Search Results
You are looking at 1 - 10 of 33 items for :
- Author or Editor: Louis J. Battan x
- Article x
- Refine by Access: All Content x
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.
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.
The use of radar-reflecting chaff for making measurements of wind velocity and divergence is discussed. Data are presented to illustrate how the chaff technique can be used in studies of phenomena of various scales.
The use of radar-reflecting chaff for making measurements of wind velocity and divergence is discussed. Data are presented to illustrate how the chaff technique can be used in studies of phenomena of various scales.
Abstract
Observations obtained by means of a zenith pointing, 3-cm pulsed-Doppler radar were used to estimate the turbulence spreading of the Doppler spectrum. This was done by comparing estimates of updraft velocity made by two schemes. One of them is independent of turbulence spreading effects providing they affect both tails of the spectrum. The second scheme is subject to errors when the spread of the spectrum is affected by factors other than the range of the terminal velocities of the detectable particles. In a small thunderstorm, the turbulence spreading of the Doppler spectrum in the region where rain was most likely, averaged 0.1 m sec−1 and had a standard deviation of 1 m sec−1.
Abstract
Observations obtained by means of a zenith pointing, 3-cm pulsed-Doppler radar were used to estimate the turbulence spreading of the Doppler spectrum. This was done by comparing estimates of updraft velocity made by two schemes. One of them is independent of turbulence spreading effects providing they affect both tails of the spectrum. The second scheme is subject to errors when the spread of the spectrum is affected by factors other than the range of the terminal velocities of the detectable particles. In a small thunderstorm, the turbulence spreading of the Doppler spectrum in the region where rain was most likely, averaged 0.1 m sec−1 and had a standard deviation of 1 m sec−1.
Abstract
During the summers of 1958 to 1962, convective clouds over a mountain range in southeastern Arizona were seeded by means of airborne silver-iodide generators. The data collected do not allow a conclusion that the seeding influenced the amount of cloud-to-ground lightning.
Abstract
During the summers of 1958 to 1962, convective clouds over a mountain range in southeastern Arizona were seeded by means of airborne silver-iodide generators. The data collected do not allow a conclusion that the seeding influenced the amount of cloud-to-ground lightning.
Abstract
Two groups of days, one with “heavy rain” and one with “light rain,” have been studied. Radar observations, cloud photographs and visual counts of cloud-to-ground lightning were examined. It is concluded that, at least in convective clouds in southeastern Arizona and probably in convective clouds in other geographical regions as well, the microphysical properties of the clouds are not of dominant importance in determining how much precipitation reaches the ground. It is inferred that the quantity of rainfall is mostly governed by those properties of the atmosphere which determine the size, strength and duration of the updrafts. The observations also show that as the quantity of rainfall increases so does the frequency of cloud-to-ground lightning.
Abstract
Two groups of days, one with “heavy rain” and one with “light rain,” have been studied. Radar observations, cloud photographs and visual counts of cloud-to-ground lightning were examined. It is concluded that, at least in convective clouds in southeastern Arizona and probably in convective clouds in other geographical regions as well, the microphysical properties of the clouds are not of dominant importance in determining how much precipitation reaches the ground. It is inferred that the quantity of rainfall is mostly governed by those properties of the atmosphere which determine the size, strength and duration of the updrafts. The observations also show that as the quantity of rainfall increases so does the frequency of cloud-to-ground lightning.
