A study of stratospheric chlorine partitioning based on new satellite...

Santee, M., I. A. MacKenzie, G. L. Manney, M. Chipperfield, P. F. Bernath, K. A. Walker, C. D. Boone, L. Froidevaux, N. Livesey, and J. W. Waters (2008), A study of stratospheric chlorine partitioning based on new satellite measurements and modeling, J. Geophys. Res., 113, D12307, doi:10.1029/2007JD009057.

Two recent satellite instruments, the Microwave Limb Sounder (MLS) on Aura and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on SCISAT-1, provide an unparalleled opportunity to investigate stratospheric chlorine partitioning. We use measurements of ClO, HCl, ClONO2, and other species from MLS and ACE-FTS to study the evolution of reactive and reservoir chlorine throughout the lower stratosphere during two Arctic and two Antarctic winters characterizing both relatively cold and relatively warm and disturbed conditions in each hemisphere. At middle latitudes, and at high latitudes at the beginning of winter, HCl greatly exceeds ClONO2, representing ~0.7–0.8 of estimated total inorganic chlorine. Nearly complete chlorine activation is seen inside the winter polar vortices. In the Arctic, chlorine recovery follows different paths in the two winters: In 2004/2005, deactivation initially takes place through reformation of ClONO2, then both reservoirs are produced concurrently but ClONO2 continues to significantly exceed HCl, and finally slow repartitioning between ClONO2 and HCl occurs; in 2005/2006, HCl and ClONO2 rise at comparable rates in some regions. In the Antarctic, chlorine deactivation proceeds in a similar manner in both winters, with a rapid rise in HCl accompanying the decrease in ClO. The measurements are compared to customized runs of the SLIMCAT three-dimensional chemical transport model. Measured and modeled values typically agree well outside the winter polar regions. In contrast, partly because of the equilibrium scheme used to parameterize polar stratospheric clouds, the model overestimates the magnitude, spatial extent, and duration of chlorine activation inside the polar vortices.

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