Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-1097-2009 http://www.atmos-chem-phys-discuss.net/9/1097/2009/ http://www.atmos-chem-phys-discuss.net/9/1097/2009/acpd-9-1097-2009.html http://www.atmos-chem-phys-discuss.net/9/1097/2009/acpd-9-1097-2009.pdf 1097 1121 2009-01-14 The impact of tropical recirculation on polar composition S. E. Strahan susan.e.strahan@.nasa.gov M. R. Schoeberl S. D. Steenrod Goddard Earth Science and Technology Center, University of Maryland, Baltimore County, Baltimore, MD, USA NASA Goddard Space Flight Center, Greenbelt, MD, USA We derive the tropical modal age of air from an analysis of the water vapor tape recorder. We combine the observationally derived modal age with mean age of air from CO₂ and SF₆ to create diagnostics for the independent evaluation of the vertical transport rate and horizontal recirculation into the tropics between 16–32 km. These diagnostics are applied to two Global Modeling Initiative (GMI) chemistry and transport model (CTM) age tracer simulations to give new insights into the tropical transport characteristics of the meteorological fields from the GEOS4-GCM and the GEOS4-DAS. Both simulations are found to have modal ages that are in reasonable agreement with the empirically derived age (i.e., transit times) over the entire altitude range. Both simulations show too little horizontal recirculation into the tropics above 22 km, with the GEOS4-DAS fields having greater recirculation. Using CH₄ as a proxy for mean age, comparisons between HALOE and model CH₄ in the Antarctic demonstrate how the strength of tropical recirculation affects polar composition in both CTM experiments. The better the tropical recirculation is simulated, the better the CH₄ simulation is in the Antarctic. Mean age in the Antarctic lower stratosphere can be compromised by poor representation of tropical ascent, tropical recirculation, or vortex barrier strength. The connection between polar and tropical composition shown in this study demonstrates the importance of diagnosing each of these processes separately in order to verify the adequate representation of the processes contributing to polar composition in models. Andrews, A. E., Boering, K. A., Daube, B. C., et al.: Mean ages of stratospheric air derived from in situ observations of CO₂, CH₄, and N₂O, J. Geophys. Res., 106, 32295–32314, 2001. Andrews, D. G., Holton, J. R., and Leovy, C. B.: Middle Atmosphere Dynamics, Academic, San Diego, Calif., 489 pp., 1987. Bloom, S. C., da Silva, A. M., Dee, D. P., et al.: The Goddard Earth Observation System Data Assimilation System, GEOS DAS Version 4.0.3: Documentation and Validation, NASA TM-2005-104606 V26, 2005. Douglass, A. R., Prather, M. J., Hall, T. M., Strahan, S. E., Rasch, P. J., Sparling, L. C., Coy, L., and Rodriguez, J. M.: Choosing meteorological input for the global modeling initiative assessment of high-speed aircraft, J. Geophys. Res., 104, 27545–27564, 1999. Duncan, B. N., Strahan, S. E., Yoshida, Y., Steenrod, S. D., and Livesey, N.: Model study of cross-tropopause transport of biomass burning pollution, Atmos. Chem. Phys., 7, 3713–3736, 2007. Eyring, V., Butchart, N., Waugh, D. W., et al.: Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past, J. Geophys. Res., 111, D22308, doi:10.1029/2006JD007327, 2006. Fisher, M., O'Neill, A., and Sutton, R.: Rapid descent of mesospheric air into the stratospheric polar vortex, Geophys. Res. Lett., 20, 1267–1270, 1993. Hall, T. M. and Plumb, R. A.: Age as a diagnostic of stratospheric transport, J. Geophys. Res., 99, 1059–1070, 1994. Hall, T. M. and Waugh, D. W.: Timescales for the stratospheric circulation derived from tracers, J. Geophys. Res., 102, 8991–9001, 1997. Hall, T. M., Waugh, D. W., Boering, K. A., and Plumb, R. A.: Evaluation of transport in stratospheric models, J. Geophys. Res., 104, 18815–18839, 1999. Haynes, P. H., Marks, C. J., McIntyre, M. E., Shepherd, T. G., and Shine, K. P.: On the "downward control" of extratropical diabatic circulations by eddy-induced mean zonal forces, J. Atmos. Sci., 48, 651–679, 1991. Mote, P. W., Rosenlof, K. H., McIntyre, M. E., Carr, E. S., Gille, J. C., Holton, J. R., Kinnersley, J. S., Pumphrey, H. C., Russell, J. M., and Waters, J. W.: An atmospheric tape recorder: The imprint of tropical tropopause temperatures on stratospheric water vapor, J. Geophys. Res., 101, 3989–4006, 1996. Mote, P. W., Dunkerton, T., McIntyre, M., Ray, E., Haynes, P., and Russell, J.: Vertical velocity, vertical diffusion, and dilution by midlatitude air in the tropical lower stratosphere, J. Geophys. Res., 103, 8651–8666, 1998. Plumb, R.: A "tropical pipe" mode of stratospheric transport, J. Geophys. Res., 101, 18569–18585, 1996. Read, W., Lambert, A., Bacmeister, J., et al.: Aura Microwave Limb Sounder upper tropospheric and lower stratospheric H₂O and relative humidity with respect to ice validation, J. Geophys. Res., 112, D24S35, doi:10.1029/2007JD008752, 2007. Rosenfield, J. E. and Schoeberl, M. R.: On the origin of polar vortex air, J. Geophys. Res., 106, 33485–33497, 2001. Russell, J. M., III, Tuck, A. F., Gordley, L. L., Park, J. H., Drayson, S. R., Harries, J. E., Cicerone, R. J., and Crutzen, P. J.: The Halogen Occultation Experiment, J. Geophys. Res., 98, 10777–10797, 1993. Schoeberl, M. R., Douglass, A. R., Zhu, Z. X., and Pawson, S.: A comparison of the lower stratospheric age spectra derived from a general circulation model and two data assimilation systems, J. Geophys. Res., 108, D4113, doi:10.1029/2002JD002652, 2003. Schoeberl, M. R., Douglass, A. R., Polansky, B., Boone, C., Walker, K., and Bernath, P.: Estimation of stratospheric age spectrum from chemical tracers, J. Geophys. Res., 110, D21303, doi:10.1029/2005JD00125, 2005. Schoeberl, M. R., Douglass, A. R., Stolarski, R. S., Pawson, S., Strahan, S. E., and Read, W.: Comparison of lower stratosphere tropical mean vertical velocities, J. Geophys. Res., 113, D24109, doi:10.1029/2008JD010221, 2008. Strahan, S. E. and Douglass, A. R.: Evaluating the credibility of transport processes in simulations of ozone recovery using the Global Modeling Initiative three-dimensional model, J. Geophys. Res., D05110, doi:10.1029/2003JD004238, 2004. Strahan, S. E. and Polansky, B. C.: Meteorological implementation issues in chemistry and transport models, Atmos. Chem. Phys., 6, 2895–2910, 2006. Strahan, S. E., Duncan, B. N., and Hoor, P.: Observationally derived transport diagnostics for the lowermost stratosphere and their application to the GMI chemistry and transport model, Atmos. Chem. Phys., 7, 2435–2445, 2007. Waters, J. W., Froidevaux, L., Harwood, R. S., et al.: The Earth Observing System Microwave Limb Sounder (EOS MLS) on the Aura satellite, IEEE T. Geosci. Remote Sens., 44, 1075–1092, 2006. Waugh, D. W. and Eyring, V.: Quantitative performance metrics for stratospheric-resolving chemistry-climate models, Atmos. Chem. Phys., 8, 5699–5713, 2008. Waugh, D. and Hall, T.: Age of stratospheric air: Theory, Observations and Models, Rev. Geophys., 40, 1010, doi:10.1029/2000RG000101, 2002. Waugh, D. W., Strahan, S. E., and Newman, P. A.: Sensitivity of stratospheric inorganic chlorine to differences in transport, Atmos. Chem. Phys., 7, 4935–4941, 2007.