Inferring the Sun's Far-Side Magnetic Flux for Operations Using
Time-Distance Helioseismic Imaging
Abstract
Solar wind models are highly dependent on global magnetic fields at the
solar surface as their inner boundary condition, and the lack of global
field data is a significant problem plaguing solar wind modeling.
Currently, only direct observations of the near-side magnetic field
exist and far-side approximations are incapable of predicting growth of
existing active regions or new magnetic flux emergence. To fill this
data gap, we develop a method that calibrates far-side helioseismic
images, which are calculated using near-side Doppler observations, to
far-side magnetic flux maps. The calibration employs multiple
machine-learning methods that use EUV 304 Å data as a bridge. These
algorithms determine a relation 1) between the near-side AIA 304 Å data
and HMI magnetic field data, and 2) between STEREO 304 Å data and
far-side helioseismic images obtained from a newly developed
time-distance helioseismic far-side imaging method. The resulting
magnetic flux maps have been further calibrated using maps produced by a
flux transport model. The various data products from this work —
far-side acoustic maps, far-side STEREO EUV-derived magnetic flux maps,
and near-real-time acoustically-driven far-side magnetic flux maps,
along with maps of the associated uncertainties — are being made
available to enable a synchronic global magnetic flux input into coronal
and solar wind models.