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Status of GONG+ Magnetograms

Status of GONG+ Magnetograms. How GONG makes magnetograms Performance Problems Solutions Schedule Data availability Pilot Projects. How GONG Makes Magnetograms. Photospheric 6768 Å Ni I line profile LCD & polarizer transmits LCP or RCP Switches state every second

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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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