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  • Minschwaner, K., A. E. Dessler, and P. Sawaengphokhai, 2006: Multi-model Analysis of the Water Vapor Feedback in the Tropical Upper Troposphere. J Climate, 19, 5455-5464.

We investigate relationships between the mean humidity in the tropical upper troposphere and tropical sea surface temperatures in seventeen coupled ocean-atmosphere global climate models. This analysis builds on a prior study of humidity and surface temperature measurements that suggested an overall positive climate feedback by water vapor in the tropical upper troposphere, whereby the mean specific humidity increases with warmer sea surface temperature (SST). The model results for present-day simulations show a large range in mean humidity, mean air temperature, and mean SST, but they consistently show increases in upper tropospheric specific humidity with warmer SST. The model average increase in water vapor at 250 mb with convective mean SST is 44 ppmv per K, with a standard deviation of 14 ppmv per K. Furthermore, the implied feedback in the models is not as strong as would be the case if relative humidity remained constant in the upper troposphere. The model mean decrease in relative humidity is -2.3+-1.0 % per K at 250 mb, whereas observations indicate decreases of -4.8+-1.7 % per K near 215 mb. These two values agree within the respective ranges of uncertainty, indicating that current global climate models are simulating with reasonable accuracy the observed behavior of water vapor
in the tropical upper troposphere.


Last Updated: 2007-02-27

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