Search Results

You are looking at 21 - 30 of 35 items for

  • Author or Editor: William L. Woodley x
  • All content x
Clear All Modify Search
Daniel Rosenfeld, William L. Woodley, Terrence W. Krauss, and Viktor Makitov

Abstract

Documentation during January and February 2000 of the structure of severe convective storms in Mendoza, Argentina, with a cloud-physics jet aircraft penetrating the major feeder clouds from cloud base to the −45°C isotherm level is reported. Complementary radar, satellite, and radiosonde measurements are incorporated into the study. The main research goal was the description of the microphysical evolution of the convective feeders of the hailstorms from cloud base to the anvil in an attempt to gain insights into the microphysical evolution of the clouds that are associated with the high frequency of large hail in the region. The aircraft penetrated preferentially the tops of young growing elements, which were typically the major feeders to severe hailstorms, producing hail that is large (>3 cm) in size. Cloud bases typically were at 6°–14°C, with typical base updrafts of 4–7 m s−1. The cloud updrafts increased with height, exceeding 25 m s−1 at heights ≥7 km and, on occasion, 40 m s−1 at heights >8 km. Thermal buoyancies of 5°–8°C were measured in the convective towers at heights of 8–10 km. The vertical wind shear was weak below 6 km but increased strongly above that level as the west winds cleared the Andes barrier, which averages 6.1 km to the west of Mendoza. The clouds had very little coalescence and contained no detectable precipitation-sized particles >100 μm at temperatures >−15°C. Nearly adiabatic cloud water with most cloud water still not converted into precipitation-sized hydrometeors (>100 μm in diameter) was found in cloud filaments within the strongest updrafts up to the level of homogeneous freezing, reaching 4 g m−3 at −38°C in one cloud before vanishing abruptly at colder temperatures. Graupel >1 mm appeared at the tops of growing new towers at temperatures <−27°C, in agreement with radar first-echo heights of about 8 km.

Full access
William L. Woodley, Daniel Rosenfeld, and Bernard A. Silverman

Abstract

Randomized, cold-cloud, rain-enhancement experiments were carried out during 1991–98 in the Bhumibol catchment area in northwestern Thailand. Exploratory experimentation in 1991 and 1993 was followed by a demonstration experiment, limited to A-type experimental units, to determine the potential of on-top silver iodide seeding for the enhancement of area (1964 km2) rainfall. Analyses in a companion paper () established that the Thai cold-cloud demonstration experiment, evaluated according to its original design, failed to reach statistical significance in the time allotted to the experiment, although the probabilities that the seeding effects were positive on the treated cells and units are 72% and 79%, respectively. The results of exploratory examination of the entire demonstration experiment, including both A- and B-type experimental units, are presented herein. The exploratory studies involved both cell [392 seeded (S) and 335 nonseeded (NS)] and unit (35 S and 35 NS) analyses, a bivariate analysis of the joint effects on cells and units, and the analysis of pooled results from the exploratory experiment and the entire demonstration experiment. The results of these exploratory studies strengthen the case for seeding-induced changes in rainfall that were indicated in the evaluation of the a priori demonstration experiment. A multiple regression analysis to account for some of the natural rainfall variability suggests, however, that the apparent seeding effect has been overestimated by about a factor of 2 (i.e., +92% versus +48%). Temporal plots and analyses of unit rain-volume rates and cumulative rain volumes for seeding effects revealed stronger statistical support for convective masses within the unit not having seeded ancestry, as determined by radar, than for convective clusters with seeded ancestry. This result suggests that the effect of seeding, which begins with the directly treated cells, is propagated to nonseeded clouds within the unit. Enhanced downdrafts and/or “secondary seeding,” as discussed herein, are posited as possible propagation mechanisms. Partitioning of the data by a crude aircraft measure of coalescence intensity revealed that the rain volume from NS units increased as coalescence intensity increased, whereas the greatest mean S rainfall was observed in the moderate coalescence category. The apparent seeding effects were >100% for units having clouds with weak to moderate coalescence and were nonexistent for units having clouds with strong coalescence. This was true also upon analysis of the cell sample. The implications of this and all results are discussed in the context of the conceptual model guiding the experimentation.

Full access
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.)

Full access
WILLIAM L. WOODLEY, JOSEPH H. GOLDEN, BRADLEY C. HALTER, and JAMES T. BUNTING

Abstract

Two waterspouts were observed aloft from a private aircraft recently near Lower Matecumbe Key, Florida. Color slides and zoom movies of both waterspout vortices on the sea surface and aloft were obtained. A detailed description of the equipment used and a discussion of the synoptic pattern of that day are presented. The data show some interesting details regarding the dynamics of the observed waterspout circulations. Both waterspouts traversed a similar path. A subsequent ground survey of the paths taken over the Key, together with damage reports and eyewitness accounts, indicate that the second waterspout was much more intense than the first.

The authors plan to make detailed calculations, using the zoom movies, of a radial profile of the tangential and vertical wind speeds about the second waterspout vortex. Rates of forward motion and funnel diameter at various levels below the cloud base will also be obtained. An additional, more quantitative report of this interesting encounter will be forthcoming.

Full access
William L. Woodley, Cecilia G. Griffith, Joseph S. Griffin, and Scott C. Stromatt

Abstract

Quantitative precipitation estimates have been made for the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) from geosynchronous, infrared satellite imagery and a computer-automated technique that is described in this paper. Volumetric rain estimates were made for the GATE A scale (1.43 × 107 km2) and for a 3° square (1.10 × 105 km2) that enclosed the B scale for time frames ranging from all of GATE (27 June—20 September 1974) down to 6 h segments. The estimates for the square are compared with independent rain measurements made by four C-band digital radars that were complemented by shipboard raingages. The A-scale estimates are compared to rainfall estimates generated by NASA using Nimbus 5 microwave imagery. Other analyses presented include: 1) comparisons of the satellite rain estimates over Africa with raingage measurements, 2) maps of satellite-inferred locations and frequencies of new cumulonimbus cloud formation, mergers and dissipations, 3) latitudinal precipitation cross sections along several longitudes and 4) diurnal rainfall patterns.

The satellite-generated B-scale rainfall patterning is similar to, and the rain volumes are within a factor of 1.10, of those provided by radar for phases 1 and 3. The isohyetal patterns are similar in phase 2, but the satellite estimates are low, relative to the radar, by a factor of 1.73. The B-scale disparity in phase 2 is probably due to the existence of rather shallow but rain-productive convective clouds in the B scale. This disparity apparently does not carry over to the A scale in phase 2. Comparison of NASA Electronically Scanning Microwave Radiometer (ESMR) rain estimates with ours for several areas within the A scale for all GATE suggests that the former is low relative to the latter by a factor of 1.50. The satellite estimates of rainfall in Africa are similar to measurements by raingages in all phases of GATE up to 11°N and progressively greater than the gage measurements north of this latitude toward the Sahara desert.

The diurnal rainfall studies suggest a midday (about 1200 GMT) maximum of rainfall over the water areas and a late evening maximum (about 0000 GMT) over Africa and the northern part of South America. The latitudinal cross sections along several longitudes of phase rainfall clearly show the west-southwest/east-northeast orientation of the Intertropical Convergence Zone (ITCZ), the diminution of the rainfall west-southwestward from Africa into the Atlantic, and the northward progression of the ITCZ from phase 1 into phases 2 and 3. The center of action for cloud formation, merger and dissipation, and the area of maximum rainfall (>1600 mm for all of GATE) occur along the southwest African coast near 11°N. This agrees with past climatologies for this region. Superposition of the satellite-generated rainfall maps and sea surface temperature maps by phase suggests a strong relationship between the two. Almost all of the rainfall occurs within 26°C sea surface temperature envelope. The mean daily coverage of rainfall and the mean rainfall in the raining areas for the A scale for all GATE are 20% and 14.1 mm day−1, respectively. These and other results are discussed.

Full access
Joanne Simpson, William L. Woodley, Alan H. Miller, and Gerald F. Cotton

Abstract

A randomized, single-cloud, dynamic seeding experiment was conducted with airborne pyrotechnics in South Florida in 1968 with results extensively reported. In the first 40 min following seeding, large increass in rainfall (about 150 acre-ft or approximately 100% per seeded cloud) were obtained by analysis with a calibrated 10-cm radar, the accuracy of which had been tested by a raingage comparison. The statistical significance of the rainfall differences was, however, marginal, ranging from 5–20% with a series of two-tailed tests.

In the spring and early summer of 1970 an improved repeat of the experiment was conducted in two phases. Five instrumented aircraft participated in the first phase and only two in the second. Altogether 13 seeded clouds and 16 controls were obtained. All seeded clouds reached cumulonimbus stature as did 10 of the controls. The average difference in vertical growth following seeding of seeded vs control clouds was 6200 ft, significant at the 1% level.

This paper is concerned primarily with the rainfall results of the 1970 experiment and the combined 1968 and 1970 experiments, together with the results of a detailed statistical investigation of their significance. The rainfall analyses are made with the University of Miami's calibrated 10-cm radar by the method developed and tested for the 1968 data. For the first 40 min following seeding, the average seeded minus control rainfall difference is about 100 acre-ft while it is more than 250 acre-ft, or more than 100%, for the entire cloud lifetime. Significance is better than 5% for the whole cloud lifetime for the 1970 data alone and for the 1968 and 1970 data combined; it is better than 5% for the combined data for the first 40 min and better than 10% for the 1970 data alone. When the rainfall data are objectively stratified into fair and rainy days, the fair-day differences are of the order of 350–400 acre-ft and the rainy-day differences are negative. Intraday comparisons are also made, comparing seeded and control clouds on the same day. This analysis, if anything, increases seeded-control differences, which retain high significance. The main result of the statistical analysis is that for all 1968 and 1970 data combined, the positive seeding effect is not only significant but exceeds a factor of 3.

The shortcomings of the radar evaluations are discussed; it is shown that if they could be removed the rainfall conclusions would be strengthened.

Full access
John A. Augustine, Cecilia G. Griffith, William L. Woodley, and JoséG. Meitín

Abstract

In the mean the Griffith/Woodley rain estimation technique underestimated the radar-measured rain of each of the three phases (a total of 56 days) of GATE, to varying degrees, and the satellite-derived isohyets were generally too extensive relative to radar-measured patterns. Three possible error sources are investigated in the present paper: 1) the method of apportionment of satellite-derived rain at the surface; 2) resolution degradation of the digital satellite imagery; and 3) anomalous behavior of convective clouds in the tropical Atlantic relative to those of the Florida derivation data set.

To correct the satellite-derived rain patterns, a new method of apportionment was tested by recomputing the GATE satellite rain estimates. Better volumetric comparisons between radar and satellite estimates were observed for 24 h and phase periods, and comparisons of isohyetal patterns improved on all time scales.

The relative error caused by resolution degradation was quantified by comparing rain estimates produced from full resolution imagery to estimates derived from degraded imagery for an 8° latitude by 12° longitude area in the eastern tropical Pacific ocean over a 54 h period. Results showed that the volumetric rainfall estimates made at 1/3° spatial and 1 h temporal resolution would be on the order of 10% lower than estimates made with the full resolution data (1/15° and 30 min).

The remaining differences between the GATE satellite and radar estimates are attributable to different conditions prevailing in Florida and in GATE. These include significant rain from clouds that do not grow above the −20°C level (“warm rain”) and very long-lived anvils.

Full access
Joanne Simpson, William L. Woodley, and Robert M. White

A serious drought in the spring of 1971 occurred in South Florida. In view of NOAA's research experience in dynamic cumulus modification (massive silver iodide seeding to invigorate cumulus updrafts by means of release of latent heat of fusion), the state government sought our aid in combating this drought by means of a seeding effort. NOAA responded by an extension of its experimental program with both practical and research objectives.

Two of the NOAA Research Flight Facility aircraft were used for airborne pyrotechnic seeding from 1 April to 31 May 1971. A one-dimensional numercial cumulus model was run in real time on each day, eliminating 38 days in the period as unsuitable. Flights were conducted on 16 days, with actual seeding on 14. Seven suitable days were lost due to routine aircraft maintenance. Radars and raingages were used to calculate rain amounts from all seeded and many unseeded clouds.

Seeding was conducted in an attempt to promote merger by treating clouds close together in space and also the upshear towers of each previously seeded complex. A total of not less than 180,000 acre-ft of water was calculated to have fallen from the seeded clouds in two target areas totaling about 7200 n mi2. A conservative estimate attributed 100,000 acre-ft as due to seeding, although without randomization this evaluation cannot be made firm. Satellite and synoptic studies accompanied rainfall evaluation on all seeding days. Among the important scientific results is that some frontal conditions appeared suitable for dynamic seeding in Florida, offering hope for extension of the technique into dry periods.

Some aspects of NOAA's future policy in the rain enhancement aspects of weather modification are presented.

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

Abstract

No abstract available.

Full access
William L. Woodley, Jill Jordan, Anthony Barnston, Joanne Simpson, Ron Biondini, and John Flueck

Abstract

The Florida Area Cumulus Experiment of 1970–76 (FACE-1) is a single-area, randomized, exploratory experiment to determine whether seeding cumuli for dynamic effects (dynamic seeding) can be used to augment convective rainfall over a substantial target area (1.3 × 104 km2) in south Florida. Rainfall is estimated using S-band radar observations after adjustment by raingages. The two primary response variables are rain volumes in the total target (TT) and in the floating target (FT), the most intensely treated portion of the target. The experimental unit is the day and the main observational period is the 6 h after initiation of treatment (silver iodide flares on seed days and either no flares or placebos on control days). Analyses without predictors suggest apparent increases in both the location (means and medians) and the dispersion (standard deviation and interquartile range) characteristics of rainfall due to seeding in the FT and TT variables with substantial statistical support for the FT results and lesser statistical support for the TT results. Analyses of covariance using meteorologically meaningful predictor variables suggest a somewhat larger effect of seeding with stronger statistical support. These results are interpreted in terms of the FACE conceptual model.

Full access