Finestructure of Elevated Stable Layers Observed by Sounder andIn SituTower Sensors

Abstract

A study of the finestructure within elevated stable atmospheric layers is described. The observational program consisted of measurements made with fast-response turbulence sensors on a carriage traversing a 300 m tower and comparison of the carriage data with data from acoustic and radar echo sounders. Some supporting observations using a free balloon-borne sensor of the temperature structure parameter are also shown. The layers studied were found to be composed of sheets and layers in temperature, humidity and wind reminiscent of the sheet and layer structures often reported in lakes, estuaries and the oceans. Finestructure in the profiles of temperature and humidity are very highly correlated within elevated stable layers. The sheets are generally accompanied by thin zones of very large temperature and humidity structure parameter, apparently the result of Kelvin-Helmholtz instability, that account for the strong returns from these zones recorded by short wavelength radar and acoustic sounders. The distributions of turbulence properties through the layered structures are described, and some implications for models are discussed. A quite general ratio of sheet-to-layer thickness is proposed toward which the process of step formation proceeds. Measured profiles of short term averages of w′T′ show thin zones of apparently strong upward flux imbedded within generally stable regions of weak downward flux. These layers of positive flux are associated with thin superadiabatic zones in the temperature profile and suggest a much more complicated process of heat and momentum transport within stable, elevated regions than process suggested by classical turbulence theory.