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<br />efficiency will be encouraged. !nese studies will explore different ways to <br />quantify precipitation efficiency and will attempt to determine the accuracy <br />needed to make the parameter useful. Differences in cloud properties with <br />time and place will be studied systematically. <br /> <br />'l'w'o particular activities will recei'J'e emphasis. One involves analysis <br />of a special data set to be gathered in Montana during the summer of 1981 as <br />part of the Cooperative Convective Precipitation Experiment (CCOPE). <br />Measurement of precipitation efficiency will be one of the CCOPE objectives. <br />Although this program rill not contribute to the data collection phase, it <br />will help provide for effective analysis of an enormous amount of information. <br /> <br />Another area of emphasis during the first year will be evaluation of the <br />potential of satellite and radar data for estimating precipitation efficiency <br />of larger scale systems. Satellite imagery can provide cloud mass, time-lapse <br />studies can yield motion patterns and convergence rates, and infrared data can <br />give cloud altitudes. Calibrated radars can generate rainfall estimates. <br />Studies are needed to determine thesensitivi ty of these techniques to <br />variations in precipitation efficiency. <br /> <br />Because making precise measurements of the factors governing <br />precipitation efficiency is difficult and ~pensive, numerical models will be <br />a valuable adjunct to the observational and analysis activities. Models exist <br />which can be used systematically to study the effect of such factors as <br />thermal stability, entrainment, low-level versus mid-level convergence, <br />vertical rind shear, and type and size spectra of aerosol. Results of these <br />sensitivity studies will be fed back into sharper analytical and observational <br />tools for measuring the precipitation potential of natural clouds and their <br />susceptibility to modification. <br /> <br />No large field ~periments are contemplated during the first ~NO years of <br />this program. In fact, the governing philosophy will be to take advantage of <br />cloud measurement programs Wherever and whenever they are conducted in order <br />to test techniques of estimating precipitation efficiency and hypotheses <br />concerning its variability. This program will attempt to bring specialized <br />instrumentation and analytical tools to bear as an add-on to such field <br />projects. <br /> <br />Radar and lidar will be critical to measurement of precipitation <br />efficiency--especially in cumulus clouds. Improvements are needed in the <br />accuracy of radar-estimated precipitation. Technical refinements in radar <br />beam characteristics and signal processing are feasible. P-romising techniques <br />involving polarization and multiple wavelengths need to be tested. Some ' <br />program funds should go toward these, objectives during the first year or two. <br /> <br />A final observational element which is feasible during the first year <br />involves widespread cloud sampling to document spatial and temporal variations <br />of cloud properties. The idea of a "cloud census" project was given high <br />priority by the Weather Modification Advisory Board. Aircrai: instrumentation <br />is now sufficiently accurate and reliable to warrant widespread sampling and <br />intercomparisons. Airborne data storage and processing capability makes <br /> <br />- 40 - <br />