This ground-based program of millimeter spectroscopic observations of the upper stratosphere, mesosphere, and lower thermosphere investigates a wide range of photochemical and isotopic processes. Through the previous grant, the PI obtained spectral line observations of this poorly explored atmospheric region point to a number of surprises, including large variations in the D/H ratio of mesospheric water. Most of these millimeter line emissions, however, were weak, and the PI needs long integrations under good observing conditions for sufficiently accurate measurements. Thus, the investigator proposes a three-year program of millimeter spectral line observations at the significantly upgraded Kitt Peak detector configuration. Kitt Peak's improved sensitivity of millimeter spectral line measurements, increased by a factor of four, will enhance these unique constituent measurements of the upper middle atmosphere. Finally, analysis of the resulting data will improve understanding of the mesosphere and attack outstanding problems understanding transport, photochemical and solar cycle processes within the entire middle atmosphere.***
