SPECTRA I

The basic measurements consisted of CCN data, aerosol concentrations (0.1 to 3mm), DSD (3 to 50mm) and precipitation hydrometeor distributions (25mm to 1.5mm). The data were plotted for each of the 34 missions. Below is a sample of the data for a case on the 19th August 2004 in San Angelo, Texas.
 

SPECTRA II

During May and early June of 2005 the SOAR research aircraft flew on several hygroscopic seeding experiments using milled salt released from an agricultural aircraft. SF6 gas was released in updraft from the cloud-base seeder simultaneous with the release of the hygroscopic salt powder. The gas was detected on subsequent passes, indicating that the aircraft had penetrated the seeded plume.

The detection of the gas was successful in part due to the Parcel Tracking Software (PTS) that ingests the seeder coordinates and the research aircraft coordinates and directing the research aircraft towards the location of the seeder aircraft. It is evident from the initial analysis that an alteration of the cloud droplet spectra near and above cloud base, as required by the conceptual model, was found within the seeded plume. During the Texas experiments, such a seeding signature was observed as a broadening of the precipitation particle spectrum as measured in the Cloud Imaging Probe (CIP). More cases are needed in order to draw any conclusions.

For more information read our feature article SOAR pioneers cloud seeding with milled salt

This research was supported by the Weather Damage Modification Program of the Bureau of Reclamation (BOR) administered by the Texas Department of Licensing and Regulation (TDLR). The information presented here is sample data from the draft final report.