 Flux Contours for E > 30 MeV (#/cm 2/s) Integral Proton Flux Contours for E > 30 MeV (#/cm 2/s) Altitude = 500 km, Solar Maximum Altitude = 1000 km, Solar Maximum Geographic Longitude (deg) Geographic Longitude (deg) Integral Proton Flux Contours for E > 30 MeV (#/cm2 /s) Altitude = 3000 km, Solar Maximum 10000 10000 Geographic Longitude (deg) Figure 2.1 Integral proton flux contours as a function of latitude and longitude after Barth [1]. Altitudes are a) 500 km, b) 1000 km, and c) 3000 km. Note the South Atlantic Anomaly, which is visible at lower altitudes but disappears by 3000 km. obtained by the Japanese satellite MIDORI [14]. The oxygen ions shown in the polar regions in Fig. 2.2 are not trapped heavy ions, but are due to galactic cosmic rays, as discussed below. Trapped oxygen ions are evident in the region near the SAA for the same reason that proton fluxes are greatest there, i.e., the lower magnetic field in the SAA allows the ion flux to dip down to lower altitudes. The peak in trapped heavy ion fluxes is at altitudes just above the inner proton belt (i.e., 1.8 to 2 Earth radii). Because the trapped heavy ions have relatively low energies (10's of MeV/nucleon), these particles may not penetrate through spacecraft shielding and therefore are not expected to be a major concern for SEE [1]. Transient Particles In this section, the classification of "transient" particles encompasses all particles in the near- Earth space environment that are not stably trapped in the magnetosphere. This includes particles introduced into the environment by solar events such as flares and coronal mass ejections (CMEs), as well as energetic ions incident from interstellar space. 2.2.1 Solar Event Protons and Heavy Ions The activity level of the Sun is never constant, but follows a cyclical variation of active years followed by quiet years. The period of recent solar cycles has varied between 9 and 13 years, with an average of about 11 years. Solar cycle activity is frequently gauged by the observed number of sunspots, but 