Solar Ultraviolet and X-ray Energy Deposition and Partitioning in the MLT

Solar irradiance in the far-ultraviolet, extreme-ultraviolet, and soft X-ray regions of the spectrum is the primary energy source for the mesosphere and lower thermosphere (MLT). Recent measurements from the solar EUV experiment on the TIMED satellite, from the UARS, SOHO, SNOE, and SORCE satellites, and from various rocket flights, have greatly increased our knowledge of the intensity and variability of the solar spectrum. In this paper, model calculations are combined with measured solar irradiances to produce a description of ionization, dissociation, excitation, and heating rates in the MLT. Key issues and uncertainties are discussed, and a method for efficient computation of these rates in general circulation models is described.