A COMPARISON OF OBSERVATIONS AND MODEL SIMULATIONS OF TROPOSPHERIC WATER-VAPOR

Observations of tropospheric specific humidity from radiosondes for the period 1973-1986 are compared with simulated specific humidity fields from a University of Hamburg version of the European Center for Medium-Range Weather Forecasting General Circulation Model (GCM), forced by observed sea surface temperatures. The mean January and July fields are shown to be in good agreement, despite the much poorer resolution of the radiosonde network used. Temporal and spatial variations of specific humidity are examined through empirical orthogonal function analysis of tropical data. The first mode of variability of the data was similar to that of the model simulations and shows evidence of a coherent, decadal-scale variation in tropospheric moisture content. The overall agreement between the model and the data, while not complete, suggests that long-term mean patterns and decadal variations in moisture, as delineated by a sparse data network, are reasonably well simulated. More comprehensive comparisons of tropospheric moisture data with GCM simulations from different models are suggested.