Impacts of topography and land degradation on the sea breeze over eastern Spain   总被引：8，自引：0，他引：8  

J.-F. Miao  L. J. M. Kroon  J. Vilà-Guerau de Arellano  A. A. M. Holtslag 《Meteorology and Atmospheric Physics》2003,84(3-4):157-170

Summary A three-dimensional non-hydrostatic atmospheric model RAMS, version3b, is used to examine the impact of complex topography on the sea breeze under heterogeneous and degradation land use characteristics. In the study, it is shown that topography plays an important role in the sea-breeze circulation by aligning the sea breeze front to the coastline and locating the convergence zones close to the mountain range. When the sea breeze is coupled with the upslope wind, the sea-breeze circulation is strengthened by the topography.Sensitivity analyses are carried out to determine the influence of vegetation and soil moisture, i.e., land surface modifications, to this thermally driven flow. Land degradation results in an enhanced sea-breeze circulation which is characterized by a stronger onshore flow, a stronger return current, a larger updraft velocity associated with the sea-breeze front and further inland penetration. Other important features are a deeper sea-breeze depth, a larger downdraft velocity behind the sea-breeze front, and a longer offshore extent. The results also show how land changes modify the sea breeze temporal evolution resulting in an earlier onset and later end. The study stresses the convenience of using three-dimensional models with detailed land surface information to model the sea breeze in complex terrain where land use is rapidly modified.Received February 25, 2002; accepted October 7, 2002 Published online April 10, 2003  相似文献   

Representing the atmospheric boundary layer in climate models of intermediate complexity     

R. J. Ronda  R. J. Haarsma  A. A. M. Holtslag 《Climate Dynamics》2003,21(3-4):327-335

In this study the role of atmospheric boundary layer schemes in climate models is investigated. Including a boundary layer scheme in an Earth system model of intermediate complexity (EMIC) produces only minor differences in the estimated global distribution of sensible and latent heat fluxes over land (upto about 15% of the net radiation at the surface). However, neglecting of boundary layer processes, such as the development of a well-mixed layer over land or the impact of stability on the exchange coefficient in the surface layer, leads to erroneous surface temperatures, especially in convective conditions with low wind speeds. As these conditions occur frequently, introducing a boundary layer scheme in an EMIC gives reductions in June-July-August averaged surface temperature of 1–2 °C in wet areas, to 5–7 °C in desert areas. Even a relatively simple boundary layer scheme provides reasonable estimates of the surface fluxes and surface temperatures. Detailed schemes that solve explicitly the turbulent fluxes within the boundary layer are only required when vertical profiles of potential temperature are needed.  相似文献   

The Effects of Climate Change on Water Resources in the West: Introduction and Overview     

Tim Barnett  Robert Malone  William Pennell  Detlet Stammer  Bert Semtner  Warren Washington 《Climatic change》2004,62(1-3):1-11

The results of an experimental `end to end' assessment of the effects of climate change on water resources in the western United States are described. The assessment focuses on the potential effects of climate change over the first half of the 21st century on the Columbia, Sacramento/San Joaquin, and Colorado river basins. The paper describes the methodology used for the assessment, and it summarizes the principal findings of the study. The strengths and weaknesses of this study are discussed, and suggestions are made for improving future climate change assessments.  相似文献   

Atlantic sources of the Arctic Ocean surface and halocline waters   总被引：8，自引：0，他引：8  

Bert Rudels  E. Peter Jones  Ursula Schauer  Patrick Eriksson 《Polar research》2004,23(2):181-208

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A comparison of boundary layer diffusion schemes in unstable conditions over land     

A. A. M. Holtslag  E. Van Meijgaard  W. C. De Rooy 《Boundary-Layer Meteorology》1995,76(1-2):69-95

We compare the results of a local and a nonlocal scheme for vertical diffusion in the atmospheric boundary layer with observations at the 200 m tower at Cabauw. This is done for a 12 h period during daytime on 31 May 1978, which is characterised by strong insolation, clear skies, moderately strong winds and weak advection. The local diffusion scheme uses an eddy diffusivity determined independently at each point along the vertical based on local vertical gradients of wind and virtual potential temperature, similar to the usual approach in atmospheric models. The nonlocal scheme determines an eddy diffusivity profile based on a diagnosed boundary-layer height and a turbulent velocity scale. It also incorporates nonlocal (vertical) transport effects for heat and moisture. The boundary-layer diffusion schemes are forced with the locally observed fluxes for heat and moisture. The outputs of the scheme are compared with the observed mean structure along the Cabauw tower, and the radiosonde profile at a nearby location (De Bilt). Overall, the nonlocal scheme transports moisture away from the surface more rapidly than the local scheme, and deposits the moisture at higher levels. The local scheme tends to saturate the lowest model levels unrealistically in comparison with the observations. We also compare the outputs of the two diffusion schemes with the results of a transilient model simulation. Subsequently, we study the impact on the model behaviour by varying important parameters in both diffusion schemes and we investigate the sensitivity to uncertainty in the environmental conditions. Finally, we study the interaction of the diffusion schemes with a simple surface flux scheme.  相似文献   

Using satellite remote sensing to survey transport-related urban sustainability: Part 1: Methodologies for indicator quantification     

Ying Zhang  Bert Guindon 《International Journal of Applied Earth Observation and Geoinformation》2006

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An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer   总被引：2，自引：27，他引：2  

Robert J. Beare  Malcolm K. Macvean  Albert A. M. Holtslag  Joan Cuxart  Igor Esau  Jean-Christophe Golaz  Maria A. Jimenez  Marat Khairoutdinov  Branko Kosovic  David Lewellen  Thomas S. Lund  Julie K. Lundquist  Anne Mccabe  Arnold F. Moene  Yign Noh  Siegfried Raasch  Peter Sullivan 《Boundary-Layer Meteorology》2006,118(2):247-272

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.  相似文献   

Preface: GEWEX Atmospheric Boundary-layer Study (GABLS) on Stable Boundary Layers     

Bert Holtslag 《Boundary-Layer Meteorology》2006,118(2):243-246

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Single-Column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer   总被引：2，自引：15，他引：2  

J. Cuxart  A. A. M. Holtslag  R. J. Beare  E. Bazile  A. Beljaars  A. Cheng  L. Conangla  M. Ek  F. Freedman  R. Hamdi  A. Kerstein  H. Kitagawa  G. Lenderink  D. Lewellen  J. Mailhot  T. Mauritsen  V. Perov  G. Schayes  G-J. Steeneveld  G. Svensson  P. Taylor  W. Weng  S. Wunsch  K-M. Xu 《Boundary-Layer Meteorology》2006,118(2):273-303

The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.  相似文献   

Role of land-surface temperature feedback on model performance for the stable boundary layer     

A. A. M. Holtslag  G. J. Steeneveld  B. J. H. van de Wiel 《Boundary-Layer Meteorology》2007,125(2):361-376

At present a variety of boundary-layer schemes is in use in numerical models and often a large variation of model results is found. This is clear from model intercomparisons, such as organized within the GEWEX Atmospheric Boundary Layer Study (GABLS). In this paper we analyze how the specification of the land-surface temperature affects the results of a boundary-layer scheme, in particular for stable conditions. As such we use a well established column model of the boundary layer and we vary relevant parameters in the turbulence scheme for stable conditions. By doing so, we can reproduce the outcome for a variety of boundary-layer models. This is illustrated with the original set-up of the second GABLS intercomparison study using prescribed geostrophic winds and land-surface temperatures as inspired by (but not identical to) observations of CASES-99 for a period of more than two diurnal cycles. The model runs are repeated using a surface temperature that is calculated with a simple land-surface scheme. In the latter case, it is found that the range of model results in stable conditions is reduced for the sensible heat fluxes, and the profiles of potential temperature and wind speed. However, in the latter case the modelled surface temperatures are rather different than with the original set-up, which also impacts on near-surface air temperature and wind speed. As such it appears that the model results in stable conditions are strongly influenced by non-linear feedbacks in which the magnitude of the geostrophic wind speed and the related land-surface temperature play an important role.  相似文献