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.
Response and sensitivity of the nocturnal boundary layer over land to added longwave radiative forcing
McNider, R.T. ; Steeneveld, G.J. ; Holtslag, A.A.M. ; Pielke sr., R.A. ; Mackaro, S. ; Pour Biazar, A. ; Walters, J. ; Nair, U. ; Christy, J. - \ 2012
Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X
diurnal temperature-range - global climate model - surface-temperature - minimum temperature - atmospheric models - heat-flux - intermittent turbulence - vertical resolution - contrasting nights - soil-moisture
One of the most significant signals in the thermometer-observed temperature record since 1900 is the decrease in the diurnal temperature range over land, largely due to rising of the minimum temperatures. Generally, climate models have not well replicated this change in diurnal temperature range. Thus, the cause for night-time warming in the observed temperatures has been attributed to a variety of external causes. We take an alternative approach to examine the role that the internal dynamics of the stable nocturnal boundary layer (SNBL) may play in affecting the response and sensitivity of minimum temperatures to added downward longwave forcing. As indicated by previous nonlinear analyses of a truncated two-layer equation system, the SNBL can be very sensitive to changes in greenhouse gas forcing, surface roughness, heat capacity, and wind speed. A new single-column model growing out of these nonlinear studies is used to examine the SNBL. Specifically, budget analyses of the model are provided that evaluate the response of the boundary layer to forcing and sensitivity to mixing formulations. Based on these model analyses, it is likely that part of the observed long-term increase in minimum temperature is reflecting a redistribution of heat by changes in turbulence and not by an accumulation of heat in the boundary layer. Because of the sensitivity of the shelter level temperature to parameters and forcing, especially to uncertain turbulence parameterization in the SNBL, there should be caution about the use of minimum temperatures as a diagnostic global warming metric in either observations or models.
Confronting the WRF and RAMS mesoscale models with innovative observations in the Netherlands-Evaluating the boundary-layer heat budget
Steeneveld, G.J. ; Tolk, L. ; Moene, A.F. ; Hartogensis, O.K. ; Peters, W. ; Holtslag, A.A.M. - \ 2011
Journal of Geophysical Research: Atmospheres 116 (2011). - ISSN 2169-897X - 16 p.
large-eddy simulations - co2 mixing ratios - land-surface - sensible heat - contrasting nights - vertical diffusion - weather forecasts - transport models - regional-scale - diurnal cycles
The Weather Research and Forecasting Model (WRF) and the The Weather Research and Forecasting Model (WRF) and the Regional Atmospheric Mesoscale Model System (RAMS) are frequently used for (regional) weather, climate and air quality studies. This paper covers an evaluation of these models for a windy and calm episode against Cabauw tower observations (The Netherlands), with a special focus on the representation of the physical processes in the atmospheric boundary layer (ABL). In ad-dition, area averaged sensible heat flux observations by scintillometry are utilized which enables evaluation of grid scale model fluxes and flux observations at the same horizontal scale. Also, novel ABL height observations by ceilometry and of the near surface longwave radiation divergence are utilized. It appears that WRF in its basic set-up shows satisfactory model results for nearly all atmospheric near surface variables compared to field observations, while RAMS needed refining of its ABL scheme. An important inconsistency was found regarding the ABL daytime heat budget: Both model versions are only able to correctly forecast the ABL thermodynamic structure when the modeled surface sensible heat flux is much larger than both the eddy-covariance and scintillometer observations indicate. In order to clarify this discrepancy, model results for each term of the heat budget equation is evaluated against field observations. Sensitivity studies and evaluation of radiative tendencies and entrainment reveal that possible errors in these variables cannot explain the overestimation of the sensible heat flux within the current model infrastructure.
Evaluation of the Diurnal Cycle in the Atmospheric Boundary Layer Over Land as Represented by a Variety of Single-Column Models: The Second GABLS Experiment
Svensson, G. ; Holtslag, A.A.M. ; Kumar, V. ; Mauritsen, T. ; Steeneveld, G.J. ; Angevine, W.M. ; Bazile, E. ; Beljaars, A. ; Bruijn, E.I.F. de; Cheng, A. - \ 2011
Boundary-Layer Meteorology 140 (2011)2. - ISSN 0006-8314 - p. 177 - 206.
turbulence closure scheme - large-eddy simulations - part i - contrasting nights - morning transition - parameterization - mesoscale - cases-99 - surface - system
We present the main results from the second model intercomparison within the GEWEX (Global Energy andWater cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today’s numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled nearsurface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified
Modeling and Forecasting the Onset and Duration of Severe Radiation Fog under Frost Conditions
Velde, I.R. van der; Steeneveld, G.J. ; Wichers Schreur, B.G.J. ; Holtslag, A.A.M. - \ 2010
Monthly Weather Review 138 (2010). - ISSN 0027-0644 - p. 4237 - 4253.
meteorologie - weersvoorspelling - vorst - mist - modellen - meteorology - weather forecasting - frost - fog - models - nocturnal boundary-layer - land-surface - parameterization schemes - bulk parameterization - numerical prediction - contrasting nights - mesoscale - clouds - simulation - resolution
A case of a severe radiation fog during frost conditions is analyzed as a benchmark for the development of a very high resolution NWP model. Results by the Weather Research and Forecasting model (WRF) and the High resolution limited area model (HIRLAM) are evaluated against detailed observations to determine the state of the art in fog forecasting and to derive requirements for further research and development. For this particular difficult case, WRF is unable to correctly simulate the fog for none of the parameterizations and model configurations utilized. Contrary, HIRLAM does model the onset of fog, but is unable to represent it beyond the lowest model layer, which leads to an early dispersal of fog in the morning transition. The sensitivity of fog forecasts to model formulation is further analyzed with a high resolution single column version of HIRLAM, and with the Duynkerke (1991) single column model as a reference. The single column results are found to be sensitive to the proper specification of the external forcings. It is reconfirmed that high vertical resolution is essential for modeling the fog formation, the growth of the fog layer and when the fog lifts for the maintenance of a stratus deck. The properly configured column models are able to accurately model the onset of fog and its maturation, but fail in the simulation of fog persistence and subsequent dispersal. Details of the turbulence parameterization appear to be important in this process. It is concluded that, despite of all advances in numerical weather prediction, fog forecasting is still a major challenge
Observations of the radiation divergence in the surface layer and its implication for its parameterization in numerical weather prediction models
Steeneveld, G.J. ; Wokke, M.J.J. ; Groot Zwaaftink, C.D. ; Pijlman, S. ; Jacobs, A.F.G. ; Holtslag, A.A.M. - \ 2010
Journal of Geophysical Research: Atmospheres 115 (2010). - ISSN 2169-897X - 13 p.
nocturnal boundary-layer - flux divergence - climate model - contrasting nights - transport models - turbulence - greenland - cases-99 - simulations - sensitivity
This paper presents the results of 5 months of in situ observations of the diurnal cycle of longwave radiative heating rate in the lower part of the atmospheric boundary layer over grassland, with a particular focus on nighttime conditions. The observed longwave radiative heating is minimal at the evening transition, with a median value of -1.8 K h-1 between 1.3 and 10 m and -0.5 K h-1 between 10 and 20 m, respectively. After the transition, its magnitude gradually decreases during the night. For individual clear calm nights, a minimal radiative heating rate of -3.5 and -2.0 K h-1 was found for the two indicated layers. The total radiative heating rate appears dominantly controlled by the upward longwave flux divergence. Surprisingly, at noon a radiative heating rate of ~1 K h-1 was found between 1.3 and 10 m for clear calm days. The availability of these radiation divergence measurements enables evaluation of the model performance for the temperature tendency caused by radiation divergence. The mesoscale model MM5 performs poorly for the stable boundary layer, because it overestimates the surface temperature and wind speed, while it underestimates the magnitude of radiative cooling. Some computationally efficient methods based on physical modeling, statistical modeling, and dimensional analysis are proposed by examining the gathered data set. The physical modeling approach appears to perform best.
Exploring the possible role of small scale terrain drag on stable boundary layers over land
Steeneveld, G.J. ; Holtslag, A.A.M. ; Nappo, C.J. ; Wiel, B.J.H. van de; Mahrt, L. - \ 2008
Journal of Applied Meteorology and Climatology 47 (2008). - ISSN 1558-8424 - p. 2518 - 2530.
atmospheric gravity-waves - complex terrain - critical-level - surface-layer - general-circulation - contrasting nights - turbulent-flow - form drag - model - parameterization
This paper addresses the possible role of unresolved terrain drag, relative to the turbulent drag on the development of the stable atmospheric boundary layer over land. Adding a first-order estimate for terrain drag to the turbulent drag appears to provide drag that is similar to the enhanced turbulent drag obtained with the so-called long-tail mixing functions. These functions are currently used in many operational models for weather and climate, although they lack a clear physical basis. Consequently, a simple and practical quasi-empirical parameterization of terrain drag divergence for use in large-scale models is proposed and is tested in a column mode. As an outcome, the cross-isobaric mass flow (a measure for cyclone filling) with the new scheme, using realistic turbulent drag, appears to be equal to what is found with the unphysical long-tail scheme. At the same time, the new scheme produces a much more realistic less-deep boundary layer than is obtained by using the long-tail mixing function.