Estimate of Boundary-Layer Depth Over Beijing, China, Using Doppler Lidar Data During SURF-2015

Abstract

Planetary boundary-layer (PBL) structure was investigated using observations from a Doppler lidar and the 325-m Institute of Atmospheric Physics (IAP) meteorological tower in the centre of Beijing during the summer 2015 Study of Urban-impacts on Rainfall and Fog/haze (SURF-2015) field campaign. Using six fair-weather days of lidar and tower data under clear to cloudy skies, we evaluate the ability of the Doppler lidar to probe the urban boundary-layer structure, and then propose a composite method for estimating the diurnal cycle of the PBL depth using the Doppler lidar. For the convective boundary layer (CBL), a threshold method using vertical velocity variance (σ 2 w > 0.1 m 2 s −2 ) is used, since it provides more reliable CBL depths than a conventional maximum wind-shear method. The nocturnal boundary-layer (NBL) depth is defined as the height at which σ 2 w decreases to 10 % of its near-surface maximum minus a background variance. The PBL depths determined by combining these methods have average values ranging from ≈270 to ≈1500 m for the six days, with the greatest maximum depths associated with clear skies. Release of stored and anthropogenic heat contributes to the maintenance of turbulence until late evening, keeping the NBL near-neutral and deeper at night than would be expected over a natural surface. The NBL typically becomes more shallow with time, but grows in the presence of low-level nocturnal jets. While current results are promising, data over a broader range of conditions are needed to fully develop our PBL-depth algorithms.

Estudo do ciclo diário da Camada Limite Planetária durante a estação cChuvosa da Amazônia (GOAmazon 2014/15)

“…O Sodar, devido ao seu alcance vertical baixo, foi utilizado apenas para medidas na fase da CLN, em geral, subestimou (~150 m) os valores desta. Por outro lado, o Lidar que se pode verificar a fase convectiva da CLP, apresentou medições satisfatórias, principalmente, na fase de erosão da CLN e desenvolvimento da CLC, resultados que estão de acordo com descritos por Huang et al (2017), onde os autores afirmam que o Lidar produz valores semelhantes a profundidade da CLP durante o período de transição. Após este período este mostra uma subestimativa (~200 m), na fase final da CLC, onde a começa a ocorrer o decaimento da convecção.…”

Observation of nocturnal low-level wind shear and particulate matter in urban Beijing using a Doppler wind lidar

“…This weather condition was favorable for local Huang et al 2017), particularly because the high-frequency data afforded by this technology can be used to characterize low-level wind structures in detail. In addition, moving wind-profile measurements by Doppler lidar have generally been based on slow-moving ship-borne platforms (Pichugina et al 2012;Achtert et al 2015), rather than road vehicles in urban areas.…”

Spatiotemporal visualization of wind turbulence from measurements by a Windcube 200s lidar in the atmospheric boundary layer

“…Fig.5(c) means that the estimate of the integral scale of turbulence exceeds 500 m. In the distributions for the dissipation rate and the kinetic energy, we can clearly see how the thickness of the layer of intense turbulent mixing of air masses changed in time, achieving approximately 700 m at the maximum (at 13:30 Local Time). Some methods for determination of the thickness of the mixing layer mix h have been developed earlier [17][18][19][20][21]. In contrast to these methods, we determined mix h from the drop of the vertical profile ( ) k h ε down to the level of 4 10 − m 2 /s 3 .…”