SEPSTER

The SEP prediction inspired by STEREO observations (SEPSTER) is a simple model to predict the peak intensity of 14-24 MeV protons in solar energetic particle (SEP) events near 1 AU that is based on the longitudinal intensity variation of SEP events observed by both STEREO spacecraft and at the Earth and their dependence on the speed of the related coronal mass ejection derived by Richardson et al., Solar Physics, 289, 3059, 2014; DOI 10.1007/s11207-014-0524-8, Solar Physics. This method uses as input φ is the connection angle (longitude) between the solar event and the solar footpoint of the spiral magnetic field line passing the observing spacecraft, and σ is the Gaussian width; 43° is the average value found by Richardson et al. (2014). Another input is the speed of a CME. Combining this with the connection angle estimated for a 1 AU observer either using the solar event longitude or the direction of the CME, then the 14-24 MeV SEP intensity at the observer can be estimated.

If applied to all CMEs, this method produces many false alarms which may be reduced by considering the solar radio emissions associated with the CMEs or requiring a minimum speed and/or width for the CME. This is described in Richardson, Mays and Thompson, Space Weather, 2018. For example when combined with solar radio observations, for 36 events with observed intensities above 0.1 pfu at 14-24 MeV, the mean predicted to observed intensity ratio is 0.671 and around 75% of the predicted intensities are within an order of magnitude of those observed.

CME speed and connection angle. Optionally: CME width, solar radio emissions.

Peak 14-24 MeV SEP intensity