Initial test of a Bayesian approach to solar flare prediction

A test of a new Bayesian approach to solar flare prediction (Wheatland 2004a) is presented. The approach uses the past history of flaring together with phenomenological rules of flare statistics to make a prediction for the probability of occurrence of a large flare within an interval of time, or to refine an initial prediction (which may incorporate other information). The test of the method is based on data from the Geostationary Observational Environmental Satellites (GOES), and involves whole-Sun prediction of soft X-ray flares for 1976-2003. The results show that the method somewhat over-predicts the probability of all events above a moderate size, but performs well in predicting large events.Comment: 4 pages, 2 figures, Astronomical Society of Australia meeting in Brisbane, July 2004; revised versio

A Check on the Validity of Magnetic Field Reconstructions

We investigate a method to test whether a numerically computed model coronal magnetic field B departs from the divergence-free condition (also known as the solenoidality condition). The test requires a potential field B0 to be calculated, subject to Neumann boundary conditions, given by the normal components of the model field B at the boundaries. The free energy of the model field may be calculated using the volume integral of (B-B0)^2, where the integral is over the computational volume of the model field. A second estimate of the free energy is provided by calculating the difference between the volume integral of B^2 and the volume integral of B0^2. If B is divergence-free, the two estimates of the free energy should be the same. A difference between the two estimates indicates a departure from div B = 0 in the volume. The test is an implementation of a procedure proposed by Moraitis et al. (Sol. Phys. 289, 4453, 2014) and is a simpler version of the Helmholtz decomposition procedure presented by Valori et al. (Astron. Astrophys. 553, A38, 2013). We demonstrate the test in application to previously published nonlinear force-free model fields, and also investigate the influence on the results of the test of a departure from flux balance over the boundaries of the model field. Our results underline the fact that, to make meaningful statements about magnetic free energy in the corona, it is necessary to have model magnetic fields which satisfy the divergence-free condition to a good approximation.Australian Research Counci