Observations of Longitudinal Rolls in a Near Neutral Atmosphere

Abstract

Aircraft and satellite data an used to study the structure of longitudinal roll vortices in a nearly neutral (zi/L=-1.2, where zi is the inversion height and L is the Monin-Obukhov length) boundary layer over the ice-covered Bering Sea during February. Steam fog, formed over cracks and leads in the ice, was used as a tracer to delineate the various scales of roll motion seen in satellite images. The satellite information combined with aircraft data collected by the NOAA P-3 indicated the presence of a hierarchy of roll vortex motions. It is suggested that interactions of the various scales of motion resulted in certain scales dominating in one area and other scales dominating in another. Two-kilometer wavelength variations an attributed to the inflection point instability mechanism while 12?15 km variations seen to have been reinforced by the upstream topography on the Chukotka Peninsula. Organization of the fog banks on scales of 30 km was also present and may be attributable to resonant subharmonics of the basic boundary layer instability or to a mesoscale entrainment instability.