Three-Dimensional Air Trajectories Determined from Tetroon Flights in the Planetary Boundary Layer of the Los Angeles Basin

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.