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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />- 1 - <br /> <br /> <br />PREFACE <br /> <br />In the first section of this report a description is <br /> <br />given of the research aircraft and airborne instrumentation <br /> <br /> <br />used in the Cascade Project. This facility provides us with <br />the capability of tracing cloud microphysical processes <br /> <br />from the nucleation of cloud particles through to the pro- <br /> <br />duction of precipitation. Of particular interest is a <br /> <br />new instrument for the automatic counting of ice particles <br /> <br /> <br />in mixed clouds, and devices for decelerating cloud and <br /> <br /> <br />precipitation particles prior to collection in order to <br /> <br /> <br />reduce fragmentation. With the aid of the latter devices <br /> <br />we are able to collect and replicate intact ice crystals up <br /> <br />to several millimeters in size from an aircraft flying at <br /> <br />120 mph. <br />The network of ground stations, instruments, and ob- <br />servations utilized in the Cascade Project is described in <br />Section 2. The reliability of some of the ground techniques <br />is also discussed in this section. <br />Section 3 of the report contains a detailed description <br />of a theoretical model for the formation of orographic clouds <br /> <br />and precipitation. Equations are derived for the flow of <br /> <br />dry and cloudy air over a long (2 dimensional) ridge. The <br />profile of the ridge can be changed, depending on the dir- <br />ection of the wind, to approximate to that of the Cascade <br /> <br />Mountains. Using the airflow model, and equations for the <br /> <br />growth of ice particles by deposition from the vapour phase <br />