Abstract: From 0615 to 0749 UTC, 14 March 2000, a precipitation enhancement operation with AgI using an aircraft was conducted at the middle part of Shaanxi Province, China. 80 min after cloud seeding (0735 UTC), NOAA-14 satellite data showed a vivid zigzag cloud track on the satellite image. Its length is 301 km, and its average and maximum width are 8.3 and 11 km. The cloud track is very similar in shape with, but different in position and width from that of cloud seeding line. In order to determine that the cloud track is indeed caused by cloud seeding, a three-dimensional numerical model of transport and diffusion of seeding material is used to simulate the shape of seeding material concentration distribution, the turning points, width and length of seeding line. The simulated results are compared with the features of cloud track at 0735 UTC. Every segment of the cloud track is consistent with the transport and diffusion of every segment of seeding line. The transport position, length, width and the variation trend of seeding line agree with those of cloud track. All suggest that the cloud track is the direct physical reflection of cloud seeding effect on the cloud top, which can respond to the transport and diffusion of seeding material. For this study case, the main effecting duration for every segment of seeding line is from 20 to 80 min, the time for each segment of seeding line diffusing to the maximum width is from about 50 to 70 min. This time is obtained from the appearing and disappearing time, width variation of the cloud track segments and simulated results. Also, the comparisons demonstrate that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulating results are sound and trustworthy.

Abstract: Interest in weather modification in Santa Barbara County (County), California, USA dates back to 1950. This interest developed shortly after the discoveries of Drs. Schaefer and Vonnegut in the late 1940’s that established a scientific basis for weather modification (commonly referred to as cloud seeding). Two weather modification research programs have been conducted in the County. Numerous winter season operational cloud seeding projects have been conducted in the County dating back to 1950.

Abstract: From 0615 to 0749 UTC 14 March 2000, an operation of cloud seeding for precipitation enhancement by aircraft was carried out in the middle part of Shaanxi Province, China. National Oceanic and Atmospheric Administration (NOAA)-14 satellite imagery was received at 0735 UTC for the study region. A vivid cloud track appeared on the satellite imagery; its length was about 350 km, and its average width and width maximum were 9 and 14 km, respectively. Through application of a three-dimensional numerical model of the transport and diffusion of the seeding material, the simulated plume shape, the turning points, and the width and length of seeding lines agree with that of the cloud pattern indicated by the satellite imagery. The track is consistent with the transport and diffusion of the seeding line. All of these factors suggest that the cloud track that is detected by satellite imaging is the direct physical evidence of cloud seeding near the cloud top, with the cloud responding to the transport and d...

Abstract: Feasibility of cloud seeding experiments in the Korean Peninsula was examined in a comprehensive manner. Long term (1971-2000) precipitation records from 68 weather stations, the Korean topography, and the unavailability of a seeding aircraft suggested that winter orographic cloud seeding experiments with glaciogenic particles at some high peaks of Taebaek Mountain Ranges with target areas to the west of the mountain peaks might be a reasonable option to choose for precipitation enhancement if conditions are met. Wintertime (November-March) precipitation distribution patterns in Gangwon Province and related meteorological data at Daegwallyeong and Sokcho weather stations showed that strong easterly winds at 850 mb was a key to extend orographically generated precipitations to the west of the Taebaek Mountain peaks. The most prevalent synoptic patterns that were relevant to these precipitation distribution patterns were a low pressure system passing over south of the Korean Peninsula, invoking counter-clockwise circulation to bring prevailing easterly winds to Gangwon Province. Furthermore recent two year records of liquid water depths measured by a microwave radiometer at Daegwallyeong weather station showed the largest values during these events. Therefore it was suggested that these types of synoptic patterns with below freezing temperatures at seeding sites (mountain peaks near Daegwallyeong) might pose a good seeding potential. The Clark-Hall mesoscale model was employed to predict dispersion of glaciogenic seeding material (silver iodide) and the effect of seeding on precipitation. For the case chosen for seeding simulation, seeding start time was critical in precipitation enhancement, earlier start time producing more precipitation increase. Moreover, precipitation increase did not occur at the target area, the western slopes of the seeding site, but was limited only to the eastern side of the seeding site. These simulation results illustrate the difficulty of finding the right weather conditions and the seeding time for a successful precipitation enhancement at the target area. Nevertheless, it seems to be demonstrated that a numerical model is an economic and reliable tool to aid in establishing a good seeding strategy.

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.

Abstract: A modeling method for evaluating rain enhancement of cloud seeding with liquid carbon dioxide (hereinafter LC) coolant and silver iodide (AgI) ice nuclei has been developed. The method has been used to simulate a field experiment. Modeling results indicate that cloud seeding with LC and AgI in the appropriate part of cloud can induce notable change to cloud microphysical and dynamical processes, accelerating updraft velocity, speeding up formation of rain water, changing rainfall distribution, and finally increasing total rainfall. Different seeding agent like LC and AgI has different seeding effect. The mechanism of seeding LC to increase rainfall is analyzed.

Abstract: Cloud Formation Cloud Classification The Ten Cloud Genera Other Cloud Forms and Terms Keywords: clouds and cloud formation; cloud seeding

Abstract: A precipitation enhancement operation using an aircraft was conducted from 1415 to 1549 LST 14 March 2000 in Shaanxi Province. The NOAA-14 satellite data received at 1535 LST soon after the cloud seeding shows that a vivid cloud track appears on the satellite image. The length, average width and maximum width of the cloud track are 301 km, 8.3 and 11 km, respectively. Using a three-dimensional numerical model of transport and diffusion of seeding material within stratiform clouds, the spatial concentration distribution characteristics of seeding material at different times, especially at the satellite receiving time, are simulated. The model results at the satellite receiving time are compared with the features of the cloud track. The transported position of the cloud seeding material coincides with the position of the track. The width, shape and extent of diffusion of the cloud seeding material are similar to that of the cloud track. The spatial variation of width is consistent with that of the track. The simulated length of each segment of the seeding line accords with the length of every segment of the track. Each segment of the cloud track corresponds to the transport and diffusion of each segment of the seeding line. These results suggest that the cloud track is the direct physical reflection of cloud seeding at the cloud top. The comparison demonstrates that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulated results are sound and trustworthy. The area, volume, width, depth, and lateral diffusive rate corresponding to concentrations 1, 4, and 10 L−1are simulated in order to understand the variations of influencing range.

Abstract: From 0615 to 0749 UTC, 14 March 2000, a precipitation enhancement operation with AgI using an aircraft was conducted at the middle part of Shaanxi Province, China. 80 min after cloud seeding (0735 UTC), NOAA-14 satellite data showed a vivid zigzag cloud track on the satellite image. Its length is 301 km, and its average and maximum width are 8.3 and 11 km. The cloud track is very similar in shape with, but different in position and width from that of cloud seeding line. In order to determine that the cloud track is indeed caused by cloud seeding, a three-dimensional numerical model of transport and diffusion of seeding material is used to simulate the shape of seeding material concentration distribution, the turning points, width and length of seeding line. The simulated results are compared with the features of cloud track at 0735 UTC. Every segment of the cloud track is consistent with the transport and diffusion of every segment of seeding line. The transport position, length, width and the variation trend of seeding line agree with those of cloud track. All suggest that the cloud track is the direct physical reflection of cloud seeding effect on the cloud top, which can respond to the transport and diffusion of seeding material. For this study case, the main effecting duration for every segment of seeding line is from 20 to 80 min, the time for each segment of seeding line diffusing to the maximum width is from about 50 to 70 min. This time is obtained from the appearing and disappearing time, width variation of the cloud track segments and simulated results. Also, the comparisons demonstrate that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulating results are sound and trustworthy.

Abstract: The paper summarizes the results of the longtime cloud modification experimental research in Moldova and Ukraine aimed at rain enhancement. The research enabled to develop a unique technology of cloud seeding that provided significant rain augmentation from clouds of different types. The basic principle of the technology lies in selecting seeding target sites within cloud systems based on data related to its structure, evolution stage, and microphysical parameters at the time of supposed seeding. It was shown that the efficiency increases considerably if the seeding is performed precisely into the layer whose microphysical characteristics are appropriate for the transformations needed for rain production, namely, crystallization of droplet water and an abrupt increase in crystal concentration by 1-2 orders of magnitude. It was also shown that violation of this principle reduces seeding efficiency to the levels that make it economically senseless.