RHESSI and SOHOCDS Observations of Chromospheric Evaporation in Solar Flares

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RHESSI and SOHO/CDS Observations of
Chromospheric Evaporation in Solar Flares

• Ryan Milligan
• QUB/NASA-GSFC
• Peter Gallagher
• UCD/L3/NASA-GSFC

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Chromospheric Evaporation

• Electrons are accelerated during impulsive phase
  of solar flare
• These non-thermal electrons supply the necessary
  energy to heat the chromosphere and hence cause
  flows
• Enonthermal Ethermal Ekinetic

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Theory (Fisher et al.1984)

• Explosive
• Chromosphere unable to radiate energy deposited
  by non-thermal electrons
• Velocities gt 400 km/s
• Flux gt 1010-10.5 ergs cm-2 s-1

• Gentle
• Chromosphere heated directly by non-thermal
  electrons
• Velocities lt 300 km/s
• Flux lt 1010-10.5 ergs cm-2 s-1

v/2.35cs
Log F (ergs cm-2 s-1)
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Purpose of this study

• To search for signatures of chromospheric
  evaporation in a solar flare using simultaneous
  X-ray and EUV observations
• To investigate the relationship between the flux
  of non-thermal electrons (RHESSI) and the
  response of the solar atmosphere (CDS)

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M2.2 Flare CDS/EIT/GOES
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Impulsive Phase CDS/EIT/RHESSI
Region over which CDS spectra were taken (white
box)
6 - 12 keV (dashed line) Thermal
25 50 keV (solid line) Non-thermal
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RHESSI Lightcurve
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RHESSI Spectrum
? 7.3 E0 21 keV
T 18 MK EM 1049 cm-3
Power in non-thermal electrons/HXR source size ?
electron flux 2?1010 ergs cm-2 s-1
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Evidence for Upflows
Doppler shifts measured relative to a stationary
component Fe XIX ? v 260 km/s
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Flow velocity vs. Temperature
Downflows
Upflows
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Observation vs. Theory
M2.2 flare
v/2.35cs
Log F (ergs cm-2 s-1)
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Summary and Future Work

• First simultaneous observation of chromospheric
  evaporation using RHESSI and SOHO/CDS
• Non-thermal electron flux 2x1010 ergs cm-2 s-1
• Upflows in Fe XIX 260 km s-1
• Downflows in He I, O V lt 30 km s-1
• Extend this study to a large sample of flares
• Determine possible threshold between gentle and
  explosive evaporation