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SEPTEMBER 1982 J. B. SNIDER AND D. ROTTNER 1289 Yuba City t VIRGINIA ""^ RANGE tv" 1\ tIY./ """ Washoe -it'.,0 Lake ~ tfjJ- PY! ~ 0 10 U 20 ~ ee 'SCALE Of MILd = E r"''v~ ~ J/?' 5 0 5 10 U 20 ~ SCALE' 0; KILOMETiRli FIG. 2. Map of SCPP teslt area showing propagation path to COMST AR satellite. Numbered triangles mark locations of three regions seeded on 3 March 1980. 6. 3 March 1980 seeding experiments On the morning of 3 March 1980, an overcast com- posed of non-precipitating stratiform clouds covered the test area including the region of sky observed by the radiometer. At 0745 PST (1545 GMT) the radio- metric system indicated ~- 1 mm of total liquid (Fig. 1). However, both 5 cm radars observed few if any echoes. Since liquid water was detected by the radi- ometer, the site director decided to launch the cloud physics aircraft (N2UW) for measurements of L we in the vicinity of the earth-satellite propagation path. Table 1 summarizes the radiometric a~d in situ aircraft measurements of doud liquid observed during two flights near the propagation path. The first flight was a descent from 3100 to 900 m; the second flight .was an ascent over the same height interval. Both flights were along a 1350 radial extending from the Sheridan site. For the comparison shown in Table 1, the mea- sured data have been converted to the average L we (g m-3) contained in an equivalent vertical column through the clouds. The path-integrated liquid data (mm) recorded by the radiometer were converted to averagl~ L we using a cloud-thickness estimated from the aircraft data and from soundip.gs made at Sheridan at 1500 and 1800 GMT. Liquid data recorded along the flight path were averaged as a function of vertical height. Very little ice was detected by imaging probes carried on the aircraft. Although similar L we's are obtained with the air- borne and ground-based techniques, the radiometric method shows somewhat higher values than were ob- served by the aircraft probes. Surface observatIons made near the flight times show the cloud ceiling to be -600 m. Therefore, the radiometer may be de- tecting liquid that is present below the minimum al- lowable flight altitude of 900 m. Part of the difference could also be caused by different paths being sampled by the two techniques; the aircraft instruments sam- pled cloud liquid along an _70 slope rather than along the 32.60 elevation angle of the propagation path.