A global blended tropopause based on ERA data. Part II: Trends and tropical broadening

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 138; no. 664; pp. 576 - 584
• Main Authors: Wilcox, L. J., Hoskins, B. J., Shine, K. P.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.04.2012; Wiley
• Subjects: Antarctic; Earth, ocean, space; ERA-Interim; Exact sciences and technology; External geophysics; Meteorology; metrics; Physics of the high neutral atmosphere; polar regions; Arctic region; Antarctica; High latitude; Temperature distribution; Climatology; trend-surface analysis; Westerly wind; Regional scope; tropical zone; Potential vorticity; ERA-Interim; subtropical zone; Antarctic; Tropopause; warming; Reanalysis; Height; Polar region; metrics
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.910

A new tropopause definition involving a flow‐dependent blending of the traditional thermal tropopause with one based on potential vorticity has been developed and applied to the European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalyses (ERA), ERA‐40 and ERA‐Interim. Global and regional trends in tropopause characteristics for annual and solsticial seasonal means are presented here, with emphasis on significant results for the newer ERA‐Interim data for 1989–2007. The global‐mean tropopause is rising at a rate of 47 m per decade, with pressure falling at 1.0 hPa per decade and temperature falling at 0.18 K per decade. The Antarctic tropopause shows decreasing heights, warming and increasing westerly winds. The Arctic tropopause also shows a warming, but with decreasing westerly winds. In the Tropics the trends are small, but at the latitudes of the subtropical jets they are almost double the global values. It is found that these changes are mainly concentrated in the eastern hemisphere. Previous and new metrics for the rate of broadening of the Tropics, based on both height and wind, give trends in the range 0.9–2.2° per decade. For ERA‐40 the global height and pressure trends for the period 1979–2001 are similar: 39 m per decade and −0.8 hPa per decade. These values are smaller than those found from the thermal tropopause definition with this dataset, as was used in most previous studies. Copyright © 2011 Royal Meteorological Society