Abstract

Successive tetroon releases are utilized to provide an estimate of the lateral diffusion from a continuous point source as a function of downwind distance. On the average the tetroons yield a lateral standard deviation proportional to the 0.85 power of the downwind distance. The mean ratio of lateral standard deviation to downwind distance varies from 0.40 (5 km downwind) to 0.31 (40 km downwind) for tetroon releases over time intervals of 3 hours and from 0.64 to 0.49 for tetroon releases ova time intervals of 21 hours. These mean ratios are large because of the preponderance of tetroon flights within the Los Angeles Basin. The data also imply a lateral standard deviation proportional to about the 0.2 power of the time interval of tetroon release and hence, to a first approximation, to about the 0.2 power of the sampling time.

The lateral standard deviations obtained from successive tetroon releases are compared to estimates derived from individual tetroon flights through evaluation of running means of the lateral velocity. The agreement is good at a downwind distance of 5 km but becomes progressively worse with increase in down-wind distance so that, at a downwind distance of 20 km, the average lateral standard deviation derived from the individual trajectories is only 70 per cent of that derived from the series.

Abstract

During January of 1960, eight tetroons (constant volume, super-pressured balloons were released from Wallops Island for flight at approximately 3000 ft. The tetroons were tracked by the very accurate AN/FPS-16 radar, thus permitting the delineation of relatively high-frequency tetroon oscillations.

It is shown that in the mean the tetroons flew at a constant level, but that flights within an air mass exhibited small-scale vertical oscillations of mean period near 10 min, approximately the “natural” period of oscillation of air parcels in an atmosphere with the given stability. This finding offers support for consideration of the tetroon as a Lagrangian tracer.

Subsequent to passage of a cold front, two tetroons were released 20 min apart and were tracked by different radars. These two flights exhibited nearly identical large-scale vertical oscillations of mean period near 25 min. These pronounced height fluctuations apparently were associated with a vertical motion system moving at a speed of 4 kn in a direction nearly parallel to the frontal intersection with the ground.

Statistics derived from the flights indicate that at elevations near 3000 ft the velocity variance is the same in directions along and normal to the mean flow, but that the variance in the vertical is only one-quarter as great. Comparisons with other data intimate that Lagrangian transverse variances and turbulence intensities over the ocean at 3000 ft are nearly an order of magnitude smaller than Eulerian values near the earth's surface.

Abstract

During May and early June of 1963, 88 tetroon-transponder flights were made at relatively low level in the Los Angeles Basin. Five different tetroon release sites were utilized, extending from Point Dume northwest of Los Angeles to Sunset Beach southeast of Los Angeles. The tetroons, and attached transponders, were positioned at 3-min. intervals by means of the newly installed Weather Bureau WSR–57 radar on Blackjack Mountain, Catalina. Through the use of transponders the problem of ground clutter was eliminated, and tetroon positions were obtained at ranges exceeding 50 mi. even when the tetroon was only a few feet above the ground. More than 400 hr. of tetroon-tracking time were obtained, with the longest single track of 21 hr. duration.

In general, the wind speeds derived from successive tetroon positions were small, averaging 4.4 kt. for all flights and only 2.4 kt. for flights released from Corral Beach. Aircraft tracking on more than 20 of the flights confirmed that the mean tetroon floating altitude was between 1000 and 1500 ft. However, while the tetroon height over the ocean varied little, over the land in the unstable marine layer repetitive height variations of as much as 2000 ft. were noted. There was a marked tendency for tetroon heights to vary in accordance with terrain height, and, particularly in the case of the Palos Verdes Hills, a systematic vertical motion pattern was delineated.

On the basis of 7 pairs of simultaneous tetroon releases, it was found that for the first 100 min. the square of the horizontal separation distance tends to be proportional to time to the third power. However, at times greater than 100 min., the tetroons occasionally draw closer together. In the case of tetroons released from the same site, but at different times, the distance between tetroon positions tends to increase nearly linearly with time after release, attaining an average value of 15 mi. 4 hr. after release. Surprisingly, the time interval between tetroon release does not appreciably affect this latter statistic. Analysis of the spreading or diffusion of serial trajectories in a spatial frame of reference shows that the lateral standard deviation is proportional to downstream distance to the 0.8 to 0.9 power, values comparable to those derived by quite different methods.

Considered is a series of trajectories from Long Beach which indicates land and sea breeze effects, and a series of trajectories from Venice which shows a veering of the sea breeze flow with time. A few flights from Sunset Beach suggest that at times, near the base of the inversion, there may exist a large anticyclonic cell (reverse of the usual Catalina eddy) over the Los Angeles Basin.

Abstract

During July 1964 more than 90 constant volume balloon (tetroon) flights were made from the area of Atlantic City, N.J., with the primary purpose of delineating the sea breeze regime at that locale. The transponder-equipped tetroons were ballasted to float at a height of 500 ft., and were tracked by the U.S. Weather Bureau WSR-57 radar at Atlantic City. The tetroon trajectories are compared with surface winds and with (surface) geostrophic winds derived from pressure readings at four nearby weather stations. On the average, the tetroon direction differs from the surface wind direction by only a few degrees, but the tetroon speed exceeds the surface wind speed by a factor of nearly two. During pronounced sea breeze regimes the tetroon moves toward low pressure at an average angle of 20° during the morning hours and nearly 90° during the early afternoon hours. Both sequential tetroon releases and individual tetroon trajectories indicate a veering of the sea breeze flow during late afternoon and evening. The ratio of tetroon speed and geostrophic speed averages about 0.60 on non-sea breeze days and 0.35 on sea breeze days, with a tendency for the ratio to be at maximum in the late afternoon.

Tetroons released in the early morning into a gradient flow from the northwest exhibit a sharp turn to the north at the presumed position of the sea breeze front. On the basis of this turning it appears that the sea breeze front exists at sea prior to its arrival at the shore line, but the analysis is complicated by the fact that the tetroons are at some height above the surface. To the extent that tetroon trajectories represent air parcel trajectories, there is evidence that, frequently, sea breeze air is simply air from the land that has been modified by the sea surface. While the WSR-57 radar does not provide accurate tetroon-transponder height values, there is the suggestion of large vertical air motions near the sea breeze front and evidence that the sea air may, on occasion, override the land air so that the sea breeze frontal passage occurs first at some height above the ground.

The atmospheric diffusion to be expected in both sea breeze and non-sea breeze regimes is investigated through the simultaneous and sequential release of tetroons. In the case of instantaneous-point-source (relative) diffusion, the data suggest that the lateral and longitudinal standard deviations increase in proportion to about the first power of the downwind distance out to distances of the order of 10 km., but thereafter increase in proportion to about the 0.5 power. In the case of continuous-point-source diffusion, the data suggest that, at downwind distances from about 10 to 50 km., the lateral standard deviation is proportional to nearly the 0.85 power of the distance, and proportional to about the 0.2 and 0.9 power of the tetroon release interval on sea breeze and non-sea breeze days, respectively.

Abstract

An analysis is presented of low-level trajectory data obtained by means of constant level balloon flights from Cape Hatteras, N.C., during September and October 1959. An approximately constant floating level was obtained by flying the nearly constant volume Mylar balloons (tetroons) with an internal superpressure of about 100 mb. The metalized tetroons were positioned a t 1-min. intervals by means of a manually operated SP–1M radar. From knowledge of these positions, overlapping 5-min. average velocities were determined for flight durations of up to 5 hr. On some of the flights the radar return was enhanced by the addition of a radar reflective mesh to the tetroon. With the addition of this mesh, flights at altitudes of less than 5,000 ft. were tracked as far as 92 n. mi. from the radar, or approximately to the radar horizon.

Spectral analysis of the velocity data obtained from the four best flights shows some evidence for a (Lagrangian) wind speed periodicity of 26-min. period, a vertical motion periodicity of 13-min. period, and a cross-stream velocity periodicity of 17-min. period. Cross spectrum analysis shows that, with the exception of oscillations of 45-min. period, the wind speed is a t a maximum ahead of the trough in the trajectory. Thus, if the large-scale air flow is nearly geostrophic, there is evidence that kinetic energy and momentum are transported down the pressure gradient by these small-scale oscillations. The maximum upward motion of the tetroon tends to take place near the trajectory trough line for oscillations of a period exceeding 18 min. and near the trajectory crest for oscillations of smaller period. Therefore, looking downstream, the longer-period tetroon oscillations tend to be counterclockwise in a plane normal to the mean trajectory while the shorter-period oscillations tend to be clockwise. However, until more information is obtained on the small-scale temperature field and the extent to which the tetroons follow the vertical air motion, any statement regarding “direct” and “indirect” air circulations is tentative.

The ratio of one minus the cross-stream and one minus the along-stream autocorrelation Coefficients for these flights is approximately 0.6, suggesting a certain similarity between Eulerian space and Lagrangian autocorrelation coefficients. The tetroon data also indicate that initially one minus the cross-stream autocorrelation coefficient is proportional to the time, as would be anticipated from Lagrangian turbulence theory. These data tend to confirm that, for the scale of motion under consideration, the Lagrangian-Eulerian scale factor β of Hay and Pasquill has a value near 4.

Abstract

Low-level, constant volume balloon (tetroon) flights made from Yucca Flat in the Nevada Proving Grounds of the Atomic Energy Commission are utilized to yield an estimate of the nature and magnitude of vertical air motions in desert areas. It is found that during the day the tetroons oscillate as much as 10,000 feet in the vertical with vertical velocities often exceeding 5 kt., whereas during the night the vertical oscillation are on the order of 100 feet and vertical velocities seldom exceed 0.5 kt. There are indications that during the day, at this particular site, helical circulation patterns exist with axes parallel to the north-south oriented valley floor and with alternating circulation sense across the valley, while during the night the small vertical oscillations are more nearly tied to the local topography. Pure mountain influences on the tetroon trajectories could not be clearly delineated owing to the tremendous vertical oscillations associated with solar heating.

Abstract

The dominant period of air parcel oscillation in the vertical within the planetary boundary layer is estimated from vertical velocity spectra derived from 40 constant volume balloon (tetroon) flights in the vicinity of the 460 m BREN tower at the Nevada Test Site. Lapse rates obtained from the tower show that in the mean the dominant periodicity closely corresponds to the Brunt-Vaisala period for lapse rates <0.9C (100 m)⁻¹.

Abstract

During July 1966, nearly 100 tetroon flights were made at the National Reactor Testing Station (NRTS), Idaho Falls, with the primary purpose of verifying the existence of longitudinal roll-vortices, or helices, in the planetary boundary layer. The transponder-equipped constant volume ballons (tetroons) were ballasted to float 300 m above the ground and were tracked by two M-33 radars. One radar tracked two tetroons released simultaneously from sites 500 m apart (in a direction normal to the mean flow) and the other radar tracked two tetroons released simultaneously from the same sites about one-half hour later.

In the flat, desert-like region of NRTS, there is evidence that counter-rotating helices of about 2 km diameter frequently exist during the afternoon. Basically, the helical motion appears to be one of solid rotation, with an average absolute value for the vorticity in the transverse plane of 4 × 10⁻³ sec⁻¹, a magnitude similar to that derived from the vertical shear of the longitudinal wind. There is evidence that these helical structures move in a direction normal to the mean flow with a speed of about 1 m sec⁻¹. During the afternoon, the average value of the tetroon-derived horizontal stress is nearly 6 dyn cm⁻², and the average flux of kinetic energy from mean sheared flow to helix is nearly 6 cm² sec⁻³. There is considerable agreement between the tetroon-derived data and the theoretical and laboratory work of Faller and Lilly on helical circulations, even though the evidence from this atmospheric experiment suggests that, during the afternoon, the longitudinal vortices are driven both by buoyancy and the vertical shear of the mean flow.

Abstract

Constant-volume balloon (tetroon) flights tracked by radar across Columbus, Ohio, in March 1969, illustrate the effect of a city on the nighttime airflow at heights of 100–200 m. On the average, the urban influence on wind direction is small at a height of 100 m, but an anticyclonic turning of 10° is observed at 200 m. The anticyclonic turning is greater under inversion than under lapse conditions and greater after midnight than before; it appears to result both from an increase in the frictional force due to increased vertical mixing and from a mesoscale high pressure system formed aloft as the result of the warmer temperatures within the city. The decrease in wind speed across the city averages nearly 20% of the upwind speed under lapse conditions but is very small under inversion conditions. In both cases the region of maximum deceleration tilts downwind with height. The average upward air motion exceeds 4 cm sec⁻¹ above the down-town area under light wind conditions, and increases to 1 m sec⁻¹ as the wind speed approaches 20 m sec⁻¹. In the case of strong winds, alternating regions of upward and downward motion occur downwind of the city.

Abstract

Tetroon flights across Oklahoma City indicate the influence of an isolated urban area on the horizontal and vertical air velocity at heights near 400 m in relatively strong (13 m sec⁻¹) daytime flow. The Lagrangian measurements so obtained are collated with fixed-point measurements of horizontal and vertical velocity on a 460 m television tower. Above the city in the morning there is a mean trajectory turning toward lower pressure of 10°. This turning, presumably fractionally induced, is noted only weakly in the afternoon and not all in the evening, but there is slight evidence for a bending of the trajectories around the city at these later times. During the day the city appears as the source of a plume of ascending air motion extending at least 30 km downwind of the city, with both tetroon and tower measurements indicating a mean upward velocity of almost 0.4 m sec⁻¹ ten kilometers downwind of city-center at heights near 400 m. On the average the magnitude of the stress determined from the covariance of the eddy velocity components along the tetroon flights is about 70% of the magnitude measured on the tower, and there is a correlation of nearly 0.5 between individual measurements of stress by the two techniques. The magnitude of the tetroon stress is intimately related to building height and density, with a stress maximum of at least 3 dyn cm⁻² located 10 km downwind of city-center in comparison with stress values near 1 dyn cm⁻² beyond the city outskirts. The fraction of the stress associated with Lagrangian oscillations of 1–10 min period (in comparison with 1–30 min period) increases from 20% upwind of the city to 80% downwind of the city in the daytime average.