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Due to the randomness of wind power generation, the output power of a wind farm will fluctuate. As a result, the power grid can face the need for increased reserve capacity, increasing scheduling difficulties and wind farm abandonment. An effective way to address these problems is to accurately predict the output power of wind farms. Traditional prediction methods usually make predictions based on wind data obtained at a single height. However, with long prediction periods, prediction errors are relatively large because the wind speed and direction at different heights have spatiotemporal correlations within a wind farm. In the model presented here, the wind power data are first decomposed by a ‘complete ensemble empirical mode decomposition with adaptive noise’ model to obtain modal components with different fluctuation characteristics. Then, the characteristics of wind speed, wind direction, air pressure and other data at different heights are extracted for spatiotemporal feature fusion. Actual measurement data from a wind farm in Chongqing, China are used to verify the feasibility and effectiveness of the proposed method.

The analysis of the recent gravity measurements of Jupiter and Saturn reveal that the zonal winds observed on their surfaces reach several thousand kilometres deep into their atmospheres. However, it remains unclear which mechanism prevents them from penetrating deeper. Recent models suggest that a stably stratified region would yield the desired effect.In this study we systematically explore the dynamics in a spherical shell where the lower third is stably stratified while convection in the outer region drives multiple zonal winds, similar to those observed on Jupiter or Saturn. We perform numerical simulations with the magnetohydrodynamic code MagIC and ignore magnetic effects in order to simplify the problem. Using a rigid lower boundary condition, vigorous multiple jets begin to develop at mid to high latitudes once the stable stratification is strong enough to effectively decouple the jet dynamics from the lower boundary. We find that the jet amplitude decay at the stable layer boundary is proportional to Ω/N, where Ω is the rotation rate and N the Brunt-Väisälä frequency that quantifies the degree of stable stratification.Furthermore, the penetration depth of the jets is directly proportional to the jet width, i.e. the stable layer acts as a low-pass filter on the zonal winds. The structure of the winds also changes. In the convective region they are invariant along the axis of rotation, as expected. However, in the stable layer the location of the peaks in the zonal wind profile become more radially invariant with depth. This shift from cylindrical to a more spherical geometry inthe flow structure occurs due to meridional flows at the interface, thermal winds and the inverse buoyancy force in the stable layer.

Air–water mixing associated with high turbulence is a common hydraulic phenomenon, where the transport of entrained air bubbles and the dissipation of turbulent energy are key processes affecting the air–water mass transfer. Herein hydraulic jumps were selected as a seminal case of self-air-entrainment in transitional water flow, and the air–water flow properties were investigated at high Froude numbers from 10.5 to 13.5. The analysis of air concentration distributions and bubble size spectra enabled deviation of the rates of bubble diffusion and turbulence dissipation. The study was facilitated with re-analyses of earlier experimental data for smaller Froude numbers between 3.8 and 10. The spatial evolution of the diffusion and dissipation rates suggested that the diffusion of air bubbles and dissipation of turbulent structures were not independent processes, and, at high Froude numbers, the mix of air and water was subject to re-aeration of the turbulent shear layer by the roller.

Long-span bridges in mountainous areas are greatly disturbed by wind, and the wind field in the mountain gorge bridge site is extremely complex. Therefore, it is of great engineering significance to accurately evaluate the wind field characteristics of this kind of terrain. In this paper, to enhance understanding of this kind of wind field, the wind field in a mountainous gorge is measured for a long time using wind radar, and the mean wind parameters is statistically analyzed. The results show that the mean wind parameters vary greatly under different wind directions, and the wind speed profile does not meet the power-law model. Therefore, a mixed model suitable for the wind speed profile in a mountainous gorge is proposed. Additionally, GEV distribution and Logistic distribution are found to be suitable for describing the distribution characteristics of wind speed and angle of attack, respectively. In addition, considering the correlation between wind parameters, this paper also constructs the joint probability model of wind speed and angle of attack at different heights by the Copula function. Thus, a combined wind parameters profile model is developed under different exceedance probabilities based on the inverse first-order reliability method (IFORM). This study can provide a reference for the construction of the joint probability model of wind parameters.

Resource shortages and environmental pollution of the world are becoming more and more serious, wind Turbine generation as a kind of clean energy power generation has attracted much attention. The difficulty of wind power generation lies in the randomness of natural wind energy, which leads to the instability of the output power of Wind Turbine Generators (WTGs). The traditional variable pitch controller cannot realize global precision control of the wind power system. To solve the problem, this paper combines Takagi-Sugeno (T-S) fuzzy model with optimal control theory to design a robust controller. The unique novelty of the controller is that when the wind speed is higher than the rated, no matter how much the wind speed is, even if it is far from the balance point of the system, the controller can make the output power at a constant value, that is, increase the global stability of the wind power system. Specifically, the wind power system was divided into several linear subsystems, and the state feedback controller of each subsystem was designed through optimal control. Then, the subsystem controllers were merged by superposing membership functions, forming a controller of the entire system. Finally, wind turbine generators (WTGs) were modeled and simulated in Matlab/Simulink. The results show that the proposed controller kept the output power of WTGs constant under the global step wind of 13–25 m/s and the stochastic wind of 14–15 m/s. Our design enables the precision control at any wind speed, and improves the stability of power output of WTGs.

We use wind sensitivity experiments to understand the wind forcing dependencies of the level of no motion as the depth of maximum overturning and the e-folding pycnocline scale, as well as their relationship to northward transport of the mid-depth Atlantic meridional overturning circulation (AMOC) which extends vertically to the depth of maximum overturning of the upper AMOC cell. In contrast to previous studies, we investigate the interplay of nonlocal and local wind effects on a decadal timescale. We use 30-year simulations with a high-resolution ocean general circulation model (OGCM) which is an eddy-resolving version of the Max Planck Institute for Meteorology ocean model (MPIOM). Our findings deviate from the common perspective that the AMOC is a nonlocal phenomenon only, because northward transport and its depth scales depend on both nonlocal Southern Ocean wind effects and local wind effects in the Northern Hemisphere downwelling region where Ekman pumping takes place. Southern Ocean wind forcing predominantly determines the magnitude of the pycnocline scale throughout the basin, whereas Northern Hemisphere winds additionally influence the level of no motion locally. In that respect, the level of no motion is a better proxy for northward transport and mid-depth velocity profiles than the pycnocline scale, since the wind forcing dependencies of the level of no motion and maximum overturning are equal. The changes in maximum overturning with wind forcing are explained by the changes in the level of no motion only. This is because wind-driven Ekman compensation is baroclinic and occurs above the level of no motion, and the internal vertical velocity shear that is not influenced by the external Ekman cells stays approximately constant. The analysis of the wind experiments suggests a hemisphere-dependent scaling of the strength of AMOC. We put forward the idea that the ability of numerical models to capture the spatial and temporal variations of the level of no motion is crucial to reproduce the mid-depth cell in an appropriate way both quantitatively and dynamically.

Rocky planets with temperate conditions provide the best chance for discovering habitable worlds and life outside the Solar System. In the last decades, new instrumental facilities and large observational campaigns have been driven by the quest for habitable worlds. Climate models aimed at studying the habitability of rocky planets are essential tools to pay off these technological and observational endeavours. In this context, we present EOS-ESTM, a fast and flexible model aimed at exploring the impact on habitability of multiple climate factors, including those unconstrained by observations. EOS-ESTM is built on ESTM, a seasonal-latitudinal energy balance model featuring an advanced treatment of the meridional and vertical transport. The novel features of EOS-ESTM include: (1) parameterizations for simulating the climate impact of oceans, land, ice, and clouds as a function of temperature and stellar zenith distance; (2) a procedure (EOS) for calculating the radiative transfer in atmospheres with terrestrial and non-terrestrial compositions illuminated by solar- and non-solar-type stars. By feeding EOS-ESTM with Earth's stellar, orbital and planetary parameters we derive a reference model that satisfies a large number of observational constraints of the Earth's climate system. Validation tests of non-terrestrial conditions yield predictions that are in line with comparable results obtained with a hierarchy of climate models. The application of EOS-ESTM to planetary atmospheres in maximum greenhouse conditions demonstrates the possibility of tracking the snowball transition at the outer edge of the HZ for a variety of planetary parameters, paving the road for multi-parametric studies of the HZ., 22 pages, 14 figures, 10 tables, accepted for publication in MNRAS

Measurements of wind and momentum fluxes are not typically at the centre of field studies on (shallow) cumulus convection, but the mesoscale organization of convection is likely closely tied to patterns in wind. This study combines in situ high-frequency turbulence measurements from a gust probe onboard a Cessna aircraft with downward profiling Doppler wind lidar (DWL) measurements onboard a Falcon aircraft to study variability in the wind profile and momentum fluxes in regions of convection. The dual-aircraft measurements were made during three prototype flights in shallow convective regimes over German agricultural areas (two of which had hilly topography, one flat) in late spring 2019, including forced cumulus humilis under weak winds and “popcorn” cumuli during stronger wind and wind shear after front passages. All flights show pronounced meso-gamma (2–20 km) scale variability in the wind, with the largest wind variance (on the order of 2–4 m2 s−2) towards cloud base and in the cloud layer on flights with large vertical wind shear. The wind and wind variance profiles measured in situ and by lidar compare very well, despite the DWL's coarse (∼ 8 km) horizontal footprint. This highlights the presence of wind fluctuations on scales larger than a few kilometres and that wind lidars can be used more deliberately in field studies to map (mesoscale) flows. Cloudy transects are associated with more than twice the momentum flux compared with cloud-free transects. The contribution of the updraft to the total momentum flux, typically one-third to two-thirds, is far less than the typical contribution of the updraft to buoyancy flux. Even on the same flight day, momentum flux profiles can differ per track, with one case of counter-gradient momentum transport when the updraft does carry substantial momentum flux. Scales beyond 1 km contribute significantly to the momentum flux and there is clear evidence for compensating flux contributions across scales. The results demonstrate that momentum flux profiles and their variability require understanding of motions across a range of scales, with non-negligible contributions of the clear-sky fluxes and of mesoscales that are likely coupled to the convection.

Clouds are assumed to play an important role in the Arctic amplification process. This motivated a detailed investigation of cloud processes, including radiative and turbulent fluxes. Data from the aircraft campaign ACLOUD were analyzed with a focus on the mean and turbulent structure of the cloudy boundary layer over the Fram Strait marginal sea ice zone in late spring and early summer 2017. Vertical profiles of turbulence moments are presented from contrasting atmospheric boundary layers (ABLs) from 4 d. They differ by the magnitude of wind speed, boundary-layer height, stability, the strength of the cloud-top radiative cooling and the number of cloud layers. Turbulence statistics up to third-order moments are presented, which were obtained from horizontal-level flights and from slanted profiles. It is shown that both of these flight patterns complement each other and form a data set that resolves the vertical structure of the ABL turbulence well. The comparison of the 4 d shows that especially during weak wind, even in shallow Arctic ABLs with mixing ratios below 3 g kg−1, cloud-top cooling can serve as a main source of turbulent kinetic energy (TKE). Well-mixed ABLs are generated where TKE is increased and vertical velocity variance shows pronounced maxima in the cloud layer. Negative vertical velocity skewness points then to upside-down convection. Turbulent heat fluxes are directed upward in the cloud layer as a result of cold downdrafts. In two cases with single-layer stratocumulus, turbulent transport of heat flux and of temperature variance are both negative in the cloud layer, suggesting an important role of large eddies. In contrast, in a case with weak cloud-top cooling, these quantities are positive in the ABL due to the heating from the surface. Based on observations and results of a mixed-layer model it is shown that the maxima of turbulent fluxes are, however, smaller than the jump of the net terrestrial radiation flux across the upper part of a cloud due to the (i) shallowness of the mixed layer and (ii) the presence of a downward entrainment heat flux. The mixed-layer model also shows that the buoyancy production of TKE is substantially smaller in stratocumulus over the Arctic sea ice compared to subtropics due to a smaller surface moisture flux and smaller decrease in specific humidity (or even humidity inversions) right above the cloud top. In a case of strong wind, wind shear shapes the ABL turbulent structure, especially over rough sea ice, despite the presence of a strong cloud-top cooling. In the presence of mid-level clouds, cloud-top radiative cooling and thus also TKE in the lowermost cloud layer are strongly reduced, and the ABL turbulent structure becomes governed by stability, i.e., by the surface–air temperature difference and wind speed. A comparison of slightly unstable and weakly stable cases shows a strong reduction of TKE due to increased stability even though the absolute value of wind speed was similar. In summary, the presented study documents vertical profiles of the ABL turbulence with a high resolution in a wide range of conditions. It can serve as a basis for turbulence closure evaluation and process studies in Arctic clouds.

Winds are commonly observed in luminous active galactic nuclei (AGNs). A plausible model of those winds is magnetohydrodynamic (MHD) disc winds. In the case of disc winds from a thin accretion disc, isothermal or adiabatic assumption is usually adopted in such MHD models. In this work we perform two-dimensional MHD simulations implementing different thermal treatments (isothermal, adiabatic and radiative) to study their effects on winds from a thin accretion disc. We find that both the isothermal model and the adiabatic model overestimate the temperature, underestimate the power of disc winds, and cannot predict the local structure of the winds, compared to the results obtained by solving the energy equation with radiative cooling and heating. Based on the model with radiative cooling and heating, the ionization parameter, the column density and the velocity of the disc winds have been compared to the observed ultrafast outflows (UFOs). We find that in our simulations the UFOs can only be produced inside hundreds of Schwarzschild radius. At much larger radii, no UFOs are found. Thus, the pure MHD winds cannot interpret all the observed UFOs., Comment: 11 pages, 14 figures, published in MNRAS

The wind speed information measured by the wind speed sensor in the wind turbine generator may differ from sufficient wind speed. Therefore, this paper proposes a new effective wind speed calculation method and applies it to the optimal maximum power point tracking (MPPT) of wind energy. After estimating the turbine torque and its rotor speed, the process reverses the turbine’s aerodynamic model. The extended state observer (ESO) based on sliding mode control is used to estimate the aerodynamic torque, which solves complex and challenging tuning of the traditional ESO parameters, and replaces the conventional PI controller, thereby improving the anti-interference and robustness of the system. The sliding mode observer (SMO) is used to estimate the rotor speed. While satisfying the conditions of Lyapunov’s inequality, the design of the SMO is discussed in detail. The wind speed estimation method proposed for evaluating permanent magnet semidirect drive wind turbine and its application performance in maximum power tracking. The simulation was carried out in MATLAB/Simulink; the simulation confirmed that the estimated wind speed under different wind conditions is accurate. Compared with the traditional PI control, the utilization rate of wind energy is increased by 2%, which can be used for the MPPT control of the wind energy conversion system.

The massive mega constellation of satellites will have a significant impact on global space safety. With Starlink as an example, this paper is aimed at assessing the risk of in-orbit collision, analyzing the probability of collision in orbit in its natural operating state, and forecasting the probability of secondary collision between the collision-generated short-term debris cloud and satellites in the same orbit. The mass, size, velocity, and direction of space debris in a particular orbit of Starlink satellite are calculated based on the MASTER-8 model, and the shape characteristics of the Starlink satellite are added to the model to determine the probability of a Starlink satellite colliding with space debris in that orbit. A modified spacecraft impact disintegration model then is used to calculate the collision results and estimate the collision threat level of the short-term debris cloud formed by the Starlink satellite after its destruction to satellites in the same orbit. The results indicate that the collision probability of Starlink satellite in orbit natural operation exceeds the red warning threshold 10-4 that the satellite disintegration after the first collision will generate 14088 pieces of debris over 1 cm, of which 4092 debris are potentially dangerous to other spacecraft, and that the collision probability to a satellite in the same orbit exceeds the red warning threshold of 10-4 within 30 minutes, implying that collision avoidance needs to be improved.

Glacier height is determined by the range and orbit height of the satellite. The Range (R) is measured between the satellite and the surface of glacier using a space-borne altimeter. The satellite orbit height (H) is measured from the reference ellipsoid using Global Positioning System (GPS). The difference of orbital height and the altimeter range (H-R) is termed as the glacier height 'h.' Accuracy of the glacier height depends on the precise measurement of both orbital height and altimeter range. The orbital height measured using GPS is accurate compared to all the other tracking systems available. The optimal estimate of the satellite position is obtained using the ODTK tool by setting the mathematical model of the equation of Low Earth Orbit (LEO) satellite and the GPS measurements by applying Kalman filtering.

Swift development in wind power and extension of wind generation necessitates significant research in numerous fields. Due to this, wind power is weather dependent; it is fluctuating and is sporadic over numerous time periods. Hence, timely wind power prediction is perceived as an extensive contribution to well-grounded wind power prediction with complex patterns. In addition, a number of wind power prediction methods have been developed. For proper planning and operation of power systems with complicated patterns, wind power prediction in an accurate and timely manner is essential. This paper presents a wind power prediction method with feature selection and prediction called, Pearson Autocovariance Distinct Patterns and Attention-based Deep Learning (PACDP-ADL). In the deep learning environment, feature selection plays a crucial aspect and a prediction task. A Pearson Autocovariance Feature Selection model is used for identifying necessary features for wind power prediction and reduces the complexity of the model. Next, an Attention-based Long Short-Term Memory Wind Prediction algorithm is employed to retain required patterns and forget irrelevant patterns to acquire more satisfactory prediction precision. The proposed PACDP-ADL method is validated by utilizing the wind power data with various performance metrics such as wind power accuracy, wind power time, and true positive rate compared with the state-of-the-art method.

This article presents an analysis of the Fluid-Structure response of bladeless wind turbines that work by induced aeroelastic resonance, which can be used in cities or small towns to form part of sustainable urban planning. In it, numerical simulations of the behavior of the wind and the effect called Von Karman Vortices that it produces when surrounding the structure of the wind turbine are carried out, taking as input data the wind speeds measured by the Mariscal Sucre Meteorological Station in Quito. CFD simulations determine the excitation signal caused by the different existing wind flows, the effects that these oscillations cause on the structure are simulated through a modal study and harmonic response to resonance. The results obtained show a proportional increase in the frequency and amplitude of the vortex shedding to the increase in wind speed, causing different excitation signals that cause the wind turbine to oscillate with amplitudes between 6 and 11 cm. Finally, the transient simulations show that the presence of houses and buildings in the vicinity where the wind turbine is installed causes the direction of the vortex street to vary, as well as alterations in the frequency and amplitude of the excitation., En este artículo se presenta un análisis de la respuesta fluido-estructura de los aerogeneradores sin palas que funcionan por resonancia aeroelástica inducida, los cuales pueden ser utilizados en ciudades o pueblos pequeños para formar parte de un urbanismo sostenible. En este análisis se llevan a cabo simulaciones numéricas del comportamiento del viento y del efecto denominado vórtices de von Karman que produce al rodear la estructura del aerogenerador utilizando como datos de entrada las velocidades del viento medidas por la Estación Meteorológica Mariscal Sucre en Quito. Las simulaciones CFD determinan la señal de excitación causada por los diferentes flujos de viento existentes. Asimismo, los efectos que estas oscilaciones causan en la estructura se simulan a través de un estudio modal y respuesta armónica a resonancia. Los resultados obtenidos muestran un aumento proporcional en la frecuencia y amplitud del desprendimiento de vórtices al aumento de la velocidad del viento, lo que provoca diferentes señales de excitación que hacen que el aerogenerador oscile con amplitudes entre 6 a 11 cm. Finalmente, las simulaciones transitorias muestran que la presencia de casas y edificios en las cercanías en donde se instala el aerogenerador hacen que la dirección de la calle de vórtices varíe, así como las alteraciones en la frecuencia y amplitud de la excitación.

Here we present a machine learning–based wind reconstruction model. The model reconstructs hurricane surface winds with XGBoost, which is a decision-tree-based ensemble predictive algorithm. The model treats the symmetric and asymmetric wind fields separately. The symmetric wind field is approximated by a parametric wind profile model and two Bessel function series. The asymmetric field, accounting for asymmetries induced by the storm and its ambient environment, is represented using a small number of Laplacian eigenfunctions. The coefficients associated with Bessel functions and eigenfunctions are predicted by XGBoost based on storm and environmental features taken from NHC best-track and ERA-Interim data, respectively. We use HWIND for the observed wind fields. Three parametric wind profile models are tested in the symmetric wind model. The wind reconstruction model’s performance is insensitive to the choice of the profile model because the Bessel function series correct biases of the parametric profiles. The mean square error of the reconstructed surface winds is smaller than the climatological variance, indicating skillful reconstruction. Storm center location, eyewall size, and translation speed play important roles in controlling the magnitude of the leading asymmetries, while the phase of the asymmetries is mainly affected by storm translation direction. Vertical wind shear impacts the asymmetry phase to a lesser degree. Intended applications of this model include assessing hurricane risk using synthetic storm event sets generated by statistical–dynamical downscaling hurricane models.

A novel winding configuration named “integrated winding” was proposed to realize function of original two sets of windings, i.e. produces two independent-control magnetic fields with different pole-pairs (not slot-harmonics). The concrete realization method is through the coordinated operation of controllers, two current components with different phases are injected into the same coil to generate required magnetic fields according to star of slots. Because the magnetic field produced by the winding is only related to the instantaneous current in each coil, rather than specific connection of coils. The integrated winding not only simplifies the winding configuration, but also increases the electric loading, thus, improving torque density. The general method of integrated winding configuration and current injection rule are established. The split-phase rules of integrated winding are summarized and the feasibility of six-phase and twelve-phase integrated windings is then proved through finite element analysis (FEA). A prototype is fabricated and the experimental results verify the availability of the integrated winding.

Atmospheric turbulence is an intrinsic factor that causes uncertainty of wind speed and its power generation by wind turbine. The research of atmospheric turbulence characteristics of wind farms can be used to reduce this uncertainty. In this paper, enough measurement data getting from actual wind farms is used for information processing to quantitatively analyze the daily variation of wind speed and its power output characteristics. Furthermore, the concept of spatiotemporal diurnal modulation characteristics of atmospheric turbulence is proposed with a global scope, which is an intrinsic property of wind. Besides the daily variation characteristics, the average hourly wind speed has a short-term modulation effect on its turbulence and provides a modulation characteristic on wind speed uncertainty. Moreover, the long-term modulation process is affected by seasonal and regional factors, indicating that it has spatiotemporal characteristics. This atmospheric turbulence characteristic has similar effects on characteristic description parameters. However, the characteristics description parameters of wind speed and wind power variation fail to reflect such intrinsic characteristics that are not affected by the spatiotemporal diurnal modulation characteristics of atmospheric turbulence. This indicates that they do not have diurnal characteristics. Finally, a time-varying model combined with the spatiotemporal diurnal modulation characteristics of wind speed and its power generation is discussed by applying on the evaluation of frequency control in power systems. It is shown that the results obtained by measured data processing could improve the power generation quality of large-scale wind power effectively.

We have examined variations in electron density Ne at ionospheric F1-layer heights during geomagnetic storms at the Irkutsk ionospheric station (52° N, 104° E). We have selected geomagnetic storms of varying intensity as well as quiet days for each event for the winter and summer seasons of 2003. We have analyzed the electron density in the daytime during geomagnetic storms at 150–190 km heights. Different effects of geomagnetic storms on Ne in different seasons at these heights were found. There is a slight change in the electron density during summer geomagnetic storms. On the other hand, there is an interesting effect in winter indicating the summer-winter asymmetry of the Ne response to the geomagnetic storms at these heights in 2003: in winter there is a significant influence of disturbances on Ne at a height of 190 km and a smaller effect at lower heights.

The torus is a promisingly potential alternative to traditionally cylindrical pressure vessels due to its capability to store more hydrogen energy within limited space. Constant angle winding is widely used in practical filament winding. Hence, it is necessary to study constant angle winding on the torus. This paper presents constant winding angle curve on torus, a new winding trajectory, and gives a sufficient and necessary condition that makes it nonslip and non-bridging, and a computational formula for determining the lower bound of the winding angle of stable constant winding angle curve. By combining with semi-geodesics, we propose an integration design method for winding pattern and develop a computer aided path design system for filament winding torus, which can design constant angle winding pattern or approximate equilibrium winding for toroidal composite pressure vessels. Since our approach uses constant winding angle curve and integration trajectories besides semi-geodesics, our method has more design space for optimizing fiber path, and outperforms the existing methods.

The emergence of flexible AC transmission technology provides a new technical means for ensuring the reliable grid connection and stable operation of wind farms. Among them, the static reactive power generator has a fast response speed, which can accurately compensate for the reactive power of the wind farm and improve the power factor; this is widely used in wind farms. To obtain accurate static var generator (SVG) parameters to meet the reliability requirements of a power system, we propose an adaptive estimation method that considers the wind speed fluctuation of wind farms. First, analyzing the dynamic SVG characteristics allowed us to establish a mathematical model. Then, the corresponding relationship between the sensitivity values of the parameters to be identified and the fluctuating wind speed was established, and low and high wind speed models were constructed. Finally, for accurate estimation considering wind speed fluctuation, the parameter initial values are obtained by combining the low wind speed and high wind speed model identification parameters, and we introduce the multimode hybrid estimation of the SVG parameters, providing a new method for accurately identifying the SVG model parameters. The simulation results of the parameter estimation demonstrate the accuracy and stability of the proposed method.

Wind energy, a highly popular renewable clean energy, has been increasingly valued by the international community and been leaping forward. However, the original wind speed signal characterized by intermittent fluctuations impose heavy burdens on wind speed forecasting of wind farms. This study proposed a wind speed forecasting method by complying with a model integrating the Variational Mode Decomposition (VMD) and the Improved Multi-Objective Dragonfly Optimization Algorithm (IMODA). First, the VMD was adopted to decompose the original wind speed signal, as an attempt to obtain multiple sub-sequences (IMFs) exhibiting stable frequency domain. Second, to simplify the calculation, the sample entropy (SE) was adopted for the sequence recombination, and the respective recombined sub-sequence of the wind speed was forecasted by using four advanced neural networks. Lastly, the IMODA algorithm was adopted to fuse the forecasting results of the neural network, and the results of the optimal wind speed were forecasted. To verify the effectiveness and adaptability of the algorithm, the wind farm data in four different regions were forecasted. As indicated from the results, this algorithm could outperform other algorithms in the comprehensive forecasting accuracy and the model calculation time, and it could be effectively applied for the wind speed forecasting in wind farms.

Majority of spacecrafts rely on solar power as the main source of energy. The search for a lightweight and cost-efficient energy source with high power conversion efficiency (PCE) led to the development of organic-inorganic metal halide Perovskite solar cells (PSCs). In this paper, the performance of PSCs with different hole-transport material (HTM) prepared for in-orbit demonstration mission onboard CubeSats are compared under simulated space environment such as thermal cycling stress, high-vacuum, UV radiation and vibration. Results show that even though organic and inorganic HTM display superior initial PCE, Carbon HTM PSCs trumps them in terms of stability and is more practical for use in space. The paper also discusses the satellite mission and developed hardware for the first demonstration of Perovskite solar cells on-board a satellite to gather in-orbit information on the performance of Perovskite solar cells in low-earth orbit and how the ground test results would be verified.

The article considers proposed methodological and technical solutions aimed at improving the accuracy of dropping cargo from aircraft by taking into account the wind speed. The characteristics of lidars of different types, capable of measuring the wind speed both near the aircraft and near the Earth's surface, are discussed. The results of experiments on measuring the wind speed profile at low altitudes in the airfield area are presented. The results of modeling the trajectory of an uncontrollable load falling in wind conditions show that taking into account the wind speed significantly increases the drop accuracy. The cargo was modeled as a sphere of a specified mass with specified aerodynamic coefficients. The effect of the completeness of information about the distribution of wind speed over height on the drop accuracy is shown. In particular, options are compared when the wind speed is measured near the aircraft and near the surface of the earth. The drop accuracy indicators obtained in the course of simulation are given

In this paper, the direct current (DC) winding induced voltage in wound-field flux-switching (WFFS) machines is qualitatively analyzed with air-gap field modulation principle. Operation principle and effective harmonics of DC winding induced voltage are modelled and deduced. It is found that only air-gap field harmonics with specific spatial orders, which numerically equals to odd times of half stator poles, can contribute to DC winding induced voltage. Harmonic order of DC winding induced voltages under open-circuit only, armature reaction only, and on-load condition, are predicted for m-phase WFFS machines with any feasible stator/rotor pole number combinations. Different armature winding configurations, including concentrated winding and distributed winding, are also analyzed and compared using the winding factor. Finite element analysis is employed to verify the prediction results. Finally, a prototype is built and tested for validation.

Underwater navigation system is an indispensable part for autonomous underwater vehicles. Due to the indiscernibility of satellite signal, however, the underwater navigation problem is quite challenging, and a satellite-free navigation scheme should be looked for. Polarization navigation, inspired by insects’ capability of autonomous homing and foraging, is an alternative solution to satellite navigation with great application potential. Underwater polarization provides an indirect sun compass to animals for orientation determination. However, it is difficult to apply terrestrial solar-tracking methodologies in underwater situations due to the refraction of polarized skylight at the air–water interface. To resolve this issue, an underwater solar-tracking algorithm is developed based on the underwater refraction-polarization pattern inside the Snell's window. By employing Snell's law and Fresnel refraction formula to decouple the refractive ray bending and polarization deflection, the celestial polarization pattern is obtained based on underwater measurement. To further improve the accuracy, the degree of polarization is employed as a weight factor for E-vector. A long-lasting underwater experiment was conducted to validate the effectiveness of the proposed approach, and the results showed the root-mean-square errors of solar zenith and azimuth employing this algorithm were 0.3° and 1.3°, respectively. Our experimental results show that the refraction-polarization pattern inside the Snell's window exhibits immense potential to improve the solar-tracking accuracy for underwater navigation.

A short review of the pattern and morphology of the equatorial plasma drift velocities, particularly during the evening-time Pre-reversal enhancement (PRE) period in the African region had been presented. The seasonal PRE peak values across some locations in the West-African region were considered and compared with other sectors of the world. While most plasma drift observations in the African region were calculated from ionosonde measurements, the observations from other sectors involved direct measurement from satellite and the Incoherent Scatter Radar (ISR) observations. The importance of the PRE in ionospheric electrodynamics was highlighted, the better in the use of either the virtual or real heights of the F-layer in inferring vertical drift velocities were enumerated, revealing the strengths and weakness of each method. The general observations revealed that PRE peak magnitude is commonly weaker in the African region in comparison with the American/Peruvian and Indian sectors, seasonal and solar activity dependent, and could be higher during either magnetic quiet or disturbed activity than when both magnetic activity conditions are combined. The first work to present a regional PRE model around the African equatorial ionization anomaly region (Adebesin et al model) was mentioned. The relevance of the E × B drift in quantifying the daytime equatorial electrojet (EEJ) current was also discussed.

Very low Earth orbits (VLEOs) have been proposed as a beneficial space mission regime due to their propensity to increase instrument spatial resolution and reduce launch cost per unit mass. However, for visual instruments, these benefits come at the cost of a decreased instrument swath width. This reduction results in longer revisit periods for regions on Earth and longer time until global coverage is achieved. Conversely, light detection and ranging (lidar) as an active remote sensing technique, can benefit from larger swath widths at lower altitudes, due to the increased signal-to-noise ratio. Investigation of this relationship shows that lidar swath width is inversely proportional to altitude squared, and, as a result, the number of spacecraft required to provide a desired lidar coverage also decreases approximately in inverse proportion to altitude squared. Investigation of suitable propulsion systems shows that although propellant mass and number of thrusters required for orbit maintenance increases with decreasing altitude, the overall system mass, and hence launch cost, will, in general, tend to decrease with decreasing altitude due to the lower number of spacecraft required. For a given mission, spacecraft bus, and propulsion system, a VLEO altitude can be identified that will result in the minimum overall mission cost.

The Madden–Julian oscillation (MJO) and the boreal summer intraseasonal oscillation (BSISO) are fundamental modes of variability in the tropical atmosphere on the intraseasonal time scale. A linear model, using a moist shallow water equation set on an equatorial beta plane, is developed to provide a unified treatment of the two modes and to understand their growth and propagation over the Indian Ocean. Moisture is assumed to increase linearly with longitude and to decrease quadratically with latitude. Solutions are obtained through linear stability analysis, considering the gravest (n = 1) meridional mode with nonzero meridional velocity. Anomalies in zonal moisture advection and surface fluxes are both proportional to those in zonal wind, but of opposite sign. With observation-based estimates for both effects, the zonal advection dominates, and drives the planetary-scale instability. With a sufficiently small meridional moisture gradient, the horizontal structure exhibits oscillations with latitude and a northwest–southeast horizontal tilt in the Northern Hemisphere, qualitatively resembling the observed BSISO. As the meridional moisture gradient increases, the horizontal tilt decreases and the spatial pattern transforms toward the “swallowtail” structure associated with the MJO, with cyclonic gyres in both hemispheres straddling the equatorial precipitation maximum. These results suggest that the magnitude of the meridional moisture gradient shapes the horizontal structures, leading to the transformation from the BSISO-like tilted horizontal structure to the MJO-like neutral wave structure as the meridional moisture gradient changes with the seasons. The existence and behavior of these intraseasonal modes can be understood as a consequence of phase speed matching between the equatorial mode with zero meridional velocity (analogous to the dry Kelvin wave) and a local off-equatorial component that is characterized by considering an otherwise similar system on an f plane.

Atmospheric escape of close-in exoplanets can be driven by high energy radiation from the host star. The planetary outflows interacting with the stellar wind may generate observable transit signals that depend on the strength of the stellar wind. We perform detailed radiation-hydrodynamics simulations of the atmospheric escape of hot Jupiters with including the wind from the host star in a self-consistent, dynamically coupled manner. We show that the planetary outflow is shaped by the balance between its thermal pressure and the ram pressure of the stellar wind. We use the simulation outputs to calculate the Lyman-$\alpha$ and H$\alpha$ transit signatures. Strong winds can confine the outflow and decrease the Lyman-$\alpha$ transit depth. Contrastingly, the wind effect on H$\alpha$ is weak because of the small contribution from the uppermost atmosphere of the planet. Observing both of the lines is important to understand the effect of the UV radiation and wind from the host. The atmospheric mass-loss rate is approximately independent of the strength of the wind. We also discuss the effect of the coronal mass ejections on the signatures. We argue that around M dwarfs the effect can be significant in every transit., Comment: 5 pages, 4 figures, accepted for publication in MNRAS

In this paper, the drivetrain identification problem of a horizontal axis gear-driven wind turbine has been considered. The identification problem leads to a precise model of the drivetrain of the wind turbines which plays a key role in the production and transmission of electrical energy. This process consists of two stages: First, offline identification which needs the input–output data from the drivetrain system. These data are obtained from the FAST code. FAST (Fatigue, Aerodynamics, Structures, and Turbulence) is a valid aeroelastic code in the simulation aeroelastic field of offshore and onshore wind turbines. In region 2 (wind velocity is between the cut-in and rated velocities), the generator torque is input, and rotor speed is output. It is supposed that the wind velocity is neglected in the identification process (the identification process is not considered in the presence of wind or done in the low wind velocities bellower than the cut-in wind velocity). In the second stage, after completion of the offline identification process, the drivetrain model of the wind turbine is obtained but the aerodynamic torque in the real performance of the wind turbine is still unknown. In this stage, to estimate the aerodynamic torque, high order sliding mode estimator is used and the unknown states are estimated by using the Extended Kalman Filter (EKF)

In the Martian atmosphere, CO2 clusters are predicted to exist at high altitudes motivating a deeper understanding of their photochemistry. Here the authors use quantum chemistry calculations and multi-coincidence mass spectrometry to show that a size-dependent structural transition enhances the production of $${{{{{{{{\rm{O}}}}}}}}}_{2}^{+}$$ O 2 + from photoionized CO2 clusters.

This paper examines if wind might be an additional energy source for solar powered, crewed Mars missions during dusty days. Wind data from Viking Lander 2 is analyzed from a wind engineering point of view, as it is done on Earth, to evaluate wind turbine sites. It is assumed that wind energy will not be the primary energy source used on a crewed Mars mission but an additional option during times of global dust storms, when solar power is suffering from an increase of atmospheric optical depth, which is seen as one of the largest drawbacks of solar arrays. In order to evaluate if wind energy might be a reliable energy source during dust storms, when the energy yield of solar cells is reduced, it will be investigated whether wind strength has a positive correlation with increased atmospheric optical depth. This is, in case wind speed is generally capable of providing a significant amount of power, a further requirement if wind turbines should compensate the power loss of solar arrays during increased atmospheric optical depth. For a first estimate of the amount of wind turbines needed to maintain energy output during a storm a case study is done which regards power production during the 1977b global dust storm.

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly in the eastern region. However, there are still few reports on the spread-F over Argentina owing to a lack of ionosonde data. This work presents the analysis of the spread-F (range spread-F and frequency spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucuman, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data show that spread-F and plasma bubble occurrence rates peak in local summer and are minimum in equinox and winter, respectively. There is a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities.

El Niño and La Niña exhibit asymmetric evolution characteristics during their decay phases. The decay speed of El Niño is significantly greater than that of La Niña. This study systematically and quantitatively investigates the relative contributions of the equatorial western Pacific (WP) and central-eastern Pacific (CEP) wind stress anomalies to ENSO decay and its asymmetry through data analysis, numerical experiments, and dynamic and thermodynamic diagnoses. It is demonstrated that the sea surface temperature anomalies (SSTAs) forced by the wind stress anomalies in the equatorial CEP play a dominant role in ENSO decay and contribute to ENSO decay asymmetry, while the forcing by the equatorial WP wind stress anomalies has a small contribution. Diagnoses of the oceanic mixed layer heat budget indicate that anomalous zonal advection term and vertical advection term forced by the wind stress anomalies in the equatorial CEP are the most important dynamic terms contributed to ENSO decay. Both terms in El Niño decay phase are much larger than in La Niña decay phase, resulting in a larger decay speed in El Niño than in La Niña. The contributions of these two terms do not depend on the equatorial WP wind field, confirming that the equatorial WP wind stress anomalies do not act as a pivotal part in ENSO asymmetric decay. Moreover, it is demonstrated that within the equatorial CEP, dominant contribution comes from the wind stress anomalies in the equatorial central Pacific, in which those in the equatorial southern central Pacific play a major role. Significance Statement Previous studies proposed why wind fields in the equatorial western Pacific (WP) or central-eastern Pacific (CEP) are asymmetric and how the asymmetric wind fields affect ENSO decay and decay asymmetry. By using an oceanic general circulation model, we quantitatively estimate the relative contributions of the wind stress anomalies over the equatorial WP and CEP. It is demonstrated that the wind stress anomalies over the equatorial CEP and the associated ocean response play a dominant role in the asymmetric decay. Additionally, it is further illustrated the predominant role comes from the wind stress anomalies in the equatorial southern central Pacific within the equatorial CEP. Our study provides a physical explanation on the ENSO decay and its asymmetry.

Jupiter’s atmosphere is one of the most turbulent places in the solar system. Whereas observations of lightning and thunderstorms point to moist convection as a small-scale energy source for Jupiter’s large-scale vortices and zonal jets, this has never been demonstrated due to the coarse resolution of pre-Juno measurements. The Juno spacecraft discovered that Jovian high latitudes host a cluster of large cyclones with diameter of around 5,000 km, each associated with intermediate- (roughly between 500 and 1,600 km) and smaller-scale vortices and filaments of around 100 km. Here, we analyse infrared images from Juno with a high resolution of 10 km. We unveil a dynamical regime associated with a significant energy source of convective origin that peaks at 100 km scales and in which energy gets subsequently transferred upscale to the large circumpolar and polar cyclones. Although this energy route has never been observed on another planet, it is surprisingly consistent with idealized studies of rapidly rotating Rayleigh–Bénard convection, lending theoretical support to our analyses. This energy route is expected to enhance the heat transfer from Jupiter’s hot interior to its troposphere and may also be relevant to the Earth’s atmosphere, helping us better understand the dynamics of our own planet.

Energetic particle precipitation associated with pulsating aurora (PsA) can reach down to lower mesospheric altitudes and deplete ozone. It is well documented that pulsating aurora is a common phenomenon during substorm recovery phases. This indicates that using magnetic indices to model the chemistry induced by PsA electrons could underestimate the energy deposition in the atmosphere. Integrating satellite measurements of precipitating electrons in models is considered to be an alternative way to account for such an underestimation. One way to do this is to test and validate the existing ion chemistry models using integrated measurements from satellite and ground-based observations. By using satellite measurements, an average or typical spectrum of PsA electrons can be constructed and used as an input in models to study the effects of the energetic electrons in the atmosphere. In this study, we compare electron densities from the EISCAT (European Incoherent Scatter scientific radar system) radars with auroral ion chemistry and the energetics model by using pulsating aurora spectra derived from the Polar Operational Environmental Satellite (POES) as an energy input for the model. We found a good agreement between the model and EISCAT electron densities in the region dominated by patchy pulsating aurora. However, the magnitude of the observed electron densities suggests a significant difference in the flux of precipitating electrons for different pulsating aurora types (structures) observed.

To mitigate uncertainties in wind resource assessments and to improve the estimation of energy production of a wind project, this work uses a decision tree machine learning model to assess the effectiveness of hub-height wind speed, rotor-equivalent wind speed, and lapse rate as variables in power prediction. Atmospheric data is used to train regression trees and correlate the power outputs to wind profiles and meteorological characteristics to be able to predict power responses according to physical patterns. The decision tree model was trained for four vertical wind profile classifications to showcase the need for multiple calculations of wind speed at various levels of the rotor layer. Results indicate that when compared to traditional power curve methods, the decision tree combining rotor-equivalent wind speed and lapse rate improves prediction accuracy by 22% for the given data-set, while also proving to be the most effective method in power prediction for all classified vertical wind profile types. Models incorporating lapse rate into predictions performed better than those without it, showing the importance of considering atmospheric criteria in wind power prediction analyses.

This study formulates three-dimensional (3D) residual flow, treating both stationary and transient waves. The zonal and meridional momentum equations contain four terms: the geostrophic wind tendency, Coriolis force for the residual horizontal flow, product of the geostrophic wind and potential vorticity other than the constant planetary vorticity, and friction. The thermodynamic equation contains three terms: the potential temperature tendency, advection of the basic potential temperature by the residual vertical flow, and diabatic heating. The zonal mean of the 3D residual flow equals the time mean of the residual flow of the transformed Eulerian-mean equations. The new residual flow is the sum of that derived by Plumb for transient waves and the quadratic terms of the time-mean fields, which correspond approximately to the Stokes correction due to stationary waves. The 3D residual flow and momentum equations are symmetric in the zonal and meridional directions, in contrast with those formulated by Kinoshita et al., which treat the time-mean zonal-mean zonal wind as the basic wind. The newly derived formulas are applied to the climatology of the 3D structure of the deep branch of the Brewer–Dobson circulation. In the Northern Hemisphere in December–February, the residual flows are directed inward toward the polar vortex strongly over east Siberia, where the downward flow is maximized, and weakly over the Atlantic; meanwhile, they are directed outward from the vortex over North America and Europe. A longitudinal dependence of the poleward flow is also observed in the Southern Hemisphere in June–August.

The conversion of electricity to chemical energy is a key technology for absorbing the fluctuations of electricity and utilizing solar and wind-powered electricities as chemical fuels.

The paper discusses the issues of the disturbances allocations in the ionosphere that are associated with large atmospheric events - tropical cyclones of the 4–5 categories of 2014. On the basis of the characteristic spatio-temporal characteristics of the acoustic-gravity waves from atmospheric disturbances, the method is proposed for the detection of relative disturbances of the electron concentration in the frequency band characteristic of the disturbances. The observation of electron density by Langmuir probes carried out on the ESA Swarm satellites were used as experimental data. In the paper we consider all large 2014 Tropical Cyclones (TC) and discuss the statistics of the identified disturbances from TC in the ionosphere against the background of regular changes in the electron density in quiet geo-heliomagnetic conditions. The obtained results show that the wave mechanism of disturbance transmission from an atmospheric source to ionospheric heights is not the only one.

Absorption level by riometer was estimated at high-latitudes during four moderate magnetic storms that occurred in 2018 and were similar by several features. The data of riometer absorption at 30 MHz was obtained from Sodankyla Geophysical Observatory in Finland (67.36°N, 26.63°E). Particle precipitations were estimated by POES satellite data. According to our results, the character of development of the magnetic disturbance and the similarity/difference of Space Weather parameter variations (IMF magnitude, solar wind parameters, Dst variation) did not played the leading role in the absorption peak value. The absorption level in the auroral oval during the considered similar moderate magnetic disturbances depended on the combination of factors: simultaneous electron bursts of particular energies, the number of precipitating particles in these bursts and the moment of the storm at which such precipitation bursts occurred. The highest absorption was caused by the large electron precipitations with energies of >40 keV and >130 keV that occurred just after the maximal storm development at the very beginning of the recovery phase of the storm.

The two leading perturbations acting on satellites in the orbital decay region of low Earth orbit are gravitational nonsphericity of the Earth and atmospheric drag. A detailed understanding of thei...

This article presents a novel approach for the joint estimation of satellite attitude and size based on inverse synthetic aperture radar (ISAR) image interpretation and parametric optimization. The satellite's solar panel, which is segmented from the ISAR image by employing pix2pix generative adversarial network (Pix2pixGAN), is chosen for investigation in this article due to its unique rectangular structure. We innovatively use the principal component analysis (PCA) to explore the satellite solar panel's structural features in an ISAR imagery. The projection matrix is then established to link the extracted features and the satellite's absolute attitude and size. Parametric optimization is established based on the relationship between the extracted features and the satellite's absolute attitude and size. A Broyden-Fletcher-Goldfarb-Shanno (BFGS)-based fast iterative search algorithm is employed to search the satellite's absolute attitude and size simultaneously through an iterative approach. The simulation data are generated from actual satellite orbital parameters and computer-aided-design (CAD) models of the Aqua satellite in the experiments. Simulation experiments verify the effectiveness of the proposed method.

The coupled dynamics of turbulent airflow and a spectrum of waves are known to modify air–sea momentum and scalar fluxes. Waves traveling at oblique angles to the wind are common in the open ocean, and their effects may be especially relevant when constraining fluxes in storm and tropical cyclone conditions. In this study, we employ large-eddy simulation for airflow over steep, strongly forced waves following and opposing oblique wind to elucidate its impacts on the wind speed magnitude and direction, drag coefficient, and wave growth/decay rate. We find that oblique wind maintains a signature of airflow separation while introducing a cross-wave component strongly modified by the waves. The directions of mean wind speed and mean wind shear vary significantly with height and are misaligned from the wind stress direction, particularly toward the surface. As the oblique angle increases, the wave form drag remains positive, but the wave impact on the equivalent surface roughness (drag coefficient) rapidly decreases and becomes negative at large angles. Our findings have significant implications for how the sea-state-dependent drag coefficient is parameterized in forecast models. Our results also suggest that wind speed and wind stress measurements performed on a wave-following platform can be strongly contaminated by the platform motion if the instrument is inside the wave boundary layer of dominant waves. Significance Statement Surface waves increase friction at the sea surface and modify how wind forces upper-ocean currents and turbulence. Therefore, it is important to include effects of different wave conditions in weather and climate forecasts. We aim to inform more accurate forecasts by investigating wind blowing over waves propagating in oblique directions using large-eddy simulation. We find that waves traveling at a 45° angle or larger to the wind grow as expected, but do not increase or even decrease the surface friction felt by the wind—a surprising result that has significant implications for how oblique wind-waves are represented as a source of surface friction in forecast models.

Air–sea momentum and scalar fluxes are strongly influenced by the coupling dynamics between turbulent winds and a spectrum of waves. Because direct field observations are difficult, particularly in high winds, many modeling and laboratory studies have aimed to elucidate the impacts of the sea state and other surface wave features on momentum and energy fluxes between wind and waves as well as on the mean wind profile and drag coefficient. Opposing wind is common under transient winds, for example, under tropical cyclones, but few studies have examined its impacts on air–sea fluxes. In this study, we employ a large-eddy simulation for wind blowing over steep sinusoidal waves of varying phase speeds, both following and opposing wind, to investigate impacts on the mean wind profile, drag coefficient, and wave growth/decay rates. The airflow dynamics and impacts rapidly change as the wave age increases for waves following wind. However, there is a rather smooth transition from the slowest waves following wind to the fastest waves opposing wind, with gradual enhancement of a flow perturbation identified by a strong vorticity layer detached from the crest despite the absence of apparent airflow separation. The vorticity layer appears to increase the effective surface roughness and wave form drag (wave attenuation rate) substantially for faster waves opposing wind. Significance Statement Surface waves increase friction at the sea surface and modify how wind forces upper-ocean currents and turbulence. Therefore, it is important to include effects of different wave conditions in weather and climate forecasts. We aim to inform more accurate forecasts by investigating wind blowing over waves propagating in the opposite direction using large-eddy simulation. We find that when waves oppose wind, they decay as expected, but also increase the surface friction much more drastically than when waves follow wind. This finding has important implications for how waves opposing wind are represented as a source of surface friction in forecast models.

The article has considered an approach to determining the minimum of the secondary winding coils turns of a transformer three-phase-multiphase phase number converter. Each phase of the secondary winding of the considered converter consists of three coils connected in series placed on three different rods of the magnetic circuit. In order to solve the optimization problem, the interior-point method is used. As an example, for a three-phase-five-phase converter has determined the minimum number of turns of the secondary winding, the total power consumed by the coils of the secondary winding is calculated. A vector diagram EMF of the coils of the secondary winding is constructed, explaining the formation of a symmetrical five-phase EMF system at the terminals of the secondary winding. Using the proposed approach, it is possible to design a transformer converter of the number of phases with a three-phase primary winding and a multiphase secondary winding, the number of phases of which is more than two.

A simplified model for the position of the sun at any location on earth is shown to produce fairly accurate results when compared to values calculated in a spreadsheet from the United States National Oceanic and Atmospheric Administration (NOAA). A straightforward derivation of the model is presented, in which all terms and parameters have clear physical meaning. In the first version of the model, the only parameters are the tilt of the earth's axis and the date and time of the nearest northern hemisphere winter solstice. The differences between the elevation and azimuth calculated using the model and the NOAA results are typically a few degrees or less, and it is seen that the primary cause of these differences is the eccentricity of the earth's orbit. A simple correction is then added to the model, in which the only parameters are the earth's orbital eccentricity and the date and time of the perihelion nearest the solstice already in the model. This removes most of the differences between the model and the NOAA results. The model is shown to work in both the northern and southern hemispheres.

In general, although the climate during the Holocene has been warm, nine well-recognized cold events with an average time interval of more than one thousand years have been highlighted. The forcing mechanism of these cold events with millennial-scale cycles is still widely discussed. In the present study, two different Solar System dynamical processes collectively driven by all eight planets were considered together: the solar inertial motion and the combined planetary tidal force acting on the Sun. In this context, an attempt was made to analyze their effects on solar activity and Holocene North Atlantic cold events at the millennial-scale. These two Solar System dynamical processes were proxied by the distance between the Sun and the Solar System barycenter (DS–S) and the intensity of the combined planetary tidal force (IP–S), respectively. Using the ensemble empirical mode decomposition (EEMD) method, time series data of Solar System dynamics proxies (i.e., DS–S, and IP–S), solar activity proxies (i.e., 14C and 10Be), and a proxy of Holocene North Atlantic cold events (i.e., hematite-stained grains) were decomposed into several intrinsic mode functions (IMFs). After extracting IMF components containing millennial-scale cycles, a correlation analysis was performed. As a result, it was found that the solar inertial motion had ~2,300- and ~1,000-year cycles and the combined planetary tidal force had a ~1,500-year cycle, while the solar activity and Holocene North Atlantic cold events proxies had ~2,300-, ~1,500-, and ~1,000-year cycles, respectively. The correlation analysis revealed that the millennial-scale periodic components of the two Solar System dynamics proxies were largely correlated with that of solar activity and Holocene North Atlantic cold events, suggesting that the solar inertial motion and combined planetary tidal force may work together to impact solar activity, and thus the climate in the North Atlantic. Consequently, solar activity was weaker and the North Atlantic temperature was cooler when the Sun was far from the Solar System barycenter and/or the combined planetary tidal force was weakened. This might indicate the involvement of Solar System dynamics on Holocene North Atlantic cold events at the millennial-scale.

Earth’s upper atmosphere over low latitudes is influenced by the equatorial electrodynamics. Its influence can also be modulated by the thermospheric winds. The effect of these two forces on the thermospheric neutral behaviour in the daytime can be investigated by measuring the variations in the OI 630.0 nm dayglow emission rates as these serve as effective tracers of the altitude region of their origin. The capability to measure dayglow emissions over a large field-of-view presents a unique opportunity to investigate the upper atmospheric behaviour over large spatial extents. Diurnal measurements of OI 630.0 nm dayglow emission rates have been carried out from two different locations in India using multi-wavelength imaging echelle spectrographs, MISE, which, together cover a spatial range from 5 ° -18 ° magnetic latitude. These investigations have been carried out during January-February 2020 (winter season) when solar flux variation was nearly negligible (varied only by 4 solar flux unit from 68-72 solar flux unit). Therefore, latitudinal variations in the daily averaged oxygen dayglow emission intensities have been analyzed to assess their response to the variations in the strength of the equatorial electrodynamics and the meridional winds. The results reveal that these forces show varying effects with the poleward meridional wind contributing to an enhancement in the OI 630.0 nm dayglow emission rates closer to the magnetic equator and a decrement as one moves away from the equator. The equatorial electric field effect, however, continues to be equally effective in the low-latitudes region under consideration.