Cleft signature in proton fluxes above 100 keV

Experimental evidence is presented that the low-energy proton population, which is the signature of the polar cleft region, has a high-energy tail of above 100-keV proton fluxes. The precipitation zone of these higher-energy protons covers the same latitude band as the low-energy particles do and also experiences the same latitudinal displacements during changes in the geomagnetic conditions. The precipitation has an isotropic pitch angle distribution and the measured higher-energy intensities compare favorably with values extrapolated from the spectrum at lower energies. The statistical invariant latitude pattern described by above 100-keV precipitating protons in the magnetic local time span 0006–1800 hours is presented.