Tuesday, 11 January 2005: 1:45 PM
On the Documentation of Microphysical Signatures Following the Base-Seeding of Texas Convective Clouds Using Salt Micro-Powder
Texas has an ambitious program for the operational glaciogenic seeding of warm-season convective clouds for rain enhancement, even though this is not yet viewed generally as a proven technology. Most of the seeding to date has been done in updrafts at cloud base using silver iodide (AgI) flares or generators. Because physical and statistical evidence are the primary components of proof, the SPECTRA (Southern Plains Experiment in Cloud Seeding of Thunderstorms for Rainfall Augmentation (SPECTRA) Project will be conducted throughout Texas, southeastern New Mexico and Oklahoma during August and September 2004. This project represents a collaborative effort among various organizations in an effort to document in-cloud seeding signatures for glaciogenic and hygroscopic base-seeding in the region. Although seeding signatures have been documented for “on-top” seeding of vigorous cloud towers using ejectable AgI flares, no persuasive physical documentation exists for hygroscopic base seeding. In recognition of the increasingly prominent role of aerosols in cloud seeding concepts, the experiments will be conducted in microphysically-continental and microphysically maritime clouds as quantified by extensive measurements of natural cloud condensation nuclei (CCN) and subsequent documentation of the cloud droplet spectra resulting from the ingested CCN aerosols. The manner of AgI seeding (i.e., flares or generators) and whether seeding will be done with common (NaCl) salt powder that has been milled to model-specified optimum sizes (2 to 5 microns diameter) using a patented process will be determined randomly. SF6 gas will be released to serve as a tracer during the seeding and simulated seeding and detected later in the cloud at several levels by a gas detector aboard the fully instrumented Texas cloud physics aircraft as an indicator of when and where it had intercepted the seeded plume. Comparisons will be made of the habits and concentrations of the water and ice hydrometeors within the seeded plumes within the convective clouds using the array of particle measuring sensors on the aircraft. Assuming the program goes as planned, its results and their implications for the operational seeding efforts in Texas and elsewhere will be presented and discussed at the meeting.