JWM Vol. 37 Abstracts

IS AIR POLLUTION IMPACTING WINTER OROGRAPHIC PRECIPITATION IN UTAH?

Don A. Griffith, Mark E. Solak and David P. Yorty
North American Weather Consultants, Inc. Sandy, Utah, USA

Abstract: Winter precipitation data from selected locations within the States of Utah and Nevada were analyzed to determine if there were any indications of reductions in mountainous precipitation when compared with upwind valley precipitation. This work followed the approached utilized in a comprehensive study of precipitation in Israel and California that indicated the orographic component of precipitation was declining at precipitation stations at mountain locations which were downwind of major cities. The authors of that study theorized that these reductions were due to the transport of air pollution from the cities into winter storms at these downwind mountainous locations leading to microphysical changes within the affected clouds resulting in reductions in observed precipitation. The work which we performed in Utah and Nevada indicated similar reductions in mountainous precipitation downwind of the Salt Lake City/Provo metropolitan complex. These indicated reductions in precipitation extended downwind of the first mountain barrier into a mountain valley location and into the upwind slope of a second mountain barrier some 80 km downwind. Reductions in precipitation at other mountain stations in Utah and Nevada were not indicated. These stations were located in more rural settings which may suggest that air pollution from major cities may in fact be related to the reductions in precipitation that are indicated downwind of the Salt Lake City/Provo metropolitan complex.

THE SANTA BARBARA CLOUD SEEDING PROJECT IN COASTAL SOUTHERN CALIFORNIA, SUMMARY OF RESULTS AND THEIR IMPLICATIONS

Don A. Griffith and Mark E. Solak
North American Weather Consultants Sandy, Utah
and Robert B. Almy and Dennis Gibbs
Santa Barbara County Water Agency Santa Barbara, California

No Abstract Available

OBSERVATIONS OF RIME ICING IN THE WASATCH MOUNTAINS OF UTAH: IMPLICATIONS FOR WINTER SEASON CLOUD SEEDING

Mark E. Solak, David P. Yorty and Don A. Griffith
North American Weather Consultants Sandy, Utah, USA

Abstract: Mountain-top measurements of rime ice accumulations during the winter season of 2003-2004 in the Wasatch Range southeast of Salt Lake City, Utah, were analyzed to estimate and characterize the seasonal occurrence of supercooled liquid water during more than twenty storms, specifically toward assessment of winter cloud seeding opportunities in the region. The data indicated substantial periods of supercooled liquid water occurrence and colder than anticipated temperatures overall during riming periods. Using precipitation measurements at a nearby site, the apparent relative precipitation efficiency of storms and periods of storms was estimated. In many cases, rather orderly transitions in apparent precipitation efficiency have been documented and many periods of sustained inefficient precipitation production were noted. These and other findings suggest substantial cloud seeding opportunity for snowpack augmentation and provide useful insights regarding seeding opportunity recognition. Descriptive statistics and storm case examples are summarized.

RANDOMIZED PROPANE SEEDING EXPERIMENT: WASATCH PLATEAU, UTAH

Arlin B. Super* and James A. Heimbach, Jr.**
*St. Cloud, MN
** Springvale, ME

Abstract: A randomized experiment to test propane cloud seeding effectiveness was conducted on the Utah's Wasatch Plateau during the 2003/04 winter. Propane dispensers were operated at a previously used high altitude site well up the windward slope. The primary target precipitation gauge was 4.3 km downwind, on top the plateau, where earlier plume tracking demonstrated routine targeting with seeding site winds from the southwest quadrant. Gauges were maintained upwind and downwind of the primary target, along the expected plume trajectory, but no more than 6.5 km downwind of the propane dispensers because of targeting uncertainties. A well-correlated crosswind control gauge provided the covariate used in all statistical testing. The experiment was completely automated with 2 hr experimental periods declared when a specified icing rate was exceeded at the seeding site. Each period contained a pair of experimental units, one seeded and one placebo, with treatment by random decision. Three different statistical tests were applied. Statistically significant seeding-caused precipitation increases were strongly suggested by the exploratory experiment for the entire population of 98 experimental units, for a partition of 69 units with wind directions expected to result in successful targeting, and for the same wind directions but excluding highest natural snowfalls. Intriguing but inconclusive suggestions of possible positive seeding effects resulted when supercooled liquid water (icing) was detected, with warmer temperatures and for lighter wind speeds. Hypothetical estimates suggest about an 8% precipitation increase had all experimental hours been seeded during the 3.5 month project period.

THE SERIOUS FLAWS OF THE ACADEMIES’ REPORT ON WEATHER MODIFICATION RESEARCH

Roland List
Department of Physics, University of Toronto, Toronto, M5S 1A7, Canada

Abstract: The Report “Critical Issues in Weather Modification Research” by the National Research Council of the National Academies (the Report, in short) stresses lack of physical understanding as the reason for rejecting all success claims in modification (involving convective clouds). This conclusion is reached without realizing that statistics provides the only scientific tool to link the physics of clouds to the interference of seeding; it weighs the quality of the basic physical hypotheses underlying the seeding. Yet statistics, the cornerstone in the assessment of weather modification experiments, is not even discussed in the bulk of the Report. The faults in the Executive Summary are easily spotted. The main body of the Report, however, is well written and its even bigger flaws are hidden in beautiful prose. The main failings of the Report will be described below.

OBSERVATIONS OF PRECIPITATION DEVELOPMENT – AN EXAMPLE FROM THE UAE PROJECT

Daniel Breed, Tara Jensen, and Roelof Bruintjes
National Center for Atmospheric Research Boulder, CO 80307

Abstract: Radar and aircraft observations from the 12 September 2004 case study, collected during a field project in the United Arab Emirates, are presented in the context of discerning precipitation development. The focus of the field projects was convective clouds forming over and near the Oman mountains in the eastern Arabian Penisula, as part of a larger feasibility study on precipitation enhancement and a subsequent randomized cloud seeding experiment. The radar data show that earlier convection likely pre-conditioned the region with mid-level moisture and ice particles. Subsequent cells and storms developed significant precipitation as they grew above 6 km (around -5° C). This is consistent with the concept that recycling particles into the same and adjacent turrets is an important process in precipitation development. However, the data set presented is quite limited and more details from other cases (both seeded and unseeded) are needed to generalize precipitation development in UAE clouds.