Numerical Modeling System Research Articles

Advances in Urban Meteorological Research in China

Over the past decades, a large number of studies have been carried out in the field of urban meteorology in China. This paper summarizes the main progress in urban meteorology research from four aspects: urban meteorological observation network and field campaign, multi-scale model of urban meteorology, interaction between urban meteorology and atmospheric environment, and the impacts of urbanization on weather and climate. Major advances are as follows. China’s major cities have established or are improving comprehensive urban meteorological observation networks characterized by multi-platform, multi-variable, multi-scale, multi-link, and multi-function. Beijing, Nanjing, Shanghai, and other cities carried out urban meteorological field campaigns, which were included in the WMO research demonstration project. Wind tunnel experiments and scale-model outdoor experiments were successfully conducted. Multi-scale urban meteorological and air quality prediction numerical model systems have been developed and put into operational use. The urban heat island effect; urban impacts on precipitation, regional climate, and air quality; urban planning; and interaction between urban meteorology and atmospheric environment are extensively investigated. Finally, efforts to improve observational technology, data assimilation, and urban system modeling, to explore the impacts of urbanization on environment and human health, and to provide integrated urban hydro-meteorological climate and environmental services are planned ahead.

Multiscale modelling of cage effects on the transport of effluents from open aquaculture systems.

Most Atlantic salmon mariculture operations use open sea cages for the grow out phase. The ultimate fate and effects of the effluents and the possibilities of disease transfer between fish farms are major concerns for farmers, governance and the general public alike. Numerical model systems applied to studying and managing effluents and disease transfer in mariculture must realistically resolve the hydrodynamics in the vicinity of the fish farms. In the present study, the effects of the aquaculture structures on the current patterns were introduced in the ocean model system SINMOD. The drag parameters for the ocean model were determined by comparing the simulation results from the ANSYS Fluent ® software suite and SINMOD in an idealized channel setting with uniform currents. The model was run for a number of realistic scenarios in high horizontal resolution (∼30 m) with sea cages influencing the flow field. Comparisons between extensive current measurements and the simulation results showed that the model system reproduced the current local current field well. By running simulation scenarios with and without the effects of the sea cages on the flow field, it was possible to assess the importance of such effects for numerical dispersal models and aquaculture environment interactions simulations and hence for assessment of environmental impacts.

Advanced delay assured numerical heuristic modelling for peer to peer project management in cloud assisted internet of things platform

The Cloud assisted Internet of Things (CIoT) refers to the billions of physical devices that are associated to share data with the Internet by utilizing the distributed or peer to peer networking services. However, the Devices which are associated in the peer to peer project management services by means of remote systems and processors are getting smaller and less expensive every day. In the recent past, the peer to peer network faces several different issues in data handling problems and control, reliability in transmitting data, project database management, transmission Delay, Transmission Energy, workload, computational time and the performance have been emerged as a significant issues in peer to peer project management services. In this research, an advanced Delay assured numerical heuristic modelling system(DANHM) has been presented which helps to address resource allocation, transmission Delay, Transmission Energy, workload issues in cloud assisted IoT platform for the peer to peer network and computing. This method helps in minimizing the requirement for human mediation, and helps clients can get Quality of service(QoS) and quicker project management services in the peer to peer network management by considering the significant edge servers and Cloud computing systems. The exploratory results shows promising outcomes in the data management for speed, performance factor, QoS ratio, transmission delay, reliability of data, accuracy, Transmission energy, work load allocation in accordance with traditional project management computing system which are used in practice.

A modeling study of estuarine–shelf circulation using a composite tidal and subtidal open boundary condition

We investigated the performance of a tidally and subtidally forced open boundary condition (TST-OBC) on the estuarine–shelf circulation in a limited-area, down-scaling numerical modeling system for the northern South China Sea. We forced the modeling system with amplified tidal forces and subtidal forcing of spatiotemporally variable wind and river discharge. TST-OBC numerically and physically accommodates the circulation driven by the regional tides, subtidal forces, external forcing from its upscale solution, and internally generated disturbances. The advantages of TST-OBC are the separation of fast tidal and slow subtidal modes, active and dual-wave transmitting schemes, consistent treatment of barotropic and baroclinic circulation, and thermodynamic variables, which enable the model to capture observed circulation characteristics. The results differ from the results obtained using the Flather-type OBC, which over-restores internal to external solutions with a notable accumulation of spurious disturbances along the open boundaries. Disturbances with both tidal and subtidal signals that arrive at the open boundaries are well-treated by adopting TST-OBC, although it is currently feasible for the one-way downscaling applications.

Review of Chinese atmospheric science research over the past 70 years: Synoptic meteorology

Synoptic meteorology is a branch of meteorology that uses synoptic weather observations and charts for the diagnosis, study, and forecasting of weather. Weather refers to the specific state of the atmosphere near the Earth’s surface during a short period of time. The spatial distribution of meteorological elements in the atmosphere can be represented by a variety of transient weather phenomena, which are caused by weather systems of different spatial and temporal scales. Weather is closely related to people’s life, and its development and evolution have always been the focus of atmospheric scientific research and operation. The development of synoptic meteorology is closely related to the development of observation systems, dynamical theories and numerical models. In China, observation networks have been built since the early 1950s. Up to now, a comprehensive meteorological observation system based on ground, air and space has been established. In particular, the development of a new generation of dense radar networks, the development of the Fengyun satellite series and the implementation of a series of large field experiments have brought our understanding of weather from large-scale environment to thermal dynamics, cloud microphysical structure and evolution characteristics of meso and micro-scale weather systems. The development of observation has also promoted the development of theory, numerical model and simulation. In the early days, China mainly used foreign numerical models. Lately, China has developed numerical model systems with independent intellectual property rights. Based on the results of high-resolution numerical simulations, in-depth understanding of the initiation and evolution mechanism and predictability of weather at different scales has been obtained. Synoptic meteorology has gradually changed from an initially independent development to a multidisciplinary approach, and the interaction between weather and the change of climate and environment has become a hot and frontier topic in atmospheric science. This paper reviews the important scientific and technological achievements made in China over the past 70 years in the fields of synoptic meteorology based on the literatures in China and abroad, from six aspects respectively including atmospheric dynamics, synoptic-scale weather, typhoon and tropical weather, severe convective weather, numerical weather prediction and data assimilation, weather and climate, atmospheric physics and atmospheric environment.

A study of feedbacks and the formation of climate trends in the Arctic climate system

The role of the ocean in the response of the climate system to an increase in the atmospheric CO2 concentration is investigated by using a system of numerical models, ICMMG-PlaSim. The results of this study are summarized as follows: a) the ocean, to some extent (up to 20%), contributes to the increase in the annual mean state and to the decrease in the amplitude of seasonal oscillations (by 2-3%), which ultimately leads to insignificant changes in the summer period and to a significant mitigation of winter, b) the ocean stabilizes the annual mean state of the Arctic oscillation, making it practically unchanged with increasing CO2 concentration but, at the same time, contributes to the significant increase in the amplitude of the seasonal cycle of this oscillation, c) the ocean enhances the temperature (or thermal) component of the seasonal variation associated with the appearance of additional areas freed from ice cover, with an additional average increase in the temperature of the atmosphere at the ice edge. Besides, the ocean enhances the seasonal oscillations of this component, so that the summer manifestations become much stronger, d) our tests have revealed that the role of the Arctic dipole under global warming is insignificant. These conclusions, though, may undergo significant changes under a more detailed consideration of carbon cycles in the atmosphere, ocean, and land.

Modelling of the Impact of the Retention Reservoir on the Flood Protection of the City – A Case Study for the City of Kalisz (Central Poland)

Floods are natural phenomena related to the circulation of water in nature and they cannot be avoided. Despite the methods of predicting floods, technological development and civilization progress, the flood risk has been still increasing. The relevant hydrotechnical advancement, rational spatial development and optimal water management have a significant impact on reducing the consequences of flooding. Particularly retention reservoirs are decisive to rising flood safety and living conditions of urban residents who are at risk of flooding. The construction of a retention reservoir is a serious engineering, economic and eco-scale challenge. It must be preceded by numerous studies and analyses necessary to carry out the entire construction process and subsequent operation in an optimal way. At present, a number of engineering and environmental analyses are supported by the use of forecasting and computational tools based on the mathematical description of a given physical phenomenon. With their use, it is possible to determine, at the design level, the impact of a technical facility on various elements of the natural or the human environment. The paper presents the impact analyses of a planned retention reservoir located on the Prosna river in the flood protection system in Kalisz (Poland). The flood protection system is insufficient in Kalisz and its weakness was demonstrated, among others, by flood in May, 2010. Analyses were based on data received from the unsteady flow numerical modelling system and optimisation methods to support the management process of retention reservoir resources for extreme periods. The formulated task of dynamic optimisation due to its non-linearity was simplified to a static task by discretisation of an independent variable.

Enhancement of a numerical model system for reliably predicting morphological development in the Saalach River

ABSTRACT Rivers are dynamic systems, changing over time on their own or due to engineering measures and structures. At rivers which are regularly monitored, information on sediment balance can be used to evaluate the morphological development and to assess the impact of such measures. In this paper, we show that the performance of a numerical model can be improved by quantify boundary conditions, and that the simulation results of such a well-developed model will be more useful for civil engineers. As a case study, we develop a model system based on TELEMAC-SISYPHE to study the morphology of the Saalach River, where erosion and sedimentation impacts local ecology and human safety. Based on the available measurements and a sediment balance concept, we estimate the amount of sediment supplied to the river section downstream of a reservoir as well as the volume of the bed sediment transported along the river channel in different years. Using this information as boundary conditions for calibration and validation cases, the model provides a realistic and accurate representation of the river. Furthermore, our model has been successfully employed on the Saalach River to evaluate an alternative strategy for a more sustainable river management.

Verification of a bioclimatic modeling system in a growing suburb in Melbourne

Urban climate knowledge has been increasingly integrated into urban design and planning practices. Numerical modeling systems, such as climatic and bioclimatic tools, are currently more popular than onsite field measurements. This higher popularity is mainly due to the complicated interactions in 3D urban environments and the spatial distribution of various climatic parameters that cannot be captured thoroughly via on-site measurements alone. Such modeling systems also offer better solutions to overcome the nonlinearity of urban climate in forecasting different “what if scenarios.”This paper provides an overview of different types of climatic and bioclimatic modeling systems and presents their main benefits and shortcomings. In the second part of this study, one of the most commonly used tools in urban climate studies, namely, ENVI-met, was selected, and its reliability in different contexts was investigated by reviewing past researches. The applicability of ENVI-met in accurately simulating the influence of future urban growth on one of the fastest growing suburbs in Melbourne, was tested by conducting a sensitivity analysis on inputs and control parameters, backed up with a series of field measurements in selected points. RMSE value was calculated for different runs of the initial ENVI-met model with adjusted control parameters (e.g., factor of short-wave adjustment, initial air temperature, relative humidity, roughness length, wind speed, albedo of walls, and albedo of roofs). The model achieved the optimum performance by altering the short-wave adjustment factor from 0.5 to 1; therefore, ENVI-met was considered a reliable tool for relative comparison of urban dynamics. The findings of this study not only help planners select the most practical modeling systems that address project objectives but also educate them on limitations associated with using ENVI-met.

Investigation of mechanical behaviour of a quasi-brittle material using Karagozian and Case concrete (KCC) model

Abstract The mechanical behaviour of a quasi-brittle material, i.e. Pietra Serena sandstone, was investigated both numerically and experimentally in order to build a reliable numerical modelling system applicable to more complex cases. The Karagozian and Case concrete (KCC) model was exploited as the material constitutive law and a new method to utilise this model for efficient and accurate simulation of quasi-brittle materials is discussed. The capability of this model is evaluated by comparing the results of the numerical simulations with the corresponding experimental results, and the method itself is critically assessed.

Simulating dune evolution on managed coastlines: Exploring management options with the Coastal Recovery from Storms Tool (CReST)

Despite the importance of coastal dunes to many low-lying coastal communities and ecosystems, our understanding of how both climatic and anthropogenic pressures affect foredune evolution on time scales of years to decades is relatively poor. However, recently developed coupled numerical modeling tools have allowed for the exploration of the erosion and growth of coastal foredunes on time scales of hours to years. For example, Windsurf is a new process-based numerical modeling system (Cohn et al. 2019a) that simulates the evolution of dune-backed sandy coastal systems in response to wave, wind, and water level forcings. CReST, developed as a front-end interface to Windsurf, aims to add the ability to incorporate beach nourishment and dune construction, beach and dune grading, dune grass planting scenarios, dune grass removal, and the presence of hard engineering structures into the model framework to better account for the complex dynamics of managed coastlines. Initial model sensitivity tests suggest that the model provides a flexible framework to investigate the complex interactions between beaches and dunes for a variety of exploratory and applied applications.

Numerical Simulation Modeling of a GSHP and WSHP System for an Office Building in the Hot Summer and Cold Winter Region of China: A Case Study in Suzhou

This paper studies the long-term performance of a Ground Source Heat Pump (GSHP) system and a Water Source Heat Pump (WSHP) system for an office building in Suzhou, which is a hot summer and cold winter climate region of China. The hot summer and cold winter region is the most urbanized region of China and has subtropical monsoon climate, therefore, Heating, Ventilation, and Air Conditioning (HVAC) systems are in great demand. Due to the fact that 42.5% of Suzhou’s total area is covered by lakes and rivers, the city has an abundance of surface water resources. Based on Suzhou’s meteorological data and the thermal characteristics of the building envelope, an office building model was created and the dynamic cooling and heating load was calculated using Transient System Simulation (TRNSYS) simulation software. Two numerical HVAC modeling systems were created: a GSHP system for which the data of an in-situ Thermal Response Test (TRT) was used and a WSHP system for which the Tai Lake water temperature was used. Simulating the performance of both systems over a 20-year period, the two systems were analyzed for their Coefficient of Performance (COP), heat source temperature variation, and energy consumption. The results show that the GSHP system causes ground heat accumulation, which reduces the system’s COP and increases energy consumption. The study also revealed that compared with the GSHP system, the WSHP system has a more stable long-term performance for buildings in Suzhou.

Modeling key processes affecting Al speciation and transport in estuaries

Assessments of the impacts of aluminium (Al) to aquatic organisms in estuarine waters have suffered from the lack of available models that can accurately predict the presence of toxic physico-chemical forms (species) of Al at adequate spatial and temporal resolution. In the present work, transport and distribution of river-discharged Al species through changing environmental conditions in the Sandnesfjorden estuary, South-Eastern Norway, was predicted using a numerical model system at relatively high spatial (32 m × 32 m in horizontal) and temporal (1 h) resolution. New model code was implemented, including dynamic, salinity-dependent speciation and transformation processes, based on in situ measurements from several Norwegian estuaries as well as experimental data. This is the first time such elemental speciation code including LMM, colloidal, particle and sediment species is utilized in an estuary case in combination with high resolution hydrodynamics and compared to an extensive observational dataset. Good agreement was obtained between modeled and observed total and fractionated Al concentration at several stations along the fjord transect. Without including background contribution of Al from the coastal water, the model predicted too low Al concentrations (by up to approximately a factor 4) near the fjord mouth. The surface Al concentrations were also underestimated due to overestimated near-surface vertical mixing in the hydrodynamic model. The observed correlation between salinity and total Al concentration was well reproduced by the model in situations with low upper layer volume flux, typical under low river flow conditions. In contrast, the predicted surface salinity and total Al concentration were less correlated under high-flux conditions. As the general trends of Al concentrations and speciation were well reproduced, this study demonstrated that by including carefully chosen transfer rates, the model can be used to predict spatio-temporal distribution of total contamination as well as concentration levels of the elemental species.

Programme for the development of weather and climate numerical modelling systems in South Africa

Programme for the development of weather and climate numerical modelling systems in South Africa

Evaluation of dynamical properties of open quantum systems using the driven Liouville-von Neumann approach: methodological considerations

Methodological aspects of using the driven Liouville-von Neumann (DLvN) approach for simulating dynamical properties of molecular junctions are discussed. As a model system we consider a non-interacting resonant level uniformly coupled to a single Fermionic bath. We demonstrate how a finite system can mimic the depopulation dynamics of the dot into an infinite band bath of continuous and uniform density of states. We further show how the effects of spurious energy resolved currents, appearing due to the approximate nature of the equilibrium state obtained in DLvN calculations, can be avoided. Several ways to approach the wide band limit, which is often adopted in analytical treatments, using a finite numerical model system are discussed including brute-force increase of the lead model bandwidth as well as efficient cancellation or direct subtraction of finite-bandwidth effect. These methodological considerations may be relevant also for other numerical schemes that aim to study non-equilibrium thermodynamics via simulations of open quantum systems.

Performance assessment of CHIMERE and EURAD-IM’ dust modules

The purpose of this study is to investigate how two different atmospheric 3D modelling systems, with different dust modules, simulate a Saharan dust episode, using satellite data and in-situ observations to validate their performances. The episode occurred during 19–23 February 2016 and impacted the Iberian Peninsula. The two numerical modelling systems applied are the CHIMERE and the EURAD-IM chemistry transport models with different dust modules, both forced by the same WRF meteorological input. A common domain and resolution (27 × 27 km2) was adopted for the modelling setup. The comparison and evaluation of the two modelling results have shown that both models are able to capture the occurrence of the natural event, which was initiated by a cut-off low above the coast of Morocco, inducing a strong meridional transport of dust loaded air from Algeria straight towards eastern parts of the Iberian Peninsula. The most notable differences between the two model outputs concern the emission strengths and the emission source regions. In fact, different emission patterns and strengths are simulated by each model despite they use the same soil database, identical clay/silt/sand contribution for each soil type, and the same meteorological simulation. In general, CHIMERE simulates higher PM10, PM2.5, and dust concentrations than EURAD-IM for this event. In the South of Portugal, CHIMERE shows better agreement with observations, while in Central Portugal, EURAD-IM is closer to particle related measurements.

Insights into the Summer Diurnal Cycle over Eastern South Africa

Abstract Adopting a state-of-the-art numerical model system, we investigate how the diurnal variations in precipitation and local breeze systems are characterized by lower-boundary conditions related to the Drakensberg highland and warm SST associated with the Agulhas Current. A control simulation can simulate the hydrometeorological climates in the region realistically, but the terrestrial rainfall is overestimated. During daytime, the precipitation is confined to the Drakensberg highland, and there is an onshore local breeze, while during midnight to morning, the rainfall is confined to the Agulhas Current, and the breeze is offshore. These variations are captured by the numerical simulation, although the timing of maximum rainfall is early over the land and delayed over the ocean. The sensitivity experiment in which the Drakensberg is absent shows a drastic modification in the diurnal variations over land and ocean. The terrestrial precipitation is largely decreased around the Drakensberg and is largest along the coast during daytime. The nocturnal marine precipitation along the Agulhas Current is also reduced. Although the daily residual breeze is still pronounced even without the Drakensberg, wind speed is weakened. We attribute this to the reduction of precipitation. In another sensitivity experiment with smoothened warm SST due to the Agulhas Current, the amplitudes of diurnal variations are not modified remarkably, but the coastal rainfall is diminished to some extent due to less evaporation along the Agulhas Current. This study concludes that the Drakensberg plays a crucial role for the diurnal cycle, and the impact of the Agulhas Current is limited on the diurnal cycle of the coastal precipitation in this region.

The Generation and Forecast of Extreme Winds during the Origin and Progression of the 2017 Tubbs Fire

On 8–9 October 2017, fourteen wildfires developed rapidly during a strong Diablo wind event in northern California including the Tubbs Fire, which travelled over 19 km in 3.25 h. Here, we applied the CAWFE® coupled numerical weather prediction-fire modeling system to investigate the airflow regime and extreme wind peaks underlying the extreme fire behavior using simulations that refine from a 10 km to a 185 m horizontal grid spacing. We found that as Diablo winds travelled south down the Sacramento Valley and fanned out southwestward over the Wine Country, their strength waxed and waned and their direction wavered, creating varying locations near fire origins where wind overrunning topography reached 30–40 m/s, along with streaks and bursts of strong winds in the lee of some topographic features and stagnation downstream of others. Despite a statically stable layer in the lowest 1.5 km, the high Froude number flow sometimes resembled a hydraulic jump. Elsewhere, the flow behaved similarly to neutrally-stratified flow over small hills, creating wind extrema that exceeded 40 m/s at the crest of some lesser hills including near the Tubbs fire ignition, but which shed bursts of high speed winds that travel downstream at approximately 5–7-min intervals. Nonetheless, simulated fire growth lagged satellite detection of fire arrival in Santa Rosa by up to 1 h, although whether the data detect fire line or spotting is ambiguous. A forecast simulation with a 370 m horizontal grid spacing produced an on-time fire line arrival in Santa Rosa, with calculations executed 4 times faster than real time on a single computer processor.

Effect of street design on pedestrian thermal comfort

ABSTRACTThe number of people living in urban areas is projected to increase significantly in most of the cities around the world. To address the future population increase, local governments develop new planning scenarios to increase the density in certain areas that can accommodate the growth. However, the potential threat to human health and pedestrian comfort will be exacerbated, if planning professionals exclude climatic conscious urban design in their practices. Increasing numbers of the hot days and frequent occurrence of heatwave events cause a serious threat to human life. This study investigates the effect of the future structural plans on pedestrian thermal comfort through numerical simulation using City North, Melbourne as a case study. The effect of street design towards the development of a comfortable microclimate at street level for pedestrians is investigated. To provide knowledge readily interpretable from the planning perspective, the existing and future scenarios for different street profiles are modelled and the consequences of microclimatic parameters and thermal comfort are assessed. A three-dimensional numerical modelling system, ENVI-met was used for the simulation. A clear reduction of average daytime temperature (T), mean radiant temperature (MRT) and Physiological Equivalent Temperatures (PET) were observed across the study area after implementing the ‘Plan Melbourne’ strategies. The outcomes of this study will assist urban planners in developing policies which can effectively decrease the vulnerability to the heat stress at the pedestrian level.

The Potential for Upscaling Kelp (Saccharina latissima) Cultivation in Salmon-Driven Integrated Multi-Trophic Aquaculture (IMTA)

Integrated multi-trophic aquaculture (IMTA) has the potential of reducing open-cage fish farming impacts on the environment while also introducing new value chains. The aim of this study was to investigate the growth and composition of the kelp Saccharina latissima in salmon-driven IMTA, and to assess the spatial extent of the influence of salmon derived nitrogen in order to evaluate the upscaling potential for IMTA. S. latissima was cultivated 100, 200 and 1,000 m east and 1,000 m west of a 5,000 tonnes salmon farm in Western Norway from February to September 2013. The proportion of salmon derived nitrogen available for the kelp showed a clear decline with distance from the farm. Accordingly, the kelp cultivated near the salmon cages grew faster during the spring season, and growth rate decreased with increasing distance from the farm. A spatially explicit numerical model system (SINMOD), including compartments for dissolved nutrients and kelp growth, was tuned to the field data and used to investigate the potential for upscaling IMTA production. The model was used to introduce a new metric – the impacted area IA - for the areal effects of IMTA in terms of the increase in production by IMTA. The model showed that a 25 hectare kelp farm in the vicinity of the studied salmon farm could take up 1.6 of the 13.5 tonnes of dissolved inorganic nitrogen released during kelp cultivation, amounting to almost 12 % of the ammonia released during the cultivation period from February to June. The 25 hectare kelp farm would have a production yield of 1,125 tonnes fresh weight (FW), being 60 % more than that of a non-IMTA kelp farm, while a 20 % increase of kelp FW could be obtained over a 110 hectar area in salmon-driven IMTA. To achieve an even mass balance, an area of approximately 220 ha-1 would be needed to cultivate enough kelp to fix an equivalent of the nitrogen released by the fish.