1. White-Light Flares: TRACE and RHESSI Observations H. Hudson (UCB), T. Metcalf & J. Wolfson (LMSAL), L. Fletcher & J. Khan (Glasgow)

2. The First Observation of a Solar Flare Carrington 1859

3. June 3, 2015RHESSI Locarno June 9, 20053 Terrestrial response to 1859 flare

4. White-Light Flares “White light” is formed deep in the solar atmosphere and is therefore energetically important (also note “white-light prominences”) White-light (and UV) continuum emission associates well, at least in part, with the hard X-ray impulsive phase There are some observations from space prior to TRACE (Yohkoh; Matthews et al., 2003), but TRACE and RHESSI are better There are now also infrared observations of solar flares (1.56 , the “opacity minimum”; Xu et al. 2004)

5. June 3, 2015RHESSI Locarno June 9, 20055

6. June 3, 2015RHESSI Locarno June 9, 20056 The Wilson depression and tilted fields

7. June 3, 2015RHESSI Locarno June 9, 20057 Contribution functions A given feature in the spectrum forms over a range of [heights], following the transfer of radiation in a given model (the contribution function) Work reported by H. Uitenbroek at SPD (May 2005) generalizes this concept to response functions dependent on temperature or magnetic changes in a dynamical model One-D radiation hydrodynamics modeling (e.g., Allred and Hawley) should account for this subtlety, and it may be less important for the continuum

8. Observational questions to be asked for WLFs What are the observational characteristics of the new TRACE capability? Is the white-light/hard X-ray association always there? Do the TRACE broad-band observations differ morphologically from earlier observations? Do white light and UV sources match? Is white-light emission present in every flare in a proportional manner?

9. Initial database TRACE catalog => events with <10 s cadence in white light and full resolution, GOES C and above Total event list consists of 33 events during RHESSI operations through 2004 11 well-covered events (X: 0; M: 7; C: 4) All 11 events have TRACE WL response All 11 events have RHESSI hard X-ray response

10. Initial database TRACE catalog => events with <10 s cadence in white light and full resolution, GOES C and above Total event list consists of 33 events during RHESSI operations through 2004 11 well-covered events (X: 0; M: 7; C: 4) All 11 events have TRACE WL response All 11 events have RHESSI hard X-ray response of course!

11. TRACE The TRACE white light channel has significant contributions from 1700 Å to 1  m The TRACE pixel size is 0.5” TRACE WL images show solar granulation, sunspots and faculae similar to other imaging at short wavelengths UV contributions to the white light channel can be reduced by subtracting the TRACE 1700 channel.

12. June 3, 2015RHESSI Locarno June 9, 200512 TRACE spectral Response Solar-cycle modulation (Lean, 1997)

13. RHESSI-TRACE WLF event list 25-JUL-02 03:55:00 03:58:00 04:03:00 C2.7 TRACE RHESSI 0039 S13E46 3-sigma 26-JUL-02 18:57:00 19:03:00 19:06:00 M1.0 TRACE RHESSI 0044 S21E21 4-OCT-02 05:34:00 05:38:00 05:41:00 M4.0 TRACE RHESSI 0137 S19W09 5-OCT-02 10:39:00 10:46:00 10:48:00 M1.2 TRACE RHESSI ?? ?? 12-NOV-02 17:58:00 18:18:00 18:24:00 C9.9 TRACE RHESSI 0180 S11W75 12-JUN-03 01:04:00 01:30:00 01:52:00 M7.3 TRACE RHESSI 0375 N13W65 23-OCT-03 02:35:00 02:41:00 02:44:00 M2.4 TRACE RHESSI 0484 N03E15 9-JAN-04 01:33:00 01:44:00 01:54:00 M3.2 TRACE RHESSI 0537 N02E49 22-JUL-04 00:14:00 00:32:00 00:43:00 M9.1 TRACE RHESSI 0652 N03E17 24-JUL-04 00:34:00 00:39:00 00:41:00 C1.6 TRACE RHESSI N12W03 24-JUL-04 13:31:00 13:37:00 13:45:00 C4.8 TRACE RHESSI 0652 N04W16

14. C7.8 13-Feb-02 WL contrast ~20% noise @ 1.8% per pixel WL observed during RHESSI 25-50 keV UV contours relatively extended WL sources are patches unresolved by TRACE WL+1700AWL difference

15. Six events from survey, 128 arc s TRACE images

16. WLF is impulsive: M4.9 GOES TRACE WL

17. June 3, 2015RHESSI Locarno June 9, 200517 TRACE WLTRACE 1700 A

18. June 3, 2015RHESSI Locarno June 9, 200518 A gradual white-light event: WL occurs in the impulsive phase

19. June 3, 2015RHESSI Locarno June 9, 200519 A gradual white-light event: RHESSI overlay

20. June 3, 2015RHESSI Locarno June 9, 200520

21. June 3, 2015RHESSI Locarno June 9, 200521 TRACE WL emission from loop tops

22. June 3, 2015RHESSI Locarno June 9, 200522 Loop-top WL emission

23. June 3, 2015RHESSI Locarno June 9, 200523 World’s record white-light flare: a C1.3!! GOES 1-8A derivative Raw WLDifference

24. June 3, 2015RHESSI Locarno June 9, 200524 Conclusions WL emission, as seen by TRACE, shows rapid small-scale features and closely resembles the UV morphology The data confirm the impulsive-phase association with hard X-rays, also found for extended non-thermal phase Sources may be extended in area, but include many tiny (arc-s scale) emission patches The data are consistent with the idea that white light correlates with total flare energy Extended events show similar morphology and don’t require further classification Contrasts can exceed 100%

25. Observational questions half-answered What are the observational characteristics of the new TRACE capability? Great Is the white-light/hard X-ray association always there? Yes Do the TRACE broad-band observations differ morphologically from earlier observations? Somewhat Do white light and UV sources match? TBD Is white-light emission present in every flare in a proportional manner? Yes

26. June 3, 2015RHESSI Locarno June 9, 200526 Tentative findings WLF contrasts in the very broad-band TRACE response do not differ much from Carrington’s => low temperatures All flares are WLFs TRACE WL emission can be seen in loops as well as footpoints WLF differs morphologically from UV emissions: more concentrated, shorter durations (nb must be careful about the “island in the tide” effect)

27. June 3, 2015RHESSI Locarno June 9, 200527 Important open questions What can we learn about WLF spectra from the new data (not only TRACE, but MDI, GONG, IVM, etc…)? How can we get around the photometric limit of granulation/p-mode noise, plus image jitter? What will the improved knowledge of flare energetics tell us?