Lidar Observations of Aerosols, Cloud Bases, and Inferred Boundary Layer Stability

Stability versus mixing within the boundary layer is a key control on both air quality and the transport of surface fluxes to the cloud layer. Additional conditions that impact air quality include local and distant sources of aerosols, and weather conditions–especially how recently rain has occurred. We examine backscatter and linear depolarization ratio (LDR) data from a vertically-pointing LiDAR ceilometer to characterize stable versus well-mixed conditions at a research observation site in Plymouth, NC as well as to identify aerosol layers aloft, clouds, precipitation, and swarms of flying insects. Backscatter is a measure of how much light an object scatters and LDR is a measure of how much of that light is depolarized which is a function of the roundness of scatterers. Initial analysis has demonstrated that aerosols, rain, cloud, and ice usually manifest within distinct regions in the backscatter vs. LDR phase space. We plan to add additional variables to the cluster analysis based on “texture” of the signals in the time-height plots in terms of gradients in the vertical and with time. In stable conditions, aerosols are often arranged in thin horizontal layers. We are testing image processing methods such as Sobel edge detection to distinguish these layers. Our goals are to determine the relative stability of the boundary layer, the altitudes of cloud bases, and whether it is raining or not.