This proposal is for a continuing program of ground-based millimeter wave spectroscopic measurements of trace gases in the earth's mesosphere and lower thermosphere (MLT), using existing astronomical receivers at Kitt Peak National Radio Astronomy Observatory (NRAO). The millimeter observations of mesospheric water isotope ratios provide unique diagnostics to investigate the signatures vertical transport of hydrogen-bearing species from above and below the mesosphere may force in the vertical profiles, as well as D/H ratios, of mesospheric water. The millimeter observations support SNOE and TIMED spacecraft observations.
