scholarly journals The impact of spin‐up and resolution on the representation of a clear convective boundary layer over London in order 100 m grid‐length versions of the Met Office Unified Model

2019 ◽  
Vol 145 (721) ◽  
pp. 1674-1689 ◽  
Author(s):  
Humphrey W. Lean ◽  
Janet F. Barlow ◽  
Christos H. Halios
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Unified Model ◽  
Convective Boundary ◽  
The Impact ◽  
Grid Length

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.

scholarly journals Integrating canopy and large-scale effects in the convective boundary-layer dynamics during the CHATS experiment

2017 ◽  
Vol 17 (3) ◽  
pp. 1623-1640 ◽  
Author(s):  
Metodija M. Shapkalijevski ◽  
Huug G. Ouwersloot ◽  
Arnold F. Moene ◽  
Jordi Vilà-Guerau de Arrellano
Keyword(s):  
Boundary Layer ◽  
Latent Heat ◽  
Convective Boundary Layer ◽  
Friction Velocity ◽  
Surface Fluxes ◽  
Convective Boundary ◽  
Diurnal Variability ◽  
Drag Coefficients ◽  
Boundary Layer Dynamics ◽  
The Impact

Abstract. By characterizing the dynamics of a convective boundary layer above a relatively sparse and uniform orchard canopy, we investigated the impact of the roughness-sublayer (RSL) representation on the predicted diurnal variability of surface fluxes and state variables. Our approach combined numerical experiments, using an atmospheric mixed-layer model including a land-surface-vegetation representation, and measurements from the Canopy Horizontal Array Turbulence Study (CHATS) field experiment near Dixon, California. The RSL is parameterized using an additional factor in the standard Monin–Obukhov similarity theory flux-profile relationships that takes into account the canopy influence on the atmospheric flow. We selected a representative case characterized by southerly wind conditions to ensure well-developed RSL over the orchard canopy. We then investigated the sensitivity of the diurnal variability of the boundary-layer dynamics to the changes in the RSL key scales, the canopy adjustment length scale, Lc, and the β = u*/|U| ratio at the top of the canopy due to their stability and dependence on canopy structure. We found that the inclusion of the RSL parameterization resulted in improved prediction of the diurnal evolution of the near-surface mean quantities (e.g. up to 50 % for the wind velocity) and transfer (drag) coefficients. We found relatively insignificant effects on the modelled surface fluxes (e.g. up to 5 % for the friction velocity, while 3 % for the sensible and latent heat), which is due to the compensating effect between the mean gradients and the drag coefficients, both of which are largely affected by the RSL parameterization. When varying Lc (from 10 to 20 m) and β (from 0.25 to 0.4 m), based on observational evidence, the predicted friction velocity is found to vary by up to 25 % and the modelled surface-energy fluxes (sensible heat, SH, and latent heat of evaporation, LE) vary up to 2 and 9 %. Consequently, the boundary-layer height varies up to 6 %. Furthermore, our analysis indicated that to interpret the CHATS measurements above the canopy, the contributions of non-local effects such as entrainment, subsidence and the advection of heat and moisture over the CHATS site need to be taken into account.

scholarly journals The Impact of Sensor Response and Airspeed on the Representation of the Convective Boundary Layer and Airmass Boundaries by Small Unmanned Aircraft Systems

2018 ◽  
Vol 35 (8) ◽  
pp. 1687-1699 ◽  
Author(s):  
Adam L. Houston ◽  
Jason M. Keeler
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Sensor Response ◽  
Unmanned Aircraft ◽  
Unmanned Aircraft Systems ◽  
Lapse Rate ◽  
Convective Boundary ◽  
Aircraft Systems ◽  
The Impact ◽  
Rotary Wing

AbstractThe objective of the research presented is to assess the impact of sensor response and aircraft airspeed on the accuracy of in situ observations collected by small unmanned aircraft systems profiling the convective boundary layer or transecting airmass boundaries. Estimates are made using simulated aircraft flown within large-eddy simulations. Both instantaneous errors (differences between observed temperature, which include the effects of sensor response and airspeed, and actual temperature) and errors in representation (differences between serial observations and representative snapshots of the atmospheric state) are considered. Synthetic data are retrieved assuming a well-aspirated first-order sensor mounted on rotary-wing aircraft operated as profilers in a simulated CBL and fixed-wing aircraft operated through transects across a simulated airmass boundary. Instantaneous errors are found to scale directly with sensor response time and airspeed for both CBL and airmass boundary experiments. Maximum errors tend to be larger for airmass boundary transects compared to the CBL profiles. Instantaneous errors for rotary-wing aircraft profiles in the CBL simulated for this work are attributable to the background lapse rate and not to turbulent temperature perturbations. For airmass boundary flights, representation accuracy is found to degrade with decreasing airspeed. This signal is most pronounced for flights that encounter the density current wake. When representation errors also include instantaneous errors resulting from sensor response, instantaneous errors are found to be dominant for flights that remain below the turbulent wake. However, for flights that encounter the wake, sensor response times generally need to exceed ~5 s before instantaneous errors become larger than errors in representation.

scholarly journals Ship plume dispersion rates in convective boundary layers for chemistry models

2008 ◽  
Vol 8 (2) ◽  
pp. 6793-6824
Author(s):  
F. Chosson ◽  
R. Paoli ◽  
B. Cuenot
Keyword(s):  
Boundary Layer ◽  
Dilution Rate ◽  
Convective Boundary Layer ◽  
Time Scale ◽  
High Dispersion ◽  
Minor Effect ◽  
Plume Rise ◽  
Plume Dispersion ◽  
Convective Boundary ◽  
The Impact

Abstract. Detailed ship plume simulations in various convective boundary layer situations have been performed using a Lagrangian Dispersion Model driven by a Large Eddy Simulation Model. The simulations focus on early stage (1–2 h) of plume dispersion regime and take into account the effects of plume rise on dispersion. Results are presented in an attempt to provide to chemical modellers community a realistic description of the impact of characteristic dispersion on exhaust ship plume chemistry. Plume dispersion simulations are used to derive analytical dilution rate functions. Even though results exhibit striking effects of plume rise parameter on dispersion patterns, it is shown that initial buoyancy fluxes at ship stack have minor effect on plume dilution rate. After initial high dispersion regimes a simple characteristic dilution time scale can be used to parameterize the subgrid plume dilution effects in large scale chemistry models. The results show that this parameter is directly related to the typical turn-over time scale of the convective boundary layer.

scholarly journals The Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface

2005 ◽  
Vol 62 (7) ◽  
pp. 2078-2097 ◽  
Author(s):  
Edward G. Patton ◽  
Peter P. Sullivan ◽  
Chin-Hoh Moeng
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Convective Boundary Layer ◽  
Land Surface ◽  
Surface Flux ◽  
Scalar Fields ◽  
Surface Fluxes ◽  
Convective Boundary ◽  
Turbulent Statistics ◽  
The Impact

Abstract This manuscript describes numerical experiments investigating the influence of 2–30-km striplike heterogeneity on wet and dry convective boundary layers coupled to the land surface. The striplike heterogeneity is shown to dramatically alter the structure of the convective boundary layer by inducing significant organized circulations that modify turbulent statistics. The impact, strength, and extent of the organized motions depend critically on the scale of the heterogeneity λ relative to the boundary layer height zi. The coupling with the land surface modifies the surface fluxes and hence the circulations resulting in some differences compared to previous studies using fixed surface forcing. Because of the coupling, surface fluxes in the middle of the patches are small compared to the patch edges. At large heterogeneity scales (λ/zi ∼18) horizontal surface-flux gradients within each patch are strong enough to counter the surface-flux gradients between wet and dry patches allowing the formation of small cells within the patch coexisting with the large-scale patch-induced circulations. The strongest patch-induced motions occur in cases with 4 < λ/zi < 9 because of strong horizontal pressure gradients across the wet and dry patches. Total boundary layer turbulence kinetic energy increases significantly for surface heterogeneity at scales between λ/zi = 4 and 9; however, entrainment rates for all cases are largely unaffected by the striplike heterogeneity. Velocity and scalar fields respond differently to variations of heterogeneity scale. The patch-induced motions have little influence on total vertical scalar flux, but the relative contribution to the flux from organized motions compared to background turbulence varies with heterogeneity scale. Patch-induced motions are shown to dramatically impact point measurements in a free-convective boundary layer. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

scholarly journals A Scale-Adaptive Turbulent Kinetic Energy Closure for the Dry Convective Boundary Layer

2018 ◽  
Vol 75 (2) ◽  
pp. 675-690 ◽  
Author(s):  
Marcin J. Kurowski ◽  
João Teixeira
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Convective Boundary Layer ◽  
Mixing Length ◽  
Subgrid Scale ◽  
Convective Boundary ◽  
Continuous Transition ◽  
Simple Method ◽  
Grid Length

Abstract A pragmatic scale-adaptive turbulent kinetic energy (TKE) closure is proposed to simulate the dry convective boundary layer for a variety of horizontal grid resolutions: from 50 m, typical of large-eddy simulation models that use three-dimensional turbulence parameterizations/closures, up to 100 km, typical of climate models that use one-dimensional turbulence and convection parameterizations/closures. Since parameterizations/closures using the TKE approach have been frequently used in these two asymptotic limits, a simple method is proposed to merge them with a mixing-length-scale formulation for intermediate resolutions. This new scale-adaptive mixing length naturally increases with increasing grid length until it saturates as the grid length reaches mesoscale-model resolution. The results obtained using this new approach for dry convective boundary layers are promising. The mean vertical profiles of potential temperature and heat flux remain in good agreement for different resolutions. A continuous transition (in terms of resolution) across the gray zone is illustrated through the partitioning between the model-resolved and the subgrid-scale transports as well as by documenting the transition of the subgrid-scale TKE source/sink terms. In summary, a natural and continuous transition across resolutions (from 50 m to 100 km) is obtained, for dry convection, using exactly the same atmospheric model for all resolutions with a simple scale-adaptive mixing-length formulation.

scholarly journals Integrating canopy and large-scale atmospheric effects in convective boundary-layer dynamics during CHATS experiment

2016 ◽  
Author(s):  
Metodija M. Shapkalijevski ◽  
G. Huug Ouwersloot ◽  
F. Arnold Moene ◽  
Jordi Vilà‐Guerau Arellano
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Friction Velocity ◽  
Surface Fluxes ◽  
Atmospheric Effects ◽  
Convective Boundary ◽  
Diurnal Variability ◽  
Drag Coefficients ◽  
Boundary Layer Dynamics ◽  
The Impact

Abstract. By characterizing the dynamics of a convective boundary layer above a relatively sparse and uniform orchard canopy, we investigated the impact of the roughness sublayer (RSL) representation on the predicted diurnal variability of surface fluxes and state variables. Our approach combined numerical experiments, using an atmospheric mixed-layer model including a land surface-vegetation representation, and measurements from the Canopy Horizontal Array Turbulence Study (CHATS) field experiment near Dixon, California. The RSL is parameterized using an additional factor in the standard Monin-Obukhov Similarity Theory flux-profile relationships that takes into account the canopy’s influence on the atmospheric flow. We selected a representative case characterised by southerly wind conditions to ensure well-developed RSL over the orchard canopy. We then investigated the sensitivity of the diurnal variability of the boundary-layer dynamics to the changes in the RSL key scales, the canopy adjustment length scale, Lc, and the β = u*/|U| ratio at the top of the canopy, due to their stability and dependence on canopy structure. We found that the inclusion of the RSL parameterisation resulted in improved prediction of the diurnal evolution of the near-surface mean quantities (e.g. up to 50 % for the wind velocity) and transfer (drag) coefficients. We found relatively insignificant effects on the modelled surface fluxes (e.g. up to 5 % for the friction velocity, while 3 % for the sensible and latent heat), which is due to the compensating effect between the mean gradients and the drag coefficients, which are both largely affected by the RSL parameterisation. When varying Lc (from 10 to 20 m) and β (from 0.25 to 0.4), based on observational evidence, the predicted friction velocity is found to vary by up to 25 % and the modeled surface energy fluxes (SH and LE) vary up to 2 % and 9 %, respectively. Consequently, the boundary-layer height varies up to 6 %. Furthermore, our analysis indicated that to interpret the CHATS measurements above the canopy, the contributions of non-local effects such as entrainment, subsidence and the advection of heat and moisture over the CHATS site need to be taken into account.

scholarly journals Investigation of the Spatial Variability of the Convective Boundary Layer Heights over an Isolated Mountain: Cases from the MATERHORN-2012 Experiment

2016 ◽  
Vol 55 (9) ◽  
pp. 1927-1952 ◽  
Author(s):  
S. Pal ◽  
S. F. J. De Wekker ◽  
G. D. Emmitt
Keyword(s):  
Boundary Layer ◽  
Spatial Variability ◽  
Convective Boundary Layer ◽  
Land Surface ◽  
Atmospheric Modeling ◽  
Spatiotemporal Variability ◽  
Leg Length ◽  
Convective Boundary ◽  
Synoptic Conditions ◽  
The Impact

AbstractSpatiotemporal variability in the convective boundary layer height zi over complex terrain is governed by numerous factors such as land surface processes, topography, and synoptic conditions. Observational datasets to evaluate weather forecast models that simulate this variability are sparse. This study aims to investigate the zi spatial variability (along a total leg length of 1800 km) around and over a steep isolated mountain (Granite Mountain) of horizontal and vertical dimensions of 8 and 0.9 km, respectively. An airborne Doppler lidar was deployed on seven flights during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) campaign conducted at Dugway Proving Ground (Utah) from 25 September to 24 October 2012. During the afternoon, an east–west zi gradient over the region with zi that was approximately 200 m higher on the eastern side than on the western side of Granite Mountain was observed. This gradient illustrates the impact of two different land surface properties on zi spatial variability, with a sparsely vegetated desert steppe region on the east and a dry, bare lake-bed desert with high subsurface soil moisture to the west of Granite Mountain. Additionally, the zi spatial variability was partly attributed to the impact of Granite Mountain on the downwind zi. Differences in zi were also observed by the radiosonde measurements in the afternoon but not in the morning as the zi variability in morning were modulated by the topography. The high-resolution lidar-derived zi measurements were used to estimate the entrainment zone thickness in the afternoon, with estimates ranging from 100 to 250 m.

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

2012 ◽  
Vol 12 (6) ◽  
pp. 13619-13665 ◽  
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 ◽  
Systematic Analysis ◽  
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 characterized as a convective boundary layer to analyse the influence of the dynamics on the chemical evolution of the ABL, using a systematic analysis that can easily be extended to other periods during HUMPPA-COPEC-2010. 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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