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Magnetic topology of blinkers
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Gerry Doyle Submitted: 2008-06-11 07:31
Here, we study brightening events in the transition region of the quiet Sun, also called `blinkers' using co-spatial and co-temporal spectroscopic, imaging and magnetogram data. The aim is to investigate the physical mechanism responsible for blinkers. We use an automated blinker identification procedure (BLIP) to identify blinker events in SoHO/CDS data. The 3D magnetic topology of the magnetic field in the blinker region is reconstructed based on SoHO/MDI magnetogram data. During 3 hrs of SoHO/CDS observations on 2006 January 18, 66 blinkers were identified in the O V 629A emission line. Out of them, a group comprising of 16 events were modelled here. They were found to be associated with the emergence of magnetic flux which gave rise to the appearance of, and multiple magnetic reconnection events across, an upper atmosphere (coronal) magnetic null point, along with a loop structure as observed with TRACE. This blinker group results from the release of energy that was accumulated during flux emergence, although whether all blinkers follow the same formation scenario requires further investigation using additional multi-instrument/multi-mission studies.
Authors: S. Subramanian, M.S. Madjarska, R.C. Maclean,
J.G. Doyle, D. Bewsher
Projects: SoHO-CDS
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Publication Status: accepted by A&A
Last Modified: 2008-09-23 21:00
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Subject will be restored when possible
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Gerry Doyle Submitted: 2007-10-11 03:51
Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we seek to investigate plasma condensation through the use of spectroscopic analysis.
In a space-time (X-T) type plot we show, for a number of transition region (TR) and coronal lines, the variation of radiance with time in an off-limb loop system. Noting a number of pixels where the radiance shows a sharp jump in value for the TR lines and a corresponding sharp decrease for the coronal lines, we investigate further and plot the radiance and velocity for these pixels as a function of time. Using standard Fourier techniques, together with a pre-whitening method, we measure all statistically significant frequencies present in the time series so created. We find that, for the cooler lines of He I 584A and O V 629A there are sharp increases in radiance, accompanied by large blueshifted velocities. In the case of O V there is then a substantial rebound to redshifted velocities when the strong brightening fades. The sharp increase in radiance and blueshifted velocity in the cooler lines is accompanied by a corresponding decrease in the radiance of the coronal lines (Mg X 624A, Fe XVI
360A, Si XII 520A), but with no corresponding change in their velocity values implying an evacuation of plasma. From the Fourier analysis, evidence is found for a possible 1st and 2nd harmonic in the He I and O V lines,
indicative of standing waves in loops. We conclude that what we are seeing is the first spectroscopic evidence of plasma condensation taking place in coronal loops.
Authors: E. O'Shea, D. Banerjee and J.G. Doyle
Projects: SoHO-CDS
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Publication Status: A&A L (in press)
Last Modified: 2007-10-11 09:40
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Subject will be restored when possible
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Gerry Doyle Submitted: 2007-10-11 03:50
Aims. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we seek to
investigate plasma condensation through the use of spectroscopic analysis.
Methods. Using a space-time (X-T) type plot we show, for a number of transition region (TR) and coronal lines, the variation of radiance with time in an off-limb loop system. Noting a number of pixels where the radiance shows a sharp jump in value for the TR lines and a corresponding sharp decrease for the coronal lines, we investigate further and plot the radiance and velocity for these
pixels as a function of time. Using standard Fourier techniques, together with a pre-whitening method, we measure all statistically significant frequencies present in the time series so created.
Results. We find that, for the cooler lines of He I 584A and O V 629A there are sharp increases in radiance, accompanied by large blueshifted velocities. In the case of O V there is then a substantial rebound to redshifted velocities when the strong brightening fades. The sharp increase in radiance and blueshifted velocity in the cooler lines is accompanied by a corresponding decrease in the radiance of the coronal lines (Mg X 624A, Fe XVI
360A, Si XII 520A), but with no corresponding change in their velocity values implying an evacuation of plasma. From the Fourier analysis, evidence is found for a possible 1st and 2nd harmonic in the He I and O V lines,
indicative of standing waves in loops.
Conclusions. We conclude that what we are seeing is the first spectroscopic evidence of plasma condensation taking place in coronal loops.
Authors: E. O'Shea, D. Banerjee and J.G. Doyle
Projects: SoHO-CDS
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Publication Status: A&A L (in press)
Last Modified: 2007-10-11 03:50
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