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- Author or Editor: WALTER H. HOECKER JR. x
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Fairly complete tornado life histories have been synthesized from over 100 still photographs and eight strips of color movie film taken of two tornadoes near Scottsbluff, Nebraska, in June 1955. Funnel height and width measurements have been made from the still photographs, and translational speed has been determined at a few points and rotational speed at one point from the movies.
Evidence of downward air motion in the vicinity of the second tornado was found, and in one instance cloud elements acting as air parcel tracers demonstrated the downward motion.
Outline tracings of photographs illustrating significant size- and shape-changes are presented and measurements of interest are attached. All drawings are scaled to give the effect of observing the tornadoes from the same distance. Time lapse between the significant stages of each tornado has been estimated.
Some definite relationships are shown to exist between the tornado height and width, and differences between the two tornadoes in time trends of the several dimensions are also shown.
A model of tornado evolution is proposed.
Fairly complete tornado life histories have been synthesized from over 100 still photographs and eight strips of color movie film taken of two tornadoes near Scottsbluff, Nebraska, in June 1955. Funnel height and width measurements have been made from the still photographs, and translational speed has been determined at a few points and rotational speed at one point from the movies.
Evidence of downward air motion in the vicinity of the second tornado was found, and in one instance cloud elements acting as air parcel tracers demonstrated the downward motion.
Outline tracings of photographs illustrating significant size- and shape-changes are presented and measurements of interest are attached. All drawings are scaled to give the effect of observing the tornadoes from the same distance. Time lapse between the significant stages of each tornado has been estimated.
Some definite relationships are shown to exist between the tornado height and width, and differences between the two tornadoes in time trends of the several dimensions are also shown.
A model of tornado evolution is proposed.
Abstract
For the first time in meteorological history the broad aspects of the southerly low-level jet over the Western Plains have been studied in fine detail both in time and space. This was accomplished in the spring of 1961 by means of a line of 13 pibal stations established between Amarillo, Tex., and Little Rock, Ark. Twenty-five consecutive hourly observations were taken at each station on a total of five different 24-hr. periods in April, May, and June. Three of the observational periods were analyzed and the jet characteristics are described. High pressure cells east of the Great Plains, whether of polar or tropical origin, produced low-level southerly jet systems. Jet speed maxima occurred between 300 and 800 m. above the ground (generally well below the 850-mb. level) and were often found in several horizontally-arranged cells. By day the jet was incoherent (with one exception) and speeds were sub-geostrophic, while at night the jet was well organized and coherent and speed maxima were as high as 1.95 times the sea level geostrophic speed. The jet lifted over mountainous regions and over intruding mesosystems. On those nights with surface inversions the speed maxima were lower in elevation and required a smaller pressure gradient for a given maximum nighttime speed than when lapse conditions existed, but their elevation apparently had no correlation with the height of the inversion itself.
Blackadar's theory of the inertial oscillation for producing the low-level nocturnal jet is easily applicable for the practicing forecaster, but Wexler's inertial boundary layer interpretation predicts the jet by day as well as by night on a basic southerly current. Both theories seemed to apply at times during the existence of the jet systems described here.
Abstract
For the first time in meteorological history the broad aspects of the southerly low-level jet over the Western Plains have been studied in fine detail both in time and space. This was accomplished in the spring of 1961 by means of a line of 13 pibal stations established between Amarillo, Tex., and Little Rock, Ark. Twenty-five consecutive hourly observations were taken at each station on a total of five different 24-hr. periods in April, May, and June. Three of the observational periods were analyzed and the jet characteristics are described. High pressure cells east of the Great Plains, whether of polar or tropical origin, produced low-level southerly jet systems. Jet speed maxima occurred between 300 and 800 m. above the ground (generally well below the 850-mb. level) and were often found in several horizontally-arranged cells. By day the jet was incoherent (with one exception) and speeds were sub-geostrophic, while at night the jet was well organized and coherent and speed maxima were as high as 1.95 times the sea level geostrophic speed. The jet lifted over mountainous regions and over intruding mesosystems. On those nights with surface inversions the speed maxima were lower in elevation and required a smaller pressure gradient for a given maximum nighttime speed than when lapse conditions existed, but their elevation apparently had no correlation with the height of the inversion itself.
Blackadar's theory of the inertial oscillation for producing the low-level nocturnal jet is easily applicable for the practicing forecaster, but Wexler's inertial boundary layer interpretation predicts the jet by day as well as by night on a basic southerly current. Both theories seemed to apply at times during the existence of the jet systems described here.
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Abstract
A composite distribution of tangential and upward components of air flow is determined by tracing particles of debris and cloud tag movements in scaled movies of a tornado. The greatest tangential speed measured is 170 m.p.h. and the greatest upward speed derived is 150 m.p.h. A distribution of the convergent radial component of motion in the lower 600 ft. of the vortex is synthesized and used t o generate a vertical speed distribution which nearly duplicates the observed vertical speed distribution.
The observed radial distribution of the vertical component of relative vorticity at three levels is shown and convergence at the 500-ft. radius is computed using the synthesized radial speed distribution. Three-dimensional trajectories of air parcels in the lower portion of the vortex are also shown.
Abstract
A composite distribution of tangential and upward components of air flow is determined by tracing particles of debris and cloud tag movements in scaled movies of a tornado. The greatest tangential speed measured is 170 m.p.h. and the greatest upward speed derived is 150 m.p.h. A distribution of the convergent radial component of motion in the lower 600 ft. of the vortex is synthesized and used t o generate a vertical speed distribution which nearly duplicates the observed vertical speed distribution.
The observed radial distribution of the vertical component of relative vorticity at three levels is shown and convergence at the 500-ft. radius is computed using the synthesized radial speed distribution. Three-dimensional trajectories of air parcels in the lower portion of the vortex are also shown.
Abstract
From the records obtained during the Weather Bureau Artificial Cloud Nucleation Project carried out in western Washington State during the winters of 1952–53 and 1953–54, it is possible to study the nature of some of the precipitation processes evident in that locality, and to form a preliminary generalized picture of certain types of cloud systems involved. Evidence is presented of natural seeding mechanisms and of the growth of hydrometeors by diffusion, coalescence, aggregation, and accretion. Typical wintertime cloud systems, and the attendant precipitation processes are illustrated.
Abstract
From the records obtained during the Weather Bureau Artificial Cloud Nucleation Project carried out in western Washington State during the winters of 1952–53 and 1953–54, it is possible to study the nature of some of the precipitation processes evident in that locality, and to form a preliminary generalized picture of certain types of cloud systems involved. Evidence is presented of natural seeding mechanisms and of the growth of hydrometeors by diffusion, coalescence, aggregation, and accretion. Typical wintertime cloud systems, and the attendant precipitation processes are illustrated.
Abstract
The three-dimensional pressure field of the Dallas tornado, April 2, 1957, is integrated from a distribution of observed tangential wind speeds. A total pressure drop of 60 mb. is computed at ground level at the axis. Variations in tornado funnel geometry are explained by changes in moisture content of the involved air and system-wide pressure changes. The effects of the moving pressure field on hypothetical vented and unvented buildings are computed. The results indicate that a dwelling, which could lose in 5 seconds about 75 percent of an imposed pressure difference, would most likely not yield due to internal pressure alone, if the imposed pressure difference were like that of the Dallas tornado.
Abstract
The three-dimensional pressure field of the Dallas tornado, April 2, 1957, is integrated from a distribution of observed tangential wind speeds. A total pressure drop of 60 mb. is computed at ground level at the axis. Variations in tornado funnel geometry are explained by changes in moisture content of the involved air and system-wide pressure changes. The effects of the moving pressure field on hypothetical vented and unvented buildings are computed. The results indicate that a dwelling, which could lose in 5 seconds about 75 percent of an imposed pressure difference, would most likely not yield due to internal pressure alone, if the imposed pressure difference were like that of the Dallas tornado.
