Causes and Consequences of Mesospheric Water Vapor Layers

Mesospheric observations from the UARS HALOE experiment have shown the existence of distinct water vapor layers both at low and at high latitudes. It has been speculated that the former are a consequence of heterogeneous chemistry acting on meteoric dust, whereas the latter are apparently associated with phase changes associated with the formation and evolution of polar mesospheric clouds. Further analysis of the HALOE water vapor observations suggest that there are two separate layers of enhanced water vapor at high latitudes and that there is a physical and/or chemical connection between the low latitude layer and the two high latitude layers. In this talk we will 1) use HALOE observations to characterize these mesospheric water vapor layers and their annual variation, 2) discuss the role of heterogeneous chemistry and surface/gas exchange on meteoric dust as a source of the lower altitude water vapor layer, and 3) explore the possibility that this altitude layer is causally connected to the formation and evolution of polar mesospheric clouds.