Observations of coherent structures from a scanning lidar over an irrigated orchard

Abstract

The exchange of mass and energy is a turbulent process that often occurs in coherent periods of time and in discrete regions of space. Prior to the development of volume imaging lidars, the study of coherent structures in the atmosphere was limited, for the most part, to time-series analysis of point-instrument data. This paper describes the use of the Los Alamos National Laboratories scanning Raman lidar to observe both temporal and spatial coherent structures, such as plume and ramp-like features, that developed over a Green Ash orchard. Most of the ramp structures identified from lidar data were between 20 and 30 m in size and had transit lifetimes of between 20 and 30 s. The validity of these results was confirmed by comparison with previously collected point-instrument data. An analysis of the multi-dimensional lidar images was also able to relate discrete spatial features, such as plumes to ramp patterns, found at the base of plumes in both the temporal and spatial domains. A further finding supports the concept that ramp development is a function of shear-scale and roughness length. The lidar represents a new tool to gain a deeper understanding of the mechanisms underlying the turbulent exchange process.