1. GONG Magnetograms - Raw to Synoptic Map J. Harvey

2. GONG Mags 101 GONG has 6 sites around the world, 85% duty Started in 1995, ~10” pixels, 1 image/min Full-disk, filter-based system using 6768 Å Built for good velocity data, not magnetograms 1995-2002 -- LOS mags done one per hour at each site, staggered by 20 min 2002-2009 – 2.5” pixels, better S/N and 1/min mags (3 G noise level) 2006 – new modulators installed for STEREO

3. GONG Classic Synoptic Map (CRs 1896-1942)

4. Modulator upgrade Large, varying zero point error Traced to asymmetric switching of LCD between ±¼ wave retardation, and temperature variations of retardation This was fixed by driver waveform shaping and temperature stabilization of LCDs An expensive scheme for correcting pre-fix data has been developed

5. Current GONG Recipe (CR2047+) 1.Average 10 minutes of FD mags Reject bad images in making the average Multiply by sec θ 2.Map to Carrington coordinates (sin B, CMD) 1 resolution: 180 x 180 2 maps: sum and weight Near limb pixels are quality weighted Flux conserved

6. Recipe – con’t. 3.Weighted merge of images –Cos 4 CMD –Build sum and weight merged images –Divide merged sum by weight 4.Pole correction identical to SOLIS 5.Publish –Once per hour, and –End of Carrington rotation

7. Sample CM map

8. Sample ‘Janus’ map

9. http://gong.nso.edu/data/magmap

10. Sample extrapolation

12. Synoptic Map Status Being produced hourly in near real time Classic maps and “Janus” versions Potential field extrapolations hourly Available on GONG web site Noise level << 1 G Zero point better than 0.1 G

13. Improvements Make snapshot maps Merge data from various sites rather than cut and paste Better calibration taking into account modulator efficiency Higher resolution maps could be made if useful

14. Problems Solar and instrument noise near limb Does not represent the full solar surface at any specific time Dubious polar correction (SOLIS recipe) Strong umbral field signals can wrap Leaves a small monopole Radial correction is bad in AR One GONG site currently has high scatter