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John A. Flueck

Abstract

Proper field experimentation in precipitation augmentation, or virtually any other topic, is not an easy task. Some general research considerations, i.e., the objectives of research, the quest for believability, and the two principal types of field studies, are discussed. The anatomy and stages of life of an experiment are presented, and the three levels or classes of an experiment (i.e., preliminary, exploratory, and confirmatory) are depicted. A number of prescriptions for improved experimentation are offered in regard to conceptual models, treatment design, treatment selection and allocation, treatment effect models, and analyses for treatment effects. Lastly, a few comments are appended on the role of statisticians in quality field research efforts.

When the well's dry, we know the worth of water. Ben Franklin, 1758 Poor Richard's Almanack

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Charles A. Doswell III and John A. Flueck

Abstract

Verification of forecasts during research field experiments is discussed and exemplified using the DOPLIGHT '87 experiment. We stress the importance of forecast verification if forecasting is to be a serious component of the research. A direct comparison and contrast is done between forecasting for field research and forecasting in the operational sense, highlighting the differences between them. Ale verification of field research program forecasting is also different from that done in operations, as a result of those forecasting differences.

DOPLIGHT '87 was a field project conducted jointly by the National Severe Storms Laboratory and the Oklahoma City National Weather Service Forecast Office, and is described in detail. During the experimental design, special attention was given to forecast design, to ensure that verification would be unambiguous and that the data collected would be appropriate for validating the forecasts. This a priori design of the forecasts to consider proper objective verification is, we believe, unique among research field programs. The forecast evaluation focuses on the contingency table and summary statistics derived from it, as treated in a companion paper by Flueck (1989; hereafter referred to as F1u89).

Results are interpreted in terms of their implications for future field research experiments and for operational forecasting. For example, it is noted that DOPLIGHT '87 forecasts of convective potential were nearly constant from the evening before an anticipated operational day to about local noon on that day. This suggests that convective storm field research operational decisions could be made as early as the evening before an anticipated operational day with negligible loss of skill. Summary measures of the forecast verification suggest that the DOPLIGHT '87 forecasters demonstrated skill roughly comparable to the forecasters at the National Severe Storms Forecast Center in issuing outlooks of convective potential. The requirement for time to assimilate the most recent data is noted both for field experiments and for operations, and some discussion of the potential impact of new data acquisition and processing systems is offered.

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John A. Flueck and Burt S. Holland

Abstract

Ratio estimators are widely utilized in the physical and atmospheric sciences, although their properties and inherent problems are often unknown or overlooked. A number of problems and properties of ratio estimators are presented and some solutions are offered. For a correlated bivariate gamma structure, approximate and exact results are given for the mean, variance and biases of the ratio of two means. The sensitivity of these results to sample size and parameters of the bivariate gamma are indicated. The application of these results to three well-known cloud seeding experiments are presented and “corrected” estimates of the corresponding seeding effects are offered.

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William L. Woodley and John A. Flueck

Abstract

No abstract available.

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John A. Flueck and Timothy J. Brown

Abstract

Research criteria and methods are presented for performing and evaluating the growing discipline of solar-weather studies. A clear distinction among preliminary, exploratory, and confirmatory studies is presented, and it is shown that this distinction affects all dimensions and findings of a study. Particular attention is given to conceptual models, variables and data, sample designs, analyses, and formal ampliative inference issues under exploratory and confirmatory conditions. The utility of the proposed criteria and methods are illustrated by evaluating two recent solar-weather claims of strong association between solar flux and stratospheric temperature at the North Pole when partitioned by the phase of the quasi-biennial oscillation. The results of the evaluation indicate that these claims are only exploratory ones and are still in need of confirming evidence. Last, a reanalysis of the solar flux and temperature relation, using some of the proposed methods, indicates that the association actually changes with time, and thus, there appears to be other, presently unknown, factors that affect this potential solar-weather relation.

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William L. Woodley, Anthony Barnston, John A. Flueck, and Ron Biondini

Abstract

FACE-2 was a confirmatory weather modification experiment conducted in south Florida in the three summers of 1978, 1979 and 1980. The results of the FACE-2 replicated and pre-specified confirmatory rainfall analyses are presented and discussed in this paper. These results are interpreted in terms of the published criteria for confirmation of the FACE-1 rainfall results. FACE-2 did not confirm the results of FACE-1, although there are indications that seeding did increase the rainfall over the FACE target area. Some explanations for the lack of confirmation are suggested.

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JoséG. Meití, William L. Woodley, and John A. Flueck

Abstract

The second phase of the Florida Area Cumulus Experiment (FACE-2) has been completed and an exploratory analysis has been conducted to investigate the possibility that cloud seeding may have affected the rainfall outside the intended target. Rainfall was estimated over a 3.5×105 km2 area centered on the target using geosynchronous, infrared satellite imagery and the Griffith-Woodley rain estimation technique. This technique was derived in South Florida by calibrating infrared images using raingage and radar observations to produce an empirical, diagnostic (a posteriori), satellite rain estimation technique. The satellite rain estimates for the extended area were adjusted based on comparisons of raingage and satellite rainfall estimates for the entire FACE target (1.3×104 km2). All daily rainfall estimates were composited in two ways: 1) in the original coordinate system and 2) in a relative coordinate system that rotates the research area as a function of wind direction. After compositing, seeding effects were sought as a function of space and time.

The results show more rainfall (in the mean) on seed than no seed days both in and downwind of the target but lesser rainfall upwind. All differences (averaging 20% downwind and −10% upwind) are confined in space to within 200 km of the center of the FACE target and in time to the 8 h period after initial treatment. In addition, the positive correlation between untreated upwind rainfall and target rainfall is degraded on seed days, suggesting possible intermittent negative effects of seeding upwind. Although the development of these differences in space and time suggests that seeding may have been partially responsible for their generation, the results do not have strong inferential (P-value) support.

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Anthony G. Barnston, William L. Woodley, John A. Flueck, and Michael H. Brown

Abstract

The Florida Area Cumulus Experiment (FACE) is a single area, randomized experiment designed to assess the ground-level rainfall effects of dynamic cloud seeding in summer on the south Florida peninsula. The second phase of FACE (FACE-2), an attempt to confirm the indication of seeding-induced rain increases in FACE-1, has been completed. A description of the FACE-2 program design and how well it was implemented in the summers of 1978, 1979 and 1980 is provided. The data reduction process and its rationale are described both for the basic rainfall data and for the predictor variables to be used in the covariate analyses. The resulting FACE-2 rainfall and covariate data are presented for each of the 61 days of experimentation without knowledge of whether actual seeding (using silver iodide) took place. (Part II will contain the confirmatory and replicated analyses of the effects of seeding, and Part III will present a number of exploratory analyses of the FACE-1 and FACE-2 data.)

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John A. Flueck, William L. Woodley, Robert W. Burpee, and Daniel O. Stram

Abstract

No abstract available.

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Jeffrey L. Stith, Don A. Griffith, R. Lynn Rose, John A. Flueck, James R. Miller Jr., and Paul L. Smith

Abstract

A gaseous tracer, sulfur hexafluoride, was used to follow the path of two different AgI cloud seeding aerosols in cumulus clouds. The materials were released at cloud base or midlevels. Plumes sampled at midlevels were found to be relatively narrow and embedded within updrafts or downdrafts; relatively high concentrations of the tracer were observed in some downdrafts. Plumes with diameters comparable to the cloud diameters were found in the upper 20% of the clouds. These observations suggest only limited dispersion of the plumes in the clouds, with greater mixing occurring at cloud top. Similar behavior of the in-cloud plume is observed in results from a two-dimensional, numerical cloud model used to simulate the introduction of seeding materials into convective clouds. Observations of the ice crystal production rates are consistent with the results of recent laboratory findings concerning the properties of the seeding agents. The usefulness of this tracer technique in studying transport, diffusion and ice activation in cumulus clouds is discussed.

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