A new method to quantify and reduce projection error in whole-solar-active-region parameters measured from vector magnetograms

Abstract

Projection error limits the use of vector magnetograms of active regions (ARs) far from disk center. In this Letter, for ARs observed up to 60o from disk center, we demonstrate a method of measuring and reducing the projection error in the magnitude of any whole-AR parameter derived from a vector magnetogram that has been deprojected to disk center. The method assumes that the center-to-limb curve of the average of the parameter's absolute values measured from the disk passage of a large number of ARs and normalized to each AR's absolute value of the parameter at central meridian, gives the average fractional projection error at each radial distance from disk center. To demonstrate the method, we use a large set of large-flux ARs and apply the method to a whole-AR parameter that is among the simplest to measure: whole-AR magnetic flux. We measure 30,845 SDO/HMI vector magnetograms covering the disk passage of 272 large-flux ARs, each having whole-AR flux >1022 Mx. We obtain the center-to-limb radial-distance run of the average projection error in measured whole-AR flux from a Chebyshev fit to the radial-distance plot of the 30,845 normalized measured values. The average projection error in the measured whole-AR flux of an AR at a given radial distance is removed by multiplying the measured flux by the correction factor given by the fit. The correction is important for both the study of evolution of ARs and for improving the accuracy of forecasting an AR's major flare/CME productivity.

10 pages, four figures; accepted for publication in ApJ Letters

References in corpus (8)

• The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches
• The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance
• Solar Flare Prediction Using SDO/HMI Vector Magnetic Field Data with a Machine-Learning Algorithm
• VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
• Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory
• Point spread function of SDO/HMI and the effects of stray light correction on the apparent properties of solar surface phenomena
• Comment on "Resolving the 180-deg Ambiguity in Solar Vector Magnetic Field Data: Evaluating the Effects of Noise, Spatial Resolution, and Method Assumptions"
• Near-Sun Speed of CMEs and the Magnetic Non-potentiality of their Source Active Regions

Cited by in corpus (13)

• The role of flux cancellation in eruptions from bipolar active regions
• Evidence of Twisting and Mixed-polarity Solar Photospheric Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations
• Propagation of Waves above a Plage as Observed by IRIS and SDO
• High-resolution observations of recurrent jets from an arch filament system
• Active Region Photospheric Magnetic Properties Derived from Line-of-sight and Radial Fields
• Restoring process of sunspot penumbra
• The Trigger Mechanism of Recurrent Solar Active Region Jets Revealed by the Magnetic Properties of a Coronal Geyser Site
• Critical magnetic field strengths for solar coronal plumes in quiet regions and coronal holes?
• Explainable Deep Learning-based Solar Flare Prediction with post hoc Attention for Operational Forecasting
• Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions
• Are the brightest coronal loops always rooted in mixed-polarity magnetic flux?
• Case study on the identification and classification of small-scale flow patterns in flaring active region
• SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation