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": . . i. :. hyp~thesis, was conducted. Although the experiment iailed to demonstrate statistically all the hypothesized steps, the reasons f'or the iailures could be traced back in the physical data set (Cooper and Lawson, 1984). This in itself is a significant result indicating the importance of' physical measurements and studies to be able to gain understanding in the underlying physical processes in each experiment. Other experiments which used this approach are Canadian studies by Isaac et al.(1977, 1982) and English and Marwitz(1981) and South African studies by Krauss et al., (1987). Results from summertime convective seeding experiments have been described in the literature (e.g., Dye et al., 1976, Holroyd et al., 1978; Sax et al., 1979, Hobbs and Politovich, 1980). Most of these experiments were conducted on semi-isolated cumulus congestus clouds to provide a relatively simple cloud dynamics framework to confirm f'undamental cause and effect relations of cloud microphysical processes. However, such clouds do not contribute significantly to rainfall at the ground. Convective complexes contribute significantly more than semi-isolated cumulus congest us clouds to the ra.itlfaU at the surface in most regions where a major part of the annual precipitation is the result of convective activity. However, convective complexes are much more complex dynamically than the smaller clouds because they are to a large extent maniiestations of mesoscale and large scale dynamical processes. There presently exists no proven methods to quantitatively predict the likelihood of success of cloud seeding, or the magnitude of the precipitation increase that might result. In addition, results from an experiment in one geographic location may not be transferable to other locations and seasonal and intra-seasonal changes in environmental conditions may produce different responses to seeding. Results from many experiments can therefore be viewed as likely indicators rather than substantive quantitative evidence for success. Future investigations should thus concentrate on establishing a physical hypothesis that incorporates all the major components of the precipitation formation processes in order to provide as sound a scientific basis as possible for estimating the magnitude of the expected effect. To attain this objective we will have to increase our understanding of the individual components of the precipitation formation process. Progress in understanding a single component of this process is intrinsically limited if understanding of all the major 12