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- Author or Editor: H. H. Schiesser x
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Abstract
During the years 1977–82 a randomized single area hail suppression experiment was conducted in Central Switzerland, testing the Soviet concept of beneficial competition. For 37 seed and 50 no-seed days, rainfall data, both in and outside of the target area, have been analyzed for a possible seeding effect. “Moving grid” analyses within a range of 100 km of the seeding center showed no statistical evidence of a seeding effect for 24 h-values. For the experimental unit (9 h), an area “upwind” (with respect to the mean wind direction) of the target showed a statistically significant increase in rainfall of 118% on seed days, although no “upwind” effect should be expected. The seed ensemble in that area is dominated by four days with large rainfall amounts. Hence it must be concluded that, despite randomization, the effect is due to natural variability. Other effects in the target or “downwind” must likewise be regarded as random. Smaller time intervals have also been tested, but the results are inconclusive.
Abstract
During the years 1977–82 a randomized single area hail suppression experiment was conducted in Central Switzerland, testing the Soviet concept of beneficial competition. For 37 seed and 50 no-seed days, rainfall data, both in and outside of the target area, have been analyzed for a possible seeding effect. “Moving grid” analyses within a range of 100 km of the seeding center showed no statistical evidence of a seeding effect for 24 h-values. For the experimental unit (9 h), an area “upwind” (with respect to the mean wind direction) of the target showed a statistically significant increase in rainfall of 118% on seed days, although no “upwind” effect should be expected. The seed ensemble in that area is dominated by four days with large rainfall amounts. Hence it must be concluded that, despite randomization, the effect is due to natural variability. Other effects in the target or “downwind” must likewise be regarded as random. Smaller time intervals have also been tested, but the results are inconclusive.
Abstract
Ground-and radar-measured patterns of hail kinetic energy from eight hailstorms have been compared. The radar patterns were shifted horizontally in such a way that the correlation coefficient between the ground and radar data reaches a maximum. The correlation coefficients increased from .7 (no shift) to .9 (optimal shift) on average. The “optimal” shift vector is in good agreement with conceptual models about the kinematics of the storms.
The influence of microphysical effects and of the storm dynamics on the agreement between the hailpad-and radar-measured quantities is discussed in detail. The melting of hailstones and the shape of hailstone spectra have been considered in additional analyses, and the impact of these effects on the ground and radar measurements could be isolated. The results imply that the melting of hailstones is more pronounced in supercell storms than in single-cell storms or in multicell storms.
Abstract
Ground-and radar-measured patterns of hail kinetic energy from eight hailstorms have been compared. The radar patterns were shifted horizontally in such a way that the correlation coefficient between the ground and radar data reaches a maximum. The correlation coefficients increased from .7 (no shift) to .9 (optimal shift) on average. The “optimal” shift vector is in good agreement with conceptual models about the kinematics of the storms.
The influence of microphysical effects and of the storm dynamics on the agreement between the hailpad-and radar-measured quantities is discussed in detail. The melting of hailstones and the shape of hailstone spectra have been considered in additional analyses, and the impact of these effects on the ground and radar measurements could be isolated. The results imply that the melting of hailstones is more pronounced in supercell storms than in single-cell storms or in multicell storms.
Abstract
The main results of a randomized hail suppression experiment, Grossversuch IV, are presented in this paper. Grossversuch IV tested the “Soviet” hail prevention method during five years (1977–81). The field experiment took place in central Switzerland with the participation of research groups from France, Italy and Switzerland.
A very dense hailpad network (330 hailpads over 1300 km2) and a carefully calibrated 10-cm radar were used to measure in two independent ways the hail kinetic energy of seeded and unseeded hail cells. The total sample included 216 cells. The main result of the confirmatory as well as most of the exploratory analyses is that there is no statistically significant difference between seeded and unseeded hail cells. A detailed discussion of the reliability of the measurements, tests and methods is given together with a discussion about possibilities of future evaluations of the Grossversuch IV data and other cloud seeding experiments.
Abstract
The main results of a randomized hail suppression experiment, Grossversuch IV, are presented in this paper. Grossversuch IV tested the “Soviet” hail prevention method during five years (1977–81). The field experiment took place in central Switzerland with the participation of research groups from France, Italy and Switzerland.
A very dense hailpad network (330 hailpads over 1300 km2) and a carefully calibrated 10-cm radar were used to measure in two independent ways the hail kinetic energy of seeded and unseeded hail cells. The total sample included 216 cells. The main result of the confirmatory as well as most of the exploratory analyses is that there is no statistically significant difference between seeded and unseeded hail cells. A detailed discussion of the reliability of the measurements, tests and methods is given together with a discussion about possibilities of future evaluations of the Grossversuch IV data and other cloud seeding experiments.
