Far-side Imaging of Active Regions: Latest Developments Irene González Hernández and the GONG andHMI far-side teams National Solar Observatory, Tucson, AZ Northwest Research Associates (CORA), Boulder, CO Stanford University, Stanford, CA

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

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

Helioseismic Imaging of the Farside Phase of the Correlation

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

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

Improving the far-side monitor Detecting medium size active regions  Reducing the noise by combining consecutive, non-overlapping maps Calibrating in terms of magnetic field strength ( using the relationship found by Gonzalez Hernandez, Hill, Lindsey 2009, ApJ) Removing the Solar Cycle variation as described by Gonzalez Hernandez, Scherrer and Hill (ApJ, 2010) Confidence Level (…. Space Weather Journal, 2010) Adding extra info on date of return and NOAA previous number if existed

Calibrating the far-side signal

González Hernández, I.; Hill, F.; Lindsey, C. Calibration of Seismic Signatures of Active Regions on the Far Side of the Sun 2007ApJ G

Confidence Level REFERENCES González Hernández, I.; Scherrer, P.; Hill, F. A New Way to Infer Variations of the Seismic Solar Radius 2009ApJ...691L..87G < González Hernández, I.; Hill, F.; Lindsey, C. Calibration of Seismic Signatures of Active Regions on the Far Side of the Sun 2007ApJ G Fontenla, J. M.; Quémerais, E.; González Hernández, I.; Lindsey, C.; Haberreiter, M Solar irradiance forecast and far-side imaging 2009AdSpR.. Pérez Hernández, F.; González Hernández, I.Green's Functions for Far- Side Seismic Images: A Polar-Expansion Approach 2010ApJ P I. González Hernández, F. Hill, P. H. Scherrer, C. Lindsey, and D. C. Braun Space Weather, 8, S06002, doi: /2009SW000560, 2010

New Calibrated Far-side maps C. Long. Latitude Phase-shift Prob. Effective-Area Date-of-return Front-side-number NOAA 11100

New Calibrated Far-side maps Helioseismic far-side maps on the left and simultaneous STEREO behind observations of AR NOAA before it appeared on the front side of the Sun on September

Further Improvements Sensitivity variation with location !! Sensitivity variation with location !! Detecting smaller active regions (signal-to-noise) Detecting smaller active regions (signal-to-noise) Duty cycle Duty cycle Hmi combination Hmi combination Area estimation Area estimation Show current calibration Show current calibration Talk about Effective area Talk about Effective area Front side study Front side study Error estimation Error estimation Integrated Index Integrated Index Polarity Polarity

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

Why the improvement? Length of series Length of series

Why the improvement? Duty Cycle Duty Cycle

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

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

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

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

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

Why the improvement? GONGMDI

The Farside Magnetic Index In collaboration with K. Jain, W. K. Tobiska and F. Hill Comparison with front-side indexes:. The graphic below shows simultaneous observations of Ly-α (lasp.colorado.edu), F 10 ( the calculated Mount Wilson Sunspot Index ( and the Far Side Magnetic Index. The sequence spans from October 2002 to December The different indexes have been scaled and shifted to aid the comparison.

Solar cycle variation

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

Conclusions and Future work MDIGONG FS % 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 !!!