The measurement of mesoscale vertical motions in the atmosphere

A technique is described for determining the three‐dimensional field of vertical air motion in the vicinity of mobile fronts. Radar reflectors are dropped from an aircraft at a height of 5 km and followed by high precision tracking radars. By making assumptions regarding the movement and conservativeness of the frontal system it has been possible to use this technique to obtain horizontal winds over a volume approximately 150 × 100 × 4 km depth with a typical drop separation of 30 km. Using the equation of continuity, vertical velocities have been calculated with an uncertainty of ± 1 ‐ 2 cm s−1. In a warm front investigated on 19 January 1969, close agreement was obtained between the rainfall observed at the surface and that computed from the vertical velocities assuming saturation of the rising air.