Calcium Chemistry in the Upper Atmosphere.

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About 100 tonnes of extra-terrestrial dust enters the earth's atmosphere each day. Because of the high entry velocity (11 - 72 km/s), most of the material ablates, giving rise to layers of metal atoms between 80 and 105 km. A number of these metals (Na, Fe, K and Ca) can be observed from the ground using lidar (laser radar), providing an important tool for studying the physics and chemistry of this transition region on the edge of space. A long-running mystery is why the Ca layer is severely depleted, containing less than 1% of the expected density. The proposed project will address this question by first studying the reactions that control calcium chemistry in the upper mesosphere, and then constructing a model that includes a detailed description of the process of meteor ablation. This model will be tested against lidar measurements of Ca atoms and Ca+ ions, from two observatories at low and mid latitudes. The model and lidar data will also be used to study the chemistry of sporadic E layers, which are concentrated layers of metallic ions and electrons that have a significant effect on radio propagation. A particular goal is to predict the lifetimes of these layers.