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Discussion papers
https://doi.org/10.5194/acp-2018-945
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-945
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Oct 2018

Research article | 19 Oct 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Global Tropopause Altitudes in Radiosondes and Reanalyses

Tao Xian1,2 and Cameron R. Homeyer1 Tao Xian and Cameron R. Homeyer
  • 1School of Meteorology, University of Oklahoma, Norman, OK 73072, USA
  • 2School of Earth and Space Sciences, University of Science and Technology of China, Anhui, 230026, China

Abstract. Accurate depictions of the tropopause and its changes are important for studies such as stratosphere-troposphere exchange and climate change.Here, the fidelity of primary lapse-rate tropopause altitudes and double tropopause frequencies in four modern reanalyses (ERA-Interim, JRA-55, MERRA-2, and CFSR) is examined using global radiosonde observations. In addition, long-term trends (1981–2015) in these tropopause properties are diagnosed in both the reanalyses and radiosondes. It is found that ERA-Interim, JRA-55, and CFSR reproduce observed tropopause altitudes with little bias and error comparable to the model vertical resolution, while MERRA-2 tropopause altitudes are biased 500–600m high. All reanalyses underestimate the double tropopause frequency (up to 30% lower than observed), with the largest biases found in JRA-55 and the smallest in CFSR. The underestimates in double tropopause frequency are primarily attributed to the coarse vertical resolution of the reanalyses. Significant increasing trends in both tropopause altitude (40–120m per decade) and double tropopause frequency (≥3% per decade) were found in both the radiosonde observations and reanalyses over the 35-year analysis period. ERA-Interim, JRA-55, and MERRA-2 broadly reproduce the patterns and signs of observed significant trends, while CFSR is inconsistent with the remaining datasets. These trends were diagnosed in both the native Eulerian coordinate system of the reanalyses and in a relative latitude coordinate system where the tropopause break (the discontinuity in tropopause altitude between the tropics and extratropics) was used as the reference latitude in each hemisphere. The tropopause break-relative coordinate facilitates the evaluation of tropopause behavior within the tropical and extratropical reservoirs and revealed significant differences in trend estimates compared to the traditional Eulerian analysis. Notably, increasing tropopause altitude trends were found to be of greater magnitude in tropopause break-relative coordinates and increasing double tropopause frequency trends were found to occur primarily poleward of the tropopause break in each hemisphere.

Tao Xian and Cameron R. Homeyer
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Status: open (until 14 Dec 2018)
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Tao Xian and Cameron R. Homeyer
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Global characteristics and trends in the tropopause (the boundary between troposphere and stratosphere) over a 35-year period (1981–2015) are evaluated using both observations and models. The use of two coordinate systems reveals previously undiagnosed changes in the tropopause altitude within the tropics and extratropics and these results have important implications for studies of climate and atmospheric composition (especially that related to stratosphere-troposphere exchange).
Global characteristics and trends in the tropopause (the boundary between troposphere and...
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