Chromospheric Evaporation

1
Chromospheric Evaporation

• Peter Gallagher
• University College Dublin
• Ryan Milligan
• Queens University Belfast

2
Chromospheric Evaporation

• Non-thermal electrons supply the necessary energy
  to heat the plasma and cause flows.
• Enonthermal -gt Ethermal Ekinetic

3
Chromospheric Response

• How does the chromosphere respond to nonthermal
  electrons?
• Assume power-law electron spectrum
• F(E) (E/Ec)-? electrons cm-2 s-1
• Chromospheric response depends on
• properties of accelerated electrons
• Low-energy cut-off (Ec).
• Power-law index (?).
• Total flux.

Loop leg
Density
4

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

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

Threshold?
v/2.35cs
Gentle
Explosive
Log F (ergs s-1 cm-2)
5
CDS and TRACE 26 March 2002 Flare

• SOHO/CDS
• He I (0.03 MK)
• O V (0.25 MK)
• Mg X (1.1 MK)
• Fe XVI (2.5 MK)
• Fe XIX (8 MK)
• TRACE 17.1 nm
• Fe IX/X (1.0 MK)

6
Footpoint Downflows

• Loops are not static
• Maximum downflow 110 km/sec
• Loops cool via conduction, radiation, and flows.
  (SHOW MOVIE)

7
RHESSI Integrated Spectrum
8
M2.2 Flare CDS/EIT/GOES
9
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

• Thermal
• T 20 MK
• EM 1049 cm-3
• Nonthermal
• Ec 24 keV
• ? 7.3
• HXR Area 1018 cm2
• gt Nonthermal Electron Flux 2x1010 ergs cm-2 s-1

12
Evidence for Upflows
Doppler shifts measured relative to a stationary
component v/c (?- ? 0)/ ? 0 In Fe XIX v
260 km s-1
13
Flow velocity vs. Temperature
Downflows
Upflows
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In context
M2.2 flare
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Future Work

• How does the chromospheric response depend on the
  nonthermal electron properties?
• We now have one event!
• Nonthermal electrons ?7.3, Ec 24 keV, F2x1010
  ergs cm-2 s-1
• Response 260 km s-1
• gt need large number of CDS/RHESSI flares
• Is there a threshold for explosive evaporation?
• gt need large number of CDS/RHESSI flares