The Southern Plains Experiment in Cloud Seeding of Thunderstorms for Rainfall Augmentation (SPECTRA)Project was designed to study convective clouds in Texas, southeastern New Mexico and Oklahoma where advertent and/or inadvertent weather modification occurs.
The objectives of the SPECTRA project were to document microphysical signatures produced by glaciogenic base seeding, document the Cloud Condensation Nuclei (CCN Wikipedia link) distribution and their effect on the cloud Drop Size Distribution (DSD), test hygroscopic seeding using milled salt and finally, conduct model simulations of seeded and non-seeded clouds.
In order to achieve these objectives, a field program was designed starting initially with Phase 1 (2004) which focused on the collection of CCN number concentrations and CCN size distributions at cloud base and measurement of the DSD spectra of convective clouds at various levels from cloud base to cloud top. Phase 2 resumed in 2005 and focused on hygroscopic seeding using milled salt.
SPECTRA Phase I
The identification of types, and frequency of occurrence, of cloud condensation nuclei (CCN) within and in the vicinity of growing convective cloud towers.
Observations of cloud-droplet spectrum, liquid water contents and hydrometeor sizes and types, as well as inferences about cloud updrafts, to determine the impact of the CCN particulates on in-cloud processes, most notably coalescence.