During the next century, as a consequence of human activities, the middle atmosphere (~10-100 km altitude) is expected to become colder, wetter, and cloudier and to become a less effective shield of solar UV radiation. Doubling the concentrations of the greenhouse gases CO2 and CH4 is predicted to cool the stratopause (~50 km) by 10-12 K and the mesopause region (~80-100 km) by 6-12 K. Unlike the lower atmosphere, the background state of the middle atmosphere and its natural variability have not been well characterized, because until recently, this region was difficult to study observationally. The development of sophisticated remote sensing techniques, and the impressive evolution of numerical models during the past decade, have provided the tools necessary to begin understanding the impact of human activities on this complex and important region of the atmosphere and to clarify its interactions with the lower atmosphere. We are proposing to develop a novel middle atmosphere temperature lidar which uses broadband tunable solid-state lasers and mesospheric Fe as the fluorescence tracer. The goal is to develop a system that is rugged and reliable, is capable of making observations during both day and night, and can be deployed at remote sites (e.g. South Pole or Equator) or operated from research aircraft (e.g. NCAR Electra or C-130). Once constructed and tested, the system will then be deployed and used to characterize the thermal structure of the middle atmosphere (35-100 km), to study Fe and Ca+ in the mesopause region, and to study the influence of tides and planetary waves. These observations will substantially improve our rather poor knowledge of middle atmosphere temperatures, quantify the natural variability, provide crucial tests of middle atmosphere circulation models, and significantly enhance our understanding of large scale waves and tides in this region. The instrument will be field tested in the final year of the project by making several mid-summer flights to the North Pole. These summertime Arctic temperature observations will be the first ever made of the mesopause region at extreme high latitudes, where atmospheric temperatures are at their absolute coldest. Instrument field testing also includes several scientific flights to the Equatorial region south of Puerto Rico to study sporadic Fe and Ca+ phenomena and to determine if it is possible to measure temperatures in the lower thermosphere (100-120 km) when high altitude sporadic Fe events occur. This project provides a unique opportunity for collaboration between the industrial group (Aerospace) that originally proposed the novel Fe lidar technique, a university group (Illinois) that is skilled in the development and field deployment of lidars for scientific studies, and a national center group (National Center for Atmospheric Research) that has the deep understanding of the scientific issues that is necessary to ensure optimum utilization of the new instrument.