CEDAR: Continuation to Daytime Potassium Doppler Lidar at Arecibo

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This one-year project aims to complete construction of a daytime potassium Doppler lidar and to test its operation at Arecibo Observatory. The Arecibo lidar, based on a narrowband injection-seeded alexandrite ring laser, has been able to make nighttime temperature and potassium density measurements in the mesosphere and lower thermosphere region since February 2001. Through seven years of operation, the nighttime technology has matured and sufficient data were collected to characterize the nocturnal thermal structure and nocturnal potassium seasonal variations. To enhance its measurement capability and to better serve the aeronomy community, in 2005 a project was proposed and received funding for three years to upgrade the Arecibo lidar to a daytime observing capability and to conduct extensive observations to study the tropical mesosphere and lower thermosphere region over the full-diurnal cycle at the Arecibo Observatory. The lidar modifications have been underway for the past three years but the Faraday filter originally intended to be used did not perform as expected. Many of the other technical goals of the previous project were achieved, such as narrowing of the field-of-view, construction of the Faraday filter test station, implementation of the new receiver optical chopper, initial observational tests, and implementation of new data processing techniques. In addition, the optical elements and hardware necessary to construct a new Faraday filter were acquired. The project will therefore complete the remaining steps to yield a daylight-optimized lidar capable of making full diurnal observations at Arecibo, where its collocation with the incoherent scatter radar will enable a wide variety of scientific studies, such as measurements of tides, gravity waves, absolute atmospheric density, metal layer chemistry, and the evolution of sporadic atom and ion layers.