Mesoscale Numerical Model Research Articles

A numerical simulation of latent heating within Typhoon Molave

The weather research and forecasting (WRF) model is a new generation mesoscale numerical model with a fine grid resolution (2 km), making it ideal to simulate the macro- and micro-physical processes and latent heating within Typhoon Molave (2009). Simulations based on a single-moment, six-class microphysical scheme are shown to be reasonable, following verification of results for the typhoon track, wind intensity, precipitation pattern, as well as inner-core thermodynamic and dynamic structures. After calculating latent heating rate, it is concluded that the total latent heat is mainly derived from condensation below the zero degree isotherm, and from deposition above this isotherm. It is revealed that cloud microphysical processes related to graupel are the most important contributors to the total latent heat. Other important latent heat contributors in the simulated Typhoon Molave are condensation of cloud water, deposition of cloud ice, deposition of snow, initiation of cloud ice crystals, deposition of graupel, accretion of cloud water by graupel, evaporation of cloud water and rainwater, sublimation of snow, sublimation of graupel, melting of graupel, and sublimation of cloud ice. In essence, the simulated latent heat profile is similar to ones recorded by the Tropical Rainfall Measuring Mission, although specific values differ slightly.

High-resolution modelling of atmospheric dispersion of dense gas using TWODEE-2.1: application to the 1986 Lake Nyos limnic eruption

Abstract. Atmospheric dispersal of a gas denser than air can threat the environment and surrounding communities if the terrain and meteorological conditions favour its accumulation in topographic depressions, thereby reaching toxic concentration levels. Numerical modelling of atmospheric gas dispersion constitutes a useful tool for gas hazard assessment studies, essential for planning risk mitigation actions. In complex terrains, microscale winds and local orographic features can have a strong influence on the gas cloud behaviour, potentially leading to inaccurate results if not captured by coarser-scale modelling. We introduce a methodology for microscale wind field characterisation based on transfer functions that couple a mesoscale numerical weather prediction model with a microscale computational fluid dynamics (CFD) model for the atmospheric boundary layer. The resulting time-dependent high-resolution microscale wind field is used as input for a shallow-layer gas dispersal model (TWODEE-2.1) to simulate the time evolution of CO2 gas concentration at different heights above the terrain. The strategy is applied to review simulations of the 1986 Lake Nyos event in Cameroon, where a huge CO2 cloud released by a limnic eruption spread downslopes from the lake, suffocating thousands of people and animals across the Nyos and adjacent secondary valleys. Besides several new features introduced in the new version of the gas dispersal code (TWODEE-2.1), we have also implemented a novel impact criterion based on the percentage of human fatalities depending on CO2 concentration and exposure time. New model results are quantitatively validated using the reported percentage of fatalities at several locations. The comparison with previous simulations that assumed coarser-scale steady winds and topography illustrates the importance of high-resolution modelling in complex terrains.

Large-eddy simulations of a Salt Lake Valley cold-air pool

Persistent cold-air pools are often poorly forecast by mesoscale numerical weather prediction models, in part due to inadequate parameterization of planetary boundary-layer physics in stable atmospheric conditions, and also because of errors in the initialization and treatment of the model surface state. In this study, an improved numerical simulation of the 27–30 January 2011 cold-air pool in Utah's Great Salt Lake Basin is obtained using a large-eddy simulation with more realistic surface state characterization. Compared to a Weather Research and Forecasting model configuration run as a mesoscale model with a planetary boundary-layer scheme where turbulence is highly parameterized, the large-eddy simulation more accurately captured turbulent interactions between the stable boundary-layer and flow aloft. The simulations were also found to be sensitive to variations in the Great Salt Lake temperature and Salt Lake Valley snow cover, illustrating the importance of land surface state in modelling cold-air pools.

Ionic transport features in concrete composites containing various shaped aggregates: a numerical study

The service life of concrete-based infrastructure and buildings is seriously shortened due to the chloride-induced durability problems. In order to clarify the transport mechanism associated with the response of inclusion structures, this paper presents a numerical study on the influence caused by morphology and heterogeneity of individual phases, in which the concrete is treated as a three-phase composite including mortar, aggregates and interfacial transition zone (ITZ). A series of meso-scale numerical models with different shapes and volume fractions of aggregates are developed for examining the effects of aggregates on ionic migration. Unlike in most of the existing published research work in this area, a multi-component ionic transport theory which takes ionic interactions into consideration has been utilised in this study. By coupling mass conservation and Poisson’s equations, the time-spatial concentration distribution results for individual ionic species are obtained. Other important factors such as the externally applied electric field, concrete heterogeneity, ionic binding and ITZ are also considered and examined in this study. Through this relatively thorough numerical analysis, some important features about the effect of aggregate shape based on multi-species modelling, which have previously not been properly investigated, are highlighted.

A comparison of vertical velocity variance measurements from wind profiling radars and sonic anemometers

Abstract. Observations of turbulence in the planetary boundary layer are critical for developing and evaluating boundary layer parameterizations in mesoscale numerical weather prediction models. These observations, however, are expensive and rarely profile the entire boundary layer. Using optimized configurations for 449 and 915 MHz wind profiling radars during the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA), improvements have been made to the historical methods of measuring vertical velocity variance through the time series of vertical velocity, as well as the Doppler spectral width. Using six heights of sonic anemometers mounted on a 300 m tower, correlations of up to R2 = 0. 74 are seen in measurements of the large-scale variances from the radar time series and R2 = 0. 79 in measurements of small-scale variance from radar spectral widths. The total variance, measured as the sum of the small and large scales, agrees well with sonic anemometers, with R2 = 0. 79. Correlation is higher in daytime convective boundary layers than nighttime stable conditions when turbulence levels are smaller. With the good agreement with the in situ measurements, highly resolved profiles up to 2 km can be accurately observed from the 449 MHz radar and 1 km from the 915 MHz radar. This optimized configuration will provide unique observations for the verification and improvement to boundary layer parameterizations in mesoscale models.

Thunderstorm activity forecasting based on the model of cumulonimbus cloud electrification

The physical and mathematical description of the model of cumulonimbus cloud electrification is presented. The model uses the forecasts of the WRF-ARW numerical mesoscale model as inputs and allows predicting the parameters of the atmospheric electric field including those typical of thunderstorm activity. The prognostic values of electric breakdown are compared with the observed thunderstorms.

Forecasting surface-layer atmospheric parameters at the Large Binocular Telescope site

In this paper, we quantify the performance of an automated weather forecast system implemented on the Large Binocular Telescope (LBT) site at Mt Graham (Arizona) in forecasting the main atmospheric parameters close to the ground. The system employs a mesoscale non-hydrostatic numerical model (Meso-Nh). To validate the model, we compare the forecasts of wind speed, wind direction, temperature and relative humidity close to the ground with the respective values measured by instrumentation installed on the telescope dome. The study is performed over a large sample of nights uniformly distributed over 2 yr. The quantitative analysis is done using classical statistical operators [bias, root-mean-square error (RMSE) and σ] and contingency tables, which allows us to extract complementary key information, such as the percentage of correct detections (PC) and the probability of obtaining a correct detection within a defined interval of values (POD). The results of our study indicate that the model performance in forecasting the atmospheric parameters we have just cited are very good, in some cases excellent: RMSE for temperature is below 1°C, for relative humidity it is 14 per cent and for the wind speed it is around 2.5 m s−1. The relative error of the RMSE for wind direction varies from 9 to 17 per cent depending on the wind speed conditions. This work is performed in the context of the ALTA (Advanced LBT Turbulence and Atmosphere) Center project, whose final goal is to provide forecasts of all the atmospheric parameters and the optical turbulence to support LBT observations, adaptive optics facilities and interferometric facilities.

Numerical analysis of atmospheric circulation and pollution transfer in the environs of Norilsk industrial region

Using a numerical mesoscale model of the atmospheric boundary layer, the dynamics of air streams in the Norilsk valley is studied for typical weather conditions. It is shown that the orographic features of the region form a wind field, horizontally inhomogeneous and highly variable in altitude. The fields of local and regional dust and heavy metal precipitations are numerically reconstructed on the basis of expedition data on snow cover pollution in the environs of the Norilsk copper plant.

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

The Impact of Vertical Resolution on Fog Forecasting in the Kilometric-Scale Model AROME: A Case Study and Statistics

Abstract The impact of vertical resolution on numerical fog forecasting is studied in detail for a specific case and evaluated statistically over a winter season. Three vertical resolutions are tested with the kilometric-scale Applications of Research to Operations at Mesoscale (AROME) numerical weather prediction model over Paris Charles de Gaulle Airport (Paris-CDG) in Paris, France. For the case studied, the vertical resolution has a strong impact on fog onset. The nocturnal jet and the turbulence created by wind shear at the top of the nocturnal boundary layer are more pronounced with a finer vertical resolution, and the turbulence close to the ground is also stronger with high vertical resolution. Local circulations created by the terrain induce different simulated processes during the fog onset. The fog is simulated as advection–radiation fog in the finer vertical resolution run and as radiation fog in the others. The vertical resolution has little impact on the mature and dissipation phases. A statistical study over a winter season confirms the results obtained in the fog case study. High vertical resolution simulates earlier onset, as well as longer-lasting and more spatially heterogeneous fogs. The high vertical resolution configuration simulates more fog events than are found at low resolution (LR); these fog events generally form north of Paris-CDG. No observations are available in this area, leading to many simulated but no observed fog events in the fine-resolution runs. The ceiling of low clouds is not well simulated by the numerical model no matter what vertical resolution is used.

Effects of surface drag on upper-level frontogenesis within a developing baroclinic wave

This paper investigates the effects of surface drag on upper-level front with a three-dimensional nonhydrostatic mesoscale numerical model (MM5). To this end, a new and simple potential vorticity intrusion (PVI) index is proposed to quantitatively describe the extent and path that surface drag affects upper-level front. From a PV perspective, the formation of the upper-level front is illustrated as the tropopause folding happens from the stratosphere. The PVI index shows a good correlation with the minimum surface pressure, and tends to increase with the deepening of the surface cyclone and upper-level front. The surface drag acts to damp and delay the development of upper-level front, which could reduce the growth rate of the PVI index. However, the damping presents different effects in different development stages. It is the most significant during the rapid development stage of the surface cyclone. Compared with no surface drag cases, the tropopause is less inclined to intrude into the troposphere due to the surface drag. Positive feedback between the surface cyclone and upper-level front could accelerate the development of the frontal system.

Surface Wind Regionalization Based on Similarity of Time-series Wind Vectors

In the complex terrain where local wind systems are formed, accurate understanding of regional wind variability is required for wind resource assessment. In this paper, cluster analysis based on the similarity of time-series wind vector was applied to classify wind regions with similar wind characteristics and the meteorological validity of regionalization method was evaluated. Wind regions in Jeju Island and Busan were classified using the wind resource map of Korea created by a mesoscale numerical weather prediction modeling. The evaluation was performed by comparing wind speed, wind direction, and wind variability of each wind region. Wind characteristics, such as mean wind speed and prevailing wind direction, in the same wind region were similar and wind characteristics in different wind regions were meteor-statistically distinct. It was able to identify a singular wind region at the top area of Mt. Halla using the inconsistency of wind direction variability. Furthermore, it was found that the regionalization results correspond with the topographic features of Jeju Island and Busan, showing the validity.

Numerical modelling approach for the management of seasonal influenced river channel entrance

The dynamic nature of a river channel entrance is commonly seasonal dependant. This is evidenced in the topography of river channel entrances in East Coast of Borneo which is influenced by both North East (NE) and South West (SW) monsoons on top of surrounding parameters such as waves and tides, sedimentation as well as climate change. Advanced numerical modelling technique is frequently used as a leading approach to investigate the complicated nature of river channel entrance to well represent actual conditions of a designated area. This paper presented a mesoscale numerical modelling method by integrating reductionist and reduced complexity model approach along with local seasonal conditions to well represent river channel entrance problem and propose management measures. The model was established with a set of numerical equilibrium equations and calibrated parameters to reflect the features of regional conditions with the combination of local validated modelling parameters. The model had accurately represented the effects of both NE and SW monsoons in terms of hydraulics and sediment dynamics at the Petagas river channel entrance, as verified by site data and satellite imagery. In addition, the accuracy of the model provides confidence in the implementation of improvement measures at the river channel entrance. The improvement scheme includes a training channel and a breakwater in improving flushing capacity, thus preventing sedimentation and upstream flooding, allowing proper navigation through the river. In conclusion, the accurate investigational result from this numerical model had successfully demonstrated its scientific role in solving dynamic river channel entrance, which can serve as a numerical modelling approach for solving similar river channel entrance problems especially in the East Coast of Borneo with predominant inter-annual seasonal variations.

The Elastic Modulus of Steel Fiber Reinforced Concrete (SFRC) with Random Distribution of Aggregate and Fiber

The present paper offers a meso-scale numerical model to investigate the effects of random distribution of aggregate particles and steel fibers on the elastic modulus of Steel Fiber Reinforced Concrete (SFRC). Meso-scale model distinctively models coarse aggregate, cementitious mortar, and Interfacial Transition Zone (ITZ) between aggregate, mortar, and steel fibers with their respective material properties. The interfaces between fibers and mortar have been assumed perfectly bonded. Random sampling principle of Monte Carlo's simulation method has been used to generate the random size, orientation, and position of aggregate particles as well as steel fibers in concrete matrix. A total of 2100 two-dimensional and three-dimensional cube specimens (150 mm) with varying volume fractions of aggregate and fiber have been randomly generated. The commercial code ABAQUS has been used to analyze the specimens under tensile loading and the calculated elastic modulus has been compared to other analytical and experimental values. Results indicate that the non-homogeneity of the matrix and random distribution of aggregate and fibers manage to disperse calculated efficiency factor of fiber with a standard deviation of 2.5% to 3.0% (for 150 mm cube specimens, it can be different for other specimens). Nevertheless, the mean value of the calculated efficiency factor agrees well with the value, recommended by Hull (1981), for uniformly-distributed fibers, equal to 0.353, and 0.151 for two and three-dimensional models respectively.

Description of radiation conditions and evaluation of the date of 137Cs release to the atmosphere using the radionuclide transfer model coupled with the forecasts by the mesoscale hydrodynamic model

The estimates of 137Cs emissions from the accident happened in Elektrostal at the beginning of April 12, 2013 are presented. The transport of radionuclides and their dry and wet deposition on the surface are computed using the Lagrangian stochastic model of the NOSTRADAMUS software package worked out by Nuclear Safety Institute of Russian Academy of Sciences. Prognostic fields of wind (horizontal and vertical components) in the lower troposphere, precipitation, and vertical and horizontal turbulence diffusivity coefficients in the lower atmosphere (up to 4 km) were used as input data. Prognostic fields were obtained using the WRF-ARW numerical mesoscale model.

Adjustment of the summertime marine atmospheric boundary layer to the western Iberia coastal morphology

AbstractDuring summer (June, July, and August), northerly winds driven by the Azores anticyclone are prevalent over western Iberia. The Quick Scatterometer Satellite 2000 to 2009 summertime estimates reveal a broad high wind speed (≥7 ms−1) area extending about 300 km from shore and along the entire Iberian west coast. Nested in this large high‐speed region, preferred maximum regions anchored in the Iberian major capes, Finisterre, Roca, and S. Vicente, are found. Composite analyses of wind maxima were performed to diagnose the typical summertime synoptic‐scale pressure distribution associated with these smaller size high‐speed regions. The flow low‐level structure was further studied with a mesoscale numerical prediction model for three northerly events characterized by typical summertime synoptic conditions. A low‐level coastal jet, setting the background conditions to the marine atmospheric boundary layer (MABL) response to topography, was found in the three cases. The causes for wind maximum downwind capes were investigated, focusing on the hypothesis that western Iberia MABL responds to hydraulic forcing. For the three events supercritical and transcritical flow conditions were identified and expansion fan signatures were found downwind each cape. Aircraft measurements, performed during one of the events, gave additional evidence of the expansion fan leeward Cape Roca. The importance of other forcing mechanisms was also assessed by considering the hypothesis of downslope wind acceleration and found to be in direct conflict with soundings and surface observations.

Citywide Impacts of Cool Roof and Rooftop Solar Photovoltaic Deployment on Near-Surface Air Temperature and Cooling Energy Demand

Assessment of mitigation strategies that combat global warming, urban heat islands (UHIs), and urban energy demand can be crucial for urban planners and energy providers, especially for hot, semi-arid urban environments where summertime cooling demands are excessive. Within this context, summertime regional impacts of cool roof and rooftop solar photovoltaic deployment on near-surface air temperature and cooling energy demand are examined for the two major USA cities of Arizona: Phoenix and Tucson. A detailed physics-based parametrization of solar photovoltaic panels is developed and implemented in a multilayer building energy model that is fully coupled to the Weather Research and Forecasting mesoscale numerical model. We conduct a suite of sensitivity experiments (with different coverage rates of cool roof and rooftop solar photovoltaic deployment) for a 10-day clear-sky extreme heat period over the Phoenix and Tucson metropolitan areas at high spatial resolution (1-km horizontal grid spacing). Results show that deployment of cool roofs and rooftop solar photovoltaic panels reduce near-surface air temperature across the diurnal cycle and decrease daily citywide cooling energy demand. During the day, cool roofs are more effective at cooling than rooftop solar photovoltaic systems, but during the night, solar panels are more efficient at reducing the UHI effect. For the maximum coverage rate deployment, cool roofs reduced daily citywide cooling energy demand by 13–14 %, while rooftop solar photovoltaic panels by 8–11 % (without considering the additional savings derived from their electricity production). The results presented here demonstrate that deployment of both roofing technologies have multiple benefits for the urban environment, while solar photovoltaic panels add additional value because they reduce the dependence on fossil fuel consumption for electricity generation.

Cold‐conveyor‐belt jet, sting jet and slantwise circulations in idealized simulations of extratropical cyclones

The present study investigates the formation of sting‐jet cyclones using an idealized configuration of a high‐resolution mesoscale numerical model. The initial set‐up is composed of axisymmetric finite‐amplitude synoptic‐scale cyclones added to a baroclinic zonal jet. When the surface cyclone is initialized on the warm‐air side of the zonal jet, a strong bent‐back warm front forms, which is a favourable condition for sting jets. A rather high vertical resolution of about 200 m in the lower troposphere is required to obtain well‐formed slantwise circulations near the cloud head and to make the distinction between cold‐conveyor‐belt jet and sting jet. In contrast, when the surface cyclone is initialized on the jet axis, the surface cyclone is more representative of the Norwegian cyclone model and the bent‐back warm front is almost non‐existent.Sting‐jet mechanisms are analyzed using backward Lagrangian trajectories. A minority group of air parcels entering the sting‐jet region undergoes diabatic cooling due to sublimation of snow and graupel. The majority group does not present such a diabatic cooling and corresponds to descending air masses from the cloud‐head region in a near‐neutral environment with respect to conditional symmetric instability. Indeed, the saturated moist potential vorticity is near zero and the momentum surfaces and saturated moist isentropes are quasi‐parallel in the main slantwise descent. The latter descent is shown to be geostrophically forced by the strong divergent component of the along‐front Q vector.Boundary‐layer processes are also analyzed. In most areas, the static stability being strong, there is no penetration of descents coming from the sting jet into the boundary layer and the peaks in surface wind gusts are connected to intrinsic boundary‐layer convective cells and parametrized turbulence. Such a penetration occurs in some areas but is not related to the strongest wind gusts.

A New Framework to Compare Mass-Flux Schemes Within the AROME Numerical Weather Prediction Model

In the Application of Research to Operations at Mesoscale (AROME) numerical weather forecast model used in operations at Meteo-France, five mass-flux schemes are available to parametrize shallow convection at kilometre resolution. All but one are based on the eddy-diffusivity–mass-flux approach, and differ in entrainment/detrainment, the updraft vertical velocity equation and the closure assumption. The fifth is based on a more classical mass-flux approach. Screen-level scores obtained with these schemes show few discrepancies and are not sufficient to highlight behaviour differences. Here, we describe and use a new experimental framework, able to compare and discriminate among different schemes. For a year, daily forecast experiments were conducted over small domains centred on the five French metropolitan radio-sounding locations. Cloud base, planetary boundary-layer height and normalized vertical profiles of specific humidity, potential temperature, wind speed and cloud condensate were compared with observations, and with each other. The framework allowed the behaviour of the different schemes in and above the boundary layer to be characterized. In particular, the impact of the entrainment/detrainment formulation, closure assumption and cloud scheme were clearly visible. Differences mainly concerned the transport intensity thus allowing schemes to be separated into two groups, with stronger or weaker updrafts. In the AROME model (with all interactions and the possible existence of compensating errors), evaluation diagnostics gave the advantage to the first group.

Sensitivity of HF radar-derived surface current self-organizing maps to various processing procedures and mesoscale wind forcing

We performed a number of sensitivity experiments by applying a mapping technique, self-organizing maps (SOM) method, to the surface current data measured by high-frequency (HF) radars in the northern Adriatic and surface winds modelled by two state-of-the-art mesoscale meteorological models, the Aladin (Aire Limitee Adaptation Dynamique Developpement InterNational) and the Weather and Research Forecasting models. Surface current data used for the SOM training were collected during a period in which radar coverage was the highest: between February and November 2008. Different pre-processing techniques, such as removal of tides and low-pass filtering, were applied to the data in order to test the sensitivity of characteristic patterns and the connectivity between different SOM solutions. Topographic error did not exceed 15 %, indicating the applicability of the SOM method to the data. The largest difference has been obtained when comparing SOM patterns originating from unprocessed and low-pass filtered data. Introduction of modelled winds in joint SOM analyses stabilized the solutions, while sensitivity to wind forcing coming from the two different meteorological models was found to be small. Such a low sensitivity is considered to be favourable for creation of an operational ocean forecasting system based on neural networks, HF radar measurements and numerical weather prediction mesoscale models.