1. 17 July 2002

2. July 17 2002 flare: TRACE observations

3. time Fletcher, Pollock & Potts 2004 ~130 separate tracks

4. Flare footpoints on ~ simultaneous magnetogram Can calculate  = vB LOS.

5. UV footpoint source intensity variations correlated with  Peaks in v B LOS for individual footpoints show significant correlation in time with peaks in the UV brightness, during impulsive phase Observations Monte-Carlo simulations Peaks within  2s 25  5% 8  2% Peaks within  8s45  5% 25  5% I 1600 Typical examples:.  v B LOS..

6. = HXR sources Footpoints and HXRs

7. RHESSI 25-50 keV RHESSI 50-100 keV 07:01:31 – 07:02:01 07:02:01 – 07:02:30 07:02:30 – 07:03:00 0.5 4.5 2.51.53.5 07:02:3- – 07:03:00 HXR sources tend to be where  is highest.

8. Search for Correlated UV footpoint pairs My quick-and-dirty previous work identified ‘highly-correlated pairs’ from linear and rank correlation coefficients.previous work Problem: this tended to find correlations in overall trends in data, rather than correlated bursty structure on ~10s of seconds timescales Solution: separate out slowly and rapidly varying components (c.f. Aschwanden work with Fourier filtering) and correlate rapidly-varying parts Technique used – wavelet à trous Iteratively decomposes signal into aperiodic variations on different timescales – seems to be best wavelet for the job

9. Pairs of correlated footpoints pairs of footpoints for which UV time profiles highly correlated (lines join pairs with linear correlation coefficient > 0.8) P1 P2 N

10. image32 px16 px8 px 4 px2 px

11. Example of à trous decomposition – 2 sources (black + green) Shortest timescale component removed – signal cleaned of high frequency noise 2 longest timescale components removed: ‘detrended’ data Only the component with characteristic timescale ~ 10s

12. Et cetera…

13. Examples of reasonably well-correlated pairs Neighbours Well-separated pairs

15. Systematic time delays or just coincidence?? If footpoint intensity variations due to particle heating, how does a ~ 5s time delay arise?

17. Sample UV source pairs at HXR footpoint regions Green = eastern source, black=western source

18. Conclusions HXR sources occur where flux reconnection rate highest Just starting looking again at correlations…. - Highly correlated UV footpoint pairs hard to find - Evidence for time lags of ~4-5 seconds between footpoint brightenings? - Have to look particularly for evidence of correlation at HXR source locations