Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 20

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Replication Data for: Artificial light at night shifts daily activity patterns but not the internal clock in Parus major
    Spoelstra, K. - \ 2017
    entrainment - artificial light at night - light pollution - circadian period - circadian phase
    Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings
    Pietersen, H.P. ; Vilà-Guerau De Arellano, J. ; Augustin, P. ; Boer, A. van de; Coster, O. de; Delbarre, H. ; Durand, P. ; Fourmentin, M. ; Gioli, B. ; Hartogensis, O.K. ; Lohou, F. ; Lothon, M. ; Ouwersloot, H.G. ; Pino, D. ; Reuder, J. - \ 2015
    Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 4241 - 4257.
    large-eddy simulation - turbulence - entrainment - transition - radiation - decay
    We study the influence of the large-scale atmospheric contribution to the dynamics of the convective boundary layer (CBL) in a situation observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. We employ two modeling approaches, the mixed-layer theory and large-eddy simulation (LES), with a complete data set of surface and upper-air atmospheric observations, to quantify the contributions of the advection of heat and moisture, and subsidence. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70 %. Constrained by surface and upper-air observations, we infer the large-scale vertical motions and horizontal advection of heat and moisture. Our findings show 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. LES results show a satisfactory correspondence of the vertical structure of turbulent variables with observations. We also find that when large-scale advection and subsidence are included in the simulation, the values for turbulent kinetic energy are lower than without these large-scale forcings. We conclude that the prototypical CBL is 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 representative for the local boundary layer.
    Measuring and modeling the effect of surface moisture on the spectral reflectance of coastal beach sand
    Nolet, C. ; Poortinga, A. ; Roosjen, P.P.J. ; Bartholomeus, H. ; Ruessink, G. - \ 2014
    PLoS ONE 9 (2014)11. - ISSN 1932-6203 - 9 p.
    aeolian sediment transport - soil-water-content - wind - entrainment - variability - penetration - light - wet
    Surface moisture is an important supply limiting factor for aeolian sand transport, which is the primary driver of coastal dune development. As such, it is critical to account for the control of surface moisture on available sand for dune building. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength () and surface moisture () over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties. The optical model performed well for volumetric moisture content 24% ( 0.97), but underestimated reflectance for between 24–30% ( 0.92), most notable around the 1940 nm water absorption peak. The soil-physical model performed very well ( 0.99) but is limited to 4% 24%. Results from a field experiment show that a short-wave infrared terrestrial laser scanner ( = 1550 nm) can accurately relate surface moisture to reflectance (standard error 2.6%), demonstrating its potential to derive spatially extensive surface moisture maps of a natural coastal beach.
    The Impact of Radiation on the GABLS3 Large-Eddy Simulation through the Night and during the Morning Transition
    Edwards, J.M. ; Basu, S. ; Bosveld, F.C. ; Holtslag, A.A.M. - \ 2014
    Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 189 - 211.
    nocturnal boundary-layer - model - entrainment - dynamics - weather - shear - flux
    Large-eddy simulation in the GABLS3 intercomparison is concerned with the developed stable boundary layer (SBL) and the ensuing morning transition. The impact of radiative transfer on simulations of this case is assessed. By the time of the reversal of the surface buoyancy flux, a modest reduction of the lapse rate in the developed SBL is apparent in simulations that include longwave radiation. Subsequently, with radiation, the developing mixed layer grows significantly more quickly, so that four hours after the transition the mixed layer is roughly 40 % deeper; the resulting profiles of potential temperature and specific humidity are in better agreement with observations. The inclusion of radiation does not substantively alter the shape of turbulent spectra, but it does indirectly reduce the variance of temperature fluctuations in the mixed layer. The deepening of the mixed layer is interpreted as a response to the reduction of the strength of the capping inversion, resulting from cumulative radiative cooling in the residual layer and around the top of the former SBL. Sensitivity studies are performed to separate the two effects. Solar radiative heating of the atmosphere has a smaller impact on the development of the mixed layer than does longwave radiative cooling and slightly reduces its rate of growth, compared to simulations including longwave radiation alone. These simulations demonstrate that nocturnal radiative processes have an important effect on the morning transition and that they should be considered in future large-eddy simulations of the transition.
    Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer
    Blay-Carreras, E. ; Pino, D. ; Vilà-Guerau de Arellano, J. ; Boer, A. van de; Coster, O. de; Darbieu, C. ; Hartogensis, O.K. ; Lohou, F. ; Lothon, M. ; Pietersen, H.P. - \ 2014
    Atmospheric Chemistry and Physics 14 (2014). - ISSN 1680-7316 - p. 4515 - 4530.
    large-eddy-simulation - morning transition - carbon-dioxide - mixed-layer - water-vapor - order-jump - part i - turbulence - entrainment - inversion
    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 aircraft systems and two manned 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 models runs 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 of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase of the entrainment buoyancy 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. Finally, we also 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.
    Quantifying the uncertainties of advection and boundary layer dynamics on the diurnal carbon dioxide budget
    Pino, D. ; Kaikkonen, J.P. ; Vilà-Guerau de Arellano, J. - \ 2013
    Journal of Geophysical Research: Atmospheres 118 (2013)16. - ISSN 2169-897X - p. 9376 - 9392.
    co2 mixing ratios - atmospheric co2 - regional-scale - error characterization - transport models - cabauw tower - tall tower - exchange - flux - entrainment
    [1] We investigate the uncertainties in the carbon dioxide (CO2) mixing ratio and inferred surface flux associated with boundary layer processes and advection by using mixed-layer theory. By extending the previous analysis presented by Pino et al. (2012), new analytical expressions are derived to quantify the uncertainty of CO2 mixing ratio or surface flux associated to, among others, boundary layer depth, early morning CO2 mixing ratio at the mixed layer or at the free atmosphere; or CO2 advection. We identify and calculate two sorts of uncertainties associated to the CO2 mixing ratio and surface flux: instantaneous and past (due to advection). The numerical experiments are guided and constrained by meteorological and CO2 observations taken at the Cabauw 213 m tower. We select 2 days (25 September 2003 and 12 March 2004) with a well-defined convective boundary layer but different CO2 advection contributions. Our sensitivity analysis shows that uncertainty of the CO2 advection in the boundary layer due to instantaneous uncertainties represents at 1600 LT on 12 March 2004 a contribution of 2¿ppm and 0.072 mg m-2s-1 in the uncertainty of the CO2 mixing ratio and inferred surface flux, respectively. Taking into account that the monthly averaged minimum CO2 surface flux for March 2004 was -0.55 mg m-2s-1, the error on the surface flux is on the order of 10%. By including CO2 advection in the analytical expressions, we demonstrate that the uncertainty of the CO2 mixing ratio or surface flux also depends on the past uncertainties of the boundary layer depth.
    Impacts of Aerosol Shortwave Radiation Absorption on the Dynamics of an Idealized Convective Atmospheric Boundary Layer
    Wilde Barbaro, E. ; Vilà-Guerau de Arellano, J. ; Krol, M.C. ; Holtslag, A.A.M. - \ 2013
    Boundary-Layer Meteorology 148 (2013)1. - ISSN 0006-8314 - p. 31 - 49.
    actinic flux - energy-budget - heating rates - closure-model - turbulence - entrainment - simulation - photolysis - climate - surface
    We investigated the impact of aerosol heat absorption on convective atmospheric boundary-layer (CBL) dynamics. Numerical experiments using a large-eddy simulation model enabled us to study the changes in the structure of a dry and shearless CBL in depthequilibrium for different vertical profiles of aerosol heating rates. Our results indicated that aerosol heat absorption decreased the depth of the CBL due to a combination of factors: (i) surface shadowing, reducing the sensible heat flux at the surface and, (ii) the development of a deeper inversion layer, stabilizing the upper CBL depending on the vertical aerosol distribution. Steady-state analytical solutions for CBL depth and potential temperature jump, derived using zero-order mixed-layer theory, agreed well with the large-eddy simulations. An analysis of the entrainment zone heat budget showed that, although the entrainment flux was controlled by the reduction in surface flux, the entrainment zone became deeper and less stably stratified. Therefore, the vertical profile of the aerosol heating rate promoted changes in both the structure and evolution of the CBL. More specifically, when absorbing aerosols were present only at the top of the CBL, we found that stratification at lower levels was the mechanism responsible for a reduction in the vertical velocity and a steeper decay of the turbulent kinetic energy throughout the CBL. The increase in the depth of the inversion layer also modified the potential temperature variance. When aerosols were present we observed that the potential temperature variance became significant already around 0.7zi (where zi is the CBL height) but less intense at the entrainment zone due to the smoother potential temperature vertical gradient.
    Convective boundary layer wind dynamics and inertial oscillations: the influence of surface stress
    Schröter, J.S. ; Moene, A.F. ; Holtslag, A.A.M. - \ 2013
    Quarterly Journal of the Royal Meteorological Society 139 (2013)676. - ISSN 0035-9009 - p. 1694 - 1711.
    low-level jets - large-eddy simulations - nocturnal jet - models - momentum - parameterization - parametrization - entrainment - fluxes - shear
    Investigating the influence of surface friction on the inertial oscillation (IO) of an extratropical, non-growing, convective boundary layer (CBL), we paid particular attention to the stability-dependent interactive coupling of shear-induced turbulence and turbulent friction, which leads to a nonlinear relationship between friction and velocity. We showed that in contrast to common perception, IO damping is controlled not only by friction but also by the dependence of friction on velocity. Furthermore, we found that surface friction not only causes damping but also modifies the restoring force. Using these basic principles, we studied the oscillatory properties (equilibrium, periodicity and damping) of the CBL by means of a model based on Monin–Obukhov surface-layer similarity (MOS) and the mixed-layer approximation. We found that the model complies with a quadratic surface stress–velocity relationship (QS) in the neutral limit, and a linear surface stress–velocity relationship (LS) in the proximity of the free-convective limit. Dynamically, the LS leads to a harmonic oscillation with a constant periodicity and exponential damping of the IO. However, the QS displays rather complex anharmonic behaviour; in comparison with the LS it produces a 50% stronger overall damping and a 100% larger contribution to the restoring force. Considering CBLs of arbitrary stability, we found that the MOS stress–velocity relation can be very well approximated by a much simpler linear combination of the LS and the QS which, respectively, represent the convective and the shear-induced contributions to friction. This enabled us to link the set of the external parameters (surface roughness, surface buoyancy flux and boundary layer depth) to a set of three effective parameters: the equilibrium velocity, the convective friction constant and the neutral friction constant. Together with the Coriolis coefficient, these parameters completely determine the IO.
    Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010
    Ouwersloot, H.G. ; Vilà-Guerau de Arellano, J. ; Nölscher, A.C. ; Krol, M.C. ; Ganzeveld, L.N. ; Breitenberger, C. ; Mammarella, I. ; Williams, J. ; Lelieveld, J. - \ 2012
    Atmospheric Chemistry and Physics 12 (2012). - ISSN 1680-7316 - p. 9335 - 9353.
    large-eddy simulation - aerosol formation - forest - model - entrainment - turbulence - evolution - inversion - emissions - exchanges
    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.
    Some observational evidence for dry soils supporting enhanced relative humidity at the convective boundary layer top
    Westra, D. ; Steeneveld, G.J. ; Holtslag, A.A.M. - \ 2012
    Journal of Hydrometeorology 13 (2012). - ISSN 1525-755X - p. 1347 - 1358.
    diurnal time scales - land-surface - cumulus onset - vertical diffusion - model - precipitation - entrainment - prediction - moisture - column
    The tendency of the relative humidity at the top of a clear convective boundary layer (RHtop) is studied as an indicator of cloud formation is studied over a semi-arid region within the conceptual framework introduced by Ek and Holtslag (2004). Typically the tendency of RHtop increases if the evaporative fraction at the land surface increases, which supports boundary layer moistening but only when boundary-layer growth is limited by atmospheric factors. This regime was supported by Cabauw observations in the original study. Here we provide new observational evidence that the tendency of RHtop can also increase as the surface becomes more dry as is consistent with another regime of the conceptual framework. The observations used are from the AMMA intensive observational campaign near Niamey, Niger, June 20-25, 2006. In addition, we evaluate whether various versions of the WRF single-column model confirm the different regimes of the conceptual framework for a typical day in the AMMA campaign. It appears that the model confirms that dryer soils can support cloud formation.
    A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios
    Pino, D. ; Vilà-Guerau de Arellano, J. ; Peters, W. ; Schröter, J.S. ; Heerwaarden, C.C. van; Krol, M.C. - \ 2012
    Atmospheric Chemistry and Physics 12 (2012). - ISSN 1680-7316 - p. 2969 - 2985.
    atmospheric co2 - transport models - sensible heat - tall tower - exchange - fluxes - ecosystem - temperature - entrainment - variability
    Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we study the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere (FA) influence the bulk CO2 mixing ratio. We find that the largest uncertainty incurred on the midday CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h), just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself is one order of magnitude smaller. If we “invert” the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth. We demonstrate these relations for a typical well characterized situation at the Cabauw site in The Netherlands, and conclude that knowledge of the temperature and carbon dioxide profiles of the atmosphere in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday.
    Boundary Layer Characteristics over Homogeneous and Heterogeneous Surfaces Simulated by MM5 and DALES
    Braam, M. ; Vilà-Guerau de Arellano, J. ; Górska, M. - \ 2011
    Journal of Applied Meteorology and Climatology 50 (2011)6. - ISSN 1558-8424 - p. 1372 - 1386.
    large-eddy simulation - relative-humidity - diurnal cycle - model - land - entrainment - diffusion - evaporation - ihop-2002 - moisture
    The multiple-single-column approach is proposed as a new concept to study the boundary layer parameterization scheme in the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). The results are compared with the Dutch Atmospheric Large-Eddy Simulation Model (DALES). Numerical experiments were performed over homogeneous and heterogeneous surfaces under clear convective boundary layer conditions. Identical simulations using MM5 and DALES were performed, which enabled an evaluation of theMM5boundary layer scheme with DALES results. From the experiment with a homogeneous surface, MM5 shows a slightly shallower, colder, and moister boundary layer than DALES. This result is produced by an underestimation of turbulent mixing near the surface and less-vigorous entrainment of heat and dry air in MM5. In the heterogeneous surface experiment, the domain is divided into dry and wet patches, with the result that both models produce a mesoscale circulation. However, relative to the homogeneous case, larger differences were found between the models in the representation of the boundary layer dynamics. In DALES, the surface heterogeneity influenced the turbulent motions, making the mesoscale circulation much stronger (wmax is 6 times as large) than in MM5. Because of this stronger circulation, the boundary layer height, bulk temperature, and humidity also displayed differences in time and spatial patterns. Because of the land–atmosphere coupling in MM5, the mesoscale circulation strengthened the surface flux heterogeneity. Cold and moist air advection close to the surface from the wet patch to the dry patch increased the sensible heat flux above the dry patch and thus the induced mesoscale flow
    The role of boundary layer dynamics on the diurnal evolution of isoprene and the hydroxyl radical over tropical forests
    Vilà-Guerau de Arellano, J. ; Patton, E.G. ; Karl, T. ; Dries, K. van den; Barth, M.C. ; Orlando, J.J. - \ 2011
    Journal of Geophysical Research: Atmospheres 116 (2011)D7. - ISSN 2169-897X - 16 p.
    large-eddy simulation - atmospheric chemistry - stiff odes - fluxes - entrainment - emissions - scalars - model - hydrocarbons - inversion
    We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized.
    Understanding the daily cycle of evapotranspiration: a method to quantify the influence of forcings and feedbacks
    Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. ; Gounou, A. ; Guichard, F. ; Couvreux, F. - \ 2010
    Journal of Hydrometeorology 11 (2010)6. - ISSN 1525-755X - p. 1405 - 1422.
    convective boundary-layer - land-atmosphere interaction - diurnal time scales - soil-moisture - surface - model - evaporation - parameterization - entrainment - inversion
    A method to analyze the daily cycle of evapotranspiration over land is presented. It quantifies the influence of external forcings, such as radiation and advection, and of internal feedbacks induced by boundary layer, surface layer, and land surface processes on evapotranspiration. It consists of a budget equation for evapotranspiration that is derived by combining a time derivative of the Penman–Monteith equation with a mixed-layer model for the convective boundary layer. Measurements and model results for days at two contrasting locations are analyzed using the method: midlatitudes (Cabauw, Netherlands) and semiarid (Niamey, Niger). The analysis shows that the time evolution of evapotranspiration is a complex interplay of forcings and feedbacks. Although evapotranspiration is initiated by radiation, it is significantly regulated by the atmospheric boundary layer and the land surface throughout the day. In both cases boundary layer feedbacks enhance the evapotranspiration up to 20 W m-2 h-1. However, in the case of Niamey this is offset by the land surface feedbacks since the soil drying reaches -30 W m-2 h-1. Remarkably, surface layer feedbacks are of negligible importance in a fully coupled system. Analysis of the boundary layer feedbacks hints at the existence of two regimes in this feedback depending on atmospheric temperature, with a gradual transition region in between the two. In the low-temperature regime specific humidity variations induced by evapotranspiration and dry-air entrainment have a strong impact on the evapotranspiration. In the high-temperature regime the impact of humidity variations is less pronounced and the effects of boundary layer feedbacks are mostly determined by temperature variations
    On inferring isoprene emission surface flux from atmospheric boundary layer concentration measurements
    Vilà-Guerau de Arellano, J. ; Dries, K. van den; Pino, D. - \ 2009
    Atmospheric Chemistry and Physics 9 (2009). - ISSN 1680-7316 - p. 3629 - 3640.
    model - hydrocarbons - entrainment - inversion - forest - parameterization - dynamics - cumulus - amazon - site
    We examine the dependence of the inferred isoprene surface emission flux from atmospheric concentration on the diurnal variability of the convective boundary layer (CBL). A series of systematic numerical experiments carried out using the mixed-layer technique enabled us to study the sensitivity of isoprene fluxes to the entrainment process, the partition of surface fluxes, the horizontal advection of warm/cold air masses and subsidence. Our findings demonstrate the key role played by the evolution of boundary layer height in modulating the retrieved isoprene flux. More specifically, inaccurate values of the potential temperature lapse rate lead to changes in the dilution capacity of the CBL and as a result the isoprene flux may be overestimated or underestimated by as much as 20%. The inferred emission flux estimated in the early morning hours is highly dependent on the accurate estimation of the discontinuity of the thermodynamic values between the residual layer and the rapidly forming CBL. Uncertainties associated with the partition of the sensible and latent heat flux also yield large deviations in the calculation of the isoprene surface flux. Similar results are obtained if we neglect the influence of warm or cold advection in the development of the CBL.We show that all the above-mentioned processes are non-linear, for which reason the dynamic and chemical evolutions of the CBL must be solved simultaneously. Based on the discussion of our results, we suggest the measurements needed to correctly apply the mixed-layer technique in order to minimize the uncertainties associated with the diurnal variability of the convective boundary layer.
    Mean and Flux Horizontal Variability of Virtual Potential Temperature, Moisture, and Carbon Dioxide: Aircraft Observations and LES Study
    Górska, M. ; Vilà-Guerau de Arellano, J. ; LeMone, M.A. ; Heerwaarden, C.C. van - \ 2008
    Monthly Weather Review 136 (2008). - ISSN 0027-0644 - p. 4435 - 4451.
    convective boundary-layer - large-eddy simulations - sensible heat - land-surface - entrainment - scale - ihop-2002 - soil - heterogeneity - cases-97
    The effects of the horizontal variability of surface properties on the turbulent fluxes of virtual potential temperature, moisture, and carbon dioxide are investigated by combining aircraft observations with large-eddy simulations (LESs). Daytime fair-weather aircraft measurements from the 2002 International H2O Project¿s 45-km Eastern Track over mixed grassland and winter wheat in southeast Kansas reveal that the western part of the atmospheric boundary layer was warmer and drier than the eastern part, with higher values of carbon dioxide to the east. The temperature and specific humidity patterns are consistent with the pattern of surface fluxes produced by the High-Resolution Land Data Assimilation System. However, the observed turbulent fluxes of virtual potential temperature, moisture, and carbon dioxide, computed as a function of longitude along the flight track, do not show a clear east¿west trend. Rather, the fluxes at 70 m above ground level related better to the surface variability quantified in terms of the normalized differential vegetation index (NDVI), with strong correlation between carbon dioxide fluxes and NDVI.
    Relative Humidity as an Indicator for Cloud Formation over Heterogeneous land surfaces
    Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. - \ 2008
    Journal of the Atmospheric Sciences 65 (2008)10. - ISSN 0022-4928 - p. 3263 - 3277.
    convective boundary-layer - large-eddy-simulation - entrainment - turbulence - shear - vegetation - evolution - models - driven - scale
    The influence of land surface heterogeneity on potential cloud formation is investigated using relative humidity as an indicator. This is done by performing numerical experiments using a large-eddy simulation model (LES). The land surface in the model was divided into two patches that had the same sum of latent and sensible heat flux but different Bowen ratios to simulate heterogeneous land surfaces. For heterogeneity in the meso-¿ scale (2¿20 km), sensitivity analyses were carried out on the heterogeneity amplitude (Bowen ratio difference between contrasting areas) and the inversion strength of potential temperature and specific humidity. The competition between absolute temperature decrease by ABL growth and dry air entrainment in heterogeneous conditions is analyzed using the LES results. First, it is shown that entrainment is located and enhanced over patches with higher Bowen ratios (warm patches) than their surroundings (cold patches). The heterogeneity-induced strong thermals can further penetrate the inversion at the ABL top, thereby reaching lower absolute temperatures than in homogeneous conditions. Second, because of the heterogeneity-induced circulations the moisture is located over the warm patch, and higher time-averaged RH values at the ABL top (RHzi) than over the cold patches are found here, even for dry atmospheres. These RHzi exceed values found over homogeneous land surfaces and are an indication that surface heterogeneity may facilitate cloud formation. In vertical profiles of RH, few differences are found between the homogeneous and heterogeneous cases, but the essential heterogeneity-induced modifications are within the domain variability.
    Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget
    Pino, D. ; Vilà-Guerau de Arellano, J. - \ 2008
    Acta Geophysica 56 (2008)1. - ISSN 1895-6572 - p. 167 - 193.
    large-eddy simulations - topped mixed layers - part ii - scalar fields - bulk models - order-jump - wind shear - entrainment - dynamics - inversion
    Effects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasi-steady barotropic boundary layer were conducted by increasing the value of the constant geostrophic wind by 5 m s-1 until the geostrophic wind was equal to 20 m s-1. The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due to the enhancement of the entrainment heat flux by the presence of shear. Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases. Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget terms is obtained with the scaling, especially for shear contribution.
    Fluxes and (co-)variances of reacting scalars in the convective boundary layer
    Vinuesa, J. ; Vilà-Guerau de Arellano, J. - \ 2003
    Tellus Series B: Chemical and Physical Meteorology 55 (2003)4. - ISSN 0280-6509 - p. 935 - 949.
    large-eddy simulation - modified k-model - chemical-reactions - turbulence - chemistry - entrainment - diffusion - impact - cloud - gases
    The effects of chemistry on the transport and the mixing of reacting scalars in the convective atmospheric boundary layer (CBL) are investigated. To do this, we use large-eddy simulation (LES) to calculate explicitly the different terms of the flux and (co)variance budget equations and to analyse in particular the role of the chemical term with respect to the thermodynamical terms. We examine a set of chemical cases that are representative of various turbulent reacting flows. The chemical scheme involves two reacting scalars undergoing a second-order reaction. In addition, we study a chemical cycle, based on a first- and a second-order reaction, to study the behaviour of chemical systems in equilibrium in turbulent flows. From the budget analysis, we found that the chemical terms become more relevant when the chemical timescale is similar to the turbulent timescale. In order to detemine the importance of the chemical terms, we compared these terms to the dynamical terms of the budget equations. For the flux of reactants, the chemical term becomes the dominant sink in the bulk of the CBL. As a result, flux profiles of reacting scalars have non-linear shapes. For the covariance, which accounts for the segregation of species in the CBL, the chemical term can act as a sink or source term. Consequently, reacting scalar covariance profiles deviate considerably from the inert scalar profile. When the chemistry is in equilibrium, the chemical term becomes negligible and therefore the flux and (co-)variance profiles are similar to those of inert scalrs. On the basis of the previous budget results, we develop a parameterisation that represents the segregation of reacting species in large-scale models under convective conditions. The parameterisation is applied to an atmospheric chemical mechanism that accounts for ozone formation and depletion in the CBL. We found a good agreement between the parameterisation and the LES results.
    The contribution of shear to the evolution of a convective boundary layer
    Pino, D. ; Vilà-Guerau de Arellano, J. ; Duynkerke, P.G. - \ 2003
    Journal of the Atmospheric Sciences 60 (2003)16. - ISSN 0022-4928 - p. 1913 - 1926.
    large-eddy simulation - mixed-layer - density interface - wind shear - entrainment - inversion - models - parameterization - dynamics - top
    The role of shear in the development and maintenance of a convective boundary layer is studied by means of observations and large eddy simulations (LESs). Particular emphasis is given to the growth of the boundary layer and to the way in which this growth is affected by surface fluxes of heat and moisture and entrainment fluxes. This paper analyzes the processes that drive the latter mechanism, which accounts for approximately 30% of the growth of the mixing layer. Typically, it is found that under pure convective conditions, without shear, the entrainment buoyancy flux at the inversion is about ¿20% of the surface buoyancy flux. This value is widely used for entrainment rate closures in general circulation models. The data collected during the Atmospheric Radiation Measurement campaign allow one to introduce realistic vertical profiles and surface fluxes into the LES runs and to compare the simulation results with the observed evolution of the boundary layer height during a convective situation with high entrainment rates and high geostrophic winds. The analysis of the turbulent kinetic energy (TKE) budget shows that the inclusion of geostrophic winds, which produce shear at the surface and in the entrainment zone, modifies the vertical profile of the various terms in the TKE budget. As a consequence, the entrainment flux is enhanced, resulting in increased growth of the boundary layer. The numerical experiments and the observations enable one to validate the efficiency of earlier representations, based on the TKE equation, which describe the evolution of the ratio between entrainment and surface buoyancy fluxes. The proposed parameterization for the entrainment and surface buoyancy flux ratio (ß), which includes the main buoyancy and shear contributions, is in good agreement with the LES results. Some aspects of the parameterization of ß, for instance, the absence of entrainment flux and its behavior during the transition between convective to neutral conditions, are discussed
    Check title to add to marked list

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.