Analysis of the surface temperature and wind forecast errors of the NCAR-AirDat operational CONUS 4-km WRF forecasting system

Investigating the characteristics of model-forecast errors using various statistical and object-oriented methods is necessary for providing useful guidance to end-users and model developers as well. To this end, the random and systematic errors (i.e., biases) of the 2-m temperature and 10-m wind predictions of the NCAR-AirDat weather research and forecasting (WRF)-based real-time four-dimensional data assimilation (RTFDDA) and forecasting system are analyzed. This system has been running operationally over a contiguous United States (CONUS) domain at a 4-km grid spacing with four forecast cycles daily from June 2009 to September 2010. In the result an exceptionally useful forecast dataset was generated and used for studying the error properties of the model forecasts, in terms of both a longer time period and a broader coverage of geographic regions than previously studied. Spatiotemporal characteristics of the errors are investigated based on the 24-h forecasts between June 2009 and April 2010, and the 72-h forecasts between May and September 2010. It was found that the biases of both wind and temperature forecasts vary greatly seasonally and diurnally, with dependency on the forecast length, station elevation, geographical location, and meteorological conditions. The temperature showed systematic cold biases during the daytime at all station elevations and warm biases during the nighttime above 1,000 m above sea level (ASL), while below 600 m ASL cold biases occurred during the nighttime. The forecasts of surface wind speed exhibited strong positive biases during the nighttime, while the negative biases were observed in the spring and summer afternoons. The surface wind speed was mostly over-predicted except for the stations located between 1,000 and 2,100 m ASL, for which negative biases were identified for most forecast cycles. The highest wind-speed errors were found over the high terrain and near sea-level stations. The wind-direction errors were relatively large at the high-terrain elevation in the Rocky and Appalachian mountain ranges and the western coastal areas and the error structure exhibited notable diurnal variability.     

A Method for Estimating the Cost of CO2 Mitigation through Afforestation

The Kyoto Protocol allows Annex I countries to use afforestation (theconversion of non-forest landto forest) to meet emissions reduction targets. We present a new method forestimating the cost of CO₂mitigation through afforestation based on econometric models of land use. Landuse models are developed from dataon observed land allocation decisions and quantify the relationship betweenthe share of land in forest and the netreturns to forestry, among other land use determinants. The econometricapproach measures the actual responsesby landowners to observed changes in net returns, in contrast to earlierstudies in which landowner responses aredictated by the researcher. Models are estimated for Maine, South Carolina,and Wisconsin. The estimated modelsare used to simulate subsidies for afforestation, which imply increases inforest area and net reductions inatmospheric CO₂ concentrations. Average cost measures – totalsubsidies divided by total carbon sequestered –are derived for afforestation programs with and without timber harvesting. Theuse of econometric land use modelsin integrated assessments of climate change is explored. We model the effectson land use patterns and the costsof CO₂ mitigation of changes in the net returns to agricultureinduced by climate change.     

Extended regional climate model projections for Europe until the mid-twentyfirst century: combining ENSEMBLES and CMIP3

This study aims at sharpening the existing knowledge of expected seasonal mean climate change and its uncertainty over Europe for the two key climate variables air temperature and precipitation amount until the mid-twentyfirst century. For this purpose, we assess and compensate the global climate model (GCM) sampling bias of the ENSEMBLES regional climate model (RCM) projections by combining them with the full set of the CMIP3 GCM ensemble. We first apply a cross-validation in order to assess the skill of different statistical data reconstruction methods in reproducing ensemble mean and standard deviation. We then select the most appropriate reconstruction method in order to fill the missing values of the ENSEMBLES simulation matrix and further extend the matrix by all available CMIP3 GCM simulations forced by the A1B emission scenario. Cross-validation identifies a randomized scaling approach as superior in reconstructing the ensemble spread. Errors in ensemble mean and standard deviation are mostly less than 0.1 K and 1.0 % for air temperature and precipitation amount, respectively. Reconstruction of the missing values reveals that expected seasonal mean climate change of the ENSEMBLES RCM projections is not significantly biased and that the associated uncertainty is not underestimated due to sampling of only a few driving GCMs. In contrast, the spread of the extended simulation matrix is partly significantly lower, sharpening our knowledge about future climate change over Europe by reducing uncertainty in some regions. Furthermore, this study gives substantial weight to recent climate change impact studies based on the ENSEMBLES projections, since it confirms the robustness of the climate forcing of these studies concerning GCM sampling.     

Vertical and Horizontal Transport of Energy and Matter by Coherent Motions in a Tall Spruce Canopy

In the framework of the EGER (ExchanGE processes in mountainous Regions) project, the contribution of coherent structures to vertical and horizontal transports in a tall spruce canopy is investigated. The combination of measurements done in both the vertical and horizontal directions allows us to investigate coherent structures, their temporal scales, their role in flux transport, vertical coupling between the sub-canopy, canopy and air above the canopy, and horizontal coupling in the sub-canopy layer. The temporal scales of coherent structures detected with the horizontally distributed systems in the sub-canopy layer are larger than the temporal scales of coherent structures detected with the vertically distributed systems. The flux contribution of coherent structures to the momentum and sensible heat transport is found to be dominant in the canopy layer. Carbon dioxide and latent heat transport by coherent structures increase with height and reach a maximum at the canopy height. The flux contribution of the ejection decreases with increasing height and becomes dominant above the canopy level. The flux fraction transported during the sweep increases with height and becomes the dominant exchange process at the upper canopy level. The determined exchange regimes indicate consistent decoupling between the sub-canopy, canopy and air above the canopy during evening, nighttime and morning hours, whereas the coupled states and coupled by sweep states between layers are observed mostly during the daytime. Furthermore, the horizontal transport of sensible heat by coherent structures is investigated, and the heterogeneity of the contribution of coherent events to the flux transport is demonstrated. A scheme to determine the horizontal coupling by coherent structures in the sub-canopy layer is proposed, and it is shown that the sub-canopy layer is horizontally coupled mainly in the wind direction. The vertical coupling in most cases is observed together with streamwise horizontal coupling, whereas the cross-stream direction is decoupled.     

On the inclusion of ground-based gravity measurements to the calibration process of a global rainfall-discharge reservoir model: case of the Durzon karst system (Larzac, southern France)

This work examines the relevance of the inclusion of ground-based gravity data in the calibration process of a global rainfall-discharge reservoir model. The analysis is performed for the Durzon karst system (Larzac, France). The first part of the study focuses on the hydrological interpretation of the ground-based gravity measurements. The second part of the study investigates further the information content of the gravity data with respect to water storage dynamics modelling. The gravity-derived information is found unable to either reduce equifinality of the single-objective, discharge-based model calibration process or enhance model performance through assimilation.     

Reforestation Programs in Southwest China： Reported Success, Observed Failure, and the Reasons Why

Ever since the disastrous floods of 1998, the Chinese government has used the Natural Forest Protection and Sloping Land Conversion Programs to promote afforestation and reforestation as means to reduce runoff, control erosion, and stabilize local livelihoods. These two ambitious programs have been reported as large-scale successes, contributing to an overall increase in China’s forest cover and to the stated goals of environmental stabilization. A small-scale field study at the project level of the implementation of these two programs in Baiwu Township, Yanyuan County, Sichuan, casts doubt upon the accuracy and reliability of these claims of success; ground observations revealed utter failure in some sites and only marginal success in others. Reasons for this discrepancy are posited as involving ecological, economic, and bureaucratic factors. Further research is suggested to determine whether these discrepancies are merely local aberrations or represent larger-scale failures in reforestation programs.     

Numerical modeling of toxic nonaqueous phase liquid removal from contaminated groundwater systems: mesh effect and discretization error estimation

Numerical modeling has now become an indispensable tool for investigating the fundamental mechanisms of toxic nonaqueous phase liquid (NAPL) removal from contaminated groundwater systems. Because the domain of a contaminated groundwater system may involve irregular shapes in geometry, it is necessary to use general quadrilateral elements, in which two neighbor sides are no longer perpendicular to each other. This can cause numerical errors on the computational simulation results due to mesh discretization effect. After the dimensionless governing equations of NAPL dissolution problems are briefly described, the propagation theory of the mesh discretization error associated with a NAPL dissolution system is first presented for a rectangular domain and then extended to a trapezoidal domain. This leads to the establishment of the finger‐amplitude growing theory that is associated with both the corner effect that takes place just at the entrance of the flow in a trapezoidal domain and the mesh discretization effect that occurs in the whole NAPL dissolution system of the trapezoidal domain. This theory can be used to make the approximate error estimation of the corresponding computational simulation results. The related theoretical analysis and numerical results have demonstrated the following: (1) both the corner effect and the mesh discretization effect can be quantitatively viewed as a kind of small perturbation, which can grow in unstable NAPL dissolution systems, so that they can have some considerable effects on the computational results of such systems; (2) the proposed finger‐amplitude growing theory associated with the corner effect at the entrance of a trapezoidal domain is useful for correctly explaining why the finger at either the top or bottom boundary grows much faster than that within the interior of the trapezoidal domain; (3) the proposed finger‐amplitude growing theory associated with the mesh discretization error in the NAPL dissolution system of a trapezoidal domain can be used for quantitatively assessing the correctness of computational simulations of NAPL dissolution front instability problems in trapezoidal domains, so that we can ensure that the computational simulation results are controlled by the physics of the NAPL dissolution system, rather than by the numerical artifacts. Copyright © 2014 John Wiley & Sons, Ltd.     

A framework of Holocene and Late Pleistocene environmental change in eastern Iran inferred from the dating of periods of alluvial fan abandonment,river terracing,and lake deposition

We review studies of the Holocene and Late Pleistocene stratigraphy of eastern Iran to infer past changes in the environment within this presently arid region. We build a scenario of widespread, and presumably climatically driven, evolution of the landscape through the Holocene. Six sites, covering a 10° range in latitude, indicate a regional abandonment of alluvial fan surfaces at ～10 ± 3 ka, with the younger (～9 ka) end of this age range supported by several of the best-constrained studies. Incision of rivers into the fan surfaces has occurred in discrete stages in the early to mid-Holocene (～9–7 ka) leading to the formation of flights of river terraces. Detailed records of lakebed deposition in the presently arid interior of Iran are rare, though the available data indicate lake highstand conditions at <7.8 ka at South Golbaf in SE Iran and at < 8.7 ± 1.1 ka at the Nimbluk plain in NE Iran. The major periods of Holocene landscape development hence correlate with a period of time where water was more abundant than at present, with incision of rivers into thick alluvial deposits possibly occurring due to a combination of decreased sediment supply and high levels of precipitation, and with the formation of inset river terraces possibly responding to century-scale fluctuations in precipitation. No major geomorphic changes are identified within the later part of the Holocene, from which we infer that increased aridity has slowed evolution of the landscape. A decrease in precipitation in the mid-Holocene may have had a detrimental effect on bronze age societies in eastern Iran as has been inferred elsewhere in the eastern Mediterranean region. The pre-Holocene environmental changes in eastern Iran are less well constrained, though there are suggestions of alluvial fan abandonment at 40–60 ka, at ～80 ka, and at ～120 ka.     

The supergene origin of ruthenian hexaferrum in Ni‐laterites

For two decades, the nature of Fe‐rich, oxygen‐bearing, Ru–Os compounds found in the supergene environment has been debated. Ru–Os–Fe‐oxides and nano‐intergrowths of ruthenium with magnetite have been proposed. We applied FE‐SEM, EMPA, μ‐Raman spectroscopy and synchrotron tts‐μXRD to Ru–Os–Fe compounds recovered from Ni‐laterites from the Dominican Republic. The results demonstrate that a significant portion of Fe exists in a common structure with the Ru–Os alloy, that is, ruthenian hexaferrum. This mineral occurs both as nanoparticles and as micrometric patches within a matrix of Fe‐oxide(s). Our data suggest that supergene ruthenian hexaferrum with a (Ru_0.4(Os,Ir)_0.1Fe_0.5)_?1.0 stoichiometry represents the most advanced weathering product of primary laurite within Ni‐laterites from the Dominican Republic.