A Further Assessment of Treatment Effects in the Florida Area Cumulus Experiment through Guided Linear Modeling

Abstract

The Florida Area Cumulus Experiment (FACE) was a two-stage program dedicated to assessing the potential of ?dynamic seeding? for enhancing convective rainfall in a fixed target area. FACE-1 (1970?76) was an exploratory cloud seeding experiment that produced substantial indications of a positive treatment effect on rain at the ground, and FACE-2 (1978?80) was a confirmatory experiment that did not confirm the treatment effect results of FACE-1. This article presents some new analyses of both the FACE-1 and FACE-2 data in an effort to better understand the role of meteorological and treatment factors on rainfall in the days selected for experimentation in Florida. The analyses rely upon a guided exploratory linear modeling of the natural target area rainfall and the potential treatment effects. In particular, a conceptual model of natural Florida rainfall is utilized to guide the construction of the exploratory linear model. After the form of the model is selected it is fitted to both the FACE-1 and the FACE-2 data sets in an attempt to reassess the effects of treatment. Two approaches are taken to assessing the treatment effects in FACE-1 and in FACF-2: cross-comparison and cross-validation. Both techniques suggest a positive treatment effect in each stage of FACE (i.e., 30?45% in FACE-1 and 10?15% in FACF-2). However, the conventional 0.05 unadjusted statistical level of support is only present in the FACE-1 data. The question of whether FACE-1 results were different from FACE-2 is unresolved. These results continue to emphasize the need to better account for the natural convective precipitation processes in south Florida prior to conducting a cloud seeding project.