ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-9143-2009 Increase of upper troposphere/lower stratosphere wave baroclinicity during the second half of the 20th century Castanheira J. M. 1 Añel J. A. 1 2 Marques C. A. F. 1 Antuña J. C. 3 Liberato M. L. R. 4 5 de la Torre L. 1 2 Gimeno L. 2 CESAM, Department of Physics, University of Aveiro, Aveiro, Portugal EPhysLab, Faculty of Sciences of Ourense, University of Vigo, Ourense, Spain Estación Lidar de Camagüey, Camagüey, Cuba Department of Physics, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal CGUL, IDL, University of Lisbon, Lisbon, Portugal 03 12 2009 9 23 9143 9153 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/9143/2009/acp-9-9143-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/9143/2009/acp-9-9143-2009.pdf

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 the baroclinic wave components of UTLS circulation (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 UTLS eddy available potential energy of the NCEP/NCAR, ERA-40, NCEP-2 and JRA-25 reanalyses. 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.

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