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Louis J. Battan

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.

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Louis J. Battan

Abstract

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Louis J. Battan

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.

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Louis J. Battan

Abstract

When employing radar for measuring rainfall rate, particularly for use in estimating the attenuation of radio waves, it is essential to take into account vertical air motions. An expression is derived to estimate, knowing the radar reflectivity, the rainfall rate-weighted, mean downward velocity of raindrops.

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Louis J. Battan

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.

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Louis J. Battan

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.

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Louis J. Battan

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.

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Louis J. Battan

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.

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Louis J. Battan

Abstract

A severe hailstorm, occuring on 10 August 1966, passed over a zenith pointing, X-band, pulsed-Doppler radar located on a mountain in southeastern Arizona. An analysis was made of measurements of radar reflectivity, mean Doppler velocity, variance of the Doppler spectrum, and calculated updraft velocity. The vertical air motions and characteristics of the hydrometeors within the storm were highly variable over distances of a few hundred meters to a few kilometers. The storm consisted of a series of updraft cores containing a number of discrete volumes, 1–2 km in diameter, of rapidly rising air with smaller accompanying eddies. The updraft cores were separated by regions of weak updrafts or downdrafts. For the most part, the highest reflectivities were outside the updraft cores. It is visualized that the hailstones within the fast-rising, distinct volumes. This process could account for the layers of clear and opaque ice within large stones by allowing them to pass through several rising volumes. It might also account for brief bursts of hail and short hailstreaks observed at the ground.

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Louis J. Battan

Abstract

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