Analysis of differences between thermodynamic and material boundary layer structure: Comparison of detection by ceilometer and microwave radiometer

Abstract

Planetary boundary layer height (PBLH) is a key parameter for air quality prediction and boundary layer meteorology studies. The height of thermodynamic boundary layer (Hθ) and material boundary layer (HC) in different seasons are compared by using microwave radiometer (MWR) and ceilometer. There are considerable differences between Hθ and HC and the causes are further studied. We found that when the boundary layer is markedly stable at night, the MWR's algorithm used to estimate PBLH has a retrieval restriction and directly leads to a much higher Hθ than HC (1 to 2.5 km higher). This unrealistic PBLH can be identified and eliminated effectively by using temperature differences from the surface to 1 km. During periods of transportation and diffusion of aerosols, strong southerly winds transporting pollutants northward above Hθ or strong northerly winds throughout the boundary layer removing pollutants will cause a much higher HC than Hθ (0.5 to 2 km higher). However, when transportation occurs in the lower layer within Hθ, HC and Hθ are consistent. The aerosol layers is able to characterize the multiple-layered structure of the nocturnal boundary layer (NBL) and the evolution of the boundary layer by using backscatter. The stable boundary layer (SBL) ranges from 0.3 to 0.6 km at night. Compared with the idealized thermodynamic boundary layer, there isn't a distinct boundary between the SBL and the growing mixing layer (ML) after sunrise. The residual layer (RL) ranges from 0.5 to 1.5 km, it lasts 4 or 5 h after sunrise and shows up again within 2 h after sunset. The maximum detectable range of Doppler Lidar has a large backscatter gradient, so is strongly consistent with the RL at night and the ML in the daytime during a pollution event. The combined observation of microwave radiometer and ceilometer can well reveal the completed characteristics of boundary layer structures.