The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part B: Results and Process Understanding

Abstract

We describe and analyze the results of the third global energy and water cycle experiment atmospheric boundary layer Study intercomparison and evaluation study for F. C. Bosveld (B) · P. Baas · E. I. F. 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.

Ten Years of Boundary-Layer and Wind-Power Meteorology at Høvsøre, Denmark

“…The LLJ's peak wind speed during a spring night was also underestimated by the WRF model (≈4 m s −1 at the simulated PBL height); this LLJ was highly ageostrophic (≈5 m s −1 higher than the geostrophic wind). These findings corroborate the results from the GABLS3 intercomparison study (Bosveld et al 2014) based on measurements from the Cabauw tower.…”

Evaluation of a Buoyancy and Shear Based Mixing Length for a Turbulence Scheme

“…The consequences of over-diffusion in the SBL is also shown in the study of a katabatic flow compared to an improved Prandtl model by Grisogono and Belušić (2008). The causes of these features are due not only to turbulence but also to land-surface thermal coupling and radiation divergence (Bosveld et al, 2014). In the GABLS1 experiment, no radiation scheme is used and the surface temperature and boundary conditions are forced, leading to a turbulence-only driven SBL.…”

“…Previous GABLS studies Svensson et al, 2011;Bosveld et al, 2014) have shown that the representation of the SBL between NWP models is highly variable. In many cases, mixing in models is too large compared to LESs and observations, with numerous consequences as discussed in Section 1.…”

“…A common methodology to develop and improve parameterizations is to compare LES statistics to single column model (SCM; Randall et al, 1996;Hourdin et al, 2013). Over the last decade, such model intercomparisons have been investigated at an international scale within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS, Holtslag, 2006) for WSBLs Svensson et al, 2011;Bosveld et al, 2014). Previous intercomparison studies have shown that strong variabilities in the mean wind and potential temperature profiles is modeled by SCM.…”

Introduction to the Third GEWEX Atmospheric Boundary Layer Study (GABLS3)

“…The subsequent paper by Bosveld et al (2014b) deals with the inter-comparison of nineteen single-column models from eleven institutes with field data. Twelve of the models participated also in GABLS2.…”