Evaluation of tropospheric humidity in AMIP II simulations

Because tropospheric humidity plays an important role in both the global water and energy cycles, it is important that humidity fields be accurately simulated by general circulation models (GCMs). The Atmospheric Model Intercomparison Project (AMIP) II provides an opportunity to compare various aspects of many GCM humidity simulations with observations. In this presentation, simulations of precipitable water, specific and relative humidity from the first five general circulation models available in AMIP II are compared with observations from radiosondes over the Northern Hemisphere.

In an earlier study (Gaffen et al. ,1997) based on 28 simulations from the first AMIP, the seasonal cycle of precipitable water (W) was fairly well simulated by the models although the simulated decadal mean values were less moist that the real atmosphere. We will show results from a similar analysis of the climatology and seasonal variability of W in these AMIP II models. Comparisons of the modeled and observed relationships between interannual variations in W and those of temperature and precipitation will also be shown. Additional comparisons of the modeled and observed distribution and variability of tropospheric specific and relative humidity will also be presented.

Gaffen, D.J., R.D. Rosen, D.A. Salstein, J.S. Boyle, 1997: Evaluation of tropospheric water vapor simulations from the Atmospheric Model Intercomparison Project. J. Climate, 10, 1648- 1661.