I.1.5 Dynamics of the outer radiation belt

The dynamic nature of the outer electron radiation belt, together with its diurnal variations mean that unless one is interested in longterm averages (such as provided by AE-8), some statistical description is desirable. This is especially true when deep dielectric charging and radiation background are of concern. No standard models for the variability are yet available, but for engineering purposes the CRRESELE model has been developed [RD.61]. An older version of the AE-8 electron model, AE-4 [RD.26], included a statistical model giving standard deviations of the logarithm of electron fluxes (assumed to be normallydistributed). It also included a model for local time flux modulation. This was a sinusoidal model providing amplitudes of the variation, with a fixed maximum at 11:00 hours local time. These have been extended and applied to the AE-8 model [RD.66], although this extension is unvalidated.