Aircraft Documentation of Microphysical Seeding Signatures in Argentine Clouds

The WMI Lear Jet was used in Argentina in January and February 2000 to document glaciogenic-seeding signatures in vigorous supercooled clouds. A seed and non-seed cloud pair was qualified on each of two research flights and multiple passes were made through the subject clouds after the treatment pass at temperatures ranging between -9^oC and -19^oC. Seeding was done from the Lear using AgI flares, which were ejected on the first pass. Pronounced seeding signatures, consisting initially of high concentrations (> 1000 L^-1) of tiny ice particles, were detected in both seeded clouds two to three minutes after the initial seeding pass. The ice concentrations were much smaller in the two non-seeded clouds even though the observations were made at temperatures at or below the measurement temperatures in the seeded clouds.

Cloud microphysical measurements also were made by the Lear Jet during operational seeding to suppress hail. A prolonged run of 8-min duration was made initially through a series of non-seeded clouds. These clouds were then compared to measurements made during a subsequent run of 7-min duration in clouds, which were being seeded with ejectable flares by another aircraft about 1 km below the monitoring aircraft. The temperatures on the two extended measurement runs ranged between -17oC and -23oC. The seeded clouds were found to have much higher ice concentrations than the non-seeded clouds. This is in accordance with the intent of the operational seeding to fill the subject clouds with high concentrations of small ice particles. The implications of these findings to hail-suppression efforts in Argentina are discussed.