A Transfer Learning Method to Generate Synthetic Synoptic Magnetograms

Current magnetohydrodynamics (MHD) models largely rely on synoptic magnetograms, such as the ones produced by the Global Oscillation Network Group (GONG). Magnetograms are currently available mostly from the front side of the Sun, which significantly reduces the accuracy of MHD modeling. Extreme Ultraviolet (EUV) images can instead be obtained from other vantage points. To investigate the potential, we explore the possibility of using EUV information from the Atmospheric Imaging Assembly (AIA) to directly generate the input for the state-of-the-art 3D MHD model European Heliospheric FORecasting Information Asset (EUHFORIA). Toward this goal, we develop a method called Transfer-Solar-GAN which combines a conditional generative adversarial network with a transfer learning approach to overcome training data set limitations. The source domain data set is constructed from multiple pairs of the central portion of co-registered AIA and Helioseismic and Magnetic Imager (HMI) line of sight (LOS) full-disk images, while the target domain is constructed from pairs of portions of AIA and GONG sine-latitude synoptic maps that we call segments. We evaluate Transfer-Solar-GAN by comparing modeled and measured solar wind velocity and magnetic field density parameters at the L₁ Lagrange point and along the Parker Solar Probe (PSP) trajectory which were determined with EUHFORIA using both empirical GONG and artificial-intelligence (AI)-synthetic synoptic magnetograms as inputs. Our results demonstrate that the Transfer-Solar-GAN model can provide the necessary information to run solar physics models by EUV information. Our proposed model is trained with only 528 paired image segments and enforces a reliable data division strategy.