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- Author or Editor: S. G. Bradley x
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Abstract
An analytic model of three-dimensional radiative transfer is modified to include cloud-cloud interactions and finite surface albedo. The spectrally integrated output is used to derive extinction coefficients for cumulus clouds from aircraft observations of cloud albedo and directional reflectance. Four independent estimates of extinction coefficient are compared for various actual and postulated boundary conditions. Surface albedo is found to be an important parameter. Results suggest it is possible to remotely detect microphysical differences between clouds growing in different air masses using broad-band measurements.
Abstract
An analytic model of three-dimensional radiative transfer is modified to include cloud-cloud interactions and finite surface albedo. The spectrally integrated output is used to derive extinction coefficients for cumulus clouds from aircraft observations of cloud albedo and directional reflectance. Four independent estimates of extinction coefficient are compared for various actual and postulated boundary conditions. Surface albedo is found to be an important parameter. Results suggest it is possible to remotely detect microphysical differences between clouds growing in different air masses using broad-band measurements.
Abstract
The design of an instrument that sorts raindrops according to fall speed is described. The apparatus consists of two rotating disks, the upper one allowing rain to fall through a slit into collectors on the lower disk. Drops are collected in a manner allowing chemical concentrations and pH to be determined as a function of drop size. Laboratory and field tests validate the detailed design theory for conditions of low windspeed.
Abstract
The design of an instrument that sorts raindrops according to fall speed is described. The apparatus consists of two rotating disks, the upper one allowing rain to fall through a slit into collectors on the lower disk. Drops are collected in a manner allowing chemical concentrations and pH to be determined as a function of drop size. Laboratory and field tests validate the detailed design theory for conditions of low windspeed.
Abstract
Raindrop size distributions are obtained from the Doppler frequency spectrum of an acoustic radar. Number concentrations of 12 drop diameters with a minimum diameter 0.14 cm are obtained and averaged over 3–15 min at 20-m range gates from 20 to 220 m. The last three range gates are used to estimate rain intensity–dependent background noise, which is dynamically subtracted from the signals. Multifrequency sounding is also used.
Intercomparisons with the vertical rain intensity profile from an X-band radar and with drop size distributions from an impact disdrometer show general agreement between instruments and demonstrate the usefulness of the acoustic profiler in giving vertical continuity below the range of electromagnetic radars. Temporal variations in raindrop size distributions are found to have an essentially flat spectrum for periodicities shorter than 12 min, although the step response to a sudden change in rainfall rate is a function of drop size. Principal component analysis applied to a time series of drop spectra shows that nearly all the variation is at the large-drop end. The utility of the acoustic radar is demonstrated for examining the microphysics of rain through time-dependent changes.
Abstract
Raindrop size distributions are obtained from the Doppler frequency spectrum of an acoustic radar. Number concentrations of 12 drop diameters with a minimum diameter 0.14 cm are obtained and averaged over 3–15 min at 20-m range gates from 20 to 220 m. The last three range gates are used to estimate rain intensity–dependent background noise, which is dynamically subtracted from the signals. Multifrequency sounding is also used.
Intercomparisons with the vertical rain intensity profile from an X-band radar and with drop size distributions from an impact disdrometer show general agreement between instruments and demonstrate the usefulness of the acoustic profiler in giving vertical continuity below the range of electromagnetic radars. Temporal variations in raindrop size distributions are found to have an essentially flat spectrum for periodicities shorter than 12 min, although the step response to a sudden change in rainfall rate is a function of drop size. Principal component analysis applied to a time series of drop spectra shows that nearly all the variation is at the large-drop end. The utility of the acoustic radar is demonstrated for examining the microphysics of rain through time-dependent changes.
Abstract
Laboratory and airborne observations show that the protective hemispheres of aircraft pyrgeometers are partly covered by water when used in cloud. This cover can reduce the incident longwave flux by as much as 60%. Improved agreement between observations and theory is obtained when a parameterization of water cover in terms of cloud liquid water content is used to correct flux divergence and cooling rate data. It is suggested that all previous in-cloud pyrgeometer measurements may suffer cloud-water contamination.
Abstract
Laboratory and airborne observations show that the protective hemispheres of aircraft pyrgeometers are partly covered by water when used in cloud. This cover can reduce the incident longwave flux by as much as 60%. Improved agreement between observations and theory is obtained when a parameterization of water cover in terms of cloud liquid water content is used to correct flux divergence and cooling rate data. It is suggested that all previous in-cloud pyrgeometer measurements may suffer cloud-water contamination.
Abstract
Precipitation and temperature data since records began in southwestern Colorado are analyzed on a seasonal basis. Interstation correlations for recent years indicate that the region responds fairly uniformly to seasonal variations in precipitation, but this was not true earlier this century when precipitation variability was higher. Changes in the dependence of precipitation on elevation are also shown. Annual precipitation totals were low about 1860, 1900, 1930–35 and 1950–55. Mean annual temperatures appear to have fallen from about 1867 to about 1930 when the trend reversed. Overall, the climate of southwestern Colorado in the 1860s appears to have been warmer and at least as dry as current normals.
Abstract
Precipitation and temperature data since records began in southwestern Colorado are analyzed on a seasonal basis. Interstation correlations for recent years indicate that the region responds fairly uniformly to seasonal variations in precipitation, but this was not true earlier this century when precipitation variability was higher. Changes in the dependence of precipitation on elevation are also shown. Annual precipitation totals were low about 1860, 1900, 1930–35 and 1950–55. Mean annual temperatures appear to have fallen from about 1867 to about 1930 when the trend reversed. Overall, the climate of southwestern Colorado in the 1860s appears to have been warmer and at least as dry as current normals.
Abstract
The effect of individual charge-modifying processes is tested by following the development joint distributions of raindrop size and charge through a fall depth of 1 km beneath a weakly electrified warm cloud. Evaporation, ion capture and coalescence all cause the small-drop charge distribution to become narrower and any initially skewed distribution to become more symmetrical. Ion capture does not result in substantial negative charging unless the initial charge distribution is very narrow. Ion diffusion charging is found not to be significant.
Abstract
The effect of individual charge-modifying processes is tested by following the development joint distributions of raindrop size and charge through a fall depth of 1 km beneath a weakly electrified warm cloud. Evaporation, ion capture and coalescence all cause the small-drop charge distribution to become narrower and any initially skewed distribution to become more symmetrical. Ion capture does not result in substantial negative charging unless the initial charge distribution is very narrow. Ion diffusion charging is found not to be significant.
Abstract
Raindrop collisional breakup is included in a model of joint size-charge distribution development. Consistent with experimental observations the model includes a finite filament (joining separating drops) that upon rupture produces charged satellite droplets. It is shown that for positive fields, large numbers of small drops carry negative charge, leading to an increasingly negative space charge with fall depth. The model also suggests that larger separated charge exists on the major drop products than previously estimated.
Abstract
Raindrop collisional breakup is included in a model of joint size-charge distribution development. Consistent with experimental observations the model includes a finite filament (joining separating drops) that upon rupture produces charged satellite droplets. It is shown that for positive fields, large numbers of small drops carry negative charge, leading to an increasingly negative space charge with fall depth. The model also suggests that larger separated charge exists on the major drop products than previously estimated.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
Data derived from an experimental investigation of the drop collision problem are described in which the numbers of satellite droplets per collision N g was found. 1026 separate collisions were observed of which 266 resulted in coalescence without breakup, and at least 405 produced the so-called satellite droplets. The value of N g varied from zero to seven, with average values N¯ g proving to be a linear function of the collision speed U, where N¯ g could be predicted by the relationship N¯ g=3.5 (U−1) if U>1 m s−1. For impact speeds of less than 1 m s−1, negligible number of satellites were produced. It proved impossible to correlate N¯ g with either the impact parameter or the drop charge, both of which could be accurately controlled, but there appeared to be a dependence of N¯ g on both a dimensionless parameter of rotational energy and a dimensionless parameter of electrostatic energy for a given collision. The statistical nature of the data is emphasized in relation to computations on raindrop distributions.
Abstract
Data derived from an experimental investigation of the drop collision problem are described in which the numbers of satellite droplets per collision N g was found. 1026 separate collisions were observed of which 266 resulted in coalescence without breakup, and at least 405 produced the so-called satellite droplets. The value of N g varied from zero to seven, with average values N¯ g proving to be a linear function of the collision speed U, where N¯ g could be predicted by the relationship N¯ g=3.5 (U−1) if U>1 m s−1. For impact speeds of less than 1 m s−1, negligible number of satellites were produced. It proved impossible to correlate N¯ g with either the impact parameter or the drop charge, both of which could be accurately controlled, but there appeared to be a dependence of N¯ g on both a dimensionless parameter of rotational energy and a dimensionless parameter of electrostatic energy for a given collision. The statistical nature of the data is emphasized in relation to computations on raindrop distributions.
Abstract
A recent treatment of the dynamic behavior of anemometer hot wires is simplified and used to show that the response of the CSIRO liquid-water hot wire can be described by a second-order differential equation. This is confirmed by experiment, and it is shown that the inherent time scale is fully calculable in terms of the thermal properties of the wire and its support and the amplifier constants. For most clouds a response time of 0.005 s can be readily achieved.
Abstract
A recent treatment of the dynamic behavior of anemometer hot wires is simplified and used to show that the response of the CSIRO liquid-water hot wire can be described by a second-order differential equation. This is confirmed by experiment, and it is shown that the inherent time scale is fully calculable in terms of the thermal properties of the wire and its support and the amplifier constants. For most clouds a response time of 0.005 s can be readily achieved.
