Initial Surface Conditions Research Articles

Numerical investigation of the influence of texture, surface drip emitter discharge rate and initial soil moisture condition on wetting pattern size

Knowledge of the dimensions of the wetted zone formed under point source surface drip irrigation is essential to the design of cost-effective and efficient irrigation systems. Numerical simulations were carried out with Hydrus-2D/3D to investigate the influence of emitter discharge rates and initial soil moisture conditions on the wetting pattern dimensions of a series of soils with varying textures. Numerical simulations of simple 2D soil tank irrigation experiments were also conducted on two soil types. Based on the simulation results, the parameters of the Schwartzman and Zur model were refined. The results showed a small influence of discharge rates >1 L h−1 on the size of the wetting pattern. The only major difference was observed for the rates lower than 0.5 L h−1, where the largest wetting patterns were observed. Higher initial soil water content caused larger wetting pattern sizes in all directions. When compared to the 2D tank experimental results, Hydrus-2D/3D predicted the wetting pattern dimensions with a relatively small root mean square error not exceeding 2.6 cm. The numerical data obtained for a wide range of textures provided the opportunity to refine the parameters of the Schwartzman and Zur model, which, when compared to experimental data from the literature, provided good estimates of wetting pattern dimensions. This suggests that this simple model, for which the only soil parameter required is the saturated hydraulic conductivity, could provide a valuable and practical tool for irrigation design.

Optimisation of Diffusion Bonding Parameters of Ti Alloys through the Structure and Surface Conditions

Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state was performed. The effect of initial structure and surface condition, as well as temperature and time, on the quality of joints was established. It is shown that, due to low-temperature superplasticity and high diffusion rate, samples with ultrafine grained structure demonstrate better bondability than coarse grained samples

Comparative Iinvestigation of the High Temperature Corrosion Resistant Model and Commercial Fe-Cr-Al-RE Alloys with Different Chromium Content

The alloys of Fe-Cr-Al-RE system are the high temperature oxidation resistant materials and they are normally are intended to apply at the temperatures up to 1200OC. Usually the composition of the mentioned system is varied by the main elements values as well as RE’s and other alloying elements amount and the variety of the latter. The high temperature behavior of the Fe-Cr-Al-RE bulk alloys and the coatings with the chromium content of up to 25wt% and the Al that of up to 5wt% is investigated widely, whereas higher chromium content alloys of the mentioned system are barely studied.The oxidation peculiarities of high (>40wt%) chromium content Fe-Cr-Al-RE model alloy with some minor additives were compared to that of the two commercial (Aluchrom YHf and PM2000) alloys of the same system. According to the experimental results the new material investigated exhibited the slowest oxidation rate (as it is shown in the Fig.1a) and the thinnest oxide scale formation comparatively to the other two alloys which makes it a quite promising high temperature oxidation resistant material [1-3].The processes taking place on the surface of model alloy exposed to high temperatures are discussed and compared to those of the two commercial alloys. The attempt to disclose the ways differentiating the oxide scale formation on the investigated low and high chromium containing alloys of Fe-Cr-Al-RE system was made and the factors influencing the slower oxide development process for the model alloy were suggested.The obtained kinetic data after the high temperature cyclic oxidation (120/15 minutes of heating up/cooling down cycling) in laboratory air at 1100OC during 2000 hours is compared for all the investigated tree alloys having either polished or rough surface conditions before the exposures at the elevated temperatures. Thus, the initial surface condition on the protective oxide scale growth kinetics was studied. Besides, the oxide scale growth rate dependence on the specimen thickness was studied as well for the alloys exposed at the same elevated temperatures during 1000 hours, where new model alloy has showed the outstanding priority comparing to the other two commercial alloys investigated (Fig. 1b). SEM analysis was applied for the evaluation of the oxidized specimens’ surfaces as well as their cross-sections. ReferencesTsurtsumia O., Kutelia E., Bulia B., Mikadze O., Materials Science Forum Vols. 595-598, 2008, (Trans Tech Publications) pp. 833-840Tsurtsumia O., Kutelia E., Bakhtiyarov S., Proceed. Of 17th Int. Corrosion Congr. USA, Las Vegas, Nevada, October, 2008Kutelia E., Tsurtsumia O., Eristavi B., Adanir H., Bakhtiyarov S., Journal on Engineering and Technology, 2006, Vol. 1, No. 4, pp. 61-71

Material Scatter in Crack Growth Rates of 7075-T7351 under Spectrum Loading

The probabilistic distribution of crack lengths at a critical location is a key input for risk assessment of structural failure of airframes due to fracture. This distribution depends on the initial surface condition of the structural component, the crack growth behaviour of the material, and the applied load history. MIL-STD-1530C suggests the use of a single master crack growth curve to derive the subsequent crack length distributions from the initial crack length distribution, without taking into consideration the well-recognized scatter in crack growth rates due to uncertainties in material properties. In this paper, we report the results of a study that aims to quantify the scatter in crack growth rates of 7075-T7351 aluminium alloy subjected to spectrum loading, and to assess its effect on risk assessment. About 80 middle-tension specimens were planned to be tested under nominally identical conditions, with the crack lengths recorded using crack cameras and direct current differential potential method. Based on the test data and the analyses, crack length distributions are developed for different times. These are then compared to the distributions derived from the master curve approach. This investigation attempts to quantitatively demonstrate the reasonableness, or otherwise, of using a single crack growth curve to derive the distributions of crack lengths for risk analyses, and the conditions under which the observations apply. The results reported here and those from other researchers show that this scatter in crack growth rates cause by variation in material properties cannot be appropriately addressed by the master crack growth curve approach for the purpose of risk analysis.

The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part A: Case Selection and Set-Up

We describe a novel methodology on the selection and composition of a single-case observational dataset from the comprehensive measurement program at the Cabauw observatory field site located in the Netherlands. The case can be regarded as the basis of the third case study conducted within the framework of the GEWEX (Global Energy and Water Exchange) Atmospheric Boundary-Layer Study (GABLS) and is meant to be used for the evaluation of single-column models. The ideal case is supposed to cover a period of at least 24 h with clear skies, moderate near-surface winds and a stable stratification during nighttime. From the multi-year data archive with Cabauw observations data for 1–2 July 2006 were found to best match the requirements, and were consequently selected for analysis. The dates contains a 24-h period with a nearly constant geostrophic wind of $$\approx $$ 7 m $$\hbox {s}^{-1}$$ , and a considerable wind shear in the vertical. It is also characterized by a pronounced low-level jet related to an inertial oscillation that developed around sunset when the atmosphere had decoupled from the surface. Detailed initial conditions, surface conditions and dynamical forcings are derived on the basis of local observations and the outcome of a conceptual and a three-dimensional atmospheric model. It appears that a very precise prescription of the forcings is a prerequisite to enable a meaningful evaluation of models against observational data.

Gloss Enhancement Behaviour of Tiles with Different Initial Surface Conditions

This work addresses gloss enhancement by industrial polishing of porcelain stoneware tiles with different initial surface conditions. Tile samples were polished using a laboratory-scale CNC tribometer that properly simulated industrial processing conditions and the results of gloss and roughness evolution were compared with models proposed in the literature. The experimental data showed very good correlation with exponential regression models for situations in which the tiles’ initial surfaces had a fairly homogeneous and stable state in terms of gloss and roughness. For cases where the tiles have less homogeneous surfaces, which is closer to the industrial reality, data analysis showed an evident deviation from the exponential models, which is further discussed in the paper.

An Inter-Comparison of Daily and Monthly In Situ, Satellite Derived and Reanalyzed Sea Surface Temperature Climatology Fields Over the Bay of Bengal

Sea surface temperature (SST) is an important and one of the most studied variables in oceanography. In the current study in situ, satellite derived and reanalyzed SST climatology fields are compared for the Bay of Bengal (BOB) region at daily and monthly scales. The analysis of these SST climatologies shows not only spatial difference but also monthly average patterns with slight variations in the form of maximum temperature peak shifts. The climatology fields reveal the spatial extent of intra-seasonal variations of BOB. These variations are more distinct in TMI satellite and in situ SST data. Root mean square error (RMSE) and correlation analysis reveal that TMI and AMSR satellite daily data are more indicative of true state of SSTs and are suitable for surface initial conditions in ocean models, while reanalyzed SSTs are suitable for monthly scale forecast.

Impact of Surface Parameter Uncertainties within the Canadian Regional Ensemble Prediction System

Abstract The aim of this study is to assess the impact of uncertainties in surface parameter and initial conditions on numerical prediction with the Canadian Regional Ensemble Prediction System (REPS). As part of this study, the Canadian version of the Interactions between Soil–Biosphere–Atmosphere (ISBA) land surface scheme has been coupled to Environment Canada’s numerical weather prediction model within the REPS. For 20 summer periods in 2009, stochastic perturbations of surface parameters have been generated in several experiments. Each experiment corresponds to 20 simulations differing by the perturbations at the initial time of one or several surface parameters or prognostic variables. The sensitivity to these perturbations is quantified especially for 2-m temperature, 10-m wind speed, cloud fraction, and precipitation up to 48-h lead time. Spatial variability of these sensitivities over the North American continent shows that soil moisture, albedo, leaf area index, and SST have the largest impacts on the screen-level variables. The temporal evolution of these sensitivities appears to be closely linked to the diurnal cycle of the boundary layer. The surface perturbations are shown to increase the ensemble spread of the REPS for all screen-level variables especially for 2-m temperature and 10-m wind speed during daytime. A preliminary study of the impact on the ensemble forecast has shown that the inclusion of the surface perturbations tends to significantly increase the 2-m temperature and 10-m wind speed skill.

Influence of the processing route of porcelain/Ti–6Al–4V interfaces on shear bond strength

This study aims at evaluating the two-fold effect of initial surface conditions and dental porcelain-to-Ti–6Al–4V alloy joining processing route on the shear bond strength. Porcelain-to-Ti–6Al–4V samples were processed by conventional furnace firing (porcelain-fused-to-metal) and hot pressing. Prior to the processing, Ti–6Al–4V cylinders were prepared by three different surface treatments: polishing, alumina or silica blasting. Within the firing process, polished and alumina blasted samples were subjected to two different cooling rates: air cooling and a slower cooling rate (65°C/min). Metal/porcelain bond strength was evaluated by shear bond test. The data were analyzed using one-way ANOVA followed by Tuckey's test (p<0.05). Before and after shear bond tests, metallic surfaces and metal/ceramic interfaces were examined by Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Shear bond strength values of the porcelain-to-Ti–6Al–4V alloy interfaces ranged from 27.1±8.9MPa for porcelain fused to polished samples up to 134.0±43.4MPa for porcelain fused to alumina blasted samples. According to the statistical analysis, no significant difference were found on the shear bond strength values for different cooling rates. Processing method was statistically significant only for the polished samples, and airborne particle abrasion was statistically significant only for the fired samples. The type of the blasting material did not cause a statistically significant difference on the shear bond strength values. Shear bond strength of dental porcelain to Ti–6Al–4V alloys can be significantly improved from controlled conditions of surface treatments and processing methods.

Removal of mercury contamination on primary mass standards by hydrogen plasma and thermal desorption

The removal of a high mercury contamination on a Pt reference mass by thermal desorption was studied directly by x-ray photoemission spectroscopy (XPS). Subsequently the contamination mechanism was investigated. Samples of PtIr and AuPt exposed to vapour of mercury in air were studied using XPS and gravimetric mass determination. We find an extremely rapid mercury contamination which takes place within minutes and reaches an initial equilibrium state after 2 h to 4 h. Roughly 1 to 2 monolayers of mercury adsorbs directly on the metal surface. A natural contamination of carbon and oxygen compounds is at the top. Due to the accumulation of mercury, we find a gain in mass which corresponds to 20 µg to 26 µg for a PtIr standard. XPS data from a historical Pt standard give strong evidence for further average mercury accumulation of (1.3 ± 0.1) µg/year during a period of more than a century. This can be explained by a two-step mechanism presented in this study. The speed of contamination depends on the initial surface conditions. Polishing activates the surface and results in an enhanced accumulation of mercury. Natural contamination by C and O can delay but not prevent contamination. We further demonstrate that the mercury contamination can be removed by both hydrogen plasma and thermal desorption. The removal of mercury by hydrogen plasma can directly be attributed to the synthesis of gaseous mercury dihydrides at low pressures.

Retrieving Clear-Sky Surface Skin Temperature for Numerical Weather Prediction Applications from Geostationary Satellite Data

Atmospheric models rely on high-accuracy, high-resolution initial radiometric and surface conditions for better short-term meteorological forecasts, as well as improved evaluation of global climate models. Remote sensing of the Earth’s energy budget, particularly with instruments flown on geostationary satellites, allows for near-real-time evaluation of cloud and surface radiation properties. The persistence and coverage of geostationary remote sensing instruments grant the frequent retrieval of near-instantaneous quasi-global skin temperature. Among other cloud and clear-sky retrieval parameters, NASA Langley provides a non-polar, high-resolution land and ocean skin temperature dataset for atmospheric modelers by applying an inverted correlated k-distribution method to clear-pixel values of top-of-atmosphere infrared temperature. The present paper shows that this method yields clear-sky skin temperature values that are, for the most part, within 2 K of measurements from ground-site instruments, like the Southern Great Plains Atmospheric Radiation Measurement (ARM) Infrared Thermometer and the National Climatic Data Center Apogee Precision Infrared Thermocouple Sensor. The level of accuracy relative to the ARM site is comparable to that of the Moderate-resolution Imaging Spectroradiometer (MODIS) with the benefit of an increased number of daily measurements without added bias or increased error. Additionally, matched comparisons of the high-resolution skin temperature product with MODIS land surface temperature reveal a level of accuracy well within 1 K for both day and night. This confidence will help in characterizing the diurnal and seasonal biases and root-mean-square differences between the retrievals and modeled values from the NASA Goddard Earth Observing System Version 5 (GEOS-5) in preparation for assimilation of the retrievals into GEOS-5. Modelers should find the immediate availability and broad coverage of these skin temperature observations valuable, which can lead to improved forecasting and more advanced global climate models.

Use of poly (methyl methacrylate) in the study of fracture of randomly damaged surfaces: I. Experimental approach

Experimental approach and statistical theory are applied to broaden knowledge of materials failure by fracture, from initial service surface conditions and during damage accumulation, using PMMA beams with repeated random surfaces, which were developed by computer controlled laser ablation, and then bent to fracture. The Central Limit Theorem was used to simulate dynamic degradation. Replicas allowed the study of probability of failure location (PFL) versus parameters of the surface topography. Results show that, depending on the auto correlation length (ACL), even at early stages of degradation, there is high correlation of PFL with RMS and average roughness, and two other proposed parameters. This correlation shows an asymptotic limit behavior that agrees with fracture mechanics results for brittle materials. As important, a Sensitivity Transitional Region (STR), dependent on the ACL, was observed, below which the PFL is uncorrelated to the parameters studied; The STR's dependence on temperature is currently being studied.

Evaluation of the Added Value of Regional Ensemble Forecasts on Global Ensemble Forecasts

Abstract The regional single-model-based Aire Limitée Adaptation Dynamique Développement International–Limited Area Ensemble Forecasting (ALADIN-LAEF) ensemble prediction system (EPS) is evaluated and compared with the global ECMWF-EPS to investigate the added value of regional to global EPS models. ALADIN-LAEF consists of 16 perturbed members at 18-km horizontal resolution, while ECMWF-EPS includes 50 perturbed members at 50-km horizontal resolution. In ALADIN-LAEF, the atmospheric initial condition uncertainty is quantified by using blending, which combines large-scale uncertainty generated by the ECMWF-EPS singular-vector approach with small-scale perturbations resolved by the ALADIN breeding technique. The surface initial condition perturbations are generated by use of the noncycling surface breeding (NCSB) technique, and different physics schemes are employed for different forecast members to account for model uncertainties. The verification and comparison have been carried out for a 2-month period during summer 2007 over central Europe. The results show a quite favorable level of performance for ALADIN-LAEF compared to ECMWF-EPS for surface weather variables. ALADIN-LAEF adds more value to precipitation forecasts and has greater skill for 10-m wind and mean sea level pressure results than does ECMWF-EPS. For 2-m temperature, ALADIN-LAEF forecasts have larger spread, are statistically more consistent, but also have less skill than ECMWF-EPS due to the strong cold bias in the ALADIN forecasts. For the upper-air weather parameters, the forecast of ALADIN-LAEF has a larger spread, but the forecast skill of ALADIN-LAEF is from neutral to slightly inferior compared to ECMWF-EPS. It may be concluded that a regional single-model-based EPS with fewer ensemble members could provide more added value in terms of greater skill for near-surface weather variables than the global EPS with larger ensemble size, whereas it may have limitations when applied to upper-air weather variables.

A land data assimilation system using the MODIS-derived land data and its application to numerical weather prediction in East Asia

Land Data Assimilation Systems have been developed to generate the surface initial conditions such as soil moisture and temperature for better prediction of weather and climate. We have constructed Korea Land Data Assimilation System (KLDAS) based on an uncoupled land surface modeling framework that integrates high-resolution in-situ observation, satellite data, land surface information from the WRF Preprocessing System (WPS) and the MODIS land products over the East Asia. To present better surface conditions, the KLDAS is driven by atmospheric forcing data from the in-situ rainfall gauges and satellite. In this study, we 1) briefly introduce the KLDAS, 2) evaluate the meteorological states near the surface and the surface fluxes reproduced by the KLDAS against the in-situ observation, and then 3) examine the performance of the mesoscale model initialized by the KLDAS. We have generated a 5-year, 10 km, hourly atmospheric forcing dataset for use in KLDAS operating across East Asia. The KLDAS has effectively reproduced the observed patterns of soil moisture, soil temperature, and surface fluxes. Further scrutiny reveals that the numerical simulations incorporating the KLDAS outputs show better agreement in both the simulated near-surface conditions and rainfall distribution over the Korean Peninsula, compared to those without the KLDAS.

Polishing Sapphire Substrates by 355 nm Ultraviolet Laser

This paper tries to investigate a novel polishing technology with high efficiency and nice surface quality for sapphire crystal that has high hardness, wear resistance, and chemical stability. A Q-switched 355 nm ultraviolet laser with nanosecond pulses was set up and used to polish sapphire substrate in different conditions in this paper. Surface roughnessRaof polished sapphire was measured with surface profiler, and the surface topography was observed with scanning electronic microscope. The effects of processing parameters as laser energy, pulse repetition rate, scanning speed, incident angle, scanning patterns, and initial surface conditions on surface roughness were analyzed.

Improving Numerical Weather Predictions of Summertime Precipitation over the Southeastern United States through a High-Resolution Initialization of the Surface State

Abstract It is hypothesized that high-resolution, accurate representations of surface properties such as soil moisture and sea surface temperature are necessary to improve simulations of summertime pulse-type convective precipitation in high-resolution models. This paper presents model verification results of a case study period from June to August 2008 over the southeastern United States using the Weather Research and Forecasting numerical weather prediction model. Experimental simulations initialized with high-resolution land surface fields from the National Aeronautics and Space Administration’s (NASA) Land Information System (LIS) and sea surface temperatures (SSTs) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) are compared to a set of control simulations initialized with interpolated fields from the National Centers for Environmental Prediction’s (NCEP) 12-km North American Mesoscale model. The LIS land surface and MODIS SSTs provide a more detailed surface initialization at a resolution comparable to the 4-km model grid spacing. Soil moisture from the LIS spinup run is shown to respond better to the extreme rainfall of Tropical Storm Fay in August 2008 over the Florida peninsula. The LIS has slightly lower errors and higher anomaly correlations in the top soil layer but exhibits a stronger dry bias in the root zone. The model sensitivity to the alternative surface initial conditions is examined for a sample case, showing that the LIS–MODIS data substantially impact surface and boundary layer properties. The Developmental Testbed Center’s Meteorological Evaluation Tools package is employed to produce verification statistics, including traditional gridded precipitation verification and output statistics from the Method for Object-Based Diagnostic Evaluation (MODE) tool. The LIS–MODIS initialization is found to produce small improvements in the skill scores of 1-h accumulated precipitation during the forecast hours of the peak diurnal convective cycle. Because there is very little union in time and space between the forecast and observed precipitation systems, results from the MODE object verification are examined to relax the stringency of traditional gridpoint precipitation verification. The MODE results indicate that the LIS–MODIS-initialized model runs increase the 10 mm h−1 matched object areas (“hits”) while simultaneously decreasing the unmatched object areas (“misses” plus “false alarms”) during most of the peak convective forecast hours, with statistically significant improvements of up to 5%. Simulated 1-h precipitation objects in the LIS–MODIS runs more closely resemble the observed objects, particularly at higher accumulation thresholds. Despite the small improvements, however, the overall low verification scores indicate that much uncertainty still exists in simulating the processes responsible for airmass-type convective precipitation systems in convection-allowing models.

Modelling aeolian sediment transport during initial soil development on an artificial catchment using WEPS and aerial images

Wind and water erosion are among the most important physical processes that affect the soil surface structure of artificial catchments, especially during earliest stages immediately after the construction. During this initial stage of a hydro-geo-system, bare surfaces are directly exposed to the atmospheric impact. Since erosion measurements are often not feasible during and immediately after construction, sediment transport and relocation can at best be estimated based on qualitative observations or photos only. While sediments transported by water remain in the catchment, the aeolian transport involves sediment exchange with surrounding areas and induces more balance-uncertainty. The objective of this study was to test a modelling approach for estimating the possible range of aeolian transport and quantifying possible contributions to the overall sediment mass balance of a catchment. The question was whether one can apply a wind erosion model to predict the effect of wind erosion on the initial soil and landscape development. We used the erosion sub-model of the raster-based Wind Erosion Prediction System (WEPS) to simulate aeolian sediment fluxes for the “Chicken Creek” catchment, located south of the city of Cottbus. This 6-ha-sized artificial hydrologic catchment was constructed in 2005. Parameters representing soil surface conditions were based on textural data and field estimations. Wind speed, wind direction, and precipitation came from a nearby meteorological station. The well-defined constructed initial surface conditions facilitated the estimation of uncertain surface parameters. The parameter surface roughness is based on wind tunnel measurements on similar surfaces, the area of loose sediment cover was estimated from photos; crust strengths and initial amount of erodible material were estimated by assuming analogies with surfaces in semi-arid regions. The simulation scenarios yielded annual net sediment losses from the catchment area during the 27-month simulation period in a range from 0.01 Mg ha −1 to about 10 Mg ha −1. Losses were mostly compensated when assuming external sediment input. The simulated masses of aeolian transport for high-erosivity scenarios correspond best with those derived from aerial image analysis. Assuming complex soil textural distributions further improved predictions of sediment distribution patterns. The results suggest that WEPS simulations combined with image analysis can be used to estimate aeolian transport during initial soil development. The model is simple enough to operate with limited data while being complex enough to capture main features such as heterogeneous soil texture distribution. The approach improved insight in ecological development of constructed systems in the initial phase after implementation of their design.

Effect of naturally formed oxide films and other variables in the early stages of Mg-alloy corrosion in NaCl solution

The influence of initial surface conditions on the subsequent corrosion behaviour of AZ31 and AZ61 magnesium alloys in 0.6 M NaCl solution has been studied using electrochemical impedance spectroscopy. For obtaining the different surface conditions, some of the specimens were immersion tested with the surface in the as-received condition, while others were tested immediately after mechanical polishing, and part of the polished specimens after six months of exposure to the laboratory atmosphere. Considering the evolution of the high-frequency capacitive arc of the Nyquist diagram, whose diameter is related to the corrosion process, a clear effect of the initial surface conditions is observed only in the early stages of testing. This effect is especially significant for the freshly polished specimens.

Evaluation of soil moisture ensemble runs to estimate precipitation variability in convection-permitting model simulations for West Africa

In this investigation, the impact of soil moisture on the precipitation amount and distribution in model simulations for West Africa was assessed. This included the examination of the dependence of precipitation on soil moisture, boundary layer parameters or convective conditions. For this purpose, different soil moisture fields from the rainy season of the year 2006 in West Africa were collected. These included three analysis fields, satellite measurements, and model output from the African Monsoon Multidisciplinary Analysis (AMMA) Land Surface Model Intercomparison Project. The different soil moisture fields were analyzed and compared first; large differences in the mean values, the north–south gradients, and the heterogeneity were revealed. The distributions were taken to initialize five convection-permitting model runs performed with the limited-area model COSMO (Consortium for Small-scale Modeling), forced by reanalyses from the European Centre for Medium-Range Weather Forecasts. A case study of a period with intense convective activity in the Sudanian and Sahelian zone was selected for the simulations. The simulated precipitation was compared with data from two satellite-based precipitation analyses and with forecasts from two global models of lower resolution. The model spread encompassed the precipitation analyses in the southern subdomain, while the latter lay far above the model results in the northern subdomain. The different soil moisture fields also influenced the turbulent fluxes at the surface, the boundary layer state and height as well as convective instability. Standard deviation of the simulations was highest for convective available potential energy, while the impact on convective inhibition was less pronounced. Only a weak negative relation of precipitation to soil moisture or conditional instability could be discerned. In this case, dry soil favored a higher boundary layer with better developed convective cells contributing to larger precipitation sums. The spread between the five precipitation forecasts suggests that a high-resolution limited-area ensemble, built by applying atmospheric variations as well as variations of the initial land surface conditions, will be a proper method to improve the prediction of mesoscale convective systems and convective precipitation for West Africa.

The Central European limited‐area ensemble forecasting system: ALADIN‐LAEF

AbstractThe Central European limited‐area ensemble forecasting system ALADIN‐LAEF (Aire Limitée Adaptation Dynamique Développement InterNational—Limited‐Area Ensemble Forecasting) has been developed within the framework of ALADIN international cooperation and the Regional Cooperation for Limited‐Area modelling in Central Europe (RC LACE). It was put into pre‐operation in March 2007. The main feature of the pre‐operational ALADIN‐LAEF was the dynamical downscaling of the global ensemble forecast from the European Centre for Medium‐range Weather Forecasts (ECMWF). In 2009, ALADIN‐LAEF was upgraded with several methods for dealing with the forecast uncertainties to improve the forecast quality. These are: (1) the blending method, which combines the large‐scale uncertainty generated by ECMWF singular vectors with the small‐scale perturbations resolved by ALADIN breeding into atmospheric initial condition perturbations; (2) the multi‐physics approach, wherein different physics schemes are used for different forecast members to account for model uncertainties; and (3) the non‐cycling surface breeding technique, which generates surface initial condition perturbations.This article illustrates the technical details of the updated ALADIN‐LAEF and investigates its performance. Detailed verification of the upgraded ALADIN‐LAEF and a comparison with its first implementation (dynamical downscaling of ECMWF ensemble forecasts) are presented for a two‐month period in summer 2007. The results show better performance and skill for the upgraded system due to the better representation of forecast uncertainties. Copyright © 2011 Royal Meteorological Society