Global tropopause altitudes in radiosondes and reanalyses
<p>Accurate depictions of the tropopause and its changes are important for studies on 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, a...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/5661/2019/acp-19-5661-2019.pdf |
| Summary: | <p>Accurate depictions of the tropopause and its changes are important for
studies on 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 reanalyses reproduce
observed tropopause altitudes with little bias (typically less than <span class="inline-formula">±150</span> m) and error comparable to the model vertical resolution. 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 attributable
to the coarse vertical resolution of the reanalyses. Significant increasing
trends in both tropopause altitude (40–120 m per decade) and double
tropopause frequency (<span class="inline-formula">≥3</span> % per decade) were found in both the
radiosonde observations and the reanalyses over the 35-year analysis period
(1981–2015). 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. Trends were diagnosed in both the native Eulerian
coordinate system of the reanalyses (fixed longitude and latitude) and in a
coordinate system where latitude is defined relative to the mean latitude of
the tropopause break (the discontinuity in tropopause altitude between the
tropics and extratropics) in each hemisphere. The coordinate relative to the tropopause break
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 coordinates relative to the tropopause break, and increasing double tropopause
frequency trends were found to occur primarily poleward of the tropopause
break in each hemisphere.</p> |
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| ISSN: | 1680-7316 1680-7324 |