Dr. Michelle Santee, Jet Propulsion Laboratory

Abstract: Daily global measurements from the Microwave Limb Sounder (MLS) on NASA's Aura satellite, launched in July 2004, enable comprehensive examination of the daily, seasonal, interannual, and interhemispheric variations in trace gas distributions in the upper troposphere and stratosphere. We use nearly eight years of MLS O3, HNO3, HCl, ClO, H2O, CO, and N2O measurements to analyze these variations and correlate them to the strength of transport barriers as diagnosed from meteorological analyses. In addition, with the release of the version 3 data set, Aura MLS now provides the first daily global observations of CH3Cl. By far the largest natural source of stratospheric chlorine, CH3Cl contributed 16% of the stratospheric total inorganic chlorine budget in 2000 and may become relatively more important in coming decades as anthropogenic halocarbons decline in response to international regulations. The unprecedented scope of the MLS data set makes it uniquely suited to studying the spatial and temporal variations in the distribution of CH3Cl at the tropopause and in the lower stratosphere. Among the topics we investigate are: chemical processing in and dispersal of chemically-processed air from the lowermost portion of the winter polar vortex and the "subvortex", the region below the strong dynamical confinement of the vortex proper; the occurrence of troposphere-to-stratosphere and stratosphere-to-troposphere transport associated with the summer monsoon circulations; and the influence of the quasi-biennial oscillation and the so-called atmospheric tape recorder on tropical trace gas abundances. The observed trace gas behavior is shown to be consistent with the evolution of transport barriers.