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- Author or Editor: A. S. Dennis x
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Abstract
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Abstract
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Abstract
Examination of radar records shows that snow trails frequently occur around the tops of showers. Evidence has been sought that showers are occasionally initiated by the seeding of supercooled cumulus clouds by snow. Certain observed radar patterns suggest strongly that showers were produced in this manner. As a check, plan diagrams with height contours have been synthesized and used to organize vertical sections obtained on different bearings. The constructed plan diagrams show showers occurring in regions of snow trails more frequently than elsewhere.
Abstract
Examination of radar records shows that snow trails frequently occur around the tops of showers. Evidence has been sought that showers are occasionally initiated by the seeding of supercooled cumulus clouds by snow. Certain observed radar patterns suggest strongly that showers were produced in this manner. As a check, plan diagrams with height contours have been synthesized and used to organize vertical sections obtained on different bearings. The constructed plan diagrams show showers occurring in regions of snow trails more frequently than elsewhere.
Abstract
No abstract available.
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Abstract
The distribution in time of individual lightning flashes recorded visually during 20 storms in New Mexico and on 23-cm radar screens during several storms in the south-central United States has been analyzed. The logarithms of the intervals between flashes within a given storm are normally distributed with a standard deviation σ of approximately one natural-log unit. The available data do not reject the hypothesis that there are no statistically significant variations in σ among storms. The autocorrelation of the intervals between flashes in one storm is very small. The implications of these findings are briefly explored.
Abstract
The distribution in time of individual lightning flashes recorded visually during 20 storms in New Mexico and on 23-cm radar screens during several storms in the south-central United States has been analyzed. The logarithms of the intervals between flashes within a given storm are normally distributed with a standard deviation σ of approximately one natural-log unit. The available data do not reject the hypothesis that there are no statistically significant variations in σ among storms. The autocorrelation of the intervals between flashes in one storm is very small. The implications of these findings are briefly explored.
Abstract
First radar echoes on a randomized cloud seeding project in North Dakota appeared closer to cloud base and at higher temperatures on seed days than on no-seed days. The average first echo temperature was near −11°C on no-seed days and −7°C on seed days.
Abstract
First radar echoes on a randomized cloud seeding project in North Dakota appeared closer to cloud base and at higher temperatures on seed days than on no-seed days. The average first echo temperature was near −11°C on no-seed days and −7°C on seed days.
Abstract
A hailstone model is developed which simulates both wet and dry hailstone growth and partial or complete melting as the hailstone falls to the ground. The simulation is obtained by a consideration of the mass and heat budgets of the hailstone as a function of its size and of the environmental conditions. Competition among hailstone embryos is not treated in this model.
The hailstone model has been run in over 50 versions of a one-dimensional, time-dependent cloud model to derive estimates of maximum hailstone size from a wide variety of convective storms. The model suggests that hailstone diameter at the ground is determined closely by the strongest updraft encountered by the stone and the temperature at that level. In the model, most hailstones spend some time above the maximum updraft and significant growth occurs during descent from that level to the freezing level. A comparison of model predictions to hailstone observations in the Rapid City area during 1968 and 1969 shows fair agreement.
The model has been used to test the concept of hail suppression through artificial glaciation of cloud water and rainwater. It suggests that results would vary with temperature at the level of maximum updraft, but that artificial cloud glaciation would lead in a majority of cases to a reduction in maximum hailstone size at the ground.
Abstract
A hailstone model is developed which simulates both wet and dry hailstone growth and partial or complete melting as the hailstone falls to the ground. The simulation is obtained by a consideration of the mass and heat budgets of the hailstone as a function of its size and of the environmental conditions. Competition among hailstone embryos is not treated in this model.
The hailstone model has been run in over 50 versions of a one-dimensional, time-dependent cloud model to derive estimates of maximum hailstone size from a wide variety of convective storms. The model suggests that hailstone diameter at the ground is determined closely by the strongest updraft encountered by the stone and the temperature at that level. In the model, most hailstones spend some time above the maximum updraft and significant growth occurs during descent from that level to the freezing level. A comparison of model predictions to hailstone observations in the Rapid City area during 1968 and 1969 shows fair agreement.
The model has been used to test the concept of hail suppression through artificial glaciation of cloud water and rainwater. It suggests that results would vary with temperature at the level of maximum updraft, but that artificial cloud glaciation would lead in a majority of cases to a reduction in maximum hailstone size at the ground.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
Salt seeding took place below one end of a line of stratocumulus clouds with 350 lb of NaCl released. Cloud base was 9000 ft and cloud tops were at 15 to 18,000 ft above sea level. Cloud top temperature was near −2C and updraft speeds below the hue were near 3 m sec−1. The resulting shower was monitored by radar with the total rainfall being estimated at 280 acre feet. No rain fell from the unseeded portion of the cloud line or from any other clouds within 50 mi.
Abstract
Salt seeding took place below one end of a line of stratocumulus clouds with 350 lb of NaCl released. Cloud base was 9000 ft and cloud tops were at 15 to 18,000 ft above sea level. Cloud top temperature was near −2C and updraft speeds below the hue were near 3 m sec−1. The resulting shower was monitored by radar with the total rainfall being estimated at 280 acre feet. No rain fell from the unseeded portion of the cloud line or from any other clouds within 50 mi.
Abstract
Silver iodide seeding of convective clouds in a number of experiments in South Dakota has yielded mixed results, including both increases and decreases in rainfall and, apparently, decreases in hail. The results vary with the synoptic situation and with location with respect to the silver iodide release point; there is tentative evidence that they can extend upwind. Two dynamic effects of seeding are postulated, namely, increased growth of seeded clouds and the suppression of neighboring clouds at distances of some tens of miles.
Abstract
Silver iodide seeding of convective clouds in a number of experiments in South Dakota has yielded mixed results, including both increases and decreases in rainfall and, apparently, decreases in hail. The results vary with the synoptic situation and with location with respect to the silver iodide release point; there is tentative evidence that they can extend upwind. Two dynamic effects of seeding are postulated, namely, increased growth of seeded clouds and the suppression of neighboring clouds at distances of some tens of miles.
