1. A comparison of CME-associated atmospheric waves observed in coronal (Fe XII 195A) and chromospheric ( He I 10830A) lines Holly R. Gilbert, Thomas E. Holzer, Barbara J. Thompson, and John T. Burkepile (2004, ApJ, 607, 540) Okamoto Takenori

2. Abstract & Conclusion Simultaneous observations -- chromospheric waves (He I) -- coronal waves (EIT) Main goal -- to begin an investigation into whether both coronal and chromospheric waves are mechanical (MHD waves) Conclusion -- chromospheric waves are imprints of mechanical waves (=coronal waves)

3. Observations Instruments coronal waves -- SOHO/EIT (195A) 10-30 min, 2”.6 /pix chromospheric waves -- Mauna Loa Solar Observatory -- Chromospheric Helium Imaging Photometer (CHIP) - He I (10830A) 3 min, 7” /pix -- Ha (6563A) - Polarimeter for Inner Coronal Studies (PICS) CME -- SOHO/LASCO C2 and C3

4. Observations (2000 November 25) CME (17:30) He wave (18:24) EIT wave (18:35) GOES peak (X1.9, 18:44) CME (19:30) another filament eruption (18:38) filament eruption (17:13)

5. CME 773 km/s (17:30) 671 km/s (19:30) direction 17:30 19:30 (halo)

6. Event 1 (2000 November 25) EIT wave 18:35 – 47 – 73 UT He wave 18:33 – 40 – 43 – 46 – 49 UT

7. Wave front tracings He wave and EIT wave -- cospatial He-wave speed ~ 300 km/s

9. the correction of wave front motion + spreading +recombination time (< the spatial resolution of CHIP instrument)

10. Observations (2001 January 20) -- He wave (18:37 UT) -- two ribbon flare (18:40 UT) -- CME (19:30 UT) -- GOES 18:33 – 18:47 (peak M1.2) – 18:59 UT -- He I brightenings & EIT dimmings (18:46 UT)

11. CME 839 km/s 19:30 direction

12. Event 2 (2001 January 20) EIT wave He wave 18:43 – 47 – 50 – 53 – 59 UT

13. Wave speed ~ 219 km/s (western part ~ 429 km/s)  cospatial

14. Formation of He I 10830A He I absorption line -- formed in the upper chromosphere -- absorption of photospheric continuum radiation at 10830 A -- depends on the column density -- collision process -- photoionization-recombination mechanism

15. Possible Physical Explanation Chromospheric waves -- not mechanical waves (MHD waves) propagating horizontally through the upper atmosphere -- but “imprints” of MHD waves travelling in the corona The bright front associated with the compressive wave travelling in the corona leads to an enhanced chromospheric absorption of the Photospheric continuum at 10830A ~ cospatial dark front in the He I.

16. Vrsnak et al. (2002) concluded the He I disturbances consist of two main parts -- a forerunner -- a main dip  corresponding Ha disturbance the cause of the main dip -- a sudden pressure jump in the corona (shock wave) - density/temperature increase (behind the shock wave) - collisional processes are enhanced - He I absorption increase Photoionization-recombination process may cause a He I enhancement in the diffuse component of the perturbation.

17. In these events -- These waves have not necessarily steepened into shocks. -- Photoionization-recombination mechanism is the main cause of increased He I absorption. It is difficult to distinguish between the two proposed pictures Without performing complicated radiative transfer calculations.

18. Dimming & Brightening EIT dimming ~ He I brightening (cospatial) Dimming -- a decrease in density of the overlying corona -- caused by the opening of magnetic field (occurring during the explosive CMEs) The expansion of dimming regions mimic the propagation of a wave. -- waves are observed propagating to much greater distances from their source region than the outward expansion of EIT dimmings or He I brightenings.