140 research outputs found
Major Surge Activity of Super-Active Region NOAA 10484
We observed two surges in H-alpha from the super-active region NOAA 10484.
The first surge was associated with an SF/C4.3 class flare. The second one was
a major surge associated with a SF/C3.9 flare. This surge was also observed
with SOHO/EIT in 195 angstrom and NoRh in 17 GHz, and showed similar evolution
in these wavelengths. The major surge had an ejective funnel-shaped spray
structure with fast expansion in linear (about 1.2 x 10^5 km) and angular
(about 65 deg) size during its maximum phase. The mass motion of the surge was
along open magnetic field lines, with average velocity about 100 km/s. The
de-twisting motion of the surge reveals relaxation of sheared and twisted
magnetic flux. The SOHO/MDI magnetograms reveal that the surges occurred at the
site of companion sunspots where positive flux emerged, converged, and canceled
against surrounding field of opposite polarity. Our observations support
magnetic reconnection models for the surges and jets.Comment: 4 pages, 3 figures; To appear in "Magnetic Coupling between the
Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten,
Astrophysics and Space Science Series, Springer-Verlag, Heidelberg, Berlin,
200
MEASUREMENT OF CORONAL MAGNETIC TWISTS DURING LOOP EMERGENCE OF NOAA 8069
Abstract. Emerging coronal loops were studied with extreme ultraviolet observations performed by SOHO/EIT on 5 and 6 August 1997 for NOAA 8069. Physical parameters (size and twist) were determined by a new stereoscopic method. The flux tubes were measured twisted when first observed by EIT. After emerging, they de-twisted as they expanded, which corresponds to a minimization of the energy. Different scenarios which take into account the conservation of the magnetic helicity are discussed in relation with structure and temperature variations
The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing
The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV
solar telescope on board ESA's Project for Onboard Autonomy 2 (PROBA2) mission
launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm
and provides images of the low solar corona over a 54x54 arcmin field-of-view
with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is
designed to monitor all space-weather-relevant events and features in the low
solar corona. Given the limited resources of the PROBA2 microsatellite, the
SWAP telescope is designed with various innovative technologies, including an
off-axis optical design and a CMOS-APS detector. This article provides
reference documentation for users of the SWAP image data.Comment: 26 pages, 9 figures, 1 movi
Radio-loud CMEs from the disk center lacking shocks at 1 AU
A coronal mass ejection (CME) associated with a type II burst and originating
close to the center of the solar disk typically results in a shock at Earth in
2-3 days and hence can be used to predict shock arrival at Earth. However, a
significant fraction (about 28%) of such CMEs producing type II bursts were not
associated with shocks at Earth. We examined a set of 21 type II bursts
observed by the Wind/WAVES experiment at decameter-hectometric (DH) wavelengths
that had CME sources very close to the disk center (within a central meridian
distance of 30 degrees), but did not have a shock at Earth. We find that the
near-Sun speeds of these CMEs average to ~644 km/s, only slightly higher than
the average speed of CMEs associated with radio-quiet shocks. However, the
fraction of halo CMEs is only ~30%, compared to 54% for the radio-quiet shocks
and 91% for all radio-loud shocks. We conclude that the disk-center radio-loud
CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks
only close to the Sun and dissipate before arriving at Earth. There is also
evidence for other possible processes that lead to the lack of shock at 1 AU:
(i) overtaking CME shocks merge and one observes a single shock at Earth, and
(ii) deflection by nearby coronal holes can push the shocks away from the
Sun-Earth line, such that Earth misses these shocks. The probability of
observing a shock at 1 AU increases rapidly above 60% when the CME speed
exceeds 1000 km/s and when the type II bursts propagate to frequencies below 1
MHz.Comment: 33 pages, 11 figures, 2 table
Recent Developments of NEMO: Detection of Solar Eruptions Characteristics
The recent developments in space instrumentation for solar observations and
telemetry have caused the necessity of advanced pattern recognition tools for
the different classes of solar events. The Extreme ultraviolet Imaging
Telescope (EIT) of solar corona on-board SOHO spacecraft has uncovered a new
class of eruptive events which are often identified as signatures of Coronal
Mass Ejection (CME) initiations on solar disk. It is evident that a crucial
task is the development of an automatic detection tool of CMEs precursors. The
Novel EIT wave Machine Observing (NEMO) (http://sidc.be/nemo) code is an
operational tool that detects automatically solar eruptions using EIT image
sequences. NEMO applies techniques based on the general statistical properties
of the underlying physical mechanisms of eruptive events on the solar disc. In
this work, the most recent updates of NEMO code - that have resulted to the
increase of the recognition efficiency of solar eruptions linked to CMEs - are
presented. These updates provide calculations of the surface of the dimming
region, implement novel clustering technique for the dimmings and set new
criteria to flag the eruptive dimmings based on their complex characteristics.
The efficiency of NEMO has been increased significantly resulting to the
extraction of dimmings observed near the solar limb and to the detection of
small-scale events as well. As a consequence, the detection efficiency of CMEs
precursors and the forecasts of CMEs have been drastically improved.
Furthermore, the catalogues of solar eruptive events that can be constructed by
NEMO may include larger number of physical parameters associated to the dimming
regions.Comment: 12 Pages, 5 figures, submitted to Solar Physic
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
Automated Detection of Coronal Loops using a Wavelet Transform Modulus Maxima Method
We propose and test a wavelet transform modulus maxima method for the au-
tomated detection and extraction of coronal loops in extreme ultraviolet images
of the solar corona. This method decomposes an image into a number of size
scales and tracks enhanced power along each ridge corresponding to a coronal
loop at each scale. We compare the results across scales and suggest the
optimum set of parameters to maximise completeness while minimising detection
of noise. For a test coronal image, we compare the global statistics (e.g.,
number of loops at each length) to previous automated coronal-loop detection
algorithms
2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT
Polar plumes are seen as elongated objects starting at the solar polar
regions. Here, we analyze these objects from a sequence of images taken
simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and
SOHO/EIT. We establish a method capable of automatically identifying plumes in
solar EUV images close to the limb at 1.01 - 1.39 R in order to study their
temporal evolution. This plume-identification method is based on a multiscale
Hough-wavelet analysis. Then two methods to determined their 3D localization
and structure are discussed: First, tomography using the filtered
back-projection and including the differential rotation of the Sun and,
secondly, conventional stereoscopic triangulation. We show that tomography and
stereoscopy are complementary to study polar plumes. We also show that this
systematic 2D identification and the proposed methods of 3D reconstruction are
well suited, on one hand, to identify plumes individually and on the other
hand, to analyze the distribution of plumes and inter-plume regions. Finally,
the results are discussed focusing on the plume position with their
cross-section area.Comment: 22 pages, 10 figures, Solar Physics articl
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