An Evaluation of the Smith-Feddes Model

Book excerpt: A model designed to produce estimates of water contents and number density distributions at any time and geographical location was published in 1974. Known by its authors names as the 'Smith-Feddes', this model is initiated by gridded, data-base information from the 3DNEPH (or RTNEPH) and Hemispherical analyses. The Smith-Feddes has been used periodically with mixed results and the implicit assumption has been that new, more definitive cloud physics information would improve the model's consistency which is investigated to develop it into a useful tool for future Air Force planning and operations. The initial phase of this study was essentially an exercise to gain familiarity with both the Smith-Feddes and the initiating analyses. Three weather situations were defined by water content and temperature-versus-altitude profiles derived from aircraft measurements. The model was then exercised for the same situations and the results of the separate analyses were then compared. This report describes this investigation and details our observations and conclusions based on the results of this comparison study. It is recommended that no further time be expended in an effort to improve the 3DNEPH/RTHNEPH, Smith-Feddes model, as it is unable to consistently produce water-content values within reasonable error bounds. However, certain cloud-physics concepts used in the model may be incorporated in a new model specifically designed to produce cloud and precipitation estimates from climatological data.