A PRELIMINARY STUDY OF AIR TRAJECTORIES IN THE LOS ANGELES BASIN AS DERIVED FROM TETROON FLIGHTS

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.