A parametric method for computing the mean water budget of the atmosphere

Using the equation of conservation of water vapor in the troposphere, the difference, evaporation at the surface minus precipitation, is expressed as a function of total cloudiness (or mean tropospheric relative humidity) and of temperature and horizontal wind at the surface and in mid-troposphere.

Computations of the annual normal values of evaporation minus precipitation using the resulting formulas together with monthly averages of the required parameters for the Northern Hemisphere, agree well in the general patterns with estimates made by Starr, Peixoto and Crisi, as well as with climatological values. However, there are large small-scale discrepancies in the three estimates.

The computations have a strong dependence on the divergence of the horizontal wind, and some of the discrepancies must be attributed to errors in evaluating the latter.

To determine the importance of anomalies of the difference, evaporation minus precipitation, computations for February 1964 and February 1962 are carried out, showing that the values of the difference between these two months are of the same order of magnitude as the monthly values themselves.

If positive values indicate wind from the south, the values of evaporation minus precipitation are inversely correlated to the meridional wind component on a broad scale. Furthermore the computations show that the anomalies in evaporation minus precipitation depend strongly not only on the anomalies of the meridional wind component but also on the anomalies of precipitable water, which in turn depend on the anomalies of surface temperature and cloudiness (or mean tropospheric relative humidity).