Multimodel assessment of the upper troposphere and Lower stratosphere: Tropics and global trends

A. Gettelman (1) , M. I. Hegglin (2) , S.-W. Son (3) , J. Kim (3) , M. Fujiwara (4) , T. Birner (5) , S. Kremser (6) , M. Rex (7) , J. A. Anel (8) , H. Akiyoshi (9) , J. Austin (10) , Slimane Bekki (11) , P. Braesicke (12) , C. Bruhl (13) , N. Butchart (14) , M. Chipperfield (15) , M. Dameris (16) , S. Dhomse (17) , H. Garny (16) , S. C. Hardiman (14) , P. Jockel (13) , D. E. Kinnison (1) , J. F. Lamarque (1) , E. Mancini (18) , Marion Marchand (11) , M. Michou (19) , Olaf Morgenstern (20) , S. Pawson (21) , G. Pitari (18) , D. A. Plummer (22) , J. A. Pyle (12) , E. Rozanov (23) , J. Scinocca (24) , T. G. Shepherd (2) , K. Shibata (25) , Dan Smale (20) , H. Teyssedre (19) , W. Tian (17)

1 NCAR - National Center for Atmospheric Research [Boulder]
2 Department of Physics [Toronto]
3 Department of Atmospheric and Oceanic Sciences [Montréal]
4 Hokkaido University [Sapporo, Japan]
5 Department of Atmospheric Science [Fort Collins]
6 Freie Universität Berlin
7 AWI - Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine
8 EPhysLab - Environmental Physics Laboratory
9 NIES - National Institute for Environmental Studies
10 GFDL - NOAA Geophysical Fluid Dynamics Laboratory
11 STRATO - LATMOS
12 Department of Chemistry [Cambridge, UK]
13 MPIC - Max-Planck-Institut für Chemie
14 United Kingdom Met Office [Exeter]
15 SEE - School of Earth and Environment [Leeds]
16 IPA - DLR Institut für Physik der Atmosphäre = DLR Institute of Atmospheric Physics
17 ICAS - Institute for Climate and Atmospheric Science [Leeds]
18 UNIVAQ - University of L'Aquila [Italy]
19 CNRM - Centre national de recherches météorologiques
20 NIWA - National Institute of Water and Atmospheric Research [Lauder]
21 GSFC - NASA Goddard Space Flight Center
22 ECCC - Environment and Climate Change Canada
23 PMOD/WRC - Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center
24 CCCma - Canadian Centre for Climate Modelling and Analysis
25 MRI - Meteorological Research Institute [Tsukuba]

The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in tropopause pressure in the 21st century, along with ∼1K increases per century in cold point tropopause temperature and 0.5–1 ppmv per century increases in water vapor above the tropical tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.

Mots clés: Chemistry; Climate; Tropopause

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

A. Gettelman, M. I. Hegglin, S.-W. Son, J. Kim, M. Fujiwara, et al.. Multimodel assessment of the upper troposphere and Lower stratosphere: Tropics and global trends. Journal of Geophysical Research: Atmospheres, 2010, 115, pp.D00M08. ⟨10.1029/2009JD013638⟩. ⟨hal-00481633⟩