed of a
simulated polar counter-cell are determined by studying the resulting
duration and intensity of the activity cycle.
Title: Introducing the first publicly available Content-Based
Image-Retrieval system for the Solar Dynamics Observatory mission
Authors: Michael, Schuh A.; Banda, J.; Angryk, R.; Martens, P. C.
Bibcode: 2013SPD....44...97M
Altcode:
Since its first presentation as a demo at the 220th American
Astronomical Society Meeting, the Solar Dynamics Observatory (SDO)
Content-Based Image-Retrieval (CBIR) system has been open for public
usage since December 2012. Incorporating the valuable feedback
gathered at the AAS meeting, as well as working closely with solar
physicists from Montana State University, this first version of our
system provides similar image search capability for the SDO image
data repository. In this work we present an overview of the system
capabilities, architecture, and future improvements. We also present
practical search examples, basic usage instructions, and some of the
science data that can be extracted from our system. This work aims to
gather more feedback on the system usability and functionality while
making the community aware of a promising new tool for exploring
SDO data.
Title: Temperature, Density, and Heating Profiles of Coronal Loops
Authors: Plowman, Joseph; Martens, P. C.; Kankelborg, C.; Ritchie,
M.; Scott, J.; Sharma, R.
Bibcode: 2013SPD....4420106P
Altcode:
We show detailed results of a combined DEM and density-sensitive line
ratio analysis of coronal loops observed simultaneously by EIS and
AIA. The temperature and density profiles of the loop are compared
to and isolated from those of the surrounding material, and these
properties are fit to an analytic strand heating model developed by
Martens (2010). This research builds on our previously reported work
by analyzing a number of coronal loops (including one observed by the
Hi-C rocket), improved background subtraction and loop fitting. These
improvements allow us to place significant constraints on the heating
distribution of coronal loops.
Title: Simulating Emission of Coronal Loops with Non-Constant
Cross-Section
Authors: Winter, Henry D.; Curme, C. D.; Reeves, K.; Martens, P. C.
Bibcode: 2013SPD....44...45W
Altcode:
The solar corona is filled with loop-like structures that appear
bright against the background when observed in the extreme ultraviolet
(EUV). These loops have several remarkable properties. Warm loops
(∼ 1 MK) appear to be ∼ 2 - 9 times as dense at their apex
as predicted by of hydrostatic atmosphere models. These loops also
appear to be of constant cross-section despite the fact that the field
strength in a potential magnetic field should decrease in the corona,
causing the loops to expand. Why many active region loops appear to be
of constant cross-section is not well understood. Theories range from
an internal twist of the magnetic field to observational effects. In
this work we simulate active region loops with different expansion
factors heated by nanoflare storms. We calculate the hydrodynamic
properties for each loop as a function of the expansion factor
Gamma. We show that even modest tapering ratios can lead to drastic
changes in the density profiles of active region loops, and they can
also explain the overpressure at the apex of these loops. Synthetic
AIA images of each loop are made to show the observable consequences
of the expansion of loops near the instrumental resolution. We find
that all loops, even those with a large expansion factor, appear
to be of near constant cross-section when images are simulated in
AIA passbands. Only when the images are simulated for a much higher
resolution instrument with 0.1” pixels does the real expansion
of the loop become apparent.Abstract (2,250 Maximum Characters):
The solar corona is filled with loop-like structures that appear
bright against the background when observed in the extreme ultraviolet
(EUV). These loops have several remarkable properties. Warm loops (∼
1 MK) appear to be ∼ 2 - 9 times as dense at their apex as predicted
by of hydrostatic atmosphere models. These loops also appear to be of
constant cross-section despite the fact that the field strength in a
potential magnetic field should decrease in the corona, causing the
loops to expand. Why many active region loops appear to be of constant
cross-section is not well understood. Theories range from an internal
twist of the magnetic field to observational effects. In this work we
simulate active region loops with different expansion factors heated by
nanoflare storms. We calculate the hydrodynamic properties for each loop
as a function of the expansion factor Gamma. We show that even modest
tapering ratios can lead to drastic changes in the density profiles
of active region loops, and they can also explain the overpressure at
the apex of these loops. Synthetic AIA images of each loop are made
to show the observable consequences of the expansion of loops near
the instrumental resolution. We find that all loops, even those with
a large expansion factor, appear to be of near constant cross-section
when images are simulated in AIA passbands. Only when the images are
simulated for a much higher resolution instrument with 0.1” pixels
does the real expansion of the loop become apparent.
Title: Outflows and Dark Bands at Arcade-like Active Region Core
Boundaries
Authors: Scott, J. T.; Martens, P. C. H.; Tarr, L.
Bibcode: 2013ApJ...765...82S
Altcode:
Observations from the EUV Imaging Spectrometer (EIS) on board
Hinode have revealed outflows and non-thermal line broadening in low
intensity regions at the edges of active regions (ARs). We use data
from Hinode's EIS, Solar Dynamic Observatory's Atmospheric Imaging
Assembly and Helioseismic and Magnetic Imager, and the Transition
Region and Coronal Explorer instrument to investigate the boundaries
of arcade-like AR cores for NOAA ARs 11112, 10978, and 9077. A narrow,
low intensity region that is observed at the core's periphery as a
dark band shows outflows and increased spectral line broadening. This
dark band is found to exist for days and appears between the bright
coronal loop structures of different coronal topologies. We find a case
where the dark band region is formed between the magnetic field from
emerging flux and the field of the pre-existing flux. A magnetic field
extrapolation indicates that this dark band is coincident with the
spine lines or magnetic separatrices in the extrapolated field. This
occurs over unipolar regions where the brightened coronal field is
separated in connectivity and topology. This separation does not appear
to be infinitesimal and an initial estimate of the minimum distance
of separation is found to be ≈1.5-3.5 Mm.
Title: On Dimensionality Reduction for Indexing and Retrieval of
Large-Scale Solar Image Data
Authors: Banda, J. M.; Angryk, R. A.; Martens, P. C. H.
Bibcode: 2013SoPh..283..113B
Altcode: 2012SoPh..tmp..120B
This work investigates the applicability of several dimensionality
reduction techniques for large-scale solar data analysis. Using a solar
benchmark dataset that contains images of multiple types of phenomena,
we investigate linear and nonlinear dimensionality reduction methods
in order to reduce our storage and processing costs and maintain a
good representation of our data in a new vector space. We present
a comparative analysis of several dimensionality reduction methods
and different numbers of target dimensions by utilizing different
classifiers in order to determine the degree of data dimensionality
reduction that can be achieved with these methods, and to discover the
method that is the most effective for solar images. After determining
the optimal number of dimensions, we then present preliminary results
on indexing and retrieval of the dimensionally reduced data.
Title: Use of a time delay dynamo model to obtain solar-like sunspot
cycles
Authors: Amouzou, E.; Nandy, D.; Muñoz-Jaramillo, A.; Martens, P.
Bibcode: 2013ASInC..10...83A
Altcode:
Using a delay-differential equation model, we simulate the solar
dynamo. We find that solar-like dynamo solutions exist in certain
parameter regimes for which the dynamo number is less than or about
equal to -3 (|N_D| > 3, N_D < 0) and that sunspot cycle periods of
11 years can be reproduced with the parameter values set at a magnetic
diffusivity of η = 3.5 × 10^{12} cm^{2}/s and a total time delay of
approximately 2.8 yr.
Title: The solar corona: What are the remaining fundamental physical
questions?
Authors: Martens, Petrus C.
Bibcode: 2013ASInC..10...25M
Altcode:
The two key unresolved physical questions in our knowledge of the
solar corona are: (1) How is the corona heated to a temperature of
several MK, and, directly related to that, why is the coronal emission
structured in nearly constant cross-section loops? And, (2) what is
the mechanism that determines the onset of solar flares and eruptions,
and, again directly related, can flares be predicted? I will introduce
these questions, discuss some proposed solutions that are not complete,
and my view on getting to the full solutions.
Title: All Quiet on the Solar Front: Origin and Heliospheric
Consequences of the Unusual Minimum of Solar Cycle 23
Authors: Nandy, D.; Muñoz-Jaramillo, A.; Martens, P. C. H.
Bibcode: 2012SunGe...7...17N
Altcode:
The magnetic activity of the Sun shapes the heliospheric space
environment through modulation of the solar wind, interplanetary
magnetic field, cosmic ray flux and solar irradiance. Sunspots -
strongly magnetized regions on the solar surface - also spawns solar
storms such as flares and coronal mass ejections which generate severe
space weather affecting space-based technologies. The Sun's magnetic
output varies in a cyclic manner going through phases of maximum and
minimum activity. Following solar cycle 23 the Sun entered a prolonged
and unusually long minimum with a large number of days without sunspots
that was unprecedented in the space age. This long phase of very low
solar activity resulted in record high cosmic ray flux at Earth, weak
solar wind speeds and low interplanetary magnetic field. We provide an
overview of this peculiar solar minimum, critically explore theories
for its origin and argue that the unusual conditions in the heliosphere
that we experienced during this minimum eventually originated in solar
internal dynamics.
Title: DEMs for EIS and AIA
Authors: Plowman, J.; Kankelborg, C.; Martens, P.; Ritchie, M.; Scott,
J.; Sharma, R.
Bibcode: 2012ASPC..456..131P
Altcode:
We present a method for constructing Differential Emission Measures
(DEMs) using data from solar imagers such as EIS and AIA. The method is
simple, and very fast (∼ 1 minute per full disk AIA image). We analyze
the fidelity of the method, and apply it to a coronal loop observed on
April 19, 2011. The method appears to give reasonable results, although
reconstructed DEMs can contain regions of moderately negative emission
measure (EM). Both EIS and AIA DEM reconstructions suggest that the loop
has a narrow temperature distribution centered at 1.2 MK, situated in a
diffuse background of broader temperature distribution centered at 3 MK.
Title: Supporting Solar Physics Research via Data Mining
Authors: Angryk, Rafal; Banda, J.; Schuh, M.; Ganesan Pillai, K.;
Tosun, H.; Martens, P.
Bibcode: 2012AAS...22020122A
Altcode:
In this talk we will briefly introduce three pillars of data mining
(i.e. frequent patterns discovery, classification, and clustering), and
discuss some possible applications of known data mining techniques which
can directly benefit solar physics research. In particular, we plan to
demonstrate applicability of frequent patterns discovery methods for
the verification of hypotheses about co-occurrence (in space and time)
of filaments and sigmoids. We will also show how classification/machine
learning algorithms can be utilized to verify human-created software
modules to discover individual types of solar phenomena. Finally,
we will discuss applicability of clustering techniques to image data
processing.
Title: Temperature And Density Analysis Of A Coronal Loop Observed
By Eis And Aia
Authors: Plowman, Joseph; Martens, P.; Kankelborg, C.; Ritchie, M.;
Scott, J.; Sharma, R.
Bibcode: 2012AAS...22030905P
Altcode:
We present a combined DEM and density-sensitive line ratio analysis of
a loop observed simultaneously by EIS and AIA. The DEMs are calculated
using a fast new method which we also describe. The temperature and
density profiles of the loop are compared to and isolated from those of
the surrounding material, and these properties are fit to an analytic
strand heating model developed by Martens (2010). Supported by an AIA
subcontract to Montana State University.
Title: Content-based Image Retrieval For Solar Physics: First Steps
And A Practical Demonstration.
Authors: Banda, Juan; Angryk, R.; Martens, P.
Bibcode: 2012AAS...22020123B
Altcode:
In this Demo/Presentation, we will introduce our open source framework
for the creation of large-scale content-based image retrieval systems
that is being for the NASA’s SDO mission. In this step-by-step
presentation we will show and talk about each of the components that
comprised our framework and describe their individual use. Before
finishing, we will also demonstrate our demo version of the CBIR system
that is in development for NASA’s SDO mission. Since this is an open
tool for researchers, we will be gathering suggestions and comments
from the participants in order to provide a more functional package
for the solar physics community.
Title: The Virtual Solar Observatory: What Are We Up To Now?
Authors: Gurman, Joseph B.; Hill, F.; Suàrez-Solà, F.; Bogart, R.;
Amezcua, A.; Martens, P.; Hourclé, J.; Hughitt, K.
Bibcode: 2012AAS...22020124G
Altcode:
In the nearly ten years of a functional Virtual Solar Observatory (VSO),
http://virtualsolar.org/, we have made it possible to query and access
sixty-seven distinct solar data products and several event lists from
nine spacecraft and fifteen observatories or observing networks. We
have used existing VSO technology, and developed new software, for
a distributed network of sites caching and serving SDO HMI and/or
AIA data. We have also developed an application programming interface
(API) that has enabled VSO search and data access capabilities in IDL,
Python, and Java. We also have quite a bit of work yet to do,
including completion of the implementation of access to SDO EVE data,
and access to some nineteen other data sets from space- and ground-based
observatories. In addition, we have been developing a new graphic user
interface that will enable the saving of user interface and search
preferences. We solicit advice from the community input prioritizing
our task list, and adding to it.
Title: Use of a Time Delay Dynamo Model to Obtain Sun-Like Sunspot
Cycles
Authors: Amouzou, Ernest C.; Nandy, D.; Munoz-Jaramillo, A.; Martens,
P. C. H.
Bibcode: 2012AAS...22020611A
Altcode:
Using a time delay-based, simplified dynamo model, we attempted to
produce results characteristic of the Sun when the parameters are
set to solar values. We found that dynamo solutions exist for dynamo
numbers less than or about equal to -3 (|ND| > 3,ND < 0) and that
sunspot cycle periods of the same order of magnitude of the 11-year
sunspot cycle can be obtained when the diffusive time scale and the
total time delay are both about four years.
Title: A Comparative Evaluation of Automated Solar Filament Detection
Authors: Schuh, Michael; Banda, J.; Bernasconi, P.; Angryk, R.;
Martens, P.
Bibcode: 2012AAS...22020105S
Altcode:
We present a comparative evaluation for automated filament detection
in H-alpha solar images. By using metadata produced by the Advanced
Automated Filament Detection and Characterization Code (AAFDCC)
module, we adapted our Trainable Feature Recognition (TFR) component
to accurately detect regions in solar images containing filaments. We
first analyze the module's metadata and then transform it into
labeled datasets for machine learning classification. Visualizations
of data transformations and classification results are presented
and accompanied by statistical findings. Our results confirm the
reliable event reporting of the AAFDCC module as well as our ability
to effectively detect solar filaments with our TFR component.
Title: Image Recognition and Feature Detection in Solar Physics
Authors: Martens, Petrus C.
Bibcode: 2012AAS...22032302M
Altcode:
The Solar Dynamics Observatory (SDO) data repository will dwarf the
archives of all previous solar physics missions put together. NASA
recognized early on that the traditional methods of analyzing the data
-- solar scientists and grad students in particular analyzing the images
by hand -- would simply not work and tasked our Feature Finding Team
(FFT) with developing automated feature recognition modules for solar
events and phenomena likely to be observed by SDO. Having these metadata
available on-line will enable solar scientist to conduct statistical
studies involving large sets of events that would be impossible now
with traditional means. We have followed a two-track approach in
our project: we have been developing some existing task-specific solar
feature finding modules to be "pipe-line" ready for the stream of SDO
data, plus we are designing a few new modules. Secondly, we took it
upon us to develop an entirely new "trainable" module that would be
capable of identifying different types of solar phenomena starting
from a limited number of user-provided examples. Both approaches
are now reaching fruition, and I will show examples and movies with
results from several of our feature finding modules. In the
second part of my presentation I will focus on our “trainable”
module, which is the most innovative in character. First, there is
the strong similarity between solar and medical X-ray images with
regard to their texture, which has allowed us to apply some advances
made in medical image recognition. Second, we have found that there
is a strong similarity between the way our trainable module works and
the way our brain recognizes images. The brain can quickly recognize
similar images from key characteristics, just as our code does. We
conclude from that that our approach represents the beginning of a
more human-like procedure for computer image recognition.
Title: Fast DEMs for EIS and AIA
Authors: Plowman, Joseph; Kankelborg, Charles; Martens, Petrus;
Ritchie, Miriam; Scott, Jason; Sharma, Rahul
Bibcode: 2012decs.confE..77P
Altcode:
We present a method for constructing Differential Emission Measures
(DEMs) using data from solar imagers such as EIS and AIA. In its
basic form, the method is very fast (approximately one minute per
full disk AIA image), although the DEMs obtained can contain regions
of moderately negative emission measure (EM). We demonstrate an
extension of the method which removes regions of negative EM while
closely matching the data. The fidelity of the method is analyzed,
its results are compared to those of the PINTofALE MCMC DEM algorithm,
and it is applied to a coronal loop observed on April 19, 2011.
Title: EUV Analysis of a Quasi-static Coronal Loop Structure
Authors: Scott, J. T.; Martens, P. C. H.; McKenzie, D. E.
Bibcode: 2012SoPh..276..113S
Altcode: 2011arXiv1110.5560S
Decaying active region 10942 is investigated from 4:00 - 16:00 UT on
24 February 2007 using a suite of EUV observing instruments. Results
from Hinode/EIS, STEREO and TRACE show that, although the active region
has decayed and no sunspot is present, the physical mechanisms that
produce distinguishable loop structures, spectral line broadening,
and plasma flows still occur. A coronal loop that appears as a
blue-shifted structure in Doppler maps is apparent in intensity
images of log(T)=6.0 - 6.3 ions. The loop structure is found to be
anti-correlated with spectral line broadening generally attributed to
non-thermal velocities. This coronal loop structure is investigated
physically (temperature, density, geometry) and temporally. Light
curves created from imaging instruments show brightening and dimming
of the loop structure on two different time scales; short pulses of
10 - 20 min and long duration dimming of two - four hours until its
disappearance. The coronal loop structure, formed from relatively
blue-shifted material that is anti-correlated with spectral line
broadening, shows a density of 1010 to 109.3
cm−3 and is visible for longer than characteristic cooling
times. The maximum non-thermal spectral line broadenings are found to
be adjacent to the footpoint of the coronal loop structure.
Title: Computer Vision for the Solar Dynamics Observatory (SDO)
Authors: Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell,
A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.;
Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.;
Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.;
DeForest, C. E.; Angryk, R. A.; De Moortel, I.; Wiegelmann, T.;
Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P.
Bibcode: 2012SoPh..275...79M
Altcode: 2011SoPh..tmp..144M; 2011SoPh..tmp..213M; 2011SoPh..tmp....8M
In Fall 2008 NASA selected a large international consortium to produce
a comprehensive automated feature-recognition system for the Solar
Dynamics Observatory (SDO). The SDO data that we consider are all of the
Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field
images from the Helioseismic and Magnetic Imager (HMI). We produce
robust, very efficient, professionally coded software modules that
can keep up with the SDO data stream and detect, trace, and analyze
numerous phenomena, including flares, sigmoids, filaments, coronal
dimmings, polarity inversion lines, sunspots, X-ray bright points,
active regions, coronal holes, EIT waves, coronal mass ejections
(CMEs), coronal oscillations, and jets. We also track the emergence and
evolution of magnetic elements down to the smallest detectable features
and will provide at least four full-disk, nonlinear, force-free magnetic
field extrapolations per day. The detection of CMEs and filaments is
accomplished with Solar and Heliospheric Observatory (SOHO)/Large
Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα
data, respectively. A completely new software element is a trainable
feature-detection module based on a generalized image-classification
algorithm. Such a trainable module can be used to find features that
have not yet been discovered (as, for example, sigmoids were in the
pre-Yohkoh era). Our codes will produce entries in the Heliophysics
Events Knowledgebase (HEK) as well as produce complete catalogs for
results that are too numerous for inclusion in the HEK, such as the
X-ray bright-point metadata. This will permit users to locate data on
individual events as well as carry out statistical studies on large
numbers of events, using the interface provided by the Virtual Solar
Observatory. The operations concept for our computer vision system is
that the data will be analyzed in near real time as soon as they arrive
at the SDO Joint Science Operations Center and have undergone basic
processing. This will allow the system to produce timely space-weather
alerts and to guide the selection and production of quicklook images and
movies, in addition to its prime mission of enabling solar science. We
briefly describe the complex and unique data-processing pipeline,
consisting of the hardware and control software required to handle
the SDO data stream and accommodate the computer-vision modules, which
has been set up at the Lockheed-Martin Space Astrophysics Laboratory
(LMSAL), with an identical copy at the Smithsonian Astrophysical
Observatory (SAO).
Title: On the Anti-correlation between Spectral Line Broadening and
Intensity in Coronal Structures Observed with EIS
Authors: Scott, J. T.; Martens, P. C. H.
Bibcode: 2011ApJ...742..101S
Altcode:
The advance in spectral resolution of the Extreme Ultraviolet Imaging
(EIS) spectrometer on board Hinode has allowed for more detailed
analysis of coronal spectral lines. Large line broadening and
blueshifted velocities have been found in the periphery of active
region (AR) cores and near the footpoints of coronal loops. This
line broadening is yet to be understood. We study the correlation of
intensity and line width for entire ARs and sub-regions selected to
include coronal features. The results show that although a slight
positive correlation can be found when considering whole images,
many sub-regions have a negative correlation between intensity and
line width. Sections of a coronal loop display some of the largest
anti-correlations found for this study with the increased line
broadening occurring directly adjacent to the footpoint section of
the loop structure, not at the footpoint itself. The broadened lines
may be due to a second Doppler-shifted component that is separate from
the main emitting feature such as a coronal loop, but related in their
excitation. The small size of these features forces the considerations
of investigator and instrumental effects. Preliminary analyses are
shown that indicate the possibility of a point-spread function that
is not azimuthally symmetric and may affect velocity and line profile
measurements.
Title: Solar Physics Automated Feature Detection: Progress and
Scientific Return
Authors: Martens, P. C.; SDO Feature Finding Team
Bibcode: 2011AGUFMSH13B1963M
Altcode:
The SDO Feature Finding Team (FFT) has been implementing 16 feature
finding modules for the last two and a half years. These modules
have been designed to analyze the incoming stream of SDO data in
near-real-time. Several modules are in regular operation now, most
others are reaching that point. Our modules detect flares, filaments,
dimming regions, sigmoids, emerging flux, bright points, jets,
oscillations, active regions, coronal holes, and several other solar
features. We are also developing a general trainable feature detection
module, which can be applied to detect any phenomenon. Automated
feature recognition has several advantages over the same by humans:
first, and most importantly, much larger amounts of images can be
analyzed by machines; second, the codes will apply consistent criteria
for the detection of phenomena, much more so than humans. Of course
the second point implies that the detection criteria must be carefully
calibrated, otherwise the outcome will be consistent, but consistently
wrong. Examples of the scientific potential unleashed our project are:
i) Draw a butterfly diagram for Active Regions, ii) Find all filaments
that coincide with sigmoids, and then correlate sigmoid handedness
with filament chirality, iii) Correlate EUV jets with small scale flux
emergence in coronal holes, iv) Draw polarity inversion line maps with
regions of high shear and large magnetic field gradients overlayed, to
pinpoint potential flaring regions. Then correlate with actual flare
occurrence. All of these tasks will be accomplished with great ease;
the power of this method is limited merely by the imagination of the
researcher. In addition our modules provide space-weather alerts for
flares, dimmings (proxies for eruptions), and flux emergence. In my
presentation I will present an overview of the output from our feature
detection codes, as well as first results of scientific analysis from
the metadata.
Title: The Double-Ring Algorithm: A Tool for Assimilating Active
Region Data Directly into Kinematic Dynamo Models
Authors: Munoz-Jaramillo, A.; Nandi, D.; Martens, P. C.; Yeates, A. R.
Bibcode: 2011AGUFMSH51B2009M
Altcode:
The emergence of tilted bipolar active regions and the dispersal of
their flux, mediated via processes such as diffusion, differential
rotation and meridional circulation is believed to be responsible for
the reversal of the Sun's polar field. This process (commonly known as
the Babcock-Leighton mechanism) is usually modeled as a near-surface,
spatially distributed α-effect in kinematic mean-field dynamo
models. However, not only this formulation leads to a relationship
between polar field strength and meridional flow speed which is
opposite to that suggested by physical insight and predicted by
surface flux-transport simulations, but also makes it very difficult to
assimilate active region data into kinematic dynamo models. With this
in mind, we present an improved double-ring algorithm for modeling the
Babcock-Leighton mechanism based on active region eruption, within
the framework of an axisymmetric dynamo model. We demonstrate that
our treatment of the Babcock-Leighton mechanism through double-ring
eruption leads to an inverse relationship between polar field strength
and meridional flow speed as expected, reconciling the discrepancy
between surface flux-transport simulations and kinematic dynamo
models. Finally, we show how this new formulation paves the way
for applications, which were not possible before, like the direct
assimilation of active region data.
Title: Simulating the Effects of Initial Pitch-angle Distributions
on Solar Flares
Authors: Winter, Henry D.; Martens, Petrus; Reeves, Katharine K.
Bibcode: 2011ApJ...735..103W
Altcode:
In this work, we model both the thermal and non-thermal components of
solar flares. The model we use, HYLOOP, combines a hydrodynamic equation
solver with a non-thermal particle tracking code to simulate the thermal
and non-thermal dynamics and emission of solar flares. In order to test
the effects of pitch-angle distribution on flare dynamics and emission,
a series of flares is simulated with non-thermal electron beams injected
at the loop apex. The pitch-angle distribution of each beam is described
by a single parameter and allowed to vary from flare to flare. We
use the results of these simulations to generate synthetic hard and
soft X-ray emissions (HXR and SXR). The light curves of the flares in
Hinode's X-ray Telescope passbands show a distinct signal that is highly
dependent on pitch-angle distribution. The simulated HXR emission in the
3-6 keV bandpass shows the formation and evolution of emission sources
that correspond well to the observations of pre-impulsive flares. This
ability to test theoretical models of thermal and non-thermal flare
dynamics directly with observations allows for the investigation
of a wide range of physical processes governing the evolution of
solar flares. We find that the initial pitch-angle distribution of
non-thermal particle populations has a profound effect on loop top
HXR and SXR emission and that apparent motion of HXR is a natural
consequence of non-thermal particle evolution in a magnetic trap.
Title: Computer Vision for the Solar Dynamics Observatory: First
Results and What's Next
Authors: Martens, P. C. H.; Sdo Feature Finding Team
Bibcode: 2011ASPC..442..543M
Altcode: 2011adass..20..543M
The Solar Dynamics Observatory (SDO) feature finding team is a large
international consortium tasked by NASA to produce a comprehensive
system for automated feature recognition for SDO. We are producing
robust and very efficient software modules that can keep up with the SDO
data stream and detect, trace, and analyze a large number of phenomena,
including flares, sigmoids, filaments, and coronal dimmings. Results
will be shown for several modules have been inaugurated since the end
of SDO commissioning last summer. In addition a description is given
of the status of the development of our trainable automated feature
finding module.
Title: Recent Improvements of Kinematic Models of the Solar Magnetic
Cycle
Authors: Muñoz-Jaramillo, Andrés; Nandy, Dibyendu; Martens, Petrus
C. H.
Bibcode: 2011shin.confE...3M
Altcode:
One of the best tools we have for understanding the origin of
solar magnetic variability are kinematic dynamo models. During the
last decade, this type of models has seen a continuous evolution
and has become increasingly successful at reproducing solar cycle
characteristics. Unfortunately, most of ingredients that make up
a kinematic dynamo model remain poorly constrained allowing one to
obtain solar-like solutions by 'tuning' the input parameters' leading
to controversy regarding which parameter set is more appropriate. In
this poster we will revisit two of those ingredients and show how to
constrain them better by using observational data and theoretical
considerations. For the turbulent magnetic diffusivity -
an ingredient which attempts to capture the effect of convective
turbulence on the large scale magnetic field - we show that combining
mixing-length theory estimates with magnetic quenching allows us
to obtain viable magnetic cycles (otherwise impossible) and that the
commonly used diffusivity profiles can be understood as a spatiotemporal
average of this process. For the poloidal source - the ingredient
which closes the cycle by regenerating the poloidal magnetic field -
we introduce a more realistic way of modeling active region emergence
and decay and find that this resolves existing discrepancies between
kinematic dynamo models and surface flux transport simulations. This
formulation has made possible to study the physical mechanisms leading
to the extended minimum of cycle 23 and paves the way for future
coupling between kinematic dynamos and models of the solar corona. This work is funded by NASA Living With a Star Grant NNX08AW53G to
Montana State University/Harvard-Smithsonian Center for Astrophysics
and the Government of India's Ramanujan Fellowship.
Title: The Unusual Minimum of Solar Cycle 23: Origin and Heliospheric
Consequences
Authors: Nandi, Dibyendu; Munoz-Jaramillo, Andres; Martens, Piet C. H.
Bibcode: 2011simi.conf....5N
Altcode:
Solar cycle 23 was characterized by very weak polar magnetic field and
a large number of sunspot-less unprecedented in almost a century. This
resulted in atypical conditions in our space environment, including
low solar radiative flux, weak solar wind and heliospheric magnetic
field and record-high cosmic rays flux. Here I will review some of
these unusual conditions in space during the recently concluded solar
minimum and present the first consistent explanation of this deep
solar minimum based on dynamo simulations.
Title: Meridional Surface Flows and the Recent Extended Solar Minimum
Authors: Martens, Petrus C.; Nandy, D.; Munoz-Jaramillo, A.
Bibcode: 2011SPD....42.1705M
Altcode: 2011BAAS..43S.1705M
Nandy, Munoz, & Martens, have published a kinematic dynamo model
that successfully reproduces the main characteristics of the recent
extended solar minimum (Nature 2011, 471, 80). The model depends on
the solar meridional flow and its return flow along the tachocline
determining the period and character of the cycle. In particular Nandy
et al. found that a meridional flow that is fast in the first half
of the cycle and then slows down around solar maximum, can lead to
an extended minimum with the characteristics of the recent minimum:
an extended period without sunspots and weak polar fields. It has
been pointed out that the observed surface meridional flows over the
last cycle do not fit the pattern assumed by Nandy et al. Hathaway &
Rightmire (Science 2010, 327-1350) find that the meridional speed of
small magnetic surface elements observed by SoHO/MDI decreased around
solar maximum and has not yet recovered. Basu & Antia (ApJ 2010,
717, 488) find surface plasma meridional flow speeds that are lower at
solar maximum 23 than at the surrounding minima, which is different
from both Hathaway and Nandy. While there is no physical reason
that solar surface flows -- both differential rotation and meridional
flow -- would vary in lockstep with flows at greater depth, as the
large radial gradients near the surface clearly indicate, and while
Nandy et al. have demonstrated that the deeper flows dominate the net
meridional mass flow, we find that there is in effect a very satisfying
agreement between the observational results of Hathaway & Rightmire,
Basu & Antia, and the model assumptions of Nandy, Munoz, &
Martens. We present an analytical model that reconciles the first two,
followed by a hydrodynamical model that demonstrates the consistency of
these observational results with the model assumptions of Nandy et al.
Title: Understanding the Origin of the Extended Minimum of Sunspot
Cycle 23
Authors: Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.
Bibcode: 2011SPD....42.1743M
Altcode: 2011BAAS..43S.1743M
The minimum of solar cycle 23 was characterized by very weak polar
field strength and a large number of sunspot-less days that was
unprecedented in the space age. This has had significant consequences in
the heliospheric space environment in terms of record-high cosmic-ray
flux and low levels of solar irradiance - which is the primary natural
driver of the climate system. During this un-anticipated phase,
there was some speculation as to whether the solar minimum could lead
to a Maunder-like grand minimum which coincided with the Little Ice
Age. Here we present the first consistent explanation of the defining
characteristics of this unusual minimum based on variations in the
solar meridional plasma flows, and discuss how our results compare with
observations. This work is funded by NASA Living With a Star Grant
NNX08AW53G to Montana State University/Harvard-Smithsonian Center for
Astrophysics and the Government of India's Ramanujan Fellowship.
Title: The Double-Ring Algorithm: Reconciling Surface Flux Transport
Simulations and Kinematic Dynamo Models
Authors: Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.;
Yeates, A. R.
Bibcode: 2011SPD....42.0205M
Altcode: 2011BAAS..43S.0205M
The emergence of tilted bipolar active regions and the dispersal of
their flux, mediated via processes such as diffusion, differential
rotation and meridional circulation is believed to be responsible
for the reversal of the Sun's polar field. This process (commonly
known as the Babcock-Leighton mechanism) is usually modeled as a
near-surface, spatially distributed α-effect in kinematic mean-field
dynamo models. However, this formulation leads to a relationship
between polar field strength and meridional flow speed which is
opposite to that suggested by physical insight and predicted by
surface flux-transport simulations. With this in mind, we present
an improved double-ring algorithm for modeling the Babcock-Leighton
mechanism based on active region eruption, within the framework of
an axisymmetric dynamo model. We demonstrate that our treatment of
the Babcock-Leighton mechanism through double-ring eruption leads to
an inverse relationship between polar field strength and meridional
flow speed as expected, reconciling the discrepancy between surface
flux-transport simulations and kinematic dynamo models. Finally,
we show how this new formulation paves the way for applications,
which were not possible before, like understanding the nature of the
extended minimum of sunspot cycle 23 and direct assimilation of active
region data. This work is funded by NASA Living With a Star Grant
NNX08AW53G to Montana State University/Harvard-Smithsonian Center for
Astrophysics and the Government of India's Ramanujan Fellowship.
Title: The unusual minimum of sunspot cycle 23 caused by meridional
plasma flow variations
Authors: Nandy, Dibyendu; Muñoz-Jaramillo, Andrés; Martens, Petrus
C. H.
Bibcode: 2011Natur.471...80N
Altcode: 2013arXiv1303.0349N
Direct observations over the past four centuries show that the number
of sunspots observed on the Sun's surface varies periodically, going
through successive maxima and minima. Following sunspot cycle 23,
the Sun went into a prolonged minimum characterized by a very weak
polar magnetic field and an unusually large number of days without
sunspots. Sunspots are strongly magnetized regions generated by a
dynamo mechanism that recreates the solar polar field mediated through
plasma flows. Here we report results from kinematic dynamo simulations
which demonstrate that a fast meridional flow in the first half of a
cycle, followed by a slower flow in the second half, reproduces both
characteristics of the minimum of sunspot cycle 23. Our model predicts
that, in general, very deep minima are associated with weak polar
fields. Sunspots govern the solar radiative energy and radio flux,
and, in conjunction with the polar field, modulate the solar wind, the
heliospheric open flux and, consequently, the cosmic ray flux at Earth.
Title: Magnetic Quenching of Turbulent Diffusivity: Reconciling
Mixing-length Theory Estimates with Kinematic Dynamo Models of the
Solar Cycle
Authors: Muñoz-Jaramillo, Andrés; Nandy, Dibyendu; Martens, Petrus
C. H.
Bibcode: 2011ApJ...727L..23M
Altcode: 2010arXiv1007.1262M
The turbulent magnetic diffusivity in the solar convection zone is
one of the most poorly constrained ingredients of mean-field dynamo
models. This lack of constraint has previously led to controversy
regarding the most appropriate set of parameters, as different
assumptions on the value of turbulent diffusivity lead to radically
different solar cycle predictions. Typically, the dynamo community
uses double-step diffusivity profiles characterized by low values of
diffusivity in the bulk of the convection zone. However, these low
diffusivity values are not consistent with theoretical estimates based
on mixing-length theory, which suggest much higher values for turbulent
diffusivity. To make matters worse, kinematic dynamo simulations cannot
yield sustainable magnetic cycles using these theoretical estimates. In
this work, we show that magnetic cycles become viable if we combine the
theoretically estimated diffusivity profile with magnetic quenching of
the diffusivity. Furthermore, we find that the main features of this
solution can be reproduced by a dynamo simulation using a prescribed
(kinematic) diffusivity profile that is based on the spatiotemporal
geometric average of the dynamically quenched diffusivity. This bridges
the gap between dynamically quenched and kinematic dynamo models,
supporting their usage as viable tools for understanding the solar
magnetic cycle.
Title: Heliophysics Data Environment: What's next? (Invited)
Authors: Martens, P.
Bibcode: 2010AGUFMSM34A..06M
Altcode:
In the last two decades the Heliophysics community has witnessed
the societal recognition of the importance of space weather and
space climate for our technology and ecology, resulting in a renewed
priority for and investment in Heliophysics. As a result of that and
the explosive development of information technology, Heliophysics has
experienced an exponential growth in the amount and variety of data
acquired, as well as the easy electronic storage and distribution of
these data. The Heliophysics community has responded well to these
challenges. The first, most obvious and most needed response, was the
development of Virtual Heliophysics Observatories. While the VxOs of
Heliophysics still need a lot of work with respect to the expansion of
search options and interoperability, I believe the basic structures and
functionalities have been established, and that they meet the needs
of the community. In the future we'll see a refinement, completion,
and integration of VxOs, not a fundamentally different approach --
in my opinion. The challenge posed by the huge increase in amount
of data is not met by VxOs alone. No individual scientist or group,
even with the assistance of tons of graduate students, can analyze the
torrent of data currently coming down from the fleet of heliospheric
observatories. Once more information technology provides an opportunity:
Automated feature recognition of solar imagery is feasible, has been
implemented in a number of instances, and is strongly supported by
NASA. For example, the SDO Feature Finding Team is developing a suite
of 16 feature recognition modules for SDO imagery that operates in
near-real time, produces space-weather warnings, and populates on-line
event catalogs. Automated feature recognition -- "computer vision"
-- not only save enormous amounts of time in the analysis of events,
it also allows for a shift from the analysis of single events to
that of sets of features and events -- the latter being by far the
most important implication of computer vision. Consider some specific
examples of possibilities here: From the on-line SDO metadata a user
can produce with a few IDL line commands information that previously
would have taken years to compile, e.g.: - Draw a butterfly diagram for
Active Regions, - Find all filaments that coincide with sigmoids and
correlate the automatically detected sigmoid handedness with filament
chirality, - Correlate EUV jets with small scale flux emergence in
coronal holes only, - Draw PIL maps with regions of high shear and
large magnetic field gradients overlayed, to pinpoint potential
flaring regions. Then correlate with actual flare occurrence. I
emphasize that the access to those metadata will be provided by VxOs,
and that the interplay between computer vision codes and data will be
facilitated by VxOs. My vision for the near and medium future for the
VxOs is then to provide a simple and seamless interface between data,
cataloged metadata, and computer vision software, either existing or
newly developed by the user. Heliospheric virtual observatories and
computer vision systems will work together to constantly monitor the
Sun, provide space weather warnings, populate catalogs of metadata,
analyze trends, and produce real-time on-line imagery of current events.
Title: Accessing SDO data in a pipeline environment using the VSO
WSDL/SOAP interface
Authors: Suarez Sola, F. I.; Hourcle, J. A.; Amezcua, A.; Bogart,
R.; Davey, A. R.; Gurman, J. B.; Hill, F.; Hughitt, V. K.; Martens,
P. C.; Spencer, J.; Vso Team
Bibcode: 2010AGUFMSH23C1869S
Altcode:
As part of the Virtual Solar Observatory (VSO) effort to support the
Solar Dynamics Observatory (SDO) data, the VSO has worked on bringing
up to date its WSDL document and SOAP interface to make it compatible
with most widely used web services core engines. (E.g. axis2, jws,
etc.) In this presentation we will explore the possibilities available
for searching and/or fetching data within pipeline code. We will explain
some of the WSDL/VSO-SDO interface intricacies and show how the vast
amount of data that is available via the VSO can be tapped via IDL,
Java, Perl or C in an uncomplicated way.
Title: A Double-ring Algorithm for Modeling Solar Active Regions:
Unifying Kinematic Dynamo Models and Surface Flux-transport
Simulations
Authors: Muñoz-Jaramillo, Andrés; Nandy, Dibyendu; Martens, Petrus
C. H.; Yeates, Anthony R.
Bibcode: 2010ApJ...720L..20M
Altcode: 2010arXiv1006.4346M
The emergence of tilted bipolar active regions (ARs) and the dispersal
of their flux, mediated via processes such as diffusion, differential
rotation, and meridional circulation, is believed to be responsible
for the reversal of the Sun's polar field. This process (commonly
known as the Babcock-Leighton mechanism) is usually modeled as a
near-surface, spatially distributed α-effect in kinematic mean-field
dynamo models. However, this formulation leads to a relationship
between polar field strength and meridional flow speed which is
opposite to that suggested by physical insight and predicted by surface
flux-transport simulations. With this in mind, we present an improved
double-ring algorithm for modeling the Babcock-Leighton mechanism
based on AR eruption, within the framework of an axisymmetric dynamo
model. Using surface flux-transport simulations, we first show that an
axisymmetric formulation—which is usually invoked in kinematic dynamo
models—can reasonably approximate the surface flux dynamics. Finally,
we demonstrate that our treatment of the Babcock-Leighton mechanism
through double-ring eruption leads to an inverse relationship between
polar field strength and meridional flow speed as expected, reconciling
the discrepancy between surface flux-transport simulations and kinematic
dynamo models.
Title: Empirical Modeling of Radiative versus Magnetic Flux for
the Sun-as-a-Star
Authors: Preminger, Dora; Nandy, Dibyendu; Chapman, Gary; Martens,
Petrus C. H.
Bibcode: 2010SoPh..264...13P
Altcode: 2010arXiv1006.4354P; 2010SoPh..tmp...92P
We study the relationship between full-disk solar radiative flux at
different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph
and other instruments extending over one or more solar cycles. We
use two different statistical methods to determine the underlying
nature of these flux - flux relationships. First, we use statistical
correlation and regression analysis and show that the relationships are
not monotonic for total solar irradiance and for continuum radiation
from the photosphere, but are approximately linear for chromospheric
and coronal radiation. Second, we use signal theory to examine the
flux - flux relationships for a temporal component. We find that
a well-defined temporal component exists and accounts for some of
the variance in the data. This temporal component arises because
active regions with high magnetic-field strength evolve, breaking
up into small-scale magnetic elements with low field strength, and
radiative and magnetic fluxes are sensitive to different active-region
components. We generate empirical models that relate radiative flux to
magnetic flux, allowing us to predict spectral-irradiance variations
from observations of disk-averaged magnetic-flux density. In most cases,
the model reconstructions can account for 85 - 90% of the variability
of the radiative flux from the chromosphere and corona. Our results
are important for understanding the relationship between magnetic and
radiative measures of solar and stellar variability.
Title: Solar Cycle Variation of Magnetic Flux Ropes in a Quasi-Static
Coronal Evolution Model
Authors: Yeates, A. R.; Constable, J. A.; Martens, P. C. H.
Bibcode: 2010SoPh..263..121Y
Altcode: 2010arXiv1003.4653Y; 2010SoPh..tmp...69Y
The structure of electric current and magnetic helicity in the solar
corona is closely linked to solar activity over the 11-year cycle,
yet is poorly understood. As an alternative to traditional current-free
"potential-field" extrapolations, we investigate a model for the global
coronal magnetic field which is non-potential and time-dependent,
following the build-up and transport of magnetic helicity due to
flux emergence and large-scale photospheric motions. This helicity
concentrates into twisted magnetic flux ropes, which may lose
equilibrium and be ejected. Here, we consider how the magnetic
structure predicted by this model - in particular the flux ropes -
varies over the solar activity cycle, based on photospheric input
data from six periods of cycle 23. The number of flux ropes doubles
from minimum to maximum, following the total length of photospheric
polarity inversion lines. However, the number of flux rope ejections
increases by a factor of eight, following the emergence rate of active
regions. This is broadly consistent with the observed cycle modulation
of coronal mass ejections, although the actual rate of ejections in the
simulation is about a fifth of the rate of observed events. The model
predicts that, even at minimum, differential rotation will produce
sheared, non-potential, magnetic structure at all latitudes.
Title: Towards better Constrained Kinematic Dynamo Models: Turbulent
Diffusivity and Diffusivity Quenching
Authors: Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.
Bibcode: 2010AAS...21640116M
Altcode:
The turbulent magnetic diffusivity in the Solar Convection Zone
(SCZ) is one of the most poorly constrained ingredients of mean-field
dynamo models. This lack of constrain has previously led to controversy
regarding which set of parameters is more appropriate (yielding better
solar like solutions) and the generation of radically different cycle
predictions. Furthermore, due to the relative freedom in the different
parameters associated with it, more often than not it is used to finely
tune the dynamo solutions. As of now, the dynamo community seems
to have settled on double step diffusivity profiles characterized
by low values of diffusivity inside most of the convection zone;
notwithstanding that these values of diffusivity are not consistent
with theoretical considerations based on mixing-length theory, which
suggest much higher values of turbulent diffusivity. To make matters
worse, standard kinematic dynamo simulations cannot yield sustainable
magnetic cycles using theoretical estimates. Here we study how magnetic
diffusivity quenching can provide a physically meaningful way out of
this discrepancy and whether standard diffusivity profiles are truly
a representation of a physical process. This work is funded by NASA
Living With a Star grant NNG05GE47G.
Title: Scaling Laws and Temperature Profiles for Solar and Stellar
Coronal Loops with Non-uniform Heating
Authors: Martens, P. C. H.
Bibcode: 2010ApJ...714.1290M
Altcode: 2008arXiv0804.2241M
The bulk of solar coronal radiative loss consists of soft X-ray
emission from quasi-static loops at the cores of active regions. In
order to develop diagnostics for determining the heating mechanism of
these loops from observations by coronal imaging instruments, I have
developed analytical solutions for the temperature structure and scaling
laws of loop strands for a set of temperature- and pressure-dependent
heating functions that encompass heating concentrated at the footpoints,
uniform heating, and heating concentrated at the loop apex. Key results
are that the temperature profile depends only weakly on the heating
distribution—not sufficiently to be of significant diagnostic
value—and that the scaling laws survive for this wide range of
heating distributions, but with the constant of proportionality in the
Rosner-Tucker-Vaiana scaling law (P 0 L ~ T 3
max) depending on the specific heating function. Furthermore,
quasi-static solutions do not exist for an excessive concentration of
heating near the loop footpoints, a result in agreement with recent
numerical simulations. It is demonstrated that a generalization of
the results to a set of solutions for strands with a functionally
prescribed variable diameter leads to only relatively small correction
factors in the scaling laws and temperature profiles for constant
diameter loop strands. A quintet of leading theoretical coronal
heating mechanisms is shown to be captured by the formalism of this
paper, and the differences in thermal structure between them may be
verified through observations. Preliminary results from full numerical
simulations demonstrate that, despite the simplifying assumptions,
the analytical solutions from this paper are accurate and stable.
Title: Computer Vision for SDO: First Results from the SDO Feature
Finding Algorithms
Authors: Martens, Petrus C.; Attrill, G.; Davey, A.; Engell, A.;
Farid, S.; Grigis, P.; Kasper, J.; Korreck, K.; Saar, S.; Su, Y.;
Testa, P.; Wills-Davey, M.; Bernasconi, P.; Raouafi, N.; Georgoulis,
M.; Deforest, C.; Peterson, J.; Berghoff, T.; Delouille, V.; Hochedez,
J.; Mampaey, B.; Verbeek, C.; Cirtain, J.; Green, S.; Timmons, R.;
Savcheva, A.; Angryk, R.; Wiegelmann, T.; McAteer, R.
Bibcode: 2010AAS...21630804M
Altcode:
The SDO Feature Finding Team produces robust and very efficient
software modules that can keep up with the relentless SDO data stream,
and detect, trace, and analyze a large number of phenomena including:
flares, sigmoids, filaments, coronal dimmings, polarity inversion
lines, sunspots, X-ray bright points, active regions, coronal holes,
EIT waves, CME's, coronal oscillations, and jets. In addition we track
the emergence and evolution of magnetic elements down to the smallest
features that are detectable, and we will also provide at least four
full disk nonlinear force-free magnetic field extrapolations per day. During SDO commissioning we will install in the near-real time data
pipeline the modules that provide alerts for flares, coronal dimmings,
and emerging flux, as well as those that trace filaments, sigmoids,
polarity inversion lines, and active regions. We will demonstrate
the performance of these modules and illustrate their use for science
investigations.
Title: Are Active Regions as Relevant for the Solar Cycle as we Think?
Authors: Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.
Bibcode: 2010AAS...21640108M
Altcode: 2010BAAS...41R.858M
The long and short term variability of the Sun is strongly determined
by the evolution of the solar magnetic cycle, which is sustained
through the action of a magneto-hydrodynamic dynamo. In our current
understanding of the dynamo, the poloidal field (which acts as a
starting point for the cycle) is recreated through the emergence and
decay of active regions subjected to the collective effect of meridional
circulation and turbulent diffusion; a process commonly referred to as
the Babcock-Leighton mechanism. Dynamo models based on this mechanism
have been quite successful in reproducing the different properties of
the solar cycle and have also been used to make predictions of cycle
24. However, the question of whether the BL mechanism is enough to
sustain the solar cycle has not yet been addressed quantitatively. By
including real active region data in our state of the art kinematic
dynamo model we are able to take the first steps into answering this
question. This work is funded by NASA Living With a Star grant
NNG05GE47G.
Title: The Unusual Minimum of Solar Cycle 23 Explained
Authors: Nandy, Dibyendu; Munoz-Jaramillo, A.; Martens, P. C. H.
Bibcode: 2010AAS...21631703N
Altcode: 2010BAAS...41..898N
The minimum in activity between solar cycle 23 and 24 has been the
deepest in the space age, with an unusually large number of days
without sunspots and weak solar dipolar field strength. This has
had consequences for the heliosphere and planetary atmospheres -
given the weak solar wind, low solar irradiance and radio flux and
historically high values of cosmic ray flux that has characterized
this minimum epoch. The origin of this peculiar minimum has not
yet been clearly understood. Here we present the first theoretical
explanation of this deep minimum based on simulations of the solar
dynamo mechanism - which seeks to explain the origin and variability
of solar magnetic fields. Our simulations have uncovered a somewhat
surprising explanation, which however, provides a consistent solution
to both of the unusual features of this minimum; namely, the long period
when sunspots were missing and the very weak solar polar field strength.
Title: The SDO flare detective
Authors: Grigis, Paolo; Davey, A.; Martens, P.; Testa, P.; Timmons,
R.; Su, Y.; SDO Feature Finding Team
Bibcode: 2010AAS...21640208G
Altcode: 2010BAAS...41..874G
We present the flare detective, a software module to automatically
detect and characterize solar flares observed with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The
flare detective works in two steps. First, flares are detected in
EUV images by analyzing lightcurves in macropixels. At this time,
only basic quantities such as time intervals, positions, and peak
fluxes will be determined. This will allow the module to keep up
with the extremely large size of the incoming data stream and provide
near real-time information for space weather monitoring. Second, the
flare detective will be run again on the subset of images around the
time intervals where a flare has been already detected, where more
sophisticated (and slower) processing will be performed to better
characterize the flare and provide physically important parameters such
as temperatures and emission measures, projected areas and lightcurves
in different channels. The events detected will be made available to
the Heliophysics Events Knowledgebase (HEK) and also as a flare list
in text format accessible on the web. This module is part of a larger
effort to detect and track solar features and events that is optimized
to run on the very large datasets provided by SDO.
Title: SDO Data Access Via The Virtual Solar Observatory
Authors: Hill, Frank; Gurman, J.; Martens, P.; Bogart, R.; Davey, A.;
Hourcle, J.; Suarez Sola, F.; Hughitt, K.; Spencer, J.; Reardon, K.;
Amezcua, A.
Bibcode: 2010AAS...21640218H
Altcode: 2010BAAS...41Q.876H
The launch of SDO brings not only the prospect of new solar physics
discoveries, but also a flood of data. The sustained data rate of
150 Mbs (about 1.6 TB per day) is the highest yet produced by a
solar physics observatory, and the handling of the data requires new
methods. One approach is to distribute the data storage and request
system over a number of distinct sites to reduce the bandwidth
requirements at a single location. The VSO, in conjunction with the
Joint Science and Operations Center (JSOC) at Stanford and a network of
partial archive sites currently at CfA, NSO, ROB, and MPIS, is now able
to provide metadata search and data retrieval services for the SDO AIA
and HMI instruments. EVE data will also be included in the future. This
talk will describe how SDO data can be accessed via the VSO.
Title: Comparison of a Global Magnetic Evolution Model with
Observations of Coronal Mass Ejections
Authors: Yeates, A. R.; Attrill, G. D. R.; Nandy, Dibyendu; Mackay,
D. H.; Martens, P. C. H.; van Ballegooijen, A. A.
Bibcode: 2010ApJ...709.1238Y
Altcode: 2009arXiv0912.3347Y
The relative importance of different initiation mechanisms for coronal
mass ejections (CMEs) on the Sun is uncertain. One possible mechanism is
the loss of equilibrium of coronal magnetic flux ropes formed gradually
by large-scale surface motions. In this paper, the locations of flux
rope ejections in a recently developed quasi-static global evolution
model are compared with observed CME source locations over a 4.5 month
period in 1999. Using extreme ultraviolet data, the low-coronal source
locations are determined unambiguously for 98 out of 330 CMEs. An
alternative method of determining the source locations using recorded
Hα events was found to be too inaccurate. Despite the incomplete
observations, positive correlation (with coefficient up to 0.49) is
found between the distributions of observed and simulated ejections,
but only when binned into periods of 1 month or longer. This binning
timescale corresponds to the time interval at which magnetogram data are
assimilated into the coronal simulations, and the correlation arises
primarily from the large-scale surface magnetic field distribution;
only a weak dependence is found on the magnetic helicity imparted to the
emerging active regions. The simulations are limited in two main ways:
they produce fewer ejections, and they do not reproduce the strong
clustering of observed CME sources into active regions. Due to this
clustering, the horizontal gradient of radial photospheric magnetic
field is better correlated with the observed CME source distribution
(coefficient 0.67). Our results suggest that while the gradual formation
of magnetic flux ropes over weeks can account for many observed CMEs,
especially at higher latitudes, there exists a second class of CMEs (at
least half) for which dynamic active region flux emergence on shorter
timescales must be the dominant factor. Improving our understanding
of CME initiation in future will require both more comprehensive
observations of CME source regions and more detailed magnetic field
simulations.
Title: Automated Feature and Event Detection with SDO AIA and HMI Data
Authors: Davey, Alisdair; Martens, P. C. H.; Attrill, G. D. R.;
Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar,
S. H.; Su, Y.; Testa, P.; Wills-Davey, M.; Savcheva, A.; Bernasconi,
P. N.; Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F. .; Cirtain,
J. W.; Deforest, C. E.; Angryk, R. A.; de Moortel, I.; Wiegelmann,
T.; Georgouli, M. K.; McAteer, R. T. J.; Hurlburt, N.; Timmons, R.
Bibcode: 2010cosp...38.2878D
Altcode: 2010cosp.meet.2878D
The Solar Dynamics Observatory (SDO) represents a new frontier in
quantity and quality of solar data. At about 1.5 TB/day, the data will
not be easily digestible by solar physicists using the same methods
that have been employed for images from previous missions. In order for
solar scientists to use the SDO data effectively they need meta-data
that will allow them to identify and retrieve data sets that address
their particular science questions. We are building a comprehensive
computer vision pipeline for SDO, abstracting complete metadata
on many of the features and events detectable on the Sun without
human intervention. Our project unites more than a dozen individual,
existing codes into a systematic tool that can be used by the entire
solar community. The feature finding codes will run as part of the SDO
Event Detection System (EDS) at the Joint Science Operations Center
(JSOC; joint between Stanford and LMSAL). The metadata produced will
be stored in the Heliophysics Event Knowledgebase (HEK), which will be
accessible on-line for the rest of the world directly or via the Virtual
Solar Observatory (VSO) . Solar scientists will be able to use the
HEK to select event and feature data to download for science studies.
Title: Enabling Distributed Search and Access to SDO Data with the
Virtual Solar Observatory
Authors: Davey, Alisdair; Martens, P.; Gurman, J.; Hourcle, J.; Hill,
F.; Suarez-Sola, F.; Amezcua, A.; Bogart, R.; Spencer, J.
Bibcode: 2010cosp...38.2881D
Altcode: 2010cosp.meet.2881D
The Virtual Solar Observatory (VSO) will be an integral part of
distributing Solar Dynamics Observatory (SDO) data to the Solar Physics
community and in enabling it to be searched by scientists. A daily
data volume of 1.5TB presents unique challenges, and the VSO has been
working on enhancing various aspects of its infrastructure to deal with
them. The VSO will provide a dedicated interface to SDO data, providing
common methods users of VSO already know, as well as new methods that
reflect the needs of interacting with AIA, HMI and EVE data. VSO has
created a data distribution architecture based up the Joint Science
Operations Center (JSOC) infrastructure, that in partnership with
NASA Solar Data Analysis Center, National Solar Observatory, Royal
Observatory Belgium, University College Lancashire, Max Planck Institute
for Solar System Research and the Institute d'Astrophysique Spatiale
(Orsay) will enable scientists to retrieve SDO data of interest in
the fastest possible way. VSO is working closely with the Helioviewer
and Heliophysics Event Knowledgebase (HEK) teams to ensure we will
be able to use their efforts and be used by their efforts for data
retrieval. In this manner, graphical, IDL-based and event approaches
to data discovery will be fully supported by the VSO.
Title: The SDO Flare Detective
Authors: Grigis, P. C.; Davey, A. R.; Martens, P. C.; Su, Y.; Testa,
P.; Timmons, R. P.
Bibcode: 2009AGUFMSH51B1277G
Altcode:
We present the flare detective, a software module to automatically
detect and characterize solar flares observed with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The
flare detective works in two steps. First, flares will be detected
in EUV images by analysing lightcurves in macropixels. At this time,
only basic quantities such as time intervals, positions, and peak
fluxes will be determined. This will allow the module to keep up
with the extremely large size of the incoming data stream and provide
near real-time information for space weather monitoring. Second, the
flare detective will be run again on the subset of images around the
time intervals where a flare has been already detected, where more
sophisticated (and slower) processing will be performed to better
characterize the flare and provide physically important parameters such
as temperatures and emission measures, projected areas and lightcurves
in different channels. The events detected will be made available to
the Heliophysics Knowledgebase (HEK) and also as a flare list in text
format accessible on the web. This module is part of a larger effort
to detect and track solar features and events that is optimized to
run on very large datasets such as the ones provided by SDO.
Title: Computer Vision for the Solar Dynamics Observatory
Authors: Martens, P. C.
Bibcode: 2009AGUFMSH51B1276M
Altcode:
NASA has selected our large international consortium last year to
produce a comprehensive system for automated feature recognition in
SDO images. The data we consider are all AIA and EVE data plus surface
magnetic field images from HMI. Helioseismology is addressed by another
group. We are producing robust and very efficient software modules
that can keep up with the relentless SDO data stream and detect, trace,
and analyze a large number of phenomena, including: flares, sigmoids,
filaments, coronal dimmings, polarity inversion lines, sunspots,
X-ray bright points, active regions, coronal holes, EIT waves, CME's,
coronal oscillations, and jets. In addition we will track the emergence
and evolution of magnetic elements down to the resolution limit, and we
will also provide at least four full disk nonlinear force-free magnetic
field extrapolations per day. A completely new software element that
rounds out this suite is a trainable feature detection module, which
employs a generalized image classification algorithm to produce the
texture features of the images analyzed. A user can introduce a number
of examples of the phenomenon looked for and the software will return
images with similar features. We have tested a proto-type on TRACE
data, and were able to "train" the algorithm to detect sunspots, active
regions, and loops. Such a module can be applied to find features that
have not even been discovered yet, as, for example, sigmoids were in
the pre-Yohkoh era. In addition it will be used to detect features for
which we will not develop dedicated modules, such as loops, arcades,
"null"-type geometries, anemones, delta-spots, etc. Our codes will
produce entries in the Heliophysics Events Knowledge base, and that
will permit users to locate data on individual events as well as carry
out statistical studies on large numbers of events.
Title: What do Solar Kinematic Models Tell us About the Current
Minimum?
Authors: Muñoz-Jaramillo, A.; Nandy, D.; Martens, P. C.
Bibcode: 2009AGUFMSH11A1505M
Altcode:
In the last three years the sun has reached the most unusual minimum
in the space age. Although minima as long as this one have happened
several times in the past, this one has come as a surprise in contrast
with the previous four who where fairly regular. However, such an event
is a perfect opportunity to learn more about the solar cycle and the
processes that drive it. In order to understand this event we turn
to kinematic dynamo models, which are the best tool we currently have
for understanding the solar cycle. Although modelers have been aware
of the role of the different components into setting the period of the
solar cycle, little work has been done in understanding the nature of
solar minima. Can kinematic models reproduce such an event with all
it's signatures? In this study we attempt to address this question
using our state of the art kinematic dynamo model.
Title: ERRATUM: "Helioseismic Data Inclusion in Solar Dynamo Models"
(2009, ApJ, 698, 461)
Authors: Muñoz-Jaramillo, Andrés; Nandy, Dibyendu; Martens, Petrus
C. H.
Bibcode: 2009ApJ...707.1852M
Altcode:
No abstract at ADS
Title: Helioseismic Data Inclusion in Solar Dynamo Models
Authors: Muñoz-Jaramillo, Andrés; Nandy, Dibyendu; Martens, Petrus
C. H.
Bibcode: 2009ApJ...698..461M
Altcode: 2008arXiv0811.3441M
An essential ingredient in kinematic dynamo models of the solar cycle
is the internal velocity field within the simulation domain—the
solar convection zone (SCZ). In the last decade or so, the field of
helioseismology has revolutionized our understanding of this velocity
field. In particular, the internal differential rotation of the Sun
is now fairly well constrained by helioseismic observations almost
throughout the SCZ. Helioseismology also gives us some information
about the depth dependence of the meridional circulation in the
near-surface layers of the Sun. The typical velocity inputs used in
solar dynamo models, however, continue to be an analytic fit to the
observed differential rotation profile and a theoretically constructed
meridional circulation profile that is made to match the flow speed
only at the solar surface. Here, we take the first steps toward
the use of more accurate velocity fields in solar dynamo models by
presenting methodologies for constructing differential rotation and
meridional circulation profiles that more closely conform to the best
observational constraints currently available. We also present kinematic
dynamo simulations driven by direct helioseismic measurements for
the rotation and four plausible profiles for the internal meridional
circulation—all of which are made to match the helioseismically
inferred near-surface depth dependence, but whose magnitudes are made to
vary. We discuss how the results from these dynamo simulations compare
with those that are driven by purely analytic fits to the velocity
field. Our results and analysis indicate that the latitudinal shear in
the rotation in the bulk of the SCZ plays a more important role, than
either the tachocline or surface radial shear, in the induction of the
toroidal field. We also find that it is the speed of the equatorward
counterflow in the meridional circulation right at the base of the
SCZ, and not how far into the radiative interior it penetrates, that
primarily determines the dynamo cycle period. Improved helioseismic
constraints are expected to be available from future space missions
such as the Solar Dynamics Observatory and through analysis of more
long-term continuous data sets from ground-based instruments such as
the Global Oscillation Network Group. Our analysis lays the basis for
the assimilation of these helioseismic data within dynamo models to
make future solar cycle simulations more realistic.
Title: Computer Vision for The Solar Dynamics Observatory
Authors: Martens, Petrus C.; Angryk, R. A.; Bernasconi, P. N.; Cirtain,
J. W.; Davey, A. R.; DeForest, C. E.; Delouille, V. A.; De Moortel,
I.; Georgoulis, M. K.; Grigis, P. C.; Hochedez, J. E.; Kasper, J.;
Korreck, K. E.; Reeves, K. K.; Saar, S. H.; Savcheva, A.; Su, Y.;
Testa, P.; Wiegelmann, T.; Wills-Davey, M.
Bibcode: 2009SPD....40.1711M
Altcode:
NASA funded a large international consortium last year to produce
a comprehensive system for automated feature recognition in SDO
images. The data we consider are all AIA and EVE data plus surface
magnetic field images from HMI. Helioseismology is addressed by another
group. We will produce robust and very efficient software modules
that can keep up with the relentless SDO data stream and detect, trace,
and analyze a large number of phenomena, including: flares, sigmoids,
filaments, coronal dimmings, polarity inversion lines, sunspots,
X-ray bright points, active regions, coronal holes, EIT waves, CME's,
coronal oscillations, and jets. In addition we will track the emergence
and evolution of magnetic elements down to the smallest features
that are detectable, and we will also provide at least four full
disk nonlinear force-free magnetic field extrapolations per day. A completely new software element that rounds out this suite is a
trainable feature detection module, which employs a generalized image
classification algorithm to produce the texture features of the images
analyzed. A user can introduce a number of examples of the phenomenon
looked and the software will return images with similar features. We
have tested a proto-type on TRACE data, and were able to "train" the
algorithm to detect sunspots, active regions, and loops. Such a module
can be used to find features that have not even been discovered yet,
as, for example, sigmoids were in the pre-Yohkoh era. Our codes
will produce entries in the Helio Events Knowledge base, and that will
permit users to locate data on individual events as well as carry out
statistical studies on large numbers of events, using the interface
provided by the Virtual Solar Observatory.
Title: The Virtual Solar Observatory: Where Do We Go from Here?
Authors: Gurman, Joseph B.; Bogart, R.; Spencer, J.; Hill, F.; Suarez
Sola, I.; Reardon, K.; Hourcle, J.; Hughitt, K.; Martens, P.; Davey, A.
Bibcode: 2009SPD....40.1508G
Altcode:
The Virtual Solar Observatory (VSO) continues to add features in an
effort to broaden the ways in which it can be used to aid research. We
describe and demonstrate plans for SDO data access (see also the poster
Suarez-Sola et al.), multiple catalog access (Hourclé et al.), and
new capabilities of the IDL VSO_SEARCH function, as well as describing
future capabilities in development and under consideration. Since
the VSO is funded by the Solar Data Analysis Center (SDAC), which will
be undergoing a NASA Senior Review in July, we solicit community input
to help us prioritize this new work: what should we do with the limited
resources available?
Title: The Off-Axis Properties of the Hinode X-Ray Telescope (XRT):
I. Vignetting Effect
Authors: Shin, Junho; Martens, P. C. H.; Golub, L.; Deluca, E. E.
Bibcode: 2009SPD....40.1804S
Altcode:
The X-Ray Telescope (XRT) aboard Hinode has observed a variety
of coronal structures in the range of 34x34 arc min field-of-view
(FOV) covering the full solar disk. In general, most astronomical
telescopes are designed such that the best-focused image of an object
can be achieved at or close to the on-axis position, and the optical
performance varies systematically across the FOV. The Sun is, however,
a large object whose size is about 30 arc min and coronal structures
are observed not only at the disc center but also near the limb. For
this reason, the optical structure of solar telescopes should be
designed with care for improving the uniformity of the angular
resolution over the full FOV. Since there is no unique solution for
successfully implementing this kind of off-axis variation, the optical
properties of the XRT have been examined using the data from the ground
experiments as well as from in-flight observations for the calibration
of systematic variations in the FOV. The vignetting effect is an
important optical characteristic for describing the performance of
the telescope, which reflects the ability to collect incoming light
at different locations and different photon energies. Especially,
the determination of this vignetting effect is one of the essential
calibration steps that should be performed before the observed images
are used for any scientific purposes. Because a component of the
XRT vignetting effect shows a wavelength dependence, special care
should be taken when, for example, performing temperature analyses
with thin and thick filters of flares occurring near the solar
limb. In this presentation, we introduce the results of analysis of
pre-launch calibration data obtained from MSFC/XRCF experiments. The
two-dimensional off-axis variation of the XRT point spread function
(PSF) and its energy dependence will be discussed in detail.
Title: The Unusual Minimum of Cycle 23: Observations and
Interpretation
Authors: Martens, Petrus C.; Nandy, D.; Munoz-Jaramillo, A.
Bibcode: 2009SPD....40.2403M
Altcode:
The current minimum of cycle 23 is unusual in its long duration, the
very low level to which Total Solar Irradiance (TSI) has fallen, and
the small flux of the open polar fields. The deep minimum of TSI seems
to be related to an unprecedented dearth of polar faculae, and hence to
the small amount of open flux. Based upon surface flux transport models
it has been suggested that the causes of these phenomena may be an
unusually vigorous meridional flow, or even a deviation from Joy's law
resulting in smaller Joy angles than usual for emerging flux in cycle
23. There is also the possibility of a connection with the recently
inferred emergence in polar regions of bipoles that systematically
defy Hale's law. Much speculation has been going on as to the
consequences of this exceptional minimum: are we entering another global
minimum, is this the end of the 80 year period of exceptionally high
solar activity, or is this just a statistical hiccup? Dynamo simulations
are underway that may help answer this question. As an aside it must
be mentioned that the current minimum of TSI puts an upper limit in the
TSI input for global climate simulations during the Maunder minimum, and
that a possible decrease in future solar activity will result in a very
small but not insignificant reduction in the pace of global warming.
Title: Properties of a Coronal Loop Structure with EIS, TRACE,
and STEREO
Authors: Scott, Jason; Martens, P. C. H.; McKenzie, D.
Bibcode: 2009SPD....40.1217S
Altcode:
The physical properties of a coronal loop structure are investigated
using three EUV observing instruments. The density, thermal width,
and lifetime of a loop structure are found. Spectral coverage from
EIS provides density and thermal information. Observations from TRACE
and STEREO show the structure's geometry and intensity as a function
of time in multiple wavebands. The isolated loop is straightened
and characterized by a Gaussian fit to perpendicular cross-cuts of
the observed structure. This allows for the extraction of background
subtracted intensities which is important when isolating the coronal
structure for analysis. These background subtracted intensities are
then used to determine the thermal characteristics (temperature,
emission measure ), density, structure width, and lifetime. These
results provide much needed measurements of coronal loop structure.
Title: Towards Better Constrained Solar Dynamo Models: The Velocity
Field And Turbulent Diffusivity Profiles
Authors: Munoz-Jaramillo, Andres; Nandy, D.; Martens, P. C. H.
Bibcode: 2009SPD....40.0405M
Altcode:
The best tool we have for understanding the origin of solar
magnetic variability is the kinematic dynamo model. During the
last decade this type of models have seen a continuous evolution
and have become increasingly successful at reproducing solar cycle
characteristics. However, some of the key ingredients used in dynamo
models remain poorly constrained which allows one to obtain solar-like
solutions by "tuning" the input parameters. Here we present out
efforts to better constrain two of the most important ingredients of
solar dynamo models:: The internal velocity field (meridional flow and
differential rotation) and the turbulent diffusivity. To accomplish
this goal, we formulate techniques to assimilate the latest results
from helioseismology to constrain the velocity fields. We also apply
mixing length theory to the Solar Model S, in conjunction with magnetic
quenching of the turbulent diffusivity, to generate more realistic
effective turbulent diffusivity profiles for kinematic dynamo models. In
essence therefore, we try to address some of these outstanding issues in
a first-principle physics based approach, rather than an ad-hoc manner.
Title: Radiative Vs. Magnetic Flux For The Sun-as-a-star
Authors: Preminger, D.; Nandi, D.; Chapman, G.; Martens, P.
Bibcode: 2009SPD....40.1111P
Altcode:
We study the relationship between full-disk solar radiative flux at
different wavelengths and average solar photospheric magnetic flux
density, using daily measurements from the Kitt Peak magnetograph
and other instruments extending over one or more solar cycles. We
use statistical methods to determine the underlying nature of these
flux-flux relationships. For total solar irradiance and for continuum
radiation from the photosphere, the relationships are non-linear, but
for chromospheric and coronal radiation the relationships are linear. We
find that scatter plots of radiative flux vs Kitt Peak magnetic flux
density show significant variance, due in part to the presence of a
temporal component in some of the flux-flux relationships. This temporal
relationship arises because an active region with high magnetic field
strength evolves, breaking up into small-scale components with low
field strength, while the Kitt Peak magnetic field measurements are
somewhat insensitive to very strong and very weak magnetic fields. We
find that average magnetic flux density measured by Kitt Peak can be
used as a proxy for radiative flux, but with limited accuracy.
Title: Modeling Thermal and Nonthermal Flare Dynamics with HyLoop
Authors: Winter, Henry (Trae) D., III; Martens, P.
Bibcode: 2009SPD....40.3607W
Altcode:
It is generally agreed that the energy for solar flares comes from
stressed magnetic fields. However, the mechanisms that convert that
energy into the heating of the thermal plasma and the acceleration
of nonthermal particles remain a topic of debate. In order to test
models governing flare heating and particle acceleration, state of
the art numerical codes that can simulate both the interaction of
thermal and nonthermal particles in a self-consistent manner and
the electromagnetic emission are required. To this end, the HyLoop
simulation suite was developed. HyLoop combines a hydrodynamic equation
solver with a nonthermal particle tracking code to simulate the thermal
and nonthermal dynamics and emission of solar flares. A sophisticated
imaging package allows for the direct comparison of simulated results
to current and future solar observatories including XRT and RHESSI. In
order to test the effects of pitch-angle distribution on flare dynamics
and emission, a series of flares were simulated with nonthermal
electron beams injected at the loop apex. The pitch-angle distribution
of each beam was described by a single parameter and allowed to vary
from flare to flare. The lightcurves of the flares in XRT bandpasses
showed a distinct signal that was a highly dependent on pitch-angle
distribution. The simulated HXR emission in the 3-6 keV bandpass showed
the formation and evolution of emission sources that corresponded well
to the observations of pre-impulsive flares. The initial conditions
of the simulations necessitated a significantly different physical
interpretation of this motion than previous work. This ability to test
theoretical models of thermal and nonthermal flare dynamics directly
with observations allows for the investigation of a wide range of
physical processes governing the release of energy in solar flares.
Title: The Virtual Solar Observatory—A Resource for International
Heliophysics Research
Authors: Hill, Frank; Martens, Piet; Yoshimura, Keji; Gurman, Joseph;
Hourclé, Joseph; Dimitoglou, George; Suárez-Solá, Igor; Wampler,
Steve; Reardon, Kevin; Davey, Alisdair; Bogart, Richard S.; Tian,
Karen Q.
Bibcode: 2009EM&P..104..315H
Altcode: 2008EM&P..tmp...47H
The Virtual Solar Observatory (VSO) has been developed to allow
researchers, educators, and the general public to access data
and images from the major sources of on-line solar data. The VSO
substantially reduces the effort required to locate disparate data
sets, and removes the need for the user to locate the data and
learn multiple interfaces. The VSO provides a single interface to
about 60 geographically distributed data sets including space- and
ground-based sources. These data sets incorporate several physical
variables including magnetic field, intensity, Doppler velocity, etc.,
and all wavelengths from X-ray to radio. All layers of the sun, from
the interior to the corona, are included. In this paper we describe
the system and present the interface that the user will encounter. We
also discuss future enhancements planned for the system.
Title: Solar Coronal Structure and Stray Light in TRACE
Authors: DeForest, C. E.; Martens, P. C. H.; Wills-Davey, M. J.
Bibcode: 2009ApJ...690.1264D
Altcode: 2008arXiv0808.3980D
Using the 2004 Venus transit of the Sun to constrain a semiempirical
point-spread function (PSF) for the TRACE EUV solar telescope, we
have measured the effect of stray light in that telescope. We find
that 43% of 171 Å EUV light that enters TRACE is scattered, either
through diffraction off the entrance filter grid or through other
nonspecular effects. We carry this result forward, via known-PSF
deconvolution of TRACE images, to identify its effect on analysis
of TRACE data. Known-PSF deconvolution by this derived PSF greatly
reduces the effect of visible haze in the TRACE 171 Å images, enhances
bright features, and reveals that the smooth background component of
the corona is considerably less bright (and hence more rarefied) than
might otherwise be supposed. Deconvolution reveals that some prior
conclusions about the Sun appear to have been based on stray light in
the images. In particular, the diffuse background "quiet corona" becomes
consistent with hydrostatic support of the coronal plasma; feature
contrast is greatly increased, possibly affecting derived parameters
such as the form of the coronal heating function; and essentially all
existing differential emission measure studies of small features appear
to be affected by contamination from nearby features. We speculate on
further implications of stray light for interpretation of EUV images
from TRACE and similar instruments, and advocate deconvolution as a
standard tool for image analysis with future instruments.
Title: Analysis of Two Coronal Loops with Combined TRACE and
SOHO/CDS Data
Authors: Scott, J. T.; Martens, P. C. H.; Cirtain, J. W.
Bibcode: 2008SoPh..252..293S
Altcode: 2008SoPh..tmp..160S
We use an innovative research technique to analyze combined images from
the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric
Observatory (SOHO) and the Transition Region and Coronal Explorer
(TRACE). We produce a high spatial and temporal resolution simulated
CDS raster or "composite" map from TRACE data and use this composite
map to jointly analyze data from both instruments. We show some of
the advantages of using the "composite" map method for coronal loop
studies. We investigate two postflare loop structures. We find cool
material (250 000 K) concentrated at the tips or apex of the loops. This
material is found to be above its scale height and therefore not in
hydrostatic equilibrium. The exposure times of the composite map and
TRACE images are used to give an estimate of another loop's cooling
time. The contribution to the emission in the TRACE images for the
spectral lines present in its narrow passband is estimated by using the
CDS spectral data and CHIANTI to derive synthetic spectra. We obtain
cospatial and cotemporal data collected by both instruments in SOHO
Joint Observations Program (JOP) 146 and show how the combination of
these data can be utilized to obtain more accurate measurements of
coronal plasmas than if analyzed individually.
Title: Effect of the Magnetic Quenching of the Turbulent Diffusivity
in a Mean-Field Kinematic Solar Dynamo
Authors: Muñoz-Jaramillo, A.; Nandy, D.; Martens, P. C.
Bibcode: 2008AGUSMSP41A..09M
Altcode:
The fundamental model used to study the solar dynamo mechanism is
based on the electromagnetic induction equation coupled with Ohm's
law. Apart from mean-field or other phenomenological source terms
(such as a Babcock-Leighton alpha-effect), the resultant dynamo
equation is composed of two terms: An advection and a diffusion
term. Depending on the relative importance of these two terms, the
dynamo can operate either in an advection-dominated or a diffusion
dominated regime. One of the parameters that determine which of these
regimes the dynamo operates in is the effective magnetic diffusivity,
this parameter is expected to be enhanced by convective turbulence
in stellar convection zones. The diffusivity values can range from
104 cm2/s in the radiative zone (where there is no turbulence) to
1012-14 cm2/s in the upper convection zone. The depth dependence of
this effective diffusivity is not particularly well-constrained and
most commonly used profiles involve a relatively low diffusivity in
the convection zone (1010-11 cm2/s) - which makes the dynamo operate
in the advection-dominated regime. The underlying problem here is
that these values of diffusivity are not consistent with theoretical
considerations based on mixing-length theory, which suggest much higher
values of turbulent diffusivity; this would make the dynamo operate
in a diffusion-dominated regime. However, a possible solution to this
inconsistency may be in the quenching effect that strong magnetic
fields have on turbulence. We have recently developed a kinematic solar
dynamo based on a novel numerical technique called the exponential-
propagation method. Using this model, we study magnetic diffusivity
quenching and discuss how its effect may reconcile the theoretically
suggested turbulent diffusivity values with the effective diffusivity
profiles most commonly used in this type of models.
Title: Moving Beyond Time: New VSO Searches
Authors: Davey, A.; Bogart, R.; Gurman, J.; Hill, F.; Hourcle, J.;
Martens, P.; Suarez Sola, I.; VSO Team
Bibcode: 2008AGUSMSP54A..06D
Altcode:
Since its inception the Virtual Solar Observatory (VSO) has supported
a standard set of search parameters for finding data sets of interest,
including instrument, spectral range and observable, all keyed on
a defined time range. The VSO also allows users to derive search
periods based on feature or event catalogs. Recent work on the catalog
infrastructure will enable far more complex science based queries to
derive both stand alone results and also starting points for querying
other data sets. The technical side of this work is presented at
this meeting in 'Event and Feature Catalogs in the Virtual Solar
Observatory' by Joe Hourcle et al. This abstract focuses on the
science made possible by this catalog work and from work to extend
the standard query mechanisms. In the future we will be able to answer
queries such as 'show me data sets suitable for DEM analysis' or 'give
me an image every ten minutes from this instrument.' This effort has
obvious application to handling SDO data.
Title: Still Virtual After All These Years: Recent Developments in
the Virtual Solar Observatory
Authors: Gurman, J. B.; Bogart, R. S.; Davey, A. R.; Hill, F.; Martens,
P. C.; Zarro, D. M.; Team, T. v.
Bibcode: 2008AGUSMSP51B..17G
Altcode:
While continuing to add access to data from new missions, including
Hinode and STEREO, the Virtual Solar Observatory is also being enhanced
as a research tool by the addition of new features such as the unified
representation of catalogs and event lists (to allow joined searches
in two or more catalogs) and workable representation and manipulation
of large numbers of search results (as are expected from the Solar
Dynamics Observatory database). Working with our RHESSI colleagues,
we have also been able to improve the performance of IDL-callable
vso_search and vso_get functions, to the point that use of those
routines is a practical alternative to reproducing large subsets of
mission data on one's own LAN.
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.
Bibcode: 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: Callable Virtual Observatory Functionality: Sample Use Cases
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suárez-Solá, I.; Zarro, D. M.; Davey, A. R.; Martens,
P. C.; Yoshimura, K.
Bibcode: 2007AGUFMSH51A0259G
Altcode:
A virtual observatory with an Application Programming Interface
(API) can become a powerful tool in analysis and modeling. In
particular, an API that integrates time selection on such criteria
as "most recent" and closest to a given absolute time simplifies the
user-end programming considerably. We examine three types of use cases
(nowcasting, data assimilation input, and user-defined sampling rates)
for such functionality in the Virtual Solar Observatory (VSO).
Title: Design Considerations for Data Catalogs
Authors: Hourcle, J.; Suarez-Sola, I.; Davey, A.; Tian, K.; Yoshimura,
K.; Martens, P.; Gurman, J.; Hill, F.; Bogart, R.
Bibcode: 2007AGUFMSH51A0261H
Altcode:
Mission data catalogs are typically built with the specific mission in
mind. This can create challenges when trying to abstract the metadata
to make it useful to other researchers. The deluge of data from new
missions such as STEREO and Hinode have brought in not only issues
in scale, but also complexities due to the difference in these new
experiments in the context of existing norms. We will discuss issues
and use cases to be considered in designing a mission's data systems
in order to better serve the Heliospheric community.
Title: Numerical Simulations of Power Law Heating Functions for
Quiescent Loops: Stability and Observables
Authors: Martens, P. C.; Winter, H. D.; Munetsi-Mugomba, K.
Bibcode: 2007AGUFMSH53A1053M
Altcode:
We present the numerical simulations of quiescent coronal loops
with heating functions that are power law functions of pressure and
temperature. These simulations are made using a time-dependent,
1D hydrodynamics code with heating functions that are treated as
dynamic variables which are constantly re- evaluated during the loops'
lifetimes. These numerical simulations provide a stability test for
the analytical solutions formulated by Martens (2007, submitted) for
the same heating functions. TRACE and XRT datasets are simulated to
determine if present observables can provide adequate information to
discriminate between power law heating functions.
Title: Dealing with Large Dataset Queries in the Virtual Solar
Observatory
Authors: Suarez-Sola, F. I.; Bogart, R.; Davey, A.; Gurman, J. B.;
Hill, F.; Hourcle, J.; Martens, P. C.; Tian, K.; Yoshimura, K.
Bibcode: 2007AGUFMSH51A0260S
Altcode:
The Virtual Solar Observatory (VSO) project presents a solution for
dealing with large dataset queries. One of the main problems arising
from the VSO user community has been managing queries that generate
a large amount of metadata records spanning several providers. Until
now the only way to do this was through painstakingly repeating the
same query for smaller time periods and collecting the information
at each pass. With the solution presented here we are making possible
for users to access data over any arbitrary time period in one single
query, minimizing the metadata generated, and yet allowing the user
to sample either a small subset or the whole.
Title: Flare Loop Top Sources: A diagnostic for non-thermal particle
injection
Authors: Winter, H. D.; Martens, P. C.
Bibcode: 2007AGUFMSH53A1054W
Altcode:
X-ray emitting sources have often been observed at the apex
of post-flare loops by the Hard X-Ray telescope (HXT) onboard the
Japanese Yohkoh satellite and by NASA's Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). In order to investigate the physics
behind the generation of these loop top sources we have coupled a
1D, time-dependent, hydro code with a non-thermal particle transport
code. The hydro code provides temperature and density information of the
target plasma to the particle code and the particle code provides the
dynamic heating of the plasma to the hydro code. Previous work with a
combined has shown that it is possible to create flare loop top emission
sources under certain conditions. In this work we test the relationship
between the pitch angle distribution of the injected non-thermal
particles and the generation of loop top emission source. RHESSI,
HXT and XRT datasets are synthesized from the simulations to provide
a direct link between theoretical work and observables. This work is
supported by NASA grant NAG5-12820.
Title: Combining Hydrodynamics Modeling with Test Particle Tracking
to Improve Flare Simulations
Authors: Winter, H. T.; Martens, P.; Rettenmayer, J.
Bibcode: 2007ASPC..369..501W
Altcode:
Accurate simulations of solar flares require accurately modeling of
both the thermal and non-thermal particle distributions. Most current
flare models concentrate on the evolution of the non-thermal particle
distributions while treating the thermal plasma as static. In order
to improve flare simulations Montana State University has developed
simulation codes that couple the evolution of the non-thermal particle
distribution and the thermal plasma of a flare in a self-consistent
manner.
Title: Temperature Structure of Active Region Coronal Loops as seen
by Hinode
Authors: Scott, Jason; Winter, H.; Cirtain, J.; Martens, P. C.;
McKenzie, D.
Bibcode: 2007AAS...210.9437S
Altcode: 2007BAAS...39..327S
We present preliminary results from Hinode of coronal loops. MSU's
SEMAST code is used to perform differential emission measure analysis
along active region coronal loops. The differential emission measures
are then used to investigate the temperature and density structure
of the loops. The results are then entered into the coronal loop
database and compared to theoretical models for scaling laws and
heating mechanisms. This work is supported by NASA GSRP fellowship
NNG05GK64H
Title: Analytical Solutions for Non-uniformly Heated Coronal Loops:
Numerical Verification
Authors: Martens, Petrus C.; Winter, H. D.; Munetsi-Mugomba, K.
Bibcode: 2007AAS...210.9434M
Altcode: 2007BAAS...39..223M
At last year's SPD meeting at UNH I presented purely analytical
solutions for the temperature structure and scaling laws in static
coronal loops of uniform pressure, for physically motivated heating
functions that varied from mostly footpoint heating, via distributed
heating, to mostly looptop heating. We have verified these
solutions with an adaptive grid 1D hydrodynamic loop code, and found
that for most heating profiles our analytical solutions are in agreement
with the numerical ones within a few percent. This result is remarkable
since the analytical solutions implied some drastic simplifications for
the radiative loss function and the boundary conditions. We also found
that when the heating is concentrated too strongly at the footpoints
static solutions no longer exist and the loop remains dynamic. This
confirms earlier results by Mueller and Karpen. Our results
imply that it is now very easy to construct Differential Emission
Measures (DEMs) for loops consisting of a bundle of elementary strands,
and compare these DEMS with those of actually observed loops through
forward folding. We will apply this method to joint TRACE, Hinode-XRT,
and EIS data.
Title: Science With the Virtual Solar Observatory: Today and Tomorrow
Authors: Hill, F.; Bogart, R. S.; Davey, A. R.; Gurman, J. B.; Hourcle,
J. A.; Martens, P. C.; Reardon, K. M.; Suarez-Sola, I.; Tian, K. Q.;
Yoshimura, K.
Bibcode: 2007AGUSMSM33D..05H
Altcode:
The Virtual Solar Observatory (VSO) was released to the community in
December 2004. It is designed to provide solar physicists with a tool
that allows them to locate and access solar data in an efficient manner,
thus facilitating science studies involving multiple data sets. Examples
of science projects that have been done with the VSO are a study of
halo CME speeds and their visibility in a variety of SOHO data sets,
and the calibration between helioseismic farside signals and the
characteristics of active regions. Future possible projects include
studies of farside coronal mass ejections; the relationship between
subsurface flows and solar wind speeds; statistics of the active region
life cycle; sunspot energetics, and space weather predictors.
Title: The Stars as Suns Project: Recent Results from Solar and
Stellar Dynamo Modeling
Authors: Munoz, Andres; Nandy, D.; Martens, P. C.
Bibcode: 2007AAS...210.9209M
Altcode: 2007BAAS...39..210M
Solar variability controls our space environment and is also believed
to play a role in shaping the global climate. The variability of the Sun
can be traced back to the presence and modulation of magnetic fields --
which has its origin in a dynamo mechanism working in the interior. The
"Stars as Suns" project aims to determine the long-term variability of
Sun, through a combination of stellar magnetic activity observations
of Sun-like stars and theoretical dynamo modeling. Here we present
recent results from solar and stellar dynamo studies that addresses
the goals of this project. This research is funded by a NASA Living
With a Star grant NNG05GE47G to Montana State University.
Title: Long-Term Evolution of Solar Magnetic Activity Derived From
Stellar Proxies
Authors: Nandy, D.; Martens, P. C.
Bibcode: 2007AGUSMSH54B..04N
Altcode:
The variability of the Sun over stellar and planetary evolutionary
timescales may have important consequences for planetary atmospheres
such as the Earth's, including the forcing of global climate and
evolution of life. This solar variability is in part due to the
changing magnetism of the Sun, which has origins in the solar dynamo
mechanism. A novel approach towards determining solar variability
over such long timescales - stretching to billions of years - is
to use Sun-like stars in various evolutionary phases as proxies of
solar activity. In this talk, I will review efforts to derive this
long-term variability of the Sun through theoretical dynamo modelling
and observational analysis of stellar magnetic activity. This work is
funded by the NASA Living With a Star program through grant NNG05GE47G.
Title: Online Catalog for Filament-Sigmoid Correlation
Authors: Merriot, Ivy; Pevtsov, A.; Martens, P.
Bibcode: 2007AAS...210.9504M
Altcode: 2007BAAS...39..224M
A new online catalog correlating H-alpha filaments with SXT sigmoids
gives researchers, teachers and pre-college students the ability to
access digital H-alpha images online that were previously available
only at the physical location of the NSO at Sunspot, NM. This web-based
catalog correlates SOHO's SXT sigmoids from 1993-1998 as described
in a non-online catalog created by Zach Blehm under the direction
of Richard Canfield, MSU-Bozeman, with H-alpha filament activity as
described by Ivy Merriot under the direction of Alexei Pevtsov, NSO,
and Petrus Martens, MSU-Bozeman. The H-alpha images were digitized
from film archives of the Flare Patrol Telescope at Sunspot, NM. Use
of the online catalog will be demonstrated at the poster site with
critical comments encouraged.
Title: On-orbit Measurement Of The Hinode/XRT Point Spread Function
Authors: Weber, Mark A.; Cirtain, J.; Golub, L.; DeLuca, E. E.;
Martens, P.; XRT Team
Bibcode: 2007AAS...210.9416W
Altcode: 2007BAAS...39..220W
The Hinode X-Ray Telescope provides unprecedented observations of
the solar corona in x-rays, due in part to its fine resolution. The
optical point spread function (PSF) was measured before launch at the
NASA X-Ray Calibration Facility to have a FWHM of 0.92 arc-seconds. In
this poster we describe our work to verify the PSF measurements using
on-orbit data. The US XRT team is supported by a contract from NASA to
SAO. Hinode is an international project supported by JAXA, NASA, PPARC,
and ESA. We are grateful to the Hinode team for all their efforts in
the design, development, and operation of the mission.
Title: Low Cost X-ray Optics for Studying StellarDynamo Cycles
Authors: Rust, Thomas; Acton, L.; Kankelborg, C.; Martens, P.
Bibcode: 2007AAS...210.2302R
Altcode: 2007BAAS...39..128R
Comparison of measured coronal X-ray variability over stellar magnetic
dynamo cycles with theoretical models will yield new understanding
of the solar magnetic dynamo cycle. We present the results of a study
comparing surface roughnesses of three candidate materials for use as
glancing angle X-ray reflectors. This work is part of a continuing
effort by MSU's Solar Physics Group and Space Science Engineering
Laboratory (SSEL) to design and build large aperture, low cost X-ray
optics for space experiments. The MSU proposed SADE (Starspot and
Dynamo Explorer) instrument would use arrays of nested Kirkpatrick-Baez
reflectors, called STAX (Sade Telescope Array for X-rays), for long
term measurements of soft X-ray fluxes from about a hundred nearby
solar-type stars. The advantage of the STAX design is that it uses
"off the shelf" materials bent to shape, which is far cheaper and
easier to manufacture than the polished cylindrical optics typically
used in X-ray telescopes. In order to determine whether off the shelf
materials satisfy the stringent surface smoothness requirements for
glancing angle reflectors, we have undertaken an atomic force microscope
investigation of three candidate materials. In addition, we compare
the measured and theoretical diffraction pattern of our existing STAX
test article. This comparison will provide insight into the suitability
of the candidate material, as well as the feasibility of maintaining
proper shape over the surface of the reflector by constraining the
edges in precision machined grooves. This work is supported by a grant
from MSU/NASA EPSCOR.
Title: The REU Program in Solar Physics at Montana State University
Authors: Martens, Petrus C.; Canfield, R. C.; McKenzie, D. M.
Bibcode: 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. 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: Active Region Loops: Temperature Measurements as a Function
of Time from Joint TRACE and SOHO CDS Observations
Authors: Cirtain, J. W.; Del Zanna, G.; DeLuca, E. E.; Mason, H. E.;
Martens, P. C. H.; Schmelz, J. T.
Bibcode: 2007ApJ...655..598C
Altcode:
In this paper, we aim to quantitatively investigate the structure
and time variation of quiescent active region loop structures. We
coordinated a joint program of observations (JOP 146) using TRACE, to
obtain high-cadence EUV images, and SOHO CDS, to obtain spectroscopic
data. Loop intensities are used to determine temperature as a function
of time for a single loop, taking full account of the background
emission. In many locations, the emission measure loci are consistent
with an isothermal structure. However, the results indicate significant
changes in the loop temperature (between 1 and 2 MK) over the 6 hr
observing period. It is possible that the loop structures are composed
of multiple, independently heated strands with sizes less than the
resolution of the imager and spectrometer.
Title: Space Climate and the Solar Stellar connection: What can we
learn from the stars about long-term solar variability?
Authors: Nandy, Dibyendu; Martens, P. C. H.
Bibcode: 2007AdSpR..40..891N
Altcode:
While it is well-known that solar variability influences the
near-Earth Space environment at short timescales of days - an effect
collectively termed as Space Weather, a more subtle influence of solar
variability at longer timescales is also present and just beginning to
be appreciated. Long-term solar forcing and its consequences - which has
come to be known as Space Climate - has important consequences for the
formation and evolution of planetary atmospheres, the evolution of life
and global climate on Earth. Understanding the Sun's variability and
its heliospheric influence at such scales, stretching from decennia
to stellar and planetary evolutionary timescales, is therefore of
fundamental importance. However, our knowledge of this variability,
which is in part due to the evolution of the solar magnetic dynamo,
is limited by direct solar observations which exist only from early
17th Century onwards. In this review we introduce a novel concept -
how the Solar-Stellar connection can be exploited to understand the
long-term variability of the Sun and its influence on Space Climate. We
present some preliminary studies, in which, through theoretical dynamo
modeling and analysis of magnetic activity observations of solar-like
stars at various evolutionary phases relative to the Sun, we show how
the above concept is implemented in practice.
Title: The Trace Telescope Point Spread Function for the 171 Å Filter
Authors: Gburek, S.; Sylwester, J.; Martens, P.
Bibcode: 2006SoPh..239..531G
Altcode: 2006SoPh..tmp...76G
We perform an analysis of the TRACE telescope blur from EUV
images. Theblur pattern is discussed in terms of the telescope
point-spread function (PSF) for the 171 Å filter. The analysis
performed consists of two steps. First, an initial shape for the
PSF core is determined directly from TRACE EUV images. Second,
the blind-deconvolution method is used for obtaining the final PSF
shape. The PSF core peak is fitted by analytical functions to determine
its parametric characteristics. The determined PSF includes the core
central peak and peaks caused by diffraction effects inherent in TRACE
EUV data. The diffraction portion of the PSF is studied theoretically
in the Fraunhofer diffraction limit. The temperature dependence of the
TRACE PSF shape is investigated for a selected temperature range. We
also discuss general properties of the obtained PSF and its possible
applications.
Title: The current and future roles of virtual observatories serving
the heliophysical data environment
Authors: Davey, A. R.; Bogart, R. S.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Hourcle, J. A.; Martens, P. C.; Suarez-Sola, I.; Tian, K.;
Yoshimura, K.
Bibcode: 2006AGUFMSM11C..05D
Altcode:
The Virtual Solar Observatory is just one of a growing number of
virtual observatories that serve heliophysics data. We discuss the
current capabilities of these virtual observatories, their roles in
data archiving, discovery, quality assurance, assimilation, encouraging
standards and in facilitating science. We also discuss the realistic
goals virtual observatories should have, in fulfilling the demands of
the current and near future heliophysics data environment.
Title: Simulation of Hard X-ray Looptop Sources in Solar Flares
Authors: Winter, H. D.; Martens, P. C.
Bibcode: 2006AGUFMSH23A0332W
Altcode:
Many solar flares show a non-thermal X-ray emitting source at the
apex of the post-flare loop. This behavior has been observed both by
the Hard X-Ray telescope (HXT) on board the Japanese Yohkoh satellite
and by NASA's Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI). By combining thermal plasma and non-thermal particle numerical
models we are able to simulate thermal and non-thermal flare emission
under a variety of increasingly realistic solar conditions. We find
that looptop sources can be generated by a combination of magnetic
mirroring of non-thermal particles and heated chromospheric material
flowing upward from both legs of the loop. In this work we inject
non-thermal, energetic particles with varying pitch angle distributions
and spectral indices into plasmas contained in loops defined by an
analytical magnetic field model. We monitor the evolution of these
loops over time as it would be seen by HXT and RHESSI and compare
the simulated emission to observations of flare loops. This work is
supported by NASA grant NAG5-12820.
Title: The Virtual Solar Observatory and the Heliophysics Meta-Virtual
Observatory
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suàrez-Sola, I.; Zarro, D. M.; Davey, A. R.; Martens,
P. C.; Yoshimura, K.; Reardon, K. M.
Bibcode: 2006AGUFMSM21A0246G
Altcode:
The Virtual Solar Observatory (VSO) has survived its infancy and
provides metadata search and data identification for measurements from
45 instrument data sets held at 12 online archives, as well as flare
and coronal mass ejection (CME) event lists. Like any toddler, the VSO
is good at getting into anything and everything, and is now extending
its grasp to more data sets, new missions, and new access methods
using its application programming interface (API). We discuss and
demonstrate recent changes, including developments for STEREO and SDO,
and an IDL-callable interface for the VSO API. We urge the heliophysics
community to help civilize this obstreperous youngster by providing
input on ways to make the VSO even more useful for system science
research in its role as part of the growing cluster of Heliophysics
Virtual Observatories.
Title: Stars as Suns: Unravelling Long-term Solar Variability by
Stellar Dynamo Modeling
Authors: Martens, P. C.; Nandi, D.; Munoz, A.
Bibcode: 2006AGUFMSH21B..03M
Altcode:
We have developed a very time-efficient 2.5 D dynamo code to carry out
simulations of stars that are very similar, but not identical to the
Sun. The main goal is to better understand the nature and evolution
of the solar dynamo by studying how its main characteristics (period,
activity level) vary within the parameter space close to the observed
or assumed input parameters and profiles that reproduce the solar
dynamo, and by comparing these results with the periods, X-ray and
Ca HK activity levels, that are known for many Sun-like stars. In
particular we will carry out simulations for both the Babcock-Leighton
(surface) and the mean field (convection zone) alpha-effect to determine
which one better reproduces the dynamo periods and activity levels of
Sun-like stars, and thereby is the more likely mechanism operating
in stellar (and solar) dynamos. The relevance of this work is that
a better understanding of the evolution of the dynamo mechanism will
enable us to make more confident predictions for the Sun's variability
spanning from solar cycle-like timescales to stellar evolutionary
timescales. This will provide more reliable input for space weather
and Earth's climate forecasters and increases our understanding of
the long term evolution of the Sun's magnetic field and its subsequent
effect on the Sun-Earth connection.
Title: A Time Delay Model for Solar and Stellar Dynamos
Authors: Wilmot-Smith, A. L.; Nandy, D.; Hornig, G.; Martens, P. C. H.
Bibcode: 2006ApJ...652..696W
Altcode:
Magnetohydrodynamic dynamos operating in stellar interiors produce
the diverse range of magnetic activity observed in solar-like
stars. Sophisticated dynamo models including realistic physics of
convection zone flows and flux tube dynamics have been built for
the Sun, for which appropriate observations exist to constrain such
models. Nevertheless, significant differences exist in the physics that
the models invoke, the most important being the nature and location
of the dynamo α-effect and whether it is spatially segregated from
the location of the Ω-effect. Spatial segregation of these source
layers necessitates a physical mechanism for communication between
them, involving unavoidable time delays. We construct a physically
motivated reduced dynamo model in which, through the use of time delays,
we mimic the generation of field components in spatially segregated
layers and the communication between them. The model can be adapted
to examine the underlying structures of more complicated and spatially
extended numerical dynamo models with diverse α-effect mechanisms. A
variety of dynamic behaviors arise as a direct consequence of the
introduction of time delays in the system. Various parameter regimes
give rise to periodic and aperiodic oscillations. Amplitude modulation
leads to episodes of reduced activity, such as that observed during
the Maunder minima, the length and duration of which depend on the
dynamo number. Regular activity is more easily excited in the flux
transport-dominated regime (when the time delay is smaller than the
dissipative timescale), whereas irregular activity characterizes
solutions in the diffusion-dominated regime (when the time delay is
larger than the dissipative timescale).
Title: Unravelling Long-Term Solar Variability: The Stars As Suns
Project
Authors: Nandy, D.; Martens, P. C. H.
Bibcode: 2006IAUJD...8E..13N
Altcode:
It is well known that solar variability influences the near-Earth
Space environment at short timescales of days - an effect collectively
termed as Space Weather. A lesser known and more subtle influence of
solar variability at longer timescales, is however, just beginning
to be appreciated. This long-term solar forcing, which is sometimes
referred to as Space Climate, has important consequences for the
formation and evolution of planetary atmospheres, evolution of life
and global climate on Earth. Understanding the Sun's variability and
its heliospheric influence at such scales stretching from millennia
to stellar evolutionary timescales is therefore of fundamental
importance. However, our understanding of this variability, which is
partly due to the evolution of the solar magnetic dynamo, is limited by
solar observations which exist only from early 17^th Century onwards. In
this talk I will review the "Stars as Suns" project - in which we
take a novel approach to unravelling long-term solar variability
through theoretical modelling and magnetic activity observations of
Sun-like stars, which are at various evolutionary phases relative to
the Sun. The "Stars as Suns" project is funded by the NASA Living With
a Star program through grant NNG05GE47G.
Title: A Surprising New Take on Scaling Laws
Authors: Martens, Petrus C.
Bibcode: 2006SPD....37.1705M
Altcode: 2006BAAS...38R.246M
I have derived analytical solutions for the 1D energy equation for
static solar coronal loops for a set of heating functions parametrized
as power-laws. This formalism yields a large set of solutions including
loops that are mainly heated at the footpoints, at the looptop, and
uniformly. I found that the analytical solutions are indistinguishable
from numerical solutions produced the MSU 1D hydro-code.I also find that
there is very little difference between the temperature profiles for
these very different heating functions. A surprising result is though
that the constant of proportionality in the classic RTV scaling law
(PL T^3) depends strongly on the heating function used, yielding a
potential diagnostic for the type of heating function at work in the
solar corona -- assuming most loops have the same heating profile. Loops
heated at the base have a large constant of proportionality, leading to
overdense loops compared to the case of uniform heating, and v.v. for
loops heated at the top -- an effect that had already been noticed
in numerical solutions but has been inaccurately been interpreted
as a violation of the scaling law.This work is supported by NASA
Grant NAS5-38099 for the Transition Region and Coronal Explorer, and
NNG04EA00C for the Atmospheric Imaging Assembly through subcontracts
with Lockheed-Martin Solar and Astrophysics Lab.
Title: Implementation of an Exponential Propagation Method to
Numerically Solving the 2.5 D Stellar Dynamo Equations
Authors: Munoz, Andres; Martens, P. C.; Nandy, D.
Bibcode: 2006SPD....37.1202M
Altcode: 2006BAAS...38Q.240M
Magnetic fields in stars such as the Sun originate via a MHD dynamo
mechanism working in their interior. A complete understanding of the
dynamo mechanism, which involves complex and non-linear interactions
between plasma flows and magnetic fields, remains an elusive and
outstanding problem in Astrophysics. As an integral step in a study of
stellar dynamos, part of a new MSU project entitled "Stars as Suns:
Unraveling Long-term Solar Variability by Stellar Dynamo Modeling",
a numerical solution for the 2D dynamo equations is being developed
that uses an exponential propagation method, in which, the exponential
is approximated using a projection into a Krylov subspace. As has
been found in other work, this kind of numerical scheme presents a
promising alternative to explicit schemes, since it is not subject
to the CFL condition, and to implicit methods, since an iteration
using the projection onto a Krylov subspace converges faster than an
equivalent solution of the implicit formulation. Here, we outline our
preliminary efforts towards developing this new numerical scheme for
addressing the stellar dynamo problem.This research is supported by
NASA Grant NNGO5GE47G to MSU.
Title: Testing the Methods Used to Determine Loop Temperature Profiles
Authors: Neal, Kerry; Winter, H. D.; Martens, P. C.
Bibcode: 2006SPD....37.0113N
Altcode: 2006BAAS...38..217N
Determining the heating profile of coronal loops is still a fundamental
problem in solar physics. In order to determine the heating profile of
three candidate loops we measure their temperature profiles by employing
multiple techniques; filter ratios, line ratios, emission measure
(EM) loci and differential emission measure (DEM) analysis. We find
that the temperature responses are largely influenced by the method of
analysis employed. We compare the accuracy of these methods by creating
simulations of known heating profiles along loops and repeat the methods
of analysis that were used on the observed loops. In the numerical
models the line of sight and ionization non-equilibrium effects can
be taken into account and their effects on temperature measurement
demonstrated. Results from the upcoming Atmospheric Imaging Assembly
are also simulated in preparation for the upcoming mission.This work
was sponsored by NASA GSFC Contract NNG04EA00C for the Atmospheric
Imaging Assembly and NSF REU grant ATM-0243923.
Title: Coronal Loop Database
Authors: Scott, Jason; Martens, P.
Bibcode: 2006SPD....37.0120S
Altcode: 2006BAAS...38R.218S
We have created a database of all coronal loops for which we have been
able to find measurements in the published open literature, from Skylab
to TRACE. The loops and a set of their physical parameters are stored
in the form of an IDL structure. The physical parameters considered
are: the loop half length, the electron density of the loop, and the
loop temperature. The studies that produced the physical parameters
along with their observing instruments are recorded in the database
as well. Correlations of pressure vs. temperature and heating rates
vs. loop length are investigated. Instrumental selection effects are
also considered. The loop parameters and correlations derived from the
loop database are then compared to theoretical and numerical models
for scaling laws and heating rates.This work is supported by NASA GSRP
fellowship NNG05GK64H
Title: The Hi-C Sounding Rocket Experiment
Authors: Golub, Leon; Cirtain, J.; DeLuca, E.; Nystrom, G.; Kankelborg,
C.; Klumpar, D.; Longcope, D.; Martens, P.
Bibcode: 2006SPD....37.0605G
Altcode: 2006BAAS...38R.226G
The High-resolution Coronal Imager, Hi-C, is a pathfinder
mission designed to place significant new limits on theories of
coronal heating and dynamics by measuring the structures at size
scales relevant to reconnection physics. The Hi-C instrument uses
normal-incidence EUV multilayer technology, as developed in the
NIXT and TRACE programs. A dual-channel long focal-length telescope
and large format back-illuminated CCD camera provide spectroscopic
imaging of the corona at 0.1 arcsec resolution.The main objective of
the Hi-C investigation is to determine the geometric configuration and
topology of the structures making up the inner corona. The secondary
objective is to examine the dynamics of those structures, within the
constraints of the 300-seconds of observing time available from a
sounding rocket. The mission is designed to study the mechanisms for
growth, diffusion and reconnection of magnetic fields, and to help
understand the coupling of small-scale dynamic and eruptive processes
to large-scale dynamics.Hi-C will benefit from a unique coordinated
observation opportunity with investigations such as AIA on SDO, XRT on
Solar-B, and STEREO. Hi-C will address basic plasma physics science
goals of the SSSC by observing the small-scale processes that are
ubiquitous in hot magnetized coronal plasma. The scientific objectives
of Hi-C are central to the SSSC goal of understanding the Sun's activity
and its effects on the terrestrial environment, by providing unique
and unprecedented views of the dynamic activity in the solar atmosphere.
Title: The Virtual Solar Observatory and the Heliophysics Meta-Virtual
Observatory
Authors: Gurman, Joseph B.; Bogart, R.; Tian, K.; Hill, F.;
Suárez-Sola, I.; Martens, P. C.; Yoshimura, K.; Davey, A.; Dimitoglou,
G.; Hourclé, J.
Bibcode: 2006SPD....37.0305G
Altcode: 2006BAAS...38..222G
The Virtual Solar Observatory (VSO) is now able to search for solar
data ranging from the radio to gamma rays, obtained from space and
groundbased observatories, from 26 sources at 12 data providers, and
from 1915 to the present. The solar physics community can use a Web
interface or an Application Programming Interface (API) that allows
integrating VSO searches into other software, including other Web
services. Over the next few years, this integration will be especially
obvious as the NASA Heliophysics division sponsors the development of
a heliophysics-wide virtual observatory (VO), based on existing VO's
in heliospheric, magnetospheric, and ionospheric physics as well as
the VSO. We examine some of the challenges and potential of such a
"meta-VO."
Title: Multi-Instrument Simulations of Solar Flares Using Non-Thermal
Particle Tracking
Authors: Winter, Henry D., III; Martens, P. C.
Bibcode: 2006SPD....37.1313W
Altcode: 2006BAAS...38..242W
We are combining thermal plasma and non-thermal particle numerical
models in order to improve flare simulations. Non-thermal particle
collision models provide heating and momentum deposition for the
thermal plasma. The thermal plasma models in turn provide an evolving
temperature and density structure for the non-thermal particles'
target plasma. This allows us to simulate thermal and non-thermal flare
emission under a variety of increasingly realistic solar conditions. In
this work we inject non-thermal, energetic particles into plasmas
contained in loops defined by three different analytic magnetic field
models. We monitor the evolution of these loops over time as it would
be seen by the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI), The Transition Region and Coronal Explorer (TRACE), the
Soft X-ray Telescope (SXT) and the Hard X-ray Telescope (HXT) onboard
the Yohkoh satellite as well as the upcoming X-Ray Telescope (XRT)
onboard Solar-B and the Atmospheric Imaging Array (AIA) on the Solar
Dynamics Observatory.This work is supported by NASA grant NAG5-12820.
Title: The VSO at Two and a Half
Authors: Gurman, J. B.; Hourclé, J. A.; Bogart, R. S.; Tian, K.;
Hill, F.; Suarez-Sola, I.; Wampler, S.; Davey, A. R.; Martens, P. C.;
Yoshimura, K.; Zarro, D. M.
Bibcode: 2006AGUSMSM31B..03G
Altcode:
The Virtual Solar Observatory (VSO) has survived its infancy and
provides metadata search and data identification for 26 data sets
held at 12 online archives, as well as flare and coronal mass ejection
(CME) event lists. Like any toddler, the VSO is good at getting into
anything and everything, and is now extending its grasp to more data
sets and providers, new missions, and new access methods using its
application programming interface (API). We discuss recent changes,
including developments for STEREO and SDO, and an IDL-callable interface
for the VSO API. We urge the heliophysics community to help civilize
this obstreperous youngster by providing input on ways to make the
VSO even more useful for system science research.
Title: The EUV Unresolved Corona
Authors: Cirtain, Jonathan; Martens, P. C. H.; Acton, L. W.; Weber,
Mark
Bibcode: 2006SoPh..235..295C
Altcode:
The unresolved corona for three active regions (ARs) above the solar
limb is investigated. Intensities measured for ions formed above 1 MK
are presented as a function of height above the solar surface. The
observed decrease in intensity with altitude is found to be best
fit by an exponential. Furthermore, this exponential decrease is
approximately the decrease in emission expected for a hydrostatic
planar geometry atmosphere, where the scale height temperature is
dependent on the dynamics of the AR. For two of the ARs analyzed, we
have found that the best-fit temperature derived from the exponential
fits is consistent with an isothermal hydrostatic unresolved corona.
Title: Unraveling long-term solar variability and its impact on
space climate: The stars as suns project
Authors: Nandy, D.; Martens, P. C. H.
Bibcode: 2006ilws.conf..158N
Altcode:
It is well-known that solar variability influences the near-Earth
Space environment at short timescales of days - an effect collectively
termed as Space Weather. A lesser known and more subtle influence of
solar variability at longer timescales is however just beginning to be
appreciated. This long-term solar forcing, which is sometimes referred
to as Space Climate, has important consequences for the formation
and evolution of planetary atmospheres and the evolution of life and
global climate on Earth. Understanding the Sun's variability and its
heliospheric influence at such scales stretching from millennia to
stellar evolutionary timescales is therefore of fundamental importance
and a very promising area of future research. However, our understanding
of this variability, which is in part connected to the evolution of the
solar magnetic dynamo, is limited by continuous sunspot observations,
which exist only from the early 17th Century onwards. In this paper we
review the "Stars as Suns" project - in which we take a radically new
approach to unraveling long-term solar variability through theoretical
modeling and magnetic activity observations of Sun-like stars, which
are at various evolutionary phases relative to the Sun.
Title: Multithermal Analysis of a SOHO/CDS Coronal Loop
Authors: Schmelz, J. T.; Martens, P. C. H.
Bibcode: 2006ApJ...636L..49S
Altcode: 2005astro.ph.11487S
The observations from 1998 April 20 taken with the Coronal Diagnostics
Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) of
a coronal loop on the limb have shown that the plasma was multithermal
along each line of sight investigated, both before and after background
subtraction. The latter result relied on emission measure (EM) loci
plots, but in this Letter, we used a forward-folding technique to
produce differential emission measure (DEM) curves. We also calculate
DEM-weighted temperatures for the chosen pixels and find a gradient
in temperature along the loop as a function of height that is not
compatible with the flat profiles reported by numerous authors for
loops observed with the EUV Imaging Telescope (EIT) on SOHO and
the Transition Region and Coronal Explorer (TRACE). We also find
discrepancies in excess of the mathematical expectation between some
of the observed and predicted CDS line intensities. We demonstrate
that these differences result from well-known limitations in our
knowledge of the atomic data and are to be expected. We further show
that the precision of the DEM is limited by the intrinsic width of
the ion emissivity functions that are used to calculate the DEM, which
for the EUV lines considered is of the order dlogT = 0.2-0.3. Hence,
we conclude that peaks and valleys in the DEM, while in principle not
impossible, cannot be confirmed from the data.
Title: The virtual solar observatory
Authors: Young, C. A.; Gurman, J. B.; Dimitoglou, G.; Hourcle, J.;
Bogart, R. S.; Tian, K.; Hill, F.; Suarz-Sola, I.; Wampler, S.;
Martens, P.; Yoshimura, S.; Davey, A.
Bibcode: 2006ilws.conf..226Y
Altcode:
The recent explosion of data quantity and complexity has lead to the
need for a new way to make data available, the virtual observatory. The
Virtual Solar Observatory (VSO) provides a versatile means for solar
physicists to discover and share the growing sources of data. We present
the development of the VSO, show the system in action and discuss how
data users and data providers can benefit from it.
Title: TRACE and SXT Responses to Flare Simulations Using Combined
Non-Thermal Particle and Hydrodynamic Modeling
Authors: Winter, H. D.; Martens, P.; Rettenmayer, J.
Bibcode: 2005AGUFMSH13A0296W
Altcode:
Thermal plasma and non-thermal particle numerical models are combined
in order to improve flare simulations. The non-thermal particle
collision models provide heating and momentum deposition for the
thermal plasma. The thermal plasma models in turn provide an evolving
temperature and density structure for the non-thermal particles target
plasma. This allows for the simulation of thermal and non-thermal flare
emission under a variety of increasingly realistic solar conditions. The
model flare emission is then folded through the response functions of
solar observatories in order to provide simulated data that can be
compared to observational results. Using this technique, Transition
Region and Coronal Explorer (TRACE) and Soft X-ray Telescope (SXT)
simulations are made. This provides a means to verify the predictions
of multiple flare models with observed flare behavior. This work is
supported by NASA grant NAG5-12820
Title: Flare Prediction and the Unresolved Corona
Authors: Weber, M.; Cirtain, J.; Martens, P.
Bibcode: 2005AGUFMSH13A0280W
Altcode:
Discovery of the precursors to flare onset are paramount to the
increased need for accurate space weather prediction. A potential
indicator for flaring activity may be the temperature structure of
the active region background emission. The active region background,
or unresolved active region corona (UARC), can be modeled using a
hydrostatic model for the density stratification as a function of
altitude. Exponential decreases in the intensity of EUV emission above
the limb and within active regions have been used to determine the
scale-height temperature of the UARC. ``Quiescent'' active region data
was examined, and the scale-height temperature determined was found to
be constant in time and slowly decreasing with distance from the center
of the active region. ``Flaring'' active region emission was found
to be quite different. Prior to the onset of the flare, the estimated
scale height temperature was nearly constant. Just before the peak in
the GOES 8 x-ray flux, it was determined to be multithermal, varying
by as much as 0.7 MK over the multiple spectral lines observed. The
scale-height temperatures were all observed to increase before the
flare and reached a maximum subsequent to the GOES 8 x-ray peak.This
work is supported under the TRACE mission, NASA contract SP02H8201R.
Title: REU program in Solar Physics at Montana State University
Authors: Martens, P. C.; Canfield, R. C.; McKenzie, D. M.
Bibcode: 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: The Amplitude of Stellar X-ray Cycles
Authors: Martens, P. C. H.; Chattterjee, P.; Saar, S. H.; Acton,
L. W. A.
Bibcode: 2005AAS...20710405M
Altcode: 2005BAAS...37R1334M
A decade worth of data from the Soft X-ray Telescope onboard the
Japan/US/UK mission Yohkoh shows that the Sun has a variation of
non-flaring disk-integrated soft X-ray emission (0.4 - 2.4 keV) of
about a factor 30 over its sunspot cycle. To date no cyclic variation
of that magnitude has been observed in other late-type stars. We
show that this negative result is partly explained by the inclusion of
EUV emission in stellar observations done with ROSAT: we calculated
what the solar signal would be if observed in the ROSAT passband and
found a cycle amplitude of a factor two to three. That leaves open
the question of the cycle amplitude in soft X-rays for solar-type
stars. To adress this we analysed ROSAT data for the energy band
above the C-K edge, but found no sufficiently frequent observations of
individual stars. The next best approach is to compare the measured soft
X-ray flux for singly observed stars with the average flux predicted
from the star's Rossby number: if cycles with amplitudes as large as
that of the Sun exist, the residual fluxes should be statistically
significant. From a sample of about 15 single and cyclic late-type
stars (as evidenced from Ca-K data) we find that with 99.6% certainty
the residual fluxes are due to X-ray cycles that are similar to or
greater than that of the Sun.
Title: The Magnetic Activity of Solar-like Stars at Different
Main-Sequence Ages
Authors: Lakatos, S. L.; Nandy, D.; Martens, P.
Bibcode: 2005AAS...20711104L
Altcode: 2005BAAS...37.1342L
We report on a study of modeling stellar magnetic activity inferred
through CaII H+K and ROSAT X-ray emission. The purpose of this project
is to create a subset of stars with similar properties to the Sun,
but with a wide range of ages (0.6 - 10 Gyrs); to study the CaII H+K
emission data and decipher how the stars' emission changes with age;
and to compare the X-ray activity to the CaII H+K activity. The ultimate
goal of this project is to determine and use the relationships between
the stellar parameters to understand the evolution of the magnetic
dynamo from an younger Sun to an older Sun. This research is supported
by a NSF Research Experience for Undergraduates grant ATM-0243923 and
a NASA Living With a Star grant NNG05GE47G to Montana State University.
Title: Dynamics of Active Region Loops: Temperature Measurements as
a function of Time
Authors: Cirtain, J. J.; del Zanna, G.; Mason, H.; Deluca, E.;
Martens, P.
Bibcode: 2005AGUFMSH44A..03C
Altcode:
The combination of moderate resolution EUV spectroscopy and high
resolution narrow band filter images provides the most accurate
measure of temperature and density for coronal loops to date. We will
demonstrate our technique for combining the data sets from the Coronal
Diagnostic Spectrometer on SoHO and the Transition Region and Coronal
Explorer. Background subtracted spectral intensities are used to
determine the temperature of coronal loops and the TRACE images help
determine the loop cross-section, temporal variability, and filling
factor. The resulting temperature profiles for multiple positions along
a loop leg are determined using the EM LOCI method, and a technique for
determining whether a single temperature can characterize the plasma is
also presented. We compare the results of our study to current models.
Title: Low-order stellar dynamo models
Authors: Wilmot-Smith, A. L.; Martens, P. C. H.; Nandy, D.; Priest,
E. R.; Tobias, S. M.
Bibcode: 2005MNRAS.363.1167W
Altcode: 2005MNRAS.tmp..855W
Stellar magnetic activity - which has been observed in a diverse set
of stars including the Sun - originates via a magnetohydrodynamic
dynamo mechanism working in stellar interiors. The full set of
magnetohydrodynamic equations governing stellar dynamos is highly
complex, and so direct numerical simulation is currently out of
reach computationally. An understanding of the bifurcation structure,
likely to be found in the partial differential equations governing such
dynamos, is vital if we are to understand the activity of solar-like
stars and its evolution with varying stellar parameters such as rotation
rate. Low-order models are an important aid to this understanding,
and can be derived either as approximations of the governing equations
themselves or by using bifurcation theory to obtain systems with the
desired structure. We use normal-form theory to derive a third-order
model with robust behaviour. The model is able to reproduce many of the
basic types of behaviour found in observations of solar-type stars. In
the appropriate parameter regime, a chaotic modulation of the basic
cycle is present, together with varying periods of low activity such
as that observed during the solar Maunder minima.
Title: Improving Flare Simulations by Combining Hydrodynamics Modeling
with Stochastic Particle Transport
Authors: Winter, H. T.; Martens, P.
Bibcode: 2005AGUSMSP21A..11W
Altcode:
Currently flare models include heating due to non-thermal particle
collisions as analytical, and often static, inputs to numerical
hydrodynamics codes. While this has aided in our understanding of
flare dynamics, it does not adequately represent the complexity of the
interaction between thermal and non-thermal particles in a flaring
region and cannot completely describe multi-wavelength observations
of solar flares. In order to improve the current state-of-the-art
flare simulations, we are combining thermal and stochastic non-thermal
numerical modeling codes in order to simulate flare emission under a
variety of theoretical and realistic solar conditions. The theoretical
flare emission is then folded through the response functions of solar
observatories in order to provide theoretical data that can be compared
to observational results. This provides a means to test multiple flare
models with observed flare behavior. This work was supported by NASA
grant NAG5-12820
Title: CME Population Distributions: Science Facilitated by the VSO
Authors: Davey, A.; Wills-Davey, M.; Gurman, J.; Bogart, R.;
Dimitoglou, G.; Hill, F.; Hourcle, J.; Martens, P.; Suarez Sola, I.;
Tian, K.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSP23A..09D
Altcode:
The Virtual Solar Observatory (VSO) exists to simplify and unify
access to Solar Physics data. It provides a single interface to
a broad spectrum of data types and sources which previously would
have required considerable effort to collect. Using this ability to
combine data sources, we access the entire SOHO/LASCO CME catalog and
compare it with GOES observations of X-ray flares. Because we consider
these data in their entirety, we find several instances where the
results of less extensive studies may show unintentional selection
effects. As a subpopulation, we specifically consider LASCO-observed
halo CMEs. In agreement with previous studies, we find halo CMEs are
the bulk of the fastest events. This selection effect is consistent
with randomly-distributed CMEs extending over wide angles (>120
degrees). We also examine the lack of slower halo CMEs; otherwise
randomly-distributed events are rarely Earth-directed. While geometric
and Thomson scattering issues make less-energetic halo CMEs hard to
detect, this dearth of slow observations may represent an additional
seeing threshold. The lack of low-energy detections may account for the
disparity in LASCO.s prediction of Kp ≥ 6 vs. Kp ≥ 5 geomagnetic
storms.
Title: The Virtual Solar Observatory: Still a Small Box
Authors: Gurman, J. B.; Bogart, R. S.; Davey, A. R.; Dimitoglou, G.;
Hill, F.; Hourclé, J. A.; Martens, P. C.; Suárez-Sola, I.; Tian,
K. Q.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSH43B..03G
Altcode:
Two and a half years after a design study began, and a year and a
half after development commenced, version 1.0 of the Virtual Solar
Observatory (VSO) was released at the 2004 Fall AGU meeting. Although
internal elements of the VSO have changed, the basic design has
remained the same, reflecting the team's belief in the importance of
a simple, robust mechanism for registering data provider holdings,
initiating queries at the appropriate provider sites, aggregating the
responses, allowing the user to iterate before making a final selection,
and enabling the delivery of data directly from the providers. In
order to make the VSO transparent, lightweight, and portable, the
developers employed XML for the registry, SOAP for communication
between a VSO instance and data services, and HTML for the graphic
user interface (GUI's). We discuss the internal data model, the API,
and user responses to various trial GUI's as typical design issues for
any virtual observatory. We also discuss the role of the "small box"
of data search, identification, and delivery services provided by the
VSO in the larger, Sun-Solar System Connection virtual observatory
(VxO) scheme.
Title: Building a Virtual Solar Observatory: Lessons Learned
Authors: Bogart, R. S.; Tian, K. Q.; Davey, A.; Dimitoglou, G.;
Gurman, J. B.; Hill, F.; Hourclé, J.; Martens, P. C.; Suárez-Sola,
I.; Wampler, S.; Yoshimura, K.
Bibcode: 2005AGUSMSH51B..05B
Altcode:
Two years into its development, the VSO has emerged from a drawing board
concept into a full-fledged data query and data delivery system serving
the Solar Physics community. Throughout its development, the VSO has
lived up to its `small box' motto and has built light-weight servers
that can easily run on a desktop or laptop. The two basic functions
of the VSO are data query and data delivery. For these functions, the
VSO servers act like switchboards, dispatching query/data requests
to relevant data providers. More important, these servers present
an abstraction that integrates diverse data archives, thus reducing
complexity. The design of the VSO has evolved during its implementation
in response to difficulties and user feedback. We discuss the changes
in areas such as the data model, user interface, and performance. These
lessons should be of interest to people designing and building other
virtual observatories. We also discuss challenges and opportunities
we foresee as the VSO becomes a significant and enabling research tool.
Title: EUV Observations of Active Region Dynamics
Authors: Deluca, E. E.; Cirtain, J. W.; del Zanna, G.; Mason, H. E.;
Martens, P. C.; Schmelz, J.; Golub, L.
Bibcode: 2005AGUSMSP33A..03D
Altcode:
Data collected during SoHO JOP 146, in collaboration with TRACE, is
used to investigate the physical characteristics of coronal active
region loops as a function of time and position along and across
loop structures. These data include TRACE images in all three EUV
passbands, and simultaneous CDS spectroscopic observations. Preliminary
measurements of the loop temperature both along the loop half-length
and loop cross-section are presented as a function of time. We will
show the temperature and density profiles of several structures as a
function of position, show changes in temperature and density with time
and characterize the coronal background emission. Questions raised
by these results will be greatly advanced with the high resolution
spectra available from the EIS on Solar-B.
Title: An Hour in the Life of Coronal Loops
Authors: Cirtain, J. W.; Scott, J. T.; Martens, P. C. H.; Winter, H. D.
Bibcode: 2004AAS...205.1011C
Altcode: 2004BAAS...36R1351C
Application of a new physics-based background subtraction method has
allowed for investigation of the physical properties of coronal loops
with unprecedented accuracy. We determine the temperature, emission
measure, and pressure along multiple EUV coronal loops as a function of
time and space, as well as their cross-section. With these measures of
physical observables we have calculated the rate of change of pressure
for the loops.
Title: Doing Science with the VSO: Signatures of CME Initiation
Authors: Davey, A. R.; Wills-Davey, M.; Gurman, J. B.; Bogart, R.;
Tian, K. Q.; Martens, P.; Yoshimura, K.; Hill, F.; Suarez-Sola, I.;
Hourclé, J.; Dimitoglou, G.; Wampler, S.
Bibcode: 2004AGUFMSH21B0414D
Altcode:
The Virtual Solar Observatory (VSO) was designed to simplify and unify
access to solar physics data. It provides a single interface to a broad
range of data types and sources which previously would have required
considerable effort to collect one by one. By combining access to online
data sources with published scientific catalogs, the VSO can facilitate
new science. This study seeks to investigate whether signatures of
coronal mass ejection (CME) initiation can be used to constrain CME
initiation models. We selected events from the SOHO/LASCO CME catalog,
generated a time window between the calculated CME ``start time" and
the first observation of the CME in LASCO C2, and examined EIT ``CME
Watch" and H-alpha observations identified by a VSO query as falling in
the specified time windows. We prioritized the EUV data by selecting
those events for which GOES data indicated a flare, and identified
flare sites and dimming regions in the EUV data, with the aim of more
precisely determining CME initiation locations and times. In addition,
we used H-alpha data to investigate CME's associated with by filament
eruptions. The results allow us to calculate minimum acceleration rates,
and determine correlations between coronal structures, ejection events,
and acceleration rates. We use these correlations in turn to identify
viable CME initiation mechanisms.
Title: Cosmological stabilization of moduli with steep potentials
Authors: Brustein, R.; de Alwis, S. P.; Martens, P.
Bibcode: 2004PhRvD..70l6012B
Altcode: 2004hep.th....8160B
A scenario which overcomes the well-known cosmological overshoot
problem associated with stabilizing moduli with steep potentials
in string theory is proposed. Our proposal relies on the fact that
moduli potentials are very steep and that generically their kinetic
energy quickly becomes dominant. However, moduli kinetic energy
redshifts faster than other sources when the universe expands. So,
if any additional sources are present, even in very small amounts,
they will inevitably become dominant. We show that in this case cosmic
friction allows the dissipation of the large amount of moduli kinetic
energy that is required for the field to be able to find an extremely
shallow minimum. We present the idea using analytic methods and verify
with some numerical examples.
Title: STEREO in the Virtual Solar Observatory Context
Authors: Hourcle, J. A.; Bogart, R.; Davey, A.; Gurman, J. B.; Hill,
F.; Martens, P.; Suarez-Sola, I.; Tian, K.; Yoshimura, K.
Bibcode: 2004AGUFMSH21B0413H
Altcode:
The Virtual Solar Observatory (VSO) was designed with the goal that it
handle heterogeneous data sets from multiple observatories. With its
two spacecraft and multiple instruments, the STEREO mission provides
an excellent example of solar physics research based on multiple data
sets, and a good test of the abilities of the VSO. Here we will discuss
how the VSO will meet the key challenges that STEREO presents. In
particular, the wide range of data classes and the non-stationary
viewpoints of the two spacecraft demand a flexible underlying data
model of the VSO.
Title: The Virtual Solar Observatory: status and initial operational
experience
Authors: Hill, Frank; Bogart, Richard S.; Davey, Alisdair; Dimitoglou,
George; Gurman, Joseph B.; Hourcle, Joseph A.; Martens, Petrus C.;
Suarez-Sola, Igor; Tian, Karen; Wampler, Steven; Yoshimura, Keiji
Bibcode: 2004SPIE.5493..163H
Altcode:
The Virtual Solar Observatory (VSO) is a bottom-up grassroots approach
to the development of a distributed data system for use by the solar
physics community. The beta testing version of the VSO was released in
December 2003. Since then it has been tested by approximately 50 solar
physicists. In this paper we will present the status of the project,
a summary of the community's experience with the tool, and an overview
of the lessons learned.
Title: On the Combination of TRACE and CDS data
Authors: Scott, J. T.; Cirtain, J. W.; Martens, P. C. H.; Winter, H. D.
Bibcode: 2004AAS...204.7307S
Altcode: 2004BAAS...36..801S
Data collected by the Transition Region and Coronal Explorer (TRACE)
and the Coronal Diagnostic Spectrometer (CDS) of an Active Region
above the limb is examined. We have developed a co-alignment routine
which finds the limb in each image and uses a cross correlation
feature tracking algorithm to produce co-spatial images that are
accurate to within 4\arcsec. TRACE generated an image for every CDS
exposure. We have taken these images and selected only the portion of
the TRACE field of view which was co-temporal with each CDS exposure,
in essence generating a high resolution TRACE snapshot for each of the
CDS exposures. We compare this image to the CDS raster, a composite of
all 40 exposures taken during the study. We were able to determine the
number of TRACE resolved features within each CDS pixel in an effort to
provide an accurate lower bound estimate for the CDS filling factor. We
were also able to show that structures with the same apparent brightness
in the TRACE images are not necessarily at the same temperature and
density. This research is supported by NASA TRACE grant 426960,
NASA GSRP fellowship 425175, and NASA grant NAG5-12820
Title: The Diffuse EUV Corona
Authors: Cirtain, J. W.; Martens, P. C. H.; Acton, L. W.; Scott, J. T.
Bibcode: 2004AAS...204.7304C
Altcode: 2004BAAS...36..800C
Recent investigations have shown that the EUV corona could have two
primary components; one at relatively static high temperature ( 2
MK) and another dynamic at a low temperature (below 1 MK). These two
coronal constituents are within the temperature ranges observed by
the Transition Region and Coronal Explorer (TRACE), and are easily
resolved using the spectral capabilities of the Coronal Diagnostic
Spectrometer (CDS) on SoHO. We analyze an Active Region above the limb
and determine emission measure scaling laws for the high temperature
components. We also provide an estimate of the physical properties
of the cool loops observed during the study. Through the use of the
scaling laws we have developed a method to subtract the static coronal
component from TRACE images. We then use the resultant TRACE 173 Å
images to determine the changes in temperature and density in these
loops as a function of time. This allows us to calculate the heating
rate for the dynamic cool structures. This work is supported in
part via NASA GSRP fellowship (425175)
Title: Solar and Stellar X-ray Cycles
Authors: Martens, P. C. H.; SADE Team
Bibcode: 2004AAS...204.2103M
Altcode: 2004BAAS...36Q.688M
Stern et al. have shown that Yohkoh-SXT full disk X-ray irradiance shows
an 11 year cycle with an max/min amplitude ratio of a factor 30. Similar
cyclic X-ray variation in Sun-like stars observed by ROSAT and its
predecessors is observed in only a few cases and limited to a factor
two or three. We will show, by means of detailed bandpass comparisons,
that this discrepancy cannot be ascribed to the differences in energy
response between SXT and the stellar soft X-ray detectors. Is the Sun
exceptional? After centuries of geocentric and heliocentric worldviews
we find this a difficult proposition to entertain. But perhaps the Sun
is a member of a small class of late-type stars with large amplitudes
in their X-ray cycles. The stellar X-ray observations listed in the
HEASARC catalog are too sparse to verify this hypothesis. To
resolve these and related questions we have proposed a small low-cost
stellar X-ray spectroscopic imager originally called SADE to obtain
regular time series from late and early-type stars and accretion
disks. This instrument is complimentary to the much more advanced
Chandra and XMM-Newton observatories, and allows them to focus on those
sources that require their full spatial and spectral resolution. We
will describe the basic design and spectroscopic capability of SADE
and show it meets the mission requirements.
Title: Implementation of the Virtual Solar Observatory
Authors: Davey, A. R.; Bogart, R. S.; Gurman, J. B.; Hill, F.; Hourcle,
J.; Martens, P. C.; Suarez-Sola, I.; Tian, K. Q.; Yoshimura, K.
Bibcode: 2004AAS...204.7002D
Altcode: 2004BAAS...36..796D
The Virtual Solar Observatory (VSO) integrates diverse solar data
archives into a virtual collection providing common search and delivery
services. Having developed from a prototype installation involving
four major archives, it is now in the process of expanding to include
a larger variety of archives and data types. We are also refining and
expanding its services and user interfaces and defining an API. We
have defined a working extensible data model enabling us to provide
more detailed and comprehensive search capabilities and to incorporate
additional data products. The API will allow people to construct their
own interfaces to the core VSO functionality and integrate with other
web services and other virtual observatories. Here we describe the
structure of VSO as currently implemented and what is required to
incorporate additional archives.
Title: The Virtual Solar Observatory -- the Why, What, How and Where
Authors: Hill, F.; Bogart, R. S.; Davey, A.; Dimitoglou, G.; Gurman,
J. B.; Martens, P. C.; Tian, K.; Wampler, S.
Bibcode: 2003AGUFM.U22A0012H
Altcode:
Observational solar physics almost always involves the comparison of
several data sets obtained by different instruments and stored in a
variety of archives. Currently a researcher must laboriously locate
the relevant archives, search them with idiosyncratic interfaces,
and retrieve the data by a number of methods. The VSO is a tool to
streamline this process by providing a single unified interface and
search tool for solar archives. Eventually this will be supplemented
by distributed computing tools which will enable queries based on
data itself, in addition to standard queries on metadata. The VSO
will enable a new class of solar research -- large-scale correlative
statistical studies on many data sets, thereby facilitating space
weather studies. An example of a use case is a helioseismic study of the
subsurface structure of cornal hole boundaries and possible predictive
links between the solar interior and the solar wind. An intital
prototype has been built linking archives at GSFC, Stanford, MSU, and
NSO. This prototype has been constructed using a combination of XML,
SOAP, and Perl technologies, and a beta release is available now. The
initial set of archives will soon be expanded to include archives at
HAO, NGDC, and selected NOAA feature and event catalogues. In the
next 2 years, additonal service providers will be added, the user
interface will be fully developed, and distributed computing tools
will be initiated.
Title: The Effect of Background Subtraction on the Temperature of
EIT Coronal Loops
Authors: Schmelz, J. T.; Beene, J. E.; Nasraoui, K.; Blevins, H. T.;
Martens, P. C. H.; Cirtain, J. W.
Bibcode: 2003ApJ...599..604S
Altcode:
We have selected a sample of 10 coronal loops that were clearly
visible in the 171 Å passband of the SOHO EIT, five on the limb
and five on the disk. Our analysis was limited to 171/195/284 image
``triplets''-observations taken when the instrument cycles through
the different passbands during routine operations. This cycle takes
only a few minutes, so each of these nonflaring structures did not
change significantly during the cycle. We chose five pixels along
each loop and five carefully selected background pixels. Temperature
analysis was done four different ways: (1) standard EIT analysis on
the five loop pixels with no background subtraction; (2) constant
background subtraction for each EIT image; (3) pixel pair background
subtraction; and (4) radial background array subtraction (this method
works only for loops observed above the limb). Each method produced
two estimates of temperature for each loop pixel, one from the 171:195
ratio and the second for the 195:284 ratio. Both ratios produced loops
with a uniform temperature, but each ratio results in a statistically
different temperature value, perhaps indicating that the plasma along
the line of sight was not isothermal. Background subtraction did
not affect the EIT temperature analysis, i.e., the results were the
same with and without background subtraction. The results for loops
on the limb were ``cleaner'' i.e., had less scatter, than for loops
on the disk. Finally, we did a similar temperature analysis with five
randomly chosen pixels for each data set. The results were the same as
for the loop pixels: two statistically different, uniform temperature
``structures.'' These findings indicate that EIT ratio analysis does
not generate a physically meaningful value for the electron temperature.
Title: Measurements of Flux Cancellation During Filament Formation
Authors: Wood, Paul; Martens, Piet
Bibcode: 2003SoPh..218..123W
Altcode:
We study the process of flux cancellation and filament formation in
a nest of three decaying active regions, using data from SOHO MDI
and EIT, and Hα images from Meudon and Big Bear. We find that there
are no apparent EUV loops connecting the two poles of a cancelling
feature prior to and during cancellation, suggesting an absence of
coronal magnetic connectivity between these opposite polarity flux
patches. We further find that the cancellation occurs at the ends of
the Hα sections of the filament and is accompanied by a noticeable
increase in Hα intensity and linkage of the Hα sections, but that the
locations of the links remain the weakest in Hα absorption. We present
our measurements of the amount of flux cancelled at each site and show
it is in agreement with an estimate of the axial flux contained in
the filament. We also observe two events of flux emergence, and find
that they do not influence the filament formation in this case. We
compare our results with similar measurements in recent papers and
find agreement for the amounts of cancelled flux per patch, except
for one case in a young emerging active region, for which we provide
an alternative interpretation. We conclude that our measurements of
flux cancellation are consistent with both the scenarios in which the
filament is formed through ``head-to-tail" linkage, as well as the
scenario in which filament flux tubes emerge as a whole from below
the photosphere, but that only the former scenario is consistent with
the apparent absence of coronal magnetic links between the cancelling
magnetic patches.
Title: Data Integration in the Virtual Solar Observatory
Authors: Bogart, R. S.; Davey, A.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Martens, P. C.; Tian, K. Q.; Wampler, S.
Bibcode: 2003AGUFMSH42A0503B
Altcode:
The aim of the Virtual Solar Observatory (VSO) is the integration of
diverse data archives relevant to the study of Solar Physics into a
virtual collection providing common search and delivery services. The
back-end query services are implemented as Web Services and accessible
via the Simple Object Access Protocol (SOAP). SOAP defines a remote
procedure call mechanism that employs HTTP as its transport and
encodes the client-server interactions in XML documents. In addition
to its core function in identifying relevant datasets locally, a SOAP
server at each data provider acts as a wrapper that maps descriptions
in an abstract data model to those in the provider's specific model,
and vice versa. Heterogeneous data search services can thereby be
integrated with a common interface. This allows scientists to access
multiple archives with differing data organizations at once, enhancing
their ability to discover and and analyze correlative data from multiple
sources. We have chosen two SOAP implementations for the VSO: SOAP::Lite
and OpenSOAP. The former, written in Perl, is suitable for fast and
flexible prototyping in data search applications. SOAP::Lite servers
have been set up at each of the VSO archives, and can be readily
installed at other servers. OpenSOAP, written in C with built-in
support for service description and dispatch, may prove useful in
transforming current computing utilities into Web Services. We report
on initial experiments using OpenSOAP to provide additional services
to the basic query functionality of VSO.
Title: SADE: The starspot and dynamo explorer
Authors: Martens, P. C. H.; Acton, L. W. A.; Klumpar, D.; Kankelborg,
C.; Stern, R. A.; Peres, G.; Culhane, J. L.
Bibcode: 2003AdSpR..32.1123M
Altcode:
We propose a mission called SADE, the Starspot And Dynamo Explorer, to
study dynamo activity in nearby late-type stars. The onboard instruments
will be a Ca-K telescope for magnetically dominated chromospheric
emission, and an X-ray grazing incidence telescope to study coronal
emission. We design the mission for a life-time of 15 years or longer
to capture a full activity cycle for most solar-type stars. We aim to
firmly establish the spectrum of the relation between chromospheric
and corona' emission in late-type stars, and capture one or more stars
going into or coming out of a Maunder type minimum. Operation costs will
be kept to a minimum by automating mission operations to a maximum,
and have the science operations be carried out by students at Montana
State University.
Title: Analysis of a coronal loop on the limb
Authors: Cirtain, J. W.; Martens, P. C. H.; Winter, H. D.
Bibcode: 2003AdSpR..32.1117C
Altcode:
The ability to accurately measure the temperature and density of the
solar atmosphere is essential to understanding the physical nature of
Coronal loops. After data has been corrected to account for cosmic ray
incidents on the CCD and instrumental effects, there are additional
sources of error that must also be addressed. We applied a correction
to the intensities for spectral lines to account for line of sight
effects. Having performed these procedures, the corrected intensities
from the Coronal Diagnostic Spectrometer are then used to produce
differential emission measure curves with much improved error estimates
Title: Yohkoh-SXT Observations of reconnection
Authors: Martens, P. C. H.
Bibcode: 2003AdSpR..32..905M
Altcode:
In this paper I review the different strong indications for the
occurrence of reconnection in the solar corona observed of with
Yohkoh-SXT. I make a distinction between the unique indicator of
reconnection, i.e. the change in connectivity in the magnetic field,
and non-unique signatures of reconnection, that also can originate
from other processes. I review five different types of Yohkoh-SXT
observations that indicate reconnection in the solar corona: erupting
plasmoids, X-ray jets, formation of sigmoids through "linkage", the
existence of interconnecting loops, and the rigid rotation of coronal
holes. I conclude that the presence of reconnection in the solar corona
has been established with near certainty, but that higher resolution
soft X-ray and EUV observations are needed to firmly establish the
full physical picture for each of The phenomena described.
Title: The Role of Magnetic Reconnection in the Formation of
Transequatorial Loops
Authors: Martens, P. C. H.
Bibcode: 2003SPD....34.1002M
Altcode: 2003BAAS...35..825M
Transequatorial loops often bridge large regions of very small field
strength in which no emergence other than that of tiny dipoles is
observed. It is very unlikely on theoretical grounds, and has never
been observed, that such loops emerge as pre-existing flux tubes from
below the chromosphere. Moreover, of the two active regions that these
loops connect one is usually demonstrably older than the other, so
that a loop connecting them could not have emerged with the older one,
because it would have had nowhere to connect to. Taken together this
is nearly indisputable evidence of reconnection in the corona. I
will review a number of recently published observations that support
the statements above, and consider the implications for dynamo models
from the coronal formation of transequatorial loops
Title: The Virtual Solar Observatory: The Best-Laid Schema
Authors: Gurman, J. B.; Dimitoglou, G.; Hill, F.; Wampler, S.; Bogart,
R. S.; Tian, K.; Martens, P.; Davey, A.
Bibcode: 2003SPD....34.0203G
Altcode: 2003BAAS...35..807G
Work on a protoype Virtual Solar Observatory (VSO) is now under way. The
prototype will offer access to data from online solar archives at
Stanford, NSO, Montana State, and the SDAC. We discuss some of the
features of the VSO for users, as well as the basic design and some
of the technical aspects, including the use of XML schemas and SOAP
to allow users a single access method for disparate data services.
Title: TRACE and CDS: JOP 146 Data Analysis Part I
Authors: Scott, J. T.; Cirtain, J. W.; Martens, P. C. H.
Bibcode: 2003SPD....34.1705S
Altcode: 2003BAAS...35..838S
Joint Observing Program 146 was designed to collect data on coronal
loops using the Coronal Diagnostic Spectrometer on SoHO and the
Transition Region and Coronal Explorer. These two instruments
collectively provide high spatial, temporal and temperature
resolution. Calibration of the 171 Å filter on TRACE to spectral
line intensities collected by CDS combines these qualities to produce
the most detailed data currently available for the solar corona. We
have determined an absolute value for the wavelengths of ions in
data collected on September 18, 2001. This wavelength was then used
to determine the Doppler shifts for many points along a coronal
loop. The resulting values for velocity and intensity of Mg IX were
then compared to the flux measured by the TRACE 171 Å filter. We find
a appreciable correlation between the 171 Å filter and Mg IX. We use
this determination to develop method of Differential Emission Measure
analysis that provides a DEM for any pixel along a loop at nearly the
same instant in time. This is uncharacteristic of DEM curves typically
created from CDS data, as these curves are highly time dependant.
Title: First Steps Towards a VSO
Authors: Davey, A. R.; Bogart, R. S.; Dimitoglou, G.; Gurman, J. B.;
Hill, F.; Martens, P. C.; Tian, K. Q.; Wampler, S.
Bibcode: 2003SPD....34.0311D
Altcode: 2003BAAS...35..810D
Work has started on constructing the Virtual Solar Observatory. This
poster describes some of the components of the VSO and the first steps
that have been taken to implement these components. A description of
the overall VSO structure is given, along with descriptions of data
and meta-data models, methods by which these data model are used by
the VSO, details of how VSO nodes are interconnected *
and ideas on the likely format of the VSO API. As an example, the
inclusion of Yohkoh-SXT data at MSU and the future inclusion of the
Yohkoh-Galileo project data will be discussed. *
See also ``Data Integration Using SOAP in the VSO" by Tian et al.
Title: SADE: Starspot and Dynamo Explorer
Authors: Martens, P. C. H.
Bibcode: 2003SPD....34.2003M
Altcode: 2003BAAS...35..844M
In soft X-rays the solar coronal radiance varies by a factor of 70
over the solar activity cycle. A similar variation in most stars
in the existing X-ray database has not been found (Stern 2001);
even stars which exhibit chromospheric activity cycles show only
marginal evidence for X-ray cycles. This is rather puzzling as the
time span and multiple coverage of the X-ray sky should reveal at
least a hint of such a pronounced cyclical variation. By the time
of the meeting we will have submitted a SMEX proposal with the above
acronym to determine the nature and amplitude of the variation in X-ray
emission of nearby solar analogs that have a cyclic chromospheric Ca-K
variability similar to that of the Sun. In doing so we aim to expand
our knowledge of the parameter space of stellar dynamos, which will
lead to a better understanding of the dynamo process in general --
an unresolved fundamental problem in astrophysics -- and the solar
dynamo in particular. This is an investigation at the cross-section
of the NASA themes ``Structure and Evolution of the Universe", and
the ``Sun-Earth Connection". In my presentation I will describe
the SADE instrument design, observing strategy, and possible science
results. SADE is proposed by a consortium led by MSU, including Swales,
CfA, LMSAL, UCL, OAP, and Bangalore.
Title: Building an On-line Catalog of Correlated Solar Prominence
and Sigmoid Images
Authors: Merriot, I. V.; Pevtsov, A.; Martens, P.
Bibcode: 2003SPD....34.0310M
Altcode: 2003BAAS...35R.809M
Predicting solar weather is a complex endeavor. The correlation between
X-ray sigmoids and coronal mass ejections (CMEs) has been established
but the role of the prominence in association with the sigmoid and
CME is not yet clear. This study catalogs the correlation between
prominence behavior and sigmoids --before and after-- a CME takes
place. CME, sigmoid and filament occurrences were correlated
using the Yashiro online catalog (SOHO), the SXT sigmoid catalog
(Yohkoh) and archived H-alpha film from the flare patrol telscope
(NSO/SP). When correlations were found, the H-alpha full disk images
were digitized to embrace time periods of 2-3 hours before and after
the CME event where changes in filament were notable. The culmination
of this study will be a web-based catalog of data in text and images
showing filament dynamics when sigmoids leading to CMEs are present. This study is funded, in part, by the Murdoch Foundation.
Title: Data Integration Using SOAP in the VSO
Authors: Tian, K. Q.; Bogart, R. S.; Davey, A.; Dimitoglou, G.;
Gurman, J. B.; Hill, F.; Martens, P. C.; Wampler, S.
Bibcode: 2003SPD....34.0312T
Altcode: 2003BAAS...35..810T
The Virtual Solar Observatory (VSO) project has implemented a time
interval search for all four participating data archives. The back-end
query services are implemented as web services, and are accessible
via SOAP. SOAP (Simple Object Access Protocol) defines an RPC (Remote
Procedure Call) mechanism that employs HTTP as its transport and encodes
the client-server interactions (request and response messages) in XML
(eXtensible Markup Language) documents. In addition to its core
function of identifying relevant datasets in the local archive, the SOAP
server at each data provider acts as a "wrapper" that maps descriptions
in an abstract data model to those in the provider-specific data model,
and vice versa. It is in this way that VSO integrates heterogeneous
data services and allows access to them using a common interface. Our
experience with SOAP has been fruitful. It has proven to be a better
alternative to traditional web access methods, namely POST and GET,
because of its flexibility and interoperability.
Title: Strawman Concept for A Virtual Solar Observatory
Authors: Martens, P. C. H.; Gurman, J. B.; Hill, F.; Bogart, R. S.;
Davey, A.; Dimitoglou, G.; Tian, K.; Wampler, S.
Bibcode: 2002AAS...20114103M
Altcode: 2003BAAS...35..567M
We propose here an architecture and feature set for a prototype Virtual
Solar Observatory (VSO). The prototype will not include all the features
that might eventually become part of the VSO, nor even all the features
that are concurrently under development elsewhere that should become
parts of the VSO's functionality. It is possible to approach the design
of such a system in at least two different ways. In one (top-down),
all possible features and uses of a system are studied, and the best
solution for as many as possible is proposed. This is the approach
taken by the European Grid of Solar Observations (EGSO). Alternately,
one can approach a system design from the bottom up, and ask what the
essential element or elements of the design have to be in order to have
a functioning and useful system. The VSO study group decided, after
examining different approaches to abstracting the procedures for solar
data identification and access, to build the “smallest box” possible
around that problem, rather than attempting to draw a box around all
possible aspects of a VSO. This design will be presented in the poster.
Title: The Right Amount of Glue: Technologies and Standards Relevant
to a Future Solar-Terrestrial Data Environment
Authors: Gurman, J. B.; Dimitoglou, G.; Bogart, R. S.; Tian, K. Q.;
Hill, F.; Wampler, S.; Martens, P. C.; Davey, A.
Bibcode: 2002AGUFMSH52C..03G
Altcode:
In order to meet the challenge of developing a new system science, we
will need to employ technology that enables researchers to access data
from fields with which they are at least initially unfamiliar as well as
from sources they use more regularly. At the same time, the quantity of
data to be obtained by missions such as the Solar Dynamics Observatory
demands ease and simplicity of data access. These competing demands
must in turn fit within severely constrained funding for data analysis
in such projects. \p Based on experience in only a single discipline
but with a diversity of data types and sources, we will give examples
of technology that have made a significant difference in the way people
do science. Similarly, we will show how adoption of a well-dcoumented
data format has made it easier for one community to search, reduce,
and analyze data. We will also describe a community-supported data
reduction and analysis software tree with useful features.\p We will
attempt to generalize the lessons learned in these instances to features
the broader, solar-terrestrial community might find compelling, while
avoiding overdesign of a common data environment.\p
Title: The Inadequacy of Temperature Measurements in the Solar Corona
through Narrowband Filter and Line Ratios
Authors: Martens, P. C. H.; Cirtain, J. W.; Schmelz, J. T.
Bibcode: 2002ApJ...577L.115M
Altcode:
We analyze the determination of coronal line-of-sight temperatures
with the technique of narrowband filter ratios that is currently
employed for data obtained with the Transition Region and Coronal
Explorer and the EUV Imaging Telescope on board the Solar and
Heliospheric Observatory. We demonstrate that the simple fact that
the observed differential emission measure curves in coronal loops
have a broad plateau everywhere along the length of the loop leads to
the finding of isothermal loops with different temperatures for each
pair of filters. We show that none of the temperatures thus obtained
correctly describe the state of the loop plasma, which instead must be
characterized by the full differential emission measure per pixel. We
conclude that the recent discovery of a new class of isothermal loops
is probably a mere artifact of the narrowband filter ratio method and
show that the shift in the location of the plateau in the differential
emission measure along the loop indicates significant heating near
the loop tops.
Title: Methods of Temperature and Emission Measure Determination of
Coronal Loops
Authors: Cirtain, J. W.; Schmelz, J. T.; Martens, P. C. H.
Bibcode: 2002AAS...200.1605C
Altcode: 2002BAAS...34..667C
Recent observational results from both SOHO-EIT and TRACE indicate that
coronal loops are isothermal along their length (axially). These results
are obtained from a narrowband filter ratio method that assumes that
the plasma is isothermal along the line of sight (radially). However,
these temperatures vary greatly from those derived from differential
emission measure (DEM) curves produced from spectral lines recorded by
SOHO-CDS. The DEM results indicate that the loops are neither axially
nor radially isothermal. This discrepancy was investigated by Schmelz
et al. (2001). They chose pairs of iron lines from the same CDS data
set to mimic the EIT and TRACE loop results. Ratios of different
lines gave different temperatures, indicating that the plasma was not
radially isothermal. In addition the results indicated that the loop
was axially isothermal, even though the DEM analysis of the same data
showed this result to be false. Here we have analyzed the EIT data for
the CDS loop published by Schmelz et al. (2001). We took the ratios of
the 171-to-195 and 195-to-284 filter data, and made temperature maps
of the loop. The results indicate that the loop is axially isothermal,
but different temperatures were found for each pair of filters. Both
ratio techniques force the resultant temperature to lie within the range
where the response functions (for filters) or the emissivity functions
(for lines) overlap; isothermal loops are therefore a byproduct of
the analysis. This conclusion strengthens support for the idea that
temperature and emission measure results from filter ratio methods may
be misleading or even drastically wrong. This research was funded in
part by the NASA/TRACE MODA grant for Montana State University. Solar
physics research at the University of Memphis is supported by NASA
grant NAG5-9783.
Title: The Point Spread Function of the Yohkoh Soft X-ray Telescope
Authors: McKenzie, D. E.; Gburek, S.; Acton, L. W.; Martens, P. C.
Bibcode: 2002AAS...200.5502M
Altcode: 2002BAAS...34Q.732M
The point spread function (PSF) of the Yohkoh solar observatory's Soft
X-ray Telescope has two primary components, a sharply defined core
and a diffuse wing due to photon scattering. Because the extent of the
PSF is significantly wider than a single pixel, its characterization is
useful for improvement of the quality of the SXT images. We will present
results from analyses of the two PSF components, and demonstrate our
best model of the core and scattering wing of the SXT point spread
function. An example of PSF deconvolution to remove the effects of
photon scattering will be given.
Title: How to `Subtract' Spectrally Determined Intensities from a
Coronal Loop on the Limb
Authors: Martens, P. C. H.; Cirtain, J. W.; Schmelz, J. T.
Bibcode: 2002AAS...200.0206M
Altcode: 2002BAAS...34..640M
There are two main problems in the determination of plasma emissions
within a coronal loop. First, the line of sight adds the ambient
background to the measurement. Second, scattering elevates the intensity
for pixels close to a structure (i.e. a loop) by counting photons that
actually are emitted from that structure. Here we have a possible
solution for these two problems. We show that the intensities for
the spectral lines are shown to have scale height dependence when the
plasma is not confined to a structure. Accordingly, at any distance
greater than its scale height, the ion will not have a statistically
significant contribution to the measure of intensity. Additionally,
an isolated coronal structure will have a maximum intensity value along
an exposure and within a range of pixels that effectively slice a leg
of the loop. The maximum is the location of the pixel that is most
likely the one containing the loop. All other pixels are considered
scatter until the point spread function can deconvolve the true value
for intensity per pixel. The resulting values for intensity have then
been reduced to approximate the value for intensity for the plasma
within the loop. Now the intensity has been reduced to the intensity
of the ion within the loop and the analysis of an accurate DEM is now
possible. This research was funded in part by the NASA/TRACE MODA grant
for Montana State University. Solar physics research at the University
of Memphis is supported by NASA grant NAG5-9783.
Title: Building a Virtual Solar Observatory: I Look Around and
There's a Petabyte Following Me
Authors: Gurman, J. B.; Bogart, R.; Hill, F.; Martens, P.
Bibcode: 2002AAS...200.5805G
Altcode: 2002BAAS...34..740G
The 2001 July NASA Senior Review of Sun-Earth Connections missions
and data centers directed the Solar Data Analysis Center (SDAC) to
proceed in studying and implementing a Virtual Solar Observatory (VSO)
to ease the identification of and access to distributed archives of
solar data. Any such design (cf. the National Virtual Observatory
and NASA's Planetary Data System) consists of three elements: the
distributed archives, a "broker" facility that translates metadata
from all partner archives into a single standard for searches,
and a user interface to allow searching, browsing, and download of
data. Three groups are now engaged in a six-month study that will
produce a candidate design and implementation roadmap for the VSO. We
hope to proceed with the construction of a prototype VSO in US fiscal
year 2003, with fuller deployment dependent on community reaction to
and use of the capability. We therefore invite as broad as possible
public comment and involvement, and invite interested parties to a
`birds of a feather' session at this meeting. VSO is partnered with
the European Grid of Solar Observations (EGSO), and if successful, we
hope to be able to offer the VSO as the basis for the solar component
of a Living With a Star data system.
Title: Differential Emission Measure Error Analysis
Authors: Winter, H. D.; Martens, P. C. H.
Bibcode: 2002AAS...200.0205W
Altcode: 2002BAAS...34..640W
While line ratio techniques are still the dominant method for making
measurements of solar coronal plasma parameters, such as mean electron
density and electron temperature, the isothermal approximation
on which these methods rely is a poor assumption for many solar
features. Differential emission measure (DEM) analysis eliminates
the isothermal assumption. The inverse problem that one must solve to
generate DEM curves is ill-posed, yielding multiple solutions that fit
the observed data. Forward modeling improves the situation but still
does not allow one to derive a unique solution that properly models
the observed plasma. For DEM curves to have scientific meaning an
estimate of the error must be included. We generated DEM curves for
several observed solar coronal features and determined the error in
each solution from photon statistics. This allows us to use statistical
methods to derive the best DEM fit to the data with the smallest number
of free parameters. The possible implications for the physics derived
from DEM analysis are significant. This work was supported by the MSU
NASA/TRACE MO&DA contract.
Title: SADE, the Student Astrophysical Dynamo Explorer
Authors: Martens, P.; Acton, L.; Klumpar, D.; Stern, R.; Peres, G.;
Culhane, L.
Bibcode: 2002cosp...34E1298M
Altcode: 2002cosp.meetE1298M
In soft x-rays the solar coronal radiance varies by a factor of 10-30
over the solar activity cycle. A similar variation in most stars in
the existing x-ray database has not been found (Stern 2001); even
stars which exhibit chromospheric activity cycles show only marginal
evidence for X-ray cycles. This is rather puzzling as the time span
and multiple coverage of the x-ray sky should reveal at least a hint of
such a pronounced cyclical variation. We propose a mission called the
Student Astrophysical Dynamo Explorer to measure the x-ray brightness
of about 75 stars once every 5 days for up to 15 years. Selection of
prime stars takes into account location (avoid eclipse), rotation rate,
Ca-K observations, and magnetic field strength, to focus on the best
candidates for dynamo studies. We baseline a nested 4-5 mirror system
with 200 cm^2 geometric area, with a 1.5 to 2 meter focal length, 15
arcsec on-axis resolution, and Au or Ni coatings. The strawman detector
is a back-illuminated CCD of 512x512 pixels, with pixels that can be
large as a 15 arcseconds. Available exposure time per star per visit
is about an hour and a half. We are exploring the option of adding
a visible light detector for astroseismology. To minimize operations
cost for this long duration mission we envisage tracking and commanding
from a simple ground station at Montana State University, operated by
students under the auspices of MSU's Space Science and Engineering Lab
(SSEL).
Title: Preface
Authors: Martens, P. C. H.; Cauffman, D. P.
Bibcode: 2002mwoc.confD...5M
Altcode:
No abstract at ADS
Title: The Origin of Prominences and Their Hemispheric Preference
for the Skew of Overlying X-ray Loops
Authors: Martens, P. C. H.
Bibcode: 2002mwoc.conf..135M
Altcode:
I present a ``head-to-tail'' inkage model for the formation, evolution,
and eruption of solar filaments. The magnetic field structure of the
model is based upon the observation that filaments form exclusively
in filament channels with no apparent magnetic connections above
the polarity inversion line. The formation of a filament in this
configuration is driven by flux convergence and cancellation, which
produces loop-like filaments segments with a half-turn. Filament
segments of like chirality may connect and form long quiescent
filaments. I demonstrate that the combined workings of Hale's polarity
law, Joy's law, and differential rotation introduce a strong hemispheric
preference in the chirality of filaments formed poleward of the sunspot
belt, in agreement with observations. I analyze the magnetic fine
structure of filaments formed through the model and find consistency
with the observed hemispheric preference for the skew of overlying
X-ray emitting loops observed by Yohkoh-SXT, contrary to what would
be expected from differential rotation. Finally I show that every
cancellation event that generates a filament obeying the hemispheric
chirality preference, injects a flux tube below the surface with a
poloidal field opposite to that of the ongoing cycle. I suggest that
this pattern of submergence of flux represents the specific mechanism
for the reversal of the poloidal flux in a Babcock-Leighton-Durney
type model for the solar dynamo.
Title: Analysis of a coronal loop on the limb
Authors: Cirtain, J.; Martens, P.
Bibcode: 2002cosp...34E1294C
Altcode: 2002cosp.meetE1294C
The determination of line of sight temperature and density for
coronal loops has been an elusive process. The need for the ability
to accurately measure these plasma characteristics is key to the
understanding of their physical nature. Accordingly, we have been
testing procedures to determine our best approach to this problem. We
have concluded that spectroscopically determined Differential Emission
Measures, DEMs, provide the most precise measure available with current
instrumentation. Of course there is the problem of the addition of
values for intensities from ions emitting outside the structure,
yet along the line of sight. We have also been able to show that ion
production in the quite corona follows predictions of density scaling
laws and accordingly, values for the intensity at distance greater than
the scale height are structure dependant and any line of sight effects
become negligible. Furthermore, through the use of narrow filter images
taken by TRACE, the time component of the DEM can be constrained in a
way that allows for comparison of emission from the filter to emission
from ions that are formed at approximately the same temperature. This
allows us to produce DEM curves for all points along a loop at each time
an image from TRACE exists. This allows us to track the evolution of a
loop through its lifetime in both temperature and density. Accordingly,
if the injection of energy into a loop is discrete in within the loop,
the DEM curves will provide evidence of this process.
Title: Blind Deconvolution of the SXT PSF Core Part
Authors: Gburek, S.; Sylwester, J.; Martens, P. C. H.
Bibcode: 2002mwoc.conf..417G
Altcode:
The performance and speed of blind deconvolution algorithms for
restoration of SXT images depend on good initial guess for PSF function
shape. From the analysis of several compact flare kernels we came
to conclusion that a good guess for PSF can be provided directly
from images of X-ray compact structures observed by SXT. Recently,
we conducted extensive mission-long searches for compact structures
through entire database of SXT full resolution frames. The searches
returned plenty compact structures which my serve to construct
initial approximation of the PSF for BID restoration method. We show a
selection of the most compact structures found and its location on SXT
CCD detector. Using observation for this selected set of structures
we construct constraints for Al12 PSF shrouds and compare them with
ground calibration data.
Title: Multi-Wavelength Observations of Coronal Structure and Dynamics
Authors: Martens, P. C. H.; Cauffman, D.
Bibcode: 2002mwoc.conf.....M
Altcode:
Yohkoh, a mission of Japan's Institute of Space and Astronautical
Sciences with the cooperation of the United States and United Kingdom
was launched a decade ago on 30 August 1991. This scientific meeting
has been organized in celebration of ten years of successful scientific
operation of Yohkoh. We will review the many and varied advances in our
understanding of the dynamic solar atmosphere in the past 10 years of
observations by Yohkoh in collaboration with SoHO, TRACE, Ulysses, and,
soon, HESSI. The meeting will focus on the conceptual and theoretical
advances that coordinated multi- mission and ground based observations
of the Sun have enabled in the last decade, and examine the role that
continued observations by Yohkoh will play within the context of the
programs of the current decade, such as HESSI, Solar-B, STEREO, and
the Solar Dynamics Observatory.
Title: Science objectives of the EUV spectral imager for Solar Orbiter
Authors: Martens, Petrus C.; Kankelborg, Charles C.
Bibcode: 2001ESASP.493..293M
Altcode: 2001sefs.work..293M
No abstract at ADS
Title: Simultaneous EUV imaging and spectroscopy
Authors: Kankelborg, Charles C.; Martens, Petrus C.; Thomas, Roger J.
Bibcode: 2001ESASP.493..257K
Altcode: 2001sefs.work..257K
No abstract at ADS
Title: Chromospheric Damping of Alfvén Waves
Authors: De Pontieu, B.; Martens, P. C. H.; Hudson, H. S.
Bibcode: 2001ApJ...558..859D
Altcode:
We analytically study the damping of Alfvén mode oscillations in the
chromosphere and in coronal loops. In the partially ionized chromosphere
the dominant damping process of Alfvén waves is due to collisions
between ions and neutrals. We calculate the damping time for Alfvén
waves of a given frequency, propagating through model chromospheres
of various solar structures such as active region plage, quiet sun,
and the penumbra and umbra of sunspots. For a given wave frequency,
the maximum damping always occurs at temperature minimum heights and
in the coldest structure(s), i.e., the umbra of sunspots. Energy
dissipation due to ion-neutral damping of Alfvén waves with an
energy flux of 107 ergs cm-3 s- 1 can
play a considerable role in the energy balance of umbrae, quiet sun,
and plage for Alfvén wave periods of the order, respectively, 50,
5, and 0.5 s. We also consider Alfvén waves in coronal loops and the
leakage of wave energy through the footpoints. We assume a three-layer
model of coronal loops with constant Alfvén speed vA
(and no damping) in the corona, vA varying exponentially
with height in the dissipative chromosphere, and vA again
constant in the photosphere at the end of the loop. We find an exact
analytical solution in the chromospheric part. Using these solutions, we
estimate the leakage of wave energy from the coronal volume through the
footpoint regions of the loop and find that the presence of a moderate
amount of chromospheric damping can enhance the footpoint leakage. We
apply this result to determine the damping time of standing waves in
coronal loops. The enhanced footpoint leakage also has implications
for theories of coronal heating based on resonant absorption. Finally,
we find exact expressions for the damping of Alfvén waves launched
in the photosphere and upward propagating through the chromosphere
and into the corona. The partially ionized chromosphere presents an
effective barrier for upward propagating Alfvén waves with periods
less than a few seconds.
Title: Origin and Evolution of Filament-Prominence Systems
Authors: Martens, Petrus C.; Zwaan, Cornelis
Bibcode: 2001ApJ...558..872M
Altcode:
We present a ``head-to-tail'' linkage model for the formation,
evolution, and eruption of solar filaments. The magnetic field
structure of our model is based on the observation that filaments
form exclusively in filament channels with no apparent magnetic
connections above the polarity inversion line. The formation of
a filament in this configuration is driven by flux convergence
and cancellation, which produces looplike filament segments with
a half-turn. Filament segments of like chirality may connect and
form long quiescent filaments. Such filaments are stabilized through
footpoint anchoring until further cancellation at the footpoints causes
their eruption. The eruption restores the original filament channel so
that filament formation may resume immediately. We then demonstrate
that the combined workings of Hale's polarity law, Joy's law, and
differential rotation introduce a strong hemispheric preference
in the chirality of filaments formed poleward of the sunspot belt,
which is in agreement with observations. We analyze the magnetic fine
structure of filaments formed through our model and find consistency
with the observed hemispheric preference for barb orientation and
a simple explanation for barb formation. Finally, we consider the
flux tubes retracted below the surface in the process of filament
formation. We show that every cancellation event that generates a
filament obeying the hemispheric chirality preference injects a flux
tube below the surface with a poloidal field opposite that of the
ongoing cycle. We suggest that this pattern of submergence of flux
represents the specific mechanism for the reversal of the poloidal
flux in a Babcock-Leighton-Durney-type model for the solar dynamo.
Title: The Origin of Prominences and Their Hemispheric Preferences
Authors: Martens, P. C.
Bibcode: 2001AGUSM..SH42A01M
Altcode:
We present a ``head-to-tail" linkage model for the formation,
evolution, and eruption of solar filaments. The magnetic field
structure of our model is based upon the observation that filaments
form exclusively in filament channels with no apparent magnetic
connections above the polarity inversion line. The formation of a
filament in this configuration is driven by flux convergence and
cancellation, which produces loop-like filaments segments with a
half-turn. Filament segments of like chirality may connect and form long
quiescent filaments. Such filaments are stabilized through footpoint
anchoring until further cancellation at the footpoints causes their
eruption. The eruption restores the original filament channel so that
filament formation may resume immediately. We demonstrate that the
combined workings of Hale's polarity law, Joy's law, and differential
rotation introduce a strong hemispheric preference in the chirality
of filaments formed poleward of the sunspot belt, in agreement with
observations. We analyze the magnetic fine structure of filaments formed
through our model and find consistency with the observed hemispheric
preference for barb orientation and a simple explanation for barb
formation. Finally we show that every cancellation event that generates
a filament obeying the hemispheric chirality preference, injects a flux
tube below the surface with a poloidal field opposite to that of the
ongoing cycle. We suggest that this pattern of submergence of flux
represents the specific mechanism for the reversal of the poloidal
flux in a Babcock-Leighton-Durney type model for the solar dynamo.
Title: SOHO (Solar and Heliospheric Observatory)
Authors: Martens, P.
Bibcode: 2000eaa..bookE1978M
Altcode:
The Solar and Heliospheric Observatory (SOHO) is a project of
international cooperation between ESA (the EUROPEAN SPACE AGENCY)
and NASA to study the Sun, from its deep core to the outer corona,
and the solar wind. SOHO was launched on 2 December 1995, on top of
an Atlas/Centaur combination, from Cape Canaveral Air-Force Base in
Florida. It reached its operating orbit around the L1 Sun-Earth Lagr...
Title: Solar Flares: Preflare Phase
Authors: Martens, P.
Bibcode: 2000eaa..bookE2288M
Altcode:
Solar flares are believed to be the result of a sudden conversion of
a large amount of free magnetic energy, previously stored in the solar
CORONA. The release takes place in a matter of minutes to half an hour,
and the amount of energy involved can be up to 1026 J (1033 erg)....
Title: Solar Plumbing? Constraints on the 3D geometry of
constant-width coronal loops.
Authors: Martens, P. C. H.; Kankelborg, C. C.
Bibcode: 2000SPD....31.0144M
Altcode: 2000BAAS...32R1289M
Coronal loops are observed to have nearly constant apparent width
(Klimchuk, 1999; Watko & Klimchuk, 1999). We will show that only
one basic geometry is possible for constant-width coronal loops in
a force free magnetic field. In particular, the loop must describe a
helix. Furthermore, the torsion of the loop is determined solely by
the value of the force free parameter, alpha = (curl B) / B.
Title: On the Nature of the ``Moss'' Observed by TRACE
Authors: Martens, P. C. H.; Kankelborg, C. C.; Berger, T. E.
Bibcode: 2000ApJ...537..471M
Altcode:
``Moss'' is the name given to low-lying (~3000 km), hot (~1 MK) solar
coronal plasma that has been observed recently by the Transition
Region and Coronal Explorer (TRACE). This paper investigates two
hypotheses regarding the nature of the moss: (1) emission from small,
million degree loops; (2) emission from the legs of 3-10 million
degree loops. We update the coronal radiative loss curve, using the
most recent results for coronal abundances, and use an analytical loop
model to find that the first hypothesis requires a filling factor close
to unity to reproduce the observed emission measure, while the second
hypothesis results in a filling factor of about 0.1, in agreement
with other independent multiwavelength analyses of moss. We find that
the vertical extent and the height of the moss layer above the limb
are also very well reproduced with the second hypothesis. We further
show that the observed brightness of the moss scales linearly with
the loop pressure and filling factor, independent of the loop length,
and we derive a general expression for the conversion factor.
Title: Time Variability of the ``Quiet'' Sun Observed with
TRACE. II. Physical Parameters, Temperature Evolution, and Energetics
of Extreme-Ultraviolet Nanoflares
Authors: Aschwanden, Markus J.; Tarbell, Ted D.; Nightingale, Richard
W.; Schrijver, Carolus J.; Title, Alan; Kankelborg, Charles C.;
Martens, Piet; Warren, Harry P.
Bibcode: 2000ApJ...535.1047A
Altcode:
We present a detailed analysis of the geometric and physical
parameters of 281 EUV nanoflares, simultaneously detected with the
TRACE telescope in the 171 and 195 Å wavelengths. The detection and
discrimination of these flarelike events is detailed in the first paper
in this series. We determine the loop length l, loop width w, emission
measure EM, the evolution of the electron density ne(t) and
temperature Te(t), the flare decay time τdecay,
and calculate the radiative loss time τloss, the conductive
loss time τcond, and the thermal energy Eth. The
findings are as follows: (1) EUV nanoflares in the energy range of
1024-1026 ergs represent miniature versions
of larger flares observed in soft X-rays (SXR) and hard X-rays
(HXR), scaled to lower temperatures (Te<~2 MK),
lower densities (ne<~109 cm-3),
and somewhat smaller spatial scales (l~2-20 Mm). (2) The cooling
time τdecay is compatible with the radiative cooling
time τrad, but the conductive cooling timescale
τcond is about an order of magnitude shorter, suggesting
repetitive heating cycles in time intervals of a few minutes. (3)
The frequency distribution of thermal energies of EUV nanoflares,
N(E)~10-46(E/1024)-1.8 (s-1
cm-2 ergs-1) matches that of SXR microflares
in the energy range of 1026-1029, and exceeds
that of nonthermal energies of larger flares observed in HXR by a
factor of 3-10 (in the energy range of 1029-1032
ergs). Discrepancies of the power-law slope with other studies, which
report higher values in the range of a=2.0-2.6 (Krucker & Benz;
Parnell & Jupp), are attributed to methodical differences in the
detection and discrimination of EUV microflares, as well as to different
model assumptions in the calculation of the electron density. Besides
the insufficient power of nanoflares to heat the corona, we find also
other physical limits for nanoflares at energies <~1024
ergs, such as the area coverage limit, the heating temperature limit,
the lower coronal density limit, and the chromospheric loop height
limit. Based on these quantitative physical limitations, it appears
that coronal heating requires other energy carriers that are not
luminous in EUV, SXR, and HXR.
Title: The Scaling of Solar Flare Hard X-ray Emission to Other
Flaring Objects in the Universe
Authors: Martens, P. C. H.
Bibcode: 2000IAUS..195..133M
Altcode:
Fletcher & Martens have successfully modeled solar hard X-ray
sources observed at the top and footpoints of flaring magnetic loops
with a Fokker-Planck type particle transport code. I show here that
there are invariances in the Fokker-Planck equations that make these
results applicable to environments with vastly different physical
parameters, such as hard X-ray flares in accretion disks in active
galactic nuclei, and in RS CVn and ALGOL type binaries.
Title: Having Our Cake and Eating it, Too: Fast Imaging Spectroscopy
With a Multi-Order Slitless Spectrograph
Authors: Kankelborg, C. C.; Longcope, D. W.; Martens, P. C. H.
Bibcode: 2000SPD....3102101K
Altcode: 2000BAAS...32..829K
We describe a new type of EUV imaging spectrograph that combines high
spectral, spatial and temporal resolution. The instrument consists of
a slitless spectrograph with cameras placed at several diffraction
orders. The unique information derived from simultaneous imaging
at multiple orders allows the deconvolution of spectral and spatial
information, thus overcoming the limitations of a traditional slitless
spectrograph.
Title: Highly Energetic Physical Processes and Mechanisms for Emission
from Astrophysical Plasmas
Authors: Martens, P. C. H.; Tsuruta, S.; Weber, M. A.
Bibcode: 2000IAUS..195.....M
Altcode:
No abstract at ADS
Title: Chromospheric Damping of Alfvén Waves
Authors: De Pontieu, B.; Martens, P. C. H.; Hudson, H. S.
Bibcode: 2000SPD....31.0131D
Altcode: 2000BAAS...32..806D
We study the damping of Alfvén mode oscillations on coronal loops and
in the chromosphere. First we consider damping of standing waves on
coronal loops, such as those observed in the aftermath of a flare with
the Transition Region and Coronal Explorer (TRACE). We calculate the
leakage of wave energy from the coronal volume through the footpoints
of a coronal loop, assuming constant Alfvén speed vA in
the corona and vA varying exponentially with height in the
photosphere/chromosphere at both ends of the loop. We study analytically
the influence of chromospheric damping of standing waves on a coronal
loop and find that, for a moderate amount of chromospheric damping,
the footpoint leakage can be enhanced. The damping in the partially
ionized chromosphere is mostly due to collisions between ions and
neutrals. In a second part we calculate the damping time for Alfvén
waves of a given frequency, propagating through (model) chromospheres
of various solar structures such as active region plage, quiet sun
and the penumbra and umbra of sunspots. For a given wave frequency,
the maximum damping always occurs at temperature minimum heights
and in the coldest structure(s), i.e. the umbra of a sunspot. Energy
dissipation due to ion-neutral damping of Alfvén waves could play a
considerable role in the energy balance of umbrae, quiet sun and plage
for wave periods of the order, respectively, 100, 10 and 1 s.
Title: Dynamics in Restructuring Active Regions Observed During
Soho/Yohkoh/Gbo Campaigns
Authors: Schmieder, B.; Deng, Y.; Mandrini, C. H.; Rudawy, P.; Nitta,
N.; Mason, H.; Fletcher, L.; Martens, P.; Brynildsen, N.
Bibcode: 2000AdSpR..25.1879S
Altcode:
JOP17 and JOP 33 are SOHO Joint Observing Programs in collaboration
with Yohkoh/SXT and ground based observatories (GBO's), dedicated to
observe dynamical events through the atmosphere. During runs of these
programs we observed in restructuring active regions (ARs), surges,
subflares, bright knots, but not large flares and jets. From these
observations we have been able to derive some of the responses of the
coronal and chromospheric plasma to the evolution of the photospheric
magnetic field. Emerging flux in an AR led to the formation of Arch
Filament Systems in the chromosphere, hot loops and knots in the
transition region, and X-ray loops. Frequent surges have been observed
in relation to parasitic or mixed polarities, but coronal jets have not
yet been found. We discuss the possible mechanisms acting during the
restructuring of the active regions (reconnection or ``sea-serpent''
geometries)
Title: Coronal Heating by Resonant Absorption: The Effects of
Chromospheric Coupling
Authors: Beliën, A. J. C.; Martens, P. C. H.; Keppens, R.
Bibcode: 1999ApJ...526..478B
Altcode:
We present the first 2.5 dimensional numerical model calculations
of the nonlinear wave dynamics and heating by resonant absorption
in coronal loops with thermal structuring of the transition region
and higher chromosphere. The numerical calculations were done with
the Versatile Advection Code. The transition region can move freely
and is transparent for mass motions from chromosphere to corona. The
loops are excited at the chromospheric level by linearly polarized
monochromatic Alfvén waves. We find that the efficiency of resonant
absorption can be much lower than in equivalent line-tied coronal
loop models. The inefficiency is due to the fast rate at which slow
magnetosonic waves are nonlinearly generated in the chromosphere
and transition region. This leads to considerable transfer of energy
from the Alfvén wave to the magnetosonic waves. Consequently, only a
relatively small fraction of the Poynting flux that is injected into
the loop system at the chromospheric level is available at the coronal
level. Cavity leakage and detuning also have a negative impact on the
efficiency, but less so than the nonlinear energy transfer. Inclusion
of radiative and conductive losses improves the efficiency of resonant
absorption. While the efficiency of resonant absorption heating is low,
our results indicate that heating by compression and dissipation of the
slow magnetosonic waves and shocks can easily lead to a temperature rise
of a few percent, and for larger driver amplitudes even to a rise over
10%. Hence, our results support the idea of indirect coronal heating
through the nonlinear generation of magnetosonic waves that was put
forward more than 20 yr ago. Furthermore, the large transition region
and coronal density oscillations that are associated with the slow
magnetosonic waves provide an explanation for some observed coronal
and transition region loop extreme-ultraviolet intensity variations.
Title: The Dynamical Influence Of The Transition Region And
Chromosphere On The Heating Of Coronal Loops By Resonant Absorption
Of Alfvén Waves
Authors: Belien, A. J. C.; Martens, P. C. H.; Keppens, R.
Bibcode: 1999ESASP.446..167B
Altcode: 1999soho....8..167B
We present a numerical MHD study of coronal heating by resonant
absorption of Alfvén waves using models that include an extended
chromosphere and dynamical transition region. The calculations are
done with the Versatile Advection Code (VAC) and assume axisymmetric
loop configurations. Linear polarized, monochromatic Alfvén waves are
launched at the bottom of our extended chromosphere. The efficiency of
heating by resonant absorption of these waves in the corona is measured
by the ratio of Ohmic dissipation over the incoming Poyting flux at
the bottom of our chromosphere (averaged over a driving period). The
efficiency turns out to be much smaller than in loop models that
do not take the chromospheric and transition region coupling into
account. For our model, the efficiency is typically of the order of 10%
in contrast with values over 90% in models without the coupling taken
into account. The difference can be described in terms of efficient
nonlinear generation of compressive motions in the chromosphere
and transition region, the change of the coronal cavity length as a
consequence of the continuous motion of the transition region (due to
the the Alfvén wave pressure and compressive motions), and coronal
cavity leakage due to a finite Alfvén speed ratio between corona
and chromosphere. The compressive waves and motions lead to density
variations that should be observable. To proove that, our model results
are used to simulate some coronal and transition region CDS EUV line
observations as well as broad band EIT observations. The results are
used to give an explanation of EUV coronal brightenings in terms of
mass motions.
Title: Wave Heating and Nonlinear Dynamics of Coronal Loops
Authors: Beliën, A. J. C.; Martens, P. C. H.; Keppens, R.; Tóth, G.
Bibcode: 1999ASPC..184..248B
Altcode:
We present the first results of 2.5D nonlinear magnetohydrodynamic
wave heating simulations of solar coronal loops with inclusion
of the modeling of the coupling to the transition region and
chromosphere. Magnetic flux tubes with fixed lengths are considered
but the coronal extent of the loops as situated in between the two
transition regions can vary dynamically. The numerical simulations
were carried out with the Versatile Advection Code. The loops are
excited with linearly polarized Alfvén waves at the chromospheric
base. The main finding is that resonant absorption is not efficient
since most of the Poynting flux that enters the loop will be used to
support all the nonlinearly generated magnetoacoustic motions and the
corresponding compression of coronal plasma.
Title: On the Nature of the "Moss" Observed by TRACE
Authors: Martens, P. C. H.; Kankelborg, C. C.
Bibcode: 1999AAS...194.7903M
Altcode: 1999BAAS...31..963M
Moss is the name given to low lying ( 2 Mm), hot ( 1 MK) plasma that
has recently been observed by the Transition Region and Coronal
Explorer (TRACE). The moss occurs over some but not all magnetic
plage. We investigate two hypotheses regarding the nature of the moss:
(1) emission from small, million degree loops; (2) emission from the
legs of 2-5 million degree loops. An analytical loop model is used to
demonstrate that only the second hypothesis is consistent with the
observations. It is shown that the observed brightness of the moss
should scale as the third power of the loop maximum temperature.
Title: Can Streamer Blobs Prevent the Buildup of the Interplanetary
Magnetic Field?
Authors: van Aalst, M. K.; Martens, P. C. H.; Beliën, A. J. C.
Bibcode: 1999ApJ...511L.125V
Altcode: 1998astro.ph.12099V
Coronal mass ejections continuously drag closed magnetic field lines
away from the Sun, adding new flux to the interplanetary magnetic field
(IMF). We propose that the outward-moving blobs that have been observed
in helmet streamers are evidence of ongoing, small-scale reconnection
in streamer current sheets, which may play an important role in the
prevention of an indefinite buildup of the IMF. Reconnection between
two open field lines from both sides of a streamer current sheet
creates a new closed field line, which becomes part of the helmet,
and a disconnected field line, which moves outward. The blobs are
formed by plasma from the streamer that is swept up in the trough of
the outward-moving field line. We show that this mechanism is supported
by observations from Solar and Heliospheric Observatory (SOHO)/Large
Angle and Spectrometric Coronagraph. Additionally, we propose a thorough
statistical study to quantify the contribution of blob formation to the
reduction of the IMF and indicate how this mechanism may be verified
by observations with SOHO/Ultraviolet Coronagraph Spectrometer and the
proposed NASA Solar Terrestrial Relations Observatory and ESA Polar
Orbiter missions.
Title: Scientific highlights from the Solar and Heliospheric
Observatory
Authors: Martens, P. C. H.; Muglach, K.
Bibcode: 1999ASSL..243..325M
Altcode: 1999sopo.conf..325M
No abstract at ADS
Title: Energy and momentum deposition in coronal holes. Solar
coronal hole simulations compared with interpretations of YOHKOH
SXT observations
Authors: Tziotziou, K.; Martens, P. C. H.; Hearn, A. G.
Bibcode: 1998A&A...340..203T
Altcode:
A grid of 74 coronal models with parameterized heating distribution,
representing a wide range of physical parameters, has been
calculated. We find that three of these models reproduce the recent
observations made by Hara et al. (\cite{hara:tsun}) with the soft
X-ray telescope aboard the Japanese satellite Yohkoh, which indicate
a temperature of 1.8 ~ 2.4 x es 10(6) { K with an emission measure
of 10(25.5) to 10(26.2) cm^{-5}, while other solutions reproduce the
more standard Yohkoh and Skylab observations, which have a temperature
of about 1.4 x es 10(6) { K The best fit for the coronal temperature
and emission measure gives a velocity at the Earth's orbit of only
10 {km s^{-1}. A model including acceleration by Alfven waves gives
a final velocity of 630 km s^{-1} which is in agreement with the
observations. The mechanical heating flux at the transition region
is 2.1 x es 10(5) ergcms with a weighted average dissipation scale
length of 0.1 R_{\odot}. The flux of Alfven waves is 1 x es 10(5)
ergcms . In our models the velocity of the solar wind from coronal
holes is completely determined by the Alfven wave acceleration, in
contrast to previous models in which the Alfven wave acceleration
increased the velocity of the purely thermal model only by a factor
2. Observations of the non thermal broadening of the coronal red and
green lines are consistent with this model.
Title: Reconnection, Particle Acceleration, and Hard X-ray Emission
in Eruptive Solar Flares
Authors: Martens, Petrus C.
Bibcode: 1998APS..DPP.C2M04M
Altcode:
The frequent occurrence of Hard X-ray emission from the top of flaring
loops was one of the discoveries by the Hard X-ray telescope on board
the Japanese Yohkoh satellite. I will show how the combined effect of
magnetic field convergence and pitch- angle scattering of non-thermal
electrons injected at the top of the loop results in the generation of
looptop sources with properties akin to those observed by Yohkoh. In
addition it is shown that the injection of proton beams in the loop
legs, expected from theory, reproduces the observed high temperature
``ridges" in the loop legs by mirroring and energy loss through
collisions. I will interpret these numerical results as supporting the
now widely accepted model of an erupting magnetic flux tube generating
a reconnecting current sheet in its wake, where most of the energy
release takes place. The strong similarity with the reconnection
observed in the MRX experiment in Princeton will be analyzed in detail.
Title: A Model for Hard X-Ray Emission from the Top of Flaring Loops
Authors: Fletcher, L.; Martens, P. C. H.
Bibcode: 1998ApJ...505..418F
Altcode:
The frequent occurrence of hard X-ray emission from the top of
flaring loops was one of the discoveries by the Hard X-Ray Telescope
on board the Japanese Yohkoh satellite. In this paper we take a flare
current-sheet geometry and show how the combined effect of magnetic
field convergence and pitch-angle scattering of nonthermal electrons
injected at the top of the loop results in the generation of a looptop
source with properties akin to those observed by Yohkoh. We demonstrate
that a looptop source can be produced in both impulsive and gradual
phase loops. We further present a possible mechanism for the generation
of high-temperature ``ridges'' in the loop legs.
Title: An approximate self-consistent theory of the magnetic field
of fluted penumbrae
Authors: Neukirch, T.; Martens, P. C. H.
Bibcode: 1998A&A...332.1075N
Altcode: 1997astro.ph.11351N
A self-consistent mathematical description of the magnetic field of
fluted sunspot penumbrae is presented. This description is based on
an expansion of the nonlinear force-free magnetohydrostatic equations
written in cylindrical coordinates. The lowest order solutions are
mathematically equivalent %similar to laminated force-free equilibria
in Cartesian geometry. The lowest order solutions have no toroidal
component of the magnetic field and the magnetic pressure does not
vary with azimuth but the solutions allow arbitrary variations of
the magnetic field components with azimuth. Explicit solutions are
presented which have a realistic radial profile of the magnetic field
strength and reproduce the basic features of the observations.
Title: SOHO - YOHKOH Science Collaboration
Authors: Martens, P. C.
Bibcode: 1998ASSL..229..217M
Altcode: 1998opaf.conf..217M
No abstract at ADS
Title: Hard X-Ray Emission from a Mirror Trap at the Top of
Reconnecting Loops
Authors: Martens, P. C. H.; Fletcher, L.
Bibcode: 1998ASSL..229..269M
Altcode: 1998opaf.conf..269M
No abstract at ADS
Title: MHD and Plasma Interpretation of a Prominence Eruption Observed
by SOHO (Review)
Authors: Martens, P. C. H.
Bibcode: 1998ASPC..150..294M
Altcode: 1998IAUCo.167..294M; 1998npsp.conf..294M
No abstract at ADS
Title: Filament Disparition Brusque and CME - September 25-26,
1996 Event
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Aulanier, G.;
Demoulin, P.; Martens, P. C. H.; Zarro, D.; Deforest, C.; Thompson,
B.; St. Cyr, C.; Kucera, T.; Burkepile, J. T.; White, O. R.; Hanaoka,
Y.; Nitta, N.
Bibcode: 1998ASPC..150..366V
Altcode: 1998IAUCo.167..366V; 1998npsp.conf..366V
No abstract at ADS
Title: Surges and filaments in active regions during SOHO campaigns
Authors: Schmieder, B.; Deng, Y.; Rudawy, P.; Nitta, N.; Mandrini,
C. H.; Fletcher, L.; Martens, P.; Innes, D.; Young, P.; Mason, H.
Bibcode: 1998ESASP.421..323S
Altcode: 1998sjcp.conf..323S
No abstract at ADS
Title: Foreword
Authors: Koutchmy, S.; Martens, P.; Shibata, K.
Bibcode: 1998ESASP.421...14K
Altcode: 1998sjcp.conf...14K
No abstract at ADS
Title: Coordinated Eclipse and SOHO Observations on 26 February 1998
Authors: Muglach, B. Foing K.; Beaufort, T.; Orlando, S.; Martens,
P.; Desteve, C.
Bibcode: 1998ESASP.417..337M
Altcode: 1998cesh.conf..337M
No abstract at ADS
Title: A SOHO User Manual
Authors: Martens, Petrus C.
Bibcode: 1998LNP...507..263M
Altcode: 1998sspt.conf..263M
This paper is intended to serve as the first version of the "SOHO User
Manual", a "how to" guide for those interested in analyzing existing
SOHO data, or proposing new SOHO observations. Questions addressed
are, how to use the SOHO catalogs, where to find the appropriate data
analysis software, how to request permission to use proprietary data,
how to propose and prepare SOHO observing programs.
Title: Solar Coronal Heating: AC versus DC
Authors: Milano, Leonardo J.; Gómez, Daniel O.; Martens, Petrus C. H.
Bibcode: 1997ApJ...490..442M
Altcode:
The heating of the plasma confined in active regions of the solar
corona is caused by the dissipation of magnetic stresses induced
by the photospheric motions of the loop footpoints. The aim of the
present paper is to analyze whether solar coronal heating is dominated
by slow (DC) or rapid (AC) photospheric driving motions. We describe
the dynamics of a coronal loop through the reduced magnetohydrodynamic
equations and assume a fully turbulent state in the coronal plasma. The
boundary condition for these equations is the subphotospheric velocity
field that stresses the magnetic field lines, thus replenishing
the magnetic energy that is continuously being dissipated inside the
corona. In a turbulent scenario, energy is efficiently transferred by a
direct cascade to the microscale, where viscous and Joule dissipation
take place. Therefore, for the macroscopic dynamics of the fields,
the net effect of turbulence is to produce a dramatic enhancement of
the dissipation rate. This effect of the microscale on the macroscale
is modeled through effective dissipation coefficients much larger than
the molecular ones. We consistently integrate the large-scale evolution
of a coronal loop and compute the effective dissipation coefficients
by applying a closure model (the eddy-damped, quasi-normal Markovian
approximation). For broadband power-law photospheric power spectra,
the heating of coronal loops is DC dominated. Nonetheless, a better
knowledge of the photospheric power spectrum as a function of both
frequency and wavenumber will allow for more accurate predictions of
the heating rate from this simple model.
Title: The Solar and Heliospheric Observatory (SOHO) in 1996.
Authors: Domingo, V.; Fleck, B.; Martens, P.; Sanchez, L.
Bibcode: 1997joso.proc....4D
Altcode:
This report gives a brief overview of SOHO's scientific production in
its first year of operation.
Title: An Analytical Model for Fluted Sunspots and a New
Interpretation of Evershed Flow and X-Ray Anemones
Authors: Martens, Petrus C. H.; Hurlburt, Neal E.; Title, Alan M.;
Acton, Loren W.
Bibcode: 1996ApJ...463..372M
Altcode:
We present a force-free constant-α model for the magnetic field in and
above so-called "fluted" sunspots. This model is motivated by recent
high-resolution observations of Title et al. at the Swedish Solar
Observatory in La Palma. They observed that the inclination angle of
the magnetic field in the penumbra of sunspots oscillates rapidly
with azimuth, with a period of about 60 and an amplitude of about
18°. They further find that there is little variation in the radial
direction and in absolute field strength. The resulting phenomenon
of interlocking high- and low-inclination field lines was called
"flutedness. In our model, the parameters are chosen to reproduce
the La Palma magnetograms, and an analytical expression is obtained for
the three-dimensional magnetic field emanating from the sunspot's umbra
and penumbra. The model correctly reproduces the azimuthal variation in
inclination angle, as well as the mean constancy of the magnetic field
strength, and the appearance of a highly corrugated neutral line on
the limb side of off-center sunspots. We find that the "flutedness"
results in a highly complex topology in a boundary layer extending
from the photo sphere into the chromosphere, while the coronal field is
uniform. Title et al. demonstrated that the Evershed flow occurs
in regions of nearly horizontal magnetic field, and tacitly assumed,
as is done in most of the literature, that the dark filaments in which
the flow is observed form individual magnetic flux tubes. Our magnetic
field solution suggests that the regions of nearly horizontal field
at the photo spheric boundary may not form individual magnetic flux
tubes, but rather a series of short horizontal loops bridging a neutral
line that is stretched in the radial direction along the penumbra,
up to the outer penumbral boundary. Hence, the Evershed flow could not
be a simple siphon flow in the radial direction, but would consist of
phase-coordinated flows along the many short loops bridging the neutral
line. However, the assumption of a force-free field breaks down in
this region of the atmosphere, and the topology suggested by it may
not materialize in reality. We further demonstrate that there
are large variations in the photospheric cross sections of coronal
loops, due to the complexity of the field near their photospheric
footpoints. Under the assumption of constant energy input per unit
surface area into these loops, the variation in cross section is
qualitatively consistent with the variation in X-ray brightness of
loops in penumbral "anemones" observed by Yohkoh.
Title: High resolution Lyalpha images obtained with the transition
region camera (TRC): a comparison with Hα observations
Authors: Wiik, J. E.; Foing, B. H.; Martens, P.; Fleck, B.;
Schmieder, B.
Bibcode: 1996AdSpR..17d.105W
Altcode: 1996AdSpR..17..105W
Comparing high spatial resolution (~ 1'') images observed in Lyalpha
with the Transition Region Camera (TRC) and in Hα at Sacramento Peak
and Meudon Observatories, we notice that some structures are well
correlated in the two lines (plages), while others are less correlated
(chromospheric network, filaments). This is an indication of the
inhomogeneous distribution of physical parameters in these structures.
Title: On Small Coronal Particle Acceleration Sites with Widespread
Magnetic Connections
Authors: Aurass, H.; Klein, K. -L.; Martens, P. C. H.
Bibcode: 1996ASPC..111..194A
Altcode: 1997ASPC..111..194A
For the 25 October 1994 flare in NOAA AR 7792, the authors present
radio spectral, radio imaging and Yohkoh SXT observations revealing
features of reconnection and energy release in coronal structures.
Title: SOHO Ground Segment, Science Operations, and Data Products
Authors: St. Cyr, O. C.; Sánchez-Duarte, L.; Martens, P. C. H.;
Gurman, J. B.; Larduinat, E.
Bibcode: 1995SoPh..162...39S
Altcode:
We describe the ground segment, pre-launch operations concepts, and
data products supporting the SOHO mission. Our goal is threefold:
first, we provide a historical view of the design and development of
the systems described here, as a background perspective to those who
will use the system and those who may build such systems for future
missions. Second, because we hope that many researchers from the solar
and space physics communities will visit these facilities during the
mission, we provide an overview for the benefit of the end-user. We
anticipate that visitors to GSFC may plan observations for one or more
of SOHO's complement of instruments, and such researchers may use the
facilities to analyze data gathered by the SOHO instruments. Third,
we present the working plan for investigators with groundbased or
other spacebased instruments to collaborate with SOHO.
Title: The point spread function of the soft X-ray telescope aboard
Yohkoh
Authors: Martens, Petrus C.; Acton, Loren W.; Lemen, James R.
Bibcode: 1995SoPh..157..141M
Altcode:
The point spread function of the SXT telescope aboardYohkoh has been
measured in flight configuration in three different X-ray lines
at White Sands Missile Range. We have fitted these data with an
elliptical generalization of the Moffat function. Our fitting method
consists of χ2 minimizationin Fourier space, especially
designed for matching of sharply peaked functions. We find excellent
fits with a reduced χ2 of order unity or less for single
exposure point spread functions over most of the CCD. Near the edges
of the CCD the fits are less accurate due to vignetting. From fitting
results with summation of multiple exposures we find a systematic
error in the fitting function of the order of 3% near the peak of the
point spread function, which is close to the photon noise for typical
SXT images in orbit. We find that the full width to half maximum and
fitting parameters vary significantly with CCD location. However, we
also find that point spread functions measured at the same location
are consistent to one another within the limit determined by photon
noise. A `best' analytical fit to the PSF as function of position
on the CCD is derived for use in SXT image enhancement routines. As
an aside result we have found that SXT can determine the location of
point sources to about a quarter of a 2.54 arc sec pixel.
Title: Preparing for SOHO: results from the transition region camera
Authors: Wiik, J. E.; Foing, B. H.; Schmieder, B.; Martens, P.;
Fleck, B.
Bibcode: 1994ESASP.373..433W
Altcode: 1994soho....3..433W
No abstract at ADS
Title: First Detection of Correlated Electron Beams and Plasma Jets
in Radio and Soft X-Ray Data
Authors: Aurass, H.; Klein, K. -L.; Martens, P. C. H.
Bibcode: 1994SoPh..155..203A
Altcode:
From a common analysis of solar radio spectral and imaging data of a
fast drift burst of type U(N) together with Yohkoh soft X-ray images
it is shown that the radio emission is compatible with electron beams
injected and reflected in extended loops. The electron beam production
coincides with the injection of hot matter, visible as a jetlike soft
X-ray feature in the underlying loop system.
Title: Material Ejection
Authors: Webb, David F.; Forbes, Terry G.; Aurass, Henry; Chen, James;
Martens, Piet; Rompolt, Bogdan; Rusin, Vojtech; Martin, Sara F.
Bibcode: 1994SoPh..153...73W
Altcode:
This paper reviews the major discussions and conclusions of the Flares
22 Workshop concerning the physical processes involved in mass ejecta
events, with an emphasis on large-scale phenomena, especially Coronal
Mass Ejections (CMEs). New insights have been gained from recent
data obtained from the SMM andYohkoh spacecraft and from several new
ground-based radio and optical instruments, as well as from theoretical
advances concerning the origins, driving mechanisms and long-term
evolution of CMEs.
Title: Possible detection of a stellar flare-generated particle beam
in polarized light
Authors: Saar, S. H.; Martens, P. C. H.; Huovelin, J.; Linnaluoto, S.
Bibcode: 1994A&A...286..194S
Altcode:
We present broadband linear polarization measurements of the active
dK5e flare star, BD +26 730, which show a rapid change in polarization
amplitude and direction over a two hour period. We conclude that
impact polarization resulting from flare-generated particle beams
is the most likely cause of the polarization variations. If this
interpretation is correct, this event represents the most direct
evidence to date for flare-generated particle beams in a star other
than the Sun. With proton beams as the most probable source, energy
fluxes of the order of 10^9-10^ erg/cm2/s are required to power the
observed polarization changes. Using the non-flare polarization level
(likely produced by stellar magnetic regions) and simple models,
we estimate a lower limit of 7% for the inhomogeneous component of
the magnetic region area filling factor. We compare our results with
solar flares and suggest future observational and theoretical efforts.
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.
Bibcode: 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: An Analytical Model for Fluted Sunspots and its Relation with
Evershed Flow and X-Ray Anemone
Authors: Hurlburt, Neal E.; Martens, Petrus C.; Title, Alan M.;
Acton, Loren
Bibcode: 1994ASPC...68..300H
Altcode: 1994sare.conf..300H
No abstract at ADS
Title: Volume Reconstruction of Magnetic Fields using Solar Imagery
Authors: Hurlburt, Neal E.; Martens, Petrus C. H.; Slater, Gregory L.;
Jaffey, Steven M.
Bibcode: 1994ASPC...68...30H
Altcode: 1994sare.conf...30H
No abstract at ADS
Title: A Simple Circuit Model for the December 2 1991 Flare
Authors: Martens, P. C. H.; Tsuneta, S.
Bibcode: 1994xspy.conf..327M
Altcode:
No abstract at ADS
Title: Morphological Evolution of the Post-Flare Loops of June
25-26, 1992
Authors: Anwar, B.; Hiei, E.; Hudson, H. S.; Acton, L. W.; Metacalf,
T.; Lemen, J.; Martens, P.
Bibcode: 1994xspy.conf..121A
Altcode:
No abstract at ADS
Title: An analytical model for fluted sunspots and a new
interpretation of Evershed flow
Authors: Martens, P. C.; Hurlburt, N.; Title, A. M.; Acton, L. A.
Bibcode: 1994ASIC..433..237M
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.
Bibcode: 1993BAAS...25.1179M
Altcode:
No abstract at ADS
Title: A Force-Free Model for Fluted Sunspots
Authors: Martens, P. C. H.; Hurlburt, N.; Title, A. M.
Bibcode: 1993BAAS...25R1218M
Altcode:
No abstract at ADS
Title: Computed Tomographic Reconstruction of the Soft X-ray Corona
Authors: Hurlburt, N. E.; Martens, P. C. H.; Jaffey, S. M.; Slater,
G. L.
Bibcode: 1993BAAS...25.1188H
Altcode:
No abstract at ADS
Title: Normal Incidence X-Ray Telescope Power Spectra of X-Ray
Emission from Solar Active Regions. I. Observations
Authors: Gomez, Daniel O.; Martens, Petrus C. H.; Golub, Leon
Bibcode: 1993ApJ...405..767G
Altcode:
Fourier analysis is applied to very high resolution image of coronal
active regions obtained by the Normal Incidence X-Ray Telescope is
used to find a broad isotropic power-law spectrum of the spatial
distribution of soft X-ray intensities. Magnetic structures of all
sizes are present down to the resolution limit of the instrument. Power
spectra for the X-ray intensities of a sample of topologically different
active regions are found which fall off with increasing wavenumber
as 1/k-cubed. A model is presented that relates the basic features
of coronal magnetic fluctuations to the subphotospheric hydrodynamic
turbulence that generates them. The model is used to find a theoretical
power spectrum for the X-ray intensity which falls off with increasing
wavenumber as 1/k-cubed. The implications of a turbulent regime in
active regions are discussed.
Title: Normal Incidence X-Ray Telescope Power Spectra of X-Ray
Emission from Solar Active Regions. II. Theory
Authors: Gomez, Daniel O.; Martens, Petrus C. H.; Golub, Leon
Bibcode: 1993ApJ...405..773G
Altcode:
In a previous paper, we used the very high resolution images of coronal
active regions obtained by the Normal Incidence X-Ray Telescope to
study the size distribution of X-ray-emitting structures. A Fourier
analysis of these images showed a broad-band, isotropic, power-law
spectrum for the spatial distribution of soft X-ray intensities. The
presence of a broad-band spectrum indicates that magnetic structures
of all sizes are 3" present, at least down to the resolution limit
of the instrument, which is about ¾". In the present paper, we
present a model that relates the basic features of coronal magnetic
fluctuations to the subphotospheric hydrodynamic turbulence that
generates them. The main result of this paper is that from this
model we obtain a theoretical power spectrum for the X-ray intensity,
which falls off with increasing wavenumber as k-3, fitting
remarkably well the observed spectra that we obtained from a sample
of topologically different active regions. We speculate that the
nonlinear interactions of these externally driven fluctuations will
contribute to establish a magnetohydrodynamic turbulent regime in the
corona. We suggest that the bulk of the energy delivered to the corona
from footpoint motions directly cascades down to very microscopic length
scales, where it efficiently dissipates and heats the plasma. However,
since the wavenumber range associated with the cascade and dissipation
regions are still beyond present-day spatial resolution limits, the
presence of a turbulent regime cannot be observationally confirmed.
Title: Book Review: Applying Fractals in Astronomy
Authors: Martens, P. C.; Kleczek, Josip; Heinzel, P.
Bibcode: 1993SoPh..143..401M
Altcode:
No abstract at ADS
Title: Book-Review: Applying Fractals in Astronomy
Authors: Heck, A.; Perdang, J. M.; Martens, P. C.
Bibcode: 1993SoPh..143..401H
Altcode:
No abstract at ADS
Title: Yohkoh/SXT Observations and Models For an Eruptive Flare
Authors: Martens, P. C. H.; Tsuneta, S.
Bibcode: 1992AAS...181.5502M
Altcode: 1992BAAS...24.1211M
On Dec. 2, 1991 Yohkoh/SXT obtained a unique sequence of high quality
X-ray images of what appeared to be a plasmoid ejection and two-ribbon
flare, viewed in cross-section on the Solar limb. We will show a
movie displaying the preflare plasmoid formation, the eruption of the
plasmoid followed by the onset of the flare, and finally what appears
to be the formation of postflare loops in a quadrupole type field
configuration. We have modelled this sequence of events with a simple
Martens-Kuin circuit approach, approximating the plasmoid/filament
as a line current, added to a background field consisting of three
line-dipoles. Overlays of the X-ray movie with the calculated magnetic
field morphology show excellent agreement, and thus lend further
credibility to the two-ribbon flare scenario developed by Carmichael,
Sturrock, Hirayama and many others thereafter.
Title: Erratum - Spatial Power Spectra from YOHKOH Soft X-Ray Images
Authors: Martens, P. C. H.; Gomez, D. O.
Bibcode: 1992PASJ...44..691M
Altcode:
No abstract at ADS
Title: Spatial Power-Spectra from YOHKOH Soft X-Ray Images
Authors: Martens, Petrus C. H.; Gomez, Daniel O.
Bibcode: 1992PASJ...44L.187M
Altcode:
We analyze three sequences of images from active regions, and a full
disk image obtained by Yohkoh's Soft X-ray Telescope. Two sequences
are from a region at center disk observed through different filters,
and one sequence is from the limb. After Fourier-transforming the
X-ray intensity of the images we find nearly isotropic power-spectra
with an azimuthally integrated slope of -2.1 for the center disk,
and -2.8 for the limb images. The full-disk picture yields a spectrum
of -2.4. These results are different from the active region spectra
obtained with the Normal Incidence X-ray Telescope which have a
slope of the order of -3.0, and we ascribe this to the difference in
temperature response between the instruments. However, both the SXT
and NIXT results are consistent with coronal heating as the endresult
of a downward quasistatic cascade (in lengthscales) of free magnetic
energy in the corona, driven by footpoint motions in the photosphere.
Title: Magnetohydrodynamic Non-Equilibrium - a Numerical Experiment
Authors: Martens, P.; Sun, M. T.; Wu, S. T.
Bibcode: 1992LNP...399...65M
Altcode: 1992esf..coll...65M; 1992IAUCo.133...65M
No abstract at ADS
Title: Spectra of MHD turbulence in the solar corona
Authors: Gomez, D.; Martens, P. C. H.
Bibcode: 1992MmSAI..63..755G
Altcode:
A theoretical model is presented which relates the basic features of
coronal MHD turbulence with the subphotospheric HD turbulence that
drives it. By performing a Kolmogorov-type dimensional analysis, the
observed power law spectrum was reproduced. The power law was found
to be independent of the exact subphotospheric power distribution.
Title: Coronal heating through lack of MHD equilibrium
Authors: Martens, P. C. H.; Sun, M. T.; Wu, S. T.
Bibcode: 1992AIPC..267..111M
Altcode: 1992ecsa.work..111M
We present an analytical example of a series of magnetostatic equilibria
with an endpoint. Numerical simulation demonstrates that oscillatory
behavior sets in at the endpoint, with a typical amplitude of 50
km/sec. We suggest this in situ wave generation is an energy source
for coronal heating.
Title: Can Yohkoh/SXT observe coronal MHD turbulence?
Authors: Martens, P. C. H.; Gomez, D.
Bibcode: 1992MmSAI..63..759M
Altcode:
The question of whether the Yokoh Soft-X-ray Telescope (SXT) would
be sufficiently spatially resolved for observing power spectra of
the distribution of X-ray intensity was investigated. SXT soft X-ray
images were simulated by artificially degrading the resolution of the
digitized Normal Incidence X-ray Telescope X-ray images analyzed by
Gomez and Martens (1992) were analyzed. Results of spectral analysis
of the resulting images demonstrate that the Yohkoh SXT will be able
to observe power spectra over a sufficient range of spatial scales.
Title: Shear-induced instability and arch filament eruption: A
magnetohydrodynamic (MHD) numerical simulation
Authors: Wu, S. T.; Song, M. T.; Martens, P. C. H.; Dryer, M.
Bibcode: 1991SoPh..134..353W
Altcode:
We investigate, via a two-dimensional (nonplanar) MHD simulation, a
situation wherein a bipolar magnetic field embedded in a stratified
solar atmosphere (i.e., arch-filament-like structure) undergoes
symmetrical shear motion at the footpoints. It was found that the
vertical plasma flow velocities grow exponentially leading to a
new type of global MHD-instability that could be characterized
as a `Dynamic Shearing Instability', with a growth rate of about
√8{ovV}Aa, where {ovV}A is the average Alfvén
speed and a−1 is the characteristic length scale. The
growth rate grows almost linearly until it reaches the same order of
magnitude as the Alfvén speed. Then a nonlinear MHD instability occurs
beyond this point. This simulation indicates the following physical
consequences: the central loops are pinched by opposing Lorentz forces,
and the outer closed loops stretch upward with the vertically-rising
mass flow. This instability may apply to arch filament eruptions (AFE)
and coronal mass ejections (CMEs).
Title: A Numerical Experiment on the Origin of MHD Non-Equilibrium
Authors: Martens, P. C. H.; Sun, M. T.; Wu, S. T.
Bibcode: 1991BAAS...23.1035M
Altcode:
No abstract at ADS
Title: Spectra of MHD Turbulence in the Solar Corona
Authors: Gómez, D.; Martens, P. C. H.
Bibcode: 1991BAAS...23.1062G
Altcode:
No abstract at ADS
Title: Spectra of MHD Turbulence in Coronal Active Regions (With
3 Figures)
Authors: Gomez, D.; Martens, P.; Herant, M.; Pardo, F.; Golub, L.
Bibcode: 1991mcch.conf..124G
Altcode:
No abstract at ADS
Title: SXT Observations of MHD Turbulance in Active Regions
Authors: Martens, P. C. H.; Gómez, D. O.; Slater, G.; Golub, L.
Bibcode: 1991LNP...387..291M
Altcode: 1991fpsa.conf..291M
The recent discovery from NIXT images that the Fourier transform of
the X-ray intensity in active regions is a power-law, is consistent
with 2D MHD turbulence theory. We briefly discuss this theory and its
application to the heating of the solar corona. Then we demonstrate that
SXT will be capable of observing similar spectra, even in compressed
data-transfer mode between flare observations. Finally we discuss
observing plans for verification of the hypothesis of coronal heating
through turbulent MHD cascades.
Title: Magnetic Fields in Quiescent Prominences
Authors: van Ballegooijen, A. A.; Martens, P. C. H.
Bibcode: 1990ApJ...361..283V
Altcode:
The origin of the axial fields in high-latitude quiescent prominences
is considered. The fact that almost all quiescent prominences obey
the same hemisphere-dependent rule strongly suggests that the solar
differential rotation plays an important role in producing the axial
fields. However, the observations are inconsistent with the hypothesis
that the axial fields are produced by differential rotation acting on
an existing coronal magnetic field. Several possible explanations for
this discrepancy are considered. The possibility that the sign of the
axial field depends on the topology of the magnetic field in which
the prominence is embedded is examined, as is the possibility that
the neutral line is tilted with respect to the east-west direction, so
that differential rotation causes the neutral line also to rotate with
time. The possibility that the axial fields of quiescent prominences
have their origin below the solar surface is also considered.
Title: Neutral Beams in Two-Ribbon Flares and in the Geomagnetic Tail
Authors: Martens, P. C. H.; Young, A.
Bibcode: 1990ApJS...73..333M
Altcode:
The current sheet created in the wake of an erupting filament during
a two-ribbon flare is studied. A comparison with the geomagnetic tail
shows that the physics of these systems is very similar, and therefore
the existence of super Dreicer fields and the generation of netural
beams traveling down the postflare loops with small pitch angles may
be expected. The observational evidence for neutral beams in flares is
reviewed and found to be generally supportive, while contracting the
widely held hypothesis of electron beams. A dimensional analysis further
demonstrates that the results for self-consistent numerical simulations
of the current sheet in the geomagnetic tail can directly be scaled
to the coronal current sheet, and the scaling parameters are derived.
Title: Diagnostics for Low Energy Proton Beams in Solar Flares
Authors: Martens, P. C. H.
Bibcode: 1990BAAS...22R.825M
Altcode:
No abstract at ADS
Title: Observational Evidence for Heating through MHD Turbulence in
Coronal Active Regions
Authors: Gomez, D.; Martens, P. C. H.; Herant, M.; Golub, L.
Bibcode: 1990BAAS...22Q.796G
Altcode:
No abstract at ADS
Title: A Numerical Experiment on the Critical Shear in Relation to
the Non-equilibrium of a Force-free Magnetic Field Evolution
Authors: Sun, M. T.; Wu, S. T.; Martens, P. C. H.
Bibcode: 1990BAAS...22..854S
Altcode:
No abstract at ADS
Title: A self-consistent model for beam generation in two-ribbon
flares.
Authors: Martens, P. C. H.
Bibcode: 1990ppsa.conf..259M
Altcode:
The equations governing the evolution of the current sheet created in
a solar two-ribbon flare are derived. The finite gyroradius of the
protons is explicitly accounted for. It is demonstrated that in the
dimensionless form of these equations the parameters are similar to
those for the geomagnetic tail. Consequently one can expect a similar
type of evolution.
Title: Helical flux ropes in solar prominences
Authors: Martens, P. C. H.; van Ballegooijen, A. A.
Bibcode: 1990GMS....58..337M
Altcode:
The present numerical method for the computation of force-free,
cancelling magnetic structures shows that flux cancellation at the
neutral line in a sheared magnetic arcade generates helical field
lines that can support a prominence's plasma. With increasing flux
cancellation, the axis of the helical fields moves to greater heights;
this is suggestive of a prominence eruption. Two alternative scenarios
are proposed for the formation of polar crown prominences which yield
the correct axial magnetic field sign. Both models are noted to retain
the formation of helical flux tubes through flux cancellation as their
key feature.
Title: NIXT Observations of the June 23 1988 Flare and their
Theoretical Interpretation
Authors: Martens, P. C. H.; Golub, L.; Herant, M.
Bibcode: 1990ppsa.conf..153M
Altcode:
No abstract at ADS
Title: A Self Consistent Model for Beam Generation in Two-Ribbon
Flares.
Authors: Martens, P. C. H.
Bibcode: 1990ppsa.conf..257M
Altcode:
No abstract at ADS
Title: Time-dependent corona models : scaling laws.
Authors: Korevaar, P.; Martens, P. C. H.
Bibcode: 1989A&A...226..203K
Altcode:
Scaling laws are derived for the one-dimensional time-dependent Euler
equations that describe the evolution of a spherically symmetric stellar
atmosphere. With these scaling laws the results of the time-dependent
calculations by Korevaar (1989) obtained for one star are applicable
over the whole Hertzsprung-Russell diagram and even to elliptic
galaxies. The scaling is exact for stars with the same M/R-ratio and
a good approximation for stars with a different M/R-ratio. The global
relaxation oscillation found by Korevaar (1989) is scaled to main
sequence stars, a solar coronal hole, cool giants and elliptic galaxies.
Title: A Circuit Model for Filament Eruptions and Two-Ribbon Flares
Authors: Martens, P. C. H.; Kuin, N. P. M.
Bibcode: 1989SoPh..122..263M
Altcode:
We derive a circuit model for solar filament eruptions and two-ribbon
flares which reproduces the slow energy build up and eruption of the
filament, and the energy dissipation in a current sheet at the top of
post-flare loops during the two-ribbon flare. In our model the free
magnetic energy is concentrated in a current through the filament,
another current through an underlying current sheet, and surface return
currents. The magnetic field configuration, generated by these currents
and a general photospheric background field, has a topology similar
to the field topology derived from observations.
Title: First Evidence for Particle Beams in a Stellar Flare
Authors: Saar, S. H.; Martens, P.; Huovelin, J.
Bibcode: 1989BAAS...21.1192S
Altcode:
No abstract at ADS
Title: A Study of Dissipative Structures in the Solar Corona with
High-Resolution NIXT Images
Authors: Gomez, D.; Martens, P. C. H.; Golub, L.
Bibcode: 1989BAAS...21R1150G
Altcode:
No abstract at ADS
Title: Numerical Simulation of Well Observed Filament Eruptions
Authors: Martens, P. C. H.; Huang, G.
Bibcode: 1989BAAS...21.1186M
Altcode:
No abstract at ADS
Title: Formation and Eruption of Solar Prominences
Authors: van Ballegooijen, A. A.; Martens, P. C. H.
Bibcode: 1989ApJ...343..971V
Altcode:
A model for the magnetic field associated with solar prominences is
considered. It is shown that flux cancellation at the neutral line of a
sheared magnetic arcade leads to the formation of helical field lines
which are capable, in principle, of supporting prominence plasma. A
numerical method for the computation of force-free, canceling magnetic
structures is presented. Starting from an initial potential field
we prescribe the motions of magnetic footpoints at the photosphere,
with reconnection occurring only at the neutral line. As more and more
flux cancels, magnetic flux is transferred from the arcade field to
the helical field. Results for a particular model of the photospheric
motions are presented. The magnetic structure is found to be stable: the
arcade field keeps the helical field tied down at the photosphere. The
axis of the helical field moves to larger and larger height, suggestive
of prominence eruption. These results suggest that prominence eruptions
may be trigered by flux cancellation.
Title: Theretical Analysis of the June 23 1988 Flare
Authors: Martens, P. C. H.
Bibcode: 1989BAAS...21..851M
Altcode:
No abstract at ADS
Title: Proton Acceleration in Solar Flares and in the Geomagnetic
Tail:A Comparison.
Authors: Martens, P. C. H.; Young, A.
Bibcode: 1989npvp.conf..381M
Altcode:
No abstract at ADS
Title: Preflare activity.
Authors: Priest, E. R.; Gaizauskas, V.; Hagyard, M. J.; Schmahl, E. J.;
Webb, D. F.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson,
R. S.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.;
Karpen, J. T.; Martres, M. -J.; Porter, J. G.; Schmieder, B.; Smith,
J. B., Jr.; Toomre, J.; Woodgate, B.; Waggett, P.; Bentley, R.;
Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.; Martens, P.
Bibcode: 1989epos.conf....1P
Altcode:
Contents: 1. Introduction. 2. Magnetohydrodynamic
instability. 3. Preflare magnetic and velocity fields. 4. Coronal
manifestations of preflare activity.
Title: The Generation of Neutral Beams in Two-Ribbon Flares
Authors: Young, A.; Martens, P. C. H.
Bibcode: 1988BAAS...20..977Y
Altcode:
No abstract at ADS
Title: The Generation of Proton Beams in Two-Ribbon Flares
Authors: Martens, P. C. H.
Bibcode: 1988ApJ...330L.131M
Altcode:
It is shown that, in the current sheet at the top of the arcade
of postflare loops in a two-ribbon solar flare, particle beams are
generated by direct electric-field acceleration. The acceleration
process is completely collisionless and is limited only by the
gyromotion along the component of the magnetic field perpendicular
to the sheet. This mechanism is similar to the particle acceleration
in the geomagnetic tail. Neutral beams emanate from the sheet with
almost zero pitch angle, making protons the main carriers of the beam
energy. Approximately 10 to the 35th protons/sec are generated with
a typical energy of 200 keV. Their energy distribution is a single
power law, with an upper and lower energy cut-off. Such a population
is capable of simultaneously generating the observed impulsive-phase
hard X-rays and the gamma rays.
Title: The generation of proton beams in two-ribbon flares.
Authors: Martens, P. C. H.
Bibcode: 1988sscd.conf..501M
Altcode:
It is shown that in the current sheet at the top of the arcade of
postflare loops in a two-ribbon flare, high energy particle beams are
generated by direct electric field acceleration. The plasma beams in the
current sheet are completely collisionless, and the acceleration of the
protons and electrons is limited only by the gyration along the small
component of the magnetic field perpendicular to the sheet. This process
is identical with the particle acceleration in the geomagnetic tail.
Title: Direct Electric Field Acceleration in Two-Ribbon Flares
Authors: Martens, P. C. H.; Slater, G. L.
Bibcode: 1987BAAS...19..919M
Altcode:
No abstract at ADS
Title: The thermal stability of coronal loops by nonlinear diffusion
asymptotics
Authors: Pakkert, J. W.; Verhulst, F.; Martens, P. C. H.
Bibcode: 1987A&A...179..285P
Altcode:
The thermal structure of the plasma in coronal loops is
re-investigated. The authors assume that the plasma is confined to
move along the field lines because of the high plasma β and study
the time variability of the temperature structure of the plasma along
a field line. With the supposition that the evolution of the plasma
takes place on the thermal timescale, which is much larger than the
dynamical timescale, they derive a nonlinear reaction-diffusion equation
(and some additional constraints) that describes the time-dependent
behaviour of the temperature structure. This equation is studied with
the use of nonlinear diffusion asymptotics, in particular singular
perturbation techniques.
Title: Energy conversion in the coronal plasma.
Authors: Martens, P. C. H.
Bibcode: 1986NASCP2442..407M
Altcode: 1986copp.nasa..407M
Solar and stellar X-ray emission are the observed waste products
of the interplay between magnetic fields and the motion of stellar
plasma. Theoretical understanding of the process of coronal heating is
of utmost importance, since the high temperature is what defines the
corona in the first place. Most of the research described deals with
the aspects of the several rivalling theories for coronal heating. The
rest of the papers deal with processes of energy conversion related
to flares.
Title: A coordinate free description of magnetohydrostatic equilibria.
Authors: Martens, P. C. H.
Bibcode: 1986NASCP2442..431M
Altcode: 1986copp.nasa..431M
The question what geometrical restrictions are imposed on static
magnetic fields by the magnetohydrostatic (MHS) equation is
addressed. The general mathematical problem is therefore to determine
the solutions of the MHS equations in the corona subject to an arbitrary
normal component of the magnetic field at the boundary and arbitrary
connectivity. What constraints the MHS equations impose on the geometry
of the solutions, expressed in metric tensors, will be determined.
Title: Coronal manifestations of preflare activity
Authors: Schmahl, E. J.; Webb, D. F.; Woodgate, B.; Waggett, P.;
Bentley, R.; Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.;
Martens, P.
Bibcode: 1986epos.conf.1.48S
Altcode: 1986epos.confA..48S
A variety of coronal manifestations of precursors or preheating for
flares are discussed. Researchers found that almost everyone with a
telescope sees something before flares. Whether an all-encompassing
scenario will ever be developed is not at all clear at present. The
clearest example of preflare activity appears to be activated filaments
and their manifestations, which presumably are signatures of a changing
magnetic field. But researchers have seen two similar eruptions, one
without any evidence of emerging flux (Kundu et al., 1985) and the
other with colliding poles (Simon et al., 1984). While the reconnection
of flux is generally agreed to be required to energize a flare, the
emergence of flux from below (at least on short timescales and in
compact regions) does not appear to be a necessary condition. In some
cases the cancelling of magnetic flux (Martin, 1984) by horizontal
motions instead may provide the trigger (Priest, 1985) Researchers
found similarities and some differences between these and previous
observations. The similarities, besides the frequent involvement of
filaments, include compact, multiple precursors which can occur both at
and near (not at) the flare site, and the association between coronal
sources and activity lower in the atmosphere (i.e., transition zone
and chromosphere).
Title: A dynamic model of filament eruptions and two ribbon flares.
Authors: Paul, N.; Kuin, M.; Martens, P. C. H.
Bibcode: 1986NASCP2442..241P
Altcode:
In this model not only the force balance, but also the energy balance
of the filament is taken into account. Thus a fully closed system of
equations is obtained, that describes the evolution of the filament,
first in force equilibrium during the current build-up phase, then
in the non-equilibrium phase before the eruption, and the eruption
itself. A neutral point appears above the photospheric surface in
the non-equilibrium phase, but long before the eruption. The authors
find that although the filament itself may be in non-equilibrium,
the evolution may still be slow up to the height where the eruption
takes place. The eruption of the filament itself causes a large induced
electric field at the neutral point which leads to the observed flare
phenomena.
Title: A dynamic model of filament eruptions and two ribbon flares
Authors: Kuin, N. Paul M.; Martens, Piet C. H.
Bibcode: 1986NASCP2442..241K
Altcode: 1986copp.nasa..241K
Two basically different models for the filament equilibrium by
Kippenhahn and Schluter (1957) and Kuperus and Raadu (1974) have
appeared in the literature. A further analyses by van Tend and Kuperus
(1978) added the force due to the horizontal component of the background
field to the Kuperus and Raadu model. In order to obtain a better
model which actually describes these phenomena, the evolution of the
filament has to be considered in detail. A first attempt was recently
presented by Kaastra. Kaastra did not formulate the precise energy
balance equations for the problem, as is done in the present work. In
the present model not only the force balance, but also the energy
balance of the filament is taken into account. Thus a fully closed
system of equations is obtained, that describes the evolution of the
filament, first in force equilibrium during the current build-up phase,
then in the non-equilibrium phase before the eruption, and the eruption
itself. A neutral point appears above the photospheric surface in the
non-equilibrium phase, but long before the eruption. It was found that
although the filament itself may be in non-equilibrium, the evolution
may still be slow up to the height where the eruption takes place. The
eruption of the filament itself causes a large induced electric field
at the neutral point which leads to the observed flare phenomena.
Title: An Electrical Circuit Model for Two-Ribbon Flares
Authors: Martens, P. C. H.; Kuin, N. P. M.
Bibcode: 1986BAAS...18..699M
Altcode:
No abstract at ADS
Title: Preflare energy build-up in a filament circuit.
Authors: Martens, P. C. H.
Bibcode: 1986SoPh..107...95M
Altcode: 1987SoPh..107...95M
The two-dimensional Van Tend and Kuperus (1978) scenario for pre-flare
energy build-up is extended to a fully three-dimensional model and
applied to the 16 May, 1981 flare observed at Debrecen. It is shown
that there is plenty of free energy (1033 erg) available
to explain the ensuing large two-ribbon flare. This estimate is an
order of magnitude larger than the simple estimate made by Van Tend,
as a result of the three-dimensional character of the present model. It
is further confirmed that the global form of the preflare circuit is
decisive for determining the amount of energy stored in the preflare
configuration, while the internal structure of the filament is of
little importance. This is in accordance with the similar claims of
Alfvén and Van Tend and Kuperus.
Title: Preflare activity.
Authors: Priest, E. R.; Gaizauskas, V.; Hagyard, M. J.; Schmahl, E. J.;
Webb, D. F.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson,
R. S.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.;
Karpen, J. T.; Martres, M. -J.; Porter, J. G.; Schmieder, B.; Smith,
J. B., Jr.; Toomre, J.; Woodgate, B.; Waggett, P.; Bentley, R.;
Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.; Martens, P.
Bibcode: 1986NASCP2439....1P
Altcode:
Contents: 1. Introduction: the preflare state - a review of previous
results. 2. Magnetohydrodynamic instability: magnetic reconnection,
nonlinear tearing, nonlinear reconnection experiments, emerging flux and
moving satellite sunspots, main phase reconnection in two-ribbon flares,
magnetic instability responsible for filament eruption in two-ribbon
flares. 3. Preflare magnetic and velocity fields: general morphology of
the preflare magnetic field, magnetic field shear, electric currents in
the preflare active region, characterization of the preflare velocity
field, emerging flux. 4. Coronal manifestations of preflare activity:
defining the preflare regime, specific illustrative events, comparison
of preflare X-rays and ultraviolet, preflare microwave intensity and
polarization changes, non-thermal precursors, precursors of coronal
mass ejections, short-lived and long-lived HXIS sources as possible
precursors.
Title: Absence of MHS-Equilibrium in Plasmas
Authors: Martens, P. C. H.
Bibcode: 1986mrt..conf...79M
Altcode:
No abstract at ADS
Title: Book-Review - Magnetic Fields in Astrophysics
Authors: Zeldovich, Y. B.; Ruzmaikin, A. A.; Sokoloff, D. D.; Martens,
P. C. H.
Bibcode: 1985SoPh...98..195Z
Altcode:
No abstract at ADS
Title: Book reviews
Authors: Schrijver, J.; Martens, P. C. H.
Bibcode: 1985SoPh...98..195S
Altcode:
No abstract at ADS
Title: Observations of Steady Anomalous Magnetic Heating in Thin
Current Sheets
Authors: Martens, P. C. H.; van den Oord, G. H. J.; Hoyng, P.
Bibcode: 1985SoPh...96..253M
Altcode:
A faint steadily emitting loop-like structure has been observed
by HXIS in its low energy channels (3.5-8.0 keV) on November 5/6,
1980. These HXIS observations have permitted us to follow the thermal
evolution of this loop for a period of about 15 hr and from this study
we conclude that only a fraction of 0.1% of the volume of the loop is
steadily heated at the rather large rate of 0.6 erg cm-3
s-1. We interpret this heating as the dissipation of magnetic
fields in thin current sheets and we find that the dissipation with
classical resistivity is very unlikely, while ion-kinetic tearing, as
proposed by Galeev et al. (1981), suits the observations very well. The
enhancement of the resistivity over the classical resistivity then
turns out to be a factor 4 × 104. Dissipation in extremely
thin sheets via the ion-acoustic instability (Duijveman et al., 1981)
cannot be completely excluded when the cross-field heat conductivity
is anomalously enhanced by a factor 400.
Title: Filament Evolution: Energy Build-Up, Eruption and Oscillations
Authors: Martens, P. C. H.; Kuin, N. P. M.
Bibcode: 1985BAAS...17..592M
Altcode:
No abstract at ADS
Title: New instabilities in line driven winds.
Authors: Martens, P. C. H.
Bibcode: 1985NASCP2358..226M
Altcode: 1985onhm.rept..226M
The author proposes a general three-dimensional treatment of the
stability problem of line-driven stellar winds, which leads to
the general dispersion equation. From this dispersion equation a
new instability in stellar winds is derived: the 'thermal drift
instability'. It is related to changes in absorption of radiation
caused by temperature perturbations. This mechanism results in growing,
inwardly propagating sound waves.
Title: Applications of non-linear methods in astronomy
Authors: Martens, P. C. H.
Bibcode: 1984PhR...115..315M
Altcode:
In this review I discuss catastrophes, bifurcations and strange
attractors in a non-mathematical manner by giving very simple examples
that st ill contain the essence of the phenomenon. The salientresults
of the applications of these non-linear methods in astrophysics
are reviewed and include such diverse phenomena as solar flares and
loop brightenings (catastrophes), formation of binaries and cyclic
stellar winds (bifurcations) and the solar cycle and galactic dynamics
(strange attractors). Emphasis is laid on the unifying concept of
non-linearity in (simple) differential equatio ns that can be the
framework for understanding and predicting such diverse phenomena
as mentioned above. Finally there is a discussion on the concept of
intrinsic unpredictability (as a result on non-linearity), the limit
it sets to the use of numerical models and the way it contradicts our
intuiti ve notions on deterministic systems. From October 1,
1984: Laboratory for Astronomy and Solar Physics, Code 682, NASA,
Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A.
Title: Summary of the Workshop, Conclusions - Discussion
Authors: La Dous, C.; Lago, T.; Kuin, P.; Martens, P.; Ramella, M.;
Company), The
Bibcode: 1984evml.conf..219L
Altcode:
No abstract at ADS
Title: Book-Review: Solar Magnetohydrodynamics
Authors: Priest, E. R.; Martens, P. C. H.
Bibcode: 1984Ruimt..33..119P
Altcode:
No abstract at ADS
Title: Relaxation oscillations and double temperature structures in
stellar coronae.
Authors: Hearn, A. G.; Kuin, N. P. M.; Martens, P. C. H.
Bibcode: 1983A&A...125...69H
Altcode:
Further work using the iterative method of Hearn and Vardavas (1981)
for calculating stationary models for stellar coronae has shown that
the coronae of small extent obtained with large fluxes of mechanical
energy are not stable. It is suggested that the corona undergoes a
relaxation oscillation in which a single extended corona collapses to
a double corona which in turn builds up to a single extended corona
again. Such a coronal relaxation oscillation may be an explanation
for the observed variations of mass loss from late B and early A type
supergiants and perhaps from Be stars. The inclusion of radiative
forces resulting from the absorption of photospheric radiation by
resonance lines should increase the period of the oscillation. If
these radiative forces are sufficiently strong they should stabilize
the oscillation giving a double corona structure. Such a model could
in principle explain the observed soft X-ray emission of OB supergiants
and the discrepancy between mass loss rates deduced from the ultraviolet
and radio measurements.
Title: The thermal evolution of resonantly heated coronal loops
Authors: Martens, P. C. H.; Kuin, N. P. M.
Bibcode: 1983A&A...123..216M
Altcode:
The time-dependent model of Kuin and Martens (1982) for the thermal
structure of the plasma in a coronal loop is extended to account for
the mechanism of resonant electrodynamic heating (Ionson, 1982). It
is found that, just as in the models of constant heating of Kuin and
Martens, the static thermal equilibrium for the loops is unstable
and that the time dependent solutions for the plasma in a loop are
cyclic, consisting of a short cool phase and a long hot phase. This
last phase is almost identical to the static solution and this explains
the static appearance of a loop. In addition to this cyclic behaviour
catastrophic transitions in the X-ray emission of a loop may occur, as
a result of a gradual change in the loop length or the magnetic field
strength. Finally a comparison is made with the numerical solutions
for the evolution of the plasma in coronal loops by other authors.
Title: Nonlinearity and Instability in Stellar Coronae
Authors: Martens, P. C. H.
Bibcode: 1983PhDT.......138M
Altcode:
This thesis consists of three parts. Chapter 2, the first part,
reviews applications of nonlinear methods in astronomy, in particular
in stellar coronae. Chapters 3, 4, and 5, the second part, deal with
various aspects of the acceleration and thermal stability of stellar
winds, while chapters 6 through 9 consider the thermal structure and
stability of the plasma in closed coronal loops, such as observed on the
Sun. All chapters have been published as papers in refereed journals.
Title: Nonlinearity and instability in stellar coronae
Authors: Martens, Petrus Cornelis Hendrik Piet
Bibcode: 1983PhDT.......170M
Altcode:
No abstract at ADS
Title: A thermal catastrophe in a resonantly heated coronal loop
Authors: Martens, P. C. H.; Kuperus, M.
Bibcode: 1983IAUS..102..397M
Altcode:
A theory for the thermal stability of hot coronal loops is presented,
which is based on the resonant electrodynamic heating theory of Ionson
(1982) and the evaporation/condensation scenario of Krall and Antiochos
(1980). The theory predicts that gradual changes in the length of
a loops or in its magnetic field strength can trigger catastrophic
changes in the X-ray visibility of the loop, without the need for
a change in the magnetic field topology. A natural explanation is
thereby given for the observations of X-ray brightenings in loops and
loop evacuations with coronal rain.
Title: Resonant electrodynamic heating and the thermal stability of
coronal loops
Authors: Martens, P. C. H.; Kuperus, M.
Bibcode: 1982A&A...113..324M
Altcode:
The resonant electrodynamic heating theory of Ionson (1982) and the
evaporation/condensation scenario of Krall and Antiochos (1980) are
invoked by a theory of hot coronal loop thermal stability. The theory
predicts that gradual changes in loop length or magnetic field strength
can trigger catastrophic X-ray visibility changes in the loop without
accompanying changes in magnetic field topology. This is judged to
constitute a natural explanation for observed X-ray brightening in
loops, as well as loop evacuations with coronal rain.
Title: On cool coronal loops
Authors: Martens, P. C. H.; Kuin, N. P. M.
Bibcode: 1982A&A...112..366M
Altcode:
Analytical model calculations and physical arguments are used to examine
cool equilibria in coronal loops. Static loop model assumptions include
a one-dimensional energy equation, a constant cross-sectional area, and
a loop symmetric top. It is shown, in contradiction to Hood and Priest
(1979) results, that cool loop maximum height has a minimal dependence
on the heating mechanism and the radiation losses, and does not depend
on constants of proportionality. In addition, thermal catastrophe occurs
not only as a result of loop length variations, but also as a result of
heating or pressure variations. It is also concluded that for a given
heating mechanism, thermal catastrophe occurs at only one loop length.
Title: On the thermal stability of hot coronal loops - The coupling
between chromosphere and corona
Authors: Kuin, N. P. M.; Martens, P. C. H.
Bibcode: 1982A&A...108L...1K
Altcode:
We consider the interaction of the hot plasma in coronal loops with the
underlying chromospheric plasma, and find stable static equilibria
if the coupling between corona and chromosphere is sufficiently
strong. However, for typical coronal loop conditions the interaction
is not strong enough for perfect stabilisation and an oscillatory
solution is found with a period of about a day. The latter solution
is very similar to the static solution during most of the time and
is relatively cool only during a short while. We tentatively identify
this cyclic behaviour with the observed up-flows and downflows in the
solar corona.
Title: An analytical model for stellar coronae
Authors: Martens, P. C. H.
Bibcode: 1981A&A...102..156M
Altcode:
A semianalytical model based on the assumption of an isothermal corona
and a transition region of constant pressure is developed for stationary
stellar coronae. It is shown that the temperature structure of the
transition region can be described by a one-parameter differential
equation, leading to a one-parameter set of solutions for the transition
region temperature structure. A comparison is also made of the results
obtained by assuming, first, acoustic heating, and then replacing
it by constant heating up to an arbitrary height. In the first case,
it is shown that the period and flux of the sound waves that heat the
corona are the only external parameters needed to describe the corona
and transiton region. The second case demonstrates that only the heating
function needs to be specified in order to obtain a full solution.
Title: Line driven sound waves in early type stars.
Authors: Martens, P. C. H.
Bibcode: 1979A&A....75L...7M
Altcode:
The existence of rapidly growing sound waves in the expanding
atmospheres of hot stars is demonstrated. The sound waves are amplified
by the velocity dependence of the radiative forces associated with the
impurity ion resonance lines. Strong sound waves with a period of 15
minutes to several hours may be expected. The estimated acoustic flux
produced by this mechanism is 8 billion erg/sq cm per sec for Zeta
Puppis (O4ef) and 700 million erg/sq cm per sec for Epsilon Orionis
(B0 Ia). This energy may be sufficient to heat a corona.