Effects of cloud-droplet spectra on the average surface-temperature of ice accreted on fixed cylindrical collectors

E. E. AVILA; N. E. CASTELLANO; C. P. R. SAUNDERS

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY

ROYAL METEOROLOGICAL SOCIETY

Año: 1999 vol. 125 p. 1059 - 1074

0035-9009

An experimental study of the heat balance of a stationary cylindrical collector accreting supercooled water droplets has shown a new dependence on the sizes of the water droplets in the laboratory cloud. In a study in 1967, MacMin and Payne related the steady-state heat-release during accretion to the heat loss by convection and conduction; their equation involved a numerical factor x for which they assumed a value of 0.28. The present study has shown that x is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s-' for a mean volume-weighted droplet-diameter of 18 pm, and that x approaches 0.3 for droplets greater than 30 pm diameter. The results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.of a stationary cylindrical collector accreting supercooled water droplets has shown a new dependence on the sizes of the water droplets in the laboratory cloud. In a study in 1967, MacMin and Payne related the steady-state heat-release during accretion to the heat loss by convection and conduction; their equation involved a numerical factor x for which they assumed a value of 0.28. The present study has shown that x is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s-' for a mean volume-weighted droplet-diameter of 18 pm, and that x approaches 0.3 for droplets greater than 30 pm diameter. The results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.x for which they assumed a value of 0.28. The present study has shown that x is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s-' for a mean volume-weighted droplet-diameter of 18 pm, and that x approaches 0.3 for droplets greater than 30 pm diameter. The results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.x is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s-' for a mean volume-weighted droplet-diameter of 18 pm, and that x approaches 0.3 for droplets greater than 30 pm diameter. The results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.x approaches 0.3 for droplets greater than 30 pm diameter. The results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.of small water-droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.of hailstone growth. Furthermore, the effect of droplet size may influence ice-crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.