Inferring Photospheric Velocity Fields Using a Combination of Minimum Energy Fit, Local Correlation Tracking, and Doppler Velocity

Abstract

The minimum energy fit (MEF), a velocity inversion technique, infers all components of the photospheric velocity that are consistent with the induction equation. From the set of consistent velocity fields, it selects the smallest overall flow speed by minimizing a kinetic energy functional. If partial velocity information is available from other measurements, it can be incorporated into the MEF methodology by minimizing the squared difference from that data. We incorporate the partial velocity information provided by local correlation tracking (LCT) technique and Doppler velocity measurements. We test the incorporation of these auxiliary velocity fields using the simulated magnetograms and velocitygrams. To the known velocity field we compare the results obtained from the MEF alone, the MEF with LCT constraints, and the MEF with LCT and Doppler information. We find that the combination of MEF with LCT and vertical velocity yields the best agreement. We also apply these three methods to actual vector magnetograms of AR 8210 obtained by the Imaging Vector Magnetograph. The results suggest that in this active region the helicity and energy fluxes are dominated by the horizontal rather than the vertical components of the velocity.