Wind Effects Research Articles

Sensitivity Simulations of Wind-driven Water Circulation in İzmit Bay

İzmit Bay, a 50 km long inlet at the eastern end of the Marmara Sea, is crucial for the region’s economy, culture, and marine ecosystem. The bay’s water circulation regulates nutrient distribution, stratification, sedimentation, oxygen levels, heat, and pollution levels. It is also influenced by meteorological events, such as short-term moderate to strong wind conditions. This study investigated the sensitivity of İzmit Bay Water Circulation to wind speed, direction, and duration using the MITgcm model with Orlanski boundary conditions and process-oriented modeling. The simulations showed that under weak forcing conditions, seawater temperature, salinity, and stratification do not significantly vary. However, strong forcing and wind speeds (statistically defined by percentiles of observation data) of 4.9 m/s (75%), 6.7 m/s (90%), and 10.1 m/s (99%) generate significant mesoscale and sub-mesoscale processes, depending on the direction. Westerly component winds cause downwelling at the eastern coastline, while easterly component winds bring sub-surface water to the surface. Strong winds from N, NE, and E sectors lead to the rise in lower-layer waters in the western basin, forcing them to overflow through the Hersek Delta sill into the central basin. Overall, severe wind events greater than 4.9 m/s (75%) significantly affect the bay’s hydrography by transforming the upper layer, with a decrease in temperature up to 5 °C and an increase in salinity up to 10 ppt.

N-year demand-to-capacity indexes and the design of high-rise buildings for wind

The purpose of this work is to assess the global load effects method, commonly used in current commercial practice for determining design wind effects on high-rise buildings. The assessment is performed by comparing results based on the global load effects method to their counterparts obtained by a conventional, well established structural engineering approach. That approach yields time series of the demand-to-capacity index (DCI) induced in structural members by time series of effective (aerodynamic + inertial) wind loads. The DCI time series so obtained depend upon member-specific influence coefficients, meaning that the time series of the DCIs, and therefore the peak DCIs and their times of occurrence, differ from member to member. In contrast, the global load effects method assumes that all the structural members’ peak DCIs occur at the same time, i.e., at the time of occurrence of the largest combination of base moments produced by the wind forces acting on the structure. The use of the global wind effects method in commercial practice is due to the fact that wind engineering laboratories do not have access to the structure’s influence coefficients. This work reports the novel finding that the global load effects method results in the underestimation of the DCIs of nearly all the members of the building’s structural system. Numerical examples are presented which show that the underestimation can be substantial. Therefore, the use of the global load effects method needs to be discontinued, and the estimation of the peak DCIs needs to be performed by accounting for their dependence upon the structure’s influence coefficients, a task that can only be performed by the structural engineering office.

Numerical simulation study on ship manoeuvrability in mountainous rivers: Comprehensively considering effects of nonuniform flow, shallow water, narrow banks, winds and waves

Ships navigating inland waterways, especially mountainous waterways, may encounter complex navigation environments. Under these circumstances, the force of the ship is extremely complex, the attitude of the ship may be unstable, and the control performance may decrease, possibly resulting in marine accidents. In this study, a modular-type manoeuvring model (MMG) is used to develop a ship manoeuvring model that comprehensively considers multiple factors. Based on this model, numerical simulations are conducted on the ship Seiun Maru, and Esso Osaka; the simulation results are found to be in good agreement with the results of real ship motions. Then, numerical simulations are conducted on the navigation of a 500-ton ship in a typical mountainous waterway, the Suoluo Rapids in the Lancang River, and the impact of the complex environment in this area on the safety of ship navigation is explored. The results reveal that ignoring the influence of environmental factors may put ships in dangerous situations when navigating mountain waterways. In addition, the model can effectively simulate the manoeuvring motion of a ship in a typical mountain waterway, and the calculation cost is negligible. This study provides valuable suggestions for long-distance ship manoeuvring in complex inland river environments.

Wave setup estimation at regional scale: Empirical and modeling-based multi-approach analysis in the Mediterranean Sea

Wave setup is a physical process that induces a temporal increase of the mean water level due to wave dissipation by bottom friction and breaking in the surf zone, extending over tens to hundreds of meters in the cross-shore direction. Wave setup contribution to coastal sea level solely induced by wind and atmospheric effects can increase by more than 100% under extreme events and conditions favoring its formation. It is therefore crucial to consider this phenomenon when assessing sea-level-related coastal hazards. Previous studies estimated the wave setup effect by means of numerical modeling and empirical formulations at regional and global scale. Such analyses require either high computational capacity to implement high-resolution numerical models over large domains, and/or accurate information on coastal morphological features from global or regional databases. Although the Mediterranean Sea is a fetch-limited environment, waves generated from extra-tropical cyclones are powerful enough for wave setup to develop, and subsequently for a potential significant wave setup contribution to extreme coastal sea level. Through the use of both numerical and empirical methods, we investigate the uncertainty associated to wave setup representation on the frequency and magnitude of coastal extreme sea levels occurring on sandy beaches in the Mediterranean Sea. Wave setup values are compared at beach scale between process-based modeling and empirical approaches, showing highly variable results. We also quantify the impact of wave setup on return levels of coastal sea level extremes using reconstructed sea levels. We employ various methods to calculate the wave setup component. Results show high spatial dispersion, with clear differences between the numerical and empirical approaches, especially in regions prone to the development of energetic waves. The total inter-method dispersion of 100-year return levels is often higher than 30 cm for average values of 62.4 cm. We emphasize the important limitations related to wave setup modeling (i.e., its underestimation) at large scale, and call for caution when applying empirical formulations (generally developed from local studies) at regional to global scale, which can lead to unrealistic wave setup values.

An experimental estimation method of diffusion coefficients in ternary and multicomponent systems from a single diffusion profile

Until recently, it was textbook knowledge that the diffusion coefficients could not be estimated in a multi-component system following the widely practised diffusion couple method. The recently proposed constrained diffusion couple method largely solved the problems. The need to produce two intersecting diffusion paths in a multi-component space with very well-controlled compositions of the diffusion couple end members may be tricky in certain situations, depending on the complications of diffusion paths. In this study, we have shown the estimation of all types of diffusion coefficients from a single diffusion profile without neglecting Onsager's cross terms in concentrated ternary Ni-Co-Fe, Fe-rich quaternary Fe-Ni-Co-Cr and concentrated Ni-Co-Fe-Cr-Al quinary alloys. This is applicable in ternary and multicomponent component systems (n≥3) at a stable Kirkendall marker plane position. One can even estimate the impurity diffusion coefficients utilizing the composition profiles at the ends of the diffusion couples following the Hall method, which has been rarely practised in multicomponent systems until now. We have further demonstrated the importance of estimating the tracer and intrinsic diffusion coefficients in a concentrated or multi-principal element alloy in which interdiffusion coefficients can be vague and misleading for understanding the elements' diffusional interactions and relative mobilities. We have also shown the importance of considering the vacancy wind effect in concentrated alloys. The method proposed in this study will help to generate a mobility database with relative ease in various multicomponent systems important for various applications, which was considered impossible until recently.

Determining the main driver of hypoxia potential in freshwater inland lakes

This study aimed to determine the potential for hypoxia in inland freshwater lakes via examining water quality variables, mainly dissolved oxygen (DO). To this end, field studies including environmental surveying and water column sampling at six stations along two routes in Lake Zarivar, Iran, together with laboratory analysis were conducted. Then, a stepwise multivariate regression analysis was employed to identify existing patterns and effects among variables. To secure the evolved model generalizability, the range of data was adjusted using available measurements from several similar lakes/wetlands with respect to their climate and sampling season. Finally, the evolved models’ reliability was examined using validation samples as well as a comparative performance appraisal with a benchmark model attained by the least squares regression technique. The results indicated that NH4 and pH have the most significant effect on DO. The greater amount of DO on the lake surface, i.e., wind effect, and its effect on both nitrification and ammonification processes ensure the absence of hypoxia in surface layers. Therefore, in water column monitoring programs, measuring NH4 and pH would be sufficient. Our results also demonstrated that the potential of hypoxia increases if the amount of NH4 increases in the lower layers of the water column despite releasing DO with nitrate. Strong relations between DO, as the main factor of hypoxia, with NH4 and pH, gives us the opportunity to predict the hypoxia potential and its level. Using time delay between nitrification and ammonification processes, one may predict the changes in the amount of oxygen from the changes in nitrogen.

Fighting wind with wind to improve high-speed train aerodynamics near mountains

A look at the acceleration effect of gale-force winds on high-speed trains reveals how mitigation efforts might be designed.

The analysis of the factors influencing the operation of the piston wind in the cage of the hybrid hoisting shaft and the simulation study of the operation effect

The mixed shaft in the mine is used as the main inlet and return air shaft and also as the lifting shaft. The piston wind effect caused by the frequent operation of large and efficient lifting equipment in the shaft will disturb the normal air flow in the shaft and cause the air flow disorder. So It is important to study influencing factors and the series of piston effects of inner cage operation in the hoisting shaft. This paper firstly derives a theoretical model of piston wind for double cage operation in a wellbore based on the non-constant flow theory of Bernoulli’s equation, and derives the influencing factors of piston wind. Then, according to the actual situation of the mine, a 3D fluid simulation model of cage hoisting is established. Based on the verified simulation method, the transient division of labor of piston wind effect and its influencing factors is simulated and the influence of various factors on the development law of piston wind is analyzed in detail. The study results show that the main factors influencing the piston wind are the cage operating conditions, the cage operating speed, the shaft blockage ratio and the initial ventilation speed in the shaft. The operation of the cage produces an eddy current zone, which causes air flow disorder in the wellbore and affects the ventilation effect of the shaft. The piston wind speed is the highest when the cage running against the wind, while the speed is lower running with the wind. The most complex wind flow disturbance occurs when the two cages meet, which is almost block the flow of wind in the shaft. The change of cage operating speed and wellbore blockage ratio is related to the piston wind speed and pressure changes linearly in different conditions. There is the best blockage ratio between the hoisting cage and the shaft, which can cause the highest average ventilation speed in the shaft, and the best blockage ratio of the study model is 0.32.

Performance Optimization Design Study of Box-Type Substations Subjected to the Combined Effects of Wind, Snow, and Seismic Loads

As a pivotal node in both urban and rural power grids, the box-type substation not only serves the functions of power conversion and distribution but also need to provide structural support and environmental adaptability. However, deficiencies in strength, stiffness, or vibration characteristics may lead to vibration and noise issues, and extreme environmental changes can pose risks of structural damage. This study aims to verify and optimize the seismic resistance and environmental adaptability of box-type substations through finite element simulation methods. Using SOLIDWORKS, a three-dimensional model of the box-type substation was constructed, and static and dynamic analyses were conducted using Ansys Workbench to comprehensively evaluate the dynamic response of the box-type substation under wind, snow loads, and seismic action. Through iterative simulations and a comparison of multiple design solutions, the structural optimization of the substation was achieved. The optimized structure balances strength and stiffness, significantly reducing the weight of the substation body, with the wall thickness reduced by 60%. Additionally, the phenomenon of stress concentration on the side walls was eliminated, ensuring that the equivalent stress is below the material yield strength. This research provides methods and empirical results for enhancing the performance and reliability of box-type substations under seismic conditions, confirming the feasibility of a lightweight design, while ensuring structural safety.

A machine learning approach to evaluate coastal risks related to extreme weather events in the Veneto region (Italy)

A significant and unprecedented increase of temperature has been recorded worldwide during the last decades, leading to the occurrence of numerous extreme events. Coastal areas, with their high population density, interconnected economic activities, fragile ecosystems, are particularly vulnerable to climate change impacts. These impacts can be intensified by the interactions of multiple hazards which operate at different spatio-temporal scales and affect exposure and vulnerability patterns. An integrated approach is here proposed to assess the relationship between risk factors and to evaluate the multiplicity of impacts that may affect the coastline. A new path to tackle these multi-risk events is offered by ML algorithms to effectively handle vast amounts of heterogenous data, and model complex non-linear relationships between multiple factors and feedback mechanisms. To assess impacts caused by extreme events (storm surges, extreme precipitation, wind events) in the Veneto coastal municipalities, a ML approach was developed to understand connections between atmospheric and marine hazards and impacts recorded by the Veneto region emergency archive during the 2009–2019 timeframe, identifying the most influencing factors triggering multiple risks. Additionally, the coastal municipalities were clustered considering the intrinsic relationships between impact occurrences, exposure and vulnerability features. Several algorithms were compared to estimate daily risk of impacts to occur providing hazards, exposure and vulnerability information. The MLP algorithm showed satisfactory performances (weighted-F1-score of 0.94) to estimate the relative importance of input features. The proposed algorithm was designed as support tool to increase the understanding of impacts’ occurrence in coastal areas, thus helping the adaptation planning process.

Effects of wind on deep convection in Lake Baikal during the autumnal thermal bar

The results of numerical modeling of processes of deep convection in Lake Baikal during the autumnal thermal bar are presented. Analysis of the space—time distributions of temperature under different wind conditions was conducted on an example of the Boldakov River—Maloye More Strait cross-section which is characterised by the great depths. Simulations have shown the effectiveness of wind only in the upper 250 m layers. However, cabbeling instability generated by the thermal bar can lead to convective mixing to a depth of ∼600 m.

Heat transfer performance and electrohydrodynamic characteristics optimization of a dividing-wall-type ionic wind heat exchanger

Heat exchangers play a major role in reducing emissions and conserving energy. There is a plethora of theoretical research on the enhancement of heat transfer caused by ionic wind, but there is still a lack of studies on the practical application of ionic wind in heat exchangers to increase heat exchange capacity. This work developed an original ionic wind heat exchanger with a dividing wall. It may be applied to difficult circumstances when conventional heat exchangers fail for air-to-air heat exchange. The study conducted experiments to investigate the impact of many factors, including intake air velocity, discharge spacing, and electrode distribution scheme, on the ionic wind intensity and the heat exchanger's increased heat transfer coefficient. A two-dimensional model was used to analyze the internal flow and thermal properties of the heat exchangers with wire emitters. By combining active and passive heat exchange technologies, an ionic wind heat exchanger with serrated grounded electrodes was presented. The outcomes demonstrated that a suitable intake air velocity enhances the heat exchanger's capacity for heat exchange. The improved heat exchange effect of ionic wind is more important when the inlet wind speed is less than 1 m/s. When the intake air velocity approaches 1.3 m/s, the ionic wind has less of an impact on the heat exchanger's capacity for heat exchange. The benefits of improved heat transfer are promoted by placing the emitter closer to the channel entry. Increasing the operating voltage further enhances the heat transfer enhancement ratio (HTER). The number and arrangement of wire electrodes should be chosen with consideration for the 'barrier effect' between neighboring emitters and the distance from the entrance when utilizing multiple wire electrodes. In comparison to the three-wire and five-wire electrodes, the four-wire electrode heat exchanger's HTER values were increased by 5.9 % and 14.3 %, respectively. The ionic wind heat exchanger's capacity for heat transfer is further increased using a zigzag grounding electrode. The zigzag uses a decreased aspect ratio, and the emitter is positioned slightly above the tip, improving the system's heat transfer capabilities. When compared to a heat exchanger with a flat plate grounded electrode, the four-wire electrode heat exchanger produced a 158 % increase in HTER value.

Characterising global ocean mesoscale eddy by AVISO and Haiyang-2 altimeter

ABSTRACT This work compares the Haiyang-2 (HY-2) altimeter data with the well-recognized satellite oceanographic data (AVISO) product in the global ocean in their capability of detecting mesoscale eddy. A well-established method to detect mesoscale eddies from HY-2 and AVISO was applied to the sea level anomaly (SLA) data on a global scale in 2021−2022. It is found that the number of mesoscale eddies derived from the HY-2 dataset is three times more than that from the AVISO dataset and with larger eddy kinetic energy (EKE), shorter lifespan and smaller amplitude. Besides, the monthly-averaged number of generated and terminated mesoscale eddies is similar and the temporal variation of SLA exhibits strong lunar oscillation for both datasets. Most mesoscale eddies are generated in the mid-latitude oceans due to the Coriolis force and the strong El Niño. In the western boundary of the global ocean, equator, Antarctic Ocean and other areas with strong currents, the mesoscale eddies have stronger SLA amplitudes, EKEs and vorticity. Furthermore, EKE is low at the centre and high at the eddy meander. The spatial distribution characteristics of vorticity are the same as those of EKEs in the western boundary of oceans, but the vorticity value of HY-2 data near the equator is larger than that of AVISO data. However, considering the large detection error of eddy near the equator, no further exploration will be conducted in this paper. Furthermore, mesoscale eddies tend to move in the east–west direction due to Coriolis force and wind (Ekman transport) effects and large-scale ocean circulation or the pathway of drifters also have a certain impact. Overall, similar to AVISO data, the HY-2 data is also reliable for mesoscale identification in global oceans.

Forecasting High Wind Events in the HRRR Model over Wyoming and Colorado. Part I: Evaluation of Wind Speeds and Gusts

Abstract Strong wind events cause significant societal damage ranging from loss of property and disruption of commerce to loss of life. Over portions of the United States, the strongest winds occur in the cold season and may be driven by interactions with the terrain (downslope winds, gap flow, and mountain wave activity). In the first part of this two-part series, we evaluate the High-Resolution Rapid Refresh (HRRR) model wind speed and gust forecasts for the 2016–22 winter months over Wyoming and Colorado, an area prone to downslope windstorms and gap flows due to its complex topography. The HRRR model exhibits a positive bias for low wind speeds/gusts and a large negative bias for strong wind speeds/gusts. In general, the model misses many strong wind events, but when it does predict strong winds, there is a high false alarm probability. An analysis of proxies for surface winds is conducted. Specifically, 700- and 850-mb (1 mb = 1 hPa) geopotential height gradients are found to be good proxies for strong wind speeds and gusts at two wind-prone locations in Wyoming. Given the good agreement between low-level height gradients and surface wind speeds yet a strong negative bias for strong wind speeds and gusts, there is a potential shortcoming in the boundary layer physics in the HRRR model with regard to predicting strong winds over complex terrain, which is the focus of the second part of this two-part study. Last, the sites with the largest strong wind speed bias are found to mostly sit on the leeward side of high mountains, suggesting that the HRRR model performs poorly in the prediction of downslope windstorms. Significance Statement We investigate the performance of the High-Resolution Rapid Refresh (HRRR) model with respect to strong wintertime wind speeds and gusts over the complex terrain of Wyoming and Colorado. We show that the overall performance of the HRRR model is low with regard to strong wind speed and wind gust forecasts across the investigated winter seasons, with a large negative bias in predicted strong wind speeds and gusts and a small positive bias for weak wind speeds and gusts. The largest biases are found to be on the leeward side of high mountains, indicating poor prediction of downslope winds. This study also utilizes National Weather Service forecasting metrics to understand their performance with respect to strong wind forecasts, and we find that they provide skill in forecasting these events.

Forecasting High Wind Events in the HRRR Model over Wyoming and Colorado. Part II: Sensitivity of Surface Wind Speeds to Model Resolution and Physics

Abstract Strong wind events can cause severe economic loss and societal impacts. Peak winds over Wyoming and Colorado occur during the wintertime months, and in the first part of this two-part series, it was shown that the High-Resolution Rapid Refresh (HRRR) model displays large negative biases with respect to strong wind events. In this part of the study, we address two questions: 1) does increasing the horizontal resolution improve the representation of strong wind events over this region, and 2) are the biases in HRRR-forecasted winds related to the selected planetary boundary layer (PBL), surface layer (SL), and/or land surface model (LSM) parameterizations? We conduct Weather Research and Forecasting (WRF) Model simulations to address these two main questions. Increasing the horizontal resolution leads to a small improvement in the simulation of strong wind speeds over the complex terrain of Wyoming and Colorado. In general, changes in the PBL, SL, and LSM parameterizations show much larger changes in simulated wind speeds compared to increasing the model resolution alone. Specifically, changing from the Mellor–Yamada–Nakanishi–Niino scheme to the Mellor–Yamada–Janjić PBL and SL schemes results in nearly no change in the r2 values, but there is a decrease in the magnitude of the strong wind speed bias (from −12.52 to −10.16 m s−1). We attribute these differences to differences in the diagnosis of surface wind speeds and mixing in the boundary layer. Further analysis is conducted to determine the value of 1-km forecasts of strong winds compared with wind speed diagnostics commonly used by the National Weather Service. Significance Statement Motivated by prior studies showing low skill in the prediction of strong winds using state-of-the-art weather forecast models, in this study, we aim to investigate two questions: 1) does increasing the horizontal resolution improve the prediction of strong wind events over the complex terrain of Wyoming and Colorado, and 2) are the biases in High-Resolution Rapid Refresh (HRRR) forecasted winds related to the selected planetary boundary layer, surface layer, and/or land surface model parameterizations? We find that increasing the horizontal resolution provides a slight improvement in the prediction of strong winds. Further, considerable improvement in the prediction of strong winds is found for varying boundary layer, surface layer, and land surface parameterizations.

Enhancing Urban Resilience: Strategic Management and Action Plans for Cyclonic Events through Socially Constructed Risk Processes

Cities will face increasing challenges due to the impacts of global climate change, particularly in the form of cyclonic events, necessitating a deeper understanding and the establishment of effective response mechanisms at both institutional and citizen levels. In this research, we tested the efficiency of crowdsourcing in fostering participatory resilience and improving urban management. The main aim was to design novel and accurate proactive response strategies and mitigate the adverse effects of cyclonic wind events through volunteerism, citizen science, and urban science. To achieve this goal, as a case study, the municipality of Soledad, Colombia was used. This research employed a two-phase methodological approach: (i) initially evaluating the spatial distribution of emergency response resources, and (ii) developing a geo-referenced survey to map, systematize, and categorize data and outcomes. A total of three hundred and seventy-eight residents across five neighborhoods in Soledad, which have experienced a high frequency of atmospheric wind phenomena over the past two decades, were surveyed. The results indicate that the crowdsourcing mechanism effectively enhanced the empirical understanding of atmospheric wind events in Soledad, facilitating the establishment of a geo-referenced volunteer network for real-time responses. Additionally, this study shed light on previously undocumented challenges, in terms of reducing the number of people affected, and the actions that would lead to improved urban development to reduce the impacts of cyclonic events, emphasizing the significance of citizen science in the social construction of risk and disaster risk reduction (DDR) efforts.

Large-eddy simulation of wind pressures on elevated low-rise buildings

Residential buildings in coastal communities are often elevated to mitigate flooding and wave-surge impacts. However, the elevations change the local wind field characteristics and may increase the aerodynamic pressure on buildings. Post-event reconnaissance showed that elevated buildings experienced severe structural damage to the roofs, walls, and floors during major hurricanes. Currently, our understanding of aerodynamic pressure on elevated houses is limited. In this paper, a large eddy simulation (LES)-based method is developed to better understand the wind effects on elevated buildings. The inflow generation method, discretizing and synthesizing random flow generation, is adopted to generate inflow boundary conditions satisfying the target spectrum. Two sub-grid scale models, the Smagorinsky and wall-adapted local eddy-viscosity models, are employed to represent the unresolved small-scale eddies. It is found that the eddy structure sizes can strongly affect the pressure fluctuations at the eddy separation zones. The present study advances the understanding of aerodynamics on elevated buildings and provides a reference for future LES-based research on wind effect modeling.

Tidal Composition Analysis of Global Sq Current System

AbstractIn this study, we examine the spatiotemporal variability of the global equivalent ionospheric current system estimated from geomagnetic Solar‐quiet (Sq) variations at 124 mid‐ to low‐latitude ground‐based magnetometer stations during 1–31 May 2020. In this period, geomagnetic activity was particularly low, that is, the hourly geomagnetic activity index Hp60 did not exceed 4o. The spherical harmonic analysis is performed on the Sq variations to estimate the equivalent current function at each universal time hour. Hourly maps of the global Sq current system are used to evaluate, for the first time, the tidal composition of mid‐latitude Sq currents and its temporal evolution. Although tides are known to be an important driver of Sq currents, the tidal composition analysis was difficult in previous studies that focused on Sq currents at particular longitude sectors. Our results show that the migrating tidal components (DW1, SW2, and TW3) are predominant in both hemispheres. This is as expected from the strong day‐night contrast in ionospheric conductivities. The day‐to‐day variations of the migrating tidal components are, however, not strongly correlated between the two hemispheres, suggesting that these variations arise not only from the global effect of solar radiation on ionospheric conductivities but also from the local effect of neutral winds. Variations associated with non‐migrating tides are also found. Especially, eastward‐propagating diurnal and semidiurnal tides with zonal wavenumber 1 (DE1 and SE1) are the largest non‐migrating components. Their production mechanisms remain to be understood.

Influence of Foehn Winds of Truong Son Mountains on the High Temperatures Observed in North-Central Vietnam during 31 May–5 June 2017

Abstract North-central Vietnam often experiences high temperatures. Foehn winds originating from the Truong Son Mountains (also known as Laos winds) are believed to contribute to abnormally high temperatures; however, no quantitative research has focused on foehn warming in Vietnam. In this study, we conducted numerical simulations using the Weather Research and Forecasting (WRF) Model to investigate the contribution of foehn warming to abnormally high temperatures in north-central Vietnam in early June 2017. Generally, May–June is the monsoon period in Vietnam. Consequently, foehn warming during this season is thought to be mainly caused by latent heating and precipitation mechanism. However, the primary factor in the cases covered in this study was foehn warming with an isentropic drawdown mechanism. Diabatic heating with turbulent diffusion and sensible heat flux from mountain slopes also plays significant roles. The warming effect of the foehn winds on the temperatures during the events was approximately 2°–3°C. It was concluded that the high temperature events from 31 May to 5 June 2017 were caused by synoptic-scale warm advection and foehn warming. Sensitivity experiments were conducted on the WRF Model, utilizing three atmospheric boundary layer turbulence schemes (YSU, ACM2, and MYNN), consistently yielding results for simulated temperature and relative humidity. The wind speed bias for the MYNN scheme was found to be lower than that of the other schemes. However, this study did not delve into the underlying reasons for these differences. The optimal performance of each scheme remains an open question. Significance Statement It was hypothesized that north-central Vietnam often experiences high temperatures owing to foehn winds (also known as Laos winds) descending from the Truong Son Mountains. This study conducted numerical experiments to validate this hypothesis and investigate the associated mechanisms of foehn winds in this region. Surprisingly, despite the monsoon season, the isentropic drawdown mechanism without precipitation effects provides the primary explanation for the high temperatures caused by foehn winds in north-central Vietnam, and not the latent heating and precipitation mechanism with precipitation effects that researchers expected. The results of this study contribute to better prediction of high temperatures in this region and improve our understanding of foehn winds in tropical monsoon climate zones.

Wind-driven post-bloom dispersion of Microcystis in a large shallow eutrophic lake: A case study in Lake Taihu

To clarify the wind-driven post-bloom dispersion range of Microcystis, which originally clustered on the water surface, an Individual-Based Model (IBM) of Microcystis movement considering the combined effects of wind and light was developed based on actual hydrodynamic data and Microcystis biomass. After calibrating the effects of hydrodynamics and light, 66 cases of short-term (within a week) post-bloom with satellite images from 2011 to 2017 were simulated. The results showed that there were three short-term post-bloom types: vertical reduction (VR), horizontal reduction (HR) and mixed reduction (MR). For VR type, the cyanobacterial bloom reduction rate was rapid (>160 km2/day), but the dispersion range of Microcystis was limited (<2 km/day), and a larger bloom area was likely to form in the original location when wind speed decreased. For HR type, the cyanobacterial bloom reduction rate was slow (<10 km2/day), but Microcystis exhibited a broad dispersion range (>4 km/day), often leading to smaller, thicker, and longer-lasting cyanobacterial blooms downwind, albeit with a lower probability of occurrence. The characteristics of MR lay between the two aforementioned types.