Of all the unsolved problems of the middle atmosphere, more seem to occur in the upper mesosphere (80-95km) than in any other region. One general reason for the accumulation of problems here is that radiative, chemical and dynamical equations used to model the regions below this region all contain simplifications that are invalid in the upper mesosphere. This implies that theories and modeling for this region require special attention beyond that usually required for the regions above or below it. Not only is this region difficult to model, but it is also difficult to investigate experimentally. This region is too high for access with airplanes or balloons and too low for satellite in situ measurements. Clearly, the development of reliable sensing techniques is important to the study of this region of the atmosphere. A pioneering effort in the development of radar techniques for the study of the chemistry of the upper mesosphere which includes the ionospheric D region is being carried out by Prof. Mathews, the PI on this proposal. Using large incoherent radar facilities operated by NSF at Arecibo in Puerto Rico and Millstone Hill in the Boston area, Prof. Mathews has been able to generate a valuable data set for the important study of D-region chemistry and the associated dynamics. THis proposal describes a research project to extend the observations, analyze the data, and carry out theoretical work on the modelling of mesospheric ion chemistry and the formation and maintenance of the sporadic ionization layers. The experiment results which include the electron and ion concentrations will be used as constraints on the theoretical models. also, work will be done on further refinement of the radar scattering theory and utilization.
