The desert-oasis transition zone(DOTZ)serves as a buffer area between the desert and oasis.Understanding its wind field characteristics is of great significance for the prevention and control of aeolian disasters in t...The desert-oasis transition zone(DOTZ)serves as a buffer area between the desert and oasis.Understanding its wind field characteristics is of great significance for the prevention and control of aeolian disasters in the oasis.In this study,we used meteorological data during 2013–2019 from the portable meteorological stations at five sites(site A on the edge of the oasis,sites B,C,and D in the DOTZ,and site O in the desert)in Dunhuang,China to analyze the near-surface wind field characteristics and their causes,as well as to reveal the key role of the DOTZ in oasis protection.The results showed that the mean wind speed,frequency of sand-driving wind,and directional variability of wind decreased from west to east within the DOTZ,and wind speed was significantly affected by air temperature.The terrain influenced the prevailing winds in the region,mainly from northeast and southwest.Only some areas adjacent to the oasis were controlled by southeasterly wind.This indicated that the near-surface wind field characteristics of the DOTZ were caused by the combined effects of local terrain and surface hydrothermal difference.At site D,the annual drift potential(DP)was 24.95 vector units(VU),indicating a low wind energy environment,and the resultant drift direction(RDD)showed obvious seasonal differences.Additionally,the DOTZ played an important buffering role between the desert and oasis.Compared with the desert,the mean wind speed in the oasis decreased by 64.98%,and the prevailing wind direction was more concentrated.The results of this study will be useful in interpreting the aeolian activity of the DOTZ in Dunhuang.展开更多
This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of ...This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of maximum wind(RMW)and shape parameter of the initial vortices.The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage,reflecting the degree of size expansion at the same intensity increment.The regression coefficient increases with increased RMW and decreased,with the RMW being the primary constraint.The effect of lowering on the elevation of the regression coefficient gradually stands out when the initial RMW is large.Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure,which retards the intensification while promoting size expansion,thus substantially enhancing size expansion as the vortex intensifies.Broadening the wind field outside the RMW by reducing results in abounding convection in the outer region,which promotes size expansion.Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations,when the RMW is large,the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region,thus retarding the intensification by reducing the radial imports of vorticity near the RMW.展开更多
In order to study the impacts of wind field variations in the middle and lower troposphere on the development and structure of storms,we carried out numerical experiments on cases of severe convection in the Jianghuai...In order to study the impacts of wind field variations in the middle and lower troposphere on the development and structure of storms,we carried out numerical experiments on cases of severe convection in the Jianghuai area under the background of cold vortex on April 28,2015.The results show that the structure and development of convective storms are highly sensitive to the changes of wind fields,and the adjustment of wind fields in the middle or lower troposphere will lead to significant changes in the development and structure of storms.When the wind field in the middle or lower troposphere is weakened,the development of convective storms attenuates to some extent compared with that in the control experiment,and the ways of attenuation in the two experiments are different.In the attenuation test of wind field at the middle level,convective storms obviously weaken at all stages in its development,while for the wind field at the low level,the convective storms weaken only in the initial stage of storm.On the contrary,the enhancement of the wind field in the middle or lower troposphere is conducive to the development of convection,especially the enhancement in the middle troposphere.In contrast,the convective storms develop rapidly in this test,as the most intensive one.The wind field variations have significant impacts on the structure and organization of the storm.The enhancement of wind field in the middle troposphere facilitates the intension of the middle-level rotation in convective storm,the reduction of the storm scale,and the organized evolution of convective storms.The strengthening of the wind field in the lower troposphere is conducive to the development of the low-level secondary circulation of the storm and the cyclonic vorticity at the middle and low levels on the inflowing side of the storms.展开更多
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 stochas...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.展开更多
We examined the influences of the wind fi eld and wave-current interaction(WCI)on the numerical simulation results of typhoon-induced wind waves in the northern East China Sea(NECS)using the coupled Simulating Waves N...We examined the influences of the wind fi eld and wave-current interaction(WCI)on the numerical simulation results of typhoon-induced wind waves in the northern East China Sea(NECS)using the coupled Simulating Waves Nearshore+Advanced Circulation(SWAN+ADCIRC)model.The simulations were performed during two typhoon events(Lekima and Muifa),and two widely used reanalysis wind fields,the Climate Forecast System Version 2(CFSv2)from the National Centers for Environmental Prediction(NCEP)and the fifth-generation European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis(ERA5),were compared.The results indicate that the ERA5 and CFSv2 wind fields both reliably reproduced the wind variations measured by in-situ buoys,and the accuracy of the winds from ERA5 were generally better than those from CFSv2 because CFSv2 tended to overestimate the wind speed and the simulated significant wave height(SWH),particularly the peak SWH.The WCI effects between the two wind field simulations were similar;these effects enhanced the SWH throughout the nearshore NECS during both typhoons but suppressed the SWH on the right side of the Typhoon Muifa track in the deep and off shore sea areas.In summary,variations in the water depth and current propagation direction dominate the modulation of wave height.展开更多
This paper presents a study on the improvement of wind field hindcasts for two typical tropical cyclones, i.e., Fanapi and Meranti, which occurred in 2010. The performance of the three existing models for the hindcast...This paper presents a study on the improvement of wind field hindcasts for two typical tropical cyclones, i.e., Fanapi and Meranti, which occurred in 2010. The performance of the three existing models for the hindcasting of cyclone wind fields is first examined, and then two modification methods are proposed to improve the hindcasted results. The first one is the superposition method, which superposes the wind field calculated from the parametric cyclone model on that obtained from the cross-calibrated multi-platform(CCMP) reanalysis data. The radius used for the superposition is based on an analysis of the minimum difference between the two wind fields. The other one is the direct modification method, which directly modifies the CCMP reanalysis data according to the ratio of the measured maximum wind speed to the reanalyzed value as well as the distance from the cyclone center. Using these two methods, the problem of underestimation of strong winds in reanalysis data can be overcome. Both methods show considerable improvements in the hindcasting of tropical cyclone wind fields,compared with the cyclone wind model and the reanalysis data.展开更多
Proper Orthogonal Decomposition (POD) provides a powerful modal transformation tool for stochastic dynamics. In this paper, coherency matrix-based proper orthogonal decomposition (CPOD) is presented as an innovative f...Proper Orthogonal Decomposition (POD) provides a powerful modal transformation tool for stochastic dynamics. In this paper, coherency matrix-based proper orthogonal decomposition (CPOD) is presented as an innovative form of the POD based on cross power spectral density matrices. By introducing a discretizing scheme, the CPOD-based spectral representation method is obtained for use in stochastic simulation. Moreover, some criteria are proposed that allow the truncation order of CPOD to be conveniently determined. A numerical example to illustrate the application of the proposed method for the simulation of a wind velocity field is provided.展开更多
According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical mons...According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical monsoon area. In the period of monsoon, the directions of wind, sea wave and swell are roughly consistent. Sea wave of northeasterly is always prevailing in equatorial zone. The monsoon in winter is stronger than in summer, correspondingly, average wave height is higher, and the frequencies of high sea and heavy swell are also bigger. Both of North Indian Ocean and adjacent sea area is also monsoon area, but characteristic is opposite. This paper provides specific data of wind field and wave field and variaton for ship navigation, operation and scientific experiment in the NW Pacific Ocean.展开更多
Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar(SAR) images with high horizontal resolution.The footprints of rain cells...Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar(SAR) images with high horizontal resolution.The footprints of rain cells on SAR images are caused by the scattering and attenuation of the rain drops,as well as the downward airflow.In this study,we extract sea surface wind field and its structure caused by rain cells by using a RADARSAT-2 SAR image with a spatial resolution of 100 m for case study.We extract the sea surface wind speeds from SAR image by using CMOD4 geophysical model function with outside wind directions of NCEP final operational global analysis data,Advance Scatterometer(ASCAT) onboard European Met Op-A satellite and microwave scatterometer onboard Chinese HY-2 satellite,respectively.The root-mean-square errors(RMSE) of these SAR wind speeds,validated against NCEP,ASCAT and HY-2,are 1.48 m/s,1.64 m/s and 2.14 m/s,respectively.Circular signature patterns with brighter on one side and darker on the opposite side on SAR image are interpreted as the sea surface wind speed(or sea surface roughness) variety caused by downdraft associated with rain cells.The wind speeds taken from the transect profile which superposes to the wind ambient vectors and goes through the center of the circular footprint of rain cell can be fitted as a cosine or sine curve in high linear correlation with the values of no less than 0.80.The background wind speed,the wind speed caused by rain cell and the diameter of footprint of the rain cell with kilometers or tens of kilometers can be acquired by fitting curve.Eight cases interpreted and analyzed in this study all show the same conclusion.展开更多
As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed,...As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.展开更多
Chemical spills on complex geometry are difficult to model due to the uneven concentration distribution caused by air flow over ground obstacles. Computational fluid dynamics(CFD) is one of the powerful tools to estim...Chemical spills on complex geometry are difficult to model due to the uneven concentration distribution caused by air flow over ground obstacles. Computational fluid dynamics(CFD) is one of the powerful tools to estimate the building-resolving wind flow as well as pollutant dispersion. However, it takes too much time and requires enormous computational power in emergency situations. As a time demanding task, the estimation of the chemical spill consequence for emergency response requires abundant wind field information. In this paper, a comprehensive wind field reconstruction framework is proposed, providing the ability of parameter tuning for best reconstruction accuracy. The core of the framework is a data regression model built on principal component analysis(PCA) and extreme learning machine(ELM). To improve the accuracy, the wind field estimation from the regression model is further revised from local wind observations. The optimal placement of anemometers is provided based on the maximum projection on minimum eigenspace(MPME) algorithm. The fire dynamic simulator(FDS) generates high-resolution data of wind flow over complex geometries for the framework to be implemented. The reconstructed wind field is evaluated against simulation data and an overall reconstruction error of 9% is achieved. When used in real case,the error increases to around 12% since no convergence check is available. With parameter tuning abilities,the proposed framework provides an efficient way of reconstructing the wind flow in congested areas.展开更多
To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer(ASCAT) data and buoy data of the National Data Buoy Center(NDBC) are collo...To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer(ASCAT) data and buoy data of the National Data Buoy Center(NDBC) are collocated. Buoy wind speed is converted into neutral wind at 10 m height. Then, ASCAT data are compared with the buoy data for the wind speed and direction. Subsequently, the errors between the ASCAT and the buoy wind as a function of each wave parameter are used to analyze the wave effects. Wave parameters include dominant wave period(dpd), significant wave height(swh), average wave period(apd) and the angle between the dominant wave direction(dwd) and the wind direction. Collocated data are divided into sub-datasets according to the different intervals of each wave parameter. A root mean square error(RMSE) for the wind speed and a mean absolute error(MAE) for the wind direction are calculated from the sub-datasets, which are considered as the function of wave parameters. Finally, optimal wave conditions on wind retrieved from the ASCAT are determined based on the error analyses. The results show the ocean wave parameters have correlative relationships with the RMSE of the retrieved wind speed and the MAE of the retrieved wind direction. The optimal wave conditions are presented in terms of dpd, swh, apd and angle.展开更多
The state-of-art Computational Fluid Dynamics (CFD) codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUE...The state-of-art Computational Fluid Dynamics (CFD) codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design (CAD) technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.展开更多
An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model...An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model, it is found that the elliptical model can adequately represent the real wind field and trace the process of a typhoon storm surge. The numerically simulated results of storm surges by using the elliptical model are in good agreement with the observations and markedly better than those by using the circular model.展开更多
Using a one-level numerical diagnostic model, the features of surface wind fields in Hainan Island and Leizhou Peninsula and maritime area around it are studied. In the experiments with prevailing synoptic situation f...Using a one-level numerical diagnostic model, the features of surface wind fields in Hainan Island and Leizhou Peninsula and maritime area around it are studied. In the experiments with prevailing synoptic situation for varying seasons there are obvious deflection flows, terrain slope drafts, convergence lines, sea/land breeze and mountain/valley breeze, and difference in season accounts for the features found in the mesoscale distribution.The complex terrain and seatland distribution in the area is shown to be the important cause for the formation of varying mesoscale circulation, and close relationships between local climatic distribution feature and mesoscale circulation are then revealed.展开更多
The regional wind index influencing September precipitation in western China has been defined using the 700 hPa u and v components of NCAR/NCEP reanalysis data of 1961 to 2006. There are three regional wind field indi...The regional wind index influencing September precipitation in western China has been defined using the 700 hPa u and v components of NCAR/NCEP reanalysis data of 1961 to 2006. There are three regional wind field indices: southwest, southeast, and north, and these indices reflect the change of East Asian monsoon. The relationship between the indices was studied, and results show that they not only have a close relationship, but also have independence. Moreover, there is an obvious relationship between the wind indices and the autumn in particular the September precipitation in western China. The effect of wind indices on rain occurrence is most different: the influenced area of the southwest wind index is larger than that of the southeast wind index, and the southwest wind index is a controlling factor on autumn precipitation in western China. The weakening of southwest wind is the main cause resulting in reduction of autumn precipitation on the east side of the Tibetan Plateau.展开更多
The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins ...The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.展开更多
In this paper we propose a finite element(FE) simulation method to predict tree motion in a wind field. Two FE tree models were investigated:One model was generated based on a realistic nature-looking geometric tree m...In this paper we propose a finite element(FE) simulation method to predict tree motion in a wind field. Two FE tree models were investigated:One model was generated based on a realistic nature-looking geometric tree model,and the other was a symmetric model to investigate the influence of asymmetric material properties on tree motion. The vortex-induced vibration(VIV) theory is introduced to estimate the fluctuating wind force being exerted on tree stems and the fluid-structure interaction(FSI) analysis is also included in the simulation. The results indicate that asymmetric material properties result in the crosswind displacement of the investigated node and the main swaying direction deviation. The simulation reveals that under wind loading,a tree with leaves has much larger swaying amplitude along the wind direction and longer swaying period than a tree without leaves. However,the crosswind swaying amplitude is mainly due to branch interaction. The numerical simulation proved that the inter-action of tree branches can prevent dangerous swaying motion developing.展开更多
Based on the fast algorithm of meteorological satellite guide wind vector tracing,cloud motion wind vector is calculated. According to the different characteristics of cloud motion wind field and sounding wind field,a...Based on the fast algorithm of meteorological satellite guide wind vector tracing,cloud motion wind vector is calculated. According to the different characteristics of cloud motion wind field and sounding wind field,a method which fuses conventional data with unconventional data based on variation principle is presented. The fundamental is constructing a cost function that makes the value approach conventional data and the gradient approach unconventional data. Using this method,the conventional wind and the cloud motion wind are fused. The fused wind field has high resolution. Its wind direction approaches cloud motion wind which indicates move direction of the synoptic system,and its velocity approaches conventional wind which indicates move velocity of the synoptic system. The wind field data are used for short-time forecast of severe convective weather location,which gets a good result.展开更多
基金the National Key Research and Development Program of China(2020YFA0608403)the National Natural Science Foundation of China(42171083)the Natural Science Foundation of Gansu Province,China(23JRRA601).
文摘The desert-oasis transition zone(DOTZ)serves as a buffer area between the desert and oasis.Understanding its wind field characteristics is of great significance for the prevention and control of aeolian disasters in the oasis.In this study,we used meteorological data during 2013–2019 from the portable meteorological stations at five sites(site A on the edge of the oasis,sites B,C,and D in the DOTZ,and site O in the desert)in Dunhuang,China to analyze the near-surface wind field characteristics and their causes,as well as to reveal the key role of the DOTZ in oasis protection.The results showed that the mean wind speed,frequency of sand-driving wind,and directional variability of wind decreased from west to east within the DOTZ,and wind speed was significantly affected by air temperature.The terrain influenced the prevailing winds in the region,mainly from northeast and southwest.Only some areas adjacent to the oasis were controlled by southeasterly wind.This indicated that the near-surface wind field characteristics of the DOTZ were caused by the combined effects of local terrain and surface hydrothermal difference.At site D,the annual drift potential(DP)was 24.95 vector units(VU),indicating a low wind energy environment,and the resultant drift direction(RDD)showed obvious seasonal differences.Additionally,the DOTZ played an important buffering role between the desert and oasis.Compared with the desert,the mean wind speed in the oasis decreased by 64.98%,and the prevailing wind direction was more concentrated.The results of this study will be useful in interpreting the aeolian activity of the DOTZ in Dunhuang.
基金This study is supported by the National Natural Science Foundation of China(Grant Nos.42175073 and 41975071).
文摘This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of maximum wind(RMW)and shape parameter of the initial vortices.The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage,reflecting the degree of size expansion at the same intensity increment.The regression coefficient increases with increased RMW and decreased,with the RMW being the primary constraint.The effect of lowering on the elevation of the regression coefficient gradually stands out when the initial RMW is large.Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure,which retards the intensification while promoting size expansion,thus substantially enhancing size expansion as the vortex intensifies.Broadening the wind field outside the RMW by reducing results in abounding convection in the outer region,which promotes size expansion.Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations,when the RMW is large,the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region,thus retarding the intensification by reducing the radial imports of vorticity near the RMW.
基金National Key R&D Program of China(2017YFC1502104)“333 Project”Program of Jiangsu(BRA2018100)
文摘In order to study the impacts of wind field variations in the middle and lower troposphere on the development and structure of storms,we carried out numerical experiments on cases of severe convection in the Jianghuai area under the background of cold vortex on April 28,2015.The results show that the structure and development of convective storms are highly sensitive to the changes of wind fields,and the adjustment of wind fields in the middle or lower troposphere will lead to significant changes in the development and structure of storms.When the wind field in the middle or lower troposphere is weakened,the development of convective storms attenuates to some extent compared with that in the control experiment,and the ways of attenuation in the two experiments are different.In the attenuation test of wind field at the middle level,convective storms obviously weaken at all stages in its development,while for the wind field at the low level,the convective storms weaken only in the initial stage of storm.On the contrary,the enhancement of the wind field in the middle or lower troposphere is conducive to the development of convection,especially the enhancement in the middle troposphere.In contrast,the convective storms develop rapidly in this test,as the most intensive one.The wind field variations have significant impacts on the structure and organization of the storm.The enhancement of wind field in the middle troposphere facilitates the intension of the middle-level rotation in convective storm,the reduction of the storm scale,and the organized evolution of convective storms.The strengthening of the wind field in the lower troposphere is conducive to the development of the low-level secondary circulation of the storm and the cyclonic vorticity at the middle and low levels on the inflowing side of the storms.
基金financial support for this research from a USDA-AFRI Foundational Grant (Grant No. 2012-67013-19687)from the Illinois State Water Survey at the University of Illinois at Urbana—Champaign
文摘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.
基金Supported by the National Natural Science Foundation of China(Nos.U1706216,41976010,42006027,U1806227)the Natural Science Foundation of Shandong Province,China(No.ZR2016DQ16)+2 种基金the Key Deployment Project of Center for Ocean Mega-Science,Chinese Academy of Sciences(Nos.COMS2019J02,COMS2019J05)the Chinese Academy of Sciences Strategic Priority Project(Nos.XDA19060202,XDA19060502)the National Key Research and Development Program of China(No.2016YFC1402000)。
文摘We examined the influences of the wind fi eld and wave-current interaction(WCI)on the numerical simulation results of typhoon-induced wind waves in the northern East China Sea(NECS)using the coupled Simulating Waves Nearshore+Advanced Circulation(SWAN+ADCIRC)model.The simulations were performed during two typhoon events(Lekima and Muifa),and two widely used reanalysis wind fields,the Climate Forecast System Version 2(CFSv2)from the National Centers for Environmental Prediction(NCEP)and the fifth-generation European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis(ERA5),were compared.The results indicate that the ERA5 and CFSv2 wind fields both reliably reproduced the wind variations measured by in-situ buoys,and the accuracy of the winds from ERA5 were generally better than those from CFSv2 because CFSv2 tended to overestimate the wind speed and the simulated significant wave height(SWH),particularly the peak SWH.The WCI effects between the two wind field simulations were similar;these effects enhanced the SWH throughout the nearshore NECS during both typhoons but suppressed the SWH on the right side of the Typhoon Muifa track in the deep and off shore sea areas.In summary,variations in the water depth and current propagation direction dominate the modulation of wave height.
基金supported by the National Natural Science Foundation of China(Grants No.51309092 and 51379072)the Special Fund for Public Welfare Industry of the Ministry of Water Resources of China(Grant No.201201045)+1 种基金the Natural Science Fund for Colleges and Universities in Jiangsu Province(Grant No.BK20130833)the Fundamental Research Funds for the Central Universities(Grants No.2015B16014 and 2013B03414)
文摘This paper presents a study on the improvement of wind field hindcasts for two typical tropical cyclones, i.e., Fanapi and Meranti, which occurred in 2010. The performance of the three existing models for the hindcasting of cyclone wind fields is first examined, and then two modification methods are proposed to improve the hindcasted results. The first one is the superposition method, which superposes the wind field calculated from the parametric cyclone model on that obtained from the cross-calibrated multi-platform(CCMP) reanalysis data. The radius used for the superposition is based on an analysis of the minimum difference between the two wind fields. The other one is the direct modification method, which directly modifies the CCMP reanalysis data according to the ratio of the measured maximum wind speed to the reanalyzed value as well as the distance from the cyclone center. Using these two methods, the problem of underestimation of strong winds in reanalysis data can be overcome. Both methods show considerable improvements in the hindcasting of tropical cyclone wind fields,compared with the cyclone wind model and the reanalysis data.
基金Research Fund for Communications in Western China Under Grant No. 200431800028
文摘Proper Orthogonal Decomposition (POD) provides a powerful modal transformation tool for stochastic dynamics. In this paper, coherency matrix-based proper orthogonal decomposition (CPOD) is presented as an innovative form of the POD based on cross power spectral density matrices. By introducing a discretizing scheme, the CPOD-based spectral representation method is obtained for use in stochastic simulation. Moreover, some criteria are proposed that allow the truncation order of CPOD to be conveniently determined. A numerical example to illustrate the application of the proposed method for the simulation of a wind velocity field is provided.
文摘According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical monsoon area. In the period of monsoon, the directions of wind, sea wave and swell are roughly consistent. Sea wave of northeasterly is always prevailing in equatorial zone. The monsoon in winter is stronger than in summer, correspondingly, average wave height is higher, and the frequencies of high sea and heavy swell are also bigger. Both of North Indian Ocean and adjacent sea area is also monsoon area, but characteristic is opposite. This paper provides specific data of wind field and wave field and variaton for ship navigation, operation and scientific experiment in the NW Pacific Ocean.
基金The Joint Foundation of National Natural Science Foundation of China and the Marine Science Center of Shandong Province under contract No.U1406404the National Natural Science Foundation of China under contract Nos 41506206,41306186 and41476152+1 种基金the Global Change and Air-Sea Interaction Project of China under contract No.GASI-03-03-01-01the Open funds of State Key Laboratory of Satellite Ocean Environment Dynamics under contract No.SOED1411
文摘Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar(SAR) images with high horizontal resolution.The footprints of rain cells on SAR images are caused by the scattering and attenuation of the rain drops,as well as the downward airflow.In this study,we extract sea surface wind field and its structure caused by rain cells by using a RADARSAT-2 SAR image with a spatial resolution of 100 m for case study.We extract the sea surface wind speeds from SAR image by using CMOD4 geophysical model function with outside wind directions of NCEP final operational global analysis data,Advance Scatterometer(ASCAT) onboard European Met Op-A satellite and microwave scatterometer onboard Chinese HY-2 satellite,respectively.The root-mean-square errors(RMSE) of these SAR wind speeds,validated against NCEP,ASCAT and HY-2,are 1.48 m/s,1.64 m/s and 2.14 m/s,respectively.Circular signature patterns with brighter on one side and darker on the opposite side on SAR image are interpreted as the sea surface wind speed(or sea surface roughness) variety caused by downdraft associated with rain cells.The wind speeds taken from the transect profile which superposes to the wind ambient vectors and goes through the center of the circular footprint of rain cell can be fitted as a cosine or sine curve in high linear correlation with the values of no less than 0.80.The background wind speed,the wind speed caused by rain cell and the diameter of footprint of the rain cell with kilometers or tens of kilometers can be acquired by fitting curve.Eight cases interpreted and analyzed in this study all show the same conclusion.
基金National Key Fundamental Research and Development Plan of China (2004CB418301)Natural Science Foundation of China (40830958)
文摘As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.
基金Supported by the National Natural Science Foundation of China(21706069and 61751305)the Fundamental Research Funds for the Central Universities(222201814039).
文摘Chemical spills on complex geometry are difficult to model due to the uneven concentration distribution caused by air flow over ground obstacles. Computational fluid dynamics(CFD) is one of the powerful tools to estimate the building-resolving wind flow as well as pollutant dispersion. However, it takes too much time and requires enormous computational power in emergency situations. As a time demanding task, the estimation of the chemical spill consequence for emergency response requires abundant wind field information. In this paper, a comprehensive wind field reconstruction framework is proposed, providing the ability of parameter tuning for best reconstruction accuracy. The core of the framework is a data regression model built on principal component analysis(PCA) and extreme learning machine(ELM). To improve the accuracy, the wind field estimation from the regression model is further revised from local wind observations. The optimal placement of anemometers is provided based on the maximum projection on minimum eigenspace(MPME) algorithm. The fire dynamic simulator(FDS) generates high-resolution data of wind flow over complex geometries for the framework to be implemented. The reconstructed wind field is evaluated against simulation data and an overall reconstruction error of 9% is achieved. When used in real case,the error increases to around 12% since no convergence check is available. With parameter tuning abilities,the proposed framework provides an efficient way of reconstructing the wind flow in congested areas.
基金The National Natural Science Youth Foundation of China under contract Nos 41306191 and 41306192the National High Tech-nology Development Program(863 Program) of China under contract No.2013AA09A505the Scientific Research Fund of the Second Institute of Oceanography,State Oceanic Administration of China under contract No.JG1317
文摘To improve retrieval accuracy, this paper studies wave effects on retrieved wind field from a scatterometer. First, the advanced scatterometer(ASCAT) data and buoy data of the National Data Buoy Center(NDBC) are collocated. Buoy wind speed is converted into neutral wind at 10 m height. Then, ASCAT data are compared with the buoy data for the wind speed and direction. Subsequently, the errors between the ASCAT and the buoy wind as a function of each wave parameter are used to analyze the wave effects. Wave parameters include dominant wave period(dpd), significant wave height(swh), average wave period(apd) and the angle between the dominant wave direction(dwd) and the wind direction. Collocated data are divided into sub-datasets according to the different intervals of each wave parameter. A root mean square error(RMSE) for the wind speed and a mean absolute error(MAE) for the wind direction are calculated from the sub-datasets, which are considered as the function of wave parameters. Finally, optimal wave conditions on wind retrieved from the ASCAT are determined based on the error analyses. The results show the ocean wave parameters have correlative relationships with the RMSE of the retrieved wind speed and the MAE of the retrieved wind direction. The optimal wave conditions are presented in terms of dpd, swh, apd and angle.
基金supported by the National Natural Science Foundation of China(40805004, 40705039 and 90715031)the "Mini-projecton detailed survey and evaluation of wind energy resources"supported by National Climate Center of Chinese Meteoro-logical Administration (CWERA2010002)
文摘The state-of-art Computational Fluid Dynamics (CFD) codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design (CAD) technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.
基金supported by the Nationa1 High Technology Research and Development Program of China(863 Program)(Grant No.2002AA639370)the Natural Science Foundation of Shandong Province(Grant No.Q99E02)the Special Fund of Excellent Ph.D Dissertation(200021).
文摘An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model, it is found that the elliptical model can adequately represent the real wind field and trace the process of a typhoon storm surge. The numerically simulated results of storm surges by using the elliptical model are in good agreement with the observations and markedly better than those by using the circular model.
文摘Using a one-level numerical diagnostic model, the features of surface wind fields in Hainan Island and Leizhou Peninsula and maritime area around it are studied. In the experiments with prevailing synoptic situation for varying seasons there are obvious deflection flows, terrain slope drafts, convergence lines, sea/land breeze and mountain/valley breeze, and difference in season accounts for the features found in the mesoscale distribution.The complex terrain and seatland distribution in the area is shown to be the important cause for the formation of varying mesoscale circulation, and close relationships between local climatic distribution feature and mesoscale circulation are then revealed.
基金supported by the National Natural Sciences Foundation of China (Grant No.40675066)
文摘The regional wind index influencing September precipitation in western China has been defined using the 700 hPa u and v components of NCAR/NCEP reanalysis data of 1961 to 2006. There are three regional wind field indices: southwest, southeast, and north, and these indices reflect the change of East Asian monsoon. The relationship between the indices was studied, and results show that they not only have a close relationship, but also have independence. Moreover, there is an obvious relationship between the wind indices and the autumn in particular the September precipitation in western China. The effect of wind indices on rain occurrence is most different: the influenced area of the southwest wind index is larger than that of the southeast wind index, and the southwest wind index is a controlling factor on autumn precipitation in western China. The weakening of southwest wind is the main cause resulting in reduction of autumn precipitation on the east side of the Tibetan Plateau.
基金Project(61120106010)supported by the Projects of Major International(Regional)Joint Research Program Nature Science Foundation of ChinaProject(61304215,61203078)supported by National Natural Science Foundation of China+1 种基金Project(2013000704)supported by the Beijing Outstanding Ph.D.Program Mentor,ChinaProject(61321002)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.
文摘In this paper we propose a finite element(FE) simulation method to predict tree motion in a wind field. Two FE tree models were investigated:One model was generated based on a realistic nature-looking geometric tree model,and the other was a symmetric model to investigate the influence of asymmetric material properties on tree motion. The vortex-induced vibration(VIV) theory is introduced to estimate the fluctuating wind force being exerted on tree stems and the fluid-structure interaction(FSI) analysis is also included in the simulation. The results indicate that asymmetric material properties result in the crosswind displacement of the investigated node and the main swaying direction deviation. The simulation reveals that under wind loading,a tree with leaves has much larger swaying amplitude along the wind direction and longer swaying period than a tree without leaves. However,the crosswind swaying amplitude is mainly due to branch interaction. The numerical simulation proved that the inter-action of tree branches can prevent dangerous swaying motion developing.
文摘Based on the fast algorithm of meteorological satellite guide wind vector tracing,cloud motion wind vector is calculated. According to the different characteristics of cloud motion wind field and sounding wind field,a method which fuses conventional data with unconventional data based on variation principle is presented. The fundamental is constructing a cost function that makes the value approach conventional data and the gradient approach unconventional data. Using this method,the conventional wind and the cloud motion wind are fused. The fused wind field has high resolution. Its wind direction approaches cloud motion wind which indicates move direction of the synoptic system,and its velocity approaches conventional wind which indicates move velocity of the synoptic system. The wind field data are used for short-time forecast of severe convective weather location,which gets a good result.