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Model Web

Community Coordinated Modeling Center (CCMC)  Goddard Space Flight Center

This model describes the interplanetary fluences of protons with energies greater than 10 MeV and also of protons with energies greater than 30 MeV at a distance of one Astronomical Unit (A.U. = EarthSun distance). It is based on riometer, rocket, and balloon measurements from the Earth's surface and from above the atmosphere between 1956 and 1963, and on spacecraft measurements in the vicinity of Earth between 1963 and 1985. Altogether, close to 200 events are considered. The distribution of event fluences is represented by a log normal distribution. Because of the larger data base a distinction between "ordinary" and "anomalously large" (AL) events, as in the SOLPRO model, is not necessary; the August 1972 AL does not stand out from the rest of the data base. Fluences during the seven active years of a solar cycle exceed fluences during the four quiet years by at least two orders of magnitude. The active period starts about two years before the sunspot maximum and lasts for about seven years. To obtain proton fluences from this model, one has to specify (1) the mission length at a constant heliocentric distance of 1 A.U. during the active years, and (2) the required confidence level. A confidence level of 95% means that only 5% of missions identical to the one being considered will have fluences larger than those predicted by the model. For distance r less than 1 A.U. an r3 fluence dependence is recommended and for r greater than 1 A.U., an r2 dependence. The proton fluences for energies greater than 10 MeV are about twice those calculated with earlier models. At energies greater than 30 MeV, the old and new models agree. In general, the JPL model can be considered the most reliable at this time because of the large data base used.