scholarly journals The impact of embedded valleys on daytime pollution transport over a mountain range

2015 ◽  
Vol 15 (20) ◽  
pp. 11981-11998 ◽  
Author(s):  
M. N. Lang ◽  
A. Gohm ◽  
J. S. Wagner
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Mountain Range ◽  
Topographic Effects ◽  
Pollution Transport ◽  
Convective Boundary ◽  
Vertical Exchange ◽  
Boundary Layer Height ◽  
Thermally Driven ◽  
The Impact

Abstract. Idealized large-eddy simulations were performed to investigate the impact of different mountain geometries on daytime pollution transport by thermally driven winds. The main objective was to determine interactions between plain-to-mountain and slope wind systems, and their influence on the pollution distribution over complex terrain. For this purpose, tracer analyses were conducted over a quasi-two-dimensional mountain range with embedded valleys bordered by ridges with different crest heights and a flat foreland in cross-mountain direction. The valley depth was varied systematically. It was found that different flow regimes develop dependent on the valley floor height. In the case of elevated valley floors, the plain-to-mountain wind descends into the potentially warmer valley and replaces the opposing upslope wind. This superimposed plain-to-mountain wind increases the pollution transport towards the main ridge by an additional 20 % compared to the regime with a deep valley. Due to mountain and advective venting, the vertical exchange is 3.6 times higher over complex terrain than over a flat plain. However, the calculated vertical exchange is strongly sensitive to the definition of the convective boundary layer height. In summary, the impact of the terrain geometry on the mechanisms of pollution transport confirms the necessity to account for topographic effects in future boundary layer parameterization schemes.

scholarly journals The impact of embedded valleys on daytime pollution transport over a mountain range

2015 ◽  
Vol 15 (10) ◽  
pp. 14315-14356 ◽  
Author(s):  
M. N. Lang ◽  
A. Gohm ◽  
J. S. Wagner
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Mountain Range ◽  
Topographic Effects ◽  
Pollution Transport ◽  
Vertical Exchange ◽  
Boundary Layer Height ◽  
Thermally Driven ◽  
Definition Of ◽  
The Impact

Abstract. Idealized large-eddy simulations were performed to investigate the impact of different mountain geometries on daytime pollution transport by thermally driven winds. The main objective was to determine interactions between plain-to-mountain and slope wind systems, and their influence on the pollution distribution over complex terrain. For this purpose, tracer analyses were conducted over a quasi-two-dimensional mountain range with embedded valleys and a flat foreland in cross-mountain direction. The valley depth was varied systematically. It was found that different flow regimes develop dependent on the valley floor height. In the case of elevated valley floors, the plain-to-mountain wind descends into the potentially warmer valley and replaces the opposing upslope wind. This superimposed plain-to-mountain wind increases the pollution transport towards the main ridge by additional 20% compared to the regime with a deep valley. Due to mountain and advective venting, the vertical exchange is 3.6 times higher over complex terrain than over a flat plain. However, the calculated vertical exchange is strongly sensitive to the definition of the atmospheric boundary layer height. In summary, the impact of the terrain geometry on the mechanisms of pollution transport confirms the necessity to account for topographic effects in future boundary layer parameterization schemes.

scholarly journals Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings

2014 ◽  
Vol 14 (13) ◽  
pp. 19247-19291 ◽  
Author(s):  
H. Pietersen ◽  
J. Vilà-Guerau de Arellano ◽  
P. Augustin ◽  
O. de Coster ◽  
H. Delbarre ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Surface Heterogeneity ◽  
Small Scale ◽  
Mountain Range ◽  
Convective Boundary ◽  
Good Correspondence ◽  
Data Set ◽  
Boundary Layer Height ◽  
Boundary Layer Dynamics

Abstract. We study the disturbances of CBL dynamics due to large-scale atmospheric contributions for a representative day observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign. We first reproduce the observed boundary-layer dynamics by combining the Dutch Atmospheric Large-Eddy Simulation (DALES) model with a mixed-layer theory based model. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70%. If we constrain our numerical experiments with the BLLAST comprehensive data set, we are able to quantify the contributions of advection of heat and moisture, and subsidence. We find that subsidence has a clear diurnal pattern. Supported by the presence of a nearby mountain range, this pattern suggests that not only synoptic scales exert their influence on the boundary layer, but also mesoscale circulations. Finally, we study whether the vertical and temporal evolution of turbulent variables are influenced by these large-scale forcings. Our model results show good correspondence of the vertical structure of turbulent variables with observations. Our findings further indicate that when large-scale advection and subsidence are applied, the values for turbulent kinetic are lower than without these large-scale forcings. We conclude that the prototypical CBL can still be used as a valid representation of the boundary-layer dynamics near regions characterized by complex topography and small-scale surface heterogeneity, provided that surface- and large-scale forcings are well characterized.

scholarly journals Observational and Numerical Evidence of Depressed Convective Boundary Layer Heights near a Mountain Base

2008 ◽  
Vol 47 (4) ◽  
pp. 1017-1026 ◽  
Author(s):  
Stephan F. J. De Wekker
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Layer Growth ◽  
Air Pollutant ◽  
Convective Boundary ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Numerical Studies ◽  
Thermally Driven ◽  
Show Evidence

Abstract Recent field and numerical studies show evidence of the existence of a convective boundary layer height depression near a mountain base. This depression can have implications for air pollutant transport and concentrations in complex terrain. To investigate the mechanisms underlying this phenomenon, idealized simulations with a mesoscale numerical model are performed and combined with available observations. The idealized simulations with a single mountain ridge of various dimensions suggest that the depression evolves in time, is most pronounced in the late afternoon, and becomes larger as slope steepness increases. Observations and modeling results show that the atmosphere is heated more intensely near the mountain base than far away from the mountain base, not only inside the boundary layer but also above. The enhanced heating aloft affects boundary layer growth near the mountain base and is associated with the boundary layer height depression. An analysis of the different terms in the temperature tendency equation indicates that vertical and horizontal advection of warm air, associated with the thermally driven circulation along the mountain slope, play a role in this enhanced heating aloft.

scholarly journals The impact of a foehn wind on PM10 concentrations and the urban boundary layer in complex terrain: a case study from Kraków, Poland

Tellus B ◽  
2021 ◽  
Vol 73 (1) ◽  
pp. 1-26
Author(s):  
Piotr Sekuła ◽  
Anita Bokwa ◽  
Zbigniew Ustrnul ◽  
Mirosław Zimnoch ◽  
Bogdan Bochenek
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Urban Boundary Layer ◽  
The Impact

scholarly journals Technical note: Boundary layer height determination from Lidar for improving air pollution episode modelling: development of new algorithm and evaluation

2017 ◽  
Author(s):  
Ting Yang ◽  
Zifa Wang ◽  
Wei Zhang ◽  
Alex Gbaguidi ◽  
Nubuo Sugimoto ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
High Performance ◽  
Accurate Determination ◽  
Technical Note ◽  
Strong Increase ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Retrieval Algorithms ◽  
The Impact

Abstract. Predicting air pollution events in low atmosphere over megacities requires thorough understanding of the tropospheric dynamic and chemical processes, involving notably, continuous and accurate determination of the boundary layer height (BLH). Through intensive observations experimented over Beijing (China), and an exhaustive evaluation existing algorithms applied to the BLH determination, persistent critical limitations are noticed, in particular over polluted episodes. Basically, under weak thermal convection with high aerosol loading, none of the retrieval algorithms is able to fully capture the diurnal cycle of the BLH due to pollutant insufficient vertical mixing in the boundary layer associated with the impact of gravity waves on the tropospheric structure. Subsequently, a new approach based on gravity wave theory (the cubic root gradient method: CRGM), is developed to overcome such weakness and accurately reproduce the fluctuations of the BLH under various atmospheric pollution conditions. Comprehensive evaluation of CRGM highlights its high performance in determining BLH from Lidar. In comparison with the existing retrieval algorithms, the CRGM potentially reduces related computational uncertainties and errors from BLH determination (strong increase of correlation coefficient from 0.44 to 0.91 and significant decrease of the root mean square error from 643 m to 142 m). Such newly developed technique is undoubtedly expected to contribute to improve the accuracy of air quality modelling and forecasting systems.

scholarly journals Relationship analysis of PM<sub>2.5</sub> and boundary layer height using an aerosol and turbulence detection lidar

2019 ◽  
Vol 12 (6) ◽  
pp. 3303-3315 ◽  
Author(s):  
Chong Wang ◽  
Mingjiao Jia ◽  
Haiyun Xia ◽  
Yunbin Wu ◽  
Tianwen Wei ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Weather Forecasting ◽  
Direct Detection ◽  
Vertical Wind ◽  
Precipitation Event ◽  
Cloud Base ◽  
Convective Boundary ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Relationship Analysis

Abstract. The atmospheric boundary layer height (BLH) is a key parameter in weather forecasting and air quality prediction. To investigate the relationship between BLH and air pollution under different conditions, a compact micro-pulse lidar integrating both direct-detection lidar (DDL) and coherent Doppler wind lidar (CDWL) has been built. This hybrid lidar is operated at 1.5 µm, which is eye-safe and made of all-fibre components. The BLH can be determined from aerosol density and vertical wind independently. During a 45 h continuous observation in June 2018, the stable boundary layer, residual layer and convective boundary layer are identified. The fine structure of the aerosol layers, drizzles and vertical wind near the cloud base are also detected. In comparison, the standard deviation between BLH values derived from DDL and CDWL is 0.06 km, indicating the accuracy of this work. The retrieved convective BLH is a little higher than that from ERA5 reanalysis due to different retrieval methods. Correlation between different BLH and PM2.5 is strongly negative before a precipitation event and becomes much weaker after the precipitation. Different relationships between PM2.5 and BLH may result from different BLH retrieval methods, pollutant sources and meteorological conditions.

Aspects of the convective boundary layer structure over complex terrain

1998 ◽  
Vol 32 (7) ◽  
pp. 1323-1348 ◽  
Author(s):  
M. Kossmann ◽  
R. Vögtlin ◽  
U. Corsmeier ◽  
B. Vogel ◽  
F. Fiedler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Complex Terrain ◽  
Layer Structure ◽  
Convective Boundary ◽  
Boundary Layer Structure

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

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