The behaviour of a mixed-layer model of the convective boundary layer coupled to a big leaf model of surface energy partitioning

1998 ◽  
Vol 88 (1) ◽  
pp. 87-101 ◽  
Author(s):  
C. Huntingford ◽  
J. L. Monteith
Keyword(s):  
Boundary Layer ◽  
Surface Energy ◽  
Mixed Layer ◽  
Convective Boundary Layer ◽  
Energy Partitioning ◽  
Layer Model ◽  
Convective Boundary ◽  
Big Leaf Model ◽  
Leaf Model ◽  
Mixed Layer Model

Convective Boundary Layers Driven by Nonstationary Surface Heat Fluxes

2011 ◽  
Vol 68 (4) ◽  
pp. 727-738 ◽  
Author(s):  
Robert van Driel ◽  
Harm J. J. Jonker
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Layer Model ◽  
Convective Boundary ◽  
Surface Heat Fluxes ◽  
Large Eddy ◽  
Convective Boundary Layers ◽  
Mixed Layer Model

In this study the response of dry convective boundary layers to nonstationary surface heat fluxes is systematically investigated. This is relevant not only during sunset and sunrise but also, for example, when clouds modulate incoming solar radiation. Because the time scale of the associated change in surface heat fluxes may differ from case to case, the authors consider the generic situation of oscillatory surface heat fluxes with different frequencies and amplitudes and study the response of the boundary layer in terms of transfer functions. To this end both a mixed layer model (MLM) and a large-eddy simulation (LES) model are used; the latter is used to evaluate the predictive quality of the mixed layer model. The mixed layer model performs generally quite well for slow changes in the surface heat flux and provides analytical understanding of the transfer characteristics of the boundary layer such as amplitude and phase lag. For rapidly changing surface fluxes (i.e., changes within a time frame comparable to the large eddy turnover time), it proves important to account for the time it takes for the information to travel from the surface to higher levels of the boundary layer such as the inversion zone. As a follow-up to a 1997 study by Sorbjan, who showed that the conventional convective velocity scale is inadequate as a scaling quantity during the decay phase, this paper addresses the issue of defining, in (generic) transitional situations, a velocity scale that is solely based on the surface heat flux and its history.

scholarly journals Reexamining the Gradient and Countergradient Representation of the Local and Nonlocal Heat Fluxes in the Convective Boundary Layer

2018 ◽  
Vol 75 (7) ◽  
pp. 2317-2336 ◽  
Author(s):  
Bowen Zhou ◽  
Shiwei Sun ◽  
Kai Yao ◽  
Kefeng Zhu
Keyword(s):  
Boundary Layer ◽  
Temperature Gradient ◽  
Mixed Layer ◽  
Convective Boundary Layer ◽  
Correction Term ◽  
Potential Temperature ◽  
Heat Fluxes ◽  
Gradient Term ◽  
Convective Boundary ◽  
Upper Mixed Layer

Abstract Turbulent mixing in the daytime convective boundary layer (CBL) is carried out by organized nonlocal updrafts and smaller local eddies. In the upper mixed layer of the CBL, heat fluxes associated with nonlocal updrafts are directed up the local potential temperature gradient. To reproduce such countergradient behavior in parameterizations, a class of planetary boundary layer schemes adopts a countergradient correction term in addition to the classic downgradient eddy-diffusion term. Such schemes are popular because of their simple formulation and effective performance. This study reexamines those schemes to investigate the physical representations of the gradient and countergradient (GCG) terms, and to rebut the often-implied association of the GCG terms with heat fluxes due to local and nonlocal (LNL) eddies. To do so, large-eddy simulations (LESs) of six idealized CBL cases are performed. The GCG fluxes are computed a priori with horizontally averaged LES data, while the LNL fluxes are diagnosed through conditional sampling and Fourier decomposition of the LES flow field. It is found that in the upper mixed layer, the gradient term predicts downward fluxes in the presence of positive mean potential temperature gradient but is compensated by the upward countergradient correction flux, which is larger than the total heat flux. However, neither downward local fluxes nor larger-than-total nonlocal fluxes are diagnosed from LES. The difference reflects reduced turbulence efficiency for GCG fluxes and, in terms of physics, conceptual deficiencies in the GCG representation of CBL heat fluxes.

scholarly journals Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer

2013 ◽  
Vol 13 (12) ◽  
pp. 31527-31562 ◽  
Author(s):  
E. Blay-Carreras ◽  
D. Pino ◽  
A. Van de Boer ◽  
O. De Coster ◽  
C. Darbieu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Temporal Evolution ◽  
Residual Layer ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Previous Night ◽  
Morning Transition

Abstract. Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted airplane systems and two aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the numerical simulations are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable to model the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. The simulation shows a large increase of the entrainment buoyancy heat flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Additionally, we investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.

scholarly journals Observing Entrainment Mixing, Photochemical Ozone Production, and Regional Methane Emissions by Aircraft Using a Simple Mixed-Layer Model

2016 ◽  
Author(s):  
Justin F. Trousdell ◽  
Stephen A. Conley ◽  
Andy Post ◽  
Ian C. Faloona
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Irrigation Management ◽  
Methane Emissions ◽  
Ozone Production ◽  
Published Data ◽  
Layer Model ◽  
Production Rates ◽  
Photochemical Production ◽  
Mixed Layer Model

Abstract. In situ flight data from two distinct campaigns during winter and summer seasons in the San Joaquin Valley (SJV) of California are used to calculate boundary layer entrainment rates, ozone photochemical production rates, and regional methane emissions. Flights near Fresno, California in January and February 2013 were conducted in concert with the NASA DISCOVER–AQ project. The second campaign (ArvinO3), consisting of eleven days of flights spanning June through September 2013 and in June 2014 focused on the southern end of the SJV between Bakersfield and the small town of Arvin, California, a region notorious for frequent violations of ozone air quality standards. Entrainment velocities, the parameterized rates at which free tropospheric air is incorporated into the atmospheric boundary layer (ABL), are estimated from a detailed budget of the inversion base height. During the winter campaign near Fresno, we find an average midday entrainment velocity of 1.5 cm s−1, and a maximum of 2.4 cm s−1. The entrainment velocities derived during the summer months near Bakersfield averaged 3 cm s−1 (ranging from 0.9–6.5 cm s−1), consistent with stronger surface heating in the summer months. Using published data on boundary layer heights we find that entrainment rates across the Central Valley of California have a bimodal annual distribution peaking in spring and fall when the lower tropospheric stability (LTS) is changing most rapidly. Applying the entrainment velocities to a simple mixed–layer model of three other scalars (O3, CH4, and H2O), we solve for ozone photochemical production rates and find wintertime ozone production (2.8 ± 0.7 ppb h−1) to be about one-third as large as in the summer months (8.2 ± 3.1 ppb h−1). Moreover, the summertime ozone production rates observed above Bakersfield/Arvin exhibit an inverse relationship to a proxy for the VOC : NOx ratio (aircraft [CH4] divided by surface [NO2]), consistent with a NOx–limited photochemical environment. A similar budget closure approach is used to derive the regional emissions of methane, yielding 100 Gg yr−1 for the winter near Fresno and 170 Gg yr−1 in the summer around Bakersfield. These estimates are 3.6 and 2.4 times larger, respectively, than current state inventories suggest. Finally, by performing a boundary layer budget for water vapour, surface evapotranspiration rates appear to be consistently ~ 55 % of the reference values reported by the California Irrigation Management Information System (CIMIS) for nearby weather stations.

scholarly journals Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO

2012 ◽  
Vol 12 (12) ◽  
pp. 5329-5341 ◽  
Author(s):  
B. J. H. van Stratum ◽  
J. Vilà-Guerau de Arellano ◽  
H. G. Ouwersloot ◽  
K. van den Dries ◽  
T. W. van Laar ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Atmospheric Chemistry ◽  
Chemical Species ◽  
Active Species ◽  
Chemical System ◽  
Chemical Production ◽  
Layer Model ◽  
Diurnal Variability ◽  
Mixed Layer Model

Abstract. We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO (Diel Oxidant Mechanisms in relation to Nitrogen Oxides) campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O3-NOx-VOC-HOx diurnal cycle during conditions characterized by a low NOx regime and small O3 tendencies (less than 1 ppb per hour). By focusing on the budget equations of chemical species in the mixed-layer model, we show that for species like O3, NO and NO2, the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the diel cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

A Mixed-Layer Model Of The Well-Mixed Stratocumulus-Topped Boundary Layer

2001 ◽  
Vol 100 (1) ◽  
pp. 171-187 ◽  
Author(s):  
J. L. Pelly ◽  
S. E. Belcher
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Layer Model ◽  
Mixed Layer Model

scholarly journals Study of the diurnal variability of atmospheric chemistry with respect to boundary layer dynamics during DOMINO

2012 ◽  
Vol 12 (3) ◽  
pp. 6519-6550 ◽  
Author(s):  
B. J. H. van Stratum ◽  
J. Vilà-Guerau de Arellano ◽  
H. G. Ouwersloot ◽  
K. van den Dries ◽  
T. W. van Laar ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Atmospheric Chemistry ◽  
Chemical Species ◽  
Integrated Approach ◽  
Chemical System ◽  
Chemical Production ◽  
Layer Model ◽  
Diurnal Variability ◽  
Mixed Layer Model

Abstract. We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model (MXLCH) coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: MOZART-4 and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O3-NOx-VOC-HOx diurnal cycle during conditions characterised by a low NOx regime and small O3 tendencies (less than 1 ppb per hour). By focussing on the budget equations of chemical species in the mixed-layer model, we show that for species like O3, NO and NO2, the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the daily cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

Sign in / Sign up

Export Citation Format

Share Document