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Warming maximum in the tropical upper troposphere deduced from thermal winds


Climate models and theoretical expectations have predicted that the upper troposphere should be warming faster than the surface. Surprisingly, direct temperature observations from radiosonde and satellite data have often not shown this expected trend. However, non-climatic biases have been found in such measurements. Here we apply the thermal-wind equation to wind measurements from radiosonde data, which seem to be more stable than the temperature data. We derive estimates of temperature trends for the upper troposphere to the lower stratosphere since 1970. Over the period of observations, we find a maximum warming trend of 0.65±0.47 K per decade near the 200 hPa pressure level, below the tropical tropopause. Warming patterns are consistent with model predictions except for small discrepancies close to the tropopause. Our findings are inconsistent with the trends derived from radiosonde temperature datasets and from NCEP reanalyses of temperature and wind fields. The agreement with models increases confidence in current model-based predictions of future climate change.

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Figure 1: Radiosonde wind trends for 1979–2005.
Figure 2: Trend in wind-estimated meridional temperature gradient versus the corresponding trend from temperature data for 1979–2005.
Figure 3: Meridional sections of atmospheric temperature trends.


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We acknowledge the individual modelling groups, the Program for Climate Model Diagnosis and Intercomparison and the WCRP’s Working Group on Coupled Modeling for their roles in making available the WCRP CMIP3 multimodel dataset. Support of this dataset is provided by the Office of Science, US Department of Energy. We also thank P. Thorne and L. Haimberger for providing key datasets.

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R.J.A. initiated and conducted the project, carried out all data analysis and led the writing of the manuscript as part of his PhD thesis. S.C.S. advised on methods and interpretation.

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Correspondence to Robert J. Allen.

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Supplementary figures S1-S17 and table S1 (PDF 720 kb)

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Allen, R., Sherwood, S. Warming maximum in the tropical upper troposphere deduced from thermal winds. Nature Geosci 1, 399–403 (2008).

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