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Comparison of UTH in IPCC AR4 coupled GCMs to microwave observations

PI: Viju Oommen John
Institution: University of Miami
Additional Investigators: Brian Soden
Water vapor in the upper troposphere has significant effect on the global climate due to its positive feedback mechanism. Thus, it is important to have this quantity correctly reproduced in climate models for a realistic prediction of climate change. Therefore evaluation of upper tropospheric humidity (UTH) in current climate models is an important test for their fidelity in predicting global climate. One way to evaluate model UTH is to compare it with observation. Satellite based observations give global coverage thus are suitable for climate model evaluation. Satellite sensors measure UTH using infrared and microwave techniques. In this study we plan to evaluate Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled General Circulation Models (GCMs) using microwave data measured by Advanced Microwave Sounding Unit - B (AMSU-B) instruments on board NOAA satellites. Microwave data are less affected by clouds than infrared data. Monthly mean temperature and humidity profiles from GCM output are used as inputs to a radiative transfer model to simulate radiances as observed by AMSU-B and then the comparison with the observations is done in the radiance space. This method circumvents errors that occur in the retrieval process of temperature and humidity profiles from satellite radiances. Inter-model differences as well as differences in the mean state of the models compared to observation will be addressed in detail.
  • John V. O., and B. J. Soden, 2006: Does convectively-detrained cloud ice enhance water vapor feedback?. Geophys. Res. Lett., 33, L20701, doi:10.1029/2006GL027260. Abstract. Full Article. Edit.
  • John V. O., R. P. Allan and B. J. Soden, 2009: How robust are observed and simulated precipitation responses to tropical ocean warming?. Geophys. Res. Lett., doi:10.1029/2009GL038276. In press. Abstract. Full Article. Edit.
  • John, V. O. and B. J. Soden, 2007: Temperature and humidity biases in global climate models and their impact on climate feedbacks. Geophys. Res. Lett., 34, L18704, 10.1029/2007GL030429. Abstract. Full Article. Edit.

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