Quality of wind characteristics in recent wind atlases over the North Sea
Kalverla, Peter C. ; Holtslag, Albert A.M. ; Ronda, Reinder J. ; Steeneveld, Gert Jan - \ 2020
Quarterly Journal of the Royal Meteorological Society 146 (2020)728. - ISSN 0035-9009 - p. 1498 - 1515.
DOWA - ERA-5 - low-level jets - Meteo Mast IJmuiden (MMIJ) - NEWA - North Sea - offshore wind - wind energy
Offshore wind energy production is rapidly growing as an essential element in the sustainable energy share. Wind energy siting studies require accurate wind data, and in particular the knowledge of extreme wind events (low-level jets, wind ramps, extreme shear and high wind speeds) is crucial for resource and load assessment. This study evaluates the skill of three relatively new wind atlases, i.e. ERA-5, DOWA and NEWA on the representation of extreme wind events using observations taken at the Met Mast IJmuiden over the North Sea. Overall, DOWA appears to best represent the wind speed profile with virtually no bias. ERA-5 underestimates the mean wind speed profile though the wind shear is well represented, while NEWA correctly represents the near surface wind but underestimates the wind shear. The frequency of low-level jets are also best represented by DOWA. Wind speed ramps and direction ramps are best represented by ERA-5, while DOWA appears to outperform the others concerning wind shear.
The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence
Lothon, M. ; Lohou, F. ; Pino, D. ; Vilà-Guerau De Arellano, J. ; Hartogensis, O.K. ; Boer, A. van de; Coster, O. de; Moene, A.F. ; Steeneveld, G.J. - \ 2014
Atmospheric Chemistry and Physics 14 (2014). - ISSN 1680-7316 - p. 10931 - 10960.
large-eddy-simulation - observed evening transition - doppler spectral width - low-level jets - convective turbulence - intermittent turbulence - surface-layer - kinetic-energy - drainage flow - length scales
Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period. Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.
Introduction to the Third GEWEX Atmospheric Boundary Layer Study (GABLS3)
Holtslag, A.A.M. - \ 2014
Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 127 - 132.
low-level jets - diurnal cycles - land-surface - sea-ice - model - radiation - weather
The atmospheric boundary layer (ABL) plays a dominant role in the exchange of energy, water vapour, trace gases and momentum between the earth’s surface and the overlying atmosphere. Consequently, the ABL is an important part of any numerical model in use for atmospheric and climate research, for operational weather forecasting, and for air - quality and wind - energy studies. For all these applications an overall representation is needed for boundary-layer turbulence and near-surface processes, as well as for vertical diffusion above the boundary layer. This representation is typically referred as the parametrization of vertical diffusion and turbulent mixing. It appears that models at various research groups and operational centres use rather different methods to represent turbulence and vertical diffusion and the reasons behind this diversity are not that easy to unravel. Most likely, this originates for historical reasons due to the outcome of various tuning exercises and to the num
The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part B: Results and Process Understanding
Bosveld, F.C. ; Baas, P. ; Steeneveld, G.J. ; Holtslag, A.A.M. ; Angevine, W.M. ; Bazile, E. ; Bruijn, E.I.F. de; Deacu, D. ; Edwards, J.M. ; Ek, M. ; Larson, V.E. ; Pleim, J.E. ; Raschendorfer, M. ; Svensson, G. - \ 2014
Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 157 - 187.
stably stratified conditions - observed evening transition - nonlocal closure-model - low-level jets - land-surface - morning transition - vertical diffusion - radiative-transfer - energy-balance - ecmwf model
We describe and analyze the results of the third global energy and water cycle experiment atmospheric boundary layer Study intercomparison and evaluation study for single-column models. Each of the nineteen participating models was operated with its own physics package, including land-surface, radiation and turbulent mixing schemes, for a full diurnal cycle selected from the Cabauw observatory archive. By carefully prescribing the temporal evolution of the forcings on the vertical column, the models could be evaluated against observations. We focus on the gross features of the stable boundary layer (SBL), such as the onset of evening momentum decoupling, the 2-m minimum temperature, the evolution of the inertial oscillation and the morning transition. New process diagrams are introduced to interpret the variety of model results and the relative importance of processes in the SBL; the diagrams include the results of a number of sensitivity runs performed with one of the models. The models are characterized in terms of thermal coupling to the soil, longwave radiation and turbulent mixing. It is shown that differences in longwave radiation schemes among the models have only a small effect on the simulations; however, there are significant variations in downward radiation due to different boundary-layer profiles of temperature and humidity. The differences in modelled thermal coupling to the land surface are large and explain most of the variations in 2-m air temperature and longwave incoming radiation among models. Models with strong turbulent mixing overestimate the boundary-layer height, underestimate the wind speed at 200 m, and give a relatively large downward sensible heat flux. The result is that 2-m air temperature is relatively insensitive to turbulent mixing intensity. Evening transition times spread 1.5 h around the observed time of transition, with later transitions for models with coarse resolution. Time of onset in the morning transition spreads 2 h around the observed transition time. With this case, the morning transition appeared to be difficult to study, no relation could be found between the studied processes, and the variation in the time of the morning transition among the models
Evaluation of the Weather Research and Forecasting mesoscale model for GABLS3: Impact of boundary-layer schemes, boundary conditions and spin-up
Kleczek, M.A. ; Steeneveld, G.J. ; Holtslag, A.A.M. - \ 2014
Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 213 - 243.
nonlocal closure-model - low-level jets - wrf model - part i - vertical diffusion - diurnal cycles - sea-ice - turbulence - sensitivity - parameterization
We evaluated the performance of the three-dimensional Weather Research and Forecasting (WRF) mesoscale model, specifically the performance of the planetary boundary-layer (PBL) parametrizations. For this purpose, Cabauw tower observations were used, with the study extending beyond the third GEWEX Atmospheric Boundary-Layer Study (GABLS3) one-dimensional model intercomparison. The WRF model (version 3.4.1) contains 12 different PBL parametrizations, most of which have been only partially evaluated. The GABLS3 case offers a clear opportunity to evaluate model performance, focusing on time series of near-surface weather variables, radiation and surface flux budgets, vertical structure and the nighttime inertial oscillation. The model results revealed substantial differences between the PBL schemes. Generally, non-local schemes tend to produce higher temperatures and higher wind speeds than local schemes, in particular, for nighttime. The WRF model underestimates the 2-m temperature during daytime (about TeX K) and substantially underestimates it at night (about TeX K), in contrast to the previous studies where modelled 2-m temperature was overestimated. Considering the 10-m wind speed, during the night turbulent kinetic energy based schemes tend to produce lower wind speeds than other schemes. In all simulations the sensible and latent heat fluxes were well reproduced. For the net radiation and the soil heat flux we found good agreement with daytime observations but underestimations at night. Concerning the vertical profiles, the selected non-local PBL schemes underestimate the PBL depth and the low-level jet altitude at night by about 50 m, although with the correct wind speed. The latter contradicts most previous studies and can be attributed to the revised stability function in the Yonsei University PBL scheme. The local, turbulent kinetic energy based PBL schemes estimated the low-level jet altitude and strength more accurately. Compared to the observations, all model simulations show a similar structure for the potential temperature, with a consistent cold bias (TeX2 K) in the upper PBL. In addition to the sensitivity to the PBL schemes, we studied the sensitivity to technical features such as horizontal resolution and domain size. We found a substantial difference in the model performance for a range of 12, 18 and 24 h spin-up times, longer spin-up time decreased the modelled wind speed bias, but it strengthened the negative temperature bias. The sensitivity of the model to the vertical resolution of the input and boundary conditions on the model performance is confirmed, and its influence appeared most significant for the non-local PBL parametrizations
The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part A: Case Selection and Set-Up
Bosveld, F.C. ; Baas, P. ; Meijgaard, E. van; Bruijn, E.I.F. de; Steeneveld, G.J. ; Holtslag, A.A.M. - \ 2014
Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 133 - 156.
low-level jets - land-surface - weather research - radiation fog - cabauw - climate - parametrizations - netherlands - performance - prediction
We describe a novel methodology on the selection and composition of a single-case observational dataset from the comprehensive measurement program at the Cabauw observatory field site located in the Netherlands. The case can be regarded as the basis of the third case study conducted within the framework of the GEWEX (Global Energy and Water Exchange) Atmospheric Boundary-Layer Study (GABLS) and is meant to be used for the evaluation of single-column models. The ideal case is supposed to cover a period of at least 24 h with clear skies, moderate near-surface winds and a stable stratification during nighttime. From the multi-year data archive with Cabauw observations data for 1–2 July 2006 were found to best match the requirements, and were consequently selected for analysis. The dates contains a 24-h period with a nearly constant geostrophic wind of ˜ 7 m s -1 , and a considerable wind shear in the vertical. It is also characterized by a pronounced low-level jet related to an inertial oscillation that developed around sunset when the atmosphere had decoupled from the surface. Detailed initial conditions, surface conditions and dynamical forcings are derived on the basis of local observations and the outcome of a conceptual and a three-dimensional atmospheric model. It appears that a very precise prescription of the forcings is a prerequisite to enable a meaningful evaluation of models against observational data
Stable atmospheric boundary layers and diurnal Cycles-Challenges for Weather and Climate Models
Holtslag, A.A.M. ; Svensson, G. ; Baas, P. ; Basu, S. ; Beare, B. ; Beljaars, A.C.M. ; Bosveld, F.C. ; Cuxart, J. ; Lindvall, J. ; Steeneveld, G.J. ; Tjernstrom, M. ; Wiel, B.J.H. van de - \ 2013
Bulletin of the American Meteorological Society 94 (2013). - ISSN 0003-0007 - p. 1691 - 1706.
low-level jets - land-surface - contrasting nights - soil-moisture - ecmwf model - sea-ice - turbulence - cases-99 - parameterization - fluxes
The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2 m temperature and 10 m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind-speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, we review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art, as well as findings and recommendations from three inter-comparison studies held within the “Global Energy and Water Exchanges (GEWEX)” Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models and Large Eddy Simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas and at Cabauw in the Netherlands. From these studies, we find that even for the non-cloudy boundary layer important parameterization challenges remain.
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.