Upper tropospheric water vapor observations and modeling-a summary of recent progress

One of the most controversial aspects of model simulations of global warming concerns the water vapor-radiation feedback on the upper atmosphere, particularly in the tropics. In this overview presentation, we examine recent progress in modeling and observation of the upper tropospheric water vapor and radiation. The 20-year record of satellite observations of upper tropospheric water vapor is analyzed for seasonal and interannual variability. On the seasonal time scale, the use of upper tropospheric water vapor observations for forecasting and monitoring of the monsoons is examined. On the interannual time scale, we compare AMIP-style model simulations of upper tropospheric water vapor radiances with those observed. The model simulations are shown to be strongly effected by the model convective parameterization and the ability of the model to reproduce ENSO events. We also define a spectral greenhouse parameter that quantifies the relationship between the surface temperature and the upper tropospheric water vapor radiative effects and examine the ability of the models to reproduce the observed interannual variability.