ATMOSPHERIC WATER RESOURCES RESEARCH
in association with the United States Department of the Interior, Bureau of Reclamation,
Fresno State College Foundation Fresno State College Fresno, CA
CENSARE Cloud Seeding Manual
This mode of operation was employed for a few selected cases in the 1969 water year and during portions of the 1979 and 1971 water years.
Pyrotechnic fusees similar to those used in the ground-based generators, only having a higher output rate, were burned from racks mounted on the trailing edges of the wings.
Aircraft seeding was used primarily during storm periods when the lower portions of the airmass were too stable to permit lifting or targeting of the AgI from the ground-based generators.
Certain changes in technique and mode of seeding operations occurred during the course of the CENSARE effort.
These changes were made as the result of: a better understanding of the local aerology, early indications of apparent seeding effects, the impact of inflation on the operation's budget, and the need to devote more effort to analysis which eliminated many CENSARE field operations which had provided real-time data.
The following information on yearly operational changes certainly should be considered in any review of where and when the seeding operations were effective:
1970 Water Year
The direction of the seeding activities was conducted from the field office at Jackson.
The seeding director had only a general idea of the storm movements and storm structure, except as measured in real-time by the rawinsode and radar scope precipitation presentations at Jackson.
Only a ground seeding system was utilized prior to March, 1979. Aircraft seeding in conjunction with the ground seeding system was utilized for the last four storms of the season, which ended in mid-April, 1970.
1971 Water Year
The direction of the seeding activities was again conducted from the field without the aid of real-time, broad-scale information on the movement and structure of the storms.
Both a ground seeding system and a seeding aircraft were utilized throughout the operating season.
The advantage of the dual seeding mode was somewhat offset in that the seeding director found it necessary to accompany all seeding flights as well as handle the logistics of servicing the seeding devices on the aircraft.
Three aircraft near-mishaps during the course of the season, created by unforeseen meteorological conditions, pointed up the need for continuous and accurate meteorologic information during aircraft flights.
The seeding director, therefore, should be stationed in a well-equipped weather central where accurate forecasts for seeding activities can be made.
1972 Water Year
Seeding direction was handled from a well-equipped weather central at the AWRR main office in Fresno. Budget limitations permitted only a ground seeding capability for this operating season.
Rawinsonde observations, radar scope precipitation presentations, and normal surface weather observations were available by telecopier on a near real-time basis from the Jackson field office.
Very preliminary and sketchy precipitation evaluations of the area-of-effect from the 1970 and 1971 water year seeding provided some indication that the primary increases were in the extreme north portion of the target area as well as to the west and north outside of the main target.
A minor adjustment in the targeting procedures was made for the 1972 water year based on those indications.
Namely, a slower rate of vertical diffusion of the artificial nuclei was used in targeting of the seeding effects.
This resulted in the allowance of longer travel times and distances during southeasterly surface flow, and the consequent use of a different set of generators in the existing seeding network.
4) 1973 Water Year
The direction of the seeding operations was again handled from a well-equipped weather central at the AWRR main office in Fresno.
Rawinsonde and radar observations and other general weather observations formerly available from the Jackson area were not available this season due to staff office analysis responsibilities.
It was felt that past seeding operational experience would permit a safe and qualitative seeding operation conducted from real-time weather information acquired on the Service “A” and Service “C” weather teletypes
Again this year, ground seeding was the only mode available.
Experience during the 1972 water year in targeting revealed a deficiency in the ground generator placements.
This gave cause to modify the arrangement of the generator locations for the 1973 water year. In addition, the low-level pyrotechnic generators were replaced with acetone-burning generators.
While no evaluation of the seeding results for the 1973 water year has been performed to date, it is expected that the overall effect from the operations conducted this season was further south, with some effect in the Tuolumno River watershed immediately to the south of the target area.
Also, operations were stratified more than in past years by operating high elevation generators only or operating only the lower elevation generators located upwind of the target area.
This was done to increase the number of cases for the high elevation versus low elevation stratified evaluation.
It is highly desirable that the 1973 water year seeding effects be thoroughly evaluated once the NWS precipitation data and the USGS streamflow data become available.