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<br />- )' - <br /> <br />ground generators should not be excluded. The seeding is supposed to affect the collo- <br />idal stability of the clouds and may also have significant effects on their dynamics. <br /> <br />(e) The basic evaluation of the seeding effect will be statistical in nature. <br /> <br />(f) An experiment duration of five years is contemplated. It is anticipated that a change <br />of 10-20% in seasonal rainfall will be detectable at an acceptable level of statistical <br />significance. Cloud physics and meteorological research into the precipitation proc- <br />esses is planned so that support will be available for the statistical analysis. <br /> <br />(g) The success of the seeding is to be! judged on the basis of rainfall on the ground. A <br />dense network of raingauges, many of them of the recording type, will be required to <br />obtain sufficient information on rainfall. <br /> <br />(h) The experimental unit for randomization and the primary evaluation interval is a 24- <br />hour period. On average, 6 days wi.th rain above 1 mm per 24 hours might be expected <br />within each month (Jan.-May) considered for the experiment each year. <br /> <br />(i) The measurement programme must be conducted in such a way as to provide the basic <br />understanding needed to assess the likelihood of transferability of results to other <br />areas with similar meteorological conditions. <br /> <br />3.3.2 Measurement requirements: PEP, according to the Objectives, should provide not only <br />statistical results. The successful outcome of the project requires a strong programme of <br />meso-scale and micro-physical measurements complemented by a modelling effort. <br /> <br />Measurement parameters include: <br />- precipitation amount, intensity, duration and spatial distribution at the ground; <br />synoptic meteorological variables at several points over the experimental area; <br />local radiosonde information; <br />cloud systems characteristics including their meso-scale organization for which <br />satellite information would be an important input; <br />cloud base and top heights and te~peratures, cloud liquid, ice and total water <br />content, droplet and drop size distributions; <br />ice particle type, concentration, size and distribution spectrum; <br />ice nucleus and CCN concentration below cloud base and at ground; <br />(radar) echo top heights; <br />radar reflectivity; <br />rain drop size distribution at the ground at several sites; <br />characterist ics of the seeding plume. <br /> <br />The reasons for taking these measurements are manifold: <br /> <br />(a) The power of the statistics is to be increased by the use of precipitation covariates <br />which will be sought in SSP-3. Possible examples are: synoptic situations, cloud top <br />height, ice crystal concentration, 500mb temperature, and droplet concentration. <br /> <br />(b) The microphysical measurements will be necessary to document a direct causal relation <br />between seeding and rainfall. <br /> <br />(c) Extended area effects as supported by large area rainfall measurements may also be <br />established through observed changes in the dynamics and micro-physics of cloud <br />systems. Tracer studies of seeding plumes are necessary for the same reason. <br /> <br />(d) The transferability of PEP results to other parts of the globe is of enormous interest <br />because it could significantly influence the design of operations elsewhere. However, <br />procedures and conclusions can only be transferred through conceptual models construct- <br />ed from extensive measurements in the areas of concern as well as in the PEP experi- <br />mental site. <br /> <br />(e) The measurement p.p.rameters listed above may also serve for the development of adequate <br />numerical cloud models which might be used in the prediction of weather modification <br />