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An exploration of heating mechanisms in a supra-arcade plasma sheet formed after a coronal mass ejection  

Katharine Reeves   Submitted: 2017-01-12 13:35

We perform a detailed analysis of the thermal structure of the region above the post-eruption arcade for a flare that occurred on 2011 October 22. During this event, a sheet of hot plasma is visible above the flare loops in the 131 Å bandpass of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Supra-arcade downflows (SADs) are observed traveling sunward through the post-eruption plasma sheet. We calculate differential emission measures using the AIA data and derive an emission measure weighted average temperature in the supra-arcade region. In areas where many SADs occur, the temperature of the supra-arcade plasma tends to increase, while in areas where no SADs are observed, the temperature tends to decrease. We calculate the plane-of-sky velocities in the supra-arcade plasma and use them to calculate the potential heating due to adiabatic compression and viscous heating. Ten of the 13 SADs studied have noticeable signatures in both the adiabatic and the viscous terms. The adiabatic heating due to compression of plasma in front of the SADs is on the order of 0.1 - 0.2 MK/s, which is similar in magnitude to the estimated conductive cooling rate. This result supports the notion that SADs contribute locally to the heating of plasma in the supra-arcade region. We also find that in the region without SADs, the plasma cools at a rate slower than the estimated conductive cooling, indicating additional heating mechanisms may act globally to keep the plasma temperature high.

Authors: Katharine K. Reeves, Michael S. Freed, David E. McKenzie, Sabrina L. Savage
Projects: SDO-AIA

Publication Status: Accepted to ApJ
Last Modified: 2017-01-13 06:08
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Relating CME Kinematics and Thermal Energy Release to Flare Emissions Using a Model of Solar Eruptions  

Katharine Reeves   Submitted: 2010-02-08 11:15

We use a model of solar eruptions that combines a loss-of-equilibrium coronal mass ejection (CME) model with a multi-threaded flare loop model in order to understand the relationship between the CME kinematics, thermal energy release and soft X-ray emissions in solar eruptions. We examine the correlation between CME acceleration and the peak soft X-ray flux in many modeled cases with different parameters, and find that the two quantities are well-correlated. We also examine the timing of the peak acceleration and the light curve derivative, and find that these quantities tend to peak at similar times for cases where the magnetic field is high and the inflow Alfvén Mach number is fast. Finally, we study the relationship between the total thermal energy released in the model and the calculated peak soft X-ray flux of the resulting flare. We find that there is a power law relationship between these two quantities, with Fpeaksim E α , where α is between 2.54 and 1.54, depending on the reconnection rate. This finding has repercussions for the assumptions underlying the Neupert effect, in which the peak soft X-ray flux is assumed to be proportional to the thermal energy release.

Authors: Katharine K. Reeves and Stephanie J. Moats
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2010-02-09 09:04
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Subject will be restored when possible  

Katharine Reeves   Submitted: 2007-08-28 06:42

In this paper, we present numerical simulations of solar flares that couple a loss-of-equilibrium solar eruption model with a one-dimensional hydrodynamic model. In these calculations, the eruption is initiated by footpoint motions that disrupt the balance of forces acting on a flux rope. After the eruption begins, a current sheet forms and an arcade of flare loops is created by reconnecting magnetic fields. Thermal energy input into the flare loops is found by assuming the complete thermalization of the Poynting flux swept into the current sheet. This thermal energy is input into a 1D hydrodynamic code for each loop formed in the multi-threaded flare arcade. We find that a density enhancement occurs at the loop top when the two evaporating plasma fronts in each leg of the loop collide there. Simulated flare images show that these loop-top density enhancements produce ``bars'' of bright emission similar to those observed in the Transition Region and Coronal Explorer (TRACE) 195 A bandpass and loop-top ``knots'' of bright emission seen in flare observations by the Soft X-Ray Telescope (SXT) on Yohkoh. We also simulate flare spectra from the Bragg Crystal Spectrometer (BCS) on {it Yohkoh}. We find that during the early stages of flare initiation, there are significant blueshifts in the CaXIX line, but the intensities are too faint to be observed with BCS. In general, the results of this model simulate observed flare emissions quite well, indicating that the reconnection model of solar flares is energetically consistent with observations.

Authors: Reeves, K. K., Warren, H. P. and Forbes, T. G.
Projects: Hinode,TRACE,Yohkoh-BCS,Yohkoh-SXT

Publication Status: ApJ (in press)
Last Modified: 2007-08-30 21:35
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Subject will be restored when possible  

Katharine Reeves   Submitted: 2007-08-28 06:41

In this paper, we present numerical simulations of solar flares that couple a loss-of-equilibrium solar eruption model with a one-dimensional hydrodynamic model. In these calculations, the eruption is initiated by footpoint motions that disrupt the balance of forces acting on a flux rope. After the eruption begins, a current sheet forms and an arcade of flare loops is created by reconnecting magnetic fields. Thermal energy input into the flare loops is found by assuming the complete thermalization of the Poynting flux swept into the current sheet. This thermal energy is input into a 1D hydrodynamic code for each loop formed in the multi-threaded flare arcade. We find that a density enhancement occurs at the loop top when the two evaporating plasma fronts in each leg of the loop collide there. Simulated flare images show that these loop-top density enhancements produce ``bars'' of bright emission similar to those observed in the {it Transition Region and Coronal Explorer} ({it TRACE}) 195 Å bandpass and loop-top ``knots'' of bright emission seen in flare observations by the Soft X-Ray Telescope (SXT) on {it Yohkoh}. We also simulate flare spectra from the Bragg Crystal Spectrometer (BCS) on {it Yohkoh}. We find that during the early stages of flare initiation, there are significant blueshifts in the ion{Ca}{19} line, but the intensities are too faint to be observed with BCS. In general, the results of this model simulate observed flare emissions quite well, indicating that the reconnection model of solar flares is energetically consistent with observations.

Authors: Reeves, K. K., Warren, H. P. and Forbes, T. G.
Projects: Hinode,TRACE,Yohkoh-BCS,Yohkoh-SXT

Publication Status: ApJ (in press)
Last Modified: 2007-08-28 06:41
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The Relationship between Flux Rope Acceleration and Thermal Energy Release in a Model of Eruptive Solar Phenomena  

Katharine Reeves   Submitted: 2006-08-08 11:30

In this paper, we examine the relationship between the thermal energy release rate and the flux rope acceleration in a loss of equilibrium CME model. The model consists of a flux rope in equilibrium in the corona and two point sources at the chromosphere. As the point sources are brought together quasi-statically, the equilibrium state of the flux rope is disturbed, and an eruption occurs. After the eruption begins, a current sheet forms under the flux rope. The thermal energy release rate is assumed to be equal to the Poynting flux swept into the current sheet as the flux rope accelerates. We find that the flux rope acceleration and the thermal energy release rate are well correlated when the background magnetic field is high and the reconnection rate is fast. They are not well correlated for events with low magnetic fields and slow reconnection rates.

Authors: Katharine Reeves
Projects: None

Publication Status: Published in ApJ Volume 644, Issue 1, pp. 592-597
Last Modified: 2006-08-08 11:43
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An exploration of heating mechanisms in a supra-arcade plasma sheet formed after a coronal mass ejection
Relating CME Kinematics and Thermal Energy Release to Flare Emissions Using a Model of Solar Eruptions
Subject will be restored when possible
Subject will be restored when possible
The Relationship between Flux Rope Acceleration and Thermal Energy Release in a Model of Eruptive Solar Phenomena

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