Vertical Shear Research Articles

A hybrid physics-based and data-driven model for intra-day and day-ahead wind power forecasting considering a drastically expanded predictor search space

This work presents a novel hybrid (physics- and data-driven) model for short-term (intra-day and day-ahead, 3h-24h) wind power forecasting (STWPF). Traditionally, STWPF predictors admitted very few meteorological variables only from the grid points closest to the turbines. Here, with the aim to further capture the underlying atmospheric processes ruling the wind variability in the wind farm, the approach relies on drastically expanding the predictor space, composed of numerous meteorological variables throughout a large geographical domain, retrieved from a weather forecasting model (COSMO-1). An ad-hoc genetic algorithm that optimizes the selection of predictors is designed and combined with feed-forward artificial neural networks for its cost function evaluation. The introduced model is compared to multiple benchmark models in a 16-turbine wind farm in the Swiss Jura mountains. For +12h and +24h lead times, the new approach shows a root-mean squared error normalized to the installed wind farm capacity of 11% and 11.6%, respectively. These values entail ∼16% higher forecasting skill compared to state-of-the-art predictor frameworks. Results highlight the ability of the presented approach to systematically select as predictors different variables with a well-known impact on the wind farm performance, such as the turbulent kinetic energy or the vertical wind shear. Clustering the data according to the wind direction provides substantial benefit. In addition, it provides a better understanding of the attained improvement: largest performances occur in those wind directions affected by highly complex terrain. This indicates that the proposed model can be especially suitable for wind farms in complex terrain.

Recent shortening of the mature tropical cyclone stage over the western North Pacific

AbstractThis study investigates long‐term trends related to the mature stage duration of tropical cyclones (TCs) over the western North Pacific (WNP) during June–November between 1982 and 2021. There is a significant shortening in the mean duration of the WNP mature TC stage, which is defined as the period when a TC is within 5 kt of its lifetime maximum intensity. This shortening is induced by a significant (weak) poleward migration in the starting (ending) location of the WNP mature TC stage, which can be further explained by changes in environmental conditions. From 1982 to 2021, there have been significant increases in maximum potential intensity and 700–500‐hPa relative humidity over most of the WNP, which has broadly expanded the TC‐favorable area poleward. Consequently, WNP TCs can start their mature stages and reach their lifetime maximum intensities at higher latitudes. By contrast, there are only weak changes in 850‐hPa relative vorticity and 850–200‐hPa vertical wind shear (VWS). Given the dominant role of VWS in modulating the TC weakening rate, the TC‐suppressive area over the subtropical WNP has shown lesser changes, thus leading to insignificant changes in the ending location of the mature TC stage.

Escalation of tropical cyclone impacts on the northwestern Bay of Bengal over the past decade

AbstractTropical cyclones have resulted in casualties and economic losses in the areas surrounding the Bay of Bengal (BoB). Thus, a comprehensive investigation of these tropical cyclones holds vital implications for disaster preparedness and mitigation. This paper compares the occurrence of storms in the last two decades, i.e., 2002–2011 and 2012–2021, and results reveal that such storms exhibited predominantly a northwesterly track towards the northwestern BoB, with a severer intensity but equal total storm frequencies. Over the past decade, a southeast-northwest pathway (SNP) was identified, demonstrating a higher incidence of severe tropical cyclones (STC, with lifetime maximum intensity ≥ 64 knots) over the BoB. Further analysis of the changes in the environmental conditions between these two decades indicates that a southeasterly anomaly in the steering flow contributed to the formation of the SNP. During the same period, the more favorable oceanic conditions during the last decade, including higher sea surface temperatures, a greater upper ocean heat content, a thicker warm water layer, and a thicker barrier layer beneath the SNP, favored the development of these storms by providing more heat energy to the storms. The atmospheric conditions, including increased air-sea heat fluxes, moisture, and instability within the lower troposphere, as well as reduced vertical wind shear, facilitated the development of convection within these storm systems. These favorable conditions improved the potential for storm development into STCs and elevated the risk of the northwestern BoB being impacted by more destructive storms.

A snapshot of turbulence in the Northeastern Magellan Strait

AbstractFirst-ever measurements of the turbulent kinetic energy (TKE) dissipation rate in the northeastern Strait of Magellan (Segunda Angostura region) taken in March 2019 are reported here. At the time of microstructure measurements, the magnitude of the reversing tidal current ranged between 0.8 and 1.2 ms−1. The probability distribution of the TKE dissipation rate in the water interior above the bottom boundary layer was lognormal with a high median value $${\varepsilon }_{med}^{MS}=1.2\times {10}^{-6}$$ ε med MS = 1.2 × 10 - 6 Wkg−1. Strong vertical shear, $$\left(1-2\right)\times {10}^{-2}$$ 1 - 2 × 10 - 2 s−1, in the weakly stratified water interior ensued a sub-critical gradient Richardson number $$Ri<{10}^{-1}-{10}^{-2}$$ R i < 10 - 1 - 10 - 2 . In the bottom boundary layer (BBL), the vertical shear and the TKE dissipation rate both decreased exponentially with the distance from the seafloor $$\xi$$ ξ , leading to a turbulent regime with an eddy viscosity $${K}_{M}\sim {10}^{-3}$$ K M ∼ 10 - 3 m2/s, which varied with time and location, while being independent of the vertical coordinate in the upper part of BBL (for $$\xi >\sim 2$$ ξ > ∼ 2 meters above the bottom).

Mechanism of stress transmission and feasibility of mining the lower coal seam under repeated mining in close-multiple coal seams

Mining in an upper coal seam results in the redistribution of vertical stress within a lower coal seam until a new equilibrium state is attained. Close-multiple coal seams mining faces the occurrence of multi-goafs and a complex stress environment. Based on a case study of close-multiple coal seams with repeated mining in the Qianjiaying coal mine, a stress distribution model of the floor in the coal seam striking range was established by optimizing the load form of the abutment pressure. The floor stress state after primary and repeated mining of upper coal seams was analyzed in a visual and quantitative manner. The concentrations of vertical stress, horizontal stress, and shear stress are all located in the floor under the coal rib after primary and repeated mining. The curve of stresses gradually levels off as the depth of the floor increases, indicating a diminishing influence of mining-induced stress from the upper coal seam. Based on the stress analysis by numerical simulations, the overall lower coal seam remains in a state of large-scale stress relief. Stress relief occurred twice under repeated mining, which indicates that the lower coal seam has favorable mining feasibility. The results of the study can provide scientific guidance to prevent mining accidents.

Reference optical turbulence characteristics at the Large Solar Vacuum Telescope site

Abstract Large ground-based solar telescopes are equipped with adaptive optics systems to correct wavefront distortions induced in the turbulent atmosphere. The design of the adaptive optics system strongly depends on the vertical profiles of the optical turbulence. In particular, the characteristics of the optical turbulence determine the design of tomographic adaptive optics systems, which provide image correction within a wide field of view. In the article, a new method to estimate reference optical turbulence characteristics from Era-5 reanalysis assimilated data is presented. This method is based on the dependence of the air refractive index structure constant $C_n^2$ on the vertical shears of wind speed as well as the outer scale of turbulence L0. The L0 parameter is estimated by minimization of the dispersion between the modeled and measured values of the refractive index structure constant $C_n^2$ within the surface layer. For the first time, parametrization coefficients and reference profiles of optical turbulence averaged for the period 1940–2022 are calculated for the Large Solar Vacuum Telescope (LSVT) site. The calculated optical turbulence profiles are representative; these profiles correspond to typical changes of the measured values of the Fried parameter, the isoplanatic angle, and the outer scale of turbulence at the LSVT site. The model turbulence profiles are verified taking into account the Shack–Hartmann wavefront sensor measurements at the LSVT. The higher accuracy of estimation of the optical turbulence characteristics makes it possible to refine parameters relevant to the LSVT adaptive optics system. The obtained results can be used in order to develop high-resolution solar adaptive optics technologies as applied to ground-based telescopes including those using the principles of atmospheric tomography.

Shear performance of tapered box girders with corrugated steel webs in extradosed cable-stayed bridges under cable forces

The integration of box girders with corrugated steel webs (CSWs) and an extradosed cable-stayed design gives rise to an innovative and distinctive bridge design, recognized as the extradosed cable-stayed bridge with CSWs. The synergistic integration of the technical benefits facilitates expanding the maximum span and enhancing the adaptability of this structural configuration. Subjected to cable forces, the main bridge superstructure featuring a box girder with CSWs experiences vertical shear, substantial axial force, and bending moments. Shear buckling on the CSWs emerges as a prominent issue influencing design considerations. In response to heightened internal forces near support, the main girder is typically configured with variable height. The Resal effect in the tapered girder leads to additional shear stresses from axial forces and bending moments, consequently modifying the effective shear stress on the CSWs. Therefore, traditional basic calculation assumptions that solely account for the vertical component of cable forces in shear stress calculations are frequently inaccurate. This study presents a modified theoretical method for calculating shear stress in tapered box girders with CSWs subjected to cable forces by considering the Resal effect. The proposed modified method incorporates not only the vertical shear but also considers bending moments and axial forces. The finite element simulation and experimental results showcase its remarkable accuracy, concurrently validating the presence of the Resal effect in tapered box girders with CSWs under cable forces. Additionally, this study quantitatively analyzes the shear force redistribution phenomenon induced by vertical shear, axial force, and bending moments considering the Resal effect. This reveals the shear performance of tapered box girders with CSWs under cable forces. The study is expected to provide a strategy and theoretical guideline for rapidly and efficiently obtaining the shear stresses of tapered box girders with CSWs in extradosed cable-stayed bridges under cable forces.

How does vertical wind shear influence updraft characteristics and hydrometeor distributions in supercell thunderstorms?

Abstract Vertical wind shear is known to affect supercell thunderstorms by displacing updraft hydrometeor mass downshear, thereby facilitating the storms’ longevity. Shear also impacts the size of supercell updrafts, with stronger shear leading to wider, less dilute, and stronger updrafts with likely greater hydrometeor production. To more clearly define the role of shear across different vertical layers on hydrometeor concentrations and displacements relative to supercell updrafts, a suite of idealized numerical model simulations of supercells was conducted. Shear magnitudes were systematically varied across the 0–1 km, 1–6 km, and 6–12 km AGL layers while the thermodynamic environment was held fixed. Simulations show that as shear magnitude increases, especially from 1–6 km, updrafts become wider and less dilute with an increase in hydrometeor loading, along with an increase in the low-level precipitation area/rate and total precipitation accumulation. Even with greater updraft hydrometeor loading amid stronger shear, updrafts are more intense in stronger shear simulations due to larger thermal buoyancy owing to wider, less dilute updraft cores. Furthermore, downshear hydrometeor displacements are larger in environments with stronger 1–6 km shear. In contrast, there is relatively less sensitivity of hydrometeor concentrations and displacements to variations in either 0–1 km or 6–12 km shear. Results are consistent across free tropospheric relative humidity sensitivity simulations, which show an increase in updraft size and hydrometeor mass with increasing free tropospheric relative humidity owing to a reduction in entrainment-driven dilution for wider updrafts in moister environments.

An environment-driven basin scale tropical cyclone model

This paper presents an environment-driven tropical cyclone (TC) model for the Western North Pacific basin, which comprises a revised Poisson regression genesis model, a tailored beta-advection track model, and a fast intensity model. The TC model reproduces the temporal and spatial distributions of genesis events, the motion pattern of tracks, as well as the intensity evolutions along tracks. Risk analyses for Hong Kong and along the southeast coastline of mainland China demonstrate that this model can simulate extreme TC events with high fidelity. And the Gaussian mixture model outperforms the Frank Copula in approximating the joint distributions of the annual maximum wind speeds and the corresponding wind directions. This model is driven by a set of environmental variables including relative vorticity, relative humidity, sea surface temperature, vertical wind shear, potential intensity, sub mixed layer depth stratification, mixture layer depth and so on. This enables the model to not only reproduce historical records, but also make predictions for future TC behaviors under climate change with combination of global climate models. Besides, the computational efficiency of the TC model is comparable to traditional purely statistical models. The proposed model can also be coupled with other natural hazard models to conduct multi-hazard analysis.

A Global Increase in Nearshore Tropical Cyclone Intensification

AbstractTropical Cyclones (TCs) inflict substantial coastal damages, making it pertinent to understand changing storm characteristics in the important nearshore region. Past work examined several aspects of TCs relevant for impacts in coastal regions. However, few studies explored nearshore storm intensification and its response to climate change at the global scale. Here, we address this using a suite of observations and numerical model simulations. Over the historical period 1979–2020, observations reveal a global mean TC intensification rate increase of about 3 kt per 24‐hr in regions close to the coast. Analysis of the observed large‐scale environment shows that stronger decreases in vertical wind shear and larger increases in relative humidity relative to the open oceans are responsible. Further, high‐resolution climate model simulations suggest that nearshore TC intensification will continue to rise under global warming. Idealized numerical experiments with an intermediate complexity model reveal that decreasing shear near coastlines, driven by amplified warming in the upper troposphere and changes in heating patterns, is the major pathway for these projected increases in nearshore TC intensification.

VARIASI SHEAR KEY TERHADAP STABILITAS DINDING PENAHAN TANAH KANTILEVER BETON BERTULANG

Stability parameters are very important in the analysis and design of reinforced concrete cantilever retaining wall structures. One of the parameters to increase the stability of this retaining wall is to add a shear key structure. Shear keys can increase wall stability, resist shear, increase stiffness, resist lateral loads, and increase load capacity. The purpose of this research is to determine the level of stability (overturning and shearing) of reinforced concrete cantilever retaining walls by varying the shear key dimensions with the same cross-sectional area. The method used is a quantitative method using data on the properties of soil materials, reinforced concrete, and the geometry of retaining wall structures. The analysis uses the help of Geo5 software, which is geotechnical software for solving problems in the geotechnical field. In this research, four models of reinforced concrete cantilever retaining walls have been created, including model 1 (b/h = 0), namely the model without a shear key, model 2 (b/h = 1), namely square shear key, model 3 ( b/h = 1/4) is a vertical rectangular shear key and model 4 (b/h = 4/1) is a horizontal rectangular shear key. The results of the analysis produce rolling stability with an increase in rolling moment and a decrease in moment of resistance on average of 8.32% and 4.43% respectively for the model without a shear key with a maximum rolling safe factor in the horizontal rectangular shear key model of 2.24. Likewise, the shear stability of the model with a shear key results in an increase in ground shear force and a decrease in active shear force on average of 11.76% and 105.93% respectively compared to the model without a shear key with a maximum shear safe factor in the horizontal rectangular shear key model of 3.96.

A detached-eddy simulation study on assessing the impact of extreme wind conditions on load and wake characteristics of a horizontal-axis wind turbine

This study utilizes improved delayed detached-eddy simulation (IDDES) to investigate the impact of extreme wind conditions on a horizontal-axis wind turbine, as specified by the IEC-61400 standard. The employed IDDES has a hybrid formulation, where SST K-ω is used to model the turbulence in the boundary layers and large-eddy simulation (LES) is used to resolve turbulence in separated flow regions and the wake area. It also allows for switching to a wall-modeled LES approach, depending on the incoming turbulence content. The research focuses on extreme operating gust (EOG), extreme horizontal shear (EHS), and extreme vertical shear (EVS) conditions at two Tip Speed Ratios (TSR). The loadings and wake characteristics are compared to uniform inlet velocity results to highlight the effects of extreme winds. The novelty of this research lies in its comprehensive investigation of wake behavior under extreme wind conditions, providing valuable insights for improving wind farm layout design and reliability in challenging operational environments. The analysis shows that the impact of the TSR on wind turbine loadings during EOG, EVS, and EHS events is significant. During EOG events for a turbine operating at low TSR, the thrust force and bending moment reach 2.38 and 2.57 times their respective values in uniform inflow conditions, while at the optimal TSR, the thrust force and bending moment increase by only 25%. In all extreme wind cases, there is an escalation in turbulence within the wake, and wake meandering is observed in the EHS and EVS cases.

Length and Velocity Scales in Protoplanetary Disk Turbulence

In the theory of protoplanetary disk turbulence, a widely adopted ansatz, or assumption, is that the turnover frequency of the largest turbulent eddy, Ω L , is the local Keplerian frequency Ω K . In terms of the standard dimensionless Shakura–Sunyaev α parameter that quantifies turbulent viscosity or diffusivity, this assumption leads to characteristic length and velocity scales given respectively by αH and αc , in which H and c are the local gas scale height and sound speed. However, this assumption is not applicable in cases when turbulence is forced numerically or driven by some natural processes such as vertical shear instability. Here, we explore the more general case where Ω L ≥ Ω K and show that, under these conditions, the characteristic length and velocity scales are respectively α/R′H and αR′c , where R′≡ΩL/ΩK is twice the Rossby number. It follows that α=α˜/R′ , where α˜c is the root-mean-square average of the turbulent velocities. Properly allowing for this effect naturally explains the reduced particle scale heights produced in shearing box simulations of particles in forced turbulence, and it may help with interpreting recent edge-on disk observations; more general implications for observations are also presented. For R′>1 , the effective particle Stokes numbers are increased, which has implications for particle collision dynamics and growth, as well as for planetesimal formation.

Physical mechanism for the temporary intensification of wintertime sporadic E layers in 2009

This study provides a physical mechanism for the temporary intensification of wintertime sporadic E layers (EsLs) in 2009. It is widely accepted that vertical wind shears control EsL formations. EsL intensity is minimal in winter, partially because of the weakened vertical wind shears. Despite the wintertime minimum EsL intensity, temporary intensifications of EsLs occurred for 10–30 days in some winters, the cause of which remains unclear. In this study, we conducted month-long EsL simulations in 2009 and 2011, the years when both wintertime EsL (WiEsL) intensification and sudden stratospheric warming (SSW) occurred, and when neither did, respectively. The simulations aimed to reveal the physical mechanisms of the WiEsL intensification in 2009. We succeeded in reproducing the occurrence and non-occurrence of temporary WiEsL intensification in 2009 and 2011, respectively, observed by an ionosonde at Kokubunji, Japan, although day-to-day variations in WiEsL intensity were not reproduced well. Evidently, the temporary WiEsL intensification is attributed to vertical ion convergence (VIC) intensification at altitudes of 100–120 km between 4 and 8 local time (LT) and particularly after 15 LT. The VIC intensification is caused primarily by the vertical wind shears of SW2 tides, westward propagating semi-diurnal tides with wavenumber 2. The SW2 intensification is driven by the major SSW in January–February 2009. Additionally, 6–8-day planetary waves can also affect the WiEsL intensification superposed on the SW2 amplification effects.Graphical

Interannual synchronization of the North American summer monsoon and the North Atlantic tropical cyclone genesis frequency

Variations of the North American summer monsoon (NASM) and North Atlantic tropical cyclone (NATC) activities strongly influence climate anomalies in North America, with serious potential risk to life and property. Despite the scientific importance of this topic, the possible linkage between the NASM and the NATC genesis frequency remains unexplored. Here, we aim to examine the relationship between interannual variations of the NASM intensity and the NATC genesis frequency based on observations and Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Our results show a strong association between the NASM intensity and the NATC genesis frequency during the extended boreal summer, with a good synchronization between their interannual variations. In years with stronger (weaker) NASM intensity, the NATC genesis frequency tends to be higher (lower). The observed NASM–NATC synchronization may be explained by two pathways: tropical-ocean-driven pathway and monsoon-heating-driven pathway. In the tropical-ocean-driven pathway, the tropical Pacific and Atlantic interbasin sea surface temperature (SST) anomalies play a critical role in bridging the NASM and NATC, by modulating the cross-Central American wind. Simulations of the tropical Pacific–Atlantic interbasin SST anomalies are critical for CMIP6 models to capture the observed linkage between the NASM and the vertical wind shear over the NATC main development region (MDR). In the monsoon-heating-driven pathway, the heating source due to the rainfall anomalies associated with the NASM can trigger atmospheric circulation anomalies through the Gill-type response, thereby affecting the NATC by changing the vertical wind shear over the MDR. This study demonstrates a connection between interannual variations of the NASM and the NATC genesis frequency, results of which can be used to advance our understanding of the monsoon–TC relationship and increase research focus on the interannual NASM–NATC synchronization in climate prediction.

Evolution of small-scale turbulence at large Richardson numbers

Abstract. The theory of stratified turbulent flow developed earlier by the authors is applied to data from different areas of the ocean. It is shown that turbulence can be amplified and supported even at large gradient Richardson numbers. The cause of that is the exchange between kinetic and potential energies of turbulence. Using the profiles of Brunt–Väisälä frequency and vertical current shear given in Forryan et al. (2013), the profiles of the kinetic energy dissipation rate are calculated. The results are in reasonable agreement with the experimental data.

Kinematic and Dynamic Structure of the 18 May 2020 Squall Line over South Korea

The diagonal squall line that passed through the Korean Peninsula on the 18 May 2020 was examined using wind data retrieved from multiple Doppler radar synthesis focusing on its kinematic and dynamic aspects. The low-level jet, along with warm and moist air in the lower level, served as the primary source of moisture supply during the initiation and formation process. The presence of a cold pool accompanying the squall line played a role in retaining moisture at the surface. As the squall line approached the Korean Peninsula, the convective bands in the northern segment (NS) and southern segment (SS) of the squall line exhibited distinct evolutionary patterns. The vertical wind shear in the NS area was more pronounced compared to that in the SS. The ascending inflow associated with the tilted updraft in the NS reached an altitude of 7 km, whereas it was only up to 4 km in the SS. The difference was caused by the strong descending rear flow, which obstructed the ascending inflow and let to significant updraft in the SS.

Seismic response analysis of subway station under obliquely incident SV waves

This paper aims to investigate the dynamic response characteristics of subway station under earthquakes. To this end, seismic waves are transformed into equivalent nodal loads on viscoelastic artificial boundaries using theories and methods of wave motion. The calculation formulas for equivalent nodal loads of SV waves incident at any angle are established, and ANSYS' APDL program compiles to automatically generate the viscoelastic artificial boundary and input the seismic loads. A finite element model of soil-subway station interaction was established, and the seismic response characteristics of a two-story three-span subway station under different incidence angles of SV waves were investigated using the above seismic input method. The results indicate that the incidence angle of seismic waves has a significant impact on the seismic response of subway station. Inclined incidence of seismic waves causes non-uniform loading and deformation of the subway station. Specifically, a small angle leads to predominantly transverse shear deformation, while a large angle causes mainly vertical shear deformation. The inclined incidence of seismic waves significantly increases the vertical acceleration of the subway station, with the effect becoming more pronounced as the angle increases. Additionally, special attention should be given to the joints between the structural slab and the side wall, slab and center column, as well as the two ends of the center column as they are vulnerable areas during earthquakes and require careful consideration in seismic design.

Mesoscale eddies and near-inertial internal waves modulate seasonal variations of vertical shear variance in the northern South China Sea

Mesoscale eddies and near-inertial internal waves modulate seasonal variations of vertical shear variance in the northern South China Sea

A New Refinement of Mediterranean Tropical‐Like Cyclones Characteristics

AbstractSeveral warm‐core cyclones in the Mediterranean, which were analyzed in the literature, are studied using ERA5 reanalysis, to identify the environment where they develop and distinguish tropical‐like cyclones from non‐tropical warm‐core cyclones. Initially, the cyclone phase space is analyzed to distinguish the cyclones that have a symmetrical deep warm core. Subsequently, the temporal evolution of several parameters is considered, including the distance between the area of maximum tangential wind speed and the cyclone center. Some differences are observed between the cyclones analyzed: one category of cyclones develops in areas of moderate‐low baroclinicity and intense convective processes, as occurs in tropical cyclones. Another group of cyclones develops in a strongly baroclinic environment with weak convective processes and intense vertical wind shear, as occurs in warm seclusions. Two cyclones, showing similarities with polar lows, are also identified.