STABILITY INFERENCES FROM PRECISION RAWINS

Abstract

A series of rawins, tracked by an M-33 radar, was carried out at Palestine, Texas, in November 1965. Ascent rates of about 60 m./min. and recording of balloon coordinates at half-minute intervals were used to give fine resolution. In addition to horizontal winds, the flights were analyzed for the vertical wind component, and ascent-rate of the balloon. The results suggest that some inferences as to thermal structure in the surface layer can be drawn from precision balloon tracking. A uniform rate of ascent is associated with inversion conditions. An ascent that shows two rates, a faster one through the first few hundred meters and a slower one above, occurs when the surface layer is undergoing mixing of either convective or mechanical origin. Attempts to fit an expression of the form V1/V2?=?(?z1/z2?)?p to the profile of wind speed in the surface-based layer agreed moderately well with the expectation of p?1/7 for unstable layers and p?1/3 for inversions. This somewhat weak indication was often supported by the profile of wind direction?uniform direction or slight backing through the mixed layer with rapid veering above. During ascent through unstable layers maximum vertical wind components generally exceeded 0.8 m./sec.; through stable layers they generally subceeded 0.3 m./sec.