The prediction of flares is essential for reducing the damage to technological infrastructures on Earth. Solar flares emit X-rays, highly energetic particles, and coronal mass ejections (CMEs) into the interplanetary space in the heliosphere, whereby these flares become one of the origins of space weather phenomena (e.g., Schwenn et al. The mechanism of solar flares is a long-standing puzzle.
Finally, we discuss the standard evaluation methods for operational forecasting models, such as the preparation of observation, training, and testing datasets, and the selection of verification metrics. The procedure achieved TSS = 0.70 for ≥ M-class flares and 0.59 for ≥ C-class flares using the datasets obtained from 2010 to 2017. Furthermore, we proposed the use of time-series cross-validation. The chronological split appears suitable for evaluating operational models. Here, we adopted a chronological split to divide the database into two for training and testing. We found that operational DeFN forecasts achieved TSS = 0.70 (0.84) for ≥ C-class flares with the probability threshold of 50 (40)%, although there were very few M-class flares during this period and we should continue monitoring the results for a longer time. For comparison, we evaluated the operationally forecast results from January 2019 to June 2020. The model was evaluated with the skill score of the true skill statistics (TSS) and achieved predictions with TSS = 0.80 for ≥ M-class flares and TSS = 0.63 for ≥ C-class flares. DeFN was pretrained using the datasets obtained from 2010 to 2015. Flare labels are attached to the feature database, and then, the database is standardized and input into DeFN for prediction. Active regions are automatically detected from magnetograms, and 79 features are extracted from each region nearly in real time using multiwavelength observation data.
The input database of solar observation images taken by the Solar Dynamic Observatory (SDO) is downloaded from the data archive operated by the Joint Science Operations Center (JSOC) of Stanford University. DeFN is set to run every 6 h and has been operated since January 2019. DeFN can issue probabilistic forecasts of solar flares in two categories, such as ≥ M-class and < M-class events or ≥ C-class and < C-class events, occurring in the next 24 h after observations and the maximum class of flares occurring in the next 24 h. We developed an operational solar flare prediction model using deep neural networks, named Deep Flare Net (DeFN).