Analysis and Simulation of the Stratospheric Quasi-zero Wind Layer over Korla, Xinjiang Province, China

The stratospheric quasi-zero wind layer (QZWL) is a transition region with low zonal wind speeds in the lower stratosphere at an altitude of ~20 km. The zonal wind direction above the QZWL layer is opposite to that below the QZWL layer and the north –south wind component is small. The atmospheric wind field near the stratospheric QZWL is an important factor affecting the flight altitude and dynamic control of stratospheric airships. It is therefore necessary to study the stratospheric QZWL to provide better environmental information for these aircraft. High-resolution radiosonde data were used to analyze the characteristics of the stratospheric QZWL over Korla, Xinjiang Province, China. A weak wind layer in which the wind direction suddenly reversed from westerly to easterly was observed at ~20 km in the lower stratosphere, characteristic of the stratospheric QZWL. The Weather Research and Forecasting model was used to simulate the profiles of the horizontal wind speed and direction over Korla. The forcing effect of each diagnostic term in the equation on the zonal wind speed was analyzed. The results showed that the advection term was the dominant factor forcing the zonal wind speed. The wave term had a secondary forcing role, although the forcing effect of the wave term on the zonal wind speed was significant in some regions.

Height Variation in the Summer Quasi-Zero Wind Layer over Dunhuang, Northwest China: A Diagnostic Study

This study investigates the variation in the stratospheric quasi-zero wind layer(QZWL)over Dunhuang,Gansu Province,China,on 9 August 2020 using sounding observations from the Dunhuang national reference station and the fifth generation of ECMWF atmospheric reanalysis data(ERA5).The QZWL over Dunhuang was located between 18.6 and 20.4 km on 9 August 2020.The South Asian high(SAH)and subtropical westerly jet jointly affected the QZWL.As the SAH retreated westward,the upper-level westerly jet over Dunhuang strengthened,and the jet axis height increased.As a result,the zonal westerly wind was lifted to a higher altitude,and the wind speed of 100–70 hPa increased,raising the QZWL.In addition,the east–west oscillation of the SAH occurred earlier than the adjustment of the QZWL altitude,which can be used as a forecasting indicator for the QZWL.To further explore the mechanism responsible for the QZWL adjustment,the forcing terms in the equations for zonal wind,kinetic energy,and vertical wind shear were analyzed.The results showed that the upper-level geopotential gradient was the basic physical factor forcing the local change in zonal wind and kinetic energy.The change in zonal wind and kinetic energy led to the uplift of the QZWL.The results revealed that the vertical shear of horizontal wind could adequately indicate the stratospheric QZWL location.

Horizontal structure of convergent wind shear associated with sporadic E layers over East Asia

At present,the main detection instruments for observing sporadic E(Es)layers are ground-based radars,dense networks of ground-based global navigation satellite system(GNSS)receivers,and GNSS radio occultation,but they cannot capture the whole picture of the horizontal structure of Es layers.This study employs the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension model(WACCM-X 2.1)to derive the horizontal structure of the ion convergence region(HSICR)to explore the shapes of the large-scale Es layers over East Asia for the period from June 1 to August 31,2008.The simulation produced the various shapes of the HSICRs elongated in the northwest-southeast,northeast-southwest,or composed of individual small patches.The close connection between Es layer critical frequency(foEs)and vertical ion convergence indicates that the HSICR is a good candidate for revealing and explaining the horizontal structure of the large-scale Es layers.

The research on boundary layer evolution characteristics of Typhoon Usagi based on observations by wind profilers

Vertically exploring the characteristics of the typhoon boundary layer（TBL） plays an important role in recognizing typhoon structure. The boundary layer radial direction and tangential wind characteristics of Typhoon Usagi based on the observational data of three boundary layer wind profiler stations along the route of Typhoon Usagi（No. 1319） and by combining with sounding data. The results show that：（1） maximum tangential wind appears in the vicinity of the eye area of Usagi, and it basically maintains a height of around 1 800 m when Usagi keeps a strong typhoon level, with the rapidly decreasing strength of Usagi after it lands, the speed of the maximum tangential wind and its vertical range both decrease;（2） the height of the maximum tangential wind is close to that of the inflow layer top of the typhoon, and is greater than that of the boundary layer estimated on the basis of Richardson number or potential temperature gradient, while the height of mixed layer judged on the basis of the signal-to-noise ratio（SNR） or its gradient is usually low;（3） the the boundary layer height can reach higher than2 100 m before Usagi lands. When the typhoon level or above is achieved, the boundary layer height observed by various stations does not change much, basically staying at between 1 200 and 1 600 m. With the decreasing strength of Usagi after its landfall, the boundary layer height rapidly drops.

Impacts of a wind stress and a buoyancy flux on the seasonal variation of mixing layer depth in the South China Sea

The seasonal variation of mixing layer depth （MLD） in the ocean is determined by a wind stress and a buoy- ance flux. A South China Sea （SCS） ocean data assimilation system is used to analyze the seasonal cycle of its MLD. It is found that the variability of MLD in the SCS is shallow in summer and deep in winter, as is the case in general. Owing to local atmosphere forcing and ocean dynamics, the seasonal variability shows a regional characteristic in the SCS. In the northern SCS, the MLD is shallow in summer and deep in winter, affected coherently by the wind stress and the buoyance flux. The variation of MLD in the west is close to that in the central SCS, influenced by the advection of strong western boundary currents. The eastern SCS presents an annual cycle, which is deep in summer and shallow in winter, primarily impacted by a heat flux on the air-sea interface. So regional characteristic needs to be cared in the analysis about the MLD of SCS.

Structures and Characteristics of the Windy Atmospheric Boundary Layer in the South China Sea Region during Cold Surges

An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations （period 〈 1 min） are nearly random and isotropic with weak coherency, but the gusty wind disturbances （1 rain〈period 〈 10 min） are anisotropic with rather strong coherency. However, in the windy atmospheric boundary layer at sea, compared with that over land, there are some pronounced differences： （1） the average horizontal speed is almost independent of height, and the vertical velocity is positive in the lower marine atmospheric boundary layer; （2） the vertical flux of horizontal momentum is nearly independent of height in the low layer indicating the existence of a constant flux layer, unlike during strong wind over the land surface; （3） the kinetic energy and friction velocity of turbulent fluctuations are larger than those of gusty disturbances; （4） due to the independence of horizontal speed to height, the horizontal speed itself （not its vertical gradient used over the land surface） can be used as the key parameter to parameterize the turbulent and gusty characteristics with high accuracy.

Non-Gaussian Lagrangian Stochastic Model for Wind Field Simulation in the Surface Layer

Wind field simulation in the surface layer is often used to manage natural resources in terms of air quality,gene flow(through pollen drift),and plant disease transmission(spore dispersion).Although Lagrangian stochastic(LS)models describe stochastic wind behaviors,such models assume that wind velocities follow Gaussian distributions.However,measured surface-layer wind velocities show a strong skewness and kurtosis.This paper presents an improved model,a non-Gaussian LS model,which incorporates controllable non-Gaussian random variables to simulate the targeted non-Gaussian velocity distribution with more accurate skewness and kurtosis.Wind velocity statistics generated by the non-Gaussian model are evaluated by using the field data from the Cooperative Atmospheric Surface Exchange Study,October 1999 experimental dataset and comparing the data with statistics from the original Gaussian model.Results show that the non-Gaussian model improves the wind trajectory simulation by stably producing precise skewness and kurtosis in simulated wind velocities without sacrificing other features of the traditional Gaussian LS model,such as the accuracy in the mean and variance of simulated velocities.This improvement also leads to better accuracy in friction velocity(i.e.,a coupling of three-dimensional velocities).The model can also accommodate various non-Gaussian wind fields and a wide range of skewness–kurtosis combinations.Moreover,improved skewness and kurtosis in the simulated velocity will result in a significantly different dispersion for wind/particle simulations.Thus,the non-Gaussian model is worth applying to wind field simulation in the surface layer.

Gustiness and coherent structure under weak wind period in atmospheric boundary layer

Statistical analysis of turbulent and gusty characteristics in the atmospheric boundary layer under weak wind period has been carried out.The data used in the analysis were from the multilevel ultrasonic anemometer-thermometers at 47 m,120 m,and 280 m levels on Beijing 325 m meteorological tower.The time series of 3D atmospheric velocity were analyzed by using conventional Fourier spectral analysis and decompose into three parts:basic mean flow(period > 10 min),gusty disturbances(1 min < period < 10 min)and turbulence fluctuations(period < 1 min).The results show that under weak mean wind condition:1)the gusty disturbances are the most strong fluctuations,contribute about 60% kinetic energy of eddy kinetic energy and 80% downward flux of momentum,although both the eddy kinetic energy and momentum transport are small in comparison with those in strong mean wind condition;2)the gusty wind disturbances are anisotropic;3)the gusty wind disturbances have obviously coherent structure,and their horizontal and vertical component are negatively correlated and make downward transport of momentum more effectively;4)the friction velocities related to turbulence and gusty wind are approximately constant with height in the surface layer.

Boundary-Layer Wind Structure in a Landfalling Tropical Cyclone

In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of the radial component is greater in the offshoreflow side and the tangential component is greater over the sea, slightly offshore, therefore the greater total wind speed occurs in the offshore-flow side over the sea. The budget analysis suggests that： （1） a greater surface friction over land produces a greater inflow and the nonlinear effect advects the maximum inflow downstream, and （2） a smaller surface friction over the sea makes the decrease of the tangential wind component less than that over land. Moreover, the boundary layer wind structures in a tropical cyclone are related to the locations of the tropical cyclone relative to the coastline due to the different surface frictions. During tropical cyclone landfall, the impact of rough terrain on the cyclone increases, so the magnitude of the radial component of wind speed increases in the offshore-flow side and the tangential component outside the radius of maximum wind speed decreases gradually.

Robust Solution for Boundary Layer Height Detections with Coherent Doppler Wind Lidar

Although coherent Doppler wind lidar(CDWL)is promising in detecting boundary layer height(BLH),differences between BLH results are observed when different CDWL measurements are used as tracers.Here,a robust solution for BLH detections with CDWL is proposed and demonstrated:mixed layer height(MLH)is retrieved best from turbulent kinetic energy dissipation rate(TKEDR),while stable boundary layer height(SBLH)and residual layer height(RLH)can be retrieved from carrier-to-noise ratio(CNR).To study the cause of the BLH differences,an intercomparison experiment is designed with two identical CDWLs,where only one is equipped with a stability control subsystem.During the experiment,it is found that the CNR could be distorted by instrument instability because the coupling efficiency from free-space to the polarization-maintaining fiber of the telescope is sensitive to the surrounding environment.In the ML,a bias up to 2.13 km of the MLH from CNR is found,which is caused by the CNR deviation.In contrast,the MLH from TKEDR is robust as long as the accuracy of wind is guaranteed.In the SBL(RL),the CNR is found capable to retrieve SBLH and RLH simultaneously and robustly.This solution is tested during an observation period over one month.Statistical analysis shows that the root-mean-square errors(RMSE)in the MLH,SBLH,and RLH are 0.28 km,0.23 km,and 0.24 km,respectively.

The Wind Structure in Planetary Boundary Layer

The investigations on the dynamies of the PBL have been developed in recent years. Some authors emphasized macro-dynamics and others emphasized micro-structure of the PBL. In this paper, we study and review some main characteristics of the wind field in the PBL from the view point connecting the macro-dynamics and micro-stucture of the PBL, thus providing the physical basis for the further research of the dynamics and the parameterization of the PBL.

Characteristics of atmospheric boundary layer structure and its influencing factors under different sea and land positions in Europe

This study identifies quantitatively the dominant contributions of meteorological factors on the development of the boundary layer heights(BLH)in the European region,based on 32 years(1990-2021)of radiosonde observations.The spatial variability of the BLH is further discussed by location,by classifying recording stations as inland,coastal,or bay.We find that the BLH in Europe varies considerably from day to night and with the seasons.Nighttime BLH is higher in winter and lower in summer,with the highest BLH recorded at coastal stations.Daytime BLH at coastal stations shows a bimodal structure with peaks in spring and autumn;at inland and bay stations,daytime BLH is lower in winter and higher in summer.The daily amplitudes of BLH at the inland and bay stations are stronger than those at coastal stations.Based on our multiple linear regression analysis and our decoupling analysis of temperature and specific humidity,we report that the development of the nighttime BLH at all types of stations is strongly dominated by the variations of surface wind speed(and,at coastal stations,wind directions).The main contributors to daytime BLH are the near-surface temperature variability at most coastal and inland stations,and,at most bay stations,the variation of the near-surface specific humidity.

Convection:a neglected pathway for downward transfer of wind energy in the oceanic mixed layer

Upper-ocean turbulent mixing plays a vital role in mediating air-sea fluxes and determining mixed-layer properties, but its energy source, especially that near the base of the mixed layer, remains unclear. Here we report a potentially significant yet rarely discussed pathway to turbulent mixing in the convective mixed layer. During convection, as surface fluid drops rapidly in the form of convective plumes, intense turbulence kinetic energy(TKE) generated via surface processes such as wave breaking is advected downward, enhancing TKE and mixing through the layer. The related power, when integrated over the global ocean except near the surface where the direct effect of breaking waves dominates, is estimated at O(1)TW, comparable to that required by maintaining the Meridional Overturning Circulation(MOC). The mechanism in question therefore deserves greater research attention, especially in view of the potential significance of its proper representation in climate models.

Wind-Driven,Double-Gyre,Ocean Circulation in a Reduced-Gravity,2.5-Layer,Lattice Boltzmann Model

A coupled lattice Boltzmann （LB） model with second-order accuracy is applied to the reduced-gravity, shallow water, 2.5-layer model for wind-driven double-gyre ocean circulation. By introducing the secondorder integral approximation for the collision operator, the model becomes fully explicit. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretization accuracy of the LB equation. The feature of the multiple equilibria solutions is found in the numerical experiments under different Reynolds numbers based on this LB scheme. With the Reynolds number increasing from 3000 to 4000, the solution of this model is destabilized from the anti-symmetric double-gyre solution to the subtropic gyre solution and then to the subpolar gyre solution. The transitions between these equilibria states are also found in some parameter ranges. The time-dependent variability of the circulation based on this LB simulation is also discussed for varying viscosity regimes. The flow of this model exhibits oscillations with different timescales varying from subannual to interannual. The corresponding statistical oscillation modes are obtained by spectral analysis. By analyzing the spatiotemporal structures of these modes, it is found that the subannual oscillation with a 9-month period originates from the barotropic Rossby basin mode, and the interarmual oscillations with periods ranging from 1.5 years to 4.6 years originate from the recirculation gyre modes, which include the barotropic and the baroclinic recirculation gyre modes.

Layered Multi-mode Optimal Control Strategy for Multi-MW Wind Turbine

The control strategy is one of the most important renewable technology,and an increasing number of multi-MW wind turbines are being developed with a variable speed-variable pitch(VS-VP)technology.The main objective of adopting a VS-VP technology is to improve the fast response speed and capture maximum energy.But the power generated by wind turbine changes rapidly because of the continuous fluctuation of wind speed and direction.At the same time,wind energy conversion systems are of high order,time delays and strong nonlinear characteristics because of many uncertain factors.Based on analyzing the all dynamic processes of wind turbine,a kind of layered multi-mode optimal control strategy is presented which is that three control strategies:bang-bang,fuzzy and adaptive proportional integral derivative(PID)are adopted according to different stages and expected performance of wind turbine to capture optimum wind power,compensate the nonlinearity and improve the wind turbine performance at low,rated and high wind speed.

贵州省不同强度区域性凝冻过程环流形势对比分析

利用贵州省84个气象站逐日观测资料以及再分析资料,对4种不同强度区域性凝冻过程进行对比分析。结果表明:500 hPa位势高度场上中高纬度的亚洲东部区域距平场呈现“+-”的分布或有切断低压分布,贝加尔湖至中国华北地区以经向环流为主;850 hPa风场上云南南部以南受偏南风和西南风控制,并且在江南至华南存在西南或西风急流,是4种不同强度凝冻过程中形势场共性特征。500 hPa高度场上中高纬度地区呈两槽一脊或一槽一脊分布;风场上850 hPa东北风回流和700 hPa西南急流形成上暖下冷的形势场,同时850 hPa形成稳定低层切变线;温度场上存在冷暖冷的夹心结构,近地面层0℃线维持在900 hPa以下,均是较强等级以上的区域性凝冻过程中形势场共性特征。而对于一般性区域性凝冻过程,500 hPa位势高度场上呈多槽脊分布,风场上是否存在东北风回流和低层切变线,温度场上是否存在冷暖冷的夹心结构以及近地面层0℃线位置等特征均不统一。温度剖面图上,当近地面层0℃线位置最低时或出现冷暖冷的夹心结构时段与凝冻过程影响范围最广、灾情最重的时间段对应。

不同风场中特高压换流站阀厅屋盖风压特性试验研究

特高压(ultra high voltage,UHV)换流站阀厅的金属屋面系统在风荷载作用下易发生屋面表层风揭事故。为深入探讨该类建筑屋面的风压极值特性,基于风洞试验分别探讨了大气边界层(atmospheric-boundary-layer,ABL)风、壁面射流、均匀湍流三种风场作用下的屋面风压特性,比较了平均风剖面、风速、风向、湍流强度等因素对屋面风压的影响。结果表明:阀厅屋盖迎风前缘负风压最大,且控制风向角在45°左右;壁面射流风场下平均风压系数与脉动风压系数均超过大气边界层风场的结果;风速对阀厅屋盖的负风压系数均值和极值影响较小,而湍流度对风压系数的极值影响较大;大气边界风场时,JGJ/T 481—2019《屋盖结构风荷载标准》的最不利风压系数建议值偏于安全;而在壁面射流风场下,阀厅屋盖全风向最不利风压系数在所有区域都大于JGJ/T 481—2019的建议值,设计中应加以重视。

星-三角接法的分数槽永磁电机匝间短路故障分析

为了分析永磁电机绕组采用星-三角(Y-△)接法时发生匝间短路故障后对电机的影响,建立了绕组在Y-△接法下分别在星形(Y)接法部分和角形(△)接法部分发生匝间短路故障的电路模型,推导得到故障发生后电机三相电流。以10极12槽永磁电机为例进行二维有限元仿真,对传统的Y接法双层绕组永磁电机和Y-△接法4层绕组永磁电机发生匝间短路故障的情况进行对比分析。仿真结果表明:在Y-△接法下匝间短路故障位置的不同对电流会有很大影响;在发生匝间短路故障后Y-△接法能降低电机的转矩脉动,降低故障发生后故障相电流中的3次谐波幅值。

基于NASA World Wind的GeoTIFF影像显示方案研究

鉴于遥感影像GeoTIFF研究过程中对地理信息的需求,提出了基于World Wind的GeoTIFF显示方案。在对World Wind分层显示进行深入研究的基础上,采用添加GeoTIFF图层的方式显示影像数据和设置影像alpha值的方式透视影像覆盖区域的地表特征。实验证明该方案能够快速地显示GeoTIFF影像,能方便地查看GeoTIFF覆盖区域的地表特征。

考虑大气稳定度的风电场等效粗糙度模型研究

目前模型未充分考虑大气稳定度的影响,针对该问题,在不同大气稳定度下,通过建立风电场边界层的动量平衡关系和揭示风电场的流动不均匀性,提出一种适用于不同大气稳定度的风电场等效粗糙度模型。采用大涡模拟方法对所提模型进行验证,结果显示该方法能有效评估大气稳定度对风电场流动不均匀性以及等效粗糙度的影响,所得等效粗糙度平均误差约10%。