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1454 108 118 120 JOURNAL OF APPLIED METEOROLOGY VOLUME 35 112 116 114 11 106 102 98 108 112 Site 7 116 120 Crystal Fallout Points Guide * Guide Actual * Actual FIG. 26. GUIDE-predicted plume from site 7 along with an aircraft- observed SF6 plume. Observed precipitation in hundreths of inches is shown for the period 1800-1900 UTC as large bold numbers. The model-predicted fallout location for the fastest falling crystal is shown by open star and corrected fallout based on an aircraft plume as a solid star. The scale along outer boundary is in nautical miles. of the crest and in the lowest 200 to 300 m above the model terrain are the model-calculated values. It is im- portant to stress that we only need to be concerned about the layer below 3200 m, and in fact, we might restrict this to elevations below 2500 m. Thus, to a first approximation the simple approach of extrapolating the balloon vertical velocities for such a shallow layer seems reasonable. For the 1800 UTC data, the crystal is initiated and grows at a temperature near - 50C in a liquid water cloud of 0.2 'g m-3. This is the magnitude of liquid water observed by the research aircraft during sampling of the site 9 plumes. From earlier studies it was found that there is very little difference in particle growth and fall speeds in the model when liquid water varies between 0.1 and 0.3 g m-3. Below 0.1 g m-3 the lack of riming will extend particle trajectories several kilometers. The site 7 particle is shown to fall out about 20 kIn downwind in 28 min at a size of just over 1 mm (needle crystal) and with a maximum fall speed of 0.75 m s - I. The site 9 crystal also falls out at about 20 kIn from the dispenser in 31 min at a size of 1.2 mm. For 118 2100 UTC, the large negative vertical motions just down- wind of the ridge causes the seeded crystals to fall out just 5.5 kIn from the site 7 dispenser, with very little growth having taken place (7lllm in 18 min). Figures 26 and 27 reproduce the aircraft SF6 plume intersections (SF6 concentrations above 10 ppt are noted by symbols: "0," 10-15 ppt; "+," 15-50 ppt; "X," 50-100 ppt) in plan view, along with the pre- dicted plumes from the GUIDE model, the crystal fall- out locations, and the precipitation observed :from 1800 to 1900 UTC for sites 7 and 9, respectively. From the figures it is apparent that the actual plumes are narrower than predicted and are to the left of the predicted plume track, although they line up very well with the location of gauges showing higher precipitation v2.lues. The crystal fallout locations predicted by the model have been shifted to the northwest by a few kilometers to match the observed plume positions. These results should be considered fairly encourag- ing. They indicate that by using the rawinsonde hori- zontal and vertical motion fields and with a reasonable 114 110 106 102 98 108 118 118 112 116 120 114 114 i1 110 106 106 102 102 98 98 108 112 116 120 Site 9 Crystal Falll)ut Points Guide * Guide Actual * Actual FIG. 27. GUIDE-predicted plume from site 9 along with an aircraft- observed SF6 plume. Observed precipitation in hundreths of inches is shown for the period 1800-1900 UTC as large bold numbers. The model-predicted fallout location for the fastest fallin.g crystal is shown by an open star and corrected fallout based on aircraft plume as a solid star. The scale along outer boundary is in nautical miles.