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Status of GONG+ Magnetograms

Learn about the status of GONG magnetograms, their performance metrics, common problems, and proposed solutions discussed at the MUG Meeting in Tucson. Find out about the schedule for upgrades and data availability for pilot projects.

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Status of GONG+ Magnetograms

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  1. Status of GONG+ Magnetograms • HowGONG makes magnetograms • Performance • Problems • Solutions • Schedule • Data availability • Pilot Projects MUG Meeting, Tucson

  2. How GONG Makes Magnetograms • Photospheric 6768 Å Ni I line profile • LCD & polarizer transmits LCP or RCP • Switches state every second • Images sorted & accumulated for 1 minute • Line shift images produced in LCP and RCP • Sum is the Doppler shift image • Difference is longitudinal Zeeman splitting + • Also get intensity and line strength images MUG Meeting, Tucson

  3. Magnetogram Performance • Inst noise level ~3 G per pixel per min • Spatial resolution >5 arc second • Dynamic range < 2300 G • Scale tied to velocity cal error (~5%) • Quick look available 2 min after obs • Revealed DB ~ 100G with 15/15 X flares MUG Meeting, Tucson

  4. Magnetogram Example November 25, 2000 MUG Meeting, Tucson

  5. Problems • Slow modulation -> seeing and cloud noise • Bad near limb and sunspots (DI < 0.5%) • Asymmetric modulation -> zero error (<10 G) • Slight, time-varying input polarization • Time to switch CP states not the same • LCD near focus so its variations show • Image rotates during the day MUG Meeting, Tucson

  6. Solutions • Seeing • Stretch CP images to spatially match • Average over longer time • Zero error • Eliminate instrumental polarization  • Better LCDs  • Equalize switching time of LCD  • Adjust images after collection  MUG Meeting, Tucson

  7. Schedule • Replace old modulators/drivers (approved project) • Prototype testing successfully done • Final design underway • Network installation done by 2/2006 • Tweak older images (not an approved project yet) • Extensive earlier effort led to improvement • Now starting a review of this work • Other data products - TBD MUG Meeting, Tucson

  8. Data Availability • Quick look magnetograms 1/hour (ftp) • Quick look magnetograms 1/day (html) • Final magnetograms 1/min (DMAC) • Merged magnetogram time series (TBD) • Synoptic maps – GONG classic (html and ftp) • Other products (TBD) MUG Meeting, Tucson

  9. Two Pilot Data Projects • GONG Magnetic Activity Indices • Full disk averages w/thresholds • Meridional flow by LCT of magnetic network • Based on KPVT work of Komm et al. • Need to determine how much averaging is required to beat down supergranulation noise • Both projects just starting • May lead to standard data products MUG Meeting, Tucson

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