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at greater cost of computer resources. Additional studies are iilso possible using finer resolution. Two studies were proposed: (a) the sensitivity of dyna- mics to the formulation of the microphysics; and (b) processes of entrainment/ detrainment at the cloud boundary and internal mixing. ; The sensitivity of the dynamical properties of the cloud to the micr"ophysical characteristics is directly related to the question of the degree to which the dynamics of a cloud can be manipulated by changes in the microphysic:al pro- cesses. Dynamical properties are believed to play the dominant role! in cloud and precipitation development. If the dynamics are influenced by microphysics, this may be an effective way to effect changes in precipitation. Sensitivity tests should include systematic changes in the rate of conversion from cloud (non-precipitating liquid) to precipitating drops, the rate of conve!rsion of liquid to ice and changes in the treatment of the fall of hydrometeors. Accounting for the gravitational separation of hydrometeors has proven difficult and the last topic should provide information on model sensitivity to this for- mulation. It shou'ld also provide information on effects of changes brought about by seeding because substantial differences in fall velocities of liquid and ice hydrometeors commonly exist. Debate continues concerning the location at Ir'lhich clear air from the environment is entrained within clouds. The sUbstantially uniform (IItop hatll) composition of clouds in their early growing stage is not well matched by many cloud models, apparently due to the coarse resolution employed and inadequate replication of the internal mixing within clouds. The finer resolution experiments were recom- mended to study the effects of different grid intervals on the simulation, the importance of the resolution of different sCjiles of motion, and in particular to explore the possibility that the finer resolution will lead to new insight on the entrainment and mixing processes. 2.2.2 Model architecture tests The second type of sensitivity experiments concerned the mathematical architec- ture of the model; these might include: (a) variations in numerical schemes (for example: Smolarkiewicz's scheme), (b) formulation of equations (for example: entropy formulation, filtering methods, anelastic vs. non-anelastic, etc.), and (c) focusing techniques, (for example: stretched or nested grids). 2.2.3 Experimental approach The value of the sensitivity tests will be increased if the input data are com- mon to another experiment bei ng carri ed out 1'or the wor'kshop. Some of these tests require substantial computer resources and it is likely that relatively few participants would carry out these experiments. However, with input data common to other aspects of the workshop, it ~,ill be possible to gain much more benefit than if a unique data set were used. Data sets for the sensitivity tests will be from days in which cumulus congestus or sma 11 thunderstorms develop. The experi mE!nt on the retention of the memory of the perturbation will include two sets, one in which the outcome is strongly dependent on the perturbation and another where it is not. The finer 5.