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WALTER H. HOECKER

Abstract

Wind data from the central five stations of the 1961 Weather Bureau boundary-layer-jet research pibal line are space-averaged as point data. In this form the information is compatible with other boundary-layer wind analyses made from composites of several points. Particular attention is paid to diurnal changes of jet speed, to Richardson numbers, and to inertial oscillations. Comparisons relative to the above items are made with two serial-data jet systems, as well as with theoretical models, and some similarities are found. Relationships among the jet, the geostrophic wind, and thermal wind are shown. The hodograph patterns for a jet with a surface inversion differ markedly from a jet imbedded in a temperature lapse. A certain combination of currently forecastable meteorological variables seems to be optimal for the development of the jet after sunset.

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WALTER H. HOECKER JR.

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.

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Walter H. Hoecker

Abstract

A model has been developed for predicting diurnal height changes of quasi-constant-density Mylar tetroons resulting from the complex interaction between thermally induced density changes of the tetroon and height-dependent ambient diurnal density changes in the lower 600 m of the atmosphere. The effects of solar and nocturnal radiation on tetroon altitude are included in the model. These cyclic height variations would be additive to the effects of mechanical and thermal vertical air currents acting on the tetroon. The magnitudes of the height variations for flights at <300 m above ground are so large that they should be considered in flight planning to prevent premature grounding of the tetroons.

A diurnal surface temperature range of 13°C (24°F) and the condition that air and tetroon temperature are always equal, gives a predicted diurnal height change of ∼250 m for tetroons deployed for flight at 300 m above the surface. By applying 8°C maximum superheating by day and 7°C supercooling by night, the daily height change was decreased to ∼135 m. The magnitude of the daily change in elevation of the tetroon was found to be independent of the size of tetroon provided radiation effects were not present. Tetroons released near the time of minimum air temperature had the lowest mean float elevation over a day while those released at time of maximum air temperature had the highest average elevation. Tetroons most likely approach the condition of temperature equality with the ambient air where skies are overcast because of the strong suppression of the direct component of solar radiation by day and interference with outgoing infrared radiation at night.

Tetroons floating at lower levels experience larger height variations than those floating at higher levels. In particular, tetroons inflated to float below ∼200 m above ground in the early morning would be in danger of grounding in a few hours.

This model can aid in planning tetroon flights to prevent premature grounding and to keep tetroons nearer the desired flight level.

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Walter H. Hoecker
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Walter H. Hoecker

Abstract

Fifty-five constant volume balloons (tetroons) were released in the fall of 1971 at Oklahoma City, Okla., and were ballasted to float at about 300 m over the city (elevation 400 m MSL) to trace local air currents. Twenty seven tetroons were recovered and, of these, the thirteen that were found between 400 and 1300 km from the city were included in this study. The trajectory end points of these thirteen tetroons were used to measure the accuracy of boundary-layer trajectory estimates begun at Oklahoma City and computed for the same time periods as the tetroon flights. Boundary-layer trajectory estimates were computed from sea level geostrophic vectors, layer-average winds (surface to 1000 m above terrain) and surface winds adjusted for “normal” shear to 300 m above terrain.

Based on this study, it would appear that reasonably accurate boundary-layer trajectories can be estimated by making the following adjustments to generally available data: sea level geostrophic vectors should be backed by 20° in southerly and westerly flow and 50° in northerly flow; layer-average winds require no adjustment in northerly, 10° backing in southerly and 20° backing in westerly flow; and surface wind data need no adjustment in southerly, 10° veering in northerly and 30° veering in westerly flow.

Boundary-layer trajectory estimates made from geostrophic vectors are easily constructed graphically on sea level weather charts, and trajectory forecasts can be made by using National Weather Service forecast maps distributed by facsimile. Layer-average wind and adjusted surface wind trajectories are more suited to post analysis by computer since the data are available on magnetic tapes and the wind vector data are processed objectively.

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WALTER H. HOECKER JR.

Abstract

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Walter H. Hoecker

Abstract

A slow but steady increase in the use of tetroons for tracing atmospheric air trajectories has prompted the development of an automatic method for calculating accurate tetroon inflation factors to float tetroons at desired elevations. The inflation factors are then used in nomograph form.

Gross errors in tetroon flight altitude and premature loss of the tetroon package can result from use of inaccurate surface-free lift and surface superpressure, the required inflation factors. Therefore, a quick and easy method is described for obtaining these inflation factors by means of a computer program. The inflation-factor nomograph constructed from these factors allows rapid “computation” of the specific factors required for inflating a tetroon to fly at a selected altitude for a given set of ambient atmospheric conditions. The only input arguments needed to use the nomograph are the existing inflation-shelter and existing or predicted flight-level temperatures. Use of the nomograph in the field obviates the need for a calculator, saves much time in determining inflation factors and greatly reduces errors since no arithmetic is used.

With this program, the experimenter can design inflation-factor nomographs specifically for the location and season of the experiment, and for the size of tetroon being used, without needing to understand tetroon inflation theory. An illustrative example of the computation of a set of tetroon inflation factors and the construction of an inflation-factor nomograph is given. This system requires that the tetroon maintain superpressure at all times and elevations.

The film stress versus volume relationship and the film stress at which volume creep begins are given for the nominal 1 m3 tetroon. Volume creep rates at specified high stress values also are shown.

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Walter H. Hoecker Jr.

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.

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WALTER H. HOECKER JR.

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.

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Walter H. Hoecker

Abstract

A graphical method for flying any type constant-volume balloon at specified heights up to 500 m above mean terrain is described. The flight parameters, surface free-lift, and surface superpressure are determined from graphs whose only argument is the air temperature difference between balloon flight level and inflation shelter. Another graph corrects the flight parameters for any balloon other than the 150 cm tetroon by using the balloon's volume and volume ratio. Flight-level error is about 30 m per degree Celsius of flight-level temperature error in a normal lapse rate. The balloon will fly too low if the air temperature is warmer than estimated.

Instructions for constructing flight-parameter graphs for any particular constant-volume balloon are included along with an outline of the inflation theory. The mechanical details of correctly ballasting constant-volume balloons are given. Air ballast is used inside the balloon, thereby virtually eliminating impact dangers.

Vertical air speeds are estimated directly from a graph whose arguments are observed tetroon (150 cm) vertical speed and the tetroon's vertical distance from its equilibrium level. A correction graph allows the use of any other constant-volume balloon whose frontal area to volume ratio and drag coefficient are known.

Because of the tetroon's large drag coefficient (0.74), the tetroon's vertical speed itself may be used as first-order estimates of vertical air speed.

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