1. September 21, 2005Peter Gallagher (UCD) Chromospheric Evaporation Peter Gallagher University College Dublin Ryan Milligan Queen’s University Belfast

2. September 21, 2005Peter Gallagher (UCD)

3. September 21, 2005Peter Gallagher (UCD) Canonical Flare Model oStep 1: Acceleration. oReconnection produces power-law electron distribution. oStep 2: Propagation. oElectrons spiral along magnetic fields from corona to chromosphere. oStep 3: Heating. oElectrons deposit energy in chromosphere via Coulomb collisions. oStep 4: Evaporation. oDense chromosphere radiates and may expand.

4. September 21, 2005Peter Gallagher (UCD) Chromospheric Response oHow does the chromosphere respond to nonthermal electrons? oAssume power-law electron spectrum: of(E) ~ E -  electrons cm -2 s -1 T 1 : Nonthermal Electrons T 2 : Impulsive Heating T 3 : V UP T 3 : V DOWN Density Loop leg

5. September 21, 2005Peter Gallagher (UCD) Chromospheric Response oChromospheric response depends on properties of accelerated electrons: oLow-energy cut-off (E c ) oLower E c => more energy => more rapid and pronounced response. oPower-law index (  ) oHarder spectrum => high energy electrons penetrate deeper where chromospere better able to radiate => less rapid and pronounced response. oTotal flux oHigher flux => more energy => more rapid and pronounced response. ECEC  E f(E) nonthermalthermal

6. September 21, 2005Peter Gallagher (UCD) GentleExplosive Flux (ergs cm -2 s -1 )<10 10 >3 x 10 10 T (K)<10 6 >10 7 P (dyn cm -2 )x10x100-1000 Upflows (km s -1 )10’s100’s Downflows (km s -1 )010’s Gentle vs Explosive Evaporation

7. September 21, 2005Peter Gallagher (UCD) Gentle vs Explosive Evaporation

8. September 21, 2005Peter Gallagher (UCD)

9. September 21, 2005Peter Gallagher (UCD)

10. September 21, 2005Peter Gallagher (UCD) RHESSI Spectral Coverage

11. September 21, 2005Peter Gallagher (UCD) CDS and TRACE: 26 March 2002 Flare oSOHO/CDS oHe I (0.03 MK) oO V (0.25 MK) oMg X (1.1 MK) oFe XVI (2.5 MK) oFe XIX (8 MK) oTRACE 17.1 nm oFe IX/X (1.0 MK)

12. September 21, 2005Peter Gallagher (UCD) RHESSI Integrated Spectrum

13. September 21, 2005Peter Gallagher (UCD) Footpoint Downflows oLoops are not static. oDownflows 100 km s -1 oLoops cool via conduction, radiation, and flows.

14. September 21, 2005Peter Gallagher (UCD) M2.2 Flare – CDS/EIT/GOES

15. September 21, 2005Peter Gallagher (UCD) M2.2 Flare – CDS/EIT/GOES

16. September 21, 2005Peter Gallagher (UCD) RHESSI Lightcurve

17. September 21, 2005Peter Gallagher (UCD) RHESSI Spectrum Thermal: T ~ 20 MK EM ~ 10 49 cm -3 Nonthermal: E c ~ 24 keV  ~ 7.3 HXR Area <10 18 cm 2 => Nonthermal Electron Flux >3x10 10 ergs cm -2 s -1

18. September 21, 2005Peter Gallagher (UCD) 6 - 12 keV (dashed line) Thermal 25 – 50 keV (solid line) Non-thermal

19. September 21, 2005Peter Gallagher (UCD) Evidence for Upflows Stationary Fe XIX Component Blueshifted Fe XIX Component Doppler shifts measured relative to a stationary component: v/c = ( - 0 )/ 0 In Fe XIX v = 270 km s -1

20. September 21, 2005Peter Gallagher (UCD) Flow velocity vs. Temperature

21. September 21, 2005Peter Gallagher (UCD) Future Work oHow does the chromospheric response depend on the nonthermal electron properties? oWe only have one event! oNonthermal electrons => F>3x10 10 ergs cm -2 s -1 oResponse => ~ -30 km s -1 and 270 km s -1 oIs there a threshold for explosive evaporation? o  Heating 3kT / Q < L/c s o=> need large number of CDS/RHESSI flares