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Roberto Fraile - One of the best experts on this subject based on the ideXlab platform.
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maximum Hailstone size relationship with meteorological variables
Atmospheric Research, 2010Co-Authors: Covadonga Palencia, A Castro, Dario Giaiotti, Fulvio Stel, Roberto FraileAbstract:Abstract The damage caused to property by hail mainly depends on the size of the Hailstones. This paper explores the possibility of forecasting the maximum Hailstone size registered on a particular day using sounding data. The data employed for the study are those provided by hail events registered over an 11-year period in the hailpad network in the plain of Friuli-Venezia-Giulia, in Italy. As for the description of the atmosphere, the most common weather variables (stability indices, layer thickness, kinetic variables, temperatures, etc.) were obtained from the daily sounding carried out at Udine, a city almost in the middle of the Friulian plain. Only the days with sounding data and with dents on the hailpads were considered for the study: a minimum of 10 dents per plate was established as the lower threshold. The final sample that fulfilled these conditions included 313 days. A detailed study was carried out on the relationship between the weather variables before the hail event and daily data on hail size. The results show that the variable that relates best to hail size is the drop in surface pressure in the 12 h immediately prior to the hail event, as well as the lifted index. Principal component analysis was applied to the weather variables. The first eight principal components were used together with the drop in pressure to establish a linear forecast model. The result improves considerably when the smaller Hailstones are not considered, with sizes smaller than 10 or 15 mm.
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the influence of melting on Hailstone size distribution
Atmospheric Research, 2003Co-Authors: Roberto Fraile, A Castro, Laura Lopez, J L Sanchez, Covadonga PalenciaAbstract:AbstractThe physical properties of Hailstones registered by a hailpad network (size distribution, mass,kinetic energy) are essential data for the establishment of a regional hail climatology. Nevertheless,when comparing these data to the same properties of Hailstones inside the cloud, the melting processmust be taken into account. This paper presents a brief theoretical study of the changes effected onHailstone size distribution due to the melting process. The paper is based on previous studies dealingwith the melting of Hailstones before they reach the ground. The aim is to analyze the influence ofthis melting process on Hailstone size distribution. An initial melting simulation was carried out inorder to achieve this aim. Despite the common assumption that Hailstone size distribution on theground is exponential, it was found that when the in-cloud size distribution is exponential, on theground, there are fewer small Hailstones than what would be expected in an exponential distribution.The data registered by the hailpad network in Leo´n (Spain) for 1 year were used to estimate thesize of every Hailstone before the melting process. The results show that the Hailstone sizedistribution simulated inside the cloud resembles more closely an exponential distribution than theHailstones on the ground.The type of Hailstone size distribution inside the cloud will be the starting point for calculating theHailstone size distribution on the ground. Several equations describing the melting processes are usedtocalculate anew probability densityfunction thatinitiallycorresponds to anexponential distributionthat undergoes a partial melting process. The result is a function that is not monotonously decreasinglike the exponential function, but rather a function that has a peak for a given size. This new functionfits better the data found than the exponential function and actually resembles the gamma function.D 2003 Elsevier B.V. All rights reserved.
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the effect of silver iodide seeding on Hailstone size distributions
The Journal of Weather Modification, 2000Co-Authors: Jean Dessens, Roberto FraileAbstract:The hailpad data collected in the ANELFA operational area of southwestern France where hailstorms are extensively seeded from silver iodide ground generators show that Hailstone size distributions are modified by the seeding. In the more heavily seeded hailfalls, the number of Hailstones with diameters larger than 0.7 cm is decreased, while the number of small precipitation elements (melted or not) is increased; this result agrees with the physical hypothesis of the seeding process. As a consequence, the mean kinetic energy of the more seeded hailfalls is reduced by about 40%, which confirms a previous physical evaluation of the ANELFA project made with a lower number of hail seasons.
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Hailstone size distributions in southwestern france
Atmospheric Research, 1994Co-Authors: Jean Dessens, Roberto FraileAbstract:Abstract A hailpad network, intended to draw up a large-scale, long-term physical climatology of hailfalls, is being installed in southwestern France, one of the severely hailed regions in the world. The first five years of operation of this network have enabled the organization of a suitable standardization of the data. The classical exponential form is well adapted to represent the mean size distribution of the Hailstones sampled at several locations, but we suggest the replacement of the usual concentration parameter of this form—the number of zero diameter Hailstones—by the number of the smallest Hailstones really counted on the pads, so as not to amplify, with the regression, a relationship between this parameter and the slope parameter. There is a significant correlation between the concentration parameter and the altitude of the 0°C isotherm level, and a regression enables the determination of a concentration parameter at the 0°C level. By contrast, the correlation between the slope parameter and the altitude of the 0°C level is weak. When these results are compared with Ludlam's model of Hailstone melting, they suggest that hail mainly falls within downdrafts. With the limited amount of data presently available, no correlation appears between the distribution parameters and the storm thermodynamics, but the concentration parameter is larger while the slope parameter is smaller in the frontal storms than in the intramass ones, a result explaining why the most severe hailstorms of southwestern France are frontal.
Roland List - One of the best experts on this subject based on the ideXlab platform.
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new Hailstone physics part i heat and mass transfer hmt and growth
Journal of the Atmospheric Sciences, 2014Co-Authors: Roland ListAbstract:AbstractAn all-encompassing new theory of heat and mass transfer (HMT) and growth equations have been developed for freely falling spherical Hailstones with diameters of 0.5–8 cm. The initial six variables are diameter, liquid water content, air and Hailstone surface temperatures, net collection efficiency, and ice fraction of spongy deposit. They are replaced by three or four new ones, depending on the three growth categories. Two new variables are products of “old” ones: (i) the square root of the Reynolds number Re and the liquid water content and (ii) net collection efficiency and ice fraction of the spongy deposit. Only the products matter, not the individual parts. [The two variables in (ii) are as important as the two in (i).] Two old variables remain: air and surface temperatures. The HMT can be further compacted for hailstorms with specified pressure–air temperature–height profiles. Further, Re for free-fall reveals unexpected complexities—issues important to solve HMT problems.The “new Hailstone...
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Experimental Closure of the Heat and Mass Transfer Theory of Spheroidal Hailstones
Journal of the Atmospheric Sciences, 1995Co-Authors: Blair J. W. Greenan, Roland ListAbstract:Abstract Hailstone growth experiments were performed in a vertical icing wind tunnel using 2-cm oblate ice spheroids (axis ratio of 0.67) mounted on a gyrator system. The liquid water content ranged from 1 to 5 g m−3, air temperature from −21° to −3°C, air speed from 9 to 24 m s−1, and air pressure from 40 to 100 kPa. Icing time, ice and water mass of the Hailstone deposit, and final major and minor axis diameters were measured to determine the accretion of supercooled droplets from the air flow. An infrared imaging system was used to measure local and mean Hailstone surface temperatures. These experiments allowed calculation of the last two unknowns in the heat and mass transfer equations for spheroidal Hailstones: the net collection efficiency, Enet = 0.59 K0.15 (over a Stokes parameter range of 6 ≤ K ≤ 18), and the Nusselt number, Nu = 0.15 Re0.69 (over a Reynolds number range of 13 000 ≤ Re ≤ 50 000, that is, freely falling Hailstones with diameters of ∼1 to ∼3 cm). The net collection efficiency resul...
S O Shiryaeva - One of the best experts on this subject based on the ideXlab platform.
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nonlinear calculation of the electric field strength on the surface of a melting Hailstone in a thundercloud
Technical Physics, 2011Co-Authors: V A Koromyslov, A I Grigorev, S O Shiryaeva, Yu N ZhigalkoAbstract:The contribution of aerodynamic pressure acting on the surface of a water layer to a total electric field near the free surface of the layer is considered. The layer covers a charged melting Hailstone moving parallel to the external electrostatic field vector. An asymptotic analytical expression for the electric field strength near a water-covered Hailstone is derived in an approximation that is quadratic in the amplitude of capillary oscillations of a charged conducting liquid layer on the surface of the Hailstone. It is found that the motion of the Hailstone in ambient air influences the total electric field near the Hailstone only slightly but noticeably enhances energy exchange between neighboring oscillation modes. An air flow about the Hailstone is shown to have an appreciable effect on the possibility of nonlinear resonance energy exchange between initially excited modes and modes due to the nonlinear interaction.
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on the possibility of corona initiation at the surface of a liquid layer nonlinearly oscillating on the surface of a charged Hailstone placed in a uniform electrostatic field
Technical Physics, 2010Co-Authors: A I Grigorev, V A Koromyslov, S O ShiryaevaAbstract:An expression for the electric field strength near a watered Hailstone is derived in an approximation quadratic in the amplitude of capillary oscillations of a charged conducting liquid layer covering the Hailstone. As the number of the mode governing the initial deformation of the equilibrium spherical free surface of the liquid layer increases and its thickness decreases, the electric field strength in the neighborhood of the capillary wave crests rises. Even in the case of small charges and low electric fields, the electric field near the Hailstone is high enough to initiate a corona.
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on corona discharge near the surface of a water layer nonlinear oscillating in an external electrostatic field on the surface of a melting Hailstone
Surface Engineering and Applied Electrochemistry, 2010Co-Authors: A I Grigorev, V A Koromyslov, S O ShiryaevaAbstract:The solution to the problem of nonlinear oscillations of a water layer on the surface of a melting Hailstone in a uniform external field is found. The electric field intensity near a Hailstone’s surface is calculated. It is shown that the electric field intensity on the Hailstone tops is sufficiently high for the ignition of a corona discharge.
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the physics of charging a Hailstone freely falling in a thunderstorm cloud
Technical Physics, 2010Co-Authors: A I Grigorev, D O Kornienko, S O ShiryaevaAbstract:Interaction between a charged watered coarse Hailstone and likely charged droplets in a uniform electrostatic field is analyzed using the electrostatic methods of images. It is shown that, under certain external conditions characteristic of a thunderstorm cloud, the droplets are attracted to the likely charged Hailstone. Owing to collisions with the droplets, the Hailstone freely falling in a thunderstorm cloud can gather a charge large enough to initiate a corona discharge in its vicinity.
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On the initiation of a corona discharge near the surface of a nonlinearly oscillating liquid layer on the surface of a charged Hailstone
Technical Physics, 2009Co-Authors: A. I. Grigor’ev, V A Koromyslov, S O ShiryaevaAbstract:An expression is derived for the electric field strength near a wet Hailstone in an approximation quadratic in the oscillation amplitude of a charged liquid layer on its surface. It is found that the electric field strength in a small neighborhood of the capillary wave crests grows with the number of a mode governing the initial deformation of the equilibrium (spherical) shape of the liquid layer. Even if the charge is small (when the Rayleigh parameter of the Hailstone equals one-hundredth of the value critical for stability against the self-charge), the electric field near the Hailstone is high enough for initiating a corona discharge in its vicinity.
Fulvio Stel - One of the best experts on this subject based on the ideXlab platform.
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maximum Hailstone size relationship with meteorological variables
Atmospheric Research, 2010Co-Authors: Covadonga Palencia, A Castro, Dario Giaiotti, Fulvio Stel, Roberto FraileAbstract:Abstract The damage caused to property by hail mainly depends on the size of the Hailstones. This paper explores the possibility of forecasting the maximum Hailstone size registered on a particular day using sounding data. The data employed for the study are those provided by hail events registered over an 11-year period in the hailpad network in the plain of Friuli-Venezia-Giulia, in Italy. As for the description of the atmosphere, the most common weather variables (stability indices, layer thickness, kinetic variables, temperatures, etc.) were obtained from the daily sounding carried out at Udine, a city almost in the middle of the Friulian plain. Only the days with sounding data and with dents on the hailpads were considered for the study: a minimum of 10 dents per plate was established as the lower threshold. The final sample that fulfilled these conditions included 313 days. A detailed study was carried out on the relationship between the weather variables before the hail event and daily data on hail size. The results show that the variable that relates best to hail size is the drop in surface pressure in the 12 h immediately prior to the hail event, as well as the lifted index. Principal component analysis was applied to the weather variables. The first eight principal components were used together with the drop in pressure to establish a linear forecast model. The result improves considerably when the smaller Hailstones are not considered, with sizes smaller than 10 or 15 mm.
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the effects of environmental water vapor on Hailstone size distributions
Atmospheric Research, 2006Co-Authors: Dario Giaiotti, Fulvio StelAbstract:Abstract The aim of this work is to analyze the effects of environmental water vapor on the Hailstone size distributions as observed at the ground in the four different times-of-the-day (i.e. local morning, afternoon, evening and night) through the measurements obtained by a network of hailpads posed on the plain of Friuli Venezia Giulia (Italy). The hypothesis tested is that the observed differences in the Hailstone size distributions, i.e. larger Hailstones during nighttime than during daytime, could be related to differences in the vertical profile of environmental mixing ratio. Data obtained by a sounding carried out every 6 h in the middle of Friulian plain are used to compute the average vertical profiles in the four times-of-the-day during the warm period (i.e. from April to September). The differences in the average vertical profile of environmental mixing ratio are then used in a simple analytical model to compute their effects on the Hailstone size distributions. The results of the analytical model show that the differences in the average mixing ratio vertical profile produce effects on the Hailstone size distributions that are qualitatively (i.e. stretching of Hailstone size distribution) in agreement with the observations and with the right order of magnitude. Because of this qualitative and semi-quantitative agreement between observations and model results, the differences in the environmental water vapor are then considered as one of the main causes of the observed differences in the Hailstone size distributions in the four times-of-the-day on the plain of Friuli Venezia Giulia.
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heuristic considerations pertaining to Hailstone size distributions in the plain of friuli venezia giulia
Atmospheric Research, 2001Co-Authors: Dario Giaiotti, Elena Gianesini, Fulvio StelAbstract:Abstract In this work, the Hailstone size distributions at the ground in the plain of Friuli-Venezia Giulia are presented, as revealed through a network of polystyrene pads (hailpads), managed by volunteers, which has been active since 1988. The aim of this work is to highlight possible differences in the diurnal and seasonal behavior of hail at the ground, both from Friuli-Venezia Giulia and other countries, in order to improve the knowledge of this meteorological phenomenon. In the comparison between different countries, differences are found between the yearly size distributions of Friuli-Venezia Giulia and those of North-East Colorado, measured during the National Hail Research Experiment (NHRE). The size distributions obtained in South West France and in Friuli-Venezia Giulia are quite similar and they are slightly different from those of the Grossversuch experiment. In the comparison between different periods of the year, relevant differences are found between April and May and the other months. In particular, thunderstorms are less efficient in producing big Hailstones during the former months. The most prolific month in producing Hailstones is June, followed by September. This feature is interpreted as due to a form of synergy between the frequency of the synoptic forcing of storms and the amount of available energy at the ground. Analyzing the size distributions at different times of the day, the greatest differences are found in the intervals [00–06] and [06–12] in local time (respectively, [22–04] and [04–10] in UTC). These differences cannot be ascribed to the melting of the Hailstones during their fall.
Covadonga Palencia - One of the best experts on this subject based on the ideXlab platform.
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maximum Hailstone size relationship with meteorological variables
Atmospheric Research, 2010Co-Authors: Covadonga Palencia, A Castro, Dario Giaiotti, Fulvio Stel, Roberto FraileAbstract:Abstract The damage caused to property by hail mainly depends on the size of the Hailstones. This paper explores the possibility of forecasting the maximum Hailstone size registered on a particular day using sounding data. The data employed for the study are those provided by hail events registered over an 11-year period in the hailpad network in the plain of Friuli-Venezia-Giulia, in Italy. As for the description of the atmosphere, the most common weather variables (stability indices, layer thickness, kinetic variables, temperatures, etc.) were obtained from the daily sounding carried out at Udine, a city almost in the middle of the Friulian plain. Only the days with sounding data and with dents on the hailpads were considered for the study: a minimum of 10 dents per plate was established as the lower threshold. The final sample that fulfilled these conditions included 313 days. A detailed study was carried out on the relationship between the weather variables before the hail event and daily data on hail size. The results show that the variable that relates best to hail size is the drop in surface pressure in the 12 h immediately prior to the hail event, as well as the lifted index. Principal component analysis was applied to the weather variables. The first eight principal components were used together with the drop in pressure to establish a linear forecast model. The result improves considerably when the smaller Hailstones are not considered, with sizes smaller than 10 or 15 mm.
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the influence of melting on Hailstone size distribution
Atmospheric Research, 2003Co-Authors: Roberto Fraile, A Castro, Laura Lopez, J L Sanchez, Covadonga PalenciaAbstract:AbstractThe physical properties of Hailstones registered by a hailpad network (size distribution, mass,kinetic energy) are essential data for the establishment of a regional hail climatology. Nevertheless,when comparing these data to the same properties of Hailstones inside the cloud, the melting processmust be taken into account. This paper presents a brief theoretical study of the changes effected onHailstone size distribution due to the melting process. The paper is based on previous studies dealingwith the melting of Hailstones before they reach the ground. The aim is to analyze the influence ofthis melting process on Hailstone size distribution. An initial melting simulation was carried out inorder to achieve this aim. Despite the common assumption that Hailstone size distribution on theground is exponential, it was found that when the in-cloud size distribution is exponential, on theground, there are fewer small Hailstones than what would be expected in an exponential distribution.The data registered by the hailpad network in Leo´n (Spain) for 1 year were used to estimate thesize of every Hailstone before the melting process. The results show that the Hailstone sizedistribution simulated inside the cloud resembles more closely an exponential distribution than theHailstones on the ground.The type of Hailstone size distribution inside the cloud will be the starting point for calculating theHailstone size distribution on the ground. Several equations describing the melting processes are usedtocalculate anew probability densityfunction thatinitiallycorresponds to anexponential distributionthat undergoes a partial melting process. The result is a function that is not monotonously decreasinglike the exponential function, but rather a function that has a peak for a given size. This new functionfits better the data found than the exponential function and actually resembles the gamma function.D 2003 Elsevier B.V. All rights reserved.
