16 research outputs found
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
Multiscale Edge Detection in the Corona
Coronal Mass Ejections (CMEs) are challenging objects to detect using
automated techniques, due to their high velocity and diffuse, irregular
morphology. A necessary step to automating the detection process is to first
remove the subjectivity introduced by the observer used in the current,
standard, CME detection and tracking method. Here we describe and demonstrate a
multiscale edge detection technique that addresses this step and could serve as
one part of an automated CME detection system. This method provides a way to
objectively define a CME front with associated error estimates. These fronts
can then be used to extract CME morphology and kinematics. We apply this
technique to a CME observed on 18 April 2000 by the Large Angle Solar
COronagraph experiment (LASCO) C2/C3 and a CME observed on 21 April 2002 by
LASCO C2/C3 and the Transition Region and Coronal Explorer (TRACE). For the two
examples in this work, the heights determined by the standard manual method are
larger than those determined with the multiscale method by approximately 10%
using LASCO data and approximately 20% using TRACE data.Comment: 14 pages, 7 figures, In Solar Physics Topical Issue "Solar Image
Analysis and Visualization
EIT Observations of the Extreme Ultraviolet Sun
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT observes the Sun over a 45 x 45 arc min field of view in four emission line groups: Feix, x, Fexii, Fexv, and Heii. A post-launch determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops
Comparison of 87 GHz solar polar structures with EUV and soft X-ray emission
Polar radio brightenings at 87 GHz (3.5 mm) are compared for the first
time with features seen in EUV and soft X-rays. The data consist of
nearly simultaneous full disk images and maps from Metsähovi Radio
Observatory, SOHO/EIT, and Yohkoh/SXT on 9 selected days near the
solar minimum (1996-1997).
The observed radio brightenings corresponded to various features
seen in EUV, such as diffuse or localized intensity enhancements
(e.g., bright points and bases of polar plumes), and intensity
depressions of varying sizes (e.g., coronal holes).
Some of these features were also visible in soft X-rays.
The visibility of radio bright coronal holes seemed to depend on
how much of the polar area was exposed, due to the variation of
the B0-angle.
The observed radio depressions near the solar poles were very well
correlated with coronal holes and other EUV and/or soft X-ray
intensity drops. More than half of the coronal holes, or
coronal hole-like intensity drops in EUV and soft X-rays, had
radio brightenings inside them. Therefore coronal holes do not have
uniform radio brightness at 87 GHz.
Many of the bright points seen at lower latitudes in the EIT and SXT
images had no, or just faint, counterparts in the millimeter radio maps.
It appears that for an EUV bright point to show up at 87 GHz it has to
be bright and/or spatially large also in soft X-rays.