3,629 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)
Discovery of spatial periodicities in a coronal loop using automated edge-tracking algorithms
A new method for automated coronal loop tracking, in both spatial and temporal domains, is presented. Applying this technique to TRACE data, obtained using the 171 Ã… filter on 1998 July 14, we detect a coronal loop undergoing a 270 s kink-mode oscillation, as previously found by Aschwanden et al. However, we also detect flare-induced, and previously unnoticed, spatial periodicities on a scale of 3500 km, which occur along the coronal loop edge. Furthermore, we establish a reduction in oscillatory power for these spatial periodicities of 45% over a 222 s interval. We relate the reduction in detected oscillatory power to the physical damping of these loop-top oscillations
Coronal Mass Ejection Detection using Wavelets, Curvelets and Ridgelets: Applications for Space Weather Monitoring
Coronal mass ejections (CMEs) are large-scale eruptions of plasma and
magnetic feld that can produce adverse space weather at Earth and other
locations in the Heliosphere. Due to the intrinsic multiscale nature of
features in coronagraph images, wavelet and multiscale image processing
techniques are well suited to enhancing the visibility of CMEs and supressing
noise. However, wavelets are better suited to identifying point-like features,
such as noise or background stars, than to enhancing the visibility of the
curved form of a typical CME front. Higher order multiscale techniques, such as
ridgelets and curvelets, were therefore explored to characterise the morphology
(width, curvature) and kinematics (position, velocity, acceleration) of CMEs.
Curvelets in particular were found to be well suited to characterising CME
properties in a self-consistent manner. Curvelets are thus likely to be of
benefit to autonomous monitoring of CME properties for space weather
applications.Comment: Accepted for publication in Advances in Space Research (3 April 2010
Horizontal flows concurrent with an X2.2 flare in active region NOAA 11158
Horizontal proper motions were measured with local correlation tracking (LCT)
techniques in active region NOAA 11158 on 2011 February 15 at a time when a
major (X2.2) solar flare occurred. The measurements are based on continuum
images and magnetograms of the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory. The observed shear flows along the polarity
inversion line were rather weak (a few 100 m/s). The counter-streaming region
shifted toward the north after the flare. A small circular area with flow
speeds of up to 1.2 km/s appeared after the flare near a region of rapid
penumbral decay. The LCT signal in this region was provided by small-scale
photospheric brigthenings, which were associated with fast traveling moving
magnetic features. Umbral strengthening and rapid penumbral decay was observed
after the flare. Both phenomena were closely tied to kernels of white-light
flare emission. The white-light flare only lasted for about 15 min and peaked 4
min earlier than the X-ray flux. In comparison to other major flares, the X2.2
flare in active region NOAA 11158 only produced diminutive photospheric
signatures.Comment: 6 pages, 4 figures, accepted for publication in Astronomische
Nachrichten/A
Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons
We report on the physical properties of solar sequential chromospheric
brightenings (SCBs) observed in conjunction with moderate-sized chromospheric
flares with associated CMEs. To characterize these ephemeral events, we
developed automated procedures to identify and track subsections (kernels) of
solar flares and associated SCBs using high resolution H-alpha images.
Following the algorithmic identification and a statistical analysis, we compare
and find the following: SCBs are distinctly different from flare kernels in
their temporal characteristics of intensity, Doppler structure, duration, and
location properties. We demonstrate that flare ribbons are themselves made up
of subsections exhibiting differing characteristics. Flare kernels are measured
to have a mean propagation speed of 0.2 km/s and a maximum speed of 2.3 km/s
over a mean distance of 5 x 10^3 km. Within the studied population of SCBs,
different classes of characteristics are observed with coincident negative,
positive, or both negative and positive Doppler shifts of a few km/s. The
appearance of SCBs precede peak flare intensity by ~12 minutes and decay ~1
hour later. They are also found to propagate laterally away from flare center
in clusters at 41 km/s or 89 km/s. Given SCBs distinctive nature compared to
flares, we suggest a different physical mechanism relating to their origin than
the associated flare. We present a heuristic model of the origin of SCBs.Comment: 24 pages, 17 figure
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