Probability model for cumulative solar proton event fluences

A new model of cumulative solar proton event fluences is presented. It allows the expected total fluence to be calculated for a given confidence level and for time periods corresponding to space missions. The new model is in reasonable agreement with the JPL91 model over common proton energy range of >1 to >60 MeV. The current model extends this energy range to >300 MeV. It also incorporates more recent data which tends to make predicted fluences slightly higher than JPL91. For the first time, an analytic solution is obtained for this problem of accumulated fluence over a mission. Several techniques are used, including maximum entropy, to show the solution is well represented as a lognormal probability distribution of the total fluence. The advantages are that it is relatively easy to work with and to update as more solar proton event data become available.