1. Far-side Imaging and Activity Irene González Hernández and the GONG and MDI far-side teams National Solar Observatory, Tucson, AZ Stanford University, Stanford, CA Northwest Research Associates (CORA), Boulder, CO

2. Contents  Introduction to far-side seismic holography  Improving the far-side maps  Calibrating the seismic signal  Success Rate Variation of the mean phase with the solar cycle !  Improving the signal to noise  Future work and conclusions

3. Helioseismic Imaging of the Farside Helioseismic imaging of sunspots at their antipodes. Lindsey, C. & Braun, D.C, 1990, SoPh. Helioseismic imaging of sunspots at their antipodes. Lindsey, C. & Braun, D.C, 1990, SoPh. Seismic Images of the Far Side and Interior of the Sun Lindsey, C. & Braun, D.C, 2000, Science. Seismic Images of the Far Side and Interior of the Sun Lindsey, C. & Braun, D.C, 2000, Science. Pupil

4. Helioseismic Imaging of the Farside Phase of the Correlation

5. Prediction capability Carrington Longitude sin(latitude) Active Region NOAA-10808 Aug 29  Sep 9 2005 (GONG) AR10808 Sept 7 2005 Source: MLSO K-coronameter

6. Improving the far-side monitor FS00543 85 % MDI (HMI) GONG Time Distance ( HMI + GONG) Users able to subscribe to alerts > % |B|

7. Calibrating the far-side signal Carrington Longitude sin(latitude) Active Region NOAA-10808 Aug 29 -> Sep 9 2005 AR10808 Active Region NOAA-10923 Oct 31 -> Nov 10 2006 AR10923 sin(latitude)

8. Calibrating the far-side signal

11. “far-side” imaging of the near side 1 x 3 skip method actually extends well onto the near side!

12. Success rate MDI + GONG

13. Success Rate

14. Why the improvement? Different length of time series Different length of time series Duty Cycle Duty Cycle Phase correction Phase correction Bad data Bad data

15. Why the improvement? Phase Correction Phase Correction

16. Why the improvement? Length of series Length of series

17. Why the improvement? Duty Cycle Duty Cycle

18. Why the improvement? Mean Phase --> Temporal Variation Mean Phase --> Temporal Variation

19. Why the improvement? Mean Phase --> Temporal Variation in both instruments Mean Phase --> Temporal Variation in both instruments

20. Variation of the seismic solar radius Solar acoustic radius variation --> solar cycle variation Solar acoustic radius variation --> solar cycle variation Kholikov & Hill, 2008, SoPh

21. Solar cycle variation Mean Phase --> Solar Cycle variation --> Solar acoustic radius variation (??) Mean Phase --> Solar Cycle variation --> Solar acoustic radius variation (??)

22. Solar cycle variation Mean Phase --> Solar Cycle variation --> Solar acoustic radius variation-- > Localized to surface magnetic areas (?) Mean Phase --> Solar Cycle variation --> Solar acoustic radius variation-- > Localized to surface magnetic areas (?)

23. Far-side maps from time-distace GONG MDI September 03 2005 Courtesy of Junwei Zhao Seismic holography Time distance NOAA 10808

24. Artifacts Thomas Hartlep,Junwei Zhao Nagi N. Mansour, and Alexander G. Kosovichev Validating Time-Distance Far-Side Imaging of Solar Active Regions through Numerical Simulations Thomas Hartlep,Junwei Zhao Nagi N. Mansour, and Alexander G. Kosovichev Validating Time-Distance Far-Side Imaging of Solar Active Regions through Numerical Simulations ApJ, 689:1373–1378, 2008 December 20

25. Why the improvement? GONGMDI 060902 060903 060902 060903

26. Can we improve the Green’s Functions?  More realistic model --> Collaboration with Fernando Pérez at the IAC  Empirical calibration of the dispersion  Dispersion for several bounces

27. Conclusions and Future work MDIGONG FS00543 85 % Time Distance ( HMI + GONG) Users able to subscribe to alerts > % |B|  Improving the Maps  Calibration --> extending to the front side  Success Rate --> more accurate determination  Better Signal to Noise --> HMI data/ combination of ray paths / green’s functions / artifacts  Understanding Solar Cycle variations !!!