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

Abstract

[1] 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. O 3 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.Citation: Gettelman, A., et al. (2010), Multimodel assessment of the upper troposphere and lower stratosphere: Tropics and global trends,

The Met Office HadGEM3-ES chemistry–climate model: evaluation of stratospheric dynamics and its impact on ozone

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Role of external factors in the evolution of the ozone layer and stratospheric circulation in 21st century

“…The atmospheric composition and climate changes in the 21st century simulated with different CCMs have been presented recently in a number of publications (e.g., Austin and Wilson, 2010;Gettelman et al, 2010;Zubov et al, 2011). Main conclusions and findings of these studies have been summarized in two assessments (SPARC CCMVal, 2010;WMO, 2011).…”

Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

“…While high-resolution datasets such as those from sondes and Global Positioning System radio occultation (GPS-RO) provide critical insights on the structure of the extratropical tropopause region, no available data sources can provide the global time-resolved fields, including winds, that reanalyses provide that are necessary to understand the global effects of jet and tropopause variations. Reanalyses are thus a critical tool for UTLS studies and are also widely used as an observational reference for climate model intercomparisons (e.g., Gettelman et al, 2010). However, they are also highly dependent on the details of the underlying general circulation models and assimilation systems as well as on the input datasets and processing.…”