THE UARS PARTICLE ENVIRONMENT MONITOR

The overall objective of the particle environment monitor (PEM) is to provide comprehensive measurements of both local and global energy inp uts into the Earth's atmosphere by charged particles and Joule dissipa tion using a carefully integrated set of instruments. PEM consists of four instruments: the atmospheric X ray imaging spectrometer (AXIS), t he high-energy particle spectrometer (HEPS), the medium-energy particl e spectrometer (MEPS), and the vector magnetometer (VMAG). AXIS provid es global scale images and energy spectra of 3- to 100-keV bremsstrahl ung X rays produced by electron precipitation into the atmosphere. HEP S and MEPS provide in situ measurements of precipitating electrons in the energy range from 1 eV to 5 MeV and protons in the energy range fr om 1 eV to 150 MeV. Particles in this energy range deposit their energ y in the atmosphere at altitudes extending from several hundred kilome ters down to as low as approximately 30 km. VMAG provides the magnetic field direction needed to indicate and interpret the locations and in tensities of ionospheric and field-aligned currents as well as providi ng a reference for the particle measurements. This paper describes eac h instrument separately and also in the context of the PEM objectives which include the determination of energy deposition and ionization pr oduction rates as functions of altitude. Examples of data acquired ear ly in the Upper Atmosphere Research Satellite (UARS) mission are prese nted.