Data accumulated for more than a solar cycle by the TIROS/NOAA polar orbiting satellites are used to extract patterns of particle precipitation in several medium energy bands for varying geomagnetic conditions. While the atmospheric effects of auroral particles measured by these satellites (300 eV--20 keV) have been widely studied, the effects of medium energy (30 keV--2.5 MeV) particles have received less attention; in this paper we present average particle precipitation patterns for medium energy protons and electrons as a function of geomagnetic activity. A magnetic coordinate system is used to bin data at high latitudes to produce patterns that are then used as additional inputs to the National Center for Atmospheric Research thermosphere ionosphere mesosphere electrodynamic general circulation model (TIME-GCM) to study the effects of medium energy particles on the mesosphere and lower thermosphere. Model results obtained with these additional inputs are used to assess the significance of medium energy particles on the composition and dynamics of the region. Zonally averaged model results from the run that includes the medium energy particles show significant increases in ne, HOX, NO2, and NO and a 27 percent decrease in O3 between 70 and 80 km in the polar regions when compared to a similar run without the particles. The temperature and wind differences are small.¿ 1997 American Geophysical Union