The PIs will continue comprehensive studies of mesosphere and lower thermosphere aeronomy. This program will utilize Incoherent Scatter Radar (ISR) data and optical facilities of Arecibo Observatory, a sodium/iron resonance lidar at Arecibo on a campaign basis, and data analysis coupled with modeling/theoretical studies conducted at Penn State. The renewal grant will cover: (1) continued ISR/lidar observational and modeling investigations of the relationship (or "coupling") between small-scale neutral atmosphere structure, acoustic-gravity waves, tides and the presence of sporadic metal and ion layers; (2) temperature dependent chemistry; (3) the origin of the 6-hour tide; (4) the complex of newly observed short-period waves and ion layers in the 100-250km region; (5) the origin of the (sometimes complex) ion layer structures in the 90-100km region and their relationship to sporadic metal layers; and (6) apparent "convective" processes as observed in the sodium and ion layers as well as in the "background" ionosphere.***
