Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 5 2009 10.5194/acpd-9-21819-2009 http://www.atmos-chem-phys-discuss.net/9/21819/2009/ http://www.atmos-chem-phys-discuss.net/9/21819/2009/acpd-9-21819-2009.html http://www.atmos-chem-phys-discuss.net/9/21819/2009/acpd-9-21819-2009.pdf 21819 21846 2009-10-16 On the seasonal dependence of tropical lower-stratospheric temperature trends Q. Fu qfu@atmos.washington.edu S. Solomon P. Lin Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA Chemical Science Division, Earth System Research Laboratory, NOAA, Boulder, CO, USA This study examines the seasonality of tropical lower-stratospheric temperature trends using the Microwave Sounding Unit lower-stratospheric channel (<i>T</i>₄) for 1979–2007. We present evidence that this seasonality is a response to changes in the Brewer–Dobson circulation (BDC) driven by extratropical wave forcing. We show how the tropical <i>T</i>₄ trend can be used as an indicator of the change in the BDC, and find that the BDC is strengthening for 1979–2007 in June–November related to the Southern Hemisphere (SH) and in December–February to the Northern Hemisphere (NH). In marked contrast, we find that the BDC is weakening in March–May, apparently because of a weakening of its northern cell. The novel observational evidence on the seasonal dependence of the BDC trends presented in this study has important implications for the understanding of climate change in the stratosphere as well as testing climate model simulations. Andrews,~D G., Holton,~J R., and Leovy,~C B.: Middle Atmosphere Dynamics, Academic Press, Orlando, United States, 489~pp., 1987. Butchart,~N., Scaife,~A A., Bourqui,~M., de Grandpre,~J., Hare,~S H E., Kettleborough,~J., Langematz,~U., Manzini,~E., Sassi,~F., Shibata,~K., Shindell,~D., and Sigmond~M.: Simulations of anthropogenic change in the strength of the Brewer–Dobson circulation, Clim. Dynam., 27, 727–741, doi:10.1007/s00382-006-0162-4, 2006. Chae,~H C. and Sherwood,~S C.: Annual temperature cycle of the tropical tropopause: A~simple model study,~J. Geophys. Res., 112, D19111, doi:10.1029/2006JD007956, 2007. Christy,~J R., Spencer,~R W., Norris,~W B., Braswell,~W D., and Parker,~D E.: Error estimates of version 5.0 of MSU-AMSU bulk atmospheric temperatures,~J. Atmos. Ocean. Tech., 20, 613–629, 2003. Deckert,~R. and Dameris,~M.: Higher tropical SSTs strengthen the tropical upwelling via deep convection, Geophys. Res. Lett., 35, L10813, doi:10.1029/2008GL033719, 2008. Eichelberger,~S J. and Hartmann,~D L.: Changes in the strength of the Brewer–Dobson Circulation in a~simple AGCM, Geophys. Res. Lett., 32, L15807, doi: 10.1029/2005GL022924, 2005. Engel, A., Mobius, T., Bonisch, H., et al.: Age of stratospheric air unchanged within uncertainties over the past 30 years, Nature Geosci., 2, 28–31, 2009. Fu,~Q. and Johanson,~C M.: Satellite-derived vertical dependence of tropical tropospheric temperature trends, Geophys. Res. Lett., 32, L10703, doi:10.1029/2004GL022266, 2005. Haynes,~P H., Marks,~C J., McIntyre,~M E., Shepherd,~T G., and Shine,~K P.: On the \qutdownward control of extratropical diabatic circulations by eddy-induced mean zonal forces,~J. Atmos. Sci., 48, 651–678, 1991. Holton,~J R., Haynes,~P H., McIntyre,~M E., Douglass,~A R., Rood,~R B., and Pfister,~L.: Stratosphere-troposphere exchange, Rev. Geophys., 33, 403–439, 1995. Hu,~Y. and Tung,~K K.: Interannual and decadal variations of planetary wave activity, stratospheric cooling, and Northern Hemisphere annual mode,~J. Climate, 15, 1659–1673, 2002. Hu,~Y. and Fu,~Q.: Stratospheric warming in Southern Hemisphere high latitudes since 1979, Atmos. Chem. Phys., 9, 4329–4340, 2009. Johanson,~C M. and Fu,~Q.: Antarctic atmospheric temperature trend patterns from satellite observations, Geophys. Res. Lett., 34, L12703, doi:10.1029/2006GL029108, 2007. Kalnay,~E., Kanamitsu,~M., Kistler,~R., Collins,~W., Deaven,~D., Gandin,~L., Iredell,~M., Saha,~S., White,~C., Woollen,~J., Zhu,~Y., Chelliah,~M., Ebisuzaki,~W., Higgins,~W., Janowiak,~J., Mo,~K C., Ropelewski,~C., Wang,~J., Leetmaa,~A., Reynolds,~R., Jenne,~P., and Joseph,~D.: The NCEP/NCAR 40-year reanalysisproject, B. Am. Meteorol. Soc., 77, 437–471, 1996. Kerr-Munslow,~A M. and Norton,~W A.: Tropical wave driving of the annual cycle in tropical tropopause temperatures. Part 1: ECMWF analyses,~J. Atmos. Sci., 63, 1410–1419, 2006. Li,~F., Austin,~J., and Wilson,~J.: The strength of the Brewer–Dobson circulation in a~changing climate: a~coupled chemistry model simulation,~J. Climate, 21, 40–57, 2008. Lin,~P., Fu,~Q., Solomon,~S., and Wallace,~J M.: Temperature trend patterns in Southern Hemisphere high latitudes: novel indicators of stratospheric changes,~J. Climate, in press, doi:10.1175/2009JCLI2971.1, 2009. Mears,~C A., Schabel,~M C., and Wentz,~F J.: A~reanalysis of the MSU Channel 2 tropospheric termperatue record,~J. Climate, 16, 3650–3664, 2003. Meehl,~G A., Covey,~C., McAveney,~B., Latif,~M., and Stouffer,~R J.: Overview of the coupled model intercomparison project,~B. Am. Meteorol. Soc., 86, 89-93, doi:10.1175/BAMS-86-1-89, 2005. Ramaswamy,~V., Schwarzkopf,~M D., and Randel,~W J.: Fingerprint of ozone depletion in the spatial and temporal pattern of recent lower-stratospheric cooling, Nature, 382, 616–618, 1996. Ramaswamy,~V., Schwarzkopf,~M D., Randel,~W J., Santer,~B D., Soden,~B J., and Stenchikov,~G.: Anthropogenic and natural influences in the evolution of lower stratospheric cooling, Science, 311, 1138–1141, 2006. Randel,~W J., Wu,~F., Nedoluha,~G., Vomel,~H., and Forster,~P.: Decreases in stratospheric water vapor since 2001: Links to changes in the tropical tropopause and the Brewer–Dobson circulation,~J. Geophys. Res., 111, D12312, doi:10.1029/2005JD006744, 2006. Rind,~D., Lerner,~J., and McLinden,~C.: Changes of trace distributions in the doubled \chemCO_2 climate,~J. Geophys. Res., 106, 28 061–28 080, 2001. Rosenlof,~K H. and Reid,~G C.: Trends in the temperature and water vapor content of the tropical lower stratopshere: Sea surface connection,~J. Geophys. Res., 113, D06107, doi:10.1029/2007JD009109, 2008. Salby,~M L. and Callaghan,~P F.: Interannual changes of the stratospheric circulation: Relationship to ozone and tropospheric structure,~J. Climate, 15, 3673–3685, 2002. Shine,~K P., Bourqui,~M S., Forster,~P M F., et al.: A~comparison of model-simulated trends in stratospheric temperatures,~Q J. Roy. Meteor. Soc., 129, 1565–1588, doi:10.1256/qj.02.186, 2003. Sigmond,~M., Scinocca,~J F., and Kushner~P J.: Impact of the stratosphere on tropospheric climate change, Geophys. Res. Lett., 35, L12706, doi:10.1029/2008GL033573, 2008. Stolarski,~R S., Douglass,~A R., Steenrod,~S., and Pawson,~S.: Trends in stratospheric ozone: Lessons learned from a~3-D chemical transport model,~J. Atmos. Sci., 63, 1028–1041, 2006. Ueyama,~R. and Wallace,~J M.: To what extent does high-latitude planetary wave breaking drive tropical upwelling in the Brewer–Dobson ciculation,~J. Atomos. Sci., submitted, 2009. Yulaeva,~E., Holton,~J R., and Wallace,~J M.: On the cause of the annual cycle in tropical lower-stratospheric temperatures,~J. Atmos. Sci., 51, 169–174, 1994.