1 / 21

Chromospheric Evaporation in Solar Flares: Nonthermal Electron Acceleration and Response

This study by Peter Gallagher (UCD) and Ryan Milligan (Queen's University Belfast) explores chromospheric evaporation induced by nonthermal electrons during solar flares. Utilizing a canonical flare model, we detail the steps of acceleration, propagation, heating, and evaporation of electrons. Important factors influencing the chromospheric response, including the properties of accelerated electrons and their energy distribution, are discussed. The findings reveal insights into the distinct behaviors of gentle versus explosive evaporation, emphasizing the role of electron characteristics in determining chromospheric dynamics.

kirk-walsh
Télécharger la présentation

Chromospheric Evaporation in Solar Flares: Nonthermal Electron Acceleration and Response

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chromospheric Evaporation Peter Gallagher University College Dublin Ryan Milligan Queen’s University Belfast Peter Gallagher (UCD)

  2. Peter Gallagher (UCD)

  3. Canonical Flare Model • Step 1: Acceleration. • Reconnection produces power-law electron distribution. • Step 2: Propagation. • Electrons spiral along magnetic fields from corona to chromosphere. • Step 3: Heating. • Electrons deposit energy in chromosphere via Coulomb collisions. • Step 4: Evaporation. • Dense chromosphere radiates and may expand. Peter Gallagher (UCD)

  4. T1: Nonthermal Electrons T3: VUP T2: Impulsive Heating T3: VDOWN Chromospheric Response • How does the chromosphere respond to nonthermal electrons? • Assume power-law electron spectrum: • f(E) ~ E-electrons cm-2 s-1 Loop leg Density Peter Gallagher (UCD)

  5. Chromospheric Response • Chromospheric response depends on properties of accelerated electrons: • Low-energy cut-off (Ec) • Lower Ec=> more energy => more rapid and pronounced response. • Power-law index () • Harder spectrum => high energy electrons penetrate deeper where chromospere better able to radiate => less rapid and pronounced response. • Total flux • Higher flux => more energy => more rapid and pronounced response. EC f(E) thermal nonthermal  E Peter Gallagher (UCD)

  6. Gentle vs Explosive Evaporation Peter Gallagher (UCD)

  7. Gentle vs Explosive Evaporation Peter Gallagher (UCD)

  8. Peter Gallagher (UCD)

  9. Peter Gallagher (UCD)

  10. RHESSI Spectral Coverage Peter Gallagher (UCD)

  11. 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) Peter Gallagher (UCD)

  12. RHESSI Integrated Spectrum Peter Gallagher (UCD)

  13. Footpoint Downflows • Loops are not static. • Downflows <50 km s-1, upflows >100 km s-1 • Loops cool via conduction, radiation, and flows. Peter Gallagher (UCD)

  14. M2.2 Flare – CDS/EIT/GOES Peter Gallagher (UCD)

  15. M2.2 Flare – CDS/EIT/GOES Peter Gallagher (UCD)

  16. RHESSI Lightcurve Peter Gallagher (UCD)

  17. RHESSI Spectrum • Thermal: • T ~ 20 MK • EM ~ 1049cm-3 • Nonthermal: • Ec ~ 24 keV • ~ 7.3 • HXR Area <1018cm2 • => Nonthermal Electron Flux >3x1010 ergs cm-2 s-1 Peter Gallagher (UCD)

  18. 6 - 12 keV (dashed line) Thermal 25 – 50 keV (solid line) Non-thermal Peter Gallagher (UCD)

  19. Stationary Fe XIX Component Blueshifted Fe XIX Component Evidence for Upflows Doppler shifts measured relative to a stationary component: v/c = (- 0)/ 0 In Fe XIX v = 270 km s-1 Peter Gallagher (UCD)

  20. Flow velocity vs. Temperature Peter Gallagher (UCD)

  21. Future Work • How does the chromospheric response depend on the nonthermal electron properties? • We only have one event! • Nonthermal electrons => F>3x1010 ergs cm-2 s-1 • Response => ~ -30 km s-1 and 270 km s-1 • Is there a threshold for explosive evaporation? • Heating < expansion => 3kT / Q < L/cs • => need large number of CDS/RHESSI flares Peter Gallagher (UCD)

More Related