Analysis of low‐level, constant volume balloon (tetroon) flights over New York City

Abstract Constant volume balloon (tetroon) flights made over New York City at heights of about 300 metres during June of 1965 are analysed. The transponder‐equipped tetroons were tracked to distances exceeding 100 km by means of the wsr‐57 weather radar located in Central Manhattan. On non‐sea breeze days the tetroons tend to move towards low pressure with an angle of 35 degrees, and to move with about two‐thirds of the geostrophic wind speed. There is a correlation of 0.73 between lapse rate and tetroon‐derived r.m.s. vertical velocity, and of 0.43 between lapse rate and Lagrangian period of vertical oscillation. Tetroon‐derived vertical velocities are also used to obtain estimates of the mean Reynolds stress (1.3 dynes cm −2 at flight level) and the downwind variation of vertical diffusion over an urban area.