203 research outputs found
The NWRA Classification Infrastructure: Description and Extension to the Discriminant Analysis Flare Forecasting System (DAFFS)
A classification infrastructure built upon Discriminant Analysis has been
developed at NorthWest Research Associates for examining the statistical
differences between samples of two known populations. Originating to examine
the physical differences between flare-quiet and flare-imminent solar active
regions, we describe herein some details of the infrastructure including:
parametrization of large datasets, schemes for handling "null" and "bad" data
in multi-parameter analysis, application of non-parametric multi-dimensional
Discriminant Analysis, an extension through Bayes' theorem to probabilistic
classification, and methods invoked for evaluating classifier success. The
classifier infrastructure is applicable to a wide range of scientific questions
in solar physics. We demonstrate its application to the question of
distinguishing flare-imminent from flare-quiet solar active regions, updating
results from the original publications that were based on different data and
much smaller sample sizes. Finally, as a demonstration of "Research to
Operations" efforts in the space-weather forecasting context, we present the
Discriminant Analysis Flare Forecasting System (DAFFS), a near-real-time
operationally-running solar flare forecasting tool that was developed from the
research-directed infrastructure.Comment: J. Space Weather Space Climate: Accepted / in press; access
supplementary materials through journal; some figures are less than full
resolution for arXi
Enhanced Acoustic Emission in Relation to the Acoustic Halo Surrounding Active Region 11429
The use of acoustic holography in the high-frequency -mode spectrum can
resolve the source distributions of enhanced acoustic emissions within halo
structures surrounding active regions. In doing so, statistical methods can
then be applied to ascertain relationships with the magnetic field. This is the
focus of this study. The mechanism responsible for the detected enhancement of
acoustic sources around solar active regions has not yet been explained.
Furthermore the relationship between the magnetic field and enhanced acoustic
emission has not yet been comprehensively examined. We have used vector
magnetograms from the \Helioseismic and Magnetic Imager (HMI) on-board the
Solar Dynamics Observatory (SDO) to image the magnetic-field properties in the
halo. We have studied the acoustic morphology of an active region, with a
complex halo and "glories," and we have linked some acoustic properties to the
magnetic-field configuration. In particular, we find that acoustic sources are
significantly enhanced in regions of intermediate field strength with
inclinations no different from the distributions found in the quiet Sun.
Additionally we have identified a transition region between the active region
and the halo, in which the acoustic source power is hindered by inclined fields
of intermediate field strength. Finally, we have compared the results of
acoustic emission maps, calculated from holography, and the commonly used local
acoustic maps, finding that the two types of maps have similar properties with
respect to the magnetic field but lack spatial correlation when examining the
highest-powered regions.Comment: 19 pages, 8 figures, Accepted by Solar Physic
Achieving Consistent Doppler Measurements from SDO/HMI Vector Field Inversions
NASA's Solar Dynamics Observatory is delivering vector field observations of
the full solar disk with unprecedented temporal and spatial resolution;
however, the satellite is in a highly inclined geostationary orbit. The
relative spacecraft-Sun velocity varies by ~km/s over a day which
introduces major orbital artifacts in the Helioseismic Magnetic Imager data. We
demonstrate that the orbital artifacts contaminate all spatial and temporal
scales in the data. We describe a newly-developed three stage procedure for
mitigating these artifacts in the Doppler data derived from the Milne-Eddington
inversions in the HMI Pipeline. This procedure was applied to full disk images
of AR11084 to produce consistent Dopplergrams. The data adjustments reduce the
power in the orbital artifacts by 31dB. Furthermore, we analyze in detail the
corrected images and show that our procedure greatly improve the temporal and
spectral properties of the data without adding any new artifacts. We conclude
that this new and easily implemented procedure makes a dramatic improvement in
the consistency of the HMI data and in its usefulness for precision scientific
studies.Comment: 58 pages, 19 figures, submitted to Ap
Helioseismology of Pre-Emerging Active Regions II: Average Emergence Properties
We report on average subsurface properties of pre-emerging active regions as
compared to areas where no active region emergence was detected. Helioseismic
holography is applied to samples of the two populations (pre-emergence and
without emergence), each sample having over 100 members, which were selected to
minimize systematic bias, as described in Leka et al. We find that there are
statistically significant signatures (i.e., difference in the means of more
than a few standard errors) in the average subsurface flows and the apparent
wave speed that precede the formation of an active region. The measurements
here rule out spatially extended flows of more than about 15 m/s in the top 20
Mm below the photosphere over the course of the day preceding the start of
visible emergence. These measurements place strong constraints on models of
active region formation.Comment: 15 pages, 10 figures, ApJ (published
Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory
Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error
The Trigger Mechanism of Recurrent Solar Active Region Jets Revealed by the Magnetic Properties of a Coronal Geyser Site
Solar active region jets are small-scale collimated plasma eruptions that are
triggered from magnetic sites embedded in sunspot penumbral regions. Multiple
trigger mechanisms for recurrent jets are under debate. Vector magnetic field
data from SDO-HMI observations are used to analyze a prolific photospheric
configuration, identified in extreme ultraviolet observations as a `Coronal
Geyser', that triggered a set of at least 10 recurrent solar active region
jets. We focus on interpreting the magnetic fields of small-scale flaring sites
aiming to understand the processes that govern recurrent jet eruptions. We
perform a custom reprocessing of the SDO-HMI products, including disambiguation
and uncertainty estimation. We scrutinized the configuration and dynamics of
the photospheric magnetic structures. The magnetic configuration is described
via the analysis of the photospheric magnetic vertical fields, to identify the
process is responsible for driving the jet eruptions. We report that the two
widely debated magnetic trigger processes, namely magnetic flux cancellation
and magnetic flux emergence, appear to be responsible on a case by case basis
for generating each eruption in our set. We find that 4 of 10 jets were due to
flux cancellation while the rest were clearly not, and were more likely due to
flux emergence.Comment: 19 pages, 6 figure, and 1 table. The Astrophysical journal, In pres
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code
The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne-Eddington
spectral line inversion code used to determine the magnetic and thermodynamic
parameters of the solar photosphere from observations of the Stokes vector in
the 6173 A Fe I line by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We report on the modifications made to the
original VFISV inversion code in order to optimize its operation within the HMI
data pipeline and provide the smoothest solution in active regions. The changes
either sped up the computation or reduced the frequency with which the
algorithm failed to converge to a satisfactory solution. Additionally, coding
bugs which were detected and fixed in the original VFISV release, are reported
here.Comment: Accepted for publication in Solar Physic
Modelling and Interpreting The Effects of Spatial Resolution on Solar Magnetic Field Maps
Different methods for simulating the effects of spatial resolution on
magnetic field maps are compared, including those commonly used for
inter-instrument comparisons. The investigation first uses synthetic data, and
the results are confirmed with {\it Hinode}/SpectroPolarimeter data. Four
methods are examined, one which manipulates the Stokes spectra to simulate
spatial-resolution degradation, and three "post-facto" methods where the
magnetic field maps are manipulated directly. Throughout, statistical
comparisons of the degraded maps with the originals serve to quantify the
outcomes. Overall, we find that areas with inferred magnetic fill fractions
close to unity may be insensitive to optical spatial resolution; areas of
sub-unity fill fractions are very sensitive. Trends with worsening spatial
resolution can include increased average field strength, lower total flux, and
a field vector oriented closer to the line of sight. Further-derived quantities
such as vertical current density show variations even in areas of high average
magnetic fill-fraction. In short, unresolved maps fail to represent the
distribution of the underlying unresolved fields, and the "post-facto" methods
generally do not reproduce the effects of a smaller telescope aperture. It is
argued that selecting a method in order to reconcile disparate spatial
resolution effects should depend on the goal, as one method may better preserve
the field distribution, while another can reproduce spatial resolution
degradation. The results presented should help direct future inter-instrument
comparisons.Comment: Accepted for publication in Solar Physics. The final publication
(including full-resolution figures) will be available at
http://www.springerlink.co
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches
A new data product from the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region
Patches (SHARPs) is now available. SDO/HMI is the first space-based instrument
to map the full-disk photospheric vector magnetic field with high cadence and
continuity. The SHARP data series provide maps in patches that encompass
automatically tracked magnetic concentrations for their entire lifetime; map
quantities include the photospheric vector magnetic field and its uncertainty,
along with Doppler velocity, continuum intensity, and line-of-sight magnetic
field. Furthermore, keywords in the SHARP data series provide several
parameters that concisely characterize the magnetic-field distribution and its
deviation from a potential-field configuration. These indices may be useful for
active-region event forecasting and for identifying regions of interest. The
indices are calculated per patch and are available on a twelve-minute cadence.
Quick-look data are available within approximately three hours of observation;
definitive science products are produced approximately five weeks later. SHARP
data are available at http://jsoc.stanford.edu and maps are available in either
of two different coordinate systems. This article describes the SHARP data
products and presents examples of SHARP data and parameters.Comment: 27 pages, 7 figures. Accepted to Solar Physic
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