2015年3期 (共 篇) 引用文章 全选
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Street-level visualization is an important application of 3D city models. Challenges to street-level visualization include the cluttering of buildings due to fine detail and visualization performance. In this paper, a novel method is proposed for street-level visualization based on visual saliency evaluation. The basic idea of the method is to preserve these salient buildings in a scene while removing those that are non-salient. The method can be divided into pre-processing procedures and real-time visualization. The first step in pre-processing is to convert 3D building models at higher Levels of Detail (LoDs) into LoD1 models with simplified ground plans. Then, a number of index viewpoints are created along the streets; these indices refer to both the position and the direction of each street site. A visual saliency value is computed for each building, with respect to the index site, based on a visual difference between the original model and the generalized model. We calculate and evaluate three methods for visual saliency: local difference, global difference and minimum projection area. The real-time visualization process begins by mapping the observer to its closest indices. The street view is then generated based on the building information stored in those indexes. A user study shows that the local visual saliency method performs better than do the global visual saliency, area and image-based methods and that the framework proposed in this paper may improve the performance of 3D visualization.
本平台内已出版文章查询 , ZHU WeiLin * 已出版文章查询
本平台内已出版文章查询 , MI LiJun 已出版文章查询
本平台内已出版文章查询 , ZHOU JiaXiong 已出版文章查询
本平台内已出版文章查询 , HAO Hu 已出版文章查询
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The South China Sea where water depth is up to 5000 m is the most promising oil and gas exploration area in China in the future. The seismic data acquired in the South China Sea contain various types of multiples that need to be removed before imaging can be developed. However, compared with the conventional reflection migration, multiples carry more information of the underground structure that helps provide better subsurface imaging. This paper presents a method to modify the conventional reverse time migration so that multiple reflections can migrate to their correct locations in the subsurface. This approach replaces the numerical impulsive source with the recorded data including primaries and multiples on the surface, and replaces the recorded primary reflection data with multiples. In the reverse time migration process, multiples recorded on the surface are extrapolated backward in time to each depth level, while primaries and multiples recorded on the surface are extrapolated forward in time to the same depth levels. By matching the difference between the primary and multiple images using an objective function, this algorithm improves the primary resultant image. Synthetic tests on Sigsbee2B show that the proposed method can obtain a greater range and better underground illumination. Images of deep water in the South China Sea are obtained using multiples and their matching with primaries. They demonstrate that multiples can make up for the reflection illumination and the migration of multiples is an important research direction in the future.
Dynamic-statistics combined forecast scheme based on the abrupt decadal change component of summer precipitation in East Asia
本平台内已出版文章查询 , ZHAO JunHu 已出版文章查询
本平台内已出版文章查询 , FENG GuoLin * 已出版文章查询
本平台内已出版文章查询 , CHOU JiFan 已出版文章查询
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Based on the 1983~2011 CMAP data, the precipitation anomaly in East Asia and its nearby sea regions (hereafter called East Asia for short) demonstrates the "+-+" pattern before 1999 and the "-+-" pattern afterwards; this decadal change is contained principally in the corresponding EOF3 component. However, the NCC_CGCM forecast results are quite different, which reveal the "+-+-" pattern before 1999 and the "-+-+" pattern afterwards. Meanwhile, the probability of improving NCC_CGCM's forecast accuracy based on these key SST areas is discussed, and the dynamic-statistics combined forecast scheme is constructed for increasing the information of decadal change contained in the summer precipitation in East Asia. The independent sample forecast results indicate that this forecasting scheme can effectively modify the NCC_CGCM's decadal change information contained in the summer precipitation in East Asia (especially in the area of 30°N-55°N). The ACC is 0.25 and ACR is 61% for the forecasting result based on the V SST area, and the mean ACC is 0.03 and ACR is 51% for the seven key areas, which are better than NCC_CGCM's system error correction results (ACC is -0.01 and ACR is 49%). Besides, the modified forecast results also provide the information that the precipitation anomaly in East Asia mainly shows the "+-+" pattern before 1999 and the "-+-" pattern afterwards.
Observation analysis on characteristics of formation, evolution and transition of a long-lasting severe fog and haze episode in North China
本平台内已出版文章查询 , GUO XueLiang * 已出版文章查询
本平台内已出版文章查询 , FANG ChunGang 已出版文章查询
本平台内已出版文章查询 , ZHU ShiChao 已出版文章查询
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An unusual fog and haze event lasted for one week took place during 1-7 December, 2011 over North China. To investigate the characteristics and mechanism of formation, evolution, and transition of the fog and haze event, we studied the microphysical properties such as aerosol, cloud condensation nuclei (CCN), fog droplet spectrum and liquid water content (LWC), as well as horizontal visibility and boundary layer properties, using the data collected in the Project of Low-Visibility Weather Monitoring and Forecasting in the Beijing-Tianjin region. The results indicate that the long-lasting fog and haze event occurred in a high pressure weather system and calm wind condition. The stable boundary-layer structure resulted from temperature inversions that were built by warm advection and radiation cooling provided a favorable condition for the accumulation of polluted aerosols and the formation and development of the fog and haze event. In particular, the continuous southerly wet flow advection made the process a persistent and long-lasting event. The horizontal visibility was almost below 2 km in the whole process, and the lowest visibility was only 56 m. The average LWC was about 10-3 g m-3, and the maximum LWC reached 0.16 g m-3. The aerosol number concentration was more than 10000 cm-3, and its mass concentration ranged from 50 to 160 μg m-3. The further study shows that the fog and haze event experienced three main processes in different intensities during the whole period, each process could be divided into three main stages: aerosol accumulation, transition and mixture of aerosol and fog, and dissipation. Each stage had different physical features: the aerosol accumulation stage was characterized by the increase of aerosol number concentration in Aitken nuclei and accumulation mode sequentially. In the transition and mixing stage of fog and haze, the latent heating produced by fog droplet condensation process and high aerosol number concentration condition intensified the Brownian coagulation process, which induced the small size of aerosols to become larger ones and enhanced the CCN activation process, thereby promoting the explosive development of the fog event. The ratio of aerosol activated to CCN reached 17%, and the ratio of CCN converted to fog droplet exceeded 100%, showing an explosively broadening of fog droplet spectrum. The decrease and dissipation of the fog was caused by an increased solar radiation heating or the passage of cold frontal system.
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Assume that an oasis and its surrounding desert consist of an isolated system without mass and energy exchange with the outer environment. The characteristics of oasis evolution have been explored under the condition of system energy conservation. The results show that oasis evolves with two equilibrium states. The first equilibrium suggests a stable expansive and an unstable degraded oasis whereas the second equilibrium indicates a stable shrink and an unstable increase of the oasis area. If one equilibrium state is unstable, the components of the isolated system (oasis and desert) would tend to be no energy exchange and they each reach to energy balance respectively. Oasis would maintain its initial area in this case. Further analyses point out that the two equilibrium states have completely different characteristics. In the first equilibrium state, a higher vegetation albedo, lower soil albedo and larger canopy resistance, and direr soil both contribute to the oasis area expansion, accompanying an excessive large desert soil and vegetation canopy temperature difference (SCTD). In the second equilibrium state, however, a lower vegetation albedo, higher soil albedo and small canopy resistance, and wetter soil benefit the oasis area to stay near its initial value, following a moderate SCTD. The convergent trajectories of the initial values in phase space are influenced by the separatrices of the equilibrium points. Higher temperature is an advantage factor for initial values convergent to the oasis expansion solution.
The comparison of ensemble or deterministic dispersion modeling on global dispersion during Fukushima Dai-ichi nuclear accident
本平台内已出版文章查询 , SONG ZhenXin 已出版文章查询
本平台内已出版文章查询 , HU JiangKai 已出版文章查询
本平台内已出版文章查询 , L Kai 已出版文章查询
本平台内已出版文章查询 , TONG Hua 已出版文章查询
本平台内已出版文章查询 , LI Bing 已出版文章查询
本平台内已出版文章查询 , QIAO QingDang 已出版文章查询
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Ensemble forcasting, originally developed for weather prediction, is lately being extended to atmospheric dispersion applications, which is a new, effective methodology for improving the atmospheric dispersion numerical modeling. In March 2011, due to the massive 9.0 earthquakes and ensuing tsunami that struck off the northern coast of the island of Honshu, the Fukushima Nuclear Plant I had the substantial leak of radioactive materials into surrounding environment and atmosphere. To aim at the global dispersion modeling of atmospheric radionuclides from Fukushima Nuclear Accident, this paper presents two approaches of atmospheric dispersion forecasting: ensemble dispersion modeling (EDM) and deterministic dispersion modeling (DDM), conducts the globally dispersion modeling cases for Fukushima nuclear accident, and analyzes and evaluates the simulation results using observation data. In this paper, EDM includes three different perturbation methods: meteorological perturbation method, turbulence perturbation method, and physical parameterization ensemble forecasting method. The simulation results show that the trajectories from EDM have a better performance, which is in better agreement with the atmospheric circulation and observation data; the spread from DDM is slower and not as far as EDM. Additionally, the results from EDM display a better performance in the modeling of transport from Japan to China East Sea on April 4. The reasons for these results are: the techniques of MET and TUR are performed by adding perturbations on mean wind and turbulent velocity, respectively; the various different flow fields will result in far spreading in horizontal and the simulation results closer to observation; PHY is performed by using different diffusion physical parameterizations and produces the perturbations on vertical wind, which results the spreading in smaller range and discontinuous in horizontal. Finally, the comparative analysis between modeling results and observation data shows that all cases results are in good agreement with trends of observed radionuclides surface concentration; however, the modeling surface concentration is smaller than observation, especially in DDM and PHY. Furthermore, the EDM results show that MET and TUR are of more evolutionary advantage than PHY in modeling of average and maximum concentration. Therefore, this study can serve as a reference to atmospheric dispersion and environmental emergency response (EER).
Nonlinear advection, Coriolis force, and frictional influence in the South Channel of the Yangtze Estuary, China
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Observation data of along-estuary and lateral current velocities over a transect located at the South Channel of the Yangtze estuary was obtained during a spring tide in August 2011. Harmonic analysis was done on the current velocities to get a mean component and a semi-diurnal component. Based on these two components, the driving mechanisms of mean lateral flow and M2 lateral tidal flow are shown and analyzed respectively. The dominant driving force of mean lateral flow is nonlinear advection and that of lateral M2 tidal flow is Coriolis force. The friction plays an important role near the bottom and surface for both lateral mean flow and M2 tidal flow.
The role of cloud height and warming in the decadal weakening of atmospheric heat source over the Tibetan Plateau
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The warming over the Tibetan Plateau (TP) is very significant during last 30 years, but the thermal forcing has been weakened. The thermal weakening is attributed mainly to the enhancement of the TOA (top of atmosphere) outgoing radiation. This enhancement is opposite to the greenhouse-gas-induced weakening of the global mean TOA outgoing radiation and is also unable to be explained by the observed decrease of total cloud cover. This study presents the importance of cloud height change and the warming over the TP in modulating the TOA radiation budget and thus the thermal forcing during spring and summer. On the basis of surface observations and satellite radiation data, we found that both the TOA outgoing shortwave radiation and longwave radiation were enhanced during this period. The former enhancement is due mainly to the increase of low-level cloud cover, which has a strong reflection to shortwave radiation, especially in summer. The latter enhancement is caused mainly by the planetary warming, and it is further enhanced by the decrease of total cloud cover in spring, as clouds extinguish outgoing longwave radiation emitted from the land surface. Therefore, the radiative cooling enhancement and thus the thermal weakening over the TP is a response of the earth-atmosphere system to the unique change of cloud cover configuration and the rapid warming of the land surface. However, these trends in cloud cover and TOA outgoing radiation are not well represented in four reanalyses.
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Based upon the stochastic resonance theory, the formation mechanism of 100-kyr cycles in climate system is numerically studied in the perspective of stochastic dynamics. In this study, firstly we combine the idealized albedo model with the geological evidence and observation in climate system to construct a new albedo model. Secondly, a bistable nonlinear system is constructed by introducing the albedo model into zero-dimensional energy balance model. Finally, based on this new system, with the solar radiation cycles and stochastic perturbation simultaneously taken into account, the variation of 100-kyr cycles is analyzed by numerical simulations. The results show that, when the noise intensity reaches a certain value, the stochastic resonance can be triggered. However, the noise intensity in this level does not exist in the actual climate system. In order to explain the formation mechanism of 100-kyr glacial-interglacial cycles forced by the weak solar radiation cycles, besides the solar radiation stochastic perturbation, the stochastic dynamic effects of the other "non-solar" radiation stochastic perturbation in the climate change processes should also be considered. The stochastic dynamic simulations taking the two types of stochastic perturbation into consideration show that, when the two types of appropriately observable stochastic perturbation are introduced, the stochastic resonance also can be generated. In this situation, the contribution rate of solar radiation stochastic perturbation is about 38%, which proves the importance of solar radiation stochastic perturbation in the formation of 100-kyr climate cycles.
本平台内已出版文章查询 , FENG JianWu 已出版文章查询
本平台内已出版文章查询 , SUN JiHua 已出版文章查询
本平台内已出版文章查询 , WANG Lei 已出版文章查询
本平台内已出版文章查询 , XU AnLun 已出版文章查询
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Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance (EC) method. Basic physical parameters in the lake-air interaction processes, such as surface albedo of the lake, aerodynamic roughness length, bulk transfer coefficients, etc., were investigated using the EC data in 2012. The characteristics of turbulence fluxes over the lake including momentum flux, sensible heat flux, latent heat flux, and CO2 flux, and their controlling factors were analyzed. The total annual evaporation of the lake was also estimated based on the artificial neural network (ANN) gap-filling technique. Results showed that the total annual evaporation in 2012 was 1165 ± 15 mm, which was larger than the annual precipitation (818 mm). Local circulation between the lake and the surrounding land was found to be significant throughout the year due to the land-lake breeze or the mountain-valley breeze in this area. The prevailing winds of southeasterly and northwesterly were observed throughout the year. The sensible heat flux over this plateau lake usually had a few tens of W m-2, and generally became negative in the afternoon, indicating that heat was transferred from the lake to the atmosphere. The sensible heat flux was governed by the lake-air temperature difference and had its maximum in the early morning. The diurnal variation of the latent heat flux was controlled by vapor pressure deficit with a peak in the afternoon. The latent heat flux was dominant in the partition of available energy in daytime over this lake. The lake acted as a weak CO2 source to the atmosphere except for the midday of summer. Seasonal variations of surface albedo over the lake were related to the solar elevation angle and opacity of the water. Furthermore, compared with the observation data, the surface albedo estimated by CLM4-LISSS model was underestimated in winter and overestimated in summer.
Gas-to-particle conversion of atmospheric ammonia and sampling artifacts of ammonium in spring of Beijing
本平台内已出版文章查询 , DUAN JingChun 已出版文章查询
本平台内已出版文章查询 , TAN JiHua * 已出版文章查询
本平台内已出版文章查询 , MA YongLiang 已出版文章查询
本平台内已出版文章查询 , HE KeBin 已出版文章查询
本平台内已出版文章查询 , WANG ShuXiao 已出版文章查询
本平台内已出版文章查询 , HUANG XiaoFeng 已出版文章查询
本平台内已出版文章查询 , ZHANG YuanXun 已出版文章查询
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PM2.5 and gaseous pollutants (SO2, HNO2, HNO3, HCl, and NH3) were simultaneously collected by Partisol® Model 2300 Sequential Speciation Sampler with denuder-filter pack system in the spring of 2013 in Beijing. Water-soluble inorganic ions and gaseous pollutants were measured by Ion Chromatography. Results showed that the concentrations of NH3, NH4+ and PM2.5 had similar diurnal variation trends and their concentrations were higher at night than in daytime. The results of gas-to-particle conversion revealed that [NH3]:[NH4+] ratio was usually higher than 1; however, it was less than 1 and the concentration of NH4+ increased significantly during the haze episode, indicating that NH3 played an important role in the formation of fine particle. Research on the sampling artifacts suggested that the volatilization loss of NH4+ was prevalent in the traditional single filter-based sampling. The excess loss of HNO3 and HCl resulted from ammonium-poor aerosols and semivolatile inorganic species had severe losses in the clean day, whereas the mass of NH4+ was usually overestimated during the single filter-based sampling due to the positive artifacts. Correlation analysis was used to evaluate the influence of meteorological conditions on the volatilization loss of NH4+. It was found that the average relative humidity and temperature had great effects on the loss of NH4+. The loss of NH4+ was significantly under high temperature and low humidity, and tended to increase with the increasing of absorption of gaseous pollutants by denuder. The total mass of volatile loss of NH4+, NO3- and Cl- could not be ignored and its maximum value was 12.17 μg m-3. Therefore it is important to compensate sampling artifacts for semivolatile inorganic species.
Feasibility study on application of satellite formations for eliminating the influence from aliasing error of ocean tide model
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Currently, aliasing error of temporal signal model becomes the main factor constraining the accuracy of temporal gravity field. In provision of three types of satellite formations, i.e., GRACE-type, Pendulum-type and n-s-Cartwheel-type, which are suitable for gravity mission and composed of observation in different directions, here we design two cases and conduct a simulation experiment on the feasibility to apply satellite formations for eliminating the influence from the aliasing error of ocean tide models. The result of our experiment shows that, when the aliasing error is disregarded, n-s-Cartwheel formation can provide the best conditions for gravity field determination, which, compared with GRACE-type, can improve the accuracy by 43%. When aliasing error of the ocean tide model acts as the main source of error, the satellite formation applied in dynamic method for gravity field inversion cannot eliminate aliasing or improve the accuracy of gravity field. And due to its higher sensitivity to the high-degree variation of gravity field, the Cartwheel-type formation, which includes the radial observation, can result in the gravity field containing more high-frequency signals for the ocean tide model error, and lead to a dramatically larger error.
A SVD-based ensemble projection algorithm for calculating the conditional nonlinear optimal perturbation
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Conditional nonlinear optimal perturbation (CNOP) is an extension of the linear singular vector technique in the nonlinear regime. It represents the initial perturbation that is subjected to a given physical constraint, and results in the largest nonlinear evolution at the prediction time. CNOP-type errors play an important role in the predictability of weather and climate. Generally, when calculating CNOP in a complicated numerical model, we need the gradient of the objective function with respect to the initial perturbations to provide the descent direction for searching the phase space. The adjoint technique is widely used to calculate the gradient of the objective function. However, it is difficult and cumbersome to construct the adjoint model of a complicated numerical model, which imposes a limitation on the application of CNOP. Based on previous research, this study proposes a new ensemble projection algorithm based on singular vector decomposition (SVD). The new algorithm avoids the localization procedure of previous ensemble projection algorithms, and overcomes the uncertainty caused by choosing the localization radius empirically. The new algorithm is applied to calculate the CNOP in an intermediate forecasting model. The results show that the CNOP obtained by the new ensemble-based algorithm can effectively approximate that calculated by the adjoint algorithm, and retains the general spatial characteristics of the latter. Hence, the new SVD-based ensemble projection algorithm proposed in this study is an effective method of approximating the CNOP.
本平台内已出版文章查询 , ZHANG ChunLai * 已出版文章查询
本平台内已出版文章查询 , CHENG Hong 已出版文章查询
本平台内已出版文章查询 , KANG LiQiang 已出版文章查询
本平台内已出版文章查询 , WU YongQiu 已出版文章查询
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Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated, the wind erosion equation (WEQ), the revised wind erosion equation (RWEQ), the wind erosion prediction system (WEPS), and other soil wind erosion models have been successively established, and great advances have been achieved. Here we briefly review the soil wind erosion research course and analyze the advantages and disadvantages of the current soil wind erosion models. From the perspective of the dynamics of wind erosion, we classified the factors affecting soil wind erosion into three categories, namely, wind erosivity factors (WEF), soil antierodibility factors (SAF), and roughness interference factors (RIF). We proposed the concept of a standard plot of soil wind erosion to solve the problem of uncertainty of the soil wind erosion modulus on a spatial scale, and provided methods to set similarity conditions in wind tunnel simulation experiments and to convert the spatial scale of the wind erosion modulus from the standard plot to a large scale field. We also proposed a conceptual model on the basis of the dynamics of soil wind erosion with the theoretical basis that wind produces a shear force on the soil surface. This shear force is partitioned by barely erodible soil surfaces and roughness elements on the ground, and the amount of soil loss by wind should be calculated by comparing the shear force of the wind on barely erodible soil surfaces with the anti-erosion force of the surface soil. One advantage of this conceptual model is that the calculated soil wind erosion modulus is not subject to changes of spatial scale. Finally, we recommended continual improvement of the existing models while also establishing new models.
GRACE terrestrial water storage data assimilation based on the ensemble four-dimensional variational method PODEn4DVar: Method and validation
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Seasonal and interannual changes in the Earth's gravity field are mainly due to mass exchange among the atmosphere, ocean, and continental water sources. The terrestrial water storage changes, detected as gravity changes by the Gravity Recovery and Climate Experiment (GRACE) satellites, are mainly caused by precipitation, evapotranspiration, river transportation and downward infiltration processes. In this study, a land data assimilation system LDAS-G was developed to assimilate the GRACE terrestrial water storage (TWS) data into the Community Land Model (CLM3.5) using the POD-based ensemble four-dimensional variational assimilation method PODEn4DVar, disaggregating the GRACE large-scale terrestrial water storage changes vertically and in time, and placing constraints on the simulation of vertical hydrological variables to improve land surface hydrological simulations. The ideal experiments conducted at a single point and assimilation experiments carried out over China by the LDAS-G data assimilation system showed that the system developed in this study improved the simulation of land surface hydrological variables, indicating the potential of GRACE data assimilation in large-scale land surface hydrological research and applications.