Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 5 2009 10.5194/acpd-9-18597-2009 http://www.atmos-chem-phys-discuss.net/9/18597/2009/ http://www.atmos-chem-phys-discuss.net/9/18597/2009/acpd-9-18597-2009.html http://www.atmos-chem-phys-discuss.net/9/18597/2009/acpd-9-18597-2009.pdf 18597 18619 2009-09-09 Increase of upper troposphere/lower stratosphere wave baroclinicity during the second half of the 20th century J. M. Castanheira jcast@ua.pt J. A. Añel C. A. F. Marques J. C. Antuña M. L. R. Liberato L. de la Torre L. Gimeno CESAM, Department of Physics, University of Aveiro, Portugal EPhysLab, Faculty of Sciences of Ourense, University of Vigo, Spain Estación Lidar de Camagüay, Camagüay, Cuba Department of Physics, University of Trás-os-Montes e Alto Douro, Portugal CGUL, IDL, University of Lisbon, Portugal A strengthening of the equatorward temperature gradient in the upper troposphere/lower stratosphere (UTLS), at subtropics and midlatitudes, is consistently reproduced in several modelling studies of the atmospheric response to the increase of greenhouse gas radiative forcing. Some of those studies suggest an increase of the baroclinicity in the UTLS region because of the enhanced meridional temperature gradient. <br><br> This study presents observational evidence of an increase of UTLS wave baroclinicity, during the second half of the 20th century. The evidence is given by significant positive trends in the energy of baroclinic normal modes of the NCEP/NCAR reanalysis, and significant positive trends in the eddy available potential energy of the ERA-40 reanalysis as well as in the eddy available potential energy of the JRA-25 reanalysis. Significant positive trends in the frequency of double tropopause events in radiosonde data are also interpreted as a manifestation of an increase of the UTLS wave baroclinicity. Allen, R. J. and Sherwood, S. C.: Warming maximum in the tropical upper troposphere deduced from thermal winds, Nat. Geosci., 399–403, L03705, doi:10.1038/ngeo208, 2008. Añel, J. A., Antuña, J. C., Torre, L. de la, Castanheira, J. M. and Gimeno, L.: Climatological features of global multiple tropopause events, J. Geophys. Res., 113, D00B08, doi:10.1029/2007JD009697, 2008. Durre, I., Vose, R. S., and Wertz, D. B.: Overview of the Integrated Global Radiosonde Archive, J. Climate, 19, 53–68, 2006. 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:15810.11029/12005GL022924, 2005. 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. Garcia, R. R. and Randel, W. J.: Acceleration of the Brewer–Dobson Circulation due to Increases in Greenhouse Gases, J. Atmos. Sci., 65, 2731–2739, doi:10.1175/2008JAS2712.1, 2008. Geng, Q. and Sugi, M.: Possible Change of Extratropical Cyclone Activity due to Enhanced Greenhouse Gases and Sulfate Aerosols—Study with a High-Resolution AGCM, J. Climate, 16, 2262–2274, 2003. Kanukhina, A. Y., Suvorova, E. V., Nechaeva, L. A., Skrygina, E. K., and Pogoreltsev, A. I.: Climatic variability of the mean flow and stationary planetary waves in the NCEP/NCAR reanalysis data, Ann. Geophys., 26, 1233-1241, 2008. Liberato, M. L. R., Castanheira, J. M., de la Torre, L., DaCamara, C. C., and Gimeno, L.: Wave Energy Associated with the Variability of the Stratospheric Polar Vortex, J. Atmos. Sci., 64, 2683–2694, 2007. Ramaswamy, V. and Schwarzkopf, M. D.: Effects of ozone and well-mixed gases on annual mean stratospheric temperature trends, Geophys. Res. Lett., 29(22), 2064, doi:10.1029/2002GL015141, 2002. Randel, W. J., Seidel, D. J., and Pan, L. L.: Observational characteristics of double tropopauses, J. Geophys. Res., 112, D07309, doi:10.1029/2006JD007904, 2007. Randel, W. J., Shine, K. P., Austin, J., et al.: An update of observed stratospheric temperature trends, J. Geophys. Res., 114, D02107, doi:10.1029/2008JD010421, 2009. Schwarzkopf, M. D., and Ramaswamy, V.: Evolution of stratospheric temperature in the 20th century, Geophys. Res. Lett., 35, L03705, doi:10.1029/2007GL032489, 2008. World Meteorological Organization: Meteorology —- A threedimensional science: Second session of the Commission for Aerology, WMO Bulletin, vol IV (no 4), 134-138, 1957.