Applicability Assessment of Coherent Doppler Wind LiDAR for Monitoring during Dusty Weather at the Northern Edge of the Tibetan Plateau

Abstract: Wind profile light detection and ranging (LiDAR) is an important tool for observing features within the atmospheric boundary layer. Observations of the wind field and boundary layer height from coherent Doppler wind LiDARs (CDWLs) under sandy and dusty weather conditions were evaluated using observations from two CDWLs and one GTS radio sounding located at the northern edge of the Tibetan plateau from 1 May to 30 August 2021. The results showed that CDWL has good applicability in reproducing wind fields in dust, precipitation, and in clear-sky conditions, and that it is superior to the v wind field for real measurements of the u wind fields. In terms of the planetary boundary layer height (PBLH), the validity of the inversion of PBLH in dusty weather was higher than that under clear-sky conditions. It was found that the PBLH retrieved by the CDWL at 20:00 (BJT) was better than that at 08:00 (BJT). The diurnal variation amplitude of the PBLH before the occurrence of a sandstorm was larger than the diurnal variation amplitude of the PBLH occurring during a sandstorm.

Keywords: coherent doppler wind LiDAR; northern edge of Tibetan plateau; dusty weather; monitoring application assessment

Introduction

Sandy weather has a significant impact on arid regions, with the immediate effect of causing air pollution and mesoscale to large-scale climate change [1–3]. It was discovered that dust storms can affect the heat balance of planetary radiation, which in turn leads to climate change [4].

In recent years, scientists have conducted numerous studies on dust cycles, dust properties, and the environmental effects of dust using ground-based light detection and ranging (LiDAR) information such as the optical intensity, backscatter intensity, depolarization ratio, extinction coefficient, and dual-wavelength signal ratio [5– 7 ]. Laser wind measurement techniques have developed rapidly during the past decades and are mostly used in wind
field observation [ 8], aircraft wake measurements [ 9], turbulence measurements [ 10 ], cloud and atmospheric boundary layer characterization [11 ], and atmospheric aerosol optical characterization [12]. The fluctuation of boundary layer height with time and the effect of the entrainment layer and vertical wind speed on the boundary layer height were found using micro–pulse LiDAR observations [ 13 ]. The boundary layer height retrieved by direct detection LiDAR and coherent Doppler wind LiDAR (CDWL) were correlated with PM2.5 to study a precipitation event [ 14 ]. Ground–based and air–based LiDARs combined with ground–based aerosol mass concentrations were used to analyze the optical and physical
properties of a dust process [ 15]. The characteristics of the dust aerosol backscattering coefficient, extinction coefficient, and depolarization ratio have been gradually studied by using polarization LiDAR to monitor pollution and dust storm weather in cities [ 16 – 19 ]. The direct observation of seasonal dust weather can be used to study the frequency and intensity of dust [ 20 ] and effectively evaluate the effect of air pollution control [21 ]. LiDAR
was used to analyze the aerosol extinction coefficients for the inversion of dusty weather processes and to obtain correlations between the extinction coefficients and ground-level PM10 concentrations [22 ]. During the observation of the atmospheric boundary layer of an urban area using 3D scanning coherent Doppler LiDAR, multiple dust-devil-like vortices were detected in the area, and the temporal evolution of the precise 3D structure and vortex intensity was observed [ 23 ]. Detection means such as ground-based radar combined with satellite remote-sensing LiDAR can be used to analyze the transport characteristics and optical properties of sand and dust [24 ]. More novel experiments have been used in the past to quantify changes in aerosol transport and aerosol properties from the Sahara Desert to the Caribbean Sea by means of airborne coherent Doppler wind LiDAR experiments [25 ].Observations of dust events in Iceland have confirmed the possibility of using Doppler wind LiDAR to monitor volcanic and sedimentary aerosols [26 ]. The simultaneous 3D monitoring of wind and pollution is performed using coherent Doppler wind LiDAR, which then generates a high-resolution wind field to track local air pollution sources and their dispersal, as well as to analyze transboundary air pollution events [27].

Previously, there have been no relevant observations and studies on the long duration and continuity of dust storms and floating dust weather at the northern edge of the Tibetan plateau using the coherent Doppler wind LiDAR (CDWL). The vertical evolution pattern of dust aerosol concentration and meteorological elements during the maintenance of dusty weather is not clear. This project proposes the use of CDWL installed at the Minfeng and Yeyik stations on the northern side of the Tibetan plateau region, combined with GTS ratio soundings, to conduct a study on the evolution of the atmospheric boundary layer before and after sand and dust storms and during persistent dusty weather. The objective was to
evaluate the applicability of CDWL in the observation of boundary layer elements under sandy and dusty weather to provide new observational support for the development of currently stagnant sand and dust studies. This study was conducted as a basis for the quantitative assessment of the contribution of dusty weather to regional atmospheric dust aerosols and its impact on regional and global changes.

This paper is organized as follows: The site and data resources are described in Section 2. Section 3 provides a comparative analysis of the wind field data observed by CDWL and GTS soundings and evaluates the performance of CDWL wind field obser- vations. Section 4 compares the effect of CDWL on the planetary boundary layer height (PBLH) inversion under different weather conditions. Finally, a discussion and conclusions are provided in Sections 5 and 6. If not specified, Beijing time (BJT) is used in this paper.