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- Author or Editor: Griffith M. Morgan Jr. x
- Journal of Applied Meteorology and Climatology x
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Abstract
The Italian Po Valley hail problem is examined and a description is presented of its economic, dimensions, its climatology, and some of the meteorological factors which influence it. A brief history of hail prevention in Italy is presented, covering ancient beginnings and tracing the development of the use of explosives employed by farmers at the present time in the Po Valley.
Italy has the worst hail problem in the world, the estimated average low being $1333 per square mile W annum, nationwide, with an average loss reaching $7106 per square mile on a smaller scale in the Po Valley of North Italy.
The great crop loss to hail is not due to excessively frequent hall. Point and areal hail-day frequencies are lower than many other hail areas in the world. The great loss value is due to a combination of 1) high crop value, 2) high hall frequency during the growth season, 3) storms that are large in areal extent, 4) frequent large hail, 5) long hailfall durations, and 6) large numbers of hailstones per square foot. The meteorological cause is found in the unique terrain configuration of the Po Valley and the cyclonic development which it causes during the passage of synoptic systems.
Abstract
The Italian Po Valley hail problem is examined and a description is presented of its economic, dimensions, its climatology, and some of the meteorological factors which influence it. A brief history of hail prevention in Italy is presented, covering ancient beginnings and tracing the development of the use of explosives employed by farmers at the present time in the Po Valley.
Italy has the worst hail problem in the world, the estimated average low being $1333 per square mile W annum, nationwide, with an average loss reaching $7106 per square mile on a smaller scale in the Po Valley of North Italy.
The great crop loss to hail is not due to excessively frequent hall. Point and areal hail-day frequencies are lower than many other hail areas in the world. The great loss value is due to a combination of 1) high crop value, 2) high hall frequency during the growth season, 3) storms that are large in areal extent, 4) frequent large hail, 5) long hailfall durations, and 6) large numbers of hailstones per square foot. The meteorological cause is found in the unique terrain configuration of the Po Valley and the cyclonic development which it causes during the passage of synoptic systems.
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Studies of small-scale variability of hailfall parameters are being pursued using fine-scale networks of passive hail sensors of various designs. These studies have revealed the great variability which exists in objective hail parameters over very short distances. The objective of the fine-scale measurements is to eventually produce a statistical hailstreak model with which to assess the uncertainty produced by making areal hail estimates with coarse networks as part of hail prevention experiments. An example of such an assessment for a single hailstreak crop-loss pattern illustrates the problem and demonstrates that, for the particular damage pattern used, a square grid with 1 mi spacing would estimate the areal damage within 25% accuracy 80% of the time.
Abstract
Studies of small-scale variability of hailfall parameters are being pursued using fine-scale networks of passive hail sensors of various designs. These studies have revealed the great variability which exists in objective hail parameters over very short distances. The objective of the fine-scale measurements is to eventually produce a statistical hailstreak model with which to assess the uncertainty produced by making areal hail estimates with coarse networks as part of hail prevention experiments. An example of such an assessment for a single hailstreak crop-loss pattern illustrates the problem and demonstrates that, for the particular damage pattern used, a square grid with 1 mi spacing would estimate the areal damage within 25% accuracy 80% of the time.
Abstract
Surface winds which accompany the fall of hail have a profound effect on crop damage. Quantitative estimates of the horizontal and total flux of hailstone kinetic energy can be made with simple theoretical considerations using data obtained from a hailcube. A hailcube is a box with aluminum foil wrapped styrofoam pads on four sides and the top. The analytical procedure for obtaining the energy estimates from cubes is described. Results show that the total kinetic energy, which includes the effect of the wind speed, can be up to five times greater than the vertical kinetic energy—the energy imparted without the effect of the wind.
Abstract
Surface winds which accompany the fall of hail have a profound effect on crop damage. Quantitative estimates of the horizontal and total flux of hailstone kinetic energy can be made with simple theoretical considerations using data obtained from a hailcube. A hailcube is a box with aluminum foil wrapped styrofoam pads on four sides and the top. The analytical procedure for obtaining the energy estimates from cubes is described. Results show that the total kinetic energy, which includes the effect of the wind speed, can be up to five times greater than the vertical kinetic energy—the energy imparted without the effect of the wind.
Abstract
Potential ice nuclei, particles which become ice nuclei when properly treated, are produced in automotive exhaust. They are activated by iodine vapor and are believed to be lead particles originating from the tetraethyl lead mixed with the fuel. The sensitivity of nucleation measurements provides an excellent method of counting submicron lead particles and monitoring the automotive component of air pollution. Measurements reported here show that the production of potential ice nuclei by a gasoline engine is at least 2 × 107 per gram Pb at −10C, 1 × 1010 per gram Pb at −15C and 1 × 1012 per gram Pb at −20C.
Some simple calculations are presented, showing that large enough numbers of potential ice nuclei are produced by the routine burning of gasoline to be useful in cloud and weather modification research. In particular, a DC-6 aircraft burning 6 gal min−1 of gasoline should produce at least 4 × 1011 nuclei sec−1 at −20C.
It is demonstrated that ethylene diiodide can be added to the gasoline supply of an automobile and that the automobile will then act as an inexpensive source of large numbers of ice nuclei.
Abstract
Potential ice nuclei, particles which become ice nuclei when properly treated, are produced in automotive exhaust. They are activated by iodine vapor and are believed to be lead particles originating from the tetraethyl lead mixed with the fuel. The sensitivity of nucleation measurements provides an excellent method of counting submicron lead particles and monitoring the automotive component of air pollution. Measurements reported here show that the production of potential ice nuclei by a gasoline engine is at least 2 × 107 per gram Pb at −10C, 1 × 1010 per gram Pb at −15C and 1 × 1012 per gram Pb at −20C.
Some simple calculations are presented, showing that large enough numbers of potential ice nuclei are produced by the routine burning of gasoline to be useful in cloud and weather modification research. In particular, a DC-6 aircraft burning 6 gal min−1 of gasoline should produce at least 4 × 1011 nuclei sec−1 at −20C.
It is demonstrated that ethylene diiodide can be added to the gasoline supply of an automobile and that the automobile will then act as an inexpensive source of large numbers of ice nuclei.
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For the past three years, a Learjet has been making microphysical measurements in new cloud development on the flanks of multicellular storms in the eastern Transvaal area of South Africa. Data from an imaging probe and a forward scattering spectrometer have been averaged for each storm for all first cloud penetrations between −8° and −12°C. Clear images of drops of diameters greater than 300 μm are found in 40% of the 42 storms measured.
Most of the observed drops are associated with the more “maritime” droplet spectra. Also, the appearance of coalescence around −10°C appears to be related to cloud base temperatures and buoyancies, rather than changes in air masses, suggesting that cloud thermodynamics may play a dominant role in determining cloud microphysics in the Nelspruit area.
Abstract
For the past three years, a Learjet has been making microphysical measurements in new cloud development on the flanks of multicellular storms in the eastern Transvaal area of South Africa. Data from an imaging probe and a forward scattering spectrometer have been averaged for each storm for all first cloud penetrations between −8° and −12°C. Clear images of drops of diameters greater than 300 μm are found in 40% of the 42 storms measured.
Most of the observed drops are associated with the more “maritime” droplet spectra. Also, the appearance of coalescence around −10°C appears to be related to cloud base temperatures and buoyancies, rather than changes in air masses, suggesting that cloud thermodynamics may play a dominant role in determining cloud microphysics in the Nelspruit area.
Abstract
A description is given of a broad program to Design and Experiment to Suppress Hail (DESH) in Illinois. This program draws on results acquired during 17 years of extensive hail research in Illinois. There are two principal tasks to DESH: the determination of the desirability and the feasibility of hail suppression experimentation in Illinois and the Midwest. Socio-economic studies have led to an affirmative conclusion on the desirability issues. The feasibility decision appears affirmative and rests on certain key results. Airborne cloud base seeding in the humid midwestern environment is possible but will be more difficult and expensive than in less humid areas. Radar will be needed for short-term forecasting, aircraft operations, identification of potential hailstorms, and in the evaluation of seeding effectiveness. Weather forecasting by objective techniques will be valuable in both operations and evaluation, and adequate objective techniques have been largely developed. The overall shape of the proposed experiment is now clear. It will consist of an impact monitoring effort, which will make assessments of societal, environmental and economic impacts and communicate with the public; an operational effort to execute the experiment according to the final detailed design; and an evaluation effort combining a variety of surface, synoptic and radar data to assess the efficacy of the chosen seeding technique.
Abstract
A description is given of a broad program to Design and Experiment to Suppress Hail (DESH) in Illinois. This program draws on results acquired during 17 years of extensive hail research in Illinois. There are two principal tasks to DESH: the determination of the desirability and the feasibility of hail suppression experimentation in Illinois and the Midwest. Socio-economic studies have led to an affirmative conclusion on the desirability issues. The feasibility decision appears affirmative and rests on certain key results. Airborne cloud base seeding in the humid midwestern environment is possible but will be more difficult and expensive than in less humid areas. Radar will be needed for short-term forecasting, aircraft operations, identification of potential hailstorms, and in the evaluation of seeding effectiveness. Weather forecasting by objective techniques will be valuable in both operations and evaluation, and adequate objective techniques have been largely developed. The overall shape of the proposed experiment is now clear. It will consist of an impact monitoring effort, which will make assessments of societal, environmental and economic impacts and communicate with the public; an operational effort to execute the experiment according to the final detailed design; and an evaluation effort combining a variety of surface, synoptic and radar data to assess the efficacy of the chosen seeding technique.
