Comparisons of Tetroon and Computed Trajectories

Abstract

Forty-five tetroon flights made during the summer of 1980 for the PEPE/NEROS regions pollution studies, sponsored by the U.S. Environmental Protection Agency, were compared to computed trajectories based on National Weather Service rawinsonde wind fields. Most tetroon data were obtained for travel times of less than 10 h and travel distances of less than 150 km. Two trajectory computation algorithms were used. No significant differences were found between the two comparisons. Results of the comparisons indicate that the median measure of direction difference—the angle, determined in a clockwise sense, between tetroon and computed forward trajectory position vectors—has a bias of 11°. The average standard deviation of the direction difference is ±28°. About 10% of the total direction difference variance could be due to random tetroon motion; the remaining 90% is probably the result of error in the trajectory algorithms and/or the input data. Other significant results of the trajectory comparisons are also described.