Measurements of Boundary Layer Wind Profiles with Scanning Doppler Lidar

Abstract

Understanding characteristics of the planetary boundary layer (PBL) is important since winds and PBL height have a strong influence on the dispersion of pollutants and its precursors that are emitted from the surface and, therefore is closely related with human health. Lack of observations of parameters that influence and are influenced by PBL dynamics, such as wind and aerosol distribution, has made it difficult to define the characteristics of PBL solely on numerical model and parameterization schemes. With remote sensing techniques, continuous observation of winds and aerosols within the PBL is possible. In this study, the evolution of planetary boundary layer winds and aerosol characteristics was investigated using co-located lidar observations. Measurement of winds within the PBL was done with a wind Doppler lidar (WDL) at Seoul National University and WISE Jungnang station. Assessment of the WDL wind results was carried out by comparing observations with radiosonde soundings. In retrieving wind data from WDL radial velocity, it was concluded that using singular value decomposition (SVD) on the mean radial velocities of 15 minutes showed the best agreement with radiosonde measurements with a bias of 0.66 m s-1 and root mean square error of 2.38 m s-1. In determining PBL height, the gradient method on aerosol backscatter signal profiles from Mie-scattering lidar and the threshold method on vertical wind velocity variance were used on observation data from 25th to 31st May 2016. PBL height determined by each method showed reasonable diurnal variation, although PBL heights were irretrievable for some points due to operational shortcomings of WDL. Thermally induced winds were detected for a few days during the observation period with strong winds in the afternoon and weak at night. For those days when surface heating was a major driving force of winds, the diurnal variation of wind direction showed the characteristics of mountain and valley winds. In the case of wind observations at WISE Jungnang site, wind direction was more influenced by the synoptic weather pattern.