Wind Velocity Field Research Articles

Modelling absorption and emission profiles from accretion disc winds with WINE

Fast and massive winds are ubiquitously observed in the UV and X-ray spectra of active galactic nuclei (AGNs) and other accretion-powered sources. Several theoretical and observational pieces of evidence suggest they are launched at accretion disc scales, carrying significant mass and angular momentum. Thanks to such high-energy output, they may play an important role in transferring the energy released by accretion to the surrounding environment. In the case of AGNs, this process can help to set the so-called co-evolution between an AGN and its host galaxy, which mutually regulates their growth across cosmic time. To precisely assess the effective role of UV and X-ray winds at accretion disc scales, it is necessary to accurately measure their properties, including mass and energy rates. However, this is a challenging task, due to both the limited signal-to-noise ratio of available observations and the limitations of the models currently used in the spectral analysis. We aim to maximise the scientific return of current and future observations by improving the theoretical modelling of these winds through our Winds in the Ionised Nuclear Environment (WINE) model. WINE is a spectroscopic model specifically designed for disc winds in AGNs and compact accreting sources, which couples photoionisation and radiative transfer with special relativistic effects and a three-dimensional model of the emission profiles. We explore with WINE the main spectral features associated with the disc winds in AGNs, with a particular emphasis on the detectability of the wind emission in the total transmitted spectrum. We explore the impact of the wind ionisation, column density, velocity field, and geometry in shaping the emission profiles. We simulated observations with the X-ray microcalorimeter Resolve on board the recently launched XRISM satellite and the X-IFU on board the future Athena mission. This allows us to assess the capabilities of these telescopes in the study of disc winds in X-ray spectra of AGNs for the typical physical properties and exposure times of the sources included in the XRISM performance verification phase. The wind kinematic and geometry (together with the ionisation and column density) deeply affect both shape and strength of the wind spectral features. Thanks to this, both Resolve and, on a longer timescale X-IFU will be able to accurately constrain the main properties of disc winds over a broad range of ionisation, column densities, and covering factors. We also investigate the impact of the spectral energy distribution (SED) on the resulting appearance of the wind. Our findings reveal a dramatic difference in the gas opacity when using a soft, Narrow Line Seyfert 1-like SED compared to a canonical powerlaw SED with a spectral index of $

Empirical validation and engineering model comparison of outdoor long-range 3D GPU FDTD acoustic simulations with turbulence

We build upon previous work which introduced an acoustic GPU-accelerated 3D Finite-Difference Time-Domain solver, Empapu, equipped with a dynamic moving frame and turbulence modeled as a position-dependent refractive index for long-range outdoor sound propagation simulations. This physics-based model would serve as a benchmark to assess different engineering models, e.g., ISO 9613-2, CNOSSOS-EU and sonX, in the presence of uneven terrain with different ground properties and an inhomogeneous atmosphere. The solver now integrates an improved model of turbulence reproducing the kinetic spectral energy of velocity fluctuations, derived from wind velocity fields, with an eddy (quasiwavelet) approach, relevant in long-range propagations. This study validates our model by comparing level differences in third-octave band spectra at receiver points up to 300 m to analytical methods and measurements in a mostly flat topography comprised of asphalt and grassland. Further analysis is done by comparing results in different locations in Switzerland in the presence of uneven ground and barriers. This work will provide a physics-based basis for evaluating and comparing engineering models for outdoor sound propagation in lieu of measurements.

Effects of wind barriers on the aerodynamic forces and driving safety of vehicles on a wide bridge girder at various angles of attack

This paper presents the effects of angles of attack (AOA) on the windproof effect of wind barriers and the driving safety of highway vehicles on a wide bridge girder. The aerodynamic force coefficients of the vehicles were obtained using the force measurement technique. Computational fluid dynamics simulations were employed to investigate the mean wind velocity field on the upper surface of the girder. A comparison was made between the aerodynamic forces on a vehicle at various AOA on a bridge deck with guardrails and a deck with wind barriers. The windproof effect of wind barriers at various AOA was accessed by the safety factor of a vehicle. The results showed that the maximum of the aerodynamic forces of vehicles was not typically observed at a 0° AOA. The windproof effect of wind barriers became more pronounced as the magnitude of the AOA increased. As AOA increases, the height of the low wind velocity zone above the deck shows an upward trend. Compared to the deck with the guardrails, the height of the low wind velocity zone was much higher in the presence of wind barriers. The increase in the height of the low wind velocity zone will result in a decrease in the aerodynamic side force and an increase in the rolling moment acting on vehicles. It is also noteworthy that the installation of wind barriers can cause a reduction of overturning and side-slip safety factors of vehicles at specific AOA. This suggests that the wind barrier may potentially compromise driving safety at specific AOA.

Dynamic features and wind-resistant strategy of suspended monorail vehicle-track beam systems subjected to turbulent wind

Suspended monorail vehicles (SMV), hung beneath box beams with open bottoms, exhibit significant transverse wobble when exposed to turbulent winds, markedly impacting passenger comfort. This study presents an effective methodology for comprehensively evaluating the dynamical behavior of suspended monorail vehicle-track beam systems (SMVTBS) under wind action. First, based on the multi-rigid body dynamics theory and finite element method, an integrated vehicle-track beam interaction model is established. Then, by applying the auto-regressive (AR) linear filtering method, a turbulent wind velocity field with inherent correlations is adequately simulated through a stochastic process, which is later converted into wind force acting on both the track beam and vehicles. On this basis, the vibration responses of the SMVTBS with and without wind actions are compared, and the effects of the wind load on the vehicle-track beam dynamical behavior are revealed. Furthermore, to improve the wind-resistant performance of the SMV, several crucial design parameters are reasonably selected and effective wind-resistant strategies are proposed. Finally, the dynamic performance of the SMV is evaluated under wind action, and suitable train running speeds were recommended at different wind velocities to guarantee vehicle riding comfort. The research results can provide useful guidance for the design and operation of SMVTBS against crosswinds.

Evaluation of an immersed boundary numerical framework to address the wind field in complex urban topographies

Estimating the wind velocity field in an urban area is important for pedestrian comfort and safety, as the local wind velocities dictate the transport of heat and air pollution in urban environments. Therefore, it is an essential requirement to assess wind patterns when designing urban areas. Computational Fluid Dynamics (CFD) numerical solvers are usually employed to estimate the wind comfort in an urban area under different wind intensities and directions. However, CFD simulations are expensive in terms of time, especially when many scenarios are addressed to ensure safety and comfort for multiple conditions. Here, a CFD framework based on an immersed boundary approach to discretize the urban topography is developed and validated against experimental data in a wind tunnel and two different standard body-fitted mesh codes. The new solver employs a structured cartesian octree grid automatically generated from Lidar data of urban topographies. The advantages are eliminating the complex and time-consuming pre-processing of urban topographies and making the framework accessible to urban planners without CFD expertise. Furthermore, the code is equipped with GPU parallelization that further reduces the computational time. Provided that the best practice guidelines for urban simulations are satisfied, in particular at least 10 cells between two buildings, the code shows very good agreement in all the tests comprising of a simplified and real urban neighborhood highlighting the importance of accurately solving the complex terrain topography of an urban region when non-negligible elevation changes of the order of 20/40 meters are present.

Magnetohydrodynamic Modeling of Background Solar Wind near Mars: Comparison with MAVEN and Tianwen-1

Combined with data assimilation methods, a three-dimensional magnetohydrodynamic (MHD) numerical model is an effective tool to explore the mechanism of space weather. As a driver of space weather, the dynamic development of stream interaction regions (SIRs) near the orbit of Mars is an area of active research. In this study, we use the interplanetary total variation diminishing (TVD) MHD model to simulate solar wind parameters and model SIRs near Mars from 2021 November 15 to 2021 December 31. In this model, the MHD equations are solved by the conservation TVD Lax–Friedrichs scheme in a rotating spherical coordinate system with six component meshes used on the spherical shell. Solar wind velocity, density, temperature, and magnetic field strength are given at the inner boundary due to the characteristic waves propagating outward. We compared modeled results with observations from Mars Atmospheric Volatile EvolutioN (MAVEN) and Tianwen-1 (China’s first Mars exploration mission). Statistical analysis shows that the simulated results can capture SIRs and are in good agreement with observations; moreover, the assimilated results based on the Kalman filter improve the accuracy of numerical prediction compared with simulated results. This paper is the first attempt to simulate SIR events combined with MAVEN and Tianwen-1 in situ observations. Our work demonstrates that using the MHD model with the Kalman filter to reconstruct solar wind parameters can help us study the characteristics of SIRs near Mars, improve the capabilities of space weather forecasting, and understand the background solar wind environment.

Atmospheric transport structures shaping the “Godzilla” dust plume

Saharan dust events, having great ecological and environmental impacts, are the largest producers of the world’s dust by far. Identifying the mechanisms by which the dust is transported across the Atlantic is crucial for obtaining a complete understanding of these important events. Of these events, the so-called “Godzilla” dust intrusion of June 2020 was the largest and most impactful in the last two decades and underwent a particularly interesting transport pattern. By uncovering dominant, organizing structures derived from the wind velocity fields, known as Lagrangian coherent structures, we demonstrate the ability to describe and qualitatively predict certain aspects related to the evolution of the dust plume as it traverses the atmosphere over the Atlantic. In addition, we identify regions of high hyperbolicity, leading to drastic changes in the shape of the plume and its eventual splitting. While these tools have been quite readily adopted by the oceanographic community, they have still yet to fully take hold in the atmospheric sciences and we aim to highlight some of the advantages over traditional atmospheric transport methods.

Modeling the Transport of Solar Energetic Particles in a Corotating Interaction Region

We present a new three-dimensional (3D) magnetohydrodynamic (MHD) model and a new 3D energetic particle transport (EPT) model. The 3D MHD model numerically solves the ideal MHD equations using the relaxing total variation diminishing scheme. In the 3D MHD simulations, we use simple boundary conditions with a high-speed flow, and we can clearly identify a corotating interaction region (CIR) with the characteristics of forward shock and reverse shock. The 3D EPT model solves the Fokker–Planck transport equation for the solar energetic particles (SEPs) using backward stochastic processes, with the magnetic field and solar wind velocity field from MHD results. For comparison, the 3D EPT model results with Parker fields are also obtained. We investigate the transport of SEPs with particle sources and observers in different positions in MHD fields with a CIR, and we compare the results with those in the Parker fields. Our simulation results show that the compression region with local enhancement of the magnetic field, i.e., CIR, can act as a barrier to scatter energetic particles back, and particles can struggle to diffuse through the strong magnetic field regions. Usually, a normal anisotropy profile is commonly present in SEP simulation results with Parker fields, and it is also typically present in that with MHD fields. However, because of the compression region of the magnetic field, energetic particles may exhibit anomalous anisotropy. This result may be used to replicate the spacecraft observation phenomena of the anomalous anisotropy.

Accelerating Lagrangian transport simulations on graphics processing units: performance optimizations of Massive-Parallel Trajectory Calculations (MPTRAC) v2.6

Abstract. Lagrangian particle dispersion models are indispensable tools for the study of atmospheric transport processes. However, Lagrangian transport simulations can become numerically expensive when large numbers of air parcels are involved. To accelerate these simulations, we made considerable efforts to port the Massive-Parallel Trajectory Calculations (MPTRAC) model to graphics processing units (GPUs). Here we discuss performance optimizations of the major bottleneck of the GPU code of MPTRAC, the advection kernel. Timeline, roofline, and memory analyses of the baseline GPU code revealed that the application is memory-bound, and performance suffers from near-random memory access patterns. By changing the data structure of the horizontal wind and vertical velocity fields of the global meteorological data driving the simulations from structure of arrays (SoAs) to array of structures (AoSs) and by introducing a sorting method for better memory alignment of the particle data, performance was greatly improved. We evaluated the performance on NVIDIA A100 GPUs of the Jülich Wizard for European Leadership Science (JUWELS) Booster module at the Jülich Supercomputing Center, Germany. For our largest test case, transport simulations with 108 particles driven by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis, we found that the runtime for the full set of physics computations was reduced by 75 %, including a reduction of 85 % for the advection kernel. In addition to demonstrating the benefits of code optimization for GPUs, we show that the runtime of central processing unit (CPU-)only simulations is also improved. For our largest test case, we found a runtime reduction of 34 % for the physics computations, including a reduction of 65 % for the advection kernel. The code optimizations discussed here bring the MPTRAC model closer to applications on upcoming exascale high-performance computing systems and will also be of interest for optimizing the performance of other models using particle methods.

Multi-scale simulation of typhoon wind field at building scale utilizing mesoscale model with nested large eddy simulation

Based on the mesoscale WRF (Weather Research Forecast) and LES (Large Eddy Simulation), an integrated numerical simulation framework aiming to resolve typhoon wind fields around urban building blocks has been developed. The holistic multi-scale simulation spans four scales: macroscale (∼1000 km), mesoscale (∼100 km), microscale (∼1 km), and building scale (0.1–100m). By interactively sharing the meteorological data among different scales, this simulation framework addressed the challenge of downscaling typhoon effects in urban environments. Typhoon weather reanalysis and urban wind field simulation were conducted by the WRF model with nested computational domains incorporating high-resolution topography data. For the downscaled LES model with urban buildings, the wind profiles produced by the WRF model were used at the interface with provided turbulent fluctuations in the flow. K11 building is a 270-m-tall building located in a densely built-up area of Hong Kong. Wind velocity and pressure fields surrounding the K11 building in Hong Kong during Typhoon Kammuri were obtained by the proposed framework, and the simulation results were validated by comparing with the meteorological data and full-scale measurements at the top of the K11 building. The interactions of the wind fields and building clusters resulting in vortex shedding, separation, and channeling effects have been resolved at high resolutions. Probabilistic distributions and higher-order statistics of wind pressure, i.e., skewness and kurtosis, were presented to highlight non-Gaussian characteristics of the simulated local wind pressure on the K11 building. Based on the simulated wind pressure, wind-induced vibration of the K11 building during the typhoon was analyzed and compared to the measurements.

The Opposite Behaviors of Proton and Electron Temperatures in Relation to Solar Wind Magnetic Energy: Parker Solar Probe Observations

Solar wind heating is an outstanding issue that has been discussed for decades. Research on the connection between solar wind particle temperatures and turbulence may provide insight into this issue. Based on Parker Solar Probe observations, this paper investigates the properties of solar wind proton and electron temperatures in relation to turbulent magnetic energy, via the calculation of correlation coefficients (CCs) between particle temperatures and magnetic energy. The calculations are regulated by the spatial scale, plasma beta (β), and the angle between the solar wind velocity and background magnetic field, where the plasma beta is the ratio of plasma thermal to magnetic pressure. Results show that the correlation between proton temperature and magnetic energy is positive and can be strong with a CC exceeding 0.8. The strong correlation preferentially occurs at ion scales, with the wind velocity and background magnetic field quasi-perpendicular and over a wide beta range (β < 3.0). On the other hand, the correlation between electron temperature and magnetic energy is commonly negative, often with an intermediate or negligible CC, accordingly. The CC with an amplitude up to 0.8 can arise at larger scales with the wind velocity and background magnetic field quasi-(anti)parallel and in the low-beta case (β < 0.6). The implication of these findings on the physics of turbulent heating in the solar wind is discussed.

Wind tunnel measurement of pedestrian-level gust wind flow and comfort around irregular lift-up buildings within simplified urban arrays

The implementation of lift-up buildings has demonstrated their practicality in enhancing urban wind comfort in high-density cities. The pedestrian-level wind environment around a central lift-up building surrounded by low-rise buildings was measured using wind tunnel experiments. The time-averaged velocity field and turbulence statistics, including the turbulent kinetic energy, normal component of the Reynolds stresses, gust factor, and gust wind velocity field, were discussed. Based on the results, the pedestrian-level gust wind flow and comfort for two typical building shapes (Arc, V-shaped) were compared with Rectangular lift-up buildings under different wind directions (0∘, 90∘ and 180∘), the pedestrian-level wind environments (PLWEs) were assessed following two wind criteria for weak and windy wind conditions by wind speed thresholds and maximum allowed exceedance probabilities. The results showed that the erection of the high-rise lift-up building modified the pedestrian-level wind environment around the building groups, owing to the interaction between the downwash flow around the building and the surrounding building blocks. A region of high mean and gust wind velocity was observed at the lateral and rear side of the central lift-up building due to the lateral entrained wind and Venturi effect between elevated columns, indicating that lift-up buildings can enhance PLWEs even in the presence of surrounding buildings. The Arc-shaped lift-up building tends to generate a larger “Intolerable” area compared with V- and Rectangular-shaped buildings due to its curved surface. The wind impacts the convex portion of the building, leading to airflow divergence and facilitating downstream ventilation.

Full-scale aerodynamic study on the effects of tower wind shields and road-sign gantries on passing high-sided vehicles in the tower region at the Queensferry Crossing

A novel investigation into the impact of the tower road-sign gantry and the tower shielding on double-decker buses and trucks passing by the bridge tower based on a previously validated full-scale CFD model. Two sets of simulations were conducted for comparison of aerodynamic force conditions of vehicles as they pass by the bridge tower: first group of simulations were performed including and excluding the road-sign gantry; and the second group include and exclude the tower shielding. Conditions in different traffic lanes (one on leeward side and two on windward side) considered. The effect of changes in wind yaw angle are also considered. Mechanism exploration on the variation of vehicle aerodynamic force conditions was made based on the numerical visualization of wind velocity field and pressure field. Novel results suggest that the road-sign gantry provides a sheltering effect in some circumstances, but a destabilizing effect in others. In addition, the tower shielding shows significant impact on reducing aerodynamic forces and sudden force changes of the high-sided vehicles while they are passing by the bridge tower.

The Martian Ionospheric Response to the Co‐Rotating Interaction Region That Caused the Disappearing Solar Wind Event at Mars

AbstractAn unusually low density solar wind event was observed in December 2022 moving past both Earth and Mars. The source was traced back to a coronal hole and active region on the Sun's surface. The resulting solar wind lead to the development of a co‐rotating interaction region (CIR) and trailing rarefaction region that lasted for multiple solar rotations. Within this structure, the solar wind conditions, including density, velocity, and magnetic field magnitude and orientation drastically changed. In this study we analyze the response of the Martian ionosphere using MAVEN data to these changing solar wind conditions. The low density solar wind region associated with the December event resulted in the expansion of the Martian ionospheric boundaries. We show that the ion composition boundary (ICB) is located at extreme altitudes that are beyond previously observed locations from the MAVEN mission between 2015 and 2018. Furthermore, the boundary between shocked solar wind and the Martian ionosphere identified using electron and ion data moved together on the dayside of the planet with the changing solar wind conditions. However, at the flank region these boundaries do not move together, and we show here that the decoupling of the two boundaries may be the result of a change in the interplanetary magnetic field azimuthal angle.

Predicting wind farm wake losses with deep convolutional hierarchical encoder–decoder neural networks

Wind turbine wakes are the most significant factor affecting wind farm performance, decreasing energy production and increasing fatigue loads in downstream turbines. Wind farm turbine layouts are designed to minimize wake interactions using a suite of predictive models, including analytical wake models and computational fluid dynamics simulations (CFD). CFD simulations of wind farms are time-consuming and computationally expensive, which hinder their use in optimization studies that require hundreds of simulations to converge to an optimal turbine layout. In this work, we propose DeepWFLO, a deep convolutional hierarchical encoder–decoder neural network architecture, as an image-to-image surrogate model for predicting the wind velocity field for Wind Farm Layout Optimization (WFLO). We generate a dataset composed of image representations of the turbine layout and undisturbed flow field in the wind farm, as well as images of the corresponding wind velocity field, including wake effects generated with both analytical models and CFD simulations. The proposed DeepWFLO architecture is then trained and optimized through supervised learning with an application-tailored loss function that considers prediction errors in both wind velocity and energy production. Results on a commonly used test case show median velocity errors of 1.0%–8.0% for DeepWFLO networks trained with analytical and CFD data, respectively. We also propose a model-fusion strategy that uses analytical wake models to generate an additional input channel for the network, resulting in median velocity errors below 1.8%. Spearman rank correlations between predictions and data, which evidence the suitability of DeepWFLO for optimization purposes, range between 92.3% and 99.9%.

A Transfer Learning Method to Generate Synthetic Synoptic Magnetograms

AbstractCurrent magnetohydrodynamics (MHD) models largely rely on synoptic magnetograms, such as the ones produced by the Global Oscillation Network Group (GONG). Magnetograms are currently available mostly from the front side of the Sun, which significantly reduces the accuracy of MHD modeling. Extreme Ultraviolet (EUV) images can instead be obtained from other vantage points. To investigate the potential, we explore the possibility of using EUV information from the Atmospheric Imaging Assembly (AIA) to directly generate the input for the state‐of‐the‐art 3D MHD model European Heliospheric FORecasting Information Asset (EUHFORIA). Toward this goal, we develop a method called Transfer‐Solar‐GAN which combines a conditional generative adversarial network with a transfer learning approach to overcome training data set limitations. The source domain data set is constructed from multiple pairs of the central portion of co‐registered AIA and Helioseismic and Magnetic Imager (HMI) line of sight (LOS) full‐disk images, while the target domain is constructed from pairs of portions of AIA and GONG sine‐latitude synoptic maps that we call segments. We evaluate Transfer‐Solar‐GAN by comparing modeled and measured solar wind velocity and magnetic field density parameters at the L1 Lagrange point and along the Parker Solar Probe (PSP) trajectory which were determined with EUHFORIA using both empirical GONG and artificial‐intelligence (AI)‐synthetic synoptic magnetograms as inputs. Our results demonstrate that the Transfer‐Solar‐GAN model can provide the necessary information to run solar physics models by EUV information. Our proposed model is trained with only 528 paired image segments and enforces a reliable data division strategy.

Avaliação da resposta estrutural dinâmica não-determinística de edifícios quando submetidos a ações do vento

Abstract The construction of high-rise buildings has emerged as a constructive trend worldwide, and excessive vibration problems due to wind actions are becoming increasingly frequent. The Brazilian design standard NBR 6123 recommends that the transfer of wind actions used for structural analysis be carried out based on the pressure coefficients along the building facades for static analyses and considers their non-deterministic dynamic behaviour through a stochastic modelling method of the wind velocity field. To present an alternative approach to this methodology, this study aims to investigate the non-deterministic dynamic structural response of a real reinforced concrete building, considering the soil-structure interaction effect, using the pressure coefficients obtained through different methodologies such as numerical simulations using Computational Fluid Dynamics (CFD), international databases, and the recommendations of the Brazilian standard NBR 6123.

Examining the dynamics of a Borneo vortex using a balance approximation tool

Abstract. Cyclonic vortices that are weaker than tropical storm category can bring heavy precipitation as they propagate across the South China Sea and surrounding countries. Here we investigate the structure and dynamics responsible for the intensification of a Borneo vortex that moved from the north of Borneo across the South China Sea and impacted Vietnam and Thailand in late October 2018. This case study is examined using Met Office Unified Model (MetUM) simulations and a semi-geotriptic (SGT) balance approximation tool. Satellite observations and a MetUM simulation with 4.4 km grid initialised at 12:00 UTC on 21 October 2018 show that the westward-moving vortex is characterised by a coherent maximum in total column water and by a comma-shaped precipitation structure with the heaviest rainfall to the northwest of the circulation centre. The Borneo vortex comprises a low-level cyclonic circulation and a mid-level wave embedded in the background easterly shear flow, which strengthens with height up to around 7 km. Despite being in the tropics at 6∘ N, the low-level vortex and mid-level wave are well represented by SGT balance dynamics. The mid-level wave propagates along a vertical gradient in moist stability, i.e. the product between the specific humidity and the static stability, at 4.5 to 5 km and is characterised by a coherent signature in the potential vorticity, meridional wind, and balanced vertical velocity fields. The vertical motion is dominated by coupling with diabatic heating and is shifted relative to the potential vorticity so that the diabatic wave propagates westwards, relative to the flow, at a rate consistent with prediction from moist semi-geostrophic theory. Initial vortex development at low levels is consistent with baroclinic growth initiated by the mid-level diabatic Rossby wave, which propagates on baroclinic shear flow on the southern flank of a large-scale cold surge.

Statistical analysis of equatorial electrojet responses to the transient changes of solar wind conditions

Introduction: Prior case studies have indicated that changes in solar wind conditions have a significant impact on equatorial ionospheric electrodynamics. However, there have been limited statistical studies on this topic, impairing our understanding of the coupling between solar wind, magnetosphere, and equatorial ionosphere electrodynamics.Methods: In this study, we conducted a superposed epoch analysis of long-term data from the South America equatorial electrojet (EEJ) spanning from 2001 to 2021 examining the responses of the equatorial ionospheric electric field to step-like changes in solar wind velocity, density, dynamic pressure, and interplanetary magnetic field (IMF) Bz.Result: Our study shows that step-like changes in solar wind velocity, density, and dynamic pressure can trigger changes in EEJ within ∼20–40 min. EEJ exhibits the highest sensitivity to variations in solar wind velocity while being relatively less sensitive to changes in dynamic pressure. Furthermore, the response of EEJ shows greater responsiveness to northward IMF Bz compared to southward IMF Bz.Discussion: Our work provides statistical evidence of how changes in solar wind can lead to changes in low-latitude ionospheric EEJ. We inferred that the changes in solar wind conditions cause magnetospheric deformation and changes in magnetic reconnection rates, leading to the fluctuations of the ionospheric electric field and the resultant EEJ variations.

Efficient simulation of fully nonstationary wind velocity field by an enhanced numerical truncation method

The spectral representation method (SRM) is widely utilized to simulate the fully nonstationary wind velocity field with time-varying coherence. The simulation samples are generated by double summation of harmonic functions. Despite the fast Fourier transform (FFT) technique has been employed to accelerate the summation in the frequency dimension, the computational efficiency is still constrained by the number of simulation points and samples due to the time-consuming summation operation in the spatial dimension. In this study, a numerical truncation method is presented to further quicken the SRM-based simulation of a fully nonstationary wind velocity field. The fundamental idea is that the harmonic functions with tiny amplitude are inconsequential and can be omitted. A novel diagonal decoupling approach is first developed to rearrange the double summation. Further, the frequency truncation scheme is established to simplify the summation in the spatial dimension. Meanwhile, the FFT operations to calculate the summation in the frequency dimension are also considerably reduced. Finally, the superior performance of the proposed method on precision and efficiency is demonstrated by numerical examples.