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Spatial Offsets in Flare-CME Current Sheets  

John Raymond   Submitted: 2017-07-12 12:06

Magnetic reconnection plays an integral part in nearly all models of solar flares and coronal mass ejections (CMEs). The reconnection heats and accelerates the plasma, produces energetic electrons and ions, and changes the magnetic topology to form magnetic flux ropes and allow CMEs to escape. Structures that appear between flare loops and CME cores in optical, UV, EUV and X-ray observations have been identified as current sheets and interpreted in terms of the nature of the reconnection process and the energetics of the events. Many of these studies have used UV spectral observations of high temperature emission features in the [Fe XVIII] and Si XII lines. In this paper we discuss several surprising cases in which the [Fe XVIII] and Si XII emission peaks are spatially offset from each other. We discuss interpretations based on asymmetric reconnection, on a thin reconnection region within a broader streamer-like structure, and on projection effects. Some events seem to be easily interpreted as projection of a sheet that is extended along the line of sight that is viewed an angle, but a physical interpretation in terms of asymmetric reconnection is also plausible. Other events favor an interpretation as a thin current sheet embedded in a streamer-like structure.

Authors: Raymond, J.C., Giordano, S., Ciaravella, A.
Projects: None

Publication Status: ApJ, in press
Last Modified: 2017-07-14 08:40
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Transition Region Emission in Solar Flares  

John Raymond   Submitted: 2011-04-29 13:18

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: H. Johnson, J.C. Raymond, N.A. Murphy, S. Giordano, Y.-K. Ko, A. Ciaravella and R. Suleiman
Projects: None

Publication Status: in press
Last Modified: 2011-04-29 22:21
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The Current Sheet Associated with the 2003 November 4 Coronal Mass Ejection: Density, Temperature, Thickness and Line Width  

John Raymond   Submitted: 2008-10-22 08:30

In the wake of the 2003 November 4 coronal mass ejection associated with the largest solar flare of the last sunspot cycle, a current sheet (CS) was observed by the Ultraviolet Coronagraph Spectrometer (UVCS) as a narrow bright feature in the [Fe XVIII] (106.8 K) line. This is the first UV observation in which the CS evolution is followed from its onset. UV spectra provide diagnostics of electron temperature, emission measure, Doppler shift, line width, and size of the CS as function of time. Since the UVCS slit was inside the Mark IV K-coronameter (MK4) field of view, the combination of UV spectra and MK4 white light data provides estimates of the electron density and depth along the line of sight of the CS. The thickness of the CS in the [Fe XVIII] line is far larger than classical or anomalous resistivity would predict, and it might indicate an effective resistivity much larger than anomalous resistivity, such as that due to hyperdiffusion. The broad [Fe XVIII] line profiles in the CS cannot be explained as thermal widths. They result from a combination of bulk motions and turbulence. The Petschek reconnection mechanism and turbulent reconnection may be consistent with the observations.

Authors: A. Ciaravella and J.C. Raymond
Projects: None

Publication Status: Published in ApJ
Last Modified: 2008-10-22 13:01
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Transition Region Emission and Energy Input to Thermal Plasma During the Impulsive Phase of Solar Flares  

John Raymond   Submitted: 2007-01-11 18:43

The energy released in a solar flare is partitioned between thermal and non-thermal particle energy and lost to thermal conduction and radiation over a broad range of wavelengths. It is difficult to determine the conductive losses and the energy radiated at transition region temperatures during the impulsive phases of flares. We use UVCS measurements of O VI photons produced by 5 flares and subsequently scattered by O VI ions in the corona to determine the 5.0 < log T < 6.0 transition region luminosities. We compare them with the rates of increase of thermal energy and the conductive losses deduced from RHESSI and GOES X-ray data using areas from RHESSI images to estimate the loop volumes, cross-sectional areas and scale lengths. The transition region luminosities during the impulsive phase exceed the X-ray luminosities for the first few minutes, but they are smaller than the rates of increase of thermal energy unless the filling factor of the X-ray emitting gas is ~ 0.01. The estimated conductive losses from the hot gas are too large to be balanced by radiative losses or heating of evaporated plasma, and we conclude that the area of the flare magnetic flux tubes is much smaller than the effective area measured by RHESSI during this phase of the flares. For the 2002 July 23 flare, the energy deposited by non-thermal particles exceeds the X-ray and UV energy losses and the rate of increase of the thermal energy.

Authors: J.C. Raymond, G. Holman, A. Ciaravella, A. Panasyuk, Y.-K. Ko and J. Kohl
Projects: None

Publication Status: ApJ, in press
Last Modified: 2007-01-15 10:21
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Far UV Spectra of Fast Coronal Mass Ejections Associated with X-class Flares  

John Raymond   Submitted: 2003-08-06 14:57

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the SOHO satellite has observed very fast Coronal Mass Ejections (CMEs) associated with X-class flares. These events show spectral signatures different than those seen in most other CMEs in terms of very rapid disruption of the pre-CME streamer, very high Doppler shifts and high temperature plasma visible in the [Fe XVIII] emission line. This paper describes three very similar events on 21 April, 23 July and 24 August 2002 associated with X-class flares. We determine the physical parameters of the pre-CME streamers and discuss the geometrical and physical nature of the streamer blowouts. In the 21 April event, the hot plasma seen as [Fe XVIII] is not related to the structure seen in [Fe XXI] by SUMER at lower heights. It has the form of a rapidly expanding fan, quite likely a current sheet. In the August event, on the other hand, the [Fe XVIII] is probably a bubble of hot plasma formed by reconnection in the wake of the CME. C III emission from the July 23 flare is detected as stray light in the UVCS aperture. It precedes the hard X-ray brightening by about 2 minutes.

Authors: J.C. Raymond, A. Ciaravella, D. Dobrzycka,L. Strachan, Y.-K. Ko, M. Uzzo and N.-E. Raouafi
Projects: None

Publication Status: ApJ (In press)
Last Modified: 2003-08-06 14:57
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Abstracts by Author
Spatial Offsets in Flare-CME Current Sheets
Transition Region Emission in Solar Flares
The Current Sheet Associated with the 2003 November 4 Coronal Mass Ejection: Density, Temperature, Thickness and Line Width
Transition Region Emission and Energy Input to Thermal Plasma During the Impulsive Phase of Solar Flares
Far UV Spectra of Fast Coronal Mass Ejections Associated with X-class Flares

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