Observing Coherent Boundary Layer Motions Using Remote Sensing and Surface Pressure Measurement

Abstract

In this paper, high-frequency pressure time series measured by microbarographs are used to extract information on the existence and characteristics of convective rolls in the convective boundary layer. Rolls are identified in radar and satellite data, and it is shown that the pressure signals associated with the rolls have been detected in an array of microbarographs. The methodology of obtaining further information on roll characteristics from the array, notably orientation and drift velocity, is discussed in some detail. It is shown that the pressure time series contain signals representing the roll motion, approximately normal to the mean wind, and signals representing turbulent structures that drift along the mean wind direction. As the along-wind signals may dominate the time series, care is needed to identify the roll motion. Filtering of the higher-frequency along-wind signals can isolate the roll motion details. Also, a new approach using ?beam-steering diagrams? to discriminate rolls from gravity waves and turbulent eddies is tested in both a numerical model and an observational case. In the beam-steering diagram, multiple centers of signal cross correlation can be used to identify different features in a single set of time series from an array of stations. The observations and model show that an array of microbarographs are able to resolve rolls if they are properly distributed with their spacing being tuned according to roll wavelength.