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The North American Land Data Assimilation System project phase 2 (NLDAS‐2) has run four land surface models for a 30‐year (1979–2008) retrospective period. Land surface evapotranspiration (ET) is one of the most important model outputs from NLDAS‐2 for investigating land–atmosphere interaction or to monitor agricultural drought. Here, we evaluate hourly ET using in situ observations over the Southern Great Plains (Atmospheric Radiation Measurement/Cloud and Radiation Testbed network) for 1 January 1997–30 September 1999 and daily ET u‐sing in situ observations at the AmeriFlux network over the conterminous USA for an 8‐year period (2000–2007). The NLDAS‐2 models compare well against observations, with the National Centers for Environmental Prediction's Noah land surface model performing best, followed, in order, by the Variable Infiltration Capacity, Sacramento Soil Moisture Accounting, and Mosaic models. Daily evaluation across the AmeriFlux network shows that for all models, performance depends on season and vegetation type; they do better in spring and fall than in winter or summer and better for deciduous broadleaf forest and grasslands than for croplands or evergreen needleleaf forest. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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全球数值模式中的台风初始化Ⅱ: 业务应用 总被引：2，自引：0，他引：2
由于缺少大量有效的观测资料,台风初始化对数值天气预报业务模式而言,仍然是一个悬而末决的难题.中国国家气象中心自从1996年将台风数值预报系统投入业务运行以来,一直使用经验的人造bogus涡旋台风初始化技术.实际上,不同时期的台风有着不同的环流结构,即使同一个台风在不同的生命期也具有不同的结构特征,而这些结构特征的差异并不能依靠现有的bogus涡旋技术体现出来,这种主观方法的统一性与台风在时空上的差异性形成了强烈的反差.最近,基于国家气象中心全球资料分析同化-预报循环系统,设计和发展了一套新的台风初始化业务方案,它主要由初始涡旋形成、涡旋重定位和涡旋调整3部分过程组成.相比于业务中使用的人造bogus涡旋台风初始化方案,新方案在很大程度上减少了人为因素对台风涡旋结构的影响,而更多地是依靠数值模式自身的动力和物理过程来协调约束产生三维空间的涡旋结构.应用新方案,文中对生成于西北太平洋的2006年0605号台风格美(Kaemi)进行了数值试验,初步分析表明,新方案在实现台风涡旋环流结构的初始化方面效果较好,同时,对台风格美多个时次的预报结果也显示,相比于业务使用的bogus方案而言,新方案对台风路径平均预报误差有了大幅度的降低. 相似文献
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G. Svensson A. A. M. Holtslag V. Kumar T. Mauritsen G. J. Steeneveld W. M. Angevine E. Bazile A. Beljaars E. I. F. de Bruijn A. Cheng L. Conangla J. Cuxart M. Ek M. J. Falk F. Freedman H. Kitagawa V. E. Larson A. Lock J. Mailhot V. Masson S. Park J. Pleim S. S?derberg W. Weng M. Zampieri 《Boundary-Layer Meteorology》2011,140(2):177-206
We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water 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 near-surface 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. 相似文献
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Improvement of the Noah land surface model for warm season processes: evaluation of water and energy flux simulation 总被引：1，自引：0，他引：1
The Noah model is a land surface model of the National Centers for Environmental Prediction. It has been widely used in regional coupled weather and climate models (i.e. Weather Research and Forecasting Model, Eta Mesoscale Model) and global coupled weather and climate models (i.e. National Centers for Environmental Prediction Global Forecast System, Climate Forecast System). Therefore, its continued improvement and development are keys to enhancing our weather and climate forecast ability and water and energy flux simulation accuracy. North American Land Data Assimilation System phase 1 (NLDAS‐1) experiments indicated that the Noah model exhibited substantial bias in latent heat flux, total runoff and land skin temperature during the warm season, and such bias can significantly affect coupled weather and climate models. This paper presents a study to improve the Noah model by adding model parameterization processes such as including seasonal factor on leaf area index and root distribution and selecting optimal model parameters. We compared simulated latent heat flux, mean annual runoff and land skin temperature from the Noah control and test versions with measured latent heat flux, land surface skin temperature, mean annual runoff and satellite‐retrieved land surface skin temperature. The results show that the test version significantly reduces biases in latent heat, total runoff and land skin temperature simulation. The test version has been used for the NLDAS phase 2 (NLDAS‐2) to produce 30‐year water flux, energy flux and state variable products to support the US drought monitor of National Integrated Drought Information System. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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F. Mesinger 《Meteorology and Atmospheric Physics》1997,63(1-2):3-14
Summary Following a few historical remarks, approximations used in formulating the dynamics of limited-area and variable resolution atmospheric forecasting models are reviewed. Particular attention is given to current efforts to relax or remove the hydrostatic approximation.Turning to numerical methods used in discretizing the equations, an attempt is made to record recent work and to clarify the motivation for the various approaches being followed by different modeling centers. Topics commented upon include: semi-Lagrangian methods, numerical formulation of nonhydrostatic models, resolution, the eta (step-mountain) vs sigma or isentropic/sigma vertical coordinate, choice of the vertical grid, numerics of the propagation of gravity waves, and the box-average vs pointsample treatment of predicted variables.It is finally pointed out that the extraordinary diversity of roads being taken shows that a lot remains to be discovered as to what possible rewards may be found in exploring one or the other of the principles underlying the methods being developed.This is a revised and updated text of an invited lecture given within the One-Day Intensive Course of the International Workshop on Limited-Area and Variable Resolution Models, Beijing, China, 23–27 October 1995. 相似文献
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In North American Land Data Assimilation System Phase 2 (NLDAS‐2) Noah simulation, the NLDAS team introduced an intermediate ‘fix’ to constrain the surface exchange coefficient when the atmospheric boundary layer is stable. In the current NLDAS‐2 Noah version, this fix is used for all stable cases including snow‐free grid cells. In this study, we simply apply this fix to the grid cells in which both stable atmospheric boundary layer and snow exist simultaneously, excluding the snow‐free grid cells as we recognize that the fix in NLDAS‐2 is too strong. We conduct a 31‐year (1979–2009) NLDAS‐2 Noah interim (Noah‐I) run and use observed streamflow, evapotranspiration, land surface temperature, soil temperature, and ground heat flux to evaluate the results, including comparisons with the original NLDAS‐2 Noah run. The results show that Noah‐I has the same performance as NLDAS‐2 Noah for snow water equivalent; however, Noah‐I significantly improved the simulation of other hydrometeorological products as noted earlier when compared with NLDAS‐2 Noah and the observations. This simple modification is being included in the next Noah version used in NLDAS. The hydrometeorological products from the improved NLDAS‐2 Noah‐I are being staged on the National Centers for Environmental Prediction public server. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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