Wind Duration Research Articles

Investigating the Near-Surface Wind Fields of Downbursts Using a Series of High-Resolution Idealized Simulations

Abstract Short-lived and poorly organized convective cells, often called weakly forced thunderstorms (WFTs), are a common phenomenon during the warm season across the eastern and southeastern United States. While typically benign, wet downbursts emanating from such convection can have substantial societal impacts, including tree, power line, and property damage from strong outflow winds. Observational studies have documented the occurrence of severe (25.7 m s−1 or higher) wind speeds from wet downbursts, but the frequency of severe downbursts, including the spatial extent and temporal duration of severe winds, remains unclear. The ability for modern observing networks to reliably observe such events is also unknown; however, answering these questions is important for improving forecast skill and verifying convective warnings accurately. This study attempts to answer these questions by drawing statistical inferences from 97 high-resolution idealized simulations of single-cell downburst events. It was found that while 35% of the simulations featured severe winds, the spatial and temporal extent of such winds is limited—O(10) km2 or less and persisting for around 5 min on average. Furthermore, through a series of simulated network experiments, it is postulated that the probability that a modern mesonet observes a severe wind gust given a severe downburst is around 1%. From these results, a statistical argument is made that most tree impacts associated with pulse convection are likely caused by subsevere winds. Several implications for forecasting, warning, and verifying WFT events fall out from these discussions.

Forecasting of Airborne Conidia Quantities and Potential Insect Associations of Cryphonectria parasitica, the Causal Agent of Chestnut Blight, in England.

Sweet chestnut, an Asiatic tree introduced in many parts of Europe including the United Kingdom, is planted for nut production, timber, and amenity. Its major threat is the disease called blight, caused by the fungus Cryphonectria parasitica, which infects through wounds by airborne spores. Field trapping using sticky rods rotating traps was performed in an infected area in Devon (between May 2021 and April 2023). An improved dual hydrolysis Taqman probes real-time PCR was used. The number of spores was calculated by comparing the cycle threshold to the Ct of standards with known amounts of conidia or known target fragment copies cloned into a plasmid. Weekly spore counts were in the range of around 60 to approximately 8.5 × 103, with fluctuations of peaks (mainly in late summer-autumn 2021) and troughs. The effects of weather parameters were modelled, finding correlations between spore numbers and temperature, humidity, dewpoint, rainfall, wind speed, and wind duration. Additionally, an insect trapping was performed to confirm the presence/absence and quantity of C. parasitica conidia potentially phoretic on some insects by using the same molecular approach. None of the ten collected insect species harboured spores of this fungus.

The effects of seasonal wind regimes on the evolution of hypoxia in Chesapeake Bay: Results from a terrestrial-estuarine-ocean biogeochemical modeling system

In this study, a terrestrial-estuarine-ocean biogeochemical modeling system (DLEM-ChesROMS-ECB) was used to investigate the impact of prevailing spring-to-summer winds on hypoxia in Chesapeake Bay. The modeling system was run continuously from 1985 to 2005 under realistic wind conditions. Correlation analysis based on the 21-year simulation results revealed that the durations of spring northeasterly winds and summer southerly winds were both positively correlated with the volume of summer hypoxia. Conversely, the duration of summer northeasterly winds was negatively correlated with hypoxia. We then conducted multiple idealized sensitivity experiments to explore the underlying mechanisms governing these relationships. The results indicated that prolonged northeasterly winds in spring promoted along-channel transport of oxygen-consuming materials from the upper to the lower Bay, leading to a higher level of oxygen consumption via water column respiration (WCR). This may have led to more severe hypoxic events in the following summer. During summer, northeasterly winds increase vertical mixing as the riverine freshwater is mostly restricted to the western bank, thereby preventing the occurrence of hypoxia. Furthermore, strengthened vertical mixing increased light availability, resulting more nutrients taken up by phytoplankton. Consequently, more dissolved oxygen was produced. When comparing the differences in mass budget terms under southerly winds, the oxygen production accounted for approximately 60% of the WCR. In contrast to previous studies that mostly examined the short-term episodic effects of wind, our study underscores the importance of the impact of prolonged seasonally variable winds and biological feedback on hypoxic volume in Chesapeake Bay, which helps in the development of appropriate nutrient management strategies in a changing climate.

Trend of landfalling tropical cyclones in the East China Sea and their storm surge response

In recent years, the influence of global tropical cyclones (TCs) has a tendency to expand towards the polar direction, and the proportion of high-intensity TCs has also increased greatly. The Northwest Pacific is a high incidence area of TCs, the northward shift of landfalling TCs in China and the increase of high-intensity TCs will lead to an increased risk of storm surge in the East China Sea (ECS). However, due to the lack of long-term observations in the ECS, previous studies have focused on the analysis of individual TC, and the response mechanism of storm surge to long-term trends of TCs is not clear. Based on the long-term observations of TCs from 1949 to 2022 and the numerical experiments of storm surge, the trend of landfalling TCs in China and the response characteristics of storm surge in the ECS were studied in this paper. The observations showed that the probability of TCs entering ECS became greater in the latter 37 years compared with the former 37 years. The average intensity of landfalling TCs (maximum wind speed) increased by 36% to 30 m/s, and the average speed of landfalling TCs increased by 100% to 8 m/s. The model results showed that the intensity of the storm surge is closely related to the intensity and translation speed of TCs. Under the condition of the same translation speed of TCs, the storm surge enhanced with the intensity of TCs. For the TCs with high intensity (strong typhoon and super typhoon), the intensity of the storm surge continues to increase as the translation speed of the TCs increases. However, for the TCs with low or medium intensity (severe tropical storms and typhoons), the intensity of the storm surge reaches a peak with the increase of the translation speed of TCs. The intensity of the storm surge is determined by both the wind speed and the duration of strong wind. The TCs with faster translation speed can produce a stronger wind field but shorter duration of strong wind. Therefore, the intensity of the storm surge decreases when the translation speed of TCs exceeds the threshold value.

Conjugate hemispheric response of Earth’s ionosphere due to 2019 Antarctic minor Sudden Stratospheric Warming (SSW): Comparison with 2013 Arctic major SSW

In this paper, we attempt to compare the Antarctic SSW of 2019 with the Arctic SSW of 2013. Despite being a minor SSW, the rare Antarctic event of September 2019 caused a significant enhancement of stratospheric temperature at high latitudes with more temperature deviation than the Arctic major SSW of 2013. On the basis of the duration and extent of stratospheric zonal mean zonal wind, the 2019 SSW is comparable to major SSWs. An exceptionally strong wave 1 planetary wave was observed during the 2019 SSW. We have investigated the response of the ionospheric total electron content (TEC) during both the SSWs over two low mid-latitude locations Okinawa and Darwin, which form magnetic conjugate pair. The extent of maximum ionospheric deviations during the 2019 SSW is almost comparable to the 2013 SSW in their respective hemispheres. We have observed mostly night time enhancement in TEC during the Arctic SSW, while daytime enhancement is noted during the Antarctic SSW. Hemispheric asymmetry is observed during both the SSWs. Minor geomagnetic storm has been noticed coinciding with each SSW during different phases of the warming. The SSW, solar flux, and storm contribution on the TEC have been calculated during both the SSWs, which shows clear contribution of SSW on the total TEC despite the presence of storm and during moderately high solar activity. We have also investigated the foF2 variations from ionosonde and IRI-16 at the same two locations. The peak electron density from ionosonde responds to the warming in a manner similar to TEC. The foF2 of IRI-16 exhibits overestimation during daytime and underestimation during nighttime on quiet days during low solar activity (2019), while during moderate solar activity (2013), it overestimates during morning hours. However, it can not predict the enhancements of foF2 during SSWs.

Offshore Wind Power Resource Assessment in the Gulf of North Suez

Growing population, industrialization, and power requirements are adversely affecting the environment through increased greenhouse gases resulting from fossil fuel burning. Global greenhouse gas mitigation targets have led nations to promote clean and self-renewable sources of energy to address this environmental issue. Offshore wind power resources are relatively more attractive due to high winds, less turbulence, minimal visualization effects, and no interaction of infrastructure. The present study aims at conducting an offshore wind power resource assessment (OWPRA) at some locations in the Gulf of North Suez. For this purpose, the long-term hourly mean wind speed (WS) and wind direction above mean sea level (AMSL), as well as temperature and pressure data near the surface, are used. The data is obtained from ERA5 (fifth generation global climate reanalysis) at six (L1–L6) chosen offshore locations. The data covers a period of 43 years, between 1979 and 2021. The WS and direction are provided at 100 m AMSL, while temperature and pressure are available near water-surface level. At the L1 to L6 locations, the log-term mean WS and wind power density (WPD) values are found to be 7.55 m/s and 370 W/m2, 6.37 m/s and 225 W/m2, 6.91 m/s and 281 W/m2, 5.48 m/s and 142 W/m2, 4.30 m/s and 77 W/m2, and 5.03 and 115 W/m2 and at 100 m AMSL, respectively. The higher magnitudes of monthly and annual windy site identifier indices (MWSI and AWSI) of 18.68 and 57.41 and 12.70 and 42.94 at the L1 and L3 sites, and generally lower values of wind variability indices, are indicative of a favorable winds source, which is also supported by higher magnitudes of mean WS, WPD, annual energy yields, plant capacity factors, and wind duration at these sites. The cost of energy for the worst and the best cases are estimated as 10.120 USD/kWh and 1.274 USD/kWh at the L5 and L1 sites, corresponding to wind turbines WT1 and WT4. Based on this analysis, sites L1, L3, and L2 are recommended for wind farm development in order of preference. The wind variability and windy site identifier indices introduced will help decision-makers in targeting potential windy sites with more confidence.

Hydrodynamic Mixing of Accretion Disk Outflows in Collapsars: Implications for r-process Signatures

The astrophysical environments capable of triggering heavy-element synthesis via rapid neutron capture (the r-process) remain uncertain. While binary neutron star mergers (NSMs) are known to forge r-process elements, certain rare supernovae (SNe) have been theorized to supplement—or even dominate—r-production by NSMs. However, the most direct evidence for such SNe, unusual reddening of the emission caused by the high opacities of r-process elements, has not been observed. Recent work identified the distribution of r-process material within the SN ejecta as a key predictor of the ease with which signals associated with r-process enrichment could be discerned. Though this distribution results from hydrodynamic processes at play during the SN explosion, thus far it has been treated only in a parameterized way. We use hydrodynamic simulations to model how disk winds—the alleged locus of r-production in rare SNe—mix with initially r-process-free ejecta. We study mixing as a function of the wind mass, wind duration, and the initial SN explosion energy, and find that it increases with the first two of these and decreases with the third. This suggests that SNe accompanying the longest long-duration gamma-ray bursts are promising places to search for signs of r-process enrichment. We use semianalytic radiation transport to connect hydrodynamics to electromagnetic observables, allowing us to assess the mixing level at which the presence of r-process material can be diagnosed from SN light curves. Analytic arguments constructed atop this foundation imply that a wind-driven r-process-enriched SN model is unlikely to explain standard energetic SNe.

Accumulated Cyclone Energy-Based Tropical Cyclone Return Periods in Florida

This article introduces an accumulated cyclone energy (ACE) approach for estimating the return period of tropical cyclone (TC) wind risk in Florida. As opposed to calculating return periods directly from maximum sustained wind speed, the ACE-based approach also describes the duration of the strong winds, giving an additional dimension to the assessment of TC wind risks. Because Florida is a peninsula, TCs can move across the state within six hours of landfall, causing an underestimation of the inland wind footprint if only the six-hour reanalysis track points are employed as an input data source. This study uses four different scenarios and an inland exponential decay function to interpolate the wind speed between the six-hour reanalysis track points to feed the ACE-based return period calculation based on a 121-year record from 1900 to 2020. South Florida has the shortest return period (five to ten years) of TCs with an ACE equivalent to one hour of hurricane intensity (≥ 64 kt; 1 kt ∼ 0.51 m s−1) caused by intense historical hurricane strikes, and Polk County in inland central Florida has an equal return period due to frequent and long-duration TC occurrences, acting as an intersection for landfalling TCs in the Florida peninsula.

Duration of extreme synoptic wind speeds for North America in a changing climate and its engineering implementation

In modern wind engineering practice, wind load effects are often defined as a function of a basic design wind speed, an aerodynamic force coefficient, several multipliers to consider surrounding terrain, topographic effect, and the directionality of the wind climate. Among these variables, the basic design wind speed is associated with an averaging time (also known as gust duration), e.g., 0.02-second, 3-second, 10-minute, or one hour. The design level aerodynamic force coefficients are defined as a specific percentile within a reference period, representing the generic time duration of wind events, i.e., wind duration, which is assumed to be one hour. A recent study showed that the hurricane wind duration could differ from this assumption. There has not been any study that investigated synoptic wind duration and its engineering implementations comprehensively. It is also unclear whether climate change impacts the synoptic wind duration. Historical records, often less than 50 years, are insufficient to calculate the wind duration for threshold wind speeds at a higher return period. Therefore, this study employed 15 long-term hourly wind speed simulations covering most of North America, each of which has 70 years in the past (1050 years in total) and 80 years into a future changing climate (1200 years in total), to investigate the wind durations in the current and future changing climate. It was found that the durations for winds of about 700-year return period are close to the traditionally assumed one hour and have limited effects on the wind loads for the strength design. However, wind durations can be much longer than one hour for the lower return period level wind speeds, which can impact the wind responses for serviceability limit state design and cladding and component (C&C) design.

The clean-energy challenge

David Kramer has in the past two years written several items discussing components of the clean-energy challenge. One from the April 2022 issue is on charging electric vehicles, or EVs (page 22), and another from the September 2021 issue is on energy storage (page 20).While the stories are informative, both are missing context. For example, the story on EVs doesn’t discuss how they are only as clean and efficient as the process by which the required electricity is produced. The storage story fails to acknowledge that grid-scale storage capacity adequate to power cities or countries is not and will not be available in the foreseeable future. Even more importantly, dependence on storage is not acceptable, even if attainable, because no one knows the duration of future wind and solar droughts.I urge Physics Today to do more to rationalize the discussion of renewable energy.ISTOCK.COM/F9PHOTOSPPT|High resolutionThat renewable energy is intermittent is not contentious. That renewable energy sources must be complemented by storage or backup is not contentious. That grid-scale storage is unavailable at urban scale may be more contentious but is nonetheless true. Relying on backup implies that whenever renewables are producing power, their backup (which is paid for) sits idle. Thus, renewables don’t increase capacity; they duplicate dispatchable (always available) sources. That duplication is responsible for California’s “duck curve,” discussed by Kramer.As California and Germany have demonstrated, renewables can’t replace grid-scale dispatchables, of which there are just two, hydrocarbons and nuclear. It appears that fusion will enter the market in the same time frame as molten-salt fission reactors, but it is unlikely to be cost competitive. Fission has an attractive safety record, and molten-salt reactors are both safer still and cheaper than existing reactors. A plausible future is fusion for the rich and fission for the rest. An especially good discussion of the inadequacy of both energy storage and renewables generally is available at https://jackdevanney.substack.com/p/nuclear-and-windsolar.There are only four fundamental forces in nature, and their strengths differ dramatically. Those differences are manifest in the energy density and footprint of competing energy technologies. For example, the relative strength of nuclear forces allows hydrocarbon furnaces to be “surgically” replaced by nuclear reactors, leaving turbines and other infrastructure in place. Conversely, the extreme weakness of gravity makes storage based on raising and dropping weights unpromising.Grid-scale renewable energy is a distraction, one that is delaying productive action on an important problem. Physics Today can play an important role here. Section:ChooseTop of page <<© 2023 American Institute of Physics.

Sandstorms damage the photosynthetic activities of Haloxylon ammodendron seedlings

Haloxylon ammodendron is a preferred shrub species for buffering against wind and fixing sand in arid sandy areas of northwest China. To determine whether sandstorms cause damage to H. ammodendron seedlings, we investigated the effects of wind-blown sands on the photosynthetic function of H. ammodendron by simulating sand-carrying wind in the wind tunnel. The results showed that photosystem II (PSII) non-photochemical quenching (NPQ) was sensitive to wind erosion, and sustained blowing of sand-carrying winds enhanced NPQ reduction. The rapidly relaxing quenching NPQf made up the majority component of NPQ; the NPQf/NPQ ratio was approximately 64.4% in the sand-free wind group and nearly 56.2% in the sand-carrying wind group. The distribution of the quantum efficiency of the excitation energy indicated that the relative proportions of the quantum yield of PSII photochemistry ΦPSII, the quantum yield of quenching due to light-induced ΦNPQ, and non-light-induced ΦNO were influenced by both wind erosion and light intensity; the sand-carrying wind resulted in a relative decrease in ΦNPQ and a corresponding increase in ΦNO. The maximum quantum efficiency of PSII photochemistry Fv/Fm was relatively stable in the sand-free wind group, with an average value of approximately 0.81. Compared to sand-free wind, sand-carrying winds caused remarkable decreases in Fv/Fm. Light intensity was the main factor affecting ΦPSII, ΦNPQ, and relative electron transport rate (rETR); there was no interaction effect between the duration of sand-carrying wind and light intensity. Taken together, wind-blown sands cause irreversible damage to the photosynthesis of H. ammodendron seedlings, which is the main factor restricting population regeneration in shelterbelts.

WIND FACTOR IN SPATIAL AND TEMPORAL DYNAMICS OF WIND EROSION WITHIN VOLYN REGION

The analysis of the wind factor as a factor of wind erosion of Polissia soils is highlighted. The highest intensity of wind erosion in the Polissya zone is observed in the spring and autumn periods, when the density of vegetation cover is the lowest during the year and there is no snow cover. The temporal dynamics of the wind regime forms certain patterns, which determines the formation of the corresponding clusters of months of the year as indicators of the temporal regularity of the wind regime and clusters of administrative districts as indicators of the spatial regularity of the wind regime. The early spring period is the least long (two months), which allows it to be interpreted as transitional. This interpretation explains the inclusion in this cluster by the dynamic features of August as also the transition period from the summer wind regime to the autumn one. The winter period is characterized by an extremely strong wind regime, the lowest wind intensity is observed in the summer-autumn period. The transitional early spring period is characterized by an intermediate level of wind load, but the greatest variability of indicators, which also emphasizes the transitional nature of this time stage of the year. It was established that the maximum value of the wind factor for these areas is observed in winter and is 3,57 m3 s−3, and the minimum is observed in August and is 2,3 3,57 m3 s−3. The central and eastern regions (Manevytskyi, Kovelskyi and Rozhishchenskyi) also form a homogeneous subzone, the peculiarity of which is that the duration of strong winds in the winter period is somewhat shorter compared to the northwestern regions. The highest wind load is observed in the winter months, and the lowest at the end of summer. Geographically, the north-western and south-eastern regions of the region experience the greatest wind load. In terms of time, three consecutive periods can be distinguished: winter, early spring, and summer-autumn.

Dynamics of wave generation and dissipation processes during cold wave events in the Bohai Sea

Wave dynamics were investigated by applying the wind-wave model Simulating Waves Nearshore to the semi-enclosed Bohai Sea during cold wave events. Wind quality was examined by comparing three wind data sources with buoy observations, and then numerical experiments were conducted to investigate the impacts of model physics settings on simulated waves. After model calibration, the wave dynamics were examined from the aspects of response to various wind conditions (speed, fetch, duration), wave dominant component (wind wave or swell), as well as the dissipation processes during a pair of cold wave events (e.g., northwesterly in 2014 and northeasterly in 2015) with the consideration of spatial differences. The maximum significant wave heights during two cold wave events are similar (e.g., 3.5 m in the central Bohai Basin), which attributes to the impacts of limited fetch difference and insufficient high wind duration. Wind wave is the dominant component, which is reflected in the wave spectra (e.g., wave age less than 1.2). Spatial regions of wave dissipations controlled by whitecapping, bottom friction, and depth-induced breaking during cold wave events are quantified. Whitecapping dominates the wave energy dissipation in deep-water areas, while the bottom friction dissipation controls the major dissipation process as waves propagate towards the coast (e.g., at 5–10 m water depths). Depth-induced dissipation only occurs over a narrow strip along the southern coastal area but is significantly beyond the others. Depth-induced dissipation decreases suddenly when reaches a flat bottom, and it decreases with the increase of the width of the bottom slope.

Dynamics of gap winds in the Great Rift Valley, Ethiopia: emphasis on strong winds at Lake Abaya

Abstract. Lake Abaya, located in the Great Rift Valley (GRV) in Ethiopia, is affected by regularly occurring strong winds that cause water waves, which in turn affect the lake's ecology and food web. The driving forces for these winds, however, are yet unexplained. Hence, the main goal of this study is to provide a physical explanation for the formation of these strong winds in the GRV and especially at Lake Abaya. To this aim, two case studies were performed based on measurements, ERA5 reanalysis data and mesoscale numerical simulations conducted with the Weather Research and Forecasting (WRF) model. The simulations revealed that in both cases a gap flow downstream of the narrowest and highest part of the GRV (i.e. the pass) led to high wind speeds of up to 25 m s−1. Two types of gap flow were identified: a north-eastern gap flow and a south-western gap flow. The wind directions are in line with the orientation of the valley axis and depend on the air mass distribution north and south of the valley and the resulting along-valley pressure gradient. The air mass distribution was determined by the position of the Intertropical Convergence Zone relative to the GRV. The colder air mass was upstream of the GRV in both case studies. During the day, the convective boundary layer in the warmer air mass on the downstream side heated up more strongly and quickly than in the colder air mass. The most suitable variable describing the timing of the gap flow was found to be the pressure gradient at pass height, which corresponds roughly to the 800 hPa pressure level. In both cases the gap flow exhibited a strong daily cycle, which illustrates the importance of the thermal forcing due to differential heating over complex terrain in addition to the large-scale forcing due to air mass differences. The start, strength, and the duration of the gap winds within the valley depended on location. For both cases, the strongest winds occurred after sunset and in the ongoing night downstream of the gap and on the corresponding lee slope. The ERA5 reanalysis captures both events qualitatively well but with weaker wind speeds than in the mesoscale numerical simulations. Hence, ERA5 is suitable for a future climatological analysis of these gap flows.

Linking soil phosphorus with forest litterfall resistance and resilience to cyclone disturbance: A pantropical meta-analysis.

While tropical cyclone regimes are shifting with climate change, the mechanisms underpinning the resistance (ability to withstand disturbance-induced change) and resilience (capacity to return to pre-disturbance reference) of tropical forest litterfall to cyclones remain largely unexplored pantropically. Single-site studies in Australia and Hawaii suggest that litterfall on low-phosphorus (P) soils is more resistant and less resilient to cyclones. We conducted a meta-analysis to investigate the pantropical importance of total soil P in mediating forest litterfall resistance and resilience to 22 tropical cyclones. We evaluated cyclone-induced and post-cyclone litterfall mass (g/m2 /day), and P and nitrogen (N) fluxes (mg/m2 /day) and concentrations (mg/g), all indicators of ecosystem function and essential for nutrient cycling. Across 73 case studies in Australia, Guadeloupe, Hawaii, Mexico, Puerto Rico, and Taiwan, total litterfall mass flux increased from ~2.5 ± 0.3 to 22.5 ± 3 g/m2 /day due to cyclones, with large variation among studies. Litterfall P and N fluxes post-cyclone represented ~5% and 10% of the average annual fluxes, respectively. Post-cyclone leaf litterfall N and P concentrations were 21.6 ± 1.2% and 58.6 ± 2.3% higher than pre-cyclone means. Mixed-effects models determined that soil P negatively moderated the pantropical litterfall resistance to cyclones, with a 100 mg P/kg increase in soil P corresponding to a 32% to 38% decrease in resistance. Based on 33% of the resistance case studies, total litterfall mass flux reached pre-disturbance levels within one-year post-disturbance. A GAMM indicated that soil P, gale wind duration and time post-cyclone jointly moderate the short-term resilience of total litterfall, with the nature of the relationship between resilience and soil P contingent on time and wind duration. Across pantropical forests observed to date, our results indicate that litterfall resistance and resilience in the face of intensifying cyclones will be partially determined by total soil P.

Numerical simulation study of wind-induced snow drifting on low-sloped gable roofs

In this paper, an effective diffusion coefficient derived from previous semi-empirical formula and dynamic grid technology combined with inverse distance interpolation algorithm are applied to simulate wind-induced snow drifting on low-sloped gable roofs. The effective diffusion coefficient enhances the diffusion ability of particles near the wall surface, and the inverse distance interpolation algorithm has an explicit format, which determines the influence of the sample point on the interpolation point according to the interpolation distance, it has a low computational expense and weakens the influence of extreme points. Two measurement parameters, δH and δM, are introduced to illustrate the impact of interpolation parameters (power law p and interpolation radius R) on the single grid adjustment and snow cover. By employing these optimisations, sensitivity analyses for simulation parameters are performed, the effects of the saltation layer height, turbulent Schmidt number, falling velocity, time step size, and wind duration on snow distribution are discussed. Finally, the redistributions of snow cover on gable roofs under various wind directions are reproduced, the snow redistribution characteristics and the relationship between roof slope and snow erosion are investigated. The results can provide a reference for predicting snow loads on gable roofs.

A revisit of global wind-sea and swell climate and variability using multiplatform altimeters

A well-performed (root mean square error ≈ 0.35 m) look-up table model was established to separate the wind-sea and swell significant wave height (Hs) using 10-m sea surface wind speed (U10) and Hs data from altimeters. Based on this model, global wind-sea and swell climate and variability were investigated using 27-year jointly calibrated altimeter data. The climatology of the swell and wind-sea Hs (HWS and HSW) are in good agreement with those of the total Hs and U10, respectively. This is because of the dominance of swells in the World Ocean with respect to both occurrence frequency and energy proportion and the close coupling between wind and wind-seas. The interannual variability of HWS and HSW are closely related to some climate indices, but the responses of wind-seas and swells are different for the same atmospheric oscillation because of the large propagation distances of swells. For long-term variability, significant positive/negative long-term trends of HWS/HSW were found almost all over the World Ocean. Such opposite trends can be explained by the positive/negative trends of U10/Hs: a shorter fetch or duration of wind leads to a lower Hs, but a higher U10 leads to higher wind-sea probability and energy weight. However, large uncertainty still exists in these trends and further exploration is needed.

Statistical investigation of wind duration using a refined hurricane track model

A complete characterization of the atmospheric boundary-layer winds essentially involves speed, direction and duration. While extensive statistical analyses have been carried out to determine wind speed and directionality for appropriate wind design of buildings, there is a lack of similar research effort for wind duration. Although wind duration may have limited effects on linear, elastic structural response, it can present significant importance in the consideration of nonlinear, inelastic response due to damage accumulation and cyclic deterioration of strength and stiffness. Recent advances of performance-based wind design methodology allow the controlled nonlinear, inelastic deformation of buildings under strong winds, and hence place a demand on statistical investigation of wind duration. In this study, the wind data used for probabilistic duration analysis result from a refined hurricane track model. Specifically, both environmental flow and Coriolis force (the beta effect) are integrated into the translation module for improved modeling of hurricane movement. Based on the numerically generated wind data, the wind duration measured with the over-threshold method (i.e., uniform duration) is obtained. Furthermore, a statistical analysis framework is developed to jointly consider wind duration, speed and direction. A case study is conducted to demonstrate the efficacy of the proposed statistical analysis framework for characterization and quantification of duration in wind climate consideration. Finally, structural wind performance of a simplified single-degree-of freedom system is examined to highlight the importance of incorporating duration consideration into the performance-based wind design.

Monitoring-based analysis of wind-induced vibrations of ultra-long stay cables during an exceptional wind event

Ultra-long stay cables characterized as high flexibility are prone to large-amplitude vibrations. Much attention has been paid to the vibrations of stay cables under normal wind conditions in the past decades, while the dynamic response under extreme winds is reported rarely. This study investigates the exceptional wind-induced vibration of the stay cables of a kilometer-level cable-stayed bridge based on the monitoring data. The mean wind velocity and extreme wind duration are firstly obtained using the wind records of the structural health monitoring system (SHMS). The effects of the turbulence intensity and mean wind velocity on the cable vibrations are then analyzed. To explore the motion trajectory features, the in-plane and out-of-plane dynamic displacements are estimated by an acceleration-based approach. Besides, the modal properties, including the frequencies and damping ratios, are identified. The result shows that the stay cables present multi-modal vibrations with frequencies higher than 3 Hz, which is different from rain-wind-induced vibration (RWIV). The out-of-plane vibration amplitude under the extreme wind is much larger than that of the in-plane due to the absence of dampers. Furthermore, the out-of-plane damper is suggested to mitigate the large-amplitude vibration of ultra-long stay cables under exceptional winds.

Assessment of the wind energy potential of the territory of southern Russia

The research was carried out in order to identify promising territories for the creation and operation of economically justified and environmentally friendly wind power plants in the south of Russia. The annual duration of winds with operating speeds in most of the studied area is 50-60 % of all winds, and only at the southernmost end of the territory the duration of winds with operating speeds decreases to 20-40 %. The predominant wind directions (52 %) in the Stavropol Territory are east and west. In the Rostov region, these directions dominate for 51% of the time of the year, in the Krasnodar region, 56 %. The prevailing wind direction in Kalmykia and the Astrakhan region is less pronounced. Here the east and west directions make up 30 %, southeast and northwest – 35 %. In the Volgograd region, all paired wind directions are equally probable and amount to 20-28 % in time. In almost 75-80 % of the territory, the specific power of the wind flow is 125-500 W/m2.