检索结果-南通市图书馆

Evaluating and Improving Wind Forecasts over South China: The Role of Orographic Parameterization in the GRAPES Model

在线全文

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 2018年第6期35卷 713-722页

作者： Shuixin ZHONG zitong chen Daosheng XU Yanxia ZHANG Guangdong Province Key Laboratory of Regional Numerical Weather Prediction Institute of Tropical and Marine MeteorologyChina Meteorological Administration

Unresolved small-scale orographic（SSO） drags are parameterized in a regional model based on the Global/Regional Assimilation and Prediction System for the Tropical Mesoscale Model（GRAPES TMM）. The SSO drags are represented by adding a sink term in the momentum equations. The maximum height of the mountain within the grid box is adopted in the SSO parameterization（SSOP） scheme as compensation for the drag. The effects of the unresolved topography are parameterized as the feedbacks to the momentum tendencies on the first model level in planetary boundary layer（PBL）parameterization. The SSOP scheme has been implemented and coupled with the PBL parameterization scheme within the model physics package. A monthly simulation is designed to examine the performance of the SSOP scheme over the complex terrain areas located in the southwest of Guangdong. The verification results show that the surface wind speed bias has been much alleviated by adopting the SSOP scheme, in addition to reduction of the wind bias in the lower troposphere. The target verification over Xinyi shows that the simulations with the SSOP scheme provide improved wind estimation over the complex regions in the southwest of Guangdong.

关键词： small-scale orographic drag GRAPES_TMM PBL parameterization wind bias

Optimal location query based on k nearest neighbours

在线全文

学校读者我要写书评

暂无评论

Frontiers of Computer Science 2021年第2期15卷 105-117页

作者： Yubao LIU zitong chen Ada Wai-Chee FU Raymond Chi-Wing WONG Genan DAI School of Data and Computer Science Sun Yat-Sen UniversityGuangzhou510006China Guangdong Key Laboratory of Big Data Analysis and Processing Guangzhou510006China Department of Computer Science and Engineering Chinese University of Hong KongHong Kong999077China Department of Computer Science and Engineering The Hong Kong University of Science and TechnologyHong Kong999077China

Optimal location query in road networks is a basic operation in the location intelligence *** a set of clients and servers on a road network,the purpose of optimal location query is to obtain a location for a new server,so that a certain objective function calculated based on the locations of clients and servers is *** works assume no labels for servers and that a client only visits the nearest *** assumptions are not realistic and it renders the existing work not useful in many *** this paper,we relax these assumptions and consider the k nearest neighbours(KNN)of *** introduce the problem of KNN-based optimal location query(KOLQ)which considers the k nearest servers of clients and labeled *** also introduce a variant problem called relocation KOLQ(RKOLQ)which aims at relocating an existing server to an optimal *** main analysis algorithms are proposed for these *** experiments on the real road networks illustrate the efficiency of our proposed solutions.

关键词： optimal location query k nearest neighbours road network

Character of Convective Systems Producing Short-Term Heavy Precipitation in Central China Revealed by Kilometer and Minute Interval Observations

在线全文

学校读者我要写书评

暂无评论

Journal of Meteorological Research 2024年第3期38卷 530-541页

作者： zitong chen Yunying LI Zhiwei ZHANG Jing SUN chengzhi YE Anyuan XIONG College of Meteorology and Oceanography National University of Defense TechnologyChangsha410073China High Impact Weather Key Laboratory of China Meteorological Administration Changsha410073China Unit No.92192 of Chinese People’s Liberation Army Ningbo315000China Hubei Key Research Laboratory for Heavy Rain Monitoring and Warning Institute of Heavy RainChina Meteorological AdministrationWuhan430223China Institute of Meteorological Sciences of Hunan Province Hunan Meteorological BureauChangsha410118China National Meteorological Information Centre China Meteorological AdministrationBeijing100081China

Accurate forecasting of heavy precipitation in central China is still a challenge,within which a key issue is our still incomplete understanding of the convective systems(CSs)responsible for such *** this study,through use of an iterative rain-cell tracking algorithm,the macroscale characteristics(scale,intensity,duration,etc.)of the CSs that produced 595 short-term heavy precipitation events in Hunan Province,central China,are quantitatively analyzed,based on radar reflectivity,echo top,and rainfall observations at 1-km and 6-min intervals in April-September of *** results show that CSs present significant seasonal and diurnal *** CSs usually cover a larger echo area with stronger convective cores and thus generate more precipitation than summer CSs,though summer CSs develop more vigorously and *** initiated at 1400-1600 local time are characterized by the strongest convection and a smaller spatiotemporal scale,causing violent and transient showers with typical areal precipitation of 0.5-1 mm km^(−2),but less total *** analyses of the relationships among the scale,intensity,duration,and total precipitation of CSs reveal that the convective intensity is linearly correlated to the spatiotemporal scale of CSs,with the duration increasing on average by 0.0372 h dBZ^(−1);the echo area is significantly correlated to the total precipitation,and the duration and rainfall amount are connected with the area expansion rate(AER)of CSs:when the AER exceeds 50%,CSs expand rapidly with increasing total precipitation,but the duration is *** findings provide a helpful reference for the forecasting of short-term heavy precipitation induced by CSs in central China.

关键词： convective system radar reflectivity factor total precipitation iterative rain-cell tracking

Improvement of the Surface Pressure Operator in GRAPES and Its Application in Precipitation Forecasting in South China

在线全文

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 2013年第2期30卷 354-366页

作者： HUANG Yanyan XUE Jishan WAN Qilin chen zitong DING Weiyu ZHANG chengzhong Guangzhou Institute of Tropical and Marine Meteorology Guangzhou 510080 ~tate Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing 100081

In this study we investigated the problems involved in assimilating surface pressure in the current global and regional assimilation and prediction system, GRAPES. A new scheme of assimilating surface pressure was proposed, including a new interpolation scheme and a refreshed background covariance. The new scheme takes account of the differences between station elevation and model topography, and it especially deals with stations located at elevations below that of the first model level. Contrast experiments were conducted using both the original and the new assimilation schemes. The influence of the new interpolation scheme and the updated background covariance were investigated. Our results show that the new interpolation scheme utilized more observations and improved the quality of the mass analysis. The background covariance was refreshed using statistics resulting from the technique proposed by Parrish and Derber in 1992. Experiments show that the updated vertical covariance may have a positive influence on the analysis at higher levels of the atmosphere when assimilating surface pressure. This influence may be more significant if the quality of the background field at high levels is poor. A series of assimilation experiments were performed to test the validity of the new scheme. The corresponding simulation experiments were conducted using the analysis of both schemes as initial conditions. The results indicated that the new scheme leads to better forecasting of sea level pressure and precipitation in South China, especially the forecast of moderate and heavv rain.

关键词： GRAPES system surface pressure assimilation background covariance numerical simulation

Improved Wind and Precipitation Forecasts over South China Using a Modified Orographic Drag Parameterization Scheme

在线全文

学校读者我要写书评

暂无评论

Journal of Meteorological Research 2015年第1期29卷 132-143页

作者：钟水新陈子通 Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical Weather Prediction China Meteorological Administration State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences

To improve the wind and precipitation forecasts over South China, a modified orographic drag parameterization（OP） scheme that considers both the gravity wave drag（GWD） and the mountain blocking drag（MBD） effects was implemented in the Global/Regional Assimilation and Prediction System Tropical Mesoscale Model（GRAPES-TMM）. Simulations were performed over one month starting from 1200 UTC19 June 2013. The initial and lateral boundary conditions were obtained from the NCEP global forecast system output. The simulation results were compared among a control（CTL） experiment without the OP scheme, a GWDO experiment with the OP scheme that considers only the GWD effect, and an MBD experiment with the modified OP scheme（including both GWD and MBD）. The simulation with the modified OP scheme successfully captured the main features of precipitation, including its distribution and intensity,and improved the wind circulation forecast in the lower troposphere. The modified OP scheme appears to improve the wind forecast by accelerating the ascending air motion and reinforcing the convergence in the rainfall area. Overall, the modified OP scheme exerts positive impacts on the forecast of large-scale atmospheric fields in South China.

关键词： orographic drag parameterization (OP) gravity wave drag (GWD) wind circulation South China

Effects of forsythin extract in Forsythia leaves on intestinal microbiota and short-chain fatty acids in rats fed a high-fat diet

在线全文

学校读者我要写书评

暂无评论

Food Science and Human Wellness 2024年第2期13卷 659-667页

作者： Lanlan Gui Shaokang Wang Jing Wang Wang Liao zitong chen Da Pan Hui Xia Guiju Sun Su Tian Department of Nutrition and Food Hygiene School of Public HealthSoutheast UniversityNanjing 210009China Nanjing Municipal Center for Disease Control and Prevention Nanjing 210003China Department of Nutrition and Food Hygiene School of Public HealthHebei Medical UniversityShijiazhuang 050017China

Forsythia suspensa,belonging to the deciduous shrubs of the Luteaceae family,a traditional Chinese medicine,has effects of alleviating swelling,clearing heat,detoxification and promoting blood *** leaves of *** contain multiple chemical components and have a long history of use in folk medicines and health *** purpose of this study was to explore the effects of forsythin extract from *** leaves on intestinal microbiota and short-chain fatty acid(SCFA)content in rats with obesity induced by a high-fat *** extract in *** leaves increased the abundance of the intestinal microbiota,ameliorated intestinal microbiota disorders and inhibited the increase in total SCFA content in the intestinal tract in rats with obesity induced by a high-fat *** results suggested that forsythin extract in *** leaves may slow the development of obesity induced by a high-fat diet;thus,its active components and efficacy are worthy of further study.

关键词： Forsythin High-fat diet Intestinal microbiota Short-chain fatty acid(SCFA)

Regioselectivity of Pd-catalyzed o-carboranearylation: a theoretical view

在线全文

学校读者我要写书评

暂无评论

Organic Chemistry Frontiers 2022年第6期9卷 1686-1695页

作者： Jiying Liu Dongmin Fu zitong chen Tiantian Li Ling-Bo Qu Shi-Jun Li Wenjing Zhang Yu Lan Green Catalysis Center and College of ChemistryZhengzhou UniversityZhengzhouHenan 450001China School of Chemistry and Chemical Engineering and Chongqing Key Laboratory of Theoretical and Computational ChemistryChongqing UniversityChongqing 400030China

The mechanism and the regioselectivity of Pd-catalyzed B(4)–H arylation and B(4,5)–H diarylation foro-carborane with bidentate directing groups were investigated. The complete catalytic cycle involves Pdmediated concerted metalation–deprotonation, oxidative addition, counterion exchange, and reductiveelimination, where counterion exchange is critical. The reductive elimination is the rate- and regioselectivity-determining step for the whole catalytic cycle. B(3)-Arylation is unfavorable because the stericrepulsion between the substituent group on C(2) and the metal moiety would lead to significant distortionof o-carborane and would result in a higher activation energy for reductive elimination. The distortion ofo-carborane can be clearly observed from the change of its aromaticity in the corresponding transitionstates by the calculation of nucleus-independent chemical shifts. Moreover, counterion exchange withcarboxylate before reductive elimination significantly increases the positive charge of palladium, whichleads to a lower activation free energy for the sequential step.

关键词： elimination catalyzed reductive

The temporal and spatial distribution of ancient rice in China and its implications

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2007年第8期52卷 1071-1079页

作者： GONG zitong chen HongZhao YUAN DaGang ZHAO YuGuo WU YunJin ZHANG GanLin State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008China

The relics of ancient rice have been regarded as the most important objective evidence of the origina- tion and spread of rice *** on the records of 280 rice relics sites and the rice cropping regionalization as well as the distribution map of paddy soils,the current study compiled the temporal and spatial distribution map of ancient rice distribution in *** map shows that the distribution of ancient rice is spatially extensive and meantime comparatively concentrated,temporarily covering a long and relatively continuous *** rice relics in the Central China double and single rice cropping regions are among the earliest and the most abundant ones,possessing continuity in time *** with the discovery of ancient rice and paddy filed relics,soil micromorphology, pollen combination and element geochemistry,it is suggested that Central China was the origin center of rice cultivation in *** had been spread to the rest part of China in three major waves,also to the East Asian part like Korea and *** temporal and spatial distribution of ancient rice reflects the past environmental change,which is also meaningful to the current rice regionalization and plan- ning as well as food security in China.

关键词：古代水稻起源时空分布中国

Decompositions of the Kadomtsev-Petviashvili equation and their symmetry reductions

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2024年第3期33卷 150-159页

作者：陈孜童贾曼郝夏芝楼森岳 School of Mathematics and Statistics Ningbo UniversityNingbo 315211China School of Physical Science and Technology Ningbo UniversityNingbo 315211China College of Science Zhejiang University of TechnologyHangzhou 310014China

Starting with a decomposition conjecture,we carefully explain the basic decompositions for the Kadomtsev-Petviashvili(KP)equation as well as the necessary calculation procedures,and it is shown that the KP equation allows the Burgers-STO(BSTO)decomposition,two types of reducible coupled BSTO decompositions and the BSTO-KdV ***,we concentrate ourselves on pointing out the main idea and result of Bäcklund transformation of the KP equation based on a special superposition principle in the particular context of the BSTO *** the framework of standard Lie point symmetry theory,these decompositions are studied and the problem of computing the corresponding symmetry constraints is treated.

关键词： Kadomtsev-Petviashvili(KP)equation decomposition Bäcklund transformation symmetry reduction