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- Author or Editor: Louis J. Battan x
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Abstract
A description is given of the distributions of radar reflectivity, mean Doppler velocity, vertical air velocity and Doppler-velocity variance in two thunderstorms over eastern Colorado. A zenith-pointing Doppler radar was used to obtain data at height intervals of 152 m. It is shown that the storms were composed of a series of turbulent updrafts, resembling those observed in hailstorms in southeastern Arizona. On the basis of similarities with thunderstorms observed elsewhere, it is speculated that the variable nature of the radar reflectivities and updrafts are a characteristic feature of most thunderstorms and that they contribute significantly to the highly variable nature of hail.
Abstract
A description is given of the distributions of radar reflectivity, mean Doppler velocity, vertical air velocity and Doppler-velocity variance in two thunderstorms over eastern Colorado. A zenith-pointing Doppler radar was used to obtain data at height intervals of 152 m. It is shown that the storms were composed of a series of turbulent updrafts, resembling those observed in hailstorms in southeastern Arizona. On the basis of similarities with thunderstorms observed elsewhere, it is speculated that the variable nature of the radar reflectivities and updrafts are a characteristic feature of most thunderstorms and that they contribute significantly to the highly variable nature of hail.
Abstract
The altitudes of the average initial precipitation echoes in convective clouds in Arizona for particular days have been compared with the altitudes of the calculated cloud base. They are found to be positively correlated. The implication of this result is that the dominant precipitation initiation mechanism in convective clouds in southern Arizona is the coalescence process.
Abstract
The altitudes of the average initial precipitation echoes in convective clouds in Arizona for particular days have been compared with the altitudes of the calculated cloud base. They are found to be positively correlated. The implication of this result is that the dominant precipitation initiation mechanism in convective clouds in southern Arizona is the coalescence process.
Abstract
Observations were made of a thunderstorm which formed over a vertically-pointing X-band pulsed-doppler radar set. They show details of the vertical velocity field in the storm and yield information about the growth of the precipitation particles. It is inferred that a downdraft starts early in the life of the cloud and is accompanied by precipitation particles which break up and evaporate under the cloud base.
Abstract
Observations were made of a thunderstorm which formed over a vertically-pointing X-band pulsed-doppler radar set. They show details of the vertical velocity field in the storm and yield information about the growth of the precipitation particles. It is inferred that a downdraft starts early in the life of the cloud and is accompanied by precipitation particles which break up and evaporate under the cloud base.
Abstract
Calculations have been made of the radar reflectivity and attenuation produced by exponential distributions of dry and wet ice spheres. Appropriate data are presented in the form of tables and graphs. It is shown that attenuation by wet spheres is substantially larger than that by dry spheres. If the ice spheres axe coated with a layer of water 0.05 cm thick and extend in diameters to ∼2 cm, they would produce two-way attenuations of about 7, 5 and 1 db km−1 at wavelengths of 3.21, 5.5 and 10.0 cm, respectively. Procedures for the radar detection of hail must take into account the attenuation caused by the hail itself.
Abstract
Calculations have been made of the radar reflectivity and attenuation produced by exponential distributions of dry and wet ice spheres. Appropriate data are presented in the form of tables and graphs. It is shown that attenuation by wet spheres is substantially larger than that by dry spheres. If the ice spheres axe coated with a layer of water 0.05 cm thick and extend in diameters to ∼2 cm, they would produce two-way attenuations of about 7, 5 and 1 db km−1 at wavelengths of 3.21, 5.5 and 10.0 cm, respectively. Procedures for the radar detection of hail must take into account the attenuation caused by the hail itself.
On the basis of a review of the abstracts of articles published in the last 5 years or so a summary has been prepared of Soviet research activity in the field of radar meteorology. A wide spectrum of topics has been getting some study, but in recent years, Soviet scientists have been giving particular attention to the following areas of research: calculations of the scattering and attenuation cross sections of various hydrometeors; the use of Doppler radar to study the turbulent properties of the atmosphere; the development of procedures by which the characteristics of radar echoes can be used to identify cloud and hydrometeor types, with particular emphasis on the discrimination of severe thunderstorms from other precipitating cloud systems; the detection and measurement of hail; and the measurement of precipitation.
On the basis of a review of the abstracts of articles published in the last 5 years or so a summary has been prepared of Soviet research activity in the field of radar meteorology. A wide spectrum of topics has been getting some study, but in recent years, Soviet scientists have been giving particular attention to the following areas of research: calculations of the scattering and attenuation cross sections of various hydrometeors; the use of Doppler radar to study the turbulent properties of the atmosphere; the development of procedures by which the characteristics of radar echoes can be used to identify cloud and hydrometeor types, with particular emphasis on the discrimination of severe thunderstorms from other precipitating cloud systems; the detection and measurement of hail; and the measurement of precipitation.
Abstract
By means of a zenith-pointing radar, observations were made of the reflectivities and Doppler spectra in orthogonal planes as a dissipating shower exhibiting a bright band passed overhead. The observations have been used to test various procedures for estimating hydrometeor parameters from measurements of radar reflectivitity. They involve assumptions that the raindrop diameters were exponentially distributed, preferably in the manner prescribed by the Marshall-Palmer distribution. It is concluded that, in this case, such an assumption was not valid in regions where it was expected to be valid. As a consequence, estimates of median raindrop diameters and updraft velocities calculated from radar reflectivities were in error. The analyses indicate that raindrop size sorting under the influence of vertical wind shear can account for the observed non-exponential size distributions.
Abstract
By means of a zenith-pointing radar, observations were made of the reflectivities and Doppler spectra in orthogonal planes as a dissipating shower exhibiting a bright band passed overhead. The observations have been used to test various procedures for estimating hydrometeor parameters from measurements of radar reflectivitity. They involve assumptions that the raindrop diameters were exponentially distributed, preferably in the manner prescribed by the Marshall-Palmer distribution. It is concluded that, in this case, such an assumption was not valid in regions where it was expected to be valid. As a consequence, estimates of median raindrop diameters and updraft velocities calculated from radar reflectivities were in error. The analyses indicate that raindrop size sorting under the influence of vertical wind shear can account for the observed non-exponential size distributions.
Abstract
Convective clouds on seeded and not-seeded days were observed by means of radar and a pair of high quality, ground-based cameras. Stereographic analysis allowed calculation of cloud-top heights, bearing, and distance from the radar set. Radiosonde data were used to convert cloud-top altitudes to summit temperatures. During the periods 1957 to 1960 (Program I) and 1961 to 1964 (Program II) the total number of clouds observed were 1249 and 522, respectively. The analyses indicate that on days when silver-iodide seeding was carried out from an airplane, a higher fraction of clouds developed precipitation echoes. When all the clouds in Program I with temperatures between −18 and −42C are considered, the effects of seeding were found to be significant at the 0.07 level according to the Mann-Whitney U test. When the data for both programs are combined, the same test yields a significance level of about 0.03 for clouds with summit temperatures between −18 and −42C. The results lead to the conclusion that airborne silver-iodide seeding may influence the precipitation-initiation process in convective clouds.
Abstract
Convective clouds on seeded and not-seeded days were observed by means of radar and a pair of high quality, ground-based cameras. Stereographic analysis allowed calculation of cloud-top heights, bearing, and distance from the radar set. Radiosonde data were used to convert cloud-top altitudes to summit temperatures. During the periods 1957 to 1960 (Program I) and 1961 to 1964 (Program II) the total number of clouds observed were 1249 and 522, respectively. The analyses indicate that on days when silver-iodide seeding was carried out from an airplane, a higher fraction of clouds developed precipitation echoes. When all the clouds in Program I with temperatures between −18 and −42C are considered, the effects of seeding were found to be significant at the 0.07 level according to the Mann-Whitney U test. When the data for both programs are combined, the same test yields a significance level of about 0.03 for clouds with summit temperatures between −18 and −42C. The results lead to the conclusion that airborne silver-iodide seeding may influence the precipitation-initiation process in convective clouds.
