Last Updated: 06/12/2024


Version: v2

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

Change Log

Version 2.6 was deployed at the CCMC on May 6, 2024. The changes in version 2.6 include:

  • Only use the Leading Edge (LE) CME measurements from DONKI as input for SEPSTER predictions.
  • Updated request URL to the iSWA HAPI calls from “dscovr_plasma_1m” to “swpc_rtsw_plasma_P1M”. iSWA updated the catalog ID in Feb 2024.
  • Observatory name in Parker Spiral JSON files now changed from “DSCOVR” to “SWPC-RTSW”, inline with iSWA changes

Version 2.4 was deployed at the CCMC on June 28, 2023. The changes in version 2.4 include:

  • The use of the CCMC iSWA HAPI API to fetch solar wind speed data to run the model.
  • Improved logic for determining when to switch from DSCOVR to ACE solar wind data (obtained from iSWA). This is to address the issue of incomplete DSCOVR data that occurred when the DSCOVR data is unavailable on iSWA. The original SEPSTER logic could not handle this scenario and therefore did not switch to ACE.


  • Heliosphere / Inner Heliosphere

Space Weather Impacts

  • Solar energetic particles - SEPs (human exploration, aviation safety, aerospace assets functionality)


  • Solar Energetic Particles



Code Languages: C


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In addition to any model-specific policy, please refer to the General Publication Policy.