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Abstract
Tetroon flights across the northern California coast indicate the influence of a laterally extensive and fairly abrupt 100-m change in terrain height near the shoreline on the three-dimensional low-level air flow. Beneath the wind speed maximum at a height of 300 m, the wind speed is stronger over the land than over the sea, resulting in nearly equal horizontal mass transport between this height and the earth's surface. Across the 4-km interval bracketing the shoreline, the wind backs by 11° and 4° at heights of 200 and 400 m, respectively. The maximum upward velocity, of magnitude 6 cm sec−l, occurs 250 m above the sudden change in terrain height near the shoreline, with the compensating downward motion commencing 3 km inland. Over the hills inland from the coast, the magnitude of the tetroon height variation is closely related to the magnitude of the height variations of the underlying terrain, with tetroon oscillations in the vertical generally preceding the variations in terrain height by a distance exceeding the height of the tetroon above the ground.
Abstract
Tetroon flights across the northern California coast indicate the influence of a laterally extensive and fairly abrupt 100-m change in terrain height near the shoreline on the three-dimensional low-level air flow. Beneath the wind speed maximum at a height of 300 m, the wind speed is stronger over the land than over the sea, resulting in nearly equal horizontal mass transport between this height and the earth's surface. Across the 4-km interval bracketing the shoreline, the wind backs by 11° and 4° at heights of 200 and 400 m, respectively. The maximum upward velocity, of magnitude 6 cm sec−l, occurs 250 m above the sudden change in terrain height near the shoreline, with the compensating downward motion commencing 3 km inland. Over the hills inland from the coast, the magnitude of the tetroon height variation is closely related to the magnitude of the height variations of the underlying terrain, with tetroon oscillations in the vertical generally preceding the variations in terrain height by a distance exceeding the height of the tetroon above the ground.
Abstract
Tetroon trajectories within the Los Angeles Basin in the autumn of 1973 show that, on non-stagnation days, air located in the Los Angeles area in the morning can pass over the Puente Hills and reach the San Bernardino-Riverside area by mid-afternoon of the same day. However, the enhanced vertical mixing associated with these Hills would be expected to dilute any pollution present. Of perhaps more importance is the evidence that, on stagnation days when the atmosphere is stable, air from the Los Angeles area may drift southward in the early morning katabatic flow, stagnate for 2–3 h in the industrialized and high vehicle-density region north of Long Beach, and then move rapidly eastward with the sea breeze flow through Santa Ana Canyon, reaching the Riverside-San Bernardino area in late afternoon. In this case there would seem to be more potential for severe pollution in the latter area. However, the frequency of occurrence of this particular trajectory pattern is uncertain.
Abstract
Tetroon trajectories within the Los Angeles Basin in the autumn of 1973 show that, on non-stagnation days, air located in the Los Angeles area in the morning can pass over the Puente Hills and reach the San Bernardino-Riverside area by mid-afternoon of the same day. However, the enhanced vertical mixing associated with these Hills would be expected to dilute any pollution present. Of perhaps more importance is the evidence that, on stagnation days when the atmosphere is stable, air from the Los Angeles area may drift southward in the early morning katabatic flow, stagnate for 2–3 h in the industrialized and high vehicle-density region north of Long Beach, and then move rapidly eastward with the sea breeze flow through Santa Ana Canyon, reaching the Riverside-San Bernardino area in late afternoon. In this case there would seem to be more potential for severe pollution in the latter area. However, the frequency of occurrence of this particular trajectory pattern is uncertain.
Abstract
Pairs of constant volume balloons (tetroons) released ∼1 min apart from the same site at Haswell, Colo., and continuously tracked by two M-33 radars, are used to estimate the mutual consistency of tetroon vertical motions. In the strong well-organized vertical motion systems of midday and afternoon, it is possible unambiguously to relate the vertical oscillations of the two tetroons so long as the tetroon separation distance is less than about 3 km, implying that under these conditions the tetroons are indeed passing through the same systems (convection cells or thermals). At other times of day such a comparison becomes difficult, partly because of the smaller amplitude and period of oscillation. Where identification of the same vertical motion system is possible, the phase lag between vertical oscillations of adjacent tetroons is related in a meaningful way to the tetroon spacing and the relative position of the tetroon pair with respect to wind direction, and accordingly there is good evidence that tetroon vertical motions are basically consistent.
Abstract
Pairs of constant volume balloons (tetroons) released ∼1 min apart from the same site at Haswell, Colo., and continuously tracked by two M-33 radars, are used to estimate the mutual consistency of tetroon vertical motions. In the strong well-organized vertical motion systems of midday and afternoon, it is possible unambiguously to relate the vertical oscillations of the two tetroons so long as the tetroon separation distance is less than about 3 km, implying that under these conditions the tetroons are indeed passing through the same systems (convection cells or thermals). At other times of day such a comparison becomes difficult, partly because of the smaller amplitude and period of oscillation. Where identification of the same vertical motion system is possible, the phase lag between vertical oscillations of adjacent tetroons is related in a meaningful way to the tetroon spacing and the relative position of the tetroon pair with respect to wind direction, and accordingly there is good evidence that tetroon vertical motions are basically consistent.
Abstract
The Los Angeles Reactive Pollutant Project (LARPP) in the autumn of 1973 involved helicopter sampling of a volume of air “tagged” by means of three constant volume balloons (tetroons) released simultaneously from a point on the ground. Based on radar tracking of 35 tetroon triads at a mean height of 350 m above sea level, this paper considers the estimates of relative diffusion obtained from the rate of separation of the tetroons making up the triad. In the average, the median lateral standard deviation of tetroon position varies from 90 m after a travel time of 15 min to 800 m after 2 h, and from 140 m at a travel distance of 2 km to 1000 m at 20 km. The relative diffusion is indicated to be nearly twice as large in “neutral” as in “stable” conditions. Comparison with the results obtained by other investigators in other locations shows that the relative diffusion within the Los Angeles Basin is frequently unusually small, particularly with respect to travel time.
Abstract
The Los Angeles Reactive Pollutant Project (LARPP) in the autumn of 1973 involved helicopter sampling of a volume of air “tagged” by means of three constant volume balloons (tetroons) released simultaneously from a point on the ground. Based on radar tracking of 35 tetroon triads at a mean height of 350 m above sea level, this paper considers the estimates of relative diffusion obtained from the rate of separation of the tetroons making up the triad. In the average, the median lateral standard deviation of tetroon position varies from 90 m after a travel time of 15 min to 800 m after 2 h, and from 140 m at a travel distance of 2 km to 1000 m at 20 km. The relative diffusion is indicated to be nearly twice as large in “neutral” as in “stable” conditions. Comparison with the results obtained by other investigators in other locations shows that the relative diffusion within the Los Angeles Basin is frequently unusually small, particularly with respect to travel time.
Direct beam hourly solar radiation values, measured near solar noon under clear skies, were used to show the decrease in radiation in the United States caused by the debris cloud from the El Chichon volcanic eruption of March/April 1982. Maximum decreases of mean monthly direct beam occurred in December 1982, at Phoenix, Ariz., Boulder, Colo., and Bismarck, N.D. They were 11%, 17%, and 25% below the average December 1978–81 levels, respectively, at those locations. Data were taken from the National Oceanic and Atmospheric Administration solar radiation network.
The El Chichon cloud “arrived” at Boulder and Bismarck in August and October 1982, Respectively, as determined by the first 1982 mean monthly radiation that was significantly below (5% level) the background data regression line. The arrival time at Phoenix was most likely in August. Cloud residence time was at least 11 months at Boulder. At Bismarck and Phoenix, cloud density had not yet begun to decrease in December 1982 after three and four months residence time, respectively.
An anomalous, strong, and sudden short-period (7-day) drop in radiation was recorded in mid-May 1982 at Phoenix but not at Boulder or Bismarck. Similar mid-May drops were found, however, at Albuquerque, N.M., Las Vegas, Nev. and El Paso, Texas.
Volcanic clouds causing large percentage decreases in direct beam radiation below expected climatological levels, such as observed in 1982 with the El Chichon cloud, when combined with the long cloud residence time, would be of considerable economic concern to solar energy systems, especially those depending primarily on direct beam radiation for energy input.
Direct beam hourly solar radiation values, measured near solar noon under clear skies, were used to show the decrease in radiation in the United States caused by the debris cloud from the El Chichon volcanic eruption of March/April 1982. Maximum decreases of mean monthly direct beam occurred in December 1982, at Phoenix, Ariz., Boulder, Colo., and Bismarck, N.D. They were 11%, 17%, and 25% below the average December 1978–81 levels, respectively, at those locations. Data were taken from the National Oceanic and Atmospheric Administration solar radiation network.
The El Chichon cloud “arrived” at Boulder and Bismarck in August and October 1982, Respectively, as determined by the first 1982 mean monthly radiation that was significantly below (5% level) the background data regression line. The arrival time at Phoenix was most likely in August. Cloud residence time was at least 11 months at Boulder. At Bismarck and Phoenix, cloud density had not yet begun to decrease in December 1982 after three and four months residence time, respectively.
An anomalous, strong, and sudden short-period (7-day) drop in radiation was recorded in mid-May 1982 at Phoenix but not at Boulder or Bismarck. Similar mid-May drops were found, however, at Albuquerque, N.M., Las Vegas, Nev. and El Paso, Texas.
Volcanic clouds causing large percentage decreases in direct beam radiation below expected climatological levels, such as observed in 1982 with the El Chichon cloud, when combined with the long cloud residence time, would be of considerable economic concern to solar energy systems, especially those depending primarily on direct beam radiation for energy input.
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
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.
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.
Abstract
Between 9 September and 2 October 1969, 105 constant-volume balloons (tetroons) were released from various sites in the Los Angeles Basin for the purpose of obtaining three-dimensional air trajectories in the planetary boundary layer of the Basin. The tetroons, with transponders attached, were tracked by an M-33 radar positioned atop Mt. Thom, 5 km north of Glendale. In general, the tetroons at heights of a few hundred meters tended to move slowly westward between midnight and sunrise, slowly northward between sunrise and noon, and rapidly eastward between noon and sunset. Tetroons launched from Redondo Beach and the Long Beach area during the day distinctly show the convergence zone extending northeastward from the Palos Verdes Hills due to the confluence of sea breezes from the west and south. Tetroons released near the downtown area around sunrise tend to drift toward city center before moving northeastward into the Pasadena-Glendale area. During the day the tetroons oscillate through much of the depth of the mixed layer beneath the inversion, but at night the vertical oscillations are usually very small. The tetroon trajectories are compared with surface trajectories derived from the extensive surface wind network within the Basin, and it is shown that the ratio of trajectory separation distance to tetroon travel distance averages about 0.2 during the day and 0.4 at night. Oxidant readings obtained by a helicopter following along the tetroon trajectories are compared with fixed-point readings, and it appears that, downwind of the city center, most of the increase in oxidant during the day is due to photochemical effects on individual volumes of air and is not due to advection of previously-existing high values of oxidant into the area.
Abstract
Between 9 September and 2 October 1969, 105 constant-volume balloons (tetroons) were released from various sites in the Los Angeles Basin for the purpose of obtaining three-dimensional air trajectories in the planetary boundary layer of the Basin. The tetroons, with transponders attached, were tracked by an M-33 radar positioned atop Mt. Thom, 5 km north of Glendale. In general, the tetroons at heights of a few hundred meters tended to move slowly westward between midnight and sunrise, slowly northward between sunrise and noon, and rapidly eastward between noon and sunset. Tetroons launched from Redondo Beach and the Long Beach area during the day distinctly show the convergence zone extending northeastward from the Palos Verdes Hills due to the confluence of sea breezes from the west and south. Tetroons released near the downtown area around sunrise tend to drift toward city center before moving northeastward into the Pasadena-Glendale area. During the day the tetroons oscillate through much of the depth of the mixed layer beneath the inversion, but at night the vertical oscillations are usually very small. The tetroon trajectories are compared with surface trajectories derived from the extensive surface wind network within the Basin, and it is shown that the ratio of trajectory separation distance to tetroon travel distance averages about 0.2 during the day and 0.4 at night. Oxidant readings obtained by a helicopter following along the tetroon trajectories are compared with fixed-point readings, and it appears that, downwind of the city center, most of the increase in oxidant during the day is due to photochemical effects on individual volumes of air and is not due to advection of previously-existing high values of oxidant into the area.
