Low-energy particle observations in the quiet dayside cusp from AE-C and AE-D

Energy-time spectrograms of low-energy electrons and protons have been obtained in the high-latitude region near magnetic local noon with the photoelectron spectrometer (PES) and low-energy electron experiment (LEE) on board the AE-C and AE-D satellites. Electrons with energies between 0 and 500 eV are measured with the PES instrument, and electrons and protons between 200 eV and 25 keV are detected with the LEE instrument. The AE-C satellite was launched with a 680 orbital inclination and acquired data as it skimmed through the dayside cusp region over a wide range of local times. These observations complement those obtained from the polar-orbiting AE-D satellite, which acquired data within a few hours of magnetic local noon over a wide range of latitudes.The prenoon-postnoon asymmetry of low-energy particle characteristics reported here and in earlier studies by McDiarmid et al. (1975, 1976) is consistent with the distribution and flow directions of field-aligned currents in the cusp and auroral region. Fluxes of low-energy electrons with complex and variable energy spectra were observed at latitudes up to 860 in the prenoon region during quiet geomagnetic conditions. These electron fluxes were accompanied by a noticeable reduction in the proton flux, suggesting the presence of an electric field directed upward from the polar cap region which provides a potential of a few hundred volts