67 research outputs found
Solar Magnetic Feature Detection and Tracking for Space Weather Monitoring
We present an automated system for detecting, tracking, and cataloging
emerging active regions throughout their evolution and decay using SOHO
Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active
Region Tracking (SMART) algorithm relies on consecutive image differencing to
remove both quiet-Sun and transient magnetic features, and region-growing
techniques to group flux concentrations into classifiable features. We
determine magnetic properties such as region size, total flux, flux imbalance,
flux emergence rate, Schrijver's R-value, R* (a modified version of R), and
Falconer's measurement of non-potentiality. A persistence algorithm is used to
associate developed active regions with emerging flux regions in previous
measurements, and to track regions beyond the limb through multiple solar
rotations. We find that the total number and area of magnetic regions on disk
vary with the sunspot cycle. While sunspot numbers are a proxy to the solar
magnetic field, SMART offers a direct diagnostic of the surface magnetic field
and its variation over timescale of hours to years. SMART will form the basis
of the active region extraction and tracking algorithm for the Heliophysics
Integrated Observatory (HELIO)
A New Look at Mode Conversion in a Stratified Isothermal Atmosphere
Recent numerical investigations of wave propagation near coronal magnetic
null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have
indicated how a fast MHD wave partially converts into a slow MHD wave as the
disturbance passes from a low-beta plasma to a high-beta plasma. This is a
complex process and a clear understanding of the conversion mechanism requires
the detailed investigation of a simpler model. An investigation of mode
conversion in a stratified, isothermal atmosphere, with a uniform, vertical
magnetic field is carried out, both numerically and analytically. In contrast
to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov:
Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this
paper studies the downward propagation of waves from a low-beta to high-beta
environment. A simple expression for the amplitude of the transmitted wave is
compared with the numerical solution.Comment: 14 pages, 6 figure
Non-linear numerical simulations of magneto-acoustic wave propagation in small-scale flux tubes
We present results of non-linear, 2D, numerical simulations of
magneto-acoustic wave propagation in the photosphere and chromosphere of
small-scale flux tubes with internal structure. Waves with realistic periods of
three to five minutes are studied, after applying horizontal and vertical
oscillatory perturbations to the equilibrium model. Spurious reflections of
shock waves from the upper boundary are minimized thanks to a special boundary
condition. This has allowed us to increase the duration of the simulations and
to make it long enough to perform a statistical analysis of oscillations. The
simulations show that deep horizontal motions of the flux tube generate a slow
(magnetic) mode and a surface mode. These modes are efficiently transformed
into a slow (acoustic) mode in the vA < cS atmosphere. The slow (acoustic) mode
propagates vertically along the field lines, forms shocks and remains always
within the flux tube. It might deposit effectively the energy of the driver
into the chromosphere. When the driver oscillates with a high frequency, above
the cut-off, non-linear wave propagation occurs with the same dominant driver
period at all heights. At low frequencies, below the cut-off, the dominant
period of oscillations changes with height from that of the driver in the
photosphere to its first harmonic (half period) in the chromosphere. Depending
on the period and on the type of the driver, different shock patterns are
observed.Comment: 22 pages 6 color figures, submitted to Solar Physics, proceeding of
SOHO 19/ GONG 2007 meeting, Melbourne, Australi
The Position of High Frequency Waves with Respect to the Granulation Pattern
High frequency velocity oscillations were observed in the spectral lines Fe I
543.45nm and 543.29nm, using 2D spectroscopy with a Fabry- Perot and speckle
reconstruction, at the VTT in Tenerife. We investigate the radial component of
waves with frequencies in the range 8 - 22mHz in the internetwork, network and
a pore. We find that the occurrence of waves do not show any preference on
location and are equally distributed over down-flows and up-flows, regardless
of the activity of the observed area in the line of Fe I 543.45nm. The waves
observed in the lower formed line of Fe I 543.29nm seem to appear
preferentially over down-flows.Comment: Article has 12 pages and 7 images. It is accepted in Solar Physics
Journa
Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot
The distribution of acoustic power over sunspots shows an enhanced absorption
near the umbra--penumbra boundary. Earlier studies revealed that the region of
enhanced absorption coincides with the region of strongest transverse potential
field. The aim of this paper is to (i) utilize the high-resolution vector
magnetograms derived using Hinode SOT/SP observations and study the
relationship between the vector magnetic field and power absorption and (ii)
study the variation of power absorption in sunspot penumbrae due to the
presence of spine-like radial structures. It is found that (i) both potential
and observed transverse fields peak at a similar radial distance from the
center of the sunspot, and (ii) the magnitude of the transverse field, derived
from Hinode observations, is much larger than the potential transverse field
derived from SOHO/MDI longitudinal field observations. In the penumbra, the
radial structures called spines (intra-spines) have stronger (weaker) field
strength and are more vertical (horizontal). The absorption of acoustic power
in the spine and intra-spine shows different behaviour with the absorption
being larger in the spine as compared to the intra-spine.Comment: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on
Helio-and-Astroseismolog
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
DOT Tomography of the Solar Atmosphere VII. Chromospheric Response to Acoustic Events
We use synchronous movies from the Dutch Open Telescope sampling the
G band, Ca II and Halpha with five-wavelength profile sampling to study the
response of the chromosphere to acoustic events in the underlying photosphere.
We first compare the visibility of the chromosphere in Ca II H and Halpha,
demonstrate that studying the chromosphere requires Halpha data, and summarize
recent developments in understanding why this is so. We construct divergence
and vorticity maps of the photospheric flow field from the G-band images and
locate specific events through the appearance of bright Ca II H grains. The
reaction of the Halpha chromosphere is diagnosed in terms of brightness and
Doppler shift. We show and discuss three particular cases in detail: a regular
acoustic grain marking shock excitation by granular dynamics, a persistent
flasher which probably marks magnetic-field concentration, and an exploding
granule. All three appear to buffet overlying fibrils, most clearly in
Dopplergrams. Although our diagnostic displays to dissect these phenomena are
unprecedentedly comprehensive, adding even more information (photospheric
Doppler tomography and magnetograms, chromospheric imaging and Doppler mapping
in the ultraviolet) is warranted.Comment: accepted by Solar Physic
A comparison of flare forecasting methods. II. Benchmarks, metrics and performance results for operational solar flare forecasting systems
YesSolar flares are extremely energetic phenomena in our Solar System. Their impulsive,
often drastic radiative increases, in particular at short wavelengths, bring immediate
impacts that motivate solar physics and space weather research to understand solar
flares to the point of being able to forecast them. As data and algorithms improve
dramatically, questions must be asked concerning how well the forecasting performs;
crucially, we must ask how to rigorously measure performance in order to critically
gauge any improvements. Building upon earlier-developed methodology (Barnes et al.
2016, Paper I), international representatives of regional warning centers and research
facilities assembled in 2017 at the Institute for Space-Earth Environmental Research,
Nagoya University, Japan to – for the first time – directly compare the performance
of operational solar flare forecasting methods. Multiple quantitative evaluation metrics
are employed, with focus and discussion on evaluation methodologies given the restrictions of operational forecasting. Numerous methods performed consistently above the
“no skill” level, although which method scored top marks is decisively a function of
flare event definition and the metric used; there was no single winner. Following in
this paper series we ask why the performances differ by examining implementation
details (Leka et al. 2019, Paper III), and then we present a novel analysis method to
evaluate temporal patterns of forecasting errors in (Park et al. 2019, Paper IV). With
these works, this team presents a well-defined and robust methodology for evaluating
solar flare forecasting methods in both research and operational frameworks, and today’s performance benchmarks against which improvements and new methods may be
compared
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